Nifedipine prevents etoposide-induced caspase-3 activation, prenyl transferase degradation and loss in cell viability in pancreatic β-cells.
Emerging evidence implicates novel roles for post-translational prenylation (i.e., farnesylation and geranylgeranylation) of various signaling proteins in a variety of cellular functions including hormone secretion, survival and apoptosis. In the context of cellular apoptosis, it has been shown previously that caspase-3 activation, a hallmark of mitochondrial dysregulation, promotes hydrolysis of several key cellular proteins. We report herein that exposure of insulin-secreting INS 832/13 cells or normal rat islets to etoposide leads to significant activation of caspase-3 and subsequent degradation of the common α-subunit of farnesyl/geranylgeranyl transferases (FTase/GGTase). Furthermore, the above stated signaling steps were prevented by Z-DEVD-FMK, a known inhibitor of caspase-3. In addition, treatment of cell lysates with recombinant caspase-3 also caused FTase/GGTase α-subunit degradation. Moreover, nifedipine, a calcium channel blocker, markedly attenuated etoposide-induced caspase-3 activation, FTase/GGTase α-subunit degradation in INS 832/13 cells and normal rat islets. Further, nifedipine significantly restored etoposide-induced loss in metabolic cell viability in INS 832/13 cells. Based on these findings, we conclude that etoposide induces loss in cell viability by inducing mitochondrial dysfunction, caspase-3 activation and degradation of FTase/GGTase α-subunit. Potential significance of these findings in the context of protein prenylation and β-cell survival are discussed.
Beta-Cell Biochemistry Laboratory, John D. Dingell VA Medical Center, Detroit, MI 48201, USA.
Daleep K
DK
Arora
Abiy M
AM
Mohammed
Anjaneyulu
A
Kowluru
D019883:Alkyl and Aryl Transferases / Q000378:metabolism*; D000818:Animals; D053148:Caspase 3 / Q000378:metabolism*; D061945:Caspase Inhibitors / Q000494:pharmacology; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D005047:Etoposide / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D051231:Farnesyltranstransferase / Q000378:metabolism*; D006801:Humans; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D009543:Nifedipine / Q000494:pharmacology*; D009842:Oligopeptides / Q000494:pharmacology; D017368:Protein Prenylation / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley
D061945:Caspase Inhibitors; D009842:Oligopeptides; C110772:benzoylcarbonyl-aspartyl-glutamyl-valyl-aspartyl-fluoromethyl ketone; D005047:Etoposide; D019883:Alkyl and Aryl Transferases; C083291:geranylgeranyltransferase type-I; D051231:Farnesyltranstransferase; D053148:Caspase 3; D009543:Nifedipine