CacyBP/SIP, a Hsp90 binding chaperone, in cellular stress response

•CacyBP/SIP level increases upon cell treatment with H2O2 and radicicol.•HEp-2 cells overexpressing CacyBP/SIP are more resistant to stress-induced death.•Hsf1 binds to CacyBP/SIP gene promoter and increases CacyBP/SIP expression.•In response to stress CacyBP/SIP level increases in selected mouse brain regions. CacyBP/SIP interacts with Hsp90 and is able to protect proteins from denaturation and/or aggregation induced by elevated temperature. In this work we studied the influence of different stress factors on CacyBP/SIP level in HEp-2 cells. We have found that H2O2 and radicicol treatment resulted in a significant increase (up to 40%) in the CacyBP/SIP level. We have also found that HEp-2 cells overexpressing CacyBP/SIP were more resistant to stress-induced death. Further studies have revealed that the Hsf1 transcription factor binds to the CacyBP/SIP gene promoter and up-regulates CacyBP/SIP expression under stress conditions. To check whether the CacyBP/SIP protein might play a role in stress responses in vivo, we analyzed its level in selected brain structures of control and stressed mice. We have found that the level of the CacyBP/SIP protein was higher in the thalamus/hypothalamus, hippocampus and brainstem of stressed mice. Thus, the presented results clearly indicate that CacyBP/SIP is involved in cellular stress response.