Identification of a novel role for Mtf2 in the regulation of PRC2 mediated H3K27me3

Abstract

Polycomb repressive complex 2 (PRC2) is known to play a crucial role in the regulation of early embryonic development, differentiation, and cellular proliferation by the introduction of methyl groups at histone H3 lysine 27. The binding of the PRC2 is necessary for the repression of developmental marker genes in undifferentiated cells as well as for the timely expression during cell differentiation. Hox clusters are the eminent PRC2 target genes in the undifferentiated cells, for instance, Embryonic Stem cells (ESCs). In ESCs PRC2 inhibits the expression of the genes by the repressive histone mark, H3K27me3. Likewise, F9 carcinoma are undifferentiated cells that have the characteristic of both ESCs and cancer stem cells (CSCs). To explore the role of PRC2, F9 cells were differentiated to primitive endoderm by retinoic acid (RA) and the chromatin status was investigated by performing a series of chromatin immunoprecipitation followed by sequencing (ChIP-Seq) experiments. Low enrichment of EZH2, SUZ12, EED, and H3K27me3, as well as a significant increase in H3K4me3 associated with active transcription, was found at Hox cluster genes during cell differentiation. In contrast, knockdown of core PRC2 components (EZH2, SUZ12, and EED) in undifferentiated cells elevated the levels of H3K27me3 at Hox genes despite the global decrease of the same modification. Double inhibition of EZH1/2 by specific inhibitor was unable to curtail the hyper-trimethylation of histone H3 lysine 27 at Hox genes illustrating that EZH1 is not the complementary component of EZH2. Consistently, no changes in the expression of Hox genes were observed with the down-regulation of PRC2 as well as their expression was abated during cell differentiation. One of the sub-stoichiometric components of PRC2, Metal response element binding transcriptional factor 2 (MTF2) was found to be recruited to the Hox genes in the PRC2 dependent manner. Interestingly, knockdown of Mtf2 in the Suz12-KO cells restored the high enrichment of H3K27me3 and escalated the Hox genes expression by the augmentation of active histone mark, H3K4me3. These results demonstrate a novel role for Mtf2 in the regulation of PRC2 mediated H3K27me3 and Hox genes expression.