Enhanced Activities of OCT4 and SOX2 Promote Epigenetic Reprogramming by Shortening G1 Phase

To investigate the interplay among OCT4, SOX2, and KLF4, the VP16 activation domain is fused to one or multiple of these factors during reprogramming. Fusion of VP16 with OCT4 and SOX2 (OvSvK) significantly increases the efficiency of induced pluripotent stem cell (iPSC) generation compared to other combinations. The enhanced activities of OCT4 and SOX2 directly facilitated reprogramming by activating downstream targets, some of which are involved in cell cycle regulation. This leads to a shortened G1 phase and a shift in cell cycle dynamics toward an iPSCs-like state. Further analysis reveals that these cell cycle alterations reduced H3K27me3 levels on specific genes, thereby promoting reprogramming. Consistently, knockdown of Ccnd1 and Cdkn2a (siCcnd1, siCdkn2a) as well as overexpression of Ccne1 effectively shortened the G1 phase and enhanced reprogramming efficiency. These findings highlight the role of cell cycle modulation in epigenetic remodeling and provide mechanistic insights for optimization during somatic cell reprogramming.