PHOSPHOLIPASE D ACTIVITIES AND PHOSPHATIDYLCHOLINE TURNOVER ARE DIFFERENTIALLY RELATED TO EXPRESSION OF PROTEIN KINASE C ISOFORMS AND MARCKS IN CONTROL AND TRANSFECTED NEURAL CELLS

摘要

Phosphatidyleholine (PtdCho) and phosphatidylethanolamine (PtdEtn) are major membrane phospholipids constituting 70-80% of the total phospholipids in most cells (Vance, 1991; Kent, 1995). Accordingly, they have major roles in maintaining the structural integrity of membrane boundaries between cells and within subcellular organelles and compartments. Both PtdCho and PtdEtn are potential contributors to the generation of lipid second messengers following activation of phospholipases A_2 (PLA_2), C (PLC) and D (PLD) (Kiss et al., 1991; Kiss et al., 1994; Exton, 1990). Following activation of PLA_2, release of polyunsaturated fatty acids may result in bioactive oxygenated products including eicosanoids, leukotrienes and other derivatives. There is increasing evidence that fatty acids also may activate kinases or alter gene expression through receptors and nuclear response elements (Ailhaud et al., 1994; Graber et al., 1994). Release of diacylglycerol (DAG) and phosphatidic acid by PLC and PLD, respectively, also is important in signal transduction (Exton, 1990; Nishizuka, 1992). Initial production of DAG is part of a dual release of second messengers (DAG and inositol tris-phosphate) when phosphatidylinositol bisphosphate is hydrolyzed by PLC. Subsequent, sustained production of DAG appears to involve hydrolysis of PtdCho and PtdEtn (Nishizuka, 1992).