The binding of autocrine motility factor (AMF) to its cell surface receptor, gp78, stimulates tumor cell motility. In this report, we provide evidence that stimulation of gp78 by either AMF or a monoclonal antibody to gp78 (3F3A) increases adhesion and spreading of metastatic murine melanoma (B16a) cells on fibronectin. This gp78-regulated increase is mediated by up-regulation of surface alphaIIbbeta3++ and alpha5beta1 integrin receptors. In addition, AMF treatment of B16a cells increased

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... ocation of alphaIIbbeta3 and alpha5beta1 from the cytoplasm to the cell surface. However, alphaIIbbeta3 and alpha5beta1 demonstrate separate and unique staining patterns at the surface of B16a cells in response to stimulation of gp78. Furthermore, stimulation of B16a cells with AMF increased their invasion through Matrigel. This stimulated invasion was inhibited by antibodies to alphaIIbbeta3 but not by antibodies to alpha5beta1. The increased integrin surface expression and function in response to AMF was blocked by N-benzyl-N-hydroxy-5-phenylpentanamide, an inhibitor of 12-lipoxygenase, and calphostin C, an inhibitor of protein kinase C. The results demonstrate that AMF stimulates integrin-mediated B16a cell adhesion, spreading, and invasion, and these events are regulated by a signaling pathway involving 12-lipoxygenases and protein kinase C.