Fig. 7.

MYC enhances global transcription and phosphorylation of Ser2 of the CTD and antagonizes CDK9 sumoylation. a Ectopic expression of MYC in HEK293T cells resulted in increased global transcription. The total levels of RNAs were determined from equivalent numbers of control and Myc-MYC expressed HEK293T cells. b WB analyses showing that ectopic expression of Myc-MYC resulted in an increased level of Ser2P and reduced levels of CDK9 sumoylation. c BrU incorporation assay showing that ectopic expression of Myc-MYC resulted in elevated levels of BrU incorporation in HeLa cells. d IF staining analysis showing that ectopic expression of Myc-MYC resulted in elevated levels of Ser2P in HEK293T cells. e Expression of Myc-MYC effectively blocked CDK9 sumoylation. HeLa cells were transfected with Flag-CDK9, GFP-SUMO-1, HA-PIAS1 and Myc-MYC as indicated and sumoylation on Flag-CDK9, Myc-MYC and global sumoylation were detected by WB using anti-Flag, anti-Myc or anti-GFP as indicated. f IF staining showing that expression of Myc-MYC blocked the inhibition of PIAS1 and PIAS1/SUMO-1 on Ser2P. g WB analysis showing that knockdown of MYC in HeLa cells resulted in reduced level of Pol II Ser2P and increased CDK9 sumoylation. NC, cells treated with scrambled siRNA. h WB analysis showing that knockdown of MYC in 293T cells resulted in reduced levels of Pol II Ser2P and increased CDK9 sumoylation. NC, cells treated with scrambled siRNA. i WB analysis showing that T-cell activation induced by co-stimulation using anti-CD3 and anti-CD28 in vitro was accompanied by induction of MYC, increased Ser2P and reduced CDK9 sumoylation. j T-cell activation induced by co-stimulation using anti-CD3 and anti-CD28 in vitro was associated with increased global transcription. Total levels of RNAs were determined from the same amount of naive and T-cells treated with anti-CD3 and anti-CD28 for 8 h