ABSTRACT
The Rho family of small GTPases control cell migration, cell invasion and cell cycle. Many of these processes are perturbed in cancer and several family members show altered expression in a number of tumor types. RhoBTB2/DBC2 is an atypical member of this family of signaling proteins, containing two BTB domains in addition to its conserved Rho GTPase domain. RhoBTB2 is mutated, deleted or silenced in a large percentage of breast and lung cancers; however, the functional consequences of this loss are unclear. Here we use RNA interference in primary human epithelial cells to mimic the loss of RhoBTB2 seen in cancer cells. Through microarray analysis of global gene expression, we show that loss of RhoBTB2 results in downregulation of CXCL14-a chemokine that controls leukocyte migration and angiogenesis, and whose expression is lost through unknown mechanisms in a wide range of epithelial cancers. Loss of RhoBTB2 expression correlates with loss of CXCL14 secretion by head and neck squamous cell carcinoma cell lines, whereas reintroduction of RhoBTB2 restores CXCL14 secretion. Our studies identify CXCL14 as a gene target of RhoBTB2 and support downregulation of CXCL14 as a functional outcome of RhoBTB2 loss in cancer.
Subject(s)
Chemokines, CXC/genetics , GTP-Binding Proteins/physiology , Neoplasms/genetics , Neoplasms/physiopathology , Tumor Suppressor Proteins/physiology , Carcinoma, Squamous Cell/genetics , Cell Cycle/physiology , Cell Line, Tumor , Cell Movement/physiology , Conserved Sequence , Cullin Proteins/genetics , GTP-Binding Proteins/deficiency , GTP-Binding Proteins/genetics , Gene Expression Regulation, Neoplastic , Gene Silencing , HeLa Cells , Head and Neck Neoplasms/genetics , Humans , Leukocytes/physiology , Neoplasm Invasiveness/physiopathology , Neoplasms/blood supply , Neovascularization, Pathologic/genetics , Reference Values , Signal Transduction , Tumor Suppressor Proteins/deficiency , Tumor Suppressor Proteins/geneticsABSTRACT
Pancreatic duodenal homeobox -1 is a transcription factor that is expressed in beta and delta cells of the islets of Langerhans and in dispersed endocrine cells of the duodenum. It is involved in regulating the expression of a number of key beta-cell genes as well as somatostatin. It also plays a pivotal part in the development of the pancreas and islet cell ontogeny. Thus homozygous disruption of the gene in mice and humans results in pancreatic agenesis. Heterozygous mutations in the gene result in impaired glucose tolerance and symptoms of diabetes as seen in MODY4 and late-onset Type II (non-insulin-dependent) diabetes mellitus. In adults pancreatic duodenal homeobox-1 expression is increased in duct cells of the pancreas that have been induced to proliferate and differentiate to form new islets. Defects in pancreatic duodenal homeobox-1 could therefore contribute to Type II diabetes by affecting compensatory mechanisms that increase the rate of beta-cell neogenesis to meet the increased insulin secretory demand. It could also be a pharmacological target for beta-cell defects in Type II diabetes, while its role as a regulator of islet stem cell activity is being exploited to produce a replenishable source of islet tissue for transplantation in Type I (insulin-dependent) diabetes mellitus.
Subject(s)
Trans-Activators/physiology , Animals , Cell Differentiation , Cell Division , Diabetes Mellitus, Type 2/genetics , Gene Expression Regulation , Glucose Intolerance/genetics , Heterozygote , Homeodomain Proteins/genetics , Homeodomain Proteins/physiology , Homozygote , Humans , Islets of Langerhans/pathology , Islets of Langerhans/physiology , Mutation , Pancreas/embryology , Pancreas/growth & development , Trans-Activators/analysis , Trans-Activators/chemistry , Trans-Activators/geneticsSubject(s)
Child Nutrition Disorders/physiopathology , Infant Nutrition Disorders/physiopathology , Metabolic Syndrome/physiopathology , Prenatal Exposure Delayed Effects , Adult , Child Nutritional Physiological Phenomena , Child, Preschool , Disease , Female , Humans , Infant , Infant Nutritional Physiological Phenomena , Male , Metabolic Syndrome/genetics , Pregnancy , Preventive Medicine , ResearchABSTRACT
One of the mechanisms whereby glucose stimulates insulin gene transcription in pancreatic beta-cells involves activation of the homeodomain transcription factor PDX1 (pancreatic/duodenal homeobox-1) via a stress-activated pathway involving stress-activated protein kinase 2 (SAPK2, also termed RK/p38, CSBP, and Mxi2). In the present study we show, by Western blotting and electrophoretic mobility shift assay, that in human islets of Langerhans incubated in low glucose (3 mM) PDX1 exists as an inactive 31-kDa protein localized exclusively in the cytoplasm. Transfer of the islets to high (16 mM) glucose results in rapid (within 10 min) conversion of PDX1 to an active 46-kDa form that was present predominantly in the nucleus. Activation of PDX1 appears to involve phosphorylation, as shown by incorporation of 32Pi into the 46-kDa form of the protein. These effects of glucose could be mimicked by chemical stress (sodium arsenite), or by overexpression of SAPK2 in the beta-cell line MIN6. Overexpression of SAPK2 also stimulated PDX1-dependent transcription of a -50 to -250 region of the human insulin gene promoter linked to a firefly luciferase reporter gene. The effects of glucose were inhibited by the SAPK2 inhibitor SB 203580, and by wortmannin and LY 294002, which inhibit phosphatidylinositol 3-kinase, although the effects of stress (arsenite) were inhibited only by SB 203580. These results demonstrate that glucose regulates the insulin gene promoter through activation and nuclear translocation of PDX1 via the SAPK2 pathway.
