The Ig superfamily cell surface glycoprotein Thy-1 expressed on immune cells and neurons of rodents and humans is hypothesized to function in cell adhesion and signal transduction in T cell differentiation, proliferation, and apoptosis. This study analyzes effects of cAMP and catecholamines on transcriptional Thy-1 gene expression. Incubation of murine thymocytes or S49 mouse thymoma cells with dibutyryl-cAMP, 8-bromo-cAMP, cholera toxin, norepinephrine, or isoproterenol caused time- and concentration-dependent decreases in levels of Thy-1 mRNA assayed by Northern hybridization or T2 nuclease protection. After 4 h of treatment with 500 μM dibutyryl-cAMP or 8-bromo-cAMP, 1 nM cholera toxin, 100 μM norepinephrine, or 100 μM isoproterenol, Thy-1 mRNA levels were 60 to 96% lower than those of controls. Norepinephrine-mediated decreases in Thy-1 mRNA levels were prevented by the β-adrenergic receptor antagonist propranolol (10 μM). Dibutyryl-cAMP and norepinephrine decreased the apparent half-life of S49 cell Thy-1 mRNA from ≫6 h to 2 to 3 h, whereas nuclear run-on assays showed no cAMP or norepinephrine effect on de novo transcription of the Thy-1 gene. In mutant S49 cells lacking cAMP-dependent protein kinase A, neither dibutyryl cAMP nor norepinephrine affected Thy-1 mRNA levels. These observations show that exogenous cAMP and norepinephrine can induce decreases in steady state Thy-1 mRNA levels in T-lineage cells through posttranscriptional destabilization of Thy-1 mRNA, associated with protein kinase A-mediated protein phosphorylation. Catecholamine-mediated β-adrenergic protein kinase A-dependent Thy-1 mRNA destabilization may be an example of a more general mRNA decay system regulating cellular responses to stress.