Byungwoo Ryu

Exploration of global gene expression patterns in pancreatic adenocarcinoma using cDNA microarrays

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.

Exploring the Host Desmoplastic Response to Pancreatic Carcinoma: Gene Expression of Stromal and Neoplastic Cells at the Site of Primary Invasion

The dramatic opportunities presented by comprehensive gene profiling technologies are curbed by the problem of segregating these large amounts of gene expression data into meaningful categories for study. This is particularly evident in infiltrating carcinomas of the pancreas, in which global gene expression data primarily mirrors the prominent desmoplastic response to the infiltrating neoplasm. In an effort to better characterize the gene expression of invasive pancreatic cancers and their associated desmoplastic response, we performed in situ hybridization on pancreatic cancer tissues to characterize the expression of 12 genes identified by serial analysis of gene expression as highly expressed in invasive pancreatic cancer tissues but not in pancreatic cancer cell lines. In situ hybridization demonstrated that eight genes were expressed within the stromal and/or angioendothelial cells of the desmoplastic response to the invasive tumor, and four of these genes were specifically expressed by the stromal cells immediately adjacent to the invasive neoplastic epithelium, suggesting regional differences in gene expression within the host desmoplastic response. In contrast, four genes were specifically expressed by the invasive neoplastic epithelium, indicating important differences between in vivo and in vitro gene expression of human epithelial neoplasms. We have identified a highly organized structure of gene expression within the host stromal response to invasive pancreatic cancer that may reflect tumor-host communication and serve as a target for therapeutic intervention.

Malignant Transformation of Human Cells by Constitutive Expression of Platelet-derived Growth Factor-BB*

Platelet-derived growth factors (PDGFs) comprise a family of growth factors strongly implicated in human oncogenesis. A number of human tumors overexpress PDGF family members or have translocations activating PDGF receptors. Whereas the epidemiologic evidence implicating PDGF in human tumors is strong, malignant transformation of human cells by overexpression of PDGF has not been demonstrated. We have previously developed a human cell line by the sequential introduction of large T cells and telomerase, and we have demonstrated that these cells express functionally active PDGF receptor (PDGFR) β. In order to determine whether growth factor-mediated transformation of human cells could occur, these cells were transduced with a retrovirus encoding PDGF-BB. Constitutive expression of PDGF-BB led to malignant transformation in nude mice. This is the first demonstration of constitutive signaling causing malignant transformation of human cells. Some of the changes that occur because of constitutive growth factor expression can be reversed by the clinically approved tyrosine kinase inhibitor Glivec, whereas other changes are not reversible by tyrosine kinase inhibitors. Our model allows the assessment of epigenetic changes that occur during human carcinogenesis. In addition, these studies provide insight into the clinical failure of tyrosine kinase inhibitors as monotherapy for advanced malignancy.

The essential similarity of TGFβ and activin receptor transcriptional responses in cancer cells

The binding of activin and TGFβ to their respective receptors initiates signals that are carried by common intermediates (Smad proteins) to induce transcriptional activation of downstream genes. Mutations in tumors indicate that both receptor types convey tumor-suppressive signals, among other biologic roles, but their respective sets of transcriptional targets (transcriptomes) and the shared degree of transcriptome similarity are not well explored in these cells. Transcriptome changes were analyzed by gene expression profiling after expression of constitutively active activin type I (ALK4m) and TGFβ type I (ALK5m) receptors and by variation of Smad4 expression in cancer cells. Eleven of 15 previously reported TGFβ downstream genes were confirmed to be responsive to TGFβ and activin receptors in cancer cells. Expression profiling detected eight of these 11, as well as 13 new Smad4-dependent transcripts. Although Smad4-dependent CDKN1A/p21 induction represents the sole known effector of TGFβ and activin tumor-suppressor effects, many downstream genes have not yet been evaluated for a suppressive role. A high similarity of TGFβ and activin responses among the known and new transcriptional target genes indicated an essential redundancy of the two related inputs. This similarity helps relate the mutations seen in both receptor systems and their Smad mediators in human cancers. Key words: pancreatic cancer, activin, transforming growth factor beta, signal transduction, gene expression profiling