Rapid up-regulation of c-FLIP expression by BCR signaling through the PI3K/Akt pathway inhibits simultaneously induced Fas-mediated apoptosis in murine B lymphocytes.
Cross-linking of BCR rapidly induces protection of B cells from Fas-mediated apoptosis, which has been assumed one of the important survival mechanisms of B cells during antigen stimulation. In the mouse B cell line A20, which is sensitive to Fas-mediated apoptosis, stimulation of BCR inhibited apoptosis induced via Fas upstream of caspase-8 activation with an associated rapid increase in the expression of both short and long forms of cellular caspase-8/FLICE-inhibitory protein (c-FLIP). The c-FLIP competitively inhibited the recruitment of caspase-8 to the death-inducing signaling complex (DISC), which took as long as 3h to form after the stimulation of Fas in A20 cells. Knockdown of c-FLIP by a short hairpin RNA-expressing method rendered BCR-stimulated A20 cells sensitive to Fas-mediated apoptosis. The BCR-induced rapid expression of c-FLIP was not affected by inactivation of NF-kappaB, but was inhibited by either treatment with a PI3K inhibitor, LY294002, or expression of a dominant negative PI3K p85 subunit, both of which suppressed phosphorylation of Akt and sensitized BCR-stimulated A20 cells to Fas-mediated apoptosis. Overexpression of constitutively active Akt was shown not only to up-regulate c-FLIP expression but also to render A20 cells resistant to Fas-mediated apoptosis. Moreover, treatment with LY294002 also suppressed BCR-induced up-regulation of c-FLIP expression in spleen B cells. Taken together, BCR-stimulation was shown to rapidly trigger a survival signal against simultaneously or ongoingly stimulated Fas-mediated apoptosis by promoting a PI3K/Akt signaling pathway-mediated up-regulation of c-FLIP expression.
Moriyama
Hiroyuki
H
Graduate School of Biostudies, Kyoto University, SCRB/Building G, Yoshida Konoecho, Sakyo-ku, Kyoto 606-8501, Japan.
Yonehara
Shin
S
D000818:Animals; D017209:Apoptosis / Q000276:immunology*; D001402:B-Lymphocytes / Q000276:immunology*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D053148:Caspase 3 / Q000235:genetics / Q000378:metabolism; D053181:Caspase 8 / Q000235:genetics / Q000378:metabolism; D061945:Caspase Inhibitors; D045744:Cell Line, Tumor; D053418:Death Domain Receptor Signaling Adaptor Proteins / Q000276:immunology / Q000378:metabolism; D004789:Enzyme Activation; D016393:Lymphoma, B-Cell / Q000473:pathology; D051379:Mice; D016328:NF-kappa B / Q000235:genetics; D051058:Oncogene Protein v-akt / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D011947:Receptors, Antigen, B-Cell / Q000276:immunology* / Q000378:metabolism; D015398:Signal Transduction; D015854:Up-Regulation; D019014:fas Receptor / Q000276:immunology* / Q000378:metabolism
D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D061945:Caspase Inhibitors; D053418:Death Domain Receptor Signaling Adaptor Proteins; D016328:NF-kappa B; D011947:Receptors, Antigen, B-Cell; D019014:fas Receptor; D019869:Phosphatidylinositol 3-Kinases; D051058:Oncogene Protein v-akt; C505526:Casp8 protein, mouse; D053148:Caspase 3; D053181:Caspase 8