HOMOLOGOUS DESENSITIZATION OF ATP-STIMULATED MITOGENESIS - MECHANISM INVOLVES DESENSITIZATION OF ARACHIDONIC-ACID RELEASE AND CAMP ELEVATION BUT NOT THE ACTIVATION OF PROTEIN-KINASE-A

Prolonged incubation of quiescent 3T3, 3T6, and A431 cells with the P- 2Y purinoceptor agonists ATP, ADP, or AMPPNP reduced the mitogenic res ponses of target cells to a further challenge by these agonists, as me asured by [H-3]thymidine incorporation. The mitogenic desensitization was agonist-specific, for no effect was seen on DNA synthesis stimulat ed by epidermal growth factor, insulin, bombesin, 12-O-tetradecanoyl-p horbol-12 acetate (TPA), or adenosine. The desensitization was complet ely reversible, since after a 24 hr incubation in the absence of ATP, the cells responded fully to the mitogenic action of ATP. The presence of a low level of cycloheximide blocked recovery, suggesting that dow nregulation of the P-2Y receptor may have occurred during desensitizat ion. In Swiss 3T3 cells, stimulation of DNA synthesis occurs predomina ntly by activation of arachidonic acid release, followed by its oxidat ion to prostaglandin E(2) and stimulation of adenylyl cyclase. Interes tingly, prolonged preincubation with ATP produced a similar degree of desensitization of DNA synthesis and of ATP-dependent arachidonic acid release and cAMP accumulation. Furthermore, this was true for both wi ld type cells and mutants with a defective cAMP-dependent protein kina se (PKA). We conclude that homologous desensitization is likely due to uncoupling of the P-2Y purinoceptor from phospholipase A(2), and this process does not require activation of protein kinase A. (C) 1995 Wil ey-Liss, Inc.