Divergent Regulation of β 2-Adrenoceptors and Adenylate Cyclase in the Cyc - Mouse T Lymphoma Cell Line TL2-9

Abstract

The radiation leukemia virus-induced murine Cyc - T lymphoma cell line TL2-9 expressed one homogeneous population of β 2-adrenoceptors based on competition curves of [ 125I]cy- anopindolol with the specific antagonist ICI 118.551 and three β-adrenergic agonists. These receptors were uncoupled from adenylate cyclase due to the absence of G s. The catalytical unit was directly stimulated by MnCl 2, forskolin, and even more markedly in the simultaneous presence of both reagents. In contrast, the enzyme was inhibited in the presence of Gpp[NH]p, probably through interaction with Gi. Indeed, this inhibitory effect was constrained by preincubating cells in the presence of pertussis toxin and a 41 kDa protein was specifically ADP-ribosylated in the presence of the toxin. This cell line was therefore analogous to the Cyc - cell line derived from the murine S49 lymphoma cell line. When added to the culture medium, butyrate (2 mM) induced β 2-adrenoceptors, the expression of these uncoupled receptors depending on protein synthesis, as judged by inhibitory effects of cycloheximide. In contrast, dBcAMP (1 mM) and TPA (tumor-promoting agent phorbol ester) increased the rate of disappearance of β 2-adrenoceptors. Butyrate, dBcAMP and TPA systematically decreased adenylate cyclase activity. Besides, TPA (but neither butyrate nor dBcAMP) reduced the efficacy of Gpp[NH]p in inhibiting adenylate cyclase, suggesting a proportionately higher alteration of G i. We conclude that β 2-adrenoceptors, uncoupled from adenylate cyclase, are regulated independently from the catalytical unit and G i, in this Cyc - T lymphoma cell line.