EXTRACELLULAR ATP INDUCES ANCHORAGE-INDEPENDENT EXPRESSION OF CYCLIN-A AND RESCUES THE TRANSFORMED PHENOTYPE OF A RAS-RESISTANT MUTANT-CELLLINE

Anchorage-independent growth is characteristic of neoplastic cells, bu t the signal transduction pathways that mediate this phenotype are poo rly understood. Several important cell cycle events are dependent on c ell-substratum adhesion in non-transformed cells, including activation of G(1) cyclin-dependent kinases and expression of cyclin A; the adhe sion requirement of these events is abrogated in Ras-transformed cells . The ER-1-2 mutant rat fibroblast cell line is: 1) resistant to has-m ediated, anchorage-independent growth; 2) defective in Ras-mediated, a dhesion-independent expression of cyclin A, but not adhesion-independe nt activation of cyclin-dependent kinases; and 3) rescued for Ras-indu ced, anchorage-independent growth by ectopic expression of cyclin A We report here that extracellular ATP induces adhesion-independent expre ssion of cyclin A and rescues growth in soft agar by ER-1-2 cells that express Ras. ADP, AMP and the non-hydrolyzable analog adenosine 5'-(b eta,gamma-iminodiphosphate) are also effective, but adenosine is not. Adenine nucleotide-induced growth in soft agar is inhibited by reactiv e blue 2, an antagonist of some P-2 purinoceptors. ATP does not induce adhesion-independent expression of cyclin A in ER-1-2 or control rat fibroblasts that do not express Ras, indicating a requirement for addi tional Ras-regulated signals for expression of this gene; one such sig nal may lead to phosphorylation of the retinoblastoma protein, pRB, an d related proteins. These results suggest that extracellular ATP could play a role in the multistage carcinogenic process in vivo.