We have prepared and purified the amino terminal fragment (ATF) or urokinase-type plasminogen activator (u-PA), as well as the kringle and the growth factor domain (GFD) of which it is composed. Structural studies on these materials are currently under way. In addition, we have demonstrated that either the ATF or its GFD portion can inhibit tumour cell invasion in vitro, and that both can likewise act as mitogens and induce differentiation in certain cell lines. Our results also suggest that the fucose attached to Thr18 may be essential for at least some of these activities, since defucosylated GFD becomes inactive in mitogenesis. Clearly the ATF has activities beyond simply anchoring u-PA to the cell surface. Availability of separated, purified domains will allow both structural and functional dissection of these activities.
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