CELL CYCLE REGULATORY MECHANISMS IN SKELETAL MUSCLE CELLS

Abstract

IN MUSCLE CELLS, PROLIFERATION AND DIFFERENTIATION ARE MUTUALLY EXCLUSIVE EVENTS THAT ARE CONTROLLED BY THE TRANSCRIPTION FACTOR MYOD. DURING DIFFERENTIATION, MYOD-DEPENDENT CELL CYCLE EXIT IS MEDIATED BY P21CIP1/WAF1 AND RB1 THAT IS NECESSARY FOR CELLS TO DIFFERENTIATE. G9A, A LYSINE METHYLTRANSFERASE INHIBITS MYOGENIC DIFFERENTIATION. TO IDENTIFY G9A TARGETS, MICROARRAY ANALYSIS WAS PERFORMED. SEVERAL GENES INVOLVED IN CELL CYCLE CONTROL WERE DE-REGULATED IN G9A KNOCKDOWN CELLS. IN GAIN-OF-FUNCTION AND LOSS-OF-FUNCTION ASSAYS, G9A WAS FOUND TO PROMOTE PROLIFERATION OF CELLS AND INHIBIT CELL CYCLE EXIT. G9A-MEDIATED INHIBITION OF DIFFERENTIATION WAS RESCUED BY RE-EXPRESSION OF P21CIP1/WAF1 AND RB1. INTERESTINGLY, G9A OCCUPANCY CORRELATED WITH REPRESSIVE HISTONE METHYLATION MARKS ON P21CIP1/WAF1 AND RB1 PROMOTERS, BUT NOT ON E2F1-TARGET GENES. OUR DATA SUPPORT A MODEL IN WHICH G9A BOTH PROMOTES PROLIFERATION AND PREVENTS CELL CYCLE EXIT OF MUSCLE CELLS TO BLOCK DIFFERENTIATION. THESE