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 p56lck, calcium calmodulin kinase II, and Calcium-independent protein kinase C signaling pathways and for NF-kappaB and NF-AT nuclear translocation.
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 Ca2+ 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 Ca2+/calmodulin/calcineurin and Ca2+-independent protein kinase C signaling pathways. These findings clarify the intracellular signaling pathways triggering FasL up-regulation and apoptosis in CTL upon sHLA-I/CD8 ligation and suggest that sHLA-I molecules can be proposed as therapeutic tools to modulate immune responses.
Contini
Paola
P
Department of Internal Medicine and Center of Excellence for Biomedical Research, University of Genoa, Italy.
Ghio
Massimo
M
Merlo
Andrea
A
Poggi
Alessandro
A
Indiveri
Francesco
F
Puppo
Francesco
F
D017209:Apoptosis / Q000276:immunology*; D016827:CD8 Antigens / Q000276:immunology / Q000378:metabolism; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology* / Q000821:virology; D024202:Electrophoretic Mobility Shift Assay; D004789:Enzyme Activation / Q000276:immunology; D053222:Fas Ligand Protein; D005434:Flow Cytometry; D004854:Herpesvirus 4, Human / Q000276:immunology; D015395:Histocompatibility Antigens Class I / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / Q000276:immunology / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism*; D016328:NF-kappa B / Q000276:immunology / Q000378:metabolism; D050778:NFATC Transcription Factors / Q000276:immunology / Q000378:metabolism; D011493:Protein Kinase C / Q000276:immunology / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D034741:RNA, Small Interfering; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000276:immunology*; D048069:Tumor Necrosis Factors / Q000378:metabolism*; D015854:Up-Regulation; D051746:ZAP-70 Protein-Tyrosine Kinase / Q000276:immunology / Q000378:metabolism; D019014:fas Receptor / Q000378:metabolism*
D016827:CD8 Antigens; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D015395:Histocompatibility Antigens Class I; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D050778:NFATC Transcription Factors; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D048069:Tumor Necrosis Factors; D019014:fas Receptor; C115197:calcium-independent protein kinase C; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D051746:ZAP-70 Protein-Tyrosine Kinase; D011493:Protein Kinase C