Regulation of PPARgamma2 Gene Expression by PcG AND pRb Family Proteins in the Course of Adipogenic Differentation of Mesenchymal Stem Cells

The signal pathways associated with formation of the adipose cell phenotype converge on the regulation of expression of the tissue-specific PPAR γ 2 gene. Here we studied the interaction of Ezh2, Bmi1 and Utx proteins, which regulate the methylation levels of the H3K27, and p130 (a member of pRb family) with the promoter of PPAR γ 2 , a regulator of adipogenic differentiation (AD), in the course of AD of murine mesenchymal stem cells (MSCs) using the chromatin immunoprecipitation (ChiP). In undifferentiated cells, promoters of the PPAR γ 2 and control RUNX2 gene, a regulator of bone differentiation, accumulated high levels of Bmi1, Ezh2 and low levels of Utx. The p130 was detected in undifferentiated cells at high levels on the PPAR γ 2 , but not on the RUNX2 promoter. These protein-DNA interactions changed in the opposite way in the course of AD on the PPAR γ 2 promoter but did not change on the RUNX2 promoter. In cells with inactivated BMI1 under AD conditions there was observed a slight decrease in the H3K27me3 levels and an increase in the levels of Utx demethylase on the PPAR γ 2 promoter. Our results suggest that PPAR γ 2 expression in the terminal phase of AD in murine MSCs is activated by Utx, but is suppressed by Bmi1, Ezh2 and p130. These data support the hypothesis that in the course of differentiation there is a loss of the suppressive H3K27me3 mark in the bivalent domains of regulatory genes including PPAR γ 2 that contribute to formation of the tissue-specific phenotype.