Calmodulin binding to cellular FLICE-like inhibitory protein modulates Fas-induced signalling.
We and others have demonstrated that Fas-mediated apoptosis is a potential therapeutic target for cholangiocarcinoma. Previously, we reported that CaM (calmodulin) antagonists induced apoptosis in cholangiocarcinoma cells through Fas-related mechanisms. Further, we identified a direct interaction between CaM and Fas with recruitment of CaM into the Fas-mediated DISC (death-inducing signalling complex), suggesting a novel role for CaM in Fas signalling. Therefore we characterized the interaction of CaM with proteins recruited into the Fas-mediated DISC, including FADD (Fas-associated death domain)-containing protein, caspase 8 and c-FLIP {cellular FLICE [FADD (Fas-associated death domain)-like interleukin 1beta-converting enzyme]-like inhibitory protein}. A Ca(2+)-dependent direct interaction between CaM and FLIP(L), but not FADD or caspase 8, was demonstrated. Furthermore, a 37.3+/-5.7% increase (n=6, P=0.001) in CaM-FLIP binding was observed at 30 min after Fas stimulation, which returned to the baseline after 60 min and correlated with a Fas-induced increase in intracellular Ca(2+) that reached a peak at 30 min and decreased gradually over 60 min in cholangiocarcinoma cells. A CaM antagonist, TFP (trifluoperazine), inhibited the Fas-induced increase in CaM-FLIP binding concurrent with inhibition of ERK (extracellular-signal-regulated kinase) phosphorylation, a downstream signal of FLIP. Direct binding between CaM and FLIP(L) was demonstrated using recombinant proteins, and a CaM-binding region was identified in amino acids 197-213 of FLIP(L). Compared with overexpression of wild-type FLIP(L) that resulted in decreased spontaneous as well as Fas-induced apoptosis, mutant FLIP(L) with deletion of the CaM-binding region resulted in increased spontaneous and Fas-induced apoptosis in cholangiocarcinoma cells. Understanding the biology of CaM-FLIP binding may provide new therapeutic targets for cholangiocarcinoma and possibly other cancers.
Pawar
Pritish S
PS
Department of Pathology, University of Alabama at Birmingham, LHRB 533, 1530 3rd Ave South, Birmingham, AL 35294, USA.
Micoli
Keith J
KJ
Ding
Haitao
H
Cook
William J
WJ
Kappes
John C
JC
Chen
Yabing
Y
McDonald
Jay M
JM
D017209:Apoptosis; D001665:Binding Sites; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism*; D053181:Caspase 8 / Q000378:metabolism; D045744:Cell Line, Tumor; D006801:Humans; D015398:Signal Transduction; D019014:fas Receptor / Q000378:metabolism*
D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D002147:Calmodulin; C491901:FAS protein, human; D019014:fas Receptor; C505530:CASP8 protein, human; D053181:Caspase 8; D002118:Calcium