β-Adrenergic receptor/cAMP-mediated signaling and apoptosis of S49 lymphoma cells

Abstract

beta-Adrenergic receptor (betaAR) activation and/or increases in cAMP regulate growth and proliferation of a variety of cells and, in some cells, promote cell death. In the current studies we addressed the mechanism of this growth reduction by examining betaAR-mediated effects in the murine T-lymphoma cell line S49. Wild-type S49 cells, derived from immature thymocytes (CD4(+)/CD8(+)) undergo growth arrest and subsequent death when treated with agents that increase cAMP levels (e.g., betaAR agonists, 8-bromo-cAMP, cholera toxin, forskolin). Morphological and biochemical criteria indicate that this cell death is a result of apoptosis. In cyc(-) and kin(-) S49 cells, which lack G(s)alpha and functional protein kinase A (PKA), respectively, betaAR activation of G(s)alpha and cAMP action via PKA are critical steps in this apoptotic pathway. S49 cells that overexpress Bcl-2 are resistant to cAMP-induced apoptosis. We conclude that betaAR activation induces apoptosis in immature T lymphocytes via G(s)alpha and PKA, while overexpression of Bcl-2 prevents cell death. betaAR/cAMP/PKA-mediated apoptosis may provide a means to control proliferation of immature T cells in vivo.

The Pro-apoptotic Protein Bim Is a Convergence Point for cAMP/Protein Kinase A- and Glucocorticoid-promoted Apoptosis of Lymphoid Cells

“…8-Cl-cAMP, 8-Br-cAMP, Bt 2 -cAMP and 8-CPT-cAMP), only CPT-cAMP acts purely as a cyclic nucleotide, having no effect on S49 kin Ϫ but strongly inhibiting growth of S49 WT cells (16). We found that 8-CPT-cAMP promoted apoptosis in WT but not kin Ϫ S49 cells in a time-dependent fashion, akin to that of another cAMP analog, 8-Br-cAMP (8), with a prominent increase in apoptosis after 24 h (Fig. 1A).…”

“…11 and 25), the precise determinants of cAMP-promoted cell death are poorly understood. Previous studies in the S49 cell system have documented that cell death promoted by cAMP analogs occurs via apoptosis (8) and that apoptosis and G 1 growth arrest are independent events that occur in WT but not kin Ϫ cells (10,11), thus implicating activation of PKA in the apoptotic process. In the current studies we show that the cAMP analog 8-CPTcAMP increases phosphorylation of CREB and activates caspase-3, as well as promoting apoptosis in WT but not kin Ϫ S49 cells (Fig.…”

“…Cells-WT S49 cells undergo apoptosis in response to the agents that increase cAMP levels (8). We assessed the pro-apoptotic effects of the cAMP analog 8-CPT-cAMP (100 M) on both WT and kin Ϫ S49 cells.…”

“…The greater susceptibility of certain tumor cells to cAMP-mediated growth arrest and/or apoptosis has spurred interest in developing cAMP analogs or related agents as anti-cancer drugs (4 -6), including those for glucocorticoid-resistant malignancies (4 -7). The mechanisms of cAMP-mediated apoptosis are poorly understood, although PKA 1 is known to be involved (5,8,9). Overexpression of certain anti-apoptotic proteins, such as Bcl-2, can protect lymphoma cells from cAMP-mediated apoptosis; such protection appears to be distinct from the effects of cAMP on cell cycle arrest (10).…”

“…S49 cells, which arose in a Balb/c mouse as a transplantable T-cell tumor, grow in suspension culture with a doubling time of 16 -18 h and respond to agonists that elevate cAMP by undergoing G 1 arrest and apoptotic cell death (8,10,11). kin Ϫ S49 cells, isolated as a clonal variant by virtue of resistance to killing by cAMP analogs, lack PKA activity, cAMP-promoted G 1 growth arrest, and apoptosis (8, 10 -13).…”