Association of HSP105 with HSC70 in high molecular mass complexes in mouse FM3A cells

The 105-kDa stress proteins HSP105alpha and HSP105beta belong to a high molecular mass heat shock protein family which has been found in organisms from yeast to mammals. Here we demonstrated the interaction of HSP105 with HSP70 family proteins in mouse FM3A cells. The association of HSP105 with HSC70 was shown by immunoprecipitation using anti-HSP105 antibody. Furthermore, when cell extracts or partially purified HSP105 fractions from nonstressed or heat-shocked cells were analyzed by size exclusion chromatography, density gradient centrifugation or cross-linking, HSP105 was detected as HSP105/HSC70 complexes with molecular masses of approximately 300-500-kDa, 160-kDa or 200-kDa, respectively. Since the 160-200-kDa complexes must be HSP105/HSC70 heterodimers, the 300-500-kDa complexes seemed to consist of HSP105/HSC70 heterotetramers possibly with other proteins. Our finding that HSP105 is complexed with HSC70 suggests that HSP105 may function cooperatively with HSC70, that HSP105 regulates the function of HSC70 or that HSC70 reversibly regulates the function of HSP105 in cells under both nonstressed and stressed conditions.