Expression of Cellular Chaperones and Co-Chaperones Associated with Heat Shock Proteins Hsp90 and Hsp70 in Human Fibrosarcoma HT1080 Cells That Do Not Synthesize Hsp90β

Heat shock protein Hsp90 is an important cellular chaperone, it contributes to the folding, stabilization, and regulation of specific target proteins involved in many cellular processes. Mammalian cells contain two isoforms of Hsp90 – the inducible isoform of Hsp90α and the constitutive isoform of Hsp90β. Recently, we showed that knockout of the HSP90AB1 gene encoding the constitutive isoform of Hsp90β in human fibrosarcoma HT1080 cells (Hsp90β-KO cells) did not affect cell proliferation and resistance to heat shock and oxidative stress, and slightly reduced cell migration. This indicates the adaptation of cells and the cellular chaperone machinery to the loss of one of the key cellular chaperones, Hsp90β. In this work, using real-time quantitative PCR and Western blotting, we found that knockout of the gene encoding Hsp90β was accompanied by changes in the expression and content of individual chaperones and co-chaperones associated with Hsp90 and Hsp70 chaperone machinery. In the HSP90 family of chaperones/co-chaperones, an increase in the expression and content of the cytosolic isoform of Hsp90α remaining in the cell and up-regulation of a number of important Hsp90 co-chaperones (FKBP4, HOP) were observed. In the HSP70 family of chaperones/co-chaperones, the expression and content of key chaperones, inducible Hsp70, constitutive Hsc70 and mitochondrial GRP75, were significantly increased. As a result, some mechanisms of adaptation of Hsp90 and Hsp70 chaperone machineries in response to the loss of one of the key chaperones, Hsp90β, by cells have been established for the first time. The Hsp90b-KO cells we created that do not express Hsp90β can be considered as a cellular model of pharmacological inhibition of Hsp90β function by promising Hsp90β-specific inhibitors created for tumor therapy. The revealed changes in Hsp90- and Hsp70-associated chaperones and co-chaperones in response to the loss of Hsp90β demonstrate probable changes in the cellular chaperone machine caused by the suppression of Hsp90β by such inhibitors and can be taken into account when developing combined therapeutic strategies using Hsp90β-specific inhibitors.