FIGURE 1.

Regulation of uPAR-dependent lamellipodia formation on vitronectin by uPA ligation. Panel A shows representative micrographs of transfected HEK293 cells expressing high levels of either uPAR^wt, uPAR^W32A, or uPAR^Y57A that are plated on a reconstituted vitronectin matrix for 24 h in the presence or absence of 100 nm concentrations of the stated uPA-derivatives. To enhance detection of lamellipodia, cells were fixed, permeabilized, and stained with Alexa 488-labeled phalloidin before micrographs were taken in a fluorescence microscope. Note the absence of lamellipodia in HEK293 cells expressing either uPAR^W32A or uPAR^Y57A and the reappearance of these structures after the addition of uPA or GFD. Panel B shows an unbiased semiquantitative assessment of the induction of lamellipodia in these cells using the protocol outlined under “Materials and Methods.”