ACTIVATION OF INOSITOL PHOSPHOLIPID BREAKDOWN BY PROSTAGLANDIN-F2-ALPHA WITHOUT ANY STIMULATION OF PROLIFERATION IN QUIESCENT NIH-3T3 FIBROBLASTS

Stimulation of NIH-3T3 cells with prostaglandin F(2α) (PGF(2α)) caused a dose- and time-dependent generation of inositol phosphates. The first detectable changes were in the levels of Ins(1,4,5)P3 and Ins(1,3,4,5)P4. Increases in Ins(1,3,4)P3, InsP2 and InsP were detected later, and only minor changes were observed in putative InsP5 or InsP6. The accumulation of inositol phosphates was synergistically increased by the addition of calf serum, whereas PGF(2α) had no effects on cell proliferation in either the presence or the absence of calf serum. Stimulation of a different clone of NIH-3T3 cells (AmNIH-3T3) or Swiss 3T3 cells with PGF(2α) resulted in both inositol phospholipid breakdown and cell proliferation. No differences were found in the characteristics of PGF(2α)-stimulated inositol phosphate generation between the two clones of NIH-3T3 cells, nor was there any difference in receptor number or K(d). These results question the role of inositol phospholipid breakdown in mitogenesis and demonstrate significant differences in the biochemical properties of apparently the 'same' cells.