GENE-EXPRESSION OF THE HUMAN PROSTAGLANDIN-E RECEPTOR EP(4) SUBTYPE -DIFFERENTIAL REGULATION IN MONOCYTOID AND LYMPHOID LINEAGE CELLS BY PHORBOL ESTER

We isolated a cDNA clone encoding the human prostaglandin (PG) E recep tor EP(4) subtype and examined the gene expression in human blood cell s. Northern blot analysis revealed that the EP(4) gene is expressed at a high level in peripheral blood mononuclear cells, and at lower leve ls in cultured human blood cell Lines, THP-1 and U937 (monocytoid cell lines), MOLT-4 and Jurkat (T-cell lines), and Raji (B-cell line). To examine regulation of the EP(4) gene expression in the immune system, we studied the effects of phorbol 12-myristate 13-acetate (PMA) on the se cell lines. Gene expression was upregulated in THP-1, U937, and Raj i cells by PMA, and was downregulated in MOLT-LC and Jurkat cells. In THP-1 cells the effects of PMA were further analyzed, and the upregula tion of the EP(4) gene was shown to be followed by an increase in PGE( 2) binding sites and in PGE(2)-induced cAMP accumulation. In the strik ing contrast, other PGE receptor subtypes (EP(1), EP(2) and EP(3)) and other prostanoid receptors (IP and DP) were shown not to be upregulat ed by PMA. Therefore, this is the first demonstration of a highly spec ific upregulation of the EP(4) subtype in THP-1 cells treated with PMA , suggesting the importance of the EP(4) subtype in the immune system. In the present study we also clarified that EP(4) gene expression is regulated differently among human monocytoid and lymphoid lineage cell s, thus leading to the better understanding of the regulatory mechanis ms for the human EP(4) gene expression in the immune system.