Integrins play an important role in mediating
tumor cell-extracellular matrix (ECM) and
tumor cell-endothelial cell interactions. The
integrin alphaIIb beta3 (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 alphaIIb
beta3 integrin. Reverse transcription-PCR/Southern blotting, Northern blotting, and dot blotting demonstrated the presence of the platelet-type alphaIIb
beta3 integrin in human
melanoma WM 983B, WM 983A, and WM 35 cells. AP-2, a
monoclonal antibody (mAb) to alphaIIb beta3, 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 alphaIIb beta3. PAC-1 specifically recognizes the conformationally active form of platelet alphaIIb beta3.
Phorbol 12-myristate 13-acetate-stimulated adhesion of WM 983B cells to PAC-1 was completely blocked by an
RGD peptide, thus providing evidence that
tumor cell adhesion to PAC-1 is mediated via the alphaIIb
beta3 integrin but not the
Fc receptor. Confocal immunofluorescent studies demonstrated that
fibronectin-adherent
melanoma cells possess an intracellularly localized pool of high-affinity alphaIIb beta3. Invasion of WM 983B cells through
fibronectin was stimulated by 12(S)-hydroxyeicosatetraenoic
acid, and this stimulated invasion was blocked by the mAb PAC-1. The data suggest that
melanoma cells express the high-affinity alphaIIb
beta3 integrin, which is involved in
tumor invasion.