HSP90AB1: Helping the good and the bad.

HSP90AB1 (heat shock protein 90 kDA alpha, class B, member 1), also known as HSP90beta, is a member of the large family of HSPs which function as molecular chaperones. Chaperones, by binding to client proteins, support proper protein folding and maintain protein stability, especially after exposure to various kinds of cellular stress. Client proteins belong to various protein families including kinases, ubiquitin ligases and transcription factors. HSP90 proteins act as dimers and bind clients with the help of co-chaperones. The cochaperones influence many functions including client binding, ATPase activity or ATP binding of HSP90. HSPs are necessary for a large scale of cellular processes and therefore essential for cell survival. Since client proteins can be mutant proteins that would be degraded without the help of chaperones, HSPs also promote tumor formation and cancer cell proliferation. As such, they are also targets for new therapeutic approaches in cancer treatment. This review focuses on recent studies on HSP90AB1, if possible in comparison with its close homologue HSP90AA1.