The Cancer Effect On P53 and Natural Killer Cells

Naked Mole Rat Without NK Cells

New evidence elucidated the mechanisms of growth promoting and disrupting modes of Natural Killer (NK) cells especially in Tumor Micro Environments (TME). In a previous article on cancer exploiting modes of reproduction I explained that NK cells have an innate capacity to effect reproduction during the early stages of Blastocyst implantation and placental development. These include NK cells secreting growth promoting factors and near simultaneous disruption of epithelial cells lining spiral arteries, that penetrate the decidua to expose maternal blood to extravillous cytotrophoblasts of the developing fetal placenta.

Extravillous cytotrophoblast invasion involves a cellular transition from an epithelial to mesenchymal phenotype. Villous cytotrophoblasts undergo a partial epithelial to mesenchymal transition (EMT) when differentiating into extravillous cytotrophoblasts and gain the capacity to migrate and invade. 

An antagonistic relationship between transforming growth factor (TGF)-β and tumor necrosis factor (TNF)-α provides a glimpse into cancers influence over NK cells to permit and promote survival, extravasatation and metastasis. Multiple studies report synergism between TGF and TNF in EMT to cancer. Spatiotemporal regulation of DeltaNp63 by TGF regulated miRNAs is essential for cancer metastasis and the interplay between different p63 isoforms, related mutant p53 proteins, and p53 family members can largely determine overall anti-metastatic activity.

Mutant p53 that is co-expressed with WT p53 in human bronchial epithelial cells inhibits the response of  cancer cells to TGF. However, overexpression of mutant p53 on a p53-null background is able to attenuate the response to TGF. Mutant p53 is also implicated is chronic inflammation, a well-accepted hallmark of cancer. Numerous studies showed that the TME has a significant impact on perpetuation of the chronic inflammatory state. Mutant p53 is able to enhance the activation of NF-κB by TNFα, while concomitantly suppressing the pro-apoptotic effect of TNFα, which leads to increased invasiveness of the cancer cells. 

Blockade of TNF improved NK cell activation, hypertension, and mitochondrial oxidative stress in a preclinical rat model of preeclampsia. Rats with depleted NK cells had decreased serum and placental levels of TNF support that NK cells secrete TNF, indicating an autocrine effect. Additionally findings suggest that elevated decidual TGF suppresses the activation of specific subsets of decidual NK cells which in turn contributes to pathology associated with the onset of preeclampsia. A study looked at the cytokine profile of NK cells in early human pregnancy including TGF  and TNF and found two highly specific NK cells in peripheral blood and decidua were most likely responsible for maintenance of pregnancy by regulation of maternal immune function. 

The cancer resistant Naked Mole Rat possess no NK cells, but has a stable p53 half-life more than 10X  that found in human and mouse embryonic fibroblasts. The stability of p53 was determined to result from protein extrinsic factors yet response to DNA damage was classic, via p53 sequestration from nucleus to cytoplasm. How mole rats reproduce without decidual NK cells is an open question? p53 stability may have demoted a need for the mammalian equivalent of allorecognition at the site of Blastocyst implantation. The need for the maternal-fetal decidual NK cell mediation may have been replaced by more direct mechanisms. One option is via pheromone sensing. 

p53 and two related transcription factors p63 and p73 exhibit significant sequence similarity, can bind to the same consensus sites in DNA and activate the same target genes. However, unlike p53, with a paramount role in cancer suppression, p63 and p73 play more central developmental roles. p63 and p73 nullizygosity results in lethality, but p73-nullizygosity also causes pheromone-sensing defects that impede breeding.

Increasingly evidence points to the intricate interplay of p53, its related proteins and NK cells as primary targets for reproductive success and reducing death through cancer.