Cytokine-induced pseudopodial protrusion is coupled to tumour cell migration

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Abstract
Pseudopodia protrusion is a prominent feature of actively motile cells in vitro1,2 and invading tumour cells in vivo3; 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 cells4 and embryonic cells5 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 'senseor-gans' essential to the process of cell locomotion.