title: Increased expression of the pro-apoptotic protein BIM, a mechanism for cAMP/protein kinase A (PKA)-induced apoptosis of immature T cells.
abstract: The second messenger cAMP is proapoptotic for numerous cell types, but the mechanism for this proapoptotic action is not defined. Here, we use murine CD4(+)/CD8(+) S49 lymphoma cells and isolated thymocytes to assess this mechanism. In WT S49 cells, cAMP acts via protein kinase A (PKA) to induce G(1) phase cell cycle arrest and apoptosis. Treatment of WT and cAMP-Deathless (D-) S49 cells, which lack cAMP-promoted apoptosis, with the PKA agonist 8-(4-chlorophenylthio)-cAMP (CPT-cAMP) differentially regulates transcripts for numerous proapoptotic and antiapoptotic proteins. In contrast, kin-S49 cells (which lack PKA) show no cAMP-promoted changes in transcript expression. In this study, we use knockdown and overexpression approaches to define the role in cAMP/PKA-promoted apoptosis of the proapoptotic factor BIM (Bcl-2 interacting mediator of cell death), whose expression prominently increases in response to CPT-cAMP treatment of WT but not D- or kin- S49 cells. Conditional expression of BimL, one of the three major forms of Bim, increases apoptosis of WT, D-, and kin-S49 cells, whereas inhibition of cAMP-mediated induction of Bim isoforms by shRNAi attenuates CPT-cAMP-mediated apoptosis of WT S49 cells. Bim protein levels increase in subpopulations of CPT-cAMP-treated cells that undergo apoptosis. Thymic CD4(+)/CD8(+) cells isolated from Bim(-/-) mice corroborated the requirement of Bim expression for cAMP-promoted apoptosis. Thus, up-regulation of Bim appears to be an important determinant of cAMP/PKA-mediated apoptosis in immature T cells and may be a mechanism for such apoptosis in other cell types as well.
authors.affiliation: Department of Pharmacology, University of California San Diego, La Jolla, California 92093, USA. azambon@ucsd.edu
authors.forename: Alexander C
authors.initials: AC
authors.lastname: Zambon
authors.forename: Andrea
authors.initials: A
authors.lastname: Wilderman
authors.forename: Angela
authors.initials: A
authors.lastname: Ho
authors.forename: Paul A
authors.initials: PA
authors.lastname: Insel
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism*; D000072224:Bcl-2-Like Protein 11; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D002454:Cell Differentiation / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D057809:HEK293 Cells; D006801:Humans; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D013601:T-Lymphocytes / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology*; D013873:Thionucleotides / Q000494:pharmacology; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; C000606776:Bcl2l11 protein, mouse; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D013873:Thionucleotides; C015929:8-((4-chlorophenyl)thio)cyclic-3',5'-AMP; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases