RETINOID-INDUCED DIFFERENTIATION REGULATES PROSTAGLANDIN-H SYNTHASE AND CPLA(2) EXPRESSION IN TRACHEAL EPITHELIUM

Rat tracheal epithelial cells cultured in vitro at an air-liquid inter face can differentiate into a mucociliary or squamous phenotype depend ing on the presence or absence of retinoic acid (RA). The airway epith elium is known to produce a number of eicosanoids. We propose that eic osanoid biosynthesis is dependent on the differentiation status of the epithelium. Therefore, prostaglandin production and the expression of cytosolic phospholipase A(2) (cPLA(2)) and the prostaglandin H syntha se (PGHS) isoforms were investigated during differentiation to these t wo phenotypes. The major eicosanoid produced by both phenotypes was pr ostaglandin E(2) (PGE(2)). Proliferating undifferentiated cultures pro duced low levels of PGE(2) regardless of retinoid status. Differentiat ed mucociliary cultures produced high levels of PGE(2) (50 ng/10(6) ce lls), whereas differentiated squamous cultures produced low levels of PGE(2) (<5 ng/10(6) cells). Mucociliary cultures expressed high levels of cPLA(2) and PGHS-2 isoform mRNA and protein. In contrast squamous cultures expressed very low levels of cPLA(2) and PGHS-2 transcript an d protein. The PGHS-1 isoform was expressed in squamous but not in muc ociliary cultures. We investigated changes in expression of these enzy mes during retinoid treatment of established squamous cultures. Treatm ent with RA resulted in a rapid (24 h) downregulation of PGHS-1 mRNA e xpression. However, the cPLA(2) and PGHS-2 genes were expressed in squ amous cultures only after 3 days of RA treatment coincident with redif ferentiation of the culture to a mucociliary phenotype. These studies reveal that retinoid-induced differentiation of airway epithelium into either a mucociliary or squamous phenotype results in profound change s in the expression of cPLA(2) and PGHS isozymes that regulate prostag landin formation.