TIAM1 and squamous cell carcinoma: Interestingly, expression of Tiam1 WT and P-Rex1 WT, but not their GEF* mutants, in the epithelial squamous cell carcinoma cell line, A431, and the epithelial immortalized Madin-Darby canine kidney cell line, MDCKII, resulted in phenotypic effects similar to those observed in NIH3T3 cells (Fig. 2 and Supplementary Fig. 2).