Taherian Aliakbar, Krone Patrick H, Ovsenek Nick
Department of Anatomy and Cell Biology, College of Medicine, University of Saskatchewan, 107 Wiggins Rd., Saskatoon, Saskatchewan, Canada.
Biochem Cell Biol. 2008 Feb;86(1):37-45. doi: 10.1139/o07-154.
Hsp90 chaperone complexes function in assembly, folding, and activation of numerous substrates. The 2 vertebrate homologues encoded by the genes hsp90a and hsp90b are differentially expressed in embryonic and adult tissues and during stress; however, it is not known whether they possess identical functional activities in chaperone complexes. This question was addressed by examining potential differences between the Hsp90 isoforms with respect to both cochaperone and substrate interactions. Epitope-tagged proteins were expressed in mammalian cells or Xenopus oocytes and subjected to immunoprecipitation with an array of co-chaperones. Both isoforms were shown to participate equally in multichaperone complexes, and no significant differences in cochaperone distribution were observed. The substrates Raf-1, HSF1, Cdc37, and MEK1 interacted with both Hsp90alpha and Hsp90beta, and the relative patterns of these interactions were not affected by heat shock. The substrate kinases c-Src, CKIIB, A-raf, and Erk interacted with both isoforms; however, significantly more Hsp90alpha was recovered after heat shock. The data demonstrate that Hsp90alpha and Hsp90beta exhibit similar interactions with co-chaperones, but significantly different behaviors with respect to substrate interactions under stress conditions. These results reveal both functional similarities and key functional differences in the individual members of this protein family.
热休克蛋白90（Hsp90）伴侣复合物在众多底物的组装、折叠和激活过程中发挥作用。由hsp90a和hsp90b基因编码的两种脊椎动物同源物在胚胎和成年组织以及应激过程中差异表达；然而，尚不清楚它们在伴侣复合物中是否具有相同的功能活性。通过研究Hsp90亚型在共伴侣和底物相互作用方面的潜在差异来解决这个问题。用表位标签标记的蛋白质在哺乳动物细胞或非洲爪蟾卵母细胞中表达，并用一系列共伴侣进行免疫沉淀。结果表明，两种亚型均平等地参与多伴侣复合物的形成，且未观察到共伴侣分布存在显著差异。底物Raf-1、热休克因子1（HSF1）、细胞分裂周期蛋白37（Cdc37）和丝裂原活化蛋白激酶激酶1（MEK1）与Hsp90α和Hsp90β均相互作用，且这些相互作用的相对模式不受热休克的影响。底物激酶c-Src、酪蛋白激酶IIβ（CKIIB）、A-Raf和细胞外信号调节激酶（Erk）与两种亚型均相互作用；然而，热休克后回收的Hsp90α明显更多。数据表明，Hsp90α和Hsp90β与共伴侣表现出相似的相互作用，但在应激条件下，它们在底物相互作用方面表现出显著不同的行为。这些结果揭示了该蛋白家族各个成员之间的功能相似性和关键功能差异。
