Activation or suppression of NFkappaB by HPK1 determines sensitivity to activation-induced cell death.
Restimulation of the T-cell receptor (TCR) in activated T cells induces CD95 (Fas/Apo-1)-mediated activation-induced cell death (AICD). The TCR-proximal mechanisms leading to AICD are elusive. Here we characterize hematopoietic progenitor kinase 1 (HPK1) as a differentially regulated TCR-proximal signaling protein involved in AICD of primary T cells. We show that HPK1 is a functional component of the endogenous IkappaB kinase (IKK) complex and is crucial for TCR-mediated NFkappaB activation. While full-length HPK1 enhances IKKbeta phosphorylation, siRNA-mediated knockdown of HPK1 blunts TCR-mediated NFkappaB activation and increases cell death. We also demonstrate proteolytic processing of HPK1 into HPK1-C, specifically in AICD-sensitive primary T cells. The cleavage product HPK1-C sequesters the inactive IKK complex and suppresses NFkappaB upon TCR restimulation by binding to IKKalpha and IKKbeta. T cells of HPK1-C transgenic mice are sensitized towards TCR-mediated AICD. Consequently, preventing HPK1-C generation in primary T cells by siRNA-mediated knockdown results in decreased AICD. Thus, these results show a novel mechanism of sensitization of T lymphocytes towards AICD by suppression of NFkappaB, and propose that HPK1 is a life/death switch in T lymphocytes.
Brenner
Dirk
D
Tumor Immunology Program, German Cancer Research Center (DKFZ), Heidelberg, Germany.
Golks
Alexander
A
Kiefer
Friedemann
F
Krammer
Peter H
PH
Arnold
Rüdiger
R
D000818:Animals; D017209:Apoptosis; D019556:COS Cells; D016923:Cell Death; D002460:Cell Line; D002522:Chlorocebus aethiops; D003208:Concanavalin A / Q000494:pharmacology; D017930:Genes, Reporter; D006801:Humans; D051550:I-kappa B Kinase / Q000378:metabolism; D047468:Immunoprecipitation; D019169:Jurkat Cells; D051379:Mice; D008822:Mice, Transgenic; D016328:NF-kappa B / Q000378:metabolism*; D010641:Phenotype; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D034741:RNA, Small Interfering / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D019014:fas Receptor / Q000378:metabolism*
D016328:NF-kappa B; D034741:RNA, Small Interfering; D011948:Receptors, Antigen, T-Cell; D019014:fas Receptor; D003208:Concanavalin A; C102102:hematopoietic progenitor kinase 1; D017346:Protein Serine-Threonine Kinases; C496559:CHUK protein, human; D051550:I-kappa B Kinase; C496562:Ikbkb protein, mouse