The N-end rule pathway counteracts cell death by destroying proapoptotic protein fragments.
In the course of apoptosis, activated caspases cleave ∼500 to ∼1,000 different proteins in a mammalian cell. The dynamics of apoptosis involve a number of previously identified, caspase-generated proapoptotic protein fragments, defined as those that increase the probability of apoptosis. In contrast to activated caspases, which can be counteracted by inhibitor of apoptosis proteins, there is little understanding of antiapoptotic responses to proapoptotic protein fragments. One possibility is the regulation of proapoptotic fragments through their selective degradation. The previously identified proapoptotic fragments Cys-RIPK1, Cys-TRAF1, Asp-BRCA1, Leu-LIMK1, Tyr-NEDD9, Arg-BID, Asp-BCL(XL), Arg-BIM(EL), Asp-EPHA4, and Tyr-MET bear destabilizing N-terminal residues. Tellingly, the destabilizing nature (but not necessarily the actual identity) of N-terminal residues of proapoptotic fragments was invariably conserved in evolution. Here, we show that these proapoptotic fragments are short-lived substrates of the Arg/N-end rule pathway. Metabolic stabilization of at least one such fragment, Cys-RIPK1, greatly augmented the activation of the apoptosis-inducing effector caspase-3. In agreement with this understanding, even a partial ablation of the Arg/N-end rule pathway in two specific N-end rule mutants is shown to sensitize cells to apoptosis. We also found that caspases can inactivate components of the Arg/N-end rule pathway, suggesting a mutual suppression between this pathway and proapoptotic signaling. Together, these results identify a mechanistically specific and functionally broad antiapoptotic role of the Arg/N-end rule pathway. In conjunction with other apoptosis-suppressing circuits, the Arg/N-end rule pathway contributes to thresholds that prevent a transient or otherwise weak proapoptotic signal from reaching the point of commitment to apoptosis.
Division of Biology, California Institute of Technology, Pasadena, CA 91125, USA.
Konstantin I
KI
Piatkov
Christopher S
CS
Brower
Alexander
A
Varshavsky
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D019881:Aminoacyltransferases / Q000235:genetics / Q000378:metabolism; D000818:Animals; D000906:Antibodies / Q000276:immunology; D017209:Apoptosis / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins / Q000235:genetics* / Q000378:metabolism*; D001120:Arginine / Q000378:metabolism; D051023:BH3 Interacting Domain Death Agonist Protein / Q000235:genetics / Q000378:metabolism; D019313:BRCA1 Protein / Q000235:genetics / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D054461:Lim Kinases / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008817:Mice, Mutant Strains; D010446:Peptide Fragments / Q000235:genetics* / Q000378:metabolism*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D011817:Rabbits; D053422:Receptor-Interacting Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D047990:TNF Receptor-Associated Factor 1 / Q000235:genetics / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism; D051020:bcl-X Protein / Q000235:genetics / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D000906:Antibodies; D051017:Apoptosis Regulatory Proteins; C494811:BCL2L1 protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; D019313:BRCA1 Protein; C494812:Bcl2l1 protein, mouse; C099942:NEDD9 protein, human; D010446:Peptide Fragments; D010750:Phosphoproteins; D047990:TNF Receptor-Associated Factor 1; D051020:bcl-X Protein; D001120:Arginine; D019881:Aminoacyltransferases; C113474:UBR1 protein, human; D044767:Ubiquitin-Protein Ligases; C019727:arginyltransferase; C515892:LIMK1 protein, human; D054461:Lim Kinases; C506249:RIPK1 protein, human; D053422:Receptor-Interacting Protein Serine-Threonine Kinases; D053148:Caspase 3