STIMULATION OF CANNABINOID RECEPTOR CB1 INDUCES KROX-24 EXPRESSION INHUMAN ASTROCYTOMA-CELLS

The recent isolation and cloning of the G protein-coupled central cann abinoid receptor (CB1) from brain tissue has provided a molecular basi s to elucidate how cannabinoid compounds may mediate their psychoactiv e effects. Here we report the high expression of cannabinoid receptors in human astrocytoma tumors of different grades, in the astrocytoma c ell lines U373 MG and GL-15, as well as in normal astrocytes. From an analysis of the coupling mechanisms of functional CB1 receptors in U37 3 MG, we show that, in addition to the inhibition of adenylyl cyclase, activation by the cannabinoid agonist CP-55940 induces the expression of the immediate-early gene krox-24, also known as NGFI-A, zif/268, e gr-1, and TIS8. The amount of Krox-24 protein and the level of Krox-24 DNA binding activity, as measured by Western blot and electrophoretic mobility shift assay, respectively, were also increased by the additi on of CP-55940. These effects were blocked by incubation with pertussi s toxin but not by treatment with hydrolysis-resistant cAMP analogues, suggesting that the transduction pathway between the cannabinoid rece ptor and krox-24 involves a pertussis toxin-sensitive GTP-binding prot ein and is independent of cARIP metabolism. The specific involvement o f CB1 in Krox-24 induction was demonstrated in Chinese hamster ovary c ells transfected with the human CB1 receptor and also in experiments u sing the CB1-selective cannabinoid antagonist SR 141716A.