Site and mechanism of growth inhibition by prostaglandins. I. Active transport and intracellular accumulation of cyclopentenone prostaglandins, a reaction leading to growth inhibition.

Cyclopentenone prostaglandins (PGs) such as PGA2 or 9-deoxy-delta 9,12-13,14-dihydro-PGD2 (delta 12-PGJ2) induce growth inhibition of various lines of cultured cells. Action sites of these PGs were studied by incubating them with L-1210 murine leukemia cells. L-1210 cells accumulated both PGs in a time-dependent manner at 37 degrees C. When the uptake was analyzed with various concentrations of delta 12-PGJ2, the Michaelis-Menten type of kinetics was obtained, and the Km and Vmax were 250 microM and 2.5 nmol/min/10(6) cells, suggesting that the uptake was a carrier-mediated active transport. Competition studies with [3H]delta 12-PGJ2 showed that PGA2 was transported by the same carrier with a similar affinity. PGs without growth inhibitory activity such as PGD2, PGE2 and PGF2 alpha were neither taken up by the cells nor interfered the uptake. Subcellular distribution studies with sucrose density gradient centrifugation showed that transported delta 12-PGJ2 was present mainly in cytoplasm and nuclei without metabolism. Accumulation of the PG was attenuated greatly by preincubation of the cells at 37 degrees C for 30 min. When the effect of delta 12-PGJ2 was examined in the control and attenuated cells, a clear correlation was observed between the accumulation of the PG and its growth inhibitory effect. These results suggested that uptake and intracellular accumulation of cyclopentenone PGs are responsible for their growth inhibitory activity.