Pancreatic cancer is the fifth leading cause of cancer death in the United States. We used cDNA microarrays to analyze global gene expression patterns in 14 pancreatic cancer cell lines, 17 resected infiltrating pancreatic cancer tissues, and 5 samples of normal pancreas to identify genes that are differentially expressed in pancreatic cancer. We found more than 400 cDNAs corresponding to genes that were differentially expressed in the pancreatic cancer tissues and cell lines as compared to normal pancreas. These genes that tended to be expressed at higher levels in pancreatic cancers were associated with a variety of processes, including cell-cell and cell-matrix interactions, cytoskeletal remodeling, proteolytic activity, and Ca(++) homeostasis. Two prominent clusters of genes were related to the high rates of cellular proliferation in pancreatic cancer cell lines and the host desmoplastic response in the resected pancreatic cancer tissues. Of 149 genes identified as more highly expressed in the pancreatic cancers compared with normal pancreas, 103 genes have not been previously reported in association with pancreatic cancer. The expression patterns of 14 of these highly expressed genes were validated by either immunohistochemistry or reverse transcriptase-polymerase chain reaction as being expressed in pancreatic cancer. The overexpression of one gene in particular, 14-3-3 sigma, was found to be associated with aberrant hypomethylation in the majority of pancreatic cancers analyzed. The genes and expressed sequence tags presented in this study provide clues to the pathobiology of pancreatic cancer and implicate a large number of potentially new molecular markers for the detection and treatment of pancreatic cancer.
The recognition of biologically distinct tumor subsets is fundamental to understanding tumorigenesis. This study investigated the mutational status of the serine/threonine kinase BRAF and the cyclin E regulator FBXW7 (CDC4, FBW7, AGO, SEL10) related to two distinct pancreatic carcinoma subsets: the medullary KRAS2-wild-type and the cyclin E overexpressing tumors, respectively. Among KRAS2-wild-type carcinomas, 33% (3 of 9) contained BRAF V599E mutations; one of which was identified in the pancreatic cancer cell line COLO357. Among 74 KRAS2-mutant carcinomas, no BRAF mutations were identified. Among the KRAS2/BRAF wild-type carcinomas, no mutations within pathway members MEK1, MEK2, ERK1, ERK2, RAP1B, or BAD were found. Using pancreatic cancer microarrays and immunohistochemistry, we determined that 6% (4 of 46 and 5 of 100 in two independent panels) of pancreatic adenocarcinomas overexpress cyclin E. We identified two potential mechanisms for this overexpression including the amplification/gain of CCNE1 gene copies in the Panc-1 and Su86.86 cell lines and a novel somatic homozygous mutation (H460R, in one of 11 pancreatic cancer xenografts having allelic loss) in FBXW7, which was accompanied by cyclin E overexpression by immunohistochemistry. Both BRAF and FBXW7 mutations functionally activate kinase effectors important in pancreatic cancer and extend the potential options for therapeutic targeting of kinases in the treatment of phenotypically distinct pancreatic adenocarcinoma subsets.
The transcription factor Smad4 binds DNA in response to a TGF-beta ligand-initiated intracellular signaling cascade. SMAD4 is deleted or mutated during tumorigenesis in many human tumors. Some of these mutations occur in the N-terminal portion of the protein, the Mad homology 1 (MH1) region, which exhibits sequence-specific DNA-binding. We used alanine scanning mutagenesis and natural mutations to map the subregion of the MH1 domain necessary for that function. We created 20 individual mutations in the MH1 region of human Smad4 and assayed their effect on DNA-binding in vitro. Mutation of residues in the less conserved N- and C-terminal areas of the MH1 region had no effect on DNA-binding. However, mutations in the domain from L43 to R135 caused a dramatic reduction of the ability of Smad4 to bind DNA. Previous work demonstrated a beta-hairpin protein motif within this region to be responsible for DNA-binding, but suggested that the tumorigenic mutations occurring outside this motif may target a separate function of the MH1 domain. Our results demonstrate that the MH1 domain as a whole is very sensitive to changes in overall structure, and that tumorigenic mutations within the region of L43-R135 indeed would target DNA-binding.
Here we describe a new segment polarity gene of Drosophila melanogaster, oroshigane (oro). Identified as a dominant enhancer of Bar (B), oro is also recessive embryonic lethal, and homozygous oro embryos show variable substitution of naked cuticle with denticles. These patterns are distinctly similar to those of hedgehog (hh) and wingless (wg) embryos, which indicates that oro functions in determining embryonic segment polarity. Evidence that oro function is involved in Hh signal transduction during embryogenesis is provided by its genetic interactions with the segment polarity genes patched (ptc) and fused (fu). Furthermore, ptcIN is a dominant suppressor of the oro embryonic lethal phenotype, suggesting a close and dose-dependent relationship between oro and ptc in Hh signal transduction. oro function is also required in imaginal development. The oro1 allele significantly reduces decapentaplegic (dpp), but not hh, expression in the eye imaginal disc. Furthermore, oro enhances the fu1 wing phenotype in a dominant manner. Based upon the interactions of oro with hh, ptc, and fu, we propose that the oro gene plays important roles in Hh signal transduction.
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