How Mitochondria, p53, and ncRNAs Rule Metabolism and Innate Inflammation

The Informational Cell 

Inflammation and cellular homeostasis are not merely downstream reactions to stress; they are emergent properties of how cells process information. This information comes in the form of nucleic acids, DNA and RNA signals, originating from subcellular compartments. Recent advances reveal that the tumor suppressor p53, mitochondria, and non-coding RNAs (ncRNAs) integrate to form a unified system that links metabolism, innate immunity, and organelle integrity.

A deeper truth is emerging: Inflammation often begins as a problem of information misplacement. It arises when double-stranded RNA (dsRNA) appears in the cytosol, when DNA leaks outside the nucleus, or when telomeres can no longer contain their own signals.

Three foundational papers illuminate these intersections from different but complementary angles.

Nature Communications (2025): Reveals how p53 limits the formation of cytoplasmic chromatin fragments (CCF) in senescent cells, thereby putting a brake on inflammation.

Molecular Cell (2022): Demonstrates how endogenous RNA species, particularly from mitochondrial or nuclear sources, can trigger innate immune surveillance when they are released or de-sequestered.

Nature Cell Biology (2026): A landmark study showing that in senescent cells, p53 actively coordinates lipid metabolism to sustain membrane biosynthesis. It does this not by directly repairing DNA, but by increasing the recycling of phospholipid headgroups.

This final finding reframes p53 as a metabolic stabilizer. By linking membrane maintenance and autophagy-associated recycling to long-term survival, p53 ensures that membrane composition acts as a governor for organelle signaling and immune sensing.

When damaged or senescent cells begin leaking nuclear chromatin (especially telomeric DNA) into the cytoplasm, the cGAS–STING innate immune pathway is activated, sparking inflammatory transcription. p53 acts as a physiological brake on this process by promoting nuclear integrity and DNA repair. Crucially, mitochondria regulate how p53 senses the stress required to enforce this brake.

Similarly, p53 controls retrotransposon eruptions of RNA sequence repeats. Double-stranded RNA (dsRNA), normally a hallmark of viral infection, can emerge from within the cell when nuclear RNA-protein condensates are disturbed. These condensates normally sequester immunogenic dsRNA to prevent accidental immune triggering. When they dissolve due to stress, aging, or metabolic perturbation, endogenous dsRNA leaks out. It binds to innate immune sensors (such as RIG-I-like receptors), engaging a powerful antiviral response even in the absence of a virus.

In summary: DNA out of place -> activates cGAS–STING -> Inflammation. RNA out of place -> activates RIG-I/MAVS -> Inflammation.

Both are danger signals. Both provoke immune surveillance. And both can arise from mitochondrial transcriptional misregulation or organelle stress.

Mitochondria are not passive energy generators. With their bacterial ancestry, circular genome, and bidirectional transcription, they are uniquely capable of generating immunogenic RNA and dsRNA species. Under healthy conditions, mitochondrial RNAs are tightly sequestered. However, when mitochondrial dynamics or membrane integrity falter, these RNAs escape into the cytoplasm. There, they mimic viral RNA, activating MAVS-dependent signaling and innate immune programs.

This positions mitochondria as primary arbiters of inflammatory risk, not merely through reactive oxygen species or ATP imbalance, but through the containment of nucleic acids. p53 participates directly in this logic. By regulating mitochondrial quality control, autophagy, and lipid recycling, p53 indirectly determines whether mitochondrial RNAs remain silent or become inflammatory alarms.

If p53 is the brake and mitochondria are the engine, where do ncRNAs fit? They are the software: They adjust the sensitivity of innate sensors like RIG-I and MDA5, altering the threshold for danger responses. They serve as regulators of the RNA–protein condensates that sequester immunogenic RNA. They influence mitochondrial RNA processing and export, affecting the pool of dsRNA available for immune sensing. ncRNAs are not peripheral players; they determine how the cell interprets informational "noise", whether that noise is telomeric DNA fragments, mitochondrial dsRNA, or misprocessed nuclear transcripts.

This convergence suggests that chronic inflammation, aging, cancer immunity, and autoimmunity are not separate phenomena. They are tied together by how cells manage internal informational cues. In a world focused on therapeutic targets and biomarkers, the architecture of ncRNA and its interaction with p53 and mitochondria will define the next decade of precision immuno-metabolism.

P53 - Stability and Life Or Disorder and Death!

There is something ancient about the struggle between order and disorder in biology. A cell does not merely live by dividing, signaling, and repairing itself. It lives by maintaining interpretability. Its genome must remain legible enough to be copied, restrained enough not to erupt into instability, and coherent enough that surrounding systems — especially the immune system — can still distinguish function from failure. In that sense, p53 is not simply a tumor suppressor in the narrow modern meaning of the phrase. It is closer to a molecular governor of biological intelligibility, one of the factors that helps determine whether stress remains containable or tips into forms of disorder.

The broader role has appeared repeatedly across Codondex discussions, from Expanding Treatment Horizons to Does SARS-CoV2 Strangle P53 to kill Natural Killer Immunity?, where p53 was already being read less as an isolated tumor suppressor and more as part of a wider immune and genomic control system.

That older and deeper role becomes clearer once p53 is viewed not only through apoptosis or cell-cycle arrest, but through its relationship with the repetitive genome. Work over the last decade has shown that p53 does not merely respond to genetic insult after the fact. It can directly repress human LINE1 retrotransposons by binding the 5′UTR and promoting local repressive chromatin, and more recent work has extended that picture by showing p53-dependent restraint of LINE1-associated RNA-DNA hybrid states as well. One of the great guardians of cellular integrity is therefore also engaged in policing one of the genome’s recurrent internal threats: mobile and semi-mobile repetitive sequence that, when released from restraint, can destabilize chromosomal order and provoke inflammatory consequences. p53 directly represses human LINE1 transposons and p53-mediated regulation of LINE1 retrotransposon-derived R-loops both push that picture into sharper focus.

But the relationship runs in both directions. Transposable elements are not only targets of p53; they have also helped shape the p53 regulatory landscape itself. A substantial body of work has shown that human retrotransposons contain p53 responsive elements, meaning that the repetitive genome has donated part of the sequence architecture through which p53 now reads and regulates stress. This is one of those places where the older division between “functional genome” and “junk” becomes difficult to maintain. Repetitive sequence has not only threatened order. It has also contributed to the grammar by which order is defended.

Once that is appreciated, the immune side of the problem begins to look less like a separate field and more like a continuation of the same one. If p53 helps determine whether genomic instability remains suppressed, then it also helps determine whether such instability becomes visible to immune surveillance. Emerging views now frame p53 as a major regulator of NK-cell tumor immunosurveillance, not because NK cells are somehow subordinate to p53, but because p53 influences so many of the target-cell properties that NK cells are built to read: stress ligands, metabolic distress, microenvironmental signals, and the broader state of cellular legitimacy.

One of the clearest examples is the p53-dependent induction of ligands visible to NK activation pathways. When wild-type p53 is induced in tumor cells, NK cells can be alerted through upregulation of the NKG2D ligands ULBP1 and ULBP2. That is an important bridge. It means p53 is not only preserving internal order; it can also help convert intracellular stress into a surface-readable signal that tells NK cells something has gone wrong. The target is no longer merely unstable. It becomes interpretable to innate immune surveillance.

A parallel bridge exists through antigen processing. p53 has also been shown to increase MHC class I expression by upregulating ERAP1, a trimming enzyme involved in preparing peptides for class I presentation. That does not collapse NK and T-cell biology into one another, but it does reinforce the larger point: p53 influences whether a distressed cell remains hidden, partially legible, or fully exposed to immune scrutiny. It affects not just whether the cell survives, but how clearly that cell can be judged by the systems around it.

The recombination thread can also be preserved, though it needs to be understood in the right register. Mature NK cells do not generate their recognition receptors through classical V(D)J recombination in the way T and B cells do. Their receptors are fundamentally germline encoded. Yet that is not the end of the recombination story. Work on NK ontogeny has shown that a history of RAG expression in progenitors and NK precursors marks functionally distinct NK subsets later in the periphery, with consequences for fitness, survival, and responsiveness. Recombination machinery therefore leaves a developmental trace on NK biology, even if it does not build the mature receptor repertoire in the adaptive sense.

That developmental nuance matters because it prevents the argument from becoming either too weak or too strong. Too weak, and the relationship between recombination-linked stress and NK function disappears. Too strong, and NK cells are mistakenly described as if they were just another rearranging lymphocyte lineage. The better reading is that recombination biology, DNA damage response history, and developmental programming can shape the later functional competence of NK cells without making their mature surveillance logic identical to that of T cells.

A similar caution, and opportunity, appears in the KIR story. One of the most interesting findings in NK regulation is that KIR expression can be governed by bidirectional promoter logic and antisense transcription. In particular, KIR antisense transcripts processed into a 28-base PIWI-like small RNA have been linked to transcriptional silencing, while related work on KIR antisense lncRNAs and probabilistic promoter switching suggests that inhibitory receptor expression is shaped by a layered interaction between transcription, antisense regulation, and epigenetic commitment. This does not establish a direct p53→piRNA→KIR3DL1 pathway. But it does show that the NK lineage is not insulated from the wider world of small RNA restraint and genome-governed silencing.

That is where the Codondex theme begins to re-emerge. If p53 sits in one part of the cell as a governor of repetitive-element restraint, and if NK inhibitory receptor choice is itself touched by small-RNA and antisense-mediated silencing logic, then the two systems may not be identical, but they may still rhyme. Both are concerned with the management of unstable potential. Both are concerned with whether latent disorder is allowed to become active. Both are concerned with which signals are permitted to surface and which are held in reserve. This is not yet a single proven pathway. It is a systems-level parallel supported by a growing amount of molecular detail.

There is another reason the p53–NK connection deserves attention. In some settings, p53 activation appears able to convert repetitive-element biology into something resembling a warning flare. Pharmacologic activation of p53 has been linked to antiviral-like and immune-stimulatory states, and the broader literature now places p53 within a network that can enhance NK recognition and tumor destruction through multiple channels rather than one single canonical mechanism. The significance of that shift should not be underestimated. It means p53 is no longer best understood only as the decider of cell fate from within. It is also a participant in the communication of cellular fate to the outside world.

So the central question remains a fruitful one. Is p53 merely a brake on instability, or is it also part of the language by which instability becomes visible to elimination? The literature increasingly favors the second possibility. p53 restrains transposable elements. p53 shapes stress-ligand display. p53 influences antigen processing and MHC-I expression. p53 intersects with developmental and regulatory processes that matter to NK-cell competence and target recognition. The picture that emerges is not of a single linear circuit, but of a pressure point where genome integrity, immune legibility, and cellular fate begin to converge.

In that light, p53 can still be read as this article’s central character without overstatement. When p53 function is preserved, a cell under strain is more likely to remain ordered, to arrest, to die cleanly, or to become visible enough for immune removal. When p53 function is lost, not only does instability grow, but the cell’s interpretability may degrade with it. Disorder then becomes doubly dangerous: more abundant internally, and more ambiguous externally. That may be one of the deeper meanings of p53 in cancer and perhaps in biology more generally. It is not only a guardian against mutation. It is one of the means by which life keeps disorder readable.

Electrons Rule Your Biology!

The mitochondrial Electron Transport Chain (ETC) is responsible for almost all cellular energy - ATP. One protein, GPD2 was adopted into the inner mitochondrial membrane, perhaps because it enabled ETC production to move to its electron processing limit. To do this, lipids are metabolized when cytoplasmic GPD1-DHAP convert Glycerol Kinase to G3P, which passes two additional electrons from the cytoplasm, through GPD2, to the internalized ETC complexes. 

When Mitochondrial Membrane Potential "Δψm" is within normal range, the GPD2 electrons enhance ATP energy production. When damage to lipids, fatty chains, cholesterols or other elements, constituting the inner mitochondrial membrane, disrupt Δψm the anchored ETC proteins can move fractionally apart causing electrons passing along the chain of ETC complexes to leak.

During disrupted Δψm the additional flow of GPD2 electrons can burden the ETC complexes, resulting in unstable molecules that contain oxygen and are highly reactive known as reactive oxygen species (ROS). Prolific ROS can increase CA+ levels, damage lipids in mitochondrial membranes, which can cause dysfunction and disease. In  a normal cellular environment this process can lead to ferroptosis, an iron-dependent form of cell death, induced by lipid peroxidation. 

A key bidirectional regulator of ferroptosis, p53 can adjust metabolism of iron, lipids, glutathione peroxidase 4, reactive oxygen species, and amino acids via a canonical pathway. GPD2 is transcribed by multiple factors that interact with p53 including Nrf2 and others during stress, but findings with E2F suggest a critical function controls a p53-dependent axis that indirectly regulates E2F-mediated transcriptional repression and cellular proliferation. 

P53 can also induce apoptosis through the mitochondrial pathway, contribute to necrosis by accumulating in the mitochondrial matrix and regulating autophagy. Mitochondrial p53 accumulation is an early event  not merely a consequence of apoptosis or a consequence of binding to damaged organelles in dying cells. Now, emerging evidence shows that ferroptosis plays a crucial role in tumor suppression via p53. 

Immune cells require massive energy boosts during synapse formation and lysis of a target cell when mitochondrial fitness is essential. However, tumor micro environments (TME's) alter lipid metabolism disrupting Δψm causing immune cells to function sub-optimally. Stimulation of T cells triggers a spike in cellular ATP production that doubles intracellular levels in <30 s and causes prolonged ATP release into the extracellular space. ATP release and autocrine feedback, via purinergic receptors collectively contribute to the influx of extracellular Ca2+ that is required for IL-2 production. The process has also been described for Natural Killer (NK) cells.

In the TME innate NK cells are dysfunctional due to lipid peroxidation inhibiting glucose metabolism. If innate immune cells are initially successful, adaptive immune responses may still fail because mitochondria reposition to the immune synapse where they transfer, including to immune cells, which can assist the target to evade immune response. Rapidly proliferating cancer cells may overwhelm initial immune responses and modify immune signaling promoting cancer and vascular remodeling.

ΔΨm as a measure of functional integrity maybe the flawed alert, a blind spot for of a cells' ADP-ATP pipeline. Likewise the status of TP53, from transcription through p53 isoform, may signal wide ranging affects of ΔΨm changes that incorporate fragmentation, accumulating damaged mitochondria, mitophagy, apoptosis or normal immune signaling and response through mitochondrial biogenesis, differentiation and angiogenesis. This modal duality aligns known functions of NK cells that under physiological conditions promote angiogenesis growth (as in Blastocyst implantation and placental vascularization) or NK's classic, cytolytic role in the innate immune response. 

Mitochondrial Phospholipid (MitoPLD), is anchored to the mitochondrial surface. It regulates mitochondrial shape, facilitating fusion and in the electron-dense nuage, of adjacent mitochondria, performs a critical piRNA generating function that is known to generate a spermatocyte-specific piRNA required for meiosis. piRNA are known to be aberrantly expressed in cancer cells.

Changes in mitochondrial membrane potential and ETC complexes can also influence piRNA-mediated control of transposable elements (TE's) through energy availability, ROS generation, and direct or indirect effects on piRNA biogenesis and function. piRNA restrain TE's that disrupt genes, chromosomal stability, damage DNA, cause inflammation, disease and/or cell death. For example, increased levels of endogenous retroviruses (ERV's), a TE subclass, trigger fibro inflammation and play a role in kidney disease development.

In mammals, the transcription of TEs is important for maintaining early embryonic development and related vital aspects of NK cell immune development. Intriguingly, regardless of the cell type, p53 sites are highly enriched in the endogenous retroviral elements of the ERV1 family. This highlights the importance of this repeat family in shaping the transcriptional network of p53 and its transcriptional role in interferon-mediated antiviral immunity. 

 

 

All Roads Lead to (Ch)Romosome 19!

A hepatocellular carcinoma (HCC) co-regulatory network exists between chromosome 19 microRNA cluster (C19MC) at 19q13.42, melanoma-A antigens, IFN-γ and p53, promoting an oncogenic role of C19MC that is disrupted by metal ions zinc and nickel. IFN-γ plays a co-operative role whereas IL-6 is antagonistic, each have a major bearing on the expression of HLA molecules on cancer cells. Analysis of Mesenchymal stem cells and cancer cells predicted C19MC modulation of apoptosis in induced pluripotency and tumorigenesis.

Key, differentially expressed genes in HCC included cancer-related transcription factors (TF) EGR1, FOS, and FOSB. From mRNA and miRNA expression profiles these were most enriched in the p53 signaling pathway where mRNA levels of each decreased in HCC tissues. In addition, mRNA levels of CCNB1, CCNB2, and CHEK1, key markers of the p53 signaling pathway, were all increased. miR-181a-5p regulated FOS and EGR1 to promote the invasion and progression of HCC by p53 signaling pathway and it plays an important role in maturation or impairment of natural killer (NK) cells.

A pan-cancer analysis, on microRNA-associated gene activation, produced the top 57 miRNAs that positively correlated with at least 100 genes. miR-150, at 19q13.33 was the most active, it positively correlated with 1009 different genes each covering at least 10 cancers. It is an important hematopoietic, especially B, T, and NK, cell specific miRNA.

Rapid functional impairment of NK cells following tumor entry limits anti-tumor immunity. Gene regulatory network analysis revealed downregulation of TF regulons, over pseudo-time, as NK cells transition to their impaired end state. These included AP-1 complex TF's, Fos, Fosb (19q13.32), Jun, Junb (19p13.13), which are activated during NK cell cytolytic programs and down regulated by interactions with inhibitory ligands. Other down-regulated TF's included Irf8, Klf2 (19p13.11), Myc, which support NK cell activation and proliferation. There were no significantly upregulated TF's suggesting that the tumor-retained NK state arises from the reduced activity of core transcription factors associated with promoting mature NK cell development and expansion.

Innate immune, intra-tumoral, stimulatory dendritic cells (SDCs) and NK cells cluster together and are necessary for enhanced T cell tumor responses. In human melanoma, SDC abundance is associated with intra-tumoral expression of the cytokine producing gene FLT3LG (19q13.33) that is predominantly produced by NK cells in tumors. Computed tomography exposes patients to ionizing X-irradiation. Determined trends in the expression of 24 radiation-responsive genes linked to cancer, in vivo, found that TP53 and FLT3LG expression increased linearly with CT dose. 

Undifferentiated embryonal sarcoma of the liver displays high aneuploidy with recurrent alterations of 19q13.4 that are uniformly associated with aberrantly high levels of transcriptional activity of C19MC microRNA. Further, TP53 mutation or loss was present with all samples that also display C19MC changes. The 19q13.4 locus is gene-poor with highly repetitive sequences. Given the noncoding nature and lack of an obvious oncogene, disruption of the nearby C19MC regulatory region became a target for tumorigenesis. 

The endogenous retroviral, hot-spot deletion rate at 19p13.11-19p13.12 and 19q33-19q42 occurs at double the background deletion rate. Clustered in and around these regions are many gene families including KIR, Siglec, Leukocyte immunoglobulin-like receptors and cytokines that associate important NK gene features to proximal NK genes that were overrepresented in a meta analysis of blood pressure. 

Endogenous retroviruses that invite p53 and its transcriptional network, at retroviral hot-spots, suggest that lymphocyte progenitors, such as ILC's and expanded, NK cells are synergistically responsive to transcription from this busy region including by the top differentially expressed blood pressure genes MYADM, GZMB, CD97, NKG7, CLC, PPP1R13L , GRAMD1A as well as (RAS-KKS) Kallikrein related peptidases to educate early and expanded NK cells that shape immune responses.  

Cancer's HLA-G Backdoor

piRNA actively control transposable elements (TE) that would otherwise disrupt genes, chromosomal stability, damage DNA, cause inflammation, disease and/or cell death. For example, increased levels of endogenous retroviruses (ERV), a TE subclass, trigger fibro inflammation and play a role in kidney disease development. However, in mammals, the transcription of TEs is important for maintaining early embryonic development. piRNA also function with TE's for important aspects of Natural Killer (NK) cell immune development. Regardless of the cell type, endogenous retroviral elements of the ERV1 family, are highly enriched at p53 sites highlighting the importance of this repeat family in shaping the transcriptional network of p53.

HLA/MHC are highly polymorphic molecules, expressed on cells and recognized by NK cells. In mammals it is necessary to generate specialized NK cell subsets that are able to sense changes in the expression of each particular HLA molecule.

Decidual natural killer cells (dNK), the largest population of leukocytes at the maternal–fetal interface, have low cytotoxicity. They are believed to facilitate invasion of fetal HLA-G+ extravillous trophoblasts (EVT) into maternal tissues, essential for establishment of healthy pregnancies. dNK interaction with EVT leads to trogocytosis that acquires and internalizes HLA-G of EVT. dNK surface HLA-G was reacquired by incubation with EVT's. Activation of dNK by cytokines and/or viral products resulted in the disappearance of internalized HLA-G and restoration of cytotoxicity. Thus, the cycle provides both for NK tolerance and antiviral immune function by dNK.

A remote enhancer L, essential for HLA-G expression in EVT, describes the basis for its selective  immune tolerance at the maternal–fetal interface. Found only in genomes that lack a functional HLA-G classical promoter it raises the possibility that a retroviral element was co-opted during evolution to function in trophoblast-specific tolerogenic HLA/MHC expression. CEBP and GATA regulate EVT expression of HLA-G through enhancer L isoforms.

HLA-G1 is acquired by NK cells from tumor cells, within minutes, by activated, but not resting NK cells via trogocytosis. Once acquired, NK cells stop proliferating, are no longer cytotoxic and behave as suppressors of cytotoxic functions in nearby NK cells via the NK ILT2 (Mir-7) receptor. Mir-7 is a well researched intervention target in inflammatory diseases and belongs to a p53-dependent non-coding RNA network and MYC signaling circuit.

Cells that transcribe enhancer L isoforms and HLA-G, feed NK cells with HLA-G as an innate element for self determination, similar to the way EVT's restrain cytotoxicity of dNK. Then incoming, NK cells at the periphery of tumor microenvironments (TME) may promote vascular remodeling, as in the uterus during pregnancy, by acidifying the extracellular matrix with a2V that releases bound pro-angiogenic growth factors trapped in the extracellular matrix. After that these incoming NK cells succumb to the influence of Mir-7 resulting in low cytotoxic, inactive NK in the TME. 

Discovering resistant NK cells in the TME of a patient, for incubation, expansion and activation is a Codondex precision therapy objective based on p53 computations.

Tolerating Your Non-self!

Immune cells get comfortable with cancer
Courtesy https://deepai.org

A hallmark of cancer, autoimmunity and disease is the aberrant transcription of typically silenced, repetitive genetic elements that mimic Pathogen-Associated Molecular Patterns (PAMP's) that bind Pattern Recognition Receptors (PPR's) triggering the innate immune system and inflammation. Unrestrained, this 'viral mimicry' activates a generally conserved mechanism that, under restraint, supports homeostasis. These repetitive viral DNA sequences normally act as a quality control over genomic dysregulation responding in ways that preferentially promote immune conditions for stability. If aberrantly unrestrained and the 'viral mimicry' is transcribed it may result in undesirable immune reactions that disrupt the homeostasis of cells.

Mitochondrial DNA (mtDNA) are one source of cytosolic double stranded RNA (dsRNA) that is commonly present in cells. Trp53 Mutant Embryonic Fibroblasts (MEF's) contain innate immune stimulating endogenous dsRNA, from mtDNA that mimic PAMP's. The immune response, via RIG-1 like PRR, leads to expression of type 1 interferon (IFN) and proinflammatory cytokine genes. Further, Natural Killer cells also produce a multitude of cytokines that can promote or dampen an immune response. Wild-type p53 suppresses viral repeats and contributes to innate immunity by enhancing IFN-dependent antiviral activity independent of its function as a proapoptotic and tumor suppressor gene. 

Post-translationally modified P53, located in the cytoplasm, enhances the permeability of the mitochondrial outer membrane thus stimulating apoptosis. However, treating Trp53 mutant MEF's with DNA demethylating agent caused a huge increase in the level of transcripts encoding short interspersed nuclear elements and other species of noncoding RNAs that generated a strong type 1 IFN response. This did not occur in p53 wild-type MEF's. Thus it appears that another function of p53 is to silence repeats that can accidentally induce an immune response.

This has several implications for how we understand self versus non-self discrimination. When pathogen-associated features were quantified, specific repeats in the genome not only display PAMP's capable of stimulating PRRs but, in some instances, have seemingly maintained such features under selection. For organisms with a high degree of epigenetic regulation and chromosomal organization immuno-stimulatory repeats release a danger signal, such as repeats released after p53 mutations. Here, immune stimulation may act as back-up for the failure of other p53 functions such as apoptosis or senescence due to mutation. This supports the hypothesis that specific repeats gained favor by maintaining non-self PAMPs to act as sensors for loss of heterochromatin as an epigenetic checkpoint of quality control that avoids genome instability generally. 

When P53 mutates it begins to fail its restraint of viral suppression, this enables a 'viral mimicry' and aberrant immune reactions. These may promote survival of cells that can leverage immunity, promote angiogenesis and heightened proliferation of cancers, or other diseases under modified conditions for non-self tolerance. 

Evidence of Purposeful Evolution

Darwin's evolution challenged!

A recently published article in Nautre challenged evolution theory suggesting DNA repair was the more likely candidate driving evolutionary development than the environmental conditions thought to be the driver of natural selection. In some sense the two may be linked, but this study showed how epigenome-associated mutation bias reduced the occurrence of deleterious mutations, challenging the prevailing paradigm that mutation is a directionless force in evolution.

Quantitative assessment of DNA gain and loss through DNA double-strand break (DSB) repair processes suggests deletion-biased DSB repair causes ongoing genome shrinking in A. thaliana, whereas genome size in barley remained nearly constant.

Introduction of as little as 0.7% sequence divergence between Alu elements resulted in a significant reduction in recombination, which indicates even small degrees of sequence divergence reduce the efficiency of homology-directed DSB repair. Alu elements are the most abundant transposable elements (capable of shifting their positions) containing over one million copies dispersed throughout the human genome.

The emergence of recombination-activating genes (RAGs) in jawed vertebrates endowed adaptive immune cells with the ability to assemble a diverse set of antigen receptor genes. Innate Natural Killer (NK) cells are unable to express RAGs or RAG endonuclease activity during ontogeny. They exhibit a cell-intrinsic hyperresponsiveness, but a diminished capacity to survive following virus-driven proliferation, a reduced expression of DNA damage response mediators, and defects in the repair of DNA breaks. However, RAG expression in uncommitted hematopoietic progenitors and NK cell precursors marks functionally distinct subsets of NK cells in the periphery, demonstrating a novel role for RAG in the functional specialization of the NK cell lineage. 

The most active region of Human Chromosome 19 has a long history of recombinations that define the expression patterns of telomeric and centromeric proportions of Killer-cell immunoglobulin-like receptor (KIR) gene's encoding receptors. KIR's bind cells presenting MHC class 1 HLA haplotype combinations, that vary significantly across tissues in different population groups. Further, the deletion rate in Zinc Finger clusters (ZNF) located around 19q13.42, near KIR and C19MC between 51,012,739 and 55,620,741 are about twofold higher than the background deletion rate. 

The relationship between deletions and mutation may indeed play a direct role in rapidly evolving, innate immunity. This may just begin to explain the speed at which global populations can respond and survive pandemics caused by the likes of COVID-19. And, the '19' in its nomenclature may go beyond time to the very chromosome responsible for innate immune diversity.

Retroviral Defense And Mitochondrial Offense

Chromosomal DNA has played host to the long game of viral insertions that repeat and continue as a genetic and epigenetic symbiosis along its phosphate and pentose sugar backbone. But, the bacterial origin of mitochondria and its hosted DNA also promotes its offense. 

Research suggests that retrovirus insertions evolved from a type of transposon called a retrotransposon. The evolutionary time scales of inherited, endogenous retroviruses (ERV) and the appearance of the zinc finger gene that binds its unique sequences occur over same time scales of primate evolution. Additionaly the zinc-finger genes that inactivate transposable elements are commonly located on chromosome 19. The recurrence of independent ERV invasions can be countered by a reservoir of zinc-finger repressors that are continuously generated on copy number variant (CNV) formation hotspots.

One of the more intiguing aspects of prevalent CNV hotspots on chromosome 19 are their proximity to killer immunoglobulin receptor gene's (KIR's) and other critical gene's of the innate immune system.

Frequently occuring DNA breaks can cause genomic instability, which is a hallmark of cancer. These breaks are over represented at G4 DNA quadruplexes within, hominid-specific, SVA retrotransposons and generally occur in tumors with mutations in tumor suppressor genes, such as TP53. Cancer mutational burden is shaped by G4 DNA, replication stress and mitochondrial dysfunction, that in lung adenocarcinoma downlregulates SPATA18, a mitochondrial eating protein (MIEAP) that contributes to mitophagy. 

Genetic variations, in non-coding regions can control the activity of conserved protein-coding genes resulting in the establishment of species-specific transcriptional networks. A chromosome 19 zinc finger, ZNF558 evolved as a suppressor of LINE-1 transposons, but has since been co-opted to singly regulate SPATA18. These variations are evident from a panel of 409 human lymphoblastoid cell lines where the lengths of the ZNF558 variable number tandem repeats (VNTR) negatively correlated with its expression. 

Colon cancer cells with p53 deletion were used to analyze deregulated p53 target genes in HCT116 p53 null cells compared to HCT116-p53 +/+ cells. SPATA18 was the most upregulted gene in the differential expression providing further insight to p53 and mitophagy via SPATA18-MIEAP.

p53 response elements (p53RE) can be shaped by long terminal repeats from endogenous retroviruses, long interspersed nuclear repeats, and ALU repeats in humans and fuzzy tandem repeats in mice. Further, p53 pervasively binds to p53REs derived from retrotransposons or other mobile genetic elements and can suppress transcription of retroelements. The p53- mediated mechanisms conferring protection from retroelements is also conserved through evolution. Certainly, p53 has been shown to have other roles in DNA  context, such as playing an important role in replication restart and replication fork progression. The absence of these p53-dependent processes can lead to further genomic instability. 

The frequency of variable length, long or short nucleotide repeats and their locations within a gene may be key to the repression of DNA sequences that would otherwise cause genomic instability or protein expressions that would eat bacterial mitochondria or destroy its cell host. 

The complexity of variable length insertions is made evident when exhaustively analyzing a simple length 12 sequence for the potential frequency of each of its variable length repeats starting from a minumum variable length of 8.

Then, for TGTGGGCCCACA(12)

All possible internal variable length combinations from and including length 8:

TGTGGGCC(8)|GTGGGCCC(8)|TGTGGGCCC(9)|TGGGCCCA(8)|GTGGGCCCA(9)|TGTGGGCCCA(10|GGGCCCAC(8)|TGGGCCCAC(9)|GTGGGCCCAC(10)|TGTGGGCCCAC(11)|GGCCCACA(8)|GGGCCCACA(9)|TGGGCCCACA(10)|GTGGGCCCACA(11)|TGTGGGCCCACA(12)

For example, reviewing length (8) only:

TGTGGGCC (8) occurs 5 times

GTGGGCCC (8) occurs 8 times

TGGGCCCA (8) occurs 9 times

GGGCCCAC (8) occurs 8 times

GGCCCACA (8) occurs 5 times

Any repeat can be ranked based on its ocurrence within all possible combinations of a given sequence, known as the repeats' iScore rank. This illustrates a potential useful statistical ranking that, subject to biology may describe a repeats inherency to be more or less effective, in increments of the gene sequence. 

Repression of the most active sequences, especially in context of repeats may result in genetic variation. 

Cell's with an Index like Google?

Its been a while since I last wrote about DNA repeats or their RNA descendants. In that time advanced research has emerged relating repeats to increasing numbers of viral or other disease. Generally the repeats of interest here can be either long or short sequences of nucleotides that from part of an unspliced gene. Logically, counts of long sequences that repeat would be less than short sequences, but when normalized to their respective nucleotide lengths the indexed results can shift the relative order of repeating sequences quite dramatically.

In most knowledge systems repeats in low level data present redundancy and opportunity to improve efficacy in local or global upstream processes acting on that data. We see this in the structure of efficient alphabets that had a significant impact on whether or not a language survived continuous use. Why use ten words when precise meaning, including abstracts can be derived from three. Or why alpha when, at least for some period in the language history alphanumeric made it more effective? 

Search engines reduce their primary index to the least redundant data set used to drive efficient data access by upstream requests and processes to satisfy any query. However, at the storage level, data redundancy is permitted because energy efficiency is gained. Similarly genetic DNA is massively redundant. Redundant data stores can make highly indexed systems more efficient because frequently accessed data elements are more accessible at multiple locations and parallel processes can more efficiently satisfy upstream requests.

Repetitive sequences constitute 50%–70% of the human genome. Some of these can transpose positions, these transposable elements (TE's) are DNA transposons and retrotransposons. The latter are predominant in most mammals and can be further divided into long terminal repeat (LTR)-containing endogenous retrovirus transposons and non-LTR transposons including short interspersed nuclear elements (SINEs) and long interspersed nuclear elements (LINEs). The most abundant subclass of SINEs comprises primate-specific Alu elements in human with more abundant GC-rich DNA. Humans have up to 1.4 million copies of these repeats, which constitute about 10.6% of the genomic DNA. Long interspersed element-1 (LINE1 or L1), are abundant in AT-rich DNA, constitute 19% of the human genome and make up the largest proportion of transposable element-derived sequences.

Most TE classes are primarily involved in reduced gene expression, but Alu elements are associated with up regulated gene expression. Intronic Alu elements are capable of generating alternative splice variants in protein-coding genes that illustrate how Alu elements can alter protein function or gene expression levels. Non-coding regions were found to have a great density of TEs within regulatory sequences, most notably in repressors. TEs have a global impact on gene regulation that indicates a significant association between repetitive elements and gene regulation.

In liquid systems, phase separation is one of the most fundamental phase transition phenomena and ubiquitous in nature. De-mixing of oil and water in salad dressing is a typical example. The discovery of biological phase separation in living cells led to the identification that phase-separation dynamics are controlled by mechanical relaxation of the network-forming dense phase, where the limiting process is permeation flow of the solvent for colloidal suspensions and heat transport for pure fluids. The application of this derived governing universal law is a step to understanding and defining the liquid biological indexing equivalence of data-processing systems and inherent genetic redundancy.

Repeats have been widely implicated. In plant immunity a TE has been domesticated through histone marks and generation of alternative mRNA isoforms that were both directly linked to immune response to a particular pathogen. p53 transcription sites evolved through epigenetic methylation, deamination and histone regulation that constituted a universal mechanism found to generate various transcription-factor binding sites in short TE's or Alu repeats. In disease cytoplasmic synthesis of Alu cDNA was implicated in age related macular degeneration and there is transient increase of nearly 20-fold in the levels of Alu RNA during stress, viral infection and cancer.

In chromosomal DNA, each sequence, relative to its length may conveniently describe a phase-separated indexed location and method for discovery. Repeats within genetic DNA may present precisely sensitive phase-separated guidance to drive histone, epigenetic and transcription factors to specific genetic locations at the cells' 'end-of-line' from where the genetic response to upstream membrane bound changes begin.