Downregulation of IRS-1 protein in thapsigargin-treated human prostate epithelial cells.
Thapsigargin treatment of cultured cells leads to an increase in the intracellular calcium concentration, activation of calpain, and, in some cell types, apoptosis. Using a human prostate epithelial cell line that undergoes apoptosis in the presence of thapsigargin, we find decreased levels of IRS-1 protein levels during apoptosis. Inhibition of calpain prevents this decrease in IRS-1 protein; however, inhibitors of caspases or the proteasome are ineffective in maintaining IRS-1 levels. In terms of IGF-I-related second messenger proteins, the effect of thapsigargin is specific for IRS-1 since the protein levels of IGF-I receptor beta-subunit, Akt, Erk, and Shc are not affected. In addition to preventing the reduction in IRS-1, treatment of cells with calpain inhibitor II prevents apoptosis in response to thapsigargin. Finally, IRS-1 and calpain can be identified in protein complexes isolated using IRS-1-specific antibodies, indicating that calpain can associate with either IRS-1 or one of the proteins present in protein complexes that contain IRS-1. In total, these results suggest that IRS-1 may be targeted for degradation by calpain during apoptosis.
D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism; D002277:Carcinoma / Q000378:metabolism* / Q000503:physiopathology; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D055504:Insulin Receptor Substrate Proteins; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism; D046911:Macromolecular Substances; D008297:Male; D010750:Phosphoproteins / Q000187:drug effects / Q000378:metabolism*; D011471:Prostatic Neoplasms / Q000378:metabolism* / Q000503:physiopathology; D015290:Second Messenger Systems / Q000187:drug effects / Q000502:physiology; D019284:Thapsigargin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D004791:Enzyme Inhibitors; C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; D046911:Macromolecular Substances; D010750:Phosphoproteins; D019284:Thapsigargin; D002154:Calpain; D002118:Calcium