Intracellular distribution, activity, and Ca(2+)-dependent translocation of 12-lipoxygenase in Lewis lung tumor cells.

Abstract

The 12-lipoxygenase enzyme (12-LOX) has been found in platelets (1) and several other cell types including leukocytes, epidermal and epithelial cells (2–4), as well as in human (5,6) and rodent tumor cells (7,8). In tumor cells, the major metabolite, 12(S)-HETE, regulates their metastatic potential (9–11) through a protein kinase C-dependent mechanism (7). The intracellular distribution of 12-LOX activity varies between different cells ranging from a predominantly cytosolic (2,4,12) to an exclusive or preferred localization in membranes (5,13,14). This distribution of 12-LOX activity can change upon stimulation of cells suggesting a translocation of the enzyme (15). However, these earlier studies on 12-LOX activity did not investigate in parallel the respective subcellular distribution of the 12-LOX protein itself. In order to obtain a more complete concept of the intracellular regulation and distribution of 12-LOX, we therefore analyzed the distribution of both 12-LOX activity and of 12-LOX protein in murine Lewis lung carcinoma cells (3LL cells) and compared their 12-LOX activity with homologous 12-LOX activity in platelets. Further we asked whether activation of the 12-LOX enzyme in 3LL cells encompasses a Ca2+-dependent translocation to membranes as is the case for 12-LOX in platelets or other enzymes of arachidonate metabolism such as phospholipase A2 and 5-LOX (16,17).