Functional platelet-activating factor receptors linked to inositol lipid hydrolysis, calcium mobilization and tyrosine kinase activity in the human endometrial HEC-1B cell line.

Platelet-activating factor (PAF; sn-1-O-alkyl-2-acetyl-sn-glycero-3- phosphocholine) is thought to be an important mediator of embryo-endometrial interactions in early pregnancy, and an understanding of its role in the establishment of early human pregnancy can only follow an understanding of its mechanism of action. In a human endometrial epithelial cell line, HEC-1B, the presence of mRNA encoding the platelet-activating factor receptor was demonstrated by reverse transcription-polymerase chain reaction. The presence of functional receptors was shown by inositol trisphosphate accumulation and a rise in the concentration of intracellular free calcium evoked by platelet-activating factor in myo-[2-3H]inositol-labelled and fura-2-loaded cells, respectively. Platelet-activating factor evoked rapid and concentration-dependent increases in the concentration of intracellular free calcium and inositol trisphosphate that were inhibited by the platelet-activating factor receptor antagonist WEB 2086, indicating that the responses are receptor mediated. Inositol trisphosphate accumulation evoked by platelet-activating factor was unaffected by pretreatment with pertussis toxin. Platelet-activating factor also stimulated the tyrosine phosphorylation of at least two major proteins of 80 kDa and 44 kDa; the smaller protein is an isoform of mitogen-activated protein kinase. These results show that functional platelet-activating factor receptors are located on the endometrial epithelial cell line HEC-1B and are linked to inositol lipid hydrolysis, calcium mobilization and tyrosine kinase activity.