1. Mechanisms of cyclic AMP/protein kinase A- and glucocorticoid-mediated apoptosis using S49 lymphoma cells as a model system.
- Author
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Keshwani MM, Kanter JR, Ma Y, Wilderman A, Darshi M, Insel PA, and Taylor SS
- Subjects
- Animals, Apoptosis genetics, Apoptosis Regulatory Proteins genetics, Apoptosis Regulatory Proteins metabolism, Bcl-2-Like Protein 11, COS Cells, Cell Line, Tumor, Chlorocebus aethiops, Colforsin pharmacology, Cyclic AMP analogs & derivatives, Cyclic AMP pharmacology, Cyclic AMP-Dependent Protein Kinases genetics, Humans, Lymphoma enzymology, Lymphoma genetics, Membrane Proteins genetics, Membrane Proteins metabolism, Proto-Oncogene Proteins genetics, Proto-Oncogene Proteins metabolism, Apoptosis drug effects, Cyclic AMP metabolism, Cyclic AMP-Dependent Protein Kinases metabolism, Dexamethasone pharmacology, Lymphoma drug therapy, Models, Biological
- 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.
- Published
- 2015
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