Expression of autocrine motility factor receptor in serum‐ and protein‐independent fibrosarcoma cells: Implications for autonomy in tumor‐cell motility and metastasis

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Abstract
The motile response of serum‐dependent (Gc‐4 SD) and protein‐independent (Gc‐4 PF) murine fibrosarcoma cells to monoclonal antibody (MAb) that binds to gp78 a cell‐surface receptor (M, 78,000) for an autocrine motility factor (AMF) was analyzed. The Gc‐4 PF cells responded to the anti‐gp78 by increased motility in vitro (3‐fold) and increased lung colonization in vivo (8‐to 20‐fold), while the serum‐dependent counter‐part failed to respond to motile stimulation both in vitro and in vivo. Immuno‐analysis of cell‐surface expression and cell extracts revealed a smaller amount of gp78 in Gc‐4 SD cells than in Gc‐4 PF cells. Both cell lines secrete an equal amount of AMF to the culture media. Our results suggest that protein‐free culture of Gc‐4 PF cells is associated with high response to AMF and with high expression of its receptor, and that autonomous motile regulation may play a role in tumor dissemination.