ADENOSINE STIMULATION OF DNA-SYNTHESIS IN MAMMARY EPITHELIAL-CELLS

Adenosine increased the DNA synthesis rate and the percentage of S-pha se cells 2-3-fold in mouse mammary epithelial cells (NMuMG), with an o ptimum concentration of 10-100 mu M. This effect was not mimicked by a denosine metabolites adenine, hypoxanthine, or inosine. N-ethylcarboxa midoadenosine (NECA, a relatively non selective adenosine receptor ago nist) and 2-p-(2-carboxyethyl) phenethylamino-5'-N-ethylcarbox-amidoad enosine (CGS-21680, an A(2) selective agonist) also increased DNA synt hesis by mammary epithelial cells. However, N-6-cyclohexyladenosine (C HA, an agonist for A(1) type receptors) decreased DNA synthesis. The A (1) selective antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) ha d no effect on basal or adenosine-induced DNA synthesis, whereas the A (2) selective antagonist 3,7-dimethyl-1-propargylxanthine (DMPX) decre ased adenosine-induced DNA synthesis, Similar effects were observed in another nontumorigenic mouse mammary epithelial line, HC11, as well a s the nontumorigenic human lines MCF-10A and 184.A(1). Binding studies indicated that NMuMG cells contained approximately 3200 A(1) receptor s and about 5300 A(2) receptors per cell. Both CGS-21680 and CHA incre ased GTPase activity in isolated cell membranes, whereas only CGS-2168 0 increased activity of adenylyl cylase, Adenosine and CGS-21680 incre ased expression of a cyclic AMP responsive reporter gene. In addition, the protein kinase A inhibitor H-89 blocked the ability of adenosine and CGS-21680 to induce DNA synthesis, hut did not affect EGF-induced DNA synthesis, These results indicate that adenosine appears to be a p ossible growth promoting agent in mammary tissue, and this effect may be mediated by extracellular receptors of the A(2) type.