Hypoxia-induced immortalization of primary cells depends on Tfcp2L1 expression

Cellular senescence is a stress response mechanism that induces proliferative arrest. Hypoxia can bypass senescence and extend the lifespan of primary cells, mainly by decreasing oxidative damage. However, how hypoxia promotes these effects prior to malignant transformation is unknown. Here we observed that the lifespan of mouse embryonic fibroblasts (MEFs) is increased when they are cultured in hypoxia by reducing the expression of p16 INK4a , p15 INK4b and p21 Cip1 . We found that proliferating MEFs in hypoxia overexpress Tfcp2l1 , which is a main regulator of pluripotency and self-renewal in embryonic stem cells, as well as stemness genes including Oct3/4 , Sox2 and Nanog . Tfcp2l1 expression is lost during culture in normoxia, and its expression in hypoxia is regulated by Hif1α. Consistently, its overexpression in hypoxic levels increases the lifespan of MEFs and promotes the overexpression of stemness genes. ATAC-seq and Chip-seq experiments showed that Tfcp2l1 regulates genes that control proliferation and stemness such as Sox2 , Sox9, Jarid2 and Ezh2 . Additionally, Tfcp2l1 can replicate the hypoxic effect of increasing cellular reprogramming. Altogether, our data suggest that the activation of Tfcp2l1 by hypoxia contributes to immortalization prior to malignant transformation, facilitating tumorigenesis and dedifferentiation by regulating Sox2 , Sox9 , and Jarid2 .