FAK and paxillin promote SCC migration on type IV collagen in a β1 integrin dependent manner. (A) Overexpression of FAK and paxillin in SCC25 cells. FAK and paxillin expression vectors were stably transfected into SCC25 cells as described in Materials and Methods. FAK and paxillin expression was determined in neomycin resistant control (neo), FAK overexpressing (FAK-1, -2), and paxillin overexpressing (pax-1, -2) clones by western blot using anti-FAK and anti-paxillin (anti-pax) antibodies. This experiment was repeated with additional independently isolated clones with similar results. Representative blots are shown. (B) Densitometric quantitation of blots in Fig. 3A. (C) FAK or paxillin (pax) overexpressing clones or neomycin resistant control cells (neo) were plated on plastic (pl) tissue culture dishes or type IV collagen (col) coated plates. Some cultures were preincubated with antibodies which block attachment by β1 or β4 integrin subunits. The number of cells which migrated into the blank area of the plate within 24 hours was counted. These experiments were performed three times with similar results. Error bars indicate SEM.