Hsp60 Is Actively Secreted by Human Tumor Cells

Abstract

BackgroundHsp60, a Group I mitochondrial chaperonin, is classically considered an intracellular chaperone with residence in the mitochondria; nonetheless, in the last few years it has been found extracellularly as well as in the cell membrane. Important questions remain pertaining to extracellular Hsp60 such as how generalized is its occurrence outside cells, what are its extracellular functions and the translocation mechanisms that transport the chaperone outside of the cell. These questions are particularly relevant for cancer biology since it is believed that extracellular chaperones, like Hsp70, may play an active role in tumor growth and dissemination.Methodology/Principal FindingsSince cancer cells may undergo necrosis and apoptosis, it could be possible that extracellular Hsps are chiefly the result of cell destruction but not the product of an active, physiological process. In this work, we studied three tumor cells lines and found that they all release Hsp60 into the culture media by an active mechanism independently of cell death. Biochemical analyses of one of the cell lines revealed that Hsp60 secretion was significantly reduced, by inhibitors of exosomes and lipid rafts.Conclusions/SignificanceOur data suggest that Hsp60 release is the result of an active secretion mechanism and, since extracellular release of the chaperone was demonstrated in all tumor cell lines investigated, our observations most likely reflect a general physiological phenomenon, occurring in many tumors.

The dissociation of the Hsp60/pro-Caspase-3 complex by bis(pyridyl)oxadiazole copper complex ( CubipyOXA ) leads to cell death in NCI-H292 cancer cells

“…MTT was obtained from Sigma (Milan, Italy), and the assay was performed as described [22]. Briefly, 5 × 10 3 cells were plated in 200 μl of complete (with FCS, fetal calf serum) medium per well in 96-well plates.…”

Lipid Raft Endocytosis and Exosomal Transport Facilitate Extracellular Trafficking of Annexin A2

“…Quantification of secreted exosomes was performed by measuring the activity of acetylcholine esterase as previously described (27). Briefly, 50 l of the pelted exosomes was suspended in 100 l of PBS, 37.5 l of this PBS-diluted fraction was incubated in the presence of 1.25 mM acetylthiocholine and 0.1 mM 5Јm5Ј-dithiobis(2-nitrobenzoic acid), and the reaction mixture was brought to a final volume of 300 l in a 96-well plate.…”

Doxorubicin anti-tumor mechanisms include Hsp60 post-translational modifications leading to the Hsp60/p53 complex dissociation and instauration of replicative senescence

“…Moreover, the decrease of the intracellular levels of the chaperonin may lead to a decrease in its extracellular release. Extracellular chaperones contribute to the intercommunication between different cells, tissues, and organs, in normal as well as in pathological conditions [18,63].…”