GSE173648
Hypoxia-induced expression of Tfcp2l1 promotes cell immortalization by enhancing cellular reprogramming
Cellular senescence is a stress response mechanism maintaining tissue homeostasis by changing physiological state and inducing irreversible proliferative arrest. It has been reported that hypoxia can bypass senescence and extend lifespan of naïve primary cells, mainly, by the decrease in oxidative damage. However, it is unclear how hypoxia can promote the evasion of senescence and promote cell immortalization prior to malignant transformation.  We observed that the lifespan of MEFs is increased when they are cultured in hypoxia, reducing the expression of p16INK4a, p15INK4b and p21Cip1. In transcriptional genetic screenings, we found that proliferating naïve MEFs in hypoxia overexpress Tfcp2l1, which is a main regulator of pluripotency and self-renewal in embryonic stem cells, ESCs, as well as stemness-associated genes like Oct3/4, Sox2, Nanog. Tfcp2l1 expression is lost during culture in normoxia. The expression of Tfcp2l1 in hypoxia seems to be regulated by Hif1a and only when it is overexpressed at similar levels to those induced physiologically by hypoxia it increases lifespan of MEFs and promotes overexpression of stemness-associated genes. In Chip-seq experiments, we found that Tfcp2l1 binds and activate the expression of genes which regulate proliferation, which in many cases, are also related to stem cell properties, such as Sox2, Sox9 and Tgfa. Additionally, Tfcp2l1 can replicate the effect of hypoxia increasing cellular reprogramming and its expression correlates positively with the expression of Nanog and negatively with p21Cip1 and p16INK4a.  Altogether, our data suggests that the activation of Tfcp2l1 by hypoxia could be relevant in the immortalization prior to malignant transformation, facilitating tumorigenesis and dedifferentiation of cells. Overall design: ChIP-seq and ATAC-seq assays in MEFs undergoing senescence in normoxia or immortalized in hypoxia