73-kDa heat shock cognate protein interacts directly with P27Kip1,a cyclin-dependent kinase inhibitor, during G1/S transition

Although heat shock proteins (HSPs) were discovered as inducible proteins b y the physical stress to protect cells, recent evidence has suggested that HSPs are likely involved in cell cycle control under normal conditions with out stress. In the present study, we demonstrated that 73hsc (heat shock co gnate protein), which belongs to the HSP70 family of molecular chaperones, interacts with P27Kip1, an inhibitor of cyclin-dependent kinase, during G1/ S transition. 73hsc was detected in the immunoprecipitates with anti-P27Kip 1 antibody and, vice versa, P27Kip1 was present in the immunoprecipitates w ith anti-73hsc antibody by Western blotting using growth-stimulated rat thy roid FRTL-5 cells. This complex formation of 73hsc and P27Kip1 was cell cyc le dependent and its maximum formation was observed at G1/S transition wher e the level of P27Kip1 dramatically decreased. ATP dissociated this complex formation in a dose-dependent manner. These data indicated that 73hsc migh t be involved in the cell cycle progression through the regulation of cell cycle regulators such as P27Kip1. (C) 1999 Academic Press.