T cell receptor rearrangements in various S49 lymphoma sublines

beta-adrenergic receptor/cAMP-mediated signaling and apoptosis of S49 lymphoma cells

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.

S49 cells endogenously express subtype 2 somatostatin receptors which couple to increase protein tyrosine phosphatase activity in membranes and down-regulate Raf-1 activity in situ

S49 cells expressed type 2 somatostatin receptors (sstr2) by immunoblotting. Analysis by reverse transcription and polymerase chain reaction (RT-PCR) methodologies showed that S49 cells express predominantly sstr2A and sstr2B mRNAs; other subtypes were either not detected, in the case of sstr1, sstr3, sstr4, or variably detected, in the case of sstr5. No mutations were present in S49 cells at codon 12, 13, or 61 of the N-, K-, or H-ras genes. Nevertheless, randomly growing S49 cells contained Raf-1 activity by specific immune complex kinase assays. Treatment of S49 cells with somatostatin transiently inactivated the basal activity of Raf-1, but not that of B-Raf. Addition of somatostatin plus guanyl-5'-yl imidodiphosphate (GMPPNP) to S49 membranes stimulated PTPase activity. The concentration dependence for stimulation of PTPase activity correlated with high affinity binding of [125I-Tyr11]somatostatin-14. Both the effect of somatostatin to stimulate PTPase activity and to inactivate Raf-1 were abrogated by PTx. PTPase activity stimulated by somatostatin plus GMPPNP was recovered in a peak of high apparent M(r) (670,000) after solubilisation with Triton X-100 and Superose 6 chromatography. Furthermore, addition of activated, brain G alpha i/o subunits to fractions from control membranes stimulated PTPase activity in the high M(r) peak. Thus, S49 membranes contain a G-protein regulated PTPase (PTPase-G), and PTPase-G in these cells may reside in a high molecular weight complex.