Estradiol increases phosphorylation of the 90 kDa heat shock protein not associated with estradiol receptor in MCF-7 cells in culture

Post-translational modification of heat-shock protein 90: impact on chaperone function

Heat-shock protein 90 (Hsp90) is a molecular chaperone required for the stability and function of many signaling proteins that are often activated, mutated or overexpressed in cancer cells and that underly cancer cell proliferation and survival. Hsp90 is a conformationally flexible protein that associates with a distinct set of cochaperones depending on ATP or ADP occupancy of an N-terminal binding pocket. Nucleotide exchange and ATP hydrolysis by Hsp90 itself, with the assistance of cochaperones, drive the Hsp90 chaperone machine to bind, chaperone and release client proteins. Cycling of the Hsp90 chaperone machine is critical to its function. Although ATP binding and hydrolysis have been convincingly implicated in regulating the Hsp90 cycle, growing evidence suggests that various post-translational modifications of Hsp90, including phosphorylation, acetylation and other modifications, provide an additional overlapping or parallel level of regulation. A more complete understanding of how these various protein modifications are regulated and interact with each other at the cellular level to modulate Hsp90 chaperone activity is critical to the design of novel approaches to inhibit this medically important molecular target.

Heat shock increases turnover of 90 kDa heat shock protein phosphate groups in HeLa cells

The 90 kDa heat shock protein (hsp90) is a major phosphoprotein which associates various other cellular polypeptides such as actin, calmodulin, steroid hormone receptors and certain protein-kinases. Little is known about the function of hsp90 in recovery from stress. In this report, we describe a dramatic increase in the rate of both phosphate uptake and dephosphorylation of hsp90 in HeLa cells submitted to acute stresses. This increased turnover of hsp90 phosphate groups might reflect a greater protein binding activity of hsp90 in stressed cells.