The High Affinity aIIbfi 3 Integrin Is Involved in Invasion of Human Melanoma Cells '

Integrins play an important role in mediating tumor cell-extracellular matrix (ECM) and tumor cell-endothelial cell interactions. The integrin aIIb@33(GPIIb-IIIa) is expressed on the surface of platelets in an inactive state and requires a conformational change to recognize extracellular matrix proteins such as fibrinogen, fibronectin, vitronectin, and others. In this study, we questioned whether human melanoma cells express the allb@3 mtegrln. Reverse transcription-PCR/Southern blotting, Northern blotting, and dot blotting demonstrated the presence of the platelet-type aIIbfi3 integrin in human melanoma WM 983B, WM 983A, and WM 35 cells. AP-2, a monoclonab antibody (mAb) to aHbjI3, positively stained two human melanoma specimens, indicating expression of this integrin in vivo. Phorbol 12-myristate 13-acetate and 12(S)-hydroxyeicosatetraenoic acid, two activators of protein kinase C, stimulated adhesion of melanoma cells to immobilized fibronectin and PAC-1, a mAb to aIIb@33. PAC-1 specifically recognizes the conformationally active form of platelet aIIbfi3. Phorbol 12-myristate 13-acetate-stimulated adhesion of †̃MM 983Bcellsto PAC.1wascompletelyblockedby an RGD peptide,thus providing evidence that tumor cell adhesion to PAC-1 is mediated via the aIIbfi3 integrin but not the Fc receptor. Confocal immunofluorescent studies demonstrated that fibronectin-adherent melanoma cells possess an mtracellularly localized pool of high-affinity aHbfb3. Invasion of WM 983B cells through fibronectin was stimulated by 12(S)-hydroxyeicosatet. raenoic acid, and this stimulated invasion was blocked by the mAb PAC-1. The data suggest that melanoma cells express the high-affinity allbfi3 integrin, which is involved in tumor invasion.