Tyrosine dephosphorylation is required for Bak activation in apoptosis.
Activation of the cell-death mediator Bak commits a cell to mitochondrial apoptosis. The initial steps that govern Bak activation are poorly understood. To further clarify these pivotal events, we have investigated whether post-translational modifications of Bak impinge on its activation potential. In this study, we report that on apoptotic stimulation Bak undergoes dephosphorylation at tyrosine residue 108 (Y108), a critical event that is necessary but not sufficient for Bak activation, but is required both for early exposure of the occluded N-terminal domain and multimerisation. RNA interference (RNAi) screening identified non-receptor tyrosine phosphatases (PTPNs) required for Bak dephosphorylation and apoptotic induction through chemotherapeutic agents. Specifically, modulation of PTPN5 protein expression by siRNA and overexpression directly affected both Bak-Y108 phosphorylation and the initiation of Bak activation. We further show that MEK/ERK signalling directly affects Bak phosphorylation through inhibition of PTPN5 to promote cell survival. We propose a model of Bak activation in which the regulation of Bak dephosphorylation constitutes the initial step in the activation process, which reveals a previously unsuspected mechanism controlling the initiation of mitochondrial apoptosis.
Department of Molecular Oncology, Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, UK.
Joanna L
JL
Fox
Ferina
F
Ismail
Abul
A
Azad
Nicola
N
Ternette
Sabrina
S
Leverrier
Mariola J
MJ
Edelmann
Benedikt M
BM
Kessler
Irene M
IM
Leigh
Sarah
S
Jackson
Alan
A
Storey
D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006801:Humans; D008928:Mitochondria / Q000378:metabolism; D008969:Molecular Sequence Data; D010766:Phosphorylation; D054558:Protein Tyrosine Phosphatases, Non-Receptor / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D013912:Threonine / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism*; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000378:metabolism*
D050998:bcl-2 Homologous Antagonist-Killer Protein; D013912:Threonine; D014443:Tyrosine; D012694:Serine; D048049:Extracellular Signal-Regulated MAP Kinases; C489930:PTPN5 protein, human; D054558:Protein Tyrosine Phosphatases, Non-Receptor