B16-F1 melanoma cells express augmented glycosylation of a Mr 78,000 (gp78) cell surface glycoprotein in response to cell shape modulation which is correlated to an increased metastatic ability in vivo and motility in vitro. A monoclonal antibody (mAb) directed against gp78 was used to study its surface distribution and possible function in cell locomotion. On motile cells, gp78 is localized by immunofluorescence to the leading lamella as well as to the trailing edge, suggesting shuffling of gp78 during cell migration. When bound to the cells the mAb induced locomotory activity similar to the effect of the cells' autocrine motility-like factor (AMLF). The enhanced motility induced by either anti-gp78 mAb or autocrine motility factor (AMF) were both inhibited by pertussis toxin, indicating that the 3F3A mAb induces cell kinesis via the same pertussis toxin-sensitive G protein pathway as has been described for other motility factors. The binding of anti-gp78 mAb to its ligand was inhibited (10-fold) by preincubation with B16-F1 AMLF containing conditioned media. Based on such functional properties, it was concluded that gp78 behaves as an AMF receptor of the B16-F1 melanoma cell.

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