B cell receptor signaling mediates immediate protection from Fas-induced apoptosis upstream of caspase activation through an atypical protein kinase C isozyme and de novo protein synthesis.
Signaling through the B cell receptor (BCR) of normal splenic B cells, as well as B cell lymphoma lines, can abrogate Fas-mediated apoptosis. Using the B lymphoma line A20.2J, BCR signaling immediately inhibited Fas-induced apoptosis upstream of caspase-8 activation, as determined by Ile-Glu-Thr-Asp-(IETD)ase activity and cleavage of the caspase-8 substrate Bid. Furthermore, following overexpression of a human Fas:FLICE construct, which directly induces caspase activation in a death-inducing signaling complex-independent manner, cells could not be protected through BCR stimulation.Co-incubation with cycloheximide partially reversed protection from apoptosis and increased Fas-stimulated initiator and effector caspase activation, suggesting new protein synthesis is necessary to induce protection upstream of caspase activation. Furthermore, co-incubation with a broad-spectrum protein kinase C (PKC) inhibitor, such as bisindolylmaleimide (Bis), also partially reversed protection from apoptosis, and examination of a panel of PKC inhibitors suggested a role for atypical isozymes in protection. Bis also acted to increase initiator and effector caspase activation upon anti-IgG and anti-Fas treatment. These data suggest that BCR-induced protection is being mediated upstream of initiator caspase activation, and is partially dependent upon both PKC family members and new protein synthesis.
Hinshaw
Jennifer A
JA
Immunology Department, Jerome H. Holland Laboratory for the Biomedical Sciences, American Red Cross, Rockville 20855, USA.
Mueller
Carolyn M
CM
Scott
David W
DW
Williams
Mark S
MS
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D020169:Caspases / Q000378:metabolism*; D004789:Enzyme Activation / Q000502:physiology; D051034:Inhibitor of Apoptosis Proteins; D007527:Isoenzymes / Q000378:metabolism; D051379:Mice; D014176:Protein Biosynthesis; D011493:Protein Kinase C / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D019014:fas Receptor / Q000378:metabolism*
D051034:Inhibitor of Apoptosis Proteins; D007527:Isoenzymes; D011506:Proteins; D011947:Receptors, Antigen, B-Cell; D019014:fas Receptor; D011493:Protein Kinase C; D020169:Caspases