Mechanisms of cyclic AMP/protein kinase A- and glucocorticoid-mediated apoptosis using S49 lymphoma cells as a model system

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 112; no. 41; pp. 12681 - 12686
• Main Authors: Keshwani, Malik M., Kanter, Joan R., Ma, Yuliang, Wilderman, Andrea, Darshi, Manjula, Insel, Paul A., Taylor, Susan S.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 13-10-2015; National Acad Sciences
• Subjects: Animals; Apoptosis; Apoptosis - drug effects; Apoptosis - genetics; Apoptosis Regulatory Proteins - genetics; Apoptosis Regulatory Proteins - metabolism; Bcl-2-Like Protein 11; Biological Sciences; Cell Line, Tumor; Cells; Cercopithecus aethiops; Colforsin - pharmacology; COS Cells; Cyclic AMP - analogs & derivatives; Cyclic AMP - metabolism; Cyclic AMP - pharmacology; Cyclic AMP-Dependent Protein Kinases - genetics; Cyclic AMP-Dependent Protein Kinases - metabolism; Dexamethasone - pharmacology; Fractionation; Humans; Kinases; Lymphoma; Lymphoma - drug therapy; Lymphoma - enzymology; Lymphoma - genetics; Membrane Proteins - genetics; Membrane Proteins - metabolism; Mitochondria; Models, Biological; Mortality; Proto-Oncogene Proteins - genetics; Proto-Oncogene Proteins - metabolism; apoptosis; glucocorticoids; cAMP; PKA; lymphoma
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1516057112

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 mitochondriadependent 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 (Ser338or Thr197). 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.