Molecular cloning and expression of platelet-activating factor receptor from human leukocytes

The cDNA for a platelet-activating factor (PAF) receptor was cloned from a human leukocyte cDNA library using a 0.8-kilobase pair fragment of the guinea pig lung PAF receptor cDNA (Honda, Z., Nakamura, M., Miki, I., Minami, M., Watanabe, T., Seyama, Y., Okado, H., Toh, H., Ito, K., Miyamoto, T., and Shimizu, T. (1991) Nature 349, 342-346). The cDNA (1.8-kilobase pairs) had an open reading frame encoding 342 amino acid residues with a calculated Mr of 39,203. The clone was shown to code for a PAF receptor based on the following criteria: 1) the amino acid sequence possesses seven putative membrane spanning domains with 83% identity to the guinea pig lung PAF receptor, 2) Xenopus laevis oocytes injected with the transcript of the clone showed an electrophysiological response to PAF, and 3) COS-7 cells expressing the encoded receptor showed ligand binding with the pharmacological properties of the PAF receptor. Activation of the PAF receptor yielded inositol 1,4,5-trisphosphate production in both COS-7 cells and oocytes, and guanosine 5'-O-(2-thio)bisphosphate injection into the oocytes inhibited PAF-induced Cl- current, providing an evidence that PAF stimulates phosphoinositide turnover via G-protein(s). PAF receptor mRNA was abundant in leukocytes and less so in an undifferentiated human eosinophilic cell line (EoL-1 cells) or human erythroleukemia cells (HEL cells). The production of the mRNA was prominently increased when EoL-1 cells were treated with granulocyte macrophage colony stimulating factor, interleukin-5, and n-butyrate.