Interactions of prostaglandin E(2) receptor with laminin in mammary tumor metastasis

Abstract

Prostaglandin E{dollar}\sb2{dollar} (PGE{dollar}\sb2{dollar}) is known to contribute to mammary tumor growth and metastasis and its actions are mediated by specific cell receptors. Our previous studies showed that treatment of murine mammary tumor cells with PGE{dollar}\sb2{dollar} receptor antagonists increased their metastatic potential in vivo. To explore the mechanism by which PGE{dollar}\sb2{dollar} receptors affect metastatic behavior of tumor cells, I studied possible interactions of the tumor-PGE{dollar}\sb2{dollar} receptor with laminin, a major glycoprotein in basement membrane shown to be important in mediating tumor cell invasion. I first tested the effect of PGE{dollar}\sb2{dollar} receptor antagonists on tumor cell adhesion to laminin and synthetic laminin peptides. Mammary tumor 410.4 cells utilized both laminin and a laminin peptide PA22-2 for attachment. YIGSR, another laminin peptide recognized by some cells, failed to support adhesion of 410.4 cells. Three unrelated PGE{dollar}\sb2{dollar} receptor antagonists, LEO101, SC19220, and sodium meclofenamate, inhibited tumor cell adhesion to both laminin and peptide PA22-2, with LEO101 being most active. These PGE{dollar}\sb2{dollar} receptor antagonists had little effect on adhesion of a PGE{dollar}\sb2{dollar} receptor negative tumor cell line. To further elucidate the mechanism responsible for PGE{dollar}\sb2{dollar} receptor-modulated tumor cell adhesion, laminin receptors were characterized in mammary tumor cells. Immunoprecipitation and immunofluorescence demonstrated that integrin-type laminin receptor {dollar}\alpha\sb3\beta\sb1{dollar}, but not {dollar}\alpha\sb1\beta\sb1{dollar} or {dollar}\alpha\sb6\beta\sb1{dollar} was expressed on these tumor cells. LEO101 inhibited the expression of the {dollar}\alpha\sb3{dollar} integrin subunit about 27%, which was consistent with its inhibitory effect on tumor cell adhesion. From these results, I conclude: (1) Three PGE{dollar}\sb2{dollar} receptor antagonists inhibit mammary tumor cell attachment to laminin and laminin peptide PA22-2. (2) Among these agents, LEO101 is the most active for PA22-2-mediated cell adhesion, and the inhibitory effect is more potent than seen on intact laminin. (3) These receptor antagonists have little effect on attachment of a PGE{dollar}\sb2{dollar} receptor negative tumor cell line to peptide PA22-2. (4) These mammary tumor cells express integrin {dollar}\alpha\sb3\beta\sb1{dollar} laminin receptor. (5) Expression of {dollar}\alpha\sb3\beta\sb1{dollar} is decreased by LEO101 pre-treatment, which may be the mechanism of decreased tumor cell adhesion to laminin by PGE receptor antagonism. (6) Thus, the PGE{dollar}\sb2{dollar} receptor may function to mediate interactions between mammary tumor cells and laminin, which may consequently alter the metastatic process.