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Session II : Receptor signaling and G proteins Poster II, 27
South of Ras: Identification and Characterization of Genes Deregulated by Oncogenic
Ras Signaling
Minh-Cam Ha-Thi, Oleg Tchernitsa, Anja Schramme, Balázs Györffy, Anastassia
Malek, Christine Sers and Reinhold Schäfer
Laboratory of Molecular Tumor Pathology, Charité Universitätsmedizin Berlin,
Schumannstr. 20/21, D-10117 Berlin, Germany. E-mail: reinhold.schaefer@charite.de
The small GTPase Ras is a molecular signaling switch known to play a critical role in tumor
growth and development. The oncogenic activity of Ras signaling pathways is tightly coupled
with the deregulation of the genetic program. Therefore, it is essential to identify deregulated
target genes and to study their contribution to transformed phenotypes. We obtained a
consensus list of genes responding to oncogenic Ras signaling in pairs of normal versus Rastransformed
cells of rat, mouse and human origin by analyzing differential gene expression
using suppression subtractive hybridization (SSH) and by interrogating high-density
microarrays. To systematically study the deregulation of Ras-responsive genes in Rastransformed
cells under various experimental conditions, we established species-specific
customized microarrays representing approx. 300 Ras targets. We used Ras target microarrays
for studying the transcriptional response to conditional Ras activation in a time-resolved
manner and for identifying groups of target genes (signal-regulated transcriptional modules)
controlled by specific downstream pathways such as the mitogen-activated kinase (MAPK)
pathway or the phosphatidylinositol-3 kinase (PI3K) pathway in rodent cells. We also
identified 45 genes showing increased transcriptional expression and 56 down-regulated
genes in normal (BJELB) and H-Ras transformed human embryo fibroblasts (BJELR). To
narrow-down the number of critical target genes, we targeted signaling effectors and
individual Ras-responsive genes by RNA interference. Silencing by siRNA of the
transcriptional regulators Fra-1 and HMGA2, frequently up-regulated in Ras-transformed
cells, impairs the proliferative capacity suggesting that these targets are necessary for cellular
transformation. Likewise, knocking-down transformation-sensitive genes in non-transformed
precursor cells can result in neoplastic transformation. Using this approach, a still growing set
of genes capable of negatively affecting cellular transformation and also Ras signal
transduction is being established.
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