Using a retrovirus-mediated cDNA expression cloning approach, we identified the 
grainyhead-like 2 (GRHL2) transcription factor as novel protooncogene. 
Overexpression of GRHL2 in NIH3T3 cells induced striking morphological changes, 
an increase in cell proliferation, anchorage-independent growth, and tumor 
growth in vivo. By combining a microarray analysis and a phylogenetic 
footprinting analysis with various biochemical assays, we identified the 
epidermal growth factor receptor family member Erbb3 as a novel GRHL2 target 
gene. In breast cancer cell lines, shRNA-mediated knockdown of GRHL2 expression 
or functional inactivation of GRHL2 using dominant negative GRHL2 proteins 
induces down-regulation of ERBB3 gene expression, a striking reduction in cell 
proliferation, and morphological and phenotypical alterations characteristic of 
an epithelial-to-mesenchymal transition (EMT), thus implying contradictory roles 
of GRHL2 in breast carcinogenesis. Interestingly, we could further demonstrate 
that expression of GRHL2 is directly suppressed by the transcription factor zinc 
finger enhancer-binding protein 1 (ZEB1), which in turn is a direct target for 
repression by GRHL2, suggesting that the EMT transcription factors GRHL2 and 
ZEB1 form a double negative regulatory feedback loop in breast cancer cells. 
Finally, a comprehensive immunohistochemical analysis of GRHL2 expression in 
primary breast cancers showed loss of GRHL2 expression at the invasive front of 
primary tumors. A pathophysiological relevance of GRHL2 in breast cancer 
metastasis is further demonstrated by our finding of a statistically significant 
association between loss of GRHL2 expression in primary breast cancers and lymph 
node metastasis. We thus demonstrate a crucial role of GRHL2 in breast 
carcinogenesis.