Tyrosine Phosphorylation of Caspase-8 Abrogates Its Apoptotic Activity and Promotes Activation of c-Src.
Src family tyrosine kinases (SFKs) phosphorylate caspase-8A at tyrosine (Y) 397 resulting in suppression of apoptosis. In addition, the phosphorylation of caspase-8A at other sites including Y465 has been implicated in the regulation of caspase-8 activity. However, the functional consequences of these modifications on caspase-8 processing/activity have not been elucidated. Moreover, various Src substrates are known to act as potent Src regulators, but no such role has been explored for caspase-8. We asked whether the newly identified caspase-8 phosphorylation sites might regulate caspase-8 activation and conversely, whether caspase-8 phosphorylation might affect Src activity. Here we show that Src phosphorylates caspase-8A at multiple tyrosine sites; of these, we have focused on Y397 within the linker region and Y465 within the p12 subunit of caspase-8A. We show that phosphomimetic mutation of caspase-8A at Y465 prevents its cleavage and the subsequent activation of caspase-3 and suppresses apoptosis. Furthermore, simultaneous phosphomimetic mutation of caspase-8A at Y397 and Y465 promotes the phosphorylation of c-Src at Y416 and increases c-Src activity. Finally, we demonstrate that caspase-8 activity prevents its own tyrosine phosphorylation by Src. Together these data reveal that dual phosphorylation converts caspase-8 from a pro-apoptotic to a pro-survival mediator. Specifically, tyrosine phosphorylation by Src renders caspase-8 uncleavable and thereby inactive, and at the same time converts it to a Src activator. This novel dynamic interplay between Src and caspase-8 likely acts as a potent signal-integrating switch directing the cell towards apoptosis or survival.
Division of Critical Care, Department of Medicine, McMaster University, Hamilton, Ontario, Canada.|Division of Critical Care, Department of Medicine, Niagara Health System, Niagara, Ontario, Canada.
Jennifer Ly
JL
Tsang
Keenan Research Centre for Biomedical Science of the Li Ka Shing Knowledge Institute, Toronto, Ontario, Canada.
Song Hui
SH
Jia
Keenan Research Centre for Biomedical Science of the Li Ka Shing Knowledge Institute, Toronto, Ontario, Canada.
Jean
J
Parodo
Keenan Research Centre for Biomedical Science of the Li Ka Shing Knowledge Institute, Toronto, Ontario, Canada.
Pamela
P
Plant
Laboratory of Tissue Repair and Regeneration, Matrix Dynamics Group, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada.
Monika
M
Lodyga
Department of Medicine, University of Montreal, Montreal, Quebec, Canada.|Centre de Recherche de "Hopital du Sacre-Coeur de Montreal, Montreal, Quebec, Canada.
Emmanuel
E
Charbonney
Keenan Research Centre for Biomedical Science of the Li Ka Shing Knowledge Institute, Toronto, Ontario, Canada.|Department of Surgery, St. Michael's Hospital, Toronto, Ontario, Canada.
Katalin
K
Szaszi
Keenan Research Centre for Biomedical Science of the Li Ka Shing Knowledge Institute, Toronto, Ontario, Canada.|Department of Surgery, St. Michael's Hospital, Toronto, Ontario, Canada.
Andras
A
Kapus
Keenan Research Centre for Biomedical Science of the Li Ka Shing Knowledge Institute, Toronto, Ontario, Canada.|Department of Critical Care Medicine, St. Michael's Hospital, Toronto, Ontario, Canada.|Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, Ontario, Canada.
John C
JC
Marshall
D000595:Amino Acid Sequence; D017209:Apoptosis; D053181:Caspase 8 / Q000737:chemistry / Q000378:metabolism*; D002460:Cell Line; D004789:Enzyme Activation; D006801:Humans; D010766:Phosphorylation; D014443:Tyrosine / Q000378:metabolism*; D019061:src-Family Kinases / Q000378:metabolism*
D014443:Tyrosine; D019061:src-Family Kinases; D053181:Caspase 8