Co-chaperone for HSP70 and HSC70 chaperone proteins. Acts as a nucleotide-exchange factor (NEF) promoting the release of ADP from the HSP70 and HSC70 proteins thereby triggering client/substrate protein release. Nucleotide release is mediated via its binding to the nucleotide-binding domain (NBD) of HSPA8/HSC70 where as the substrate release is mediated via its binding to the substrate-binding domain (SBD) of HSPA8/HSC70. Inhibits the pro-apoptotic function of PPP1R15A, and has anti-apoptotic activity. Markedly increases the anti-cell death function of BCL2 induced by various stimuli. Homodimer. Forms a heteromeric complex with HSP70/HSC70. Binds to the ATPase domain of HSP/HSC70 chaperones. Interacts with NR3C1. Interacts with the N-terminal region of STK19. Interacts with PPP1R15A. Interacts with BCL2 in an ATP-dependent manner. Interacts with SIAH1, SIAH2, HSPA8 (via NBD), HSPA1A (via NBD) and HSPA1B (via NBD). Ubiquitinated; mediated by SIAH1 or SIAH2 and leading to its subsequent proteasomal degradation.