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 (PubMed:9873016, PubMed:27474739). Has anti-apoptotic activity (PubMed:10597216). Plays a role in the HSF1 nucleocytoplasmic transport (PubMed:26159920). Binds to the ATPase domain of HSP70/HSC70 chaperones (PubMed:9873016). Interacts with BCL2 (PubMed:10597216). Interacts with phospholipase C-gamma proteins (PubMed:10980614). Interacts with DNAJB6 (PubMed:22366786). Interacts (via BAG domain) with HSF1; this interaction occurs in normal and heat-shocked cells promoting HSF1 nucleocytoplasmic shuttling (PubMed:26159920). Interacts with HSPA8 (via NBD) (PubMed:27474739, PubMed:24318877). Interacts with HSPA1A (via NBD) and HSPA1B (via NBD) (PubMed:24318877). Interacts (via WW domain 1) with SYNPO2 (via PPPY motif) (PubMed:23434281). Interacts with HSPB8 (PubMed:28144995). Colocalizes with HSF1 to the nucleus upon heat stress (PubMed:26159920). The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry.