Secretion of the heat shock proteins HSP70 and HSC70 by baby hamster kidney (BHK‐21) cells

Abstract

The HSPs (heat-shock proteins) of the 70-kDa family, the constitutively expressed HSC70 (cognate 70-kDa heat-shock protein) and the stress-inducible HSP70 (stress-inducible 70-kDa heat-shock protein), have been reported to be actively secreted by various cell types. The mechanisms of the release of these HSPs are obscure, since they possess no consensus secretory signal sequence. We showed that baby hamster kidney (BHK-21) cells released HSP70 and HSC70 in a serum-free medium and that this process was the result of an active secretion of HSPs rather than the non-specific release of the proteins due to cell death. It was found that the secretion of HSP70 and HSC70 is independent of de novo protein synthesis. BFA (Brefeldin A) did not inhibit the basal secretion of HSPs, indicating that the secretion of HSP70 and HSC70 from cells occurs by a non-classical pathway. Exosomes did not contribute to the secretion of HSP70 and HSC70 by cells. MBC (methyl-beta-cyclodextrin), a substance that disrupts the lipid raft organization, considerably reduced the secretion of both HSPs, indicating that lipid rafts are involved in the secretion of HSP70 and HSC70 by BHK-21 cells. The results suggest that HSP70 and HSC70 are actively secreted by BHK-21 cells in a serum-free medium through a non-classical pathway in which lipid rafts play an important role.

Expression of the protein chaperone, clusterin, in spinal cord cells constitutively and following cellular stress, and upregulation by treatment with Hsp90 inhibitor

“…Secretion of Hsp70 has been described in experiments using a wide variety of cell types (Broquet et al 2003;Evdokimovskaya et al 2010;Guzhova et al 2001;Hightower and Guidon 1989;Mambula and Calderwood 2006) including cultured spinal astrocytes and skeletal muscle (Robinson et al 2005). Surprisingly, Hsp70 could not be detected in the medium of heat-shocked spinal cord-DRG cultures, despite strong intracellular expression and sensitivity of detection comparable to other studies.…”

Osteoblastic cell secretome: A novel role for progranulin during risedronate treatment

“…Furthermore, our findings that risedronate upregulates the synthesis and secretion of progranulin together with the concurrent induction of ERp57, HSP60, HSC70, are novel and of biological significance. Indeed, the latter three proteins have been already shown to be associated with the promotion of cell survival under stressful conditions and to prevent bone loss in osteoporosis by restoring folding of poorly-assembled bone matrix proteins [37,50]. Our collective results put forward progranulin as a novel player in bone response to stress and suggest that the molecular mechanisms of action of this class of compounds (i.e.…”

“…The term “secretome” refers to proteins released through classical as well as nonclassical secretory pathways [35]. In addition, it also includes intracellular proteins that might be released through an active mechanism involving lysosomal vesicles and lipid rafts [36,37]. In this study we identified a total of 89 proteins (19 unique to this study) which are involved in several biological processes including response to stress, cellular protein metabolic processes and protein folding (Fig.…”

“…However, an increasing number of observations show that they can be released through physiological secretion mechanisms, bind to the surfaces of adjacent cells and then have a wide variety of bioactivities, such as promoting the survival of cells under stressful conditions [37, 51-53]. In particular, Hsp60 (a group of mitochondrial chaperones) and Hsp70 are able to enter the blood stream and possess the ability to act at distant sites in the body and initiate signal transduction cascades [54].…”

HSPA8/HSC70 chaperone protein

“…147,148 It is worth mentioning that besides its intracellular location, HSPA8 is also detected in the extracellular space. It may derive from dying cells, but can also be actively released from intact cells, either free [149][150][151] or associated with exosomes. 152 Extracellular HSPA8 inhibits tumor cell growth 151 and modifies cell viability.…”