The radiation leukemia virus-induced murine Cyc- T
lymphoma cell line TL2-9 expressed one homogeneous population of beta 2-adrenoceptors based on competition curves of [125I]
cyanopindolol with the specific antagonist ICI 118.551 and three
beta-adrenergic agonists. These receptors were uncoupled from
adenylate cyclase due to the absence of Gs. The catalytical unit was directly stimulated by
MnCl2,
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 beta 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 beta 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 Gi. We conclude that beta 2-adrenoceptors, uncoupled from
adenylate cyclase, are regulated independently from the catalytical unit and Gi, in this Cyc- T
lymphoma cell line.