Pseudopodia protrusion is a prominent feature of actively motile cells in vitro and invading tumour cells in vivo; however, the function and regulation of pseudopodia are poorly understood. Tumour autocrine motility factor (AMF) represents a new class of cytokines which are secreted by tumour cells and embryonic cells and induce random motility in the producer cells or in heterologous cells with appropriate receptors. Here we report that a major effect of this factor is to induce the extension of cell pseudopodia before cell translocation. Using a new method to quantify and isolate pseudopodia, we find that human breast carcinoma cell AMF (at concentrations of 1 nM or below) stimulates random pseudopodia formation in a dose-dependent and time-dependent manner. Anti-AMF antibodies inhibit pseudopodia protrusion and cell motility, showing the importance of pseudopodia formation during locomotion. AMF-stimulated motility and pseudopodia formation occur on a wide variety of adhesive substrata which suggests that certain intrinsic motility events are independent of the attachment mechanism. Induced pseudopodia show a prominent axial actin network in the electron microscope. The number of laminin receptor and fibronectin RGD recognition sites is increased by a factor of 20 in the induced pseudopodia when compared to the average distribution in unstimulated cells. Exploratory pseudopodia regulated by cell-derived motility factors contain receptors for matrix proteins and could serve as 'senseorgans' essential to the process of cell locomotion.

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Cell locomotion is an essential requirement for invasion and metastasis of malignant cells. We have previously described the characterization of a 50-kilodalton autocrine motility factor (AMF), a cytokine that stimulates motility in human tumor cells. In this study, we investigated the elaboration of this factor in vivo by human bladder carcinoma and in vitro by a cultured transitional cell carcinoma (TCC) of the bladder cell line T24P. Urine samples from patients with bladder cancer were assayed for their capacity to stimulate migration of tumor cells. Comparing all TCC cases (22 patients) with all nonmalignant diagnoses (27 patients), we found a statistically significant (P less than .001) difference in the motility values. Invasive TCC cases (15 patients) were significantly (P less than .002) higher in regard to motility values compared with noninvasive TCC cases (8 patients), including one case of carcinoma in situ. In follow-up screening studies evaluating TCC recurrence, the recurrent tumors (9 patients) were higher (P less than .001) in regard to motility values than the tumor-free cases (11 patients). Furthermore, T24P cells showed a dose-dependent motile response to their own serum-free conditioned medium as well as to the AMF present in the urine of TCC patients. This finding is consistent with the source of AMF in the urine of these patients being the cancer itself. An enzyme-linked immunosorbent assay (ELISA) for AMF was also developed. Values determined by ELISA correlated well with the motility values measured separately. These data support the potential usefulness of AMF as a urine marker for bladder TCC.