Transcription factor HMGA2 controls the K-RAS mediated transformation-specific genetic program

A genome-wide survey of transcriptional targets responding to chronic KRAS/MAPK (mitogen-activated protein kinase) pathway activation in rat ovarian surface epithelial cells (ROSE 199) has identified multiple differentially expressed transcriptional regulators including the architectural transcription factor high mobility group AT hook 2 (HMGA2). To elucidate the role of HMGA2 in the transcriptional network affected by oncogenic signaling, we used an integrated approach combining RNAi-mediated silencing, microarray-based expression profiling, computational prediction of transcription factor binding sites in target gene promoters and phenotypic analysis. Knocking-down HMGA2 resulted in the reversion of epithelial-mesenchymal transition, loss of anchorage independence and in a substantial restoration of the gene expression pattern characteristic of non-transformed ROSE cells. Computational prediction of transcription factor binding sites in the promoters of HMGA2-regulated genes and expression profiling revealed a preferential role of activator complex-1 (AP-1) components Fra-1 and JunB in target gene regulation. Forced expression of HMGA2 did not transform normal ovarian epithelial cells, suggesting that HMGA2 up-regulation is not sufficient for inducing the transformed phenotype, but mediates cancer-specific phenotypic traits in cells expressing mutated KRAS and, hence, oncogene addiction. The Ras signaling target array was designed and produced as described (Tchernitsa et al., 2005). Briefly, we selected 121 genes recovered from subtracted cDNA libraries representing sequences differentially expressed in parental and KRAStransformed ROSE 199 cells (Tchernitsa et al., 2004). In addition, we selected genes from subtracted libraries representing sequences differentially expressed in normal 208F fibroblasts and the HRAS-transformed derivative FE-8 (Zuber et al., 2000). Previously described Ras pathway targets and 13 different genes described as housekeeping genes in many different tissues and cell lines were included to permit normalization of hybridization intensities on microarrays. The total number of gene probes is 325 on the array. Unmodified 70-mer DNA oligonucleotides were chosen as probe sets for the array. The oligonucleotide design was performed with software available on the web (