Involvement of the cAMP/protein kinase A pathway and of mitogen-activated protein kinase in the anti-proliferative effects of anandamide in human breast cancer cells

Anandamide (ANA) inhibits prolactin- and nerve growth factor (NGF)-induced proliferation of human breast cancer cells by decreasing the levels of the 100 kDa prolactin receptor (PRLr) and the high affinity trk NGF receptor, respectively, and by acting via CB1-like cannabinoid receptors, However, the intracellular signals that mediate these effects are not known, Here, se show that, in MCF-7 cells: (i) forskolin and the mitogen-activated protein kinase (MAPK) kinase inhibitor PD098059 pre,ent, and the protein kinase A inhibitor RpcAMPs mimics, the inhibitory effects of ANA on cell proliferation and PRLr/trk expression and (ii) ANA inhibits forskolin-induced cAMP formation and stimulates Raf-l translocation and MAPK: activity, in a fashion sensitive to the selective CB1 antagonist SR141716A. ANA stimulation of MAPK mas enhanced by inhibitors of ANA hydrolysis. Forskolin inhibited MAPK and ANA-induced Raf-l translocation, These findings indicate that, in MCF-7 cells, ANA inhibits adenylyl cyclase and activates MAPK, thereby exerting a down-regulation on PRLr and trk levels and a suppression of cell proliferation.