(A) Expression of TCF7L1 and TCF7L2 in adult human keratinocytes (KER) and different human SCC cell lines, including SCC12, SCC13, SRB1 and SRB12. The human skin SCC cell line SCC13 was transduced to express tet-inducible control shRNA (shNS) or shRNAs against TCF7L1 and/or TCF7L2. After drug selection, transduced cells were treated with doxycycline for five days prior to mRNA and protein isolation for (B) Real time PCR analysis or (C) Western analysis. The transduced cells with effective shRNAs were xenografted into flanks of immunodeficient mice, which were then put on a doxycycline-containing diet. Tumors were isolated and analyzed at the end of eight weeks. (D) Mass of tumors derived from SCC cells expressing control shRNAs (shNS), shRNAs against TCF7L1 (shTCF7L1#1), shRNAs against TCF7L2 (shTCF7L2#1), or both (shTCF7L1#1+shTCF7L2#1 or shTCF7L1#2+shTCF7L2#2). n = 19 (shNS), n = 5 (shTCF7L1#1), n = 3 (shTCF7L2#1), n = 5 (shTCF7L1#1+shTCF7L2#1), n = 5 (shTCF7L1#2+shTCF7L2#2). The grafted tumor mass data are presented as box and whisker plots where boxes span first and third quartiles, bars as the median values, and whiskers as minimum and maximum of all data. **p<0.01, ***p<0.001 (One-way ANOVA with Dunnett’s post-hoc test). (E) Immunohistochemical analysis of TCF7L1 and TCF7L2 expression in xenografted tumors derived from SCC cells expressing control shRNAs (shNS) or shRNAs against both TCF7L1 and TCF7L2 (shTCF7L1#1+shTCF7L2#1). Bar denotes 100 µm.