title: Caspase-cleaved HPK1 induces CD95L-independent activation-induced cell death in T and B lymphocytes.
abstract: Life and death of peripheral lymphocytes is strictly controlled to maintain physiologic levels of T and B cells. Activation-induced cell death (AICD) is one mechanism to delete superfluous lymphocytes by restimulation of their immunoreceptors and it depends partially on the CD95/CD95L system. Recently, we have shown that hematopoietic progenitor kinase 1 (HPK1) determines T-cell fate. While full-length HPK1 is essential for NF-kappaB activation in T cells, the C-terminal fragment of HPK1, HPK1-C, suppresses NF-kappaB and sensitizes toward AICD by a yet undefined cell death pathway. Here we show that upon IL-2-driven expansion of primary T cells, HPK1 is converted to HPK1-C by a caspase-3 activity below the threshold of apoptosis induction. HPK1-C selectively blocks induction of NF-kappaB-dependent antiapoptotic Bcl-2 family members but not of the proapoptotic Bcl-2 family member Bim. Interestingly, T and B lymphocytes from HPK1-C transgenic mice undergo AICD independently of the CD95/CD95L system but involving caspase-9. Knock down of HPK1/HPK1-C or Bim by small interfering RNA shows that CD95L-dependent and HPK1/HPK1-C-dependent cell death pathways complement each other in AICD of primary T cells. Our results define HPK1-C as a suppressor of antiapoptotic Bcl-2 proteins and provide a molecular basis for our understanding of CD95L-independent AICD of lymphocytes.
authors: Tumor Immunology Program, German Cancer Research Center (DKFZ), Heidelberg, Germany.
authors: Dirk
authors: D
authors: Brenner
authors: Alexander
authors: A
authors: Golks
authors: Mareike
authors: M
authors: Becker
authors: Wolfgang
authors: W
authors: Müller
authors: Christian R
authors: CR
authors: Frey
authors: Rostislav
authors: R
authors: Novak
authors: Doron
authors: D
authors: Melamed
authors: Friedemann
authors: F
authors: Kiefer
authors: Peter H
authors: PH
authors: Krammer
authors: Rüdiger
authors: R
authors: Arnold
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D001402:B-Lymphocytes / Q000201:enzymology*; D000072224:Bcl-2-Like Protein 11; D053148:Caspase 3 / Q000378:metabolism*; D053453:Caspase 9 / Q000378:metabolism*; D053222:Fas Ligand Protein / Q000378:metabolism*; D006801:Humans; D007376:Interleukin-2 / Q000378:metabolism; D008213:Lymphocyte Activation / Q000502:physiology; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D016328:NF-kappa B / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D013601:T-Lymphocytes / Q000166:cytology / Q000201:enzymology*; D019014:fas Receptor / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; C000606776:Bcl2l11 protein, mouse; D053222:Fas Ligand Protein; C508594:IL2 protein, human; D007376:Interleukin-2; D008565:Membrane Proteins; D016328:NF-kappa B; D011518:Proto-Oncogene Proteins; D019014:fas Receptor; C102102:hematopoietic progenitor kinase 1; D017346:Protein Serine-Threonine Kinases; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3; D053453:Caspase 9