Cyclic AMP/PKA-Promoted Apoptosis: Insights from Studies of S49 Lymphoma Cells

Abstract

Increases in cyclic AMP (cAMP) are pro-apoptotic in numerous cell types, but the mechanisms of cAMP-promoted apoptosis are poorly defined. We have used murine S49 T-lymphoma cells as a model to provide insight into these mechanisms. Increases in cAMP in wild-type (WT) S49 cells were first noted to kill these cells in the 1970 s, but only in recent years, it was shown that this occurs by the intrinsic (mitochondria-dependent) apoptotic pathway. The apoptotic response does not occur in protein kinase A-null (kin-) clonal variants of WT S49 cells and thus is mediated by protein kinase A (PKA). A second S49 clonal variant, cAMP-Deathless (D-), has PKA activity but lacks cAMP-promoted apoptosis. Apoptosis in WT S49 cells occurs many hours after cAMP/PKA-promoted G1 cell cycle arrest and involves increased expression of Bim, a pro-apoptotic member of the Bcl-2 (B-cell lymphoma-2) family. This increase in Bim expression does not occur in kin- or D- S49 cells and knockdown of Bim blunts cAMP-mediated apoptosis in WT cells. Cytotoxic T lymphocyte antigen-2 also appears to contribute to cAMP/PKA-promoted apoptosis of S49 cells. Based on time-dependent differences in gene expression between WT, D- and kin- S49 cells following incubation with 8-(4-chlorophenylthio)-cAMP, additional genes and proteins are likely involved in this apoptosis. Studies with S49 cells should reveal further insight regarding the mechanisms of cAMP/PKA-promoted cell death, including the identification of proteins that are targets to enhance (e. g., in cancer) or inhibit (e. g., cardiac failure) apoptosis in response to hormones, neurotransmitters, and drugs.

Proteomic and Metabolic Analyses of S49 Lymphoma Cells Reveal Novel Regulation of Mitochondria by cAMP and Protein Kinase A

“…These findings are consistent with data showing that treatment of WT cells with CPT-cAMP induces loss of mitochondrial membrane potential, mitochondrial release of cytochrome c, and second mitochondria-derived activator of caspases (SMAC) and increases caspase-3 activity (3,6).…”

“…Changes in mRNA may not, however, predict effects on protein expression as mRNA and protein expression may not highly correlate (16,17). Due to the role of mitochondria in cAMP/PKA-mediated death of S49 cells (6,7), here we used proteomic analysis to identify cAMP/PKA-mediated changes in protein expression in a mitochondria-enriched fraction of S49 cells and conducted additional studies to assess cAMP/ PKA-regulated control of mitochondrial proteins and mitochondrial function.…”

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

“…The regulation of apoptosis occurs in a cell type-specific manner, such that cAMP and glucocorticoids can be either pro-or antiapoptotic (6,7). A major effector of cAMP signaling is cAMP-dependent protein kinase A (PKA), a Ser/Thr protein kinase that consists of an R 2 C 2 holoenzyme with a regulatory subunit (PKA-R) dimer and two catalytic (PKA-Cα) subunits (8).…”

“…Abnormal regulation of cAMP/PKA signaling occurs in a variety of disorders, including Carney complex disease as well as tumors and human cancer cell lines (2,9,10). Targeting of cAMP/PKA signaling may have potential for numerous disease settings, but understanding is limited regarding the molecular mechanisms for its antiapoptotic and proapoptotic effects (6,7).…”

“…Many characteristics of the cAMP/PKA signaling system have been identified in the CD4 + CD8 + S49 T-lymphoma cell line (6,(11)(12)(13), which has served as a model system to understand cAMP-dependent gene expression networks and actions of PKA (6,14). Treatment of wild-type (WT) S49 cells with cAMP analogs, agents that increase endogenous cAMP concentrations, or with glucocorticoids (e.g., Dexamethasone, Dex) will produce G 1 -phase cell-cycle arrest and then apoptosis (11).…”