Protein Kinase C and Lipid Signalling for Cellular Regulation
It is well documented that protein kinase C (PKC) is activated by increased levels of diacylglycerol (DG) in the membrane that is produced as a result of hydrolysis of inositol phospholipids (PI) by signal-induced activation of phospholipase C (PLC) (Nishizuka, 1992). Recently, attention has been paid to the hydrolysis of other phospholipids, particularly phosphatidylcholine (PC). This reaction produces DG at a relatively later phase in cellular responses, and possible involvement of phospholipase D (PLD) in PKC activation has been postulated (see for reviews: Billah & Anthes, 1990; Exton, 1990; Cockcroft, 1992). Sustained activation of PKC is a prerequisite essential for long-term responses such as cell proliferation and differentiation. In addition, phospholipase A2 (PLA2) is activated by most of the signals which induce PI hydrolysis. Arachidonic acid regulates many physiological processes after its conversion to various eicosanoids, but products of PC hydrolysis catalyzed by PLA2 potentiate PKC activation, thereby contributing to the signal transduction (Asaoka et al., 1992a). However, the biochemical mechanism of activation of phospholipases D and A2 remains largely unknown.
KeywordsHydrolysis Dopamine Tyrosine Lipase Fluoride
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