Caspase-dependent cleavage of the retinoblastoma protein is an early step in neuronal apoptosis.
Rb-deficient embryos (Rb-/-) show abnormal degeneration of neurons and die at mid-gestation, suggesting that RB may protect against apoptosis. Having previously shown that cyclin D1 accumulates during K+-induced apoptosis of granule neurons, we chose to investigate the role of RB under these conditions. We show that RB is cleaved in its C-terminus during the onset of neuronal apoptosis. Caspase 3-like activity increases following K+ deprivation and the time course correlates with RB cleavage and apoptosis. Although the use of a specific caspase 3-like inhibitor (z-DEBD.fmk) delays RB cleavage and reduces DNA fragmentation, data implicate other caspases in these processes. However, K+ deprivation induces a gradual production of the active p20 subunit of caspase 3 (CPP32) that coincides with RB disappearance at the cellular level. Nuclear detection of a transfected HA-tagged caspase cleavage-resistant RB mutant (DEAG/D to DEAA/D) revealed a significant decrease in apoptosis of neurons expressing the RB mutant (less than 5%) relative to the wild type form of RB (40%) during K+ deprivation. Taken together, these data show that caspase-dependent cleavage of RB is an early permissive step of the apoptosis-inducing signaling pathway in neurons. They indicate a major role of RB in neuronal protection.
Boutillier
A L
AL
UMR 7519 CNRS-21, Strasbourg, France.
Trinh
E
E
Loeffler
J P
JP
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis; D053148:Caspase 3; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D002414:Cations, Monovalent; D002531:Cerebellum / Q000166:cytology; D053938:DNA Fragmentation; D051379:Mice; D009474:Neurons / Q000502:physiology*; D009842:Oligopeptides / Q000494:pharmacology; D011188:Potassium; D011994:Recombinant Proteins / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000235:genetics / Q000378:metabolism*
D000590:Amino Acid Chloromethyl Ketones; D061945:Caspase Inhibitors; D002414:Cations, Monovalent; D009842:Oligopeptides; D011994:Recombinant Proteins; D016160:Retinoblastoma Protein; C110772:benzoylcarbonyl-aspartyl-glutamyl-valyl-aspartyl-fluoromethyl ketone; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases; D011188:Potassium