Induction of integrin β3 in PGE₂-stimulated adhesion of mastocytoma P-815 cells to the Arg-Gly-Asp-enriched fragment of fibronectin.

We previously demonstrated that prostaglandin (PG) E₂ stimulates adhesion of mastocytoma P-815 cells (P-815 cells) to the Arg-Gly-Asp (RGD)-enriched matrix via the PGE₂ receptor subtype EP4 [Hatae N, Kita A, Tanaka S, Sugimoto Y, Ichikawa A. Induction of adherent activity in mastocytoma P-815 cells by the cooperation of two prostaglandin E₂ receptor subtypes, EP3 and EP4. J Biol Chem 2003;278:17977-81]. Here we investigated the role of various integrin subtypes in the induction of adherent activity in PGE(2)-stimulated P-815 cells. FACS analysis showed that P-815 cells express high levels of integrin α4, α5, β1 and β2 subunits and moderate levels of integrin αIIb, αv, β3 and β7 subunits. When treated with PGE₂, the EP4 agonist ONO-AE1-329 or the cell permeable cAMP analogue, 8-Br-cAMP, P-815 cells showed markedly increased cell surface expression of integrin αIIb, αv and β3 subunits, and these expressions were significantly reduced by addition of the protein synthesis inhibitor cycloheximide. Along with increased cell surface expression, mRNA and protein levels of the integrin β3 subunit, but not of integrin αIIb and αv subunits, were simultaneously elevated. On the other hand, adhesion of P-815 cells in response to PGE₂ or 8-Br-cAMP was abolished by antibodies specific for integrin αv and β3 subunits, but not by antibodies for integrin α4, α5, β1, β2 and β7 subunits. Moreover, treatment with tirofiban, an integrin αIIbβ3 antagonist, or eptifibatide, an integrin αvβ3/αIIbβ3 antagonist resulted in a decrease in adhesion of P-815 cells in response to PGE₂ or 8-Br-cAMP. These results suggest that de novo synthesis of the integrin β3 subunit plays a pivotal role in PGE₂-induced adhesion of P-815 cells to the RGD-enriched matrix through EP4-mediated cAMP signaling.