Cleavage of histone H2A during embryonic stem cell differentiation destabilizes nucleosomes to counteract gene activation [RNA-seq]

Histone proteolysis is a poorly understood phenomena by which the N-terminal tail of histones are irreversible cleaved by intracellular proteases. During development histone PTMs are known orchestrate gene expression and ultimately cell fate decision, therefore it will be key to decipher underlying mechanisms that lead to proteolysis during cellular differentiation. Previous reports have found that histone H2A is cleaved at the C-terminus, and here we found that the N-terminal is also proteolytically clipped and removed by the lysosomal protease Cathepsin L. Using quantitative mass spectrometry (MS), we identified L23 to be the primary site for this protease, with this clipped H2A (cH2A) form representing ~1% of the total H2A reaching a maximum after 4 days of differentiation. Using Chip-seq, we found reduced proteolysis, lead to increase acetylated H2A at promoter regions in differentiated ES cells. We also report novel readers of acetylated H2A during in pluripotency as we identified members of the pBAF complex to recognize different forms of H2A acetylation. Moreover, our data showed that this recognition is abolished upon proteolysis. All in, our data suggest that proteolysis serve as a quick mechanism to silence genes involve in pluripotency and destabilize the nucleosome core particle as indicated by protein degradation studies. RNA-seq in mESCs differentiation with CTSL KD.