Cyclic Adenosine 3′:5′-Monophosphate Metabolism in Normal and SV40-transformed WI-38 Cells

Intact SV40-transformed WI-38 cells (VA13-2RA) responded to catecholamines, prostaglandins, and adenosine with much more dramatic increases in cyclic adenosine 3':5'-monophosphate (cyclic AMP) than did normal WI-38 cells. Further, the responses of VA13-2RA to the catecholamines were independent of the cell population density, whereas the responses of WI-38 were diminished as they approached confluence. Time course studies likewise showed clear differences between VA13-2RA and its normal counterpart, in that the maximal intracellular cyclic AMP levels in response to prostaglandin E1 (PGE1) were reached much later in the transformed than in the normal cells (20 min versus 5 min). Further, the rapid decline in cellular cyclic AMP levels seen in WI-38 (as in most cell systems) was much attenuated in VA13-2RA. Basal cyclic AMP levels were lower in the transformed than in the normal cells, as has been the case with many other systems. Theophylline appeared to have two distinct effects in WI-38, namely, synergism (with prostaglandins), as expressed by increased cellular cyclic AMP levels, and reduction of cyclic AMP accumulation in the media. On the other hand, theophylline had only small (or in some cases no) effects on cyclic AMP accumulation in VA13-2RA. Adenylate cyclase activities in cell-free preparations of WI-38 and VA13-2RA cells differed in several respects. Although homogenates of WI-38 were more active than VA13-2RA preparations in the presence of PGE1 (10 µm) and NaF (10 mm), VA13-2RA activity exceeded WI-38 activity by more than 3-fold in the presence of epinephrine and, in fact, cyclic AMP accumulation in homogenates of the transformed cells was significantly greater in the presence of epinephrine than with NaF. Finally, WI-38 homogenates showed much greater cyclic nucleotide 3':5'-monophosphate phosphodiesterase activity than VA13-2RA preparations (131 ± 8 versus 7.1 ± 5.4 nmoles of cyclic AMP destroyed per mg of protein per 30 min).