The Study Of The Mechanism That Crosstalk Between Histone Lysine Acetylation And H3K4 Methylation

Histone lysine acetylation has an important role in transcriptional activation.On the one hand,histone acetylation is believed to promote transcription by neutralizing the positive charge of histone lysine residues,leading to the formation of decondensed chromatin.On the other hand,histone acetylation can promote transcription by recruiting acetylation binding proteins.Histone H3K4 methylation also plays an important role in promoting transcription.Furthermore,both H3K4 methylation,especially H3K4me3,and histone acetylation are enriched on the genomic promoter region.However,the precise mechanism underlying crosstalk between histone acetylation and H3K4 methylation has yet to be elucidated.Through an unbiased approach with in vitro pulldown followed by mass spectrometry identification,we identified that the WDR5 protein specifically binds to histone H3 tail peptides with K9 and K14 double acetylation(H3K9/14ac).WDR5 protein is one of the core subunits of the H3K4 methyltransferase SET1/MLL complex,and it also participates in the formation of a subset of acetyltransferase complexes.Further experimental results showed that like WDR5,SET1/MLL complexes also bind preferentially to the H3K9/14ac peptides,suggesting that WDR5 may be responsible for the binding of acetylated histones by SET1/MLL complexes and thus mediate the crosstalk between histone acetylation and H3K4 methylation.We demonstrate that the increase in cellular histone acetylation induced by addition of histone deacetylase inhibitors resulted in a significant augment in global histone H3K4 methylation,whereas a decrease in histone acetylation resulted in a significant reduction in H3K4 methylation.By screening a large number of mutants,we identified a D107C mutation resulted in loss of preferential binding of acetylated H3 tail without affecting the binding of unmodified H3 tail.Using CRISPR-Cas9 gene editing technique,we knocked out the endogenous WDR5 gene in the HeLa cell lines that stably expressed either wild-type Flag-WDR5 or Flag-WDR5-D107C mutant.Preliminary results showed that HDAC inhibitor treatment induced a significant increase of H3K4 methylation in Flag-WDR5 WT cells,but not in Flag-WDR5-D107C mutant cells.Together our data indicate that WDR5 can bind preferentially doubled acetylated histone H3 tail and this binding activity may mediate the crosstalk between histone acetylation and H3K4 methylation.