Kinase Activity Of Cdk11p58 And Sgt/pias1 Interaction And Apoptosis

PARTⅠ:The research of CDK11p58 protein kinase activity in apoptosisCDK11p58,a G2/M-specific protein kinase,has been shown to be associated with apoptosis in many cell lines,with largely unknown mechanisms.Our previous study proved that CDK11p58 enhanced cycloheximide(CHX)-induced apoptosis in SMMC-7721 hepatocarcinoma cells.Here we reported for the first time that ectopic expression of CDK11p58 down-regulated the expression of Bcl-2 and its Ser70,Ser87 phosphorylation in CHX-induced apoptosis in SMMC-7721 cells.Overexpression of Bcl-2 counteracted the pro-apoptotic activity of CDK11p58.Furthermore,we confirmed that the kinase activity of CDK11p58 was essential to the down-regulation of Bcl-2 as well as apoptosis.Taken together,these results demonstrated that CDK11p58 down-regulated Bcl-2 in pro-apoptosis pathway depending on its kinase activity,which elicited survival signal in hepatocarcinoma cells. PARTⅡ:The research of the interaction of SGT with PIAS1 and its function in apoptosisSmall glutamine-rich tetratricopeptide repeat-containing protein(SGT) acts as a co-chaperone,interacting with several essential chaperones,such as Hsp70 and Hsp90. Our previous study showed the pro-apoptosis activity of SGT.However,the biological mechanism remains unclear.To further investigate its functions,we used the yeast two-hybrid system to screen a human fetal liver cDNA library and identified PIAS1(protein inhibitor ofαctivated STAT 1) as an interacting partner of SGT.The association of SGT with PIAS1 was further confirmed by GST-pull down in vitro. Based on the different subcellular location of this two molecule and the fact that SGT translocates into nucleus after Geldanamycin(GA,an Hsp90 inhibitor) or other apoptosis inducer treatment,we revealed SGT interacted with PIAS1 in vivo after it translocated into the nucleus.Further studies showed that inhibition of PIAS1 expression by siRNA infected the pro-apoptosis activity of SGT.Collectively we concluded that SGT transloacted into the nucleus and induced apoptosis upon stress stimuli.SGT interacted with PIAS1 in the nucleus,and PIAS1 played a role in the pro-apoptosis process of SGT.