Heat shock protein 70 inhibits apoptosis in cancer cells through simultaneous and independent mechanisms

Gastroenterology. 2009 May;136(5):1772-82. doi: 10.1053/j.gastro.2009.01.070. Epub 2009 Feb 6.

Abstract

Background & aims: 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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis / drug effects*
  • Calcium / metabolism
  • Caspase 3 / metabolism
  • Cathepsin B / metabolism
  • Cell Line, Tumor
  • Cytosol / metabolism
  • Diterpenes / pharmacology
  • Epoxy Compounds / pharmacology
  • HSP70 Heat-Shock Proteins / pharmacology*
  • Humans
  • Lysosomal-Associated Membrane Protein 2 / pharmacology
  • Lysosomes / drug effects
  • Pancreatic Neoplasms / metabolism
  • Pancreatic Neoplasms / pathology*
  • Phenanthrenes / pharmacology
  • Quercetin / pharmacology
  • RNA, Small Interfering / pharmacology

Substances

  • Diterpenes
  • Epoxy Compounds
  • HSP70 Heat-Shock Proteins
  • Lysosomal-Associated Membrane Protein 2
  • Phenanthrenes
  • RNA, Small Interfering
  • triptolide
  • Quercetin
  • Caspase 3
  • Cathepsin B
  • Calcium