GSK-3 Is The Inhibitor Of Proteasome

The proteasomes play important roles in the turnover of the cellular proteins.Malfunction of the proteasomes has been documented in a variety of aging-related human diseases.The structure and the function of the proteasome have been studied thoroughly.Nonetheless,the exact roles of the proteasomes in the pathogenesis of the diseases have been elusive because of the deficiency of our knowledge on the regulation of the proteasomes.Recently,we have found that the protesome function is under the modulation of the metabolic factors including O-GlcNAc modification and PKA PHosPHorylation.The purpose of this study is to evaluate the role of glycogen synthesis kinase 3 in the regulation of porteasome.NRK cell NE was pretreated with GSK-3 in vitro.The effect on the degradation of GST-Sp1 and proteasome trypsin-and chymotrypsin-like peptidase activities was evaluated.To evaluate the effect of GSK-3 on the proteasome function in a living cell,GSK-3 specific inhibitor was applied to NRK or 293 T cells.The stability of GSK-CL1 and the accumulation of the Ubiquitinated proteins were determined.To further demonstrate that GSK-3 inhibits proteasome in the cell,constitutive active GSK-3 mutants,GSK-3S9 A and GSK-3R96 A,were transfected into 293 cells.Their effect on the stability GFK-CL1 was evaluated.GSK-3 pretreatment dramatically inhibited the degradation of GSP-Sp1 and the proteasome trypsin-and chymotrypsin-like peptidase activities in NRK cell NE.GSK-3 specific inhibitor promoted the clearance of GFP-CL1,and the clearance of the Ubiquitinated proteins in the living cell.Both of the constitutive active mutants of GSK-3 inhibited the proteasome function.However,no significant effect of GSK-3 on purified 26 S proteasome was observed,suggesting that GSK-3 might not act on proteasome directly,but rather through other factors in the cell.GSK-3 inhibits proteasome function in the cell.It may act on some through other factor in the cell,which is still waiting to be identified.