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-ph osphocholine) is thought to be an important mediator of embryo-endomet rial interactions in early pregnancy, and an understanding of its role in the establishment of early human pregnancy can only follow an unde rstanding of its mechanism of action. In a human endometrial epithelia l cell line, HEC-1B, the presence of mRNA encoding the platelet-activa ting factor receptor was demonstrated by reverse transcription-polymer ase 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 my o-[2-H-3]inositol-labelled and fura-2-loaded cells, respectively. Plat elet-activating factor evoked rapid and concentration-dependent increa ses in the concentration of intracellular free calcium and inositol tr isphosphate that were inhibited by the platelet-activating factor rece ptor antagonist WEB 2086, indicating that the responses are receptor m ediated. Inositol trisphosphate accumulation evoked by platelet-activa ting factor was unaffected by pretreatment with pertussis toxin. Plate let-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 th e endometrial epithelial cell line HEC-1B and are linked to inositol l ipid hydrolysis, calcium mobilization and tyrosine kinase activity.