title: Mechanisms of cyclic AMP/protein kinase A- and glucocorticoid-mediated apoptosis using S49 lymphoma cells as a model system.
abstract: Cyclic AMP/protein kinase A (cAMP/PKA) and glucocorticoids promote the death of many cell types, including cells of hematopoietic origin. In wild-type (WT) S49 T-lymphoma cells, signaling by cAMP and glucocorticoids converges on the induction of the proapoptotic B-cell lymphoma-family protein Bim to produce mitochondria-dependent apoptosis. Kin(-), a clonal variant of WT S49 cells, lacks PKA catalytic (PKA-Cα) activity and is resistant to cAMP-mediated apoptosis. Using sorbitol density gradient fractionation, we show here that in kin(-) S49 cells PKA-Cα is not only depleted but the residual PKA-Cα mislocalizes to heavier cell fractions and is not phosphorylated at two conserved residues (Ser(338) or Thr(197)). In WT S49 cells, PKA-regulatory subunit I (RI) and Bim coimmunoprecipitate upon treatment with cAMP analogs and forskolin (which increases endogenous cAMP concentrations). By contrast, in kin(-) cells, expression of PKA-RIα and Bim is prominently decreased, and increases in cAMP do not increase Bim expression. Even so, kin(-) cells undergo apoptosis in response to treatment with the glucocorticoid dexamethasone (Dex). In WT cells, glucorticoid-mediated apoptosis involves an increase in Bim, but in kin(-) cells, Dex-promoted cell death appears to occur by a caspase 3-independent apoptosis-inducing factor pathway. Thus, although cAMP/PKA-Cα and PKA-R1α/Bim mediate apoptotic cell death in WT S49 cells, kin(-) cells resist this response because of lower levels of PKA-Cα and PKA-RIα subunits as well as Bim. The findings for Dex-promoted apoptosis imply that these lymphoma cells have adapted to selective pressure that promotes cell death by altering canonical signaling pathways.
authors.affiliation: Department of Pharmacology, University of California, San Diego, La Jolla, CA 92093;
authors.forename: Malik M
authors.initials: MM
authors.lastname: Keshwani
authors.affiliation: Department of Pharmacology, University of California, San Diego, La Jolla, CA 92093;
authors.forename: Joan R
authors.initials: JR
authors.lastname: Kanter
authors.affiliation: Department of Chemistry and Biochemisty, University of California, San Diego, La Jolla, CA 92093;
authors.forename: Yuliang
authors.initials: Y
authors.lastname: Ma
authors.affiliation: Department of Pharmacology, University of California, San Diego, La Jolla, CA 92093; Department of Medicine, University of California, San Diego, La Jolla, CA 92093.
authors.forename: Andrea
authors.initials: A
authors.lastname: Wilderman
authors.affiliation: Department of Medicine, University of California, San Diego, La Jolla, CA 92093.
authors.forename: Manjula
authors.initials: M
authors.lastname: Darshi
authors.affiliation: Department of Pharmacology, University of California, San Diego, La Jolla, CA 92093; Department of Medicine, University of California, San Diego, La Jolla, CA 92093.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Insel
authors.affiliation: Department of Pharmacology, University of California, San Diego, La Jolla, CA 92093; Department of Chemistry and Biochemisty, University of California, San Diego, La Jolla, CA 92093; staylor@ucsd.edu.
authors.forename: Susan S
authors.initials: SS
authors.lastname: Taylor
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D000072224:Bcl-2-Like Protein 11; D019556:COS Cells; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology*; D006801:Humans; D008223:Lymphoma / Q000188:drug therapy* / Q000201:enzymology / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008954:Models, Biological; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D005576:Colforsin; D003907:Dexamethasone; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases
keywords: PKA; apoptosis; cAMP; glucocorticoids; lymphoma