Shared Regulatory Circuits in Pregnancy and Cancer

One of the more intriguing patterns in biology is that processes for normal development often resemble those that appear in disease. Few examples illustrate this better than the similarity between trophoblast invasion during pregnancy and the early stages of tumor growth.

In both situations, cells penetrate surrounding tissue, remodel blood vessels, and establish themselves within an environment that tolerates their presence rather than destroying them. The mechanisms that allow this to occur remain incompletely understood. Increasing evidence suggests that deubiquitinases (DUBs), enzymes that remove ubiquitin from proteins and thereby regulate signaling thresholds, may play an important role in stabilizing this permissive state.

This raises a provocative possibility: the regulatory machinery that enables the maternal–fetal interface to tolerate trophoblast invasion may share features with the mechanisms tumors exploit to evade immune detection.

During early pregnancy, decidual natural killer cells (dNK) become the dominant immune cell population in the uterus. Rather than behaving as cytotoxic killers, these cells adopt a distinct phenotype that supports; angiogenesis, spiral artery remodeling, trophoblast invasion.

The density of NK cells in the decidua is striking, often representing 50–70% of immune cells in early pregnancy. Instead of attacking invading trophoblasts, these NK cells participate in building the placenta and converting maternal spiral arteries into vessels capable of supporting fetal circulation.

Maintaining such a high density of NK cells without triggering immune destruction requires a carefully tuned balance between activation signals and inhibitory regulatory pathways. One of the central signals controlling NK cells in both peripheral tissues and the uterus is IL-15. In the decidua, IL-15 produced by stromal cells supports the recruitment, proliferation and survival of NK cells.

Recent work has identified YTHDF2, an m⁶A RNA-binding protein, as a key downstream regulator of this process. In NK cells: IL-15 → STAT5 → YTHDF2 → NK-cell homeostasis. YTHDF2 regulates the stability of specific mRNAs that determine NK survival, proliferation and maturation. Through selective RNA decay, YTHDF2 effectively tunes the functional state of NK cells.

A p53 regulatory layer likely intersects with this system. p53 is best known as a tumor suppressor that responds to DNA damage and cellular stress by regulating transcriptional programs controlling cell cycle arrest and apoptosis. But, p53 also plays an important role in immune signaling and communication between stressed cells and the immune system.

For example, p53 activation can influence immune surveillance by inducing chemokines and inflammatory mediators that recruit immune cells, including NK cells. This places p53 upstream of many of the stress-response pathways that determine whether an NK cell should eliminate a target.

p53, and repeat RNA constitute an innate sensing axis through a recently uncovered layer of regulation involving endogenous repetitive elements and innate immune sensing. Wild-type p53 helps suppress the activity of transposable elements such as LINE-1 and other repeat sequences. Loss or mutation of p53 can lead to derepression of these elements and the production of immunogenic nucleic acids. Many repetitive elements, including Alu sequences, can form double-stranded RNAs that activate innate immune sensors such as RIG-I and MDA5. Through these pathways, endogenous RNA molecules can mimic viral infection and activate interferon responses.

p53 also intersects with the cGAS–STING pathway, another major nucleic-acid sensing system. Wild-type p53 can promote activation of STING signaling by enabling cytosolic DNA accumulation through degradation of the nuclease TREX1. In contrast, mutant p53 can suppress STING signaling, helping tumors evade immune detection. Together these findings suggest that p53 may influence immune surveillance not only through classical stress pathways, but also through control of endogenous nucleic-acid signaling systems.

While RNA regulation shapes the NK-cell transcriptome, a second regulatory layer operates through ubiquitin signaling. Many proteins involved in immune activation are controlled by ubiquitination. Deubiquitinases (DUBs) reverse this process, stabilizing proteins or suppressing signaling cascades depending on the target. One DUB that has recently drawn attention is USP13 that has been shown to regulate several pathways central to immune signaling and cellular stress responses, including STING-dependent innate immune activation. Network analysis in prostate cancer datasets also show a strong interaction between USP13 and the RNA regulator YTHDF2, linking ubiquitin signaling to the RNA regulatory machinery governing NK cells. 

Interestingly, the relationship between NK cells and invasive cells is not unique to pregnancy. Studies show that NK cells often accumulate in tissues surrounding early tumors, particularly during the earliest stages of transformation. In many cancers, NK cells are present in peritumoral tissue, but become functionally suppressed or excluded as tumors progress. This pattern suggests that the immune system initially recognizes abnormal cells but may later be restrained by tumor-driven immunoregulatory mechanisms. The result is a paradox: NK cells are present but ineffective.

Taken together, these observations suggest a regulatory architecture that could stabilize environments where invasion must occur without triggering destructive immunity.

In such a system:

1. Cellular stress signals activate p53 and generate stress-response transcripts.

2. Endogenous repeat RNAs may activate innate immune sensing pathways such as RIG-I, MDA5 and STING.

3. Cytokine signaling such as IL-15 supports NK-cell expansion and survival.

4. RNA-level regulation via YTHDF2 tunes NK-cell gene expression and maturation.

5. Deubiquitinases such as USP13 modulate innate immune signaling intensity and prevent excessive inflammatory activation.

The combined effect could be a high-NK-density but low-cytotoxic environment capable of supporting tissue remodeling and vascular development. In pregnancy, this environment enables trophoblast cells to invade maternal tissue and establish the placenta. Tumors may exploit the same architecture

Early tumors face a challenge similar to that encountered by trophoblasts: they must expand and invade tissue while avoiding immune elimination.

Many tumors exhibit features reminiscent of the decidual microenvironment, including; suppressed innate immune signaling, dysfunctional or tolerized NK cells, enhanced angiogenesis and extensive tissue remodeling.  If DUBs such as USP13 help establish these permissive states, tumors could potentially co-opt the same regulatory circuits that operate at the maternal–fetal interface.

In this view, tumors may hijack a developmental program that normally allows pregnancy to proceed successfully. 

The decidua represents one of the most extreme natural examples of immune tolerance in mammals. Understanding how this system maintains large NK-cell populations without triggering inflammation could reveal new strategies for controlling immune responses in other contexts.

If deubiquitinase signaling and p53-mediated nucleic-acid sensing help stabilize this balance, they may represent a broader biological principle; the same regulatory networks that enable successful pregnancy may also be exploited by tumors to evade immune detection.

Uncovering these shared mechanisms could deepen our understanding of both reproductive biology and cancer immunology, and potentially reveal new therapeutic strategies in the process.

p53, Estrogen, and NK Cells Shape Life and Cancer

There is a hidden symmetry between pregnancy and cancer.

In both, tissues must grow rapidly, blood vessels must expand into new territories, and the body must decide whether to permit or restrain invasion. What determines the difference between a nurturing womb and a growing tumor may lie in how a few molecular players — p53, estrogen receptors, natural killer (NK) cells, and VEGF/FLT1 — coordinate their dance around oxygen, stress, and the extracellular matrix.

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The Signal: p53 Meets Estrogen at the FLT1 Gene

In 2010, a PLOS ONE study by Ciribilli et al. uncovered a remarkable piece of the puzzle.
The researchers found that the FLT1 gene — which encodes VEGFR-1, a receptor that senses vascular growth factors — carries a tiny DNA variation (a promoter SNP) that can create a p53 response element. But here’s the twist: p53 doesn’t act alone. It activates FLT1 only when estrogen receptor α (ERα) is nearby, bound to its own DNA half-sites.

This means that p53, often called the guardian of the genome, cooperates with estrogen signaling to tune the sensitivity of blood vessels to VEGF and PlGF, the key drivers of angiogenesis. The study also showed that this activation happens after genotoxic stress such as doxorubicin, but not after other DNA-damaging agents like 5-fluorouracil, underscoring how specific the stress context must be.

In parallel, hypoxia — low oxygen levels — can activate the same FLT1 promoter through HIF-1α. Under these conditions, tissues produce not only the full receptor FLT1 but also its soluble form (sFlt-1), which soaks up VEGF and PlGF like a sponge. It’s a perfect tuning mechanism: too much sFlt-1, and angiogenesis is blocked; too little, and blood vessels grow unchecked.

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The Uterine Parallel: The Angiogenic Flood

A decade later, this molecular logic finds a physiological echo in early pregnancy. In The Angiogenic Growth Factor Flood, I explored how natural killer (NK) cells in the uterine lining (the decidua) create a surge of angiogenic growth factors just before and during implantation.

These decidual NK (dNK) cells express a2V-ATPase, acidifying the extracellular matrix and activating MMP-9, a powerful enzyme that cuts through collagen and releases growth factors bound within the ECM. The result is a literal flood of VEGF and PlGF — the same molecules p53 and ERα regulate through FLT1 expression.

Independent research confirms this choreography. During the first trimester, dNK cells secrete VEGF-C, PlGF, Angiopoietin-1/2, and MMP-2/-9, guiding spiral artery remodeling — the vital widening of maternal arteries that ensures proper blood flow to the placenta (Sojka et al., Frontiers in Immunology 2022). If this process falters, preeclampsia can develop, a condition marked by shallow invasion, high vascular resistance, and — notably — elevated sFlt-1 levels in maternal blood (Levine et al., NEJM 2004).

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Two Layers, One Circuit

Taken together, these findings reveal a single two-layered circuit:

1. The receptor layer –
   p53, ERα, and HIFs determine how much FLT1/sFlt-1 the tissue expresses, setting its sensitivity to VEGF and PlGF.

2. The matrix layer –
   NK cells and trophoblasts remodel the ECM via a2V-ATPase and MMP-9, controlling the availability of those same VEGF and PlGF molecules.

When these layers synchronize, arterial remodeling proceeds smoothly: arteries dilate, resistance drops, and the embryo receives life-sustaining flow. When they desynchronize, the results diverge — preeclampsia in pregnancy, or uncontrolled angiogenesis in tumors.

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From the Womb to the Tumor

It’s no coincidence that cancer co-opts the same program. Hypoxic tumor microenvironments stabilize HIF-1α and HIF-2α, driving VEGF and FLT1 expression much like the early placenta. Meanwhile, matrix metalloproteinases (MMPs) — especially MMP-9 — break down ECM barriers and unleash angiogenic factors, supporting invasion and metastasis. Some tumors even enlist NK-like cells that, paradoxically, promote angiogenesis rather than suppress it (Gao et al., Nature Reviews Immunology 2017).

The difference is control. In pregnancy, p53 remains intact but functionally moderated, allowing invasion to stop at the right depth. In cancer, p53 mutations or inactivation remove that restraint, unleashing angiogenesis without limit. Wild-type p53 can also induce thrombospondin-1, an anti-angiogenic protein, and repress VEGF itself (Teodoro et al., Nature Cell Biology 2006). When p53 is lost, that brake disappears.

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Lessons in Balance

The elegance of this system lies in its balance. The sFlt-1/PlGF ratio, now used clinically to predict preeclampsia, captures that equilibrium numerically (Zeisler et al., NEJM 2016). Too much soluble receptor, and the flood is dammed; too little, and angiogenesis runs wild.

The parallels between the placenta and the tumor remind us that biology reuses its best designs — sometimes for creation, sometimes for destruction. Both depend on oxygen gradients, immune-matrix crosstalk, and the nuanced cooperation of p53, ERα, HIFs, and NK-cell proteases.

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Looking Ahead

Understanding this unified circuit opens therapeutic possibilities on both fronts:

• In obstetrics, modulating the sFlt-1/PlGF balance and supporting healthy NK/trophoblast-matrix signaling may prevent or reverse preeclampsia.

• In oncology, restoring p53 function, adjusting ER context, or tempering HIF-driven FLT1 and MMP-9 activity could re-normalize tumor vasculature.

• In both, recognizing NK cells as angiogenic regulators — not just killers — reframes how immune therapy and vascular therapy intersect.

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Further Reading

• The Coordinated p53 and Estrogen Receptor Cis-Regulation at an FLT1 Promoter SNP — PLOS ONE (2010)

• The Angiogenic Growth Factor Flood — Codondex Blog (2022)

• Sojka et al., Front Immunol 2022 – Uterine NK cells and spiral artery remodeling

• Levine et al., NEJM 2004 – sFlt-1 and PlGF in preeclampsia

• Zeisler et al., NEJM 2016 – sFlt-1/PlGF ratio for preeclampsia prediction

• Teodoro et al., Nat Cell Biol 2006 – p53 repression of VEGF via thrombospondin-1

• Gao et al., Nat Rev Immunol 2017 – NK cells in angiogenesis and cancer

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Indispensable Mitochondria - Cancers back door?

Immediately prior to fertilization spermatozoa are devoid of Mitochondrial DNA (mtDNA), potentially explaining an aspect about selection that may serve the legacy for maternal immune tolerance. Post fertilization, on day 11-13, outermost trophoblasts of the blastocyst dock with the decidual lining as it embeds in the uterine wall. Then, maternal vascular remodeling and placental formation begin toward successful implantation. 

Higher quality trophoblasts are associated with lower mtDNA content. Moreover, euploid blastocysts with higher mtDNA content had a lower chance to implant and mtDNA replication is strictly downregulated between fertilization and the implantation. What is it about absent or reduced mtDNA that may also relate to the mechanics of immune tolerance and vascular remodeling, which are also features of solid tumors.

The initial absence or downregulation of MtDNA, may relate an immune tolerance by uterine Natural Killer (NK) cells. As mtDNA upregulates, after day 12, it may initiate NK auto-reactivity required for maternal microvascular remodeling. This auto-immune paradox is a prerequisite for vascular remodeling, which is also seen in localized hypertension, and the likely basis of successful blastocyst implantation. Acutely, micro-hypertension induced mechanical stretch, on endothelial cells, interconnects innate and adaptive immune responses. 

The dominant cell in the decidua is an NK subset (dNK), they express low levels of IFN-γ and express proteins of Renin Angiotensin System (RAS). At day 12 RAS peptide ANP colocalizes to dNK’s suggesting that dNK RAS infers localized responsiveness.  When TFAM, required for transcription of mtDNA, was deleted from cardiomyocytes, after 32 days, animals developed cardiomyopathy and Nppa (gene encoding ANP) and Nppb expression was elevated. 

In monocytes increased endothelial stretch activates STAT3, which is involved in driving almost all pathways that control NK cytolytic activity and reciprocal regulatory interactions between NK cells and other components of the immune system. The crosstalk between STAT3 and p53/RAS signaling controls cancer cell metastasis. p53, Stat3, and, potentially, the estrogen receptor are thought to act as co-regulators, affecting mitochondrial gene expression through protein-protein interactions. Co-immunoprecipitation of p53 with TFAM suggests it may regulate mitochondrial DNA-damage repair.

Like initial trophoblasts with low level mtDNA, mature cells, like cardiomyocytes that prolong low level mtDNA may also aggravate autoimmune sponsored hypertension that remodels microvascular networks providing nutrients for growth of reduced mtDNA stem cell replicas. Indeed, mitochondrial dysfunction (from depleted mtDNA) does not affect pluripotent gene expression, but results in severe defects in lineage differentiation.

During severe sepsis, intense, on-going mtDNA damage and mitochondrial dysfunction could overwhelm the capacity for mitochondrial biogenesis, leading to a gradual decline in mtDNA levels over time. This may contribute to monocyte immune deactivation, which is associated with adverse clinical outcomes and could be reversed by IFN-γ. 

Identifying cells that optimally educate cocultured NK cells for precision IFN-γ and cytolytic responsiveness is part of the ongoing work by the Codondex team.

Angiogenic Growth Factor Flood

A previous series, about p53 culminated with "Blastocyst Development - A Perfected Cancer Model" that focused on the parallels in angiogenesis, triggered by blastocyst implantation and progression of tumors beyond ~1mm. Now, a recent study has found that conventional Natural Killer cells (cNK) control vascular remodeling in the uterus during pregnancy by acidifying the extracellular matrix (ECM) with a2V-ATPase that activates MMP-9 that degrades the ECM. Ablation of a2V-ATPase decreases Bax and p53 expression in testis and leads to implantation failure in the female mouse. The degrading ECM releases bound pro-angiogenic growth factors that contribute to Uterine artery (UtA) remodeling characterized by the loss of vascular smooth muscle cells (VSMCs) and dilation of the vessels. Without cNK, the UtA never lose VSMCs and UtA resistance remains high often leading to implantation failure.

Its logical that a timely flood of angiogenic growth factors, previously stored in the ECM would provide instant availability, but whether this explains the maternal-embryonic immune paradox remains to be determined? In the immune paradox maternal NK cells invade and maternal blood vessels are remodeled just before the arrival of trophoblasts, the external cells of the blastocyst, that carry male antigens during formation of the fetal placenta. A sudden flood of angiogenic factors preceding invading trophoblasts could provide the perfect environment required for maternal arterial/vascular remodeling.

Lymphocytes in the uterine lining (decidua) are dominated by a unique decidual natural killer (dNK) cell population. The dNK cell surface phenotype CD56bright CD16− CD3− and macrophages CD14+ CD206+(dMac) support a model whereby dNK cells, capable of killing extra-villous cytotrophoblasts (CTB), are prevented from doing so by neighboring macrophages thus protecting the fetal cells from NK cell attack. Existing research has centered on the function of the abundant and diverse sets of dNK, but now that cNK cells have been identified to play a more significant role, our understanding of the remodeling are likely to change.

In CTB exogenous p53 is able to down-regulate MMP-9 promoter activity, but endogenous p53 is not able to regulate MMP-9 expression in first trimester CTB cells. Inactivation of p53 through mutation is the most common trait in cancer. By loosing its onco-suppressive activity, p53 becomes oncogenic in almost all malignant tumors (Soussi and Lozano, 2005). Although p53 is not mutated in the human placenta, it has become functionally incompetent. Understanding why and how p53 is functionally incompetent in CTB might well be the key to understanding trophoblast invasion.

Downregulation of EMMPRIN (BSG,CD147) by p53 leads to a decrease in the activity of MMP-9 and an inhibition of tumor cell invasion. Upregulation of EMMPRIN seen in many cancers can be attributed to, at least in part, to the dysfunction of p53 and thus provides new evidence for the roles of p53 in tumor development and progression. Epithelial derived MMP-9 exhibits a novel defensive role of tumor suppressor in colitis associated cancer by activating MMP9-Notch1-ARF-p53 axis. MMP-9 mediates Notch1 signaling via p53 to regulate apoptosis, cell cycle arrest, and inflammation. 

The inter-activity of p53, cNK and MMP-9 are complexed, but this novel research may lead to the mechanisms by which arterial remodeling occurs after release of angiogenic factors from ECM. If that shares characteristics of NK invasion into developing tumor micro environment's a new therapeutic approach may arise.