These two isoforms are highly homologous with 86% amino acid sequence identity, and each of the isoforms could functionally compensate for the other ( Farrelly and Finkelstein, 1984 Bardwell and Craig, 1987 McDowell et al., 2009). In mammalian cells, Hsp90 is composed of two isoforms: the inducible Hsp90α and the constitutive Hsp90β ( Sreedhar et al., 2004). The 90-kDa heat shock protein (Hsp90) is a highly abundant and conserved molecular chaperone with ubiquitous distribution in eukaryotic cells ( Craig et al., 1993 Feder and Hofmann, 1999). Thus, microtubule stability is an essential cellular event regulated by Hsp90. These disruptive effects of Hsp90 depletion could be rescued by the expression of exogenous MAP4 or the treatment of trichostatin A that increases microtubule acetylation as well as stability. Furthermore, in Hsp90-depleted cells, the Golgi apparatus was fragmented and anterograde vesicle trafficking was impaired, with phenotypes similar to those induced by silencing MAP4. Hsp90 depletion led to the decrease in MAP4, causing microtubule deacetylation and destabilization. We showed that Hsp90 is bound to microtubule-associated protein 4 (MAP4), which is essential for maintaining microtubule acetylation and stabilization. In this study, we provide evidence that Hsp90 is required for microtubule stabilization, Golgi organization, and vesicular trafficking. Its high abundance is indicative of its involvement in some more fundamental processes. Hsp90 is an abundant and special molecular chaperone considered to be the regulator of many transcription factors and signaling kinases.

Hsp90 a molecular chaperone