Apoptosis of Antigen-Specific T Lymphocytes upon the Engagement of CD8 by Soluble HLA Class I Molecules Is Fas Ligand/Fas Mediated:Evidence for the Involvement of p56~(lck),Calcium Calmodulin Kinase II,and Calcium-Independent Protein Kinase C Signali

摘要

The binding of soluble HLA class I (sHLA-I) molecules to CD8 on EBV-specific CTL induced up-regulation of Fas ligand (FasL) mRNA and consequent sFasL protein secretion.This,in turn,triggered CTL apoptosis by FasL/Fas interaction.Molecular analysis of the biochemical pathways responsible for FasL up-regulation showed that sHLA-I/CD8 interaction firstly induced the recruitment of src-like p56~(lck) and syk-like Zap-70 protein tyrosine kinases (PTK).Interestingly,p59~(fyn) was activated upon the engagement of CD3/TCR complex but not upon the interaction of sHLA-I with CD8.In addition,sHLA-I/CD8 interaction,which is different from signaling through the CD3/TCR complex,did not induce nuclear translocation of AP-1 protein complex.These findings suggest that CD8~- and CD3/TCR-mediated activating stimuli can recruit different PTK and transcription factors.Indeed,the engagement of CD8 by sHLA-I led to the activation of Ca~(2+) calmodulin kinase II pathway,which eventually was responsible for the NF-AT nuclear translocation.In addition,we found that the ligation of sHLA-I to CD8 recruited protein kinase C,leading to NF-kappaB activation.Both NF-AT and NF-kappaB were responsible for the induction of FasL mRNA and consequent CTL apoptosis.Moreover,FasL up-regulation and CTL apoptotic death were down-regulated by pharmacological specific inhibitors of Ca~(2+)/ calmodulin/calcineurin and Ca~(2+)-independent protein kinase C signaling pathways.These findings clarify the intracellular sig-naling pathways triggering FasL up-regulation and apoptosis in CTL upon sHLA-I/CD8 ligation and suggest that sHLA-I mol-ecules can be proposed as therapeutic tools to modulate immune responses.