Valproic acid enhances Oct4 promoter activity in myogenic cells

Induced pluripotent stem (iPS) cells are reprogrammed from somatic cells through ectopic expression of stem cell-specific transcription factors, including Oct4, Nanog, Sox2, Lin28, Klf4, and c-Myc. Although iPS cells are similar to embryonic stem (ES) cells in their pluripotency, their inherited defects, such as insertion mutagenesis, employment of oncogenes, and low efficiency, associated with the reprogramming procedure have hindered their clinical application. A study has shown that valproic acid (VPA) treatment can significantly enhance the reprogramming efficiency and avoid the usage of oncogenes. To understand how VPA can enhance pluripotency, we stably transfected an Oct4 promoter driven luciferase reporter (Oct4-1.9k-Luc) into P19 embryonic carcinoma (EC) cells and C2C12 myoblasts and examined their response to VPA. We found that VPA could both activate Oct4 promoter and rescue its inhibition by retinoic acid (RA). In C2C12 myoblasts, VPA treatment also enhanced endogenous Oct4 expression but repressed that of MyoD. Furthermore, both RARalpha over-expression and mutation of a proximal hormone response element (HRE) blocked the activation effect of VPA on Oct4 promoter, implying that VPA may exert its activation effect through factors targeting this HRE. Taken together, these observations identify a molecular mechanism by which VPA directly regulate Oct4 expression to ensure the acquirement and maintenance of pluripotency.