Localization and characterization of phospholipase A2 in mouse mammary gland-derived cells.
Phospholipase A2 (PLA2) can participate in the regulation of eicosanoid biosynthesis via PLA2-mediated control of the release of arachidonic acid from phospholipids. Arachidonoyl-hydrolyzing PLA2s were examined in cells from normal mouse mammary glands and mammary carcinomas. Tumor-derived cells exhibited significant PLA2 activity(ies) with arachidonoyl containing phosphatidylcholine and phosphatidylethanolamine as substrates in cell-free assays. In contrast, arachidonoyl containing phosphatidylinositol was a poor substrate. When phosphatidylcholines with varying sn-2 fatty acyl groups were tested as substrates, activity was highest with the arachidonoyl containing lipid. The pH profiles for hydrolysis of phosphatidylcholine and phosphatidylethanolamine differed; all other aspects of PLA2-mediated hydrolysis of these two substrates were similar including a Ca2+ requirement for activity. Moreover, Ca2+ affected the subcellular localization of the enzyme activity. Activity was predominately in the supernatant fraction when cells were harvested in an EGTA (ethylene glycol bis(beta-aminoethylether)-N,N,N',N'-tetraacetic acid) containing buffer and largely in the particulate fraction when cells were harvested in a buffer containing free Ca2+. The localization of activity could be modulated from the supernatant fraction to the particulate fraction by recentrifugation in the presence of Ca2+. Normal gland-derived cells contained a PLA2 activity with properties similar to those of the tumor-derived cells. There was a significant difference in the level of activity in the normal versus tumor cells, the normal gland-derived cells had less than half the PLA2 activity of the carcinoma-derived cells.
Steiner
M R
MR
Department of Microbiology and Immunology, University of Kentucky, Lexington 40536.
D000818:Animals; D002122:Calcium Chloride / Q000494:pharmacology; D002460:Cell Line; D002474:Cell-Free System; D004533:Egtazic Acid / Q000494:pharmacology; D005260:Female; D007700:Kinetics; D008321:Mammary Glands, Animal / Q000201:enzymology*; D008325:Mammary Neoplasms, Experimental / Q000201:enzymology*; D051379:Mice; D010741:Phospholipases A / Q000032:analysis / Q000378:metabolism*; D054467:Phospholipases A2; D013379:Substrate Specificity
D004533:Egtazic Acid; D010741:Phospholipases A; D054467:Phospholipases A2; D002122:Calcium Chloride