Nanog induces suppression of senescence via down-regulation of p27^KIP1 expression

A comprehensive analysis of the molecular network of cellular factors establishing and maintaining pluripotency as well as self renewal of pluripotent stem cells is key for further progress in understanding basic stem cell biology. Nanog is necessary for the natural induction of pluripotency in early mammalian development but dispensable for both, its maintenance as well as its artificial induction. To gain further insight into the molecular activity of Nanog we analyzed the gain-of-function of Nanog in various cell models employing a recently developed biologically active recombinant cell-permeant protein, Nanog-TAT. We found that Nanog enhances proliferation of both, NIH 3T3 as well as primary fibroblast cells. Nanog transduction into primary fibroblasts results in suppression of senescence‑associated β‑galactosidase activity. Investigation of cell cycle factors revealed that transient activation of Nanog correlates with consistent down-regulation of cell cycle inhibitor p27^KIP1. By chromatin immunoprecipitation analysis we confirmed bona fide Nanog binding sites upstream to the p27^KIP1 gene, establishing a direct link between physical occupancy and functional regulation. Our data demonstrates that Nanog enhances proliferation of fibroblasts via transcriptional regulation of cell cycle inhibitor p27 gene.