Gene expression of the human prostaglandin E receptor EP4 subtype: differential regulation in monocytoid and lymphoid lineage cells by phorbol ester

We isolated a cDNA clone encoding the human prostaglandin (PG) E receptor EP₄ subtype and examined the gene expression in human blood cells. Northern blot analysis revealed that the EP₄ gene is expressed at a high level in peripheral blood mononuclear cells, and at lower levels 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 EP₄ gene expression in the immune system, we studied the effects of phorbol 12-myristate 13-acetate (PMA) on these cell lines. Gene expression was upregulated in THP-1, U937, and Raji cells by PMA, and was downregulated in MOLT-4 and Jurkat cells. In THP-1 cells the effects of PMA were further analyzed, and the upregulation of the EP₄ gene was shown to be followed by an increase in PGE₂ binding sites and in PGE₂-induced cAMP accumulation. In the striking contrast, other PGE receptor subtypes (EP₁, EP₂ and EP₃) and other prostanoid receptors (IP and DP) were shown not to be upregulated by PMA. Therefore, this is the first demonstration of a highly specific upregulation of the EP₄ subtype in THP-1 cells treated with PMA, suggesting the importance of the EP₄ subtype in the immune system. In the present study we also clarified that EP₄ gene expression is regulated differently among human monocytoid and lymphoid lineage cells, thus leading to the better understanding of the regulatory mechanisms for the human EP₄ gene expression in the immune system.