PRODUCTION AND FUNCTION OF LIPID 2ND MESSENGERS IN PROLIFERATING AND DIFFERENTIATED NEUROBLASTOMA-CELLS

Multiple cellular responses are regulated through the generation of li pid second messengers upon activation of phospholipases. One such resp onse concerns the activity of a class of kinase constituting the prote in kinase C family. The production of specific molecular species of li pid second messengers may be therefore of prime importance in the acti vation of a member of the PKC isoforms. Prompted by this possibility w e investigated the production of 1,2 diacyl-sn-glycerol (DAG) and phos phatidic acid (PtdOH) in LA-N-1 neuroblastoma cells under various phys iological states. 12-0-Tetradecanoylphorbol 13-acetate (TPA) stimulati on activated a phospholipase D (PLD) specific for phosphatidylcholine (PtdCho) in proliferating cells and a phospholipase C (PLC) specific f or phosphatidylethanolamine (PtdEtn) in retinoic acid (RA) differentia ted cells. These separate activations produced different molecular spe cies of DAG or PtdOH. PtdOH was able to stimulate the Ca2+ dependent p rotein kinase C (PKC) by a mechanism which differed from the action of DAG. PtdOH did not induce the translocation of the PKC to the membran e. Moreover PtdOH, in contrast to DAG, prevented PKC degradation by in hibiting the enzymatic hydrolysis by m-calpain. These observations sug gest that the stimulation of cells by agonists elicited the production of specific molecular species of lipid second messengers depending on the physiological status of the cells, and probably on the nature of the stimulus. It seems therefore likely that the generation of specifi c lipid second messengers may activate specific PKC isoforms resulting in a specific cellular response.