The regulatory mechanism of a client kinase controlling its own release from Hsp90 chaperone machinery through phosphorylation

Abstract

It is believed that the stability and activity of client proteins are passively regulated by the Hsp90 (heat-shock protein 90) chaperone machinery, which is known to be modulated by its intrinsic ATPase activity, co-chaperones and post-translational modifications. However, it is unclear whether client proteins themselves participate in regulation of the chaperoning process. The present study is the first example to show that a client kinase directly regulates Hsp90 activity, which is a novel level of regulation for the Hsp90 chaperone machinery. First, we prove that PKCγ (protein kinase Cγ) is a client protein of Hsp90α, and, that by interacting with PKCγ , Hsp90a prevents PKC? degradation and facilitates its cytosol-to-membrane translocation and activation. A threonine residue set, Thr115/ Thr425/Thr603, of Hsp90a is specifically phosphorylated by PKCγ , and, more interestingly, this threonine residue set serves as a 'phosphorylation switch' for Hsp90a binding or release of PKCγ . Moreover, phosphorylation of Hsp90a by PKCγ decreases the binding affinity of Hsp90α towardsATP and co-chaperones such as Cdc37 (cell-division cycle 37), thereby decreasing its chaperone activity. Further investigation demonstrated that the reciprocal regulation of Hsp90α and PKCγ plays a critical role in cancer cells, and that simultaneous inhibition of PKCγ and Hsp90α synergistically prevents cell migration and promotes apoptosis in cancer cells. © The Authors Journal compilation.