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Phosphorylation regulates apoptotic caspase function through diverse molecular mechanisms
Author(s) -
Hardy Jeanne A,
Serrano Banyuhay P,
Eron Scott J
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.602.3
Subject(s) - phosphorylation , microbiology and biotechnology , caspase , kinase , caspase 7 , phosphorylation cascade , biology , caspase 3 , caspase 2 , apoptosis , caspase 8 , chemistry , protein kinase a , protein phosphorylation , biochemistry , programmed cell death
Caspases, the cysteine proteases that execute apoptosis, are tightly regulated via phosphorylation by a series of kinases. Although all apoptotic caspases work in concert to promote apoptosis, different kinases regulate individual caspases. Several sites of caspase‐7 and −9 phosphorylation have been reported, but without knowing the molecular details, it has been impossible to exploit or control these complex interactions, which normally prevent unwanted proliferation. This work provides new molecular mechanisms for phosphorylation‐based control of both caspase‐7 and caspase‐9 function. During dysregulation, PAK2 kinase plays an anti‐apoptotic role, phosphorylating caspase‐7 and promoting unfettered cell growth and chemotherapeutic resistance. PAK2 phosphorylates caspase‐7 at two sites, inhibiting activity using two different molecular mechanisms, before and during apoptosis. Phosphorylation of caspase‐7 S30 allosterically obstructs its interaction with caspase‐9, preventing intersubunit linker processing, slowing or preventing caspase‐7 activation. S239 phosphorylation renders active caspase‐7 incapable of binding substrate, blocking later events in apoptosis. In parallel and in response to cAMP, Protein Kinase A (PKA) phosphorylates caspase‐9 at three sites preventing caspase‐9 activation and suppressing apoptosis progression. Phosphorylation of caspase‐9 by PKA at the functionally relevant site, S183, acts as an upstream block of the apoptotic cascade, inactivating caspase‐9 by a two‐stage mechanism. First, S183 phosphorylation prevents caspase‐9 self‐processing and directly blocks substrate binding. In addition, S183 phosphorylation breaks the fundamental interactions within the caspase‐9 core, promoting disassembly of the large and small subunits. This occurs despite S183 being a surface residue distal from the large: small interface. This phosphorylation‐induced disassembly promotes the formation of ordered aggregates around 20 nm in diameter. Similar aggregates of caspase‐9 have not been previously reported. This two‐stage regulatory mechanism for caspase‐9 has not been reported previously but may be conserved across the caspases. Each of these mechanisms of regulation for caspase‐7 and caspase‐7 is novel, representing new opportunities for synergistic control of caspases and their counterpart kinases. Support or Funding Information This work was supported by the National Institutes of Health (NIH) GM 080532.