Heat shock protein 70 inhibits apoptosis in cancer cells through simultaneous and independent mechanisms.
OBJECTIVE
Heat shock proteins (HSPs) are highly conserved and serve a multitude of functions that mediate cell survival. HSP70, the only inducible form of the 70-kilodalton subfamily of HSPs, is overexpressed in pancreatic cancer cells and has been shown to inhibit caspase-dependent apoptosis. We aimed to elucidate the mechanism by which HSP70 inhibits apoptosis in cancer cells.


METHODS
HSP70 expression was down-regulated in cultured pancreatic cancer cells by exposure to quercetin, triptolide, or short interfering RNAs. Intracellular Ca2+, cytosolic cathepsin B activity, caspase-3 activity, cell viability, and lysosome integrity were measured using colorimetric assays. Immunofluorescence assays were used to localize cathepsin B and Lamp2. BAPTA-AM was used to chelate intracellular Ca2+.


RESULTS
Inhibition of HSP70 increased intracellular Ca2+ levels in pancreatic and colon cancer cell lines and led to loss of lysosome integrity in pancreatic cancer cells. The release of intracellular Ca2+ and lysosomal enzymes activated caspase-dependent apoptosis independently and simultaneously.


CONCLUSIONS
HSP70 inhibits apoptosis in cancer cells by 2 mechanisms: attenuation of cytosolic calcium and stabilization of lysosomes. HSP70-mediated cell survival might occur in other types of cancer cells.
Dudeja
Vikas
V
Department of Surgery, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Mujumdar
Nameeta
N
Phillips
Phoebe
P
Chugh
Rohit
R
Borja-Cacho
Daniel
D
Dawra
Rajinder K
RK
Vickers
Selwyn M
SM
Saluja
Ashok K
AK
D017209:Apoptosis / Q000187:drug effects*; D002118:Calcium / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D002401:Cathepsin B / Q000378:metabolism; D045744:Cell Line, Tumor; D003600:Cytosol / Q000378:metabolism; D004224:Diterpenes / Q000494:pharmacology; D004852:Epoxy Compounds / Q000494:pharmacology; D018840:HSP70 Heat-Shock Proteins / Q000494:pharmacology*; D006801:Humans; D052119:Lysosomal-Associated Membrane Protein 2 / Q000494:pharmacology; D008247:Lysosomes / Q000187:drug effects; D010190:Pancreatic Neoplasms / Q000378:metabolism / Q000473:pathology*; D010616:Phenanthrenes / Q000494:pharmacology; D011794:Quercetin / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000494:pharmacology
D004224:Diterpenes; D004852:Epoxy Compounds; D018840:HSP70 Heat-Shock Proteins; D052119:Lysosomal-Associated Membrane Protein 2; D010616:Phenanthrenes; D034741:RNA, Small Interfering; C001899:triptolide; D011794:Quercetin; D053148:Caspase 3; D002401:Cathepsin B; D002118:Calcium