DAMD 17 - 02 - 1 - 0216 TITLE : EGFR - Dependent Regulation of Matrix - Independent Epithelial Cell Survival

Previous studies addressing functional aspects of nuclear factor KB (NF-KB) activation in normal and transformed keratinocytes revealed complex and seemingly contradictory roles of this transcription factor in this cell type. In normal skin, NF-KB signaling seems to inhibit squamous cell carcinoma development whereas, in squamous cell carcinoma themselves, deregulated NF-KB expression and/or signaling is frequently observed. To further investigate this paradox, we focused on NF-KB activation as it relates to the transformed phenotype of immortalized but nontumorigenic human keratinocytes (HaCaT cells). We observed that NF-KB activity contributed to survival and growth of cultured HaCaT keratinocytes as shown by use of pharmacologic NF-KB inhibitors, RNA interference, and inducible overexpression of a dominant interfering IKB construct. NF-KB activation was largely provided through interaction with extracellular matrix components because preventing cell attachment by forced suspension culture markedly reduced NFKB signaling associated with cell death (anoikis); conversely, anoikis was partially reversed by NF-KB activation induced either by tumor necrosis factor-A treatment or by overexpressing the NF-KB p65 subunit in HaCaT cells. Furthermore, overexpression of NF-KBp65 in HaCaT cells induced colony formation in soft agar and tumorigenicity in nude mice. In summary, as opposed to normal keratinocytes, immortalized HaCaT keratinocytes provide a cellular context in which deregulated NF-KB signaling supports multiple malignant traits in vitro and in vivo . (Cancer Res 2006; 66(10): 5209-15)