Phosphocholine transferase is more efficient than diacylglycerol kinase as possible attenuator of diacylglycerol signals in primordial human placenta.

Diacylglycerols (DAG) are assumed to play intracellular signal roles in rapidly growing tissues like those present in the primordial human placenta. The aim of the present study was to gain information on the capacity of DAG-kinase and CDP-choline: DAG phosphocholine transferase enzymes to eliminate DAG and behave as possible signal attenuators in these tissues. Previous and present results has provided evidence that Triton X-100 (0.05%, v/v), when incubated with placenta mince, (I) causes the accumulation of DAG by inhibiting DAG-acyltransferase and by a suggested acceleration of phosphatidylcholine (PC) decomposition, (II) inhibits the synthesis of PC and (III) increases the formation of phosphatidic acid (PA) without decreasing the conversion of PA into acylglycerols. Inhibition by the synthetic DAG: dioctanoylglycerol (DOCG) and by the DAG-analog: dioctanoylethyleneglycol (DOEG), of the Triton-induced (3H)PA-accumulation from (3H)glucose and of the increased labeling of PA with (32P)phosphate indicated some DAG-attenuating roles of DAG-kinase, but this mechanism appeared not to be very efficient. The low rate of conversion of DOCG into (32P)PADOCG species in incubations with (32P)phosphate confirmed this view. Compared to the rate of formation of PADOCG, DOCG was eliminated in the form of PCDOCG more than one order of magnitude faster. In addition, DOCG stimulated, whereas DOEG inhibited the formation of endogenous PC. These findings suggest that in the primordial human placenta transformation of DAG into PC by phosphocholine transferase and an attending stimulation of PC synthesis represent a more effective attenuator mechanism than the conversion of DAG into PA by DAG-kinase.