Tien C. Ko

Cyclin-dependent kinase inhibitors block proliferation of human gastric cancer cells

BACKGROUND Olomoucine and roscovitine are novel compounds that are designed to inhibit cyclin-dependent kinases (e.g., Cdk2 and cdc2). Cdks regulate progression through key checkpoints of the cell cycle. The purpose of this study was to determine (1) whether olomoucine and roscovitine inhibit Cdk2 and cdc2 kinase activities of the human gastric cancer cell line SIIA and (2) whether olomoucine and roscovitine block cell proliferation and cell cycle progression. METHODS SIIA cells were treated with olomoucine or roscovitine and examined for Cdk2 and cdc2 activities by using histone H1 as the substrate. Cell numbers were counted with a Coulter counter. Cell cycle distribution was analyzed by DNA flow cytometry. RESULTS Olomoucine and roscovitine completely blocked Cdk2 and cdc2 activities in SIIA cells. Both compounds were also able to inhibit proliferation of SIIA cells, as well as three other human gastric cancer cell lines (AGS, MKN45-630, and SNU-1). Cell cycle analysis showed that treatment with olomoucine or roscovitine for 24 hours led to a decrease in the S phase population and an increase in the G2/M population. CONCLUSIONS We have shown that Cdk inhibitors, olomoucine and roscovitine, are a new class of antineoplastic molecules with potential therapeutic benefits for gastric cancers.

Dietary fiber enhances a tumor suppressor signaling pathway in the gut.

Objective:To determine whether sodium butyrate (NaB), a major short-chain fatty acid produced in the human gut by bacterial fermentation of dietary fiber, enhances transforming growth factor (TGF)-β signaling and potentiates its tumor suppressor activity in the gut. Summary Background Data:The molecular mechanisms by which dietary fiber decreases the risk of colon cancers are poorly characterized. TGF-β is an important tumor suppressor in the gut and has many similar biologic activities as NaB. Therefore, we hypothesized that the chemo-preventive effects of NaB are mediated in part by enhancing TGF-β signaling and its tumor suppressor function in the gut. Methods:The effects of NaB on Smad3 expression in rat intestinal epithelial (RIE-1) cells and 6 human colon cancer cell lines were examined. The effects of NaB on TGF-β-induced Smad3 phosphorylation and plasminogen activator inhibitor-1 (PAI-1) and cyclooxygenase-2 (COX-2) gene expression were also examined in RIE-1 cells. Finally, the effects of NaB and TGF-β on anchorage-independent growth were examined in Akt-transformed RIE-1 cells. Results:NaB induced Smad3 in RIE-1 cells and in 4 human colon cancer cell lines. NaB enhanced TGF-β-induced Smad3 phosphorylation and potentiated TGF-β-induced PAI-1 expression. NaB and TGF-β synergistically inhibited anchorage-independent growth of Akt-transformed RIE-1 cells. Conclusions:These results demonstrate that NaB induces Smad3 and potentiates TGF-β signaling and its tumor suppressor activity in gut epithelial cells. Our data reveal a novel molecular mechanism that may explain in part the beneficial effects of dietary fiber in decreasing the risk of colon cancers.

Intestinal cell cycle regulation.

The intestinal epithelium is maintained by a balance between proliferation, differentiation and death that occurs as cells migrate up the crypt-villus axis. Cell cycle regulators such as cyclins, cyclin-dependent kinases (Cdks) and Cdk inhibitory proteins are expressed in a distinct pattern along the crypt-villus structure, suggesting their role in controlling intestinal cells. This is supported by observations that these cell cycle proteins are regulated by growth factors, nutrients and cell-cell contact in cultured intestinal epithelial cells. One of the key regulators of intestinal cell proliferation and differentiation is transforming growth factor-beta, which is expressed in the gut epithelium.

Selective intra-arterial methylene blue injection: A novel method of localizing gastrinoma

A 40-year-old woman had persistent Zollinger-Ellison syndrome despite excision of a 4-cm duodenal gastrinoma. Localizing studies including ultrasonography, computed tomography, magnetic resonance imaging, duodenal endoscopy, endoscopic ultrasonography, and intraoperative endoscopic transillumination of the duodenum failed to detect a tumor. Selective intra-arterial methylene blue injection was used to identify a 6-mm gastrinoma in the duodenum, which was locally excised. Postoperatively, the patient had a negative secretin provocative test result. This novel method uses selective arterial secretin injection with hepatic venous gastrin sampling to identify the vessel feeding the gastrinoma. An angiographic catheter is then positioned in this artery. At laparotomy, methylene blue is injected through this catheter to selectively stain the gastrinoma, facilitating its identification. Selective intra-arterial methylene blue injection can enhance intraoperative detection of small gastrinomas and may improve the rate of curative resection in the Zollinger-Ellison syndrome. Further evaluation of this novel localizing technique is warranted.

Common Bile Duct Obstruction by Free Floating Tumor

Tumors usually spread by local invasion or by vascular or lymphatic metastases. We report six patients in whom tumor cells were shed into the common bile duct with resulting obstruction. The three men and three women had jaundice and upper abdominal discomfort. Jaundice was intermittent in four patients. Preoperative total serum bilirubin ranged from 2.5 to 16.1 mg/dl; alkaline phosphatase ranged from 221 to 605 IU/1. Ultrsasound showed a dilated gallbladder [GB] in five patients with dilated intrahepatic ducts in three and stones in only one. ERCP showed a single filling defect in two of three patients and multiple defects in one. PTC showed multiple defects in one patient. At operation a thick gelatinous tissue fragment or clot was seen in the common bile duct of each patient. Frozen section identified tumor tissue in all. The source was GB carcinoma [2], GB adenomyoma [1], hepatic metastases of colon cancer [2] and common bile duct cancer [1]. Treatment consisted of pancreaticoduodenectomy [2], including one for GB cancer, left hepatic lobectomy [1], choledochoduodenostomy [1], common duct exploration with T-tube insertion and cholecystectomy [1]. One patient with metastatic colon cancer and another with gallbladder cancer died within one year of operation. The other four are alive from 2 to 4 years later. Conclusion: Benign or malignant tumors within the hepatobiliary tree can shed tissue into the common bile duct which can cause biliary obstruction. Any tissue fragment found in the common bile duct should be evaluated by frozen section. Recognition of this mode of tumor spread is needed for appropriate therapy of the underlying benign or malignant tumor.

Molecular and Cell Biology

The Department of Molecular and Cell Biology offers a program of graduate study leading to the PhD in molecular and cell biology. This program provides advanced training in the research methods and concepts of the study of the molecular structures and processes of cellular life. The training is intellectually focused, but at the same time offers an unusually wide range of opportunities for varied disciplinary specialization.

Effects of Aging on Gut Hormones

Medical advances in the last century have enabled people in our society to live longer and to remain healthy for a significantly greater amount of time. In 1987, 29 6 million Americans, or 12% of the population, were 64 yr of age or older. The number of elderly will likely increase, and by 2050, demographers estimate that nearly one-fifth (20%) of Americans will be at least 65 yr of age (1). It is projected that people at age 75 will live at least 11 more years, and those who reach 85 will live another 6 yr (2). Aging is associated with changes in all organ systems; the authors have been interested in the mechanisms responsible for age-related changes in the humoral control of gut function. Although it appears obvious that significant changes in the metabolism and actions of gastrointestinal (GI) hormones must occur with aging, few studies have examined rigorously age-related changes in the GI tract, especially on gut peptides. Some age-associated changes in GI hormone metabolism and gut function have been reviewed (3,4). These alterations may arise because of changes in hormone synthesis or release, or because of alterations in the responses of the target tissues to the action of gut peptides. GI function also can be affected by alterations in gut hormone receptor concentrations, postreceptor signal transduction pathways, or gene transcription and translation. In this chapter, the authors review age-related alteration in GI hormone metabolism and gut function. The authors acknowledge at the outset that their knowledge is limited; only a fraction of the potential changes that occur with growing old has been studied, and most of these studies are descriptive and failed to address the intracellular mechanisms responsible for aging in the gut. In-depth studies to decipher the molecular mechanisms responsible for age-related changes in GI hormones and gut function will be necessary in order to advance the field of gastrointestinal gerontology.