Phosphorylation of murine caspase-9 by the protein kinase casein kinase 2 regulates its cleavage by caspase-8.
Previous studies from our laboratory had indicated that cytochrome c-independent processing and activation of caspase-9 by caspase-8 contributed to early amplification of the caspase cascade in tumor necrosis factor (TNF)-alpha-treated murine cells. Here we show that murine caspase-9 is phosphorylated by casein kinase 2 (CK2) on a serine near the site of caspase-8 cleavage. CK2 has been shown to regulate cleavage of the pro-apoptotic Bid protein by phosphorylating serine residues near its caspase-8 cleavage site. Similarly, CK2 modification of Ser(348) on caspase-9 appears to render the protease refractory to cleavage by active caspase-8. This phosphorylation did not affect the ability of caspase-9 to autoprocess. Substitution of Ser(348) abolished phosphorylation but not cleavage, and a phospho-site mutant promoted apoptosis in TNF-alpha-treated caspase-9 knock-out mouse embryo fibroblasts. Furthermore, inhibition of CK2 activity and RNA interference-mediated knockdown of the kinase accelerated caspase-9 activation, whereas phosphatase inhibition delayed both caspase-9 activation and death in response to TNF receptor occupation. Taken together, these studies show that TNF receptor cross-linking promotes dephosphorylation of caspase-9, rendering it susceptible to processing by activated caspase-8 protein. Thus, our data suggest that modification of procaspase-9 to protect it from inappropriate cleavage and activation is yet another mechanism by which the oncogenic kinase CK2 promotes survival.
McDonnell
Maureen A
MA
Department of Laboratory Medicine and Pathology. University of Minnesota, Minneapolis, MN 55455, USA.
Abedin
Md Joynal
MJ
Melendez
Manuel
M
Platikanova
Teodora N
TN
Ecklund
Johanna R
JR
Ahmed
Khalil
K
Kelekar
Ameeta
A
D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001402:B-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D047390:Casein Kinase II / Q000037:antagonists & inhibitors / Q000378:metabolism*; D053181:Caspase 8 / Q000378:metabolism*; D053453:Caspase 9 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation; D045744:Cell Line, Tumor; D004789:Enzyme Activation / Q000187:drug effects; D005347:Fibroblasts; D051379:Mice; D008969:Molecular Sequence Data; D019319:Okadaic Acid / Q000494:pharmacology; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D051020:bcl-X Protein / Q000378:metabolism
D047428:Protein Kinase Inhibitors; D014409:Tumor Necrosis Factor-alpha; D051020:bcl-X Protein; D010768:Phosphoserine; D019319:Okadaic Acid; D047390:Casein Kinase II; D053181:Caspase 8; D053453:Caspase 9