Eicosanoid-mediated regulation of intracellular calcium pools and cell growth

Abstract

The inositol 1,4,5-trisphosphate (InsP{dollar}\sb3{dollar})-sensitive Ca{dollar}\sp{lcub}2+{rcub}{dollar} pools of {dollar}\rm DDT\sb1MF{lcub}-{rcub}2{dollar} smooth muscle cells empty after inhibition of the intracellular Ca{dollar}\sp{lcub}2+{rcub}{dollar}-ATPase by thapsigargin. Pool emptying causes cells to cease division and enter a stable, quiescent G{dollar}\sb0{dollar}-like state. High serum treatment of these pool-depleted quiescent cells induces the reappearance of functional Ca{dollar}\sp{lcub}2+{rcub}{dollar} pump protein, re-filling of InsP{dollar}\sb3{dollar}-sensitive Ca{dollar}\sp{lcub}2+{rcub}{dollar} pools, and re-entry of cells into the cell cycle. This recovery is mediated by the direct donation of essential fatty acids from the high serum to the pool-depleted cells. The essential fatty acids linolenic acid, linoleic acid, and arachidonic acid each induced recovery of Ca{dollar}\sp{lcub}2+{rcub}{dollar} pools and re-entry of cells into the cell cycle with an EC{dollar}\sb{lcub}50{rcub}{dollar} of approximately 5 {dollar}\mu{dollar}M; the action of each was dependent on protein synthesis. All non-essential fatty acids and growth factors tested did not promote recovery. Inhibitors of the prostanoid and lipoxygenase metabolism pathways had no effect on essential fatty acid-induced Ca{dollar}\sp{lcub}2+{rcub}{dollar} pool or growth recovery. However, the cytochrome P-450 inhibitors SKF-525A, metyrapone, and nordihydroguaiaretic acid each prevented the action of AA. Importantly, treatment of quiescent cells with either of 8,9- or 11,12-epoxyeicosatrienoic acid (EET), two of the four regiospecific cytochrome P-450 metabolites of arachidonic acid, also induced recovery. However, further metabolism of the effective EETs either to dihydroxyeicosatrienoic acid metabolites or through subsequent eicosanoid synthesizing pathways appears to be unnecessary. Evidence suggests that neither protein kinase activity nor the participation of cGMP or cAMP is involved in the EET-induced recovery process. These results are important in understanding the role of cytochrome P-450 derived eicosanoids in cellular regulation and the relationship between pool emptying and cell cycle control.