tetracycline and Carcinogenesis

The tetracycline regulatory system provides a tractable strategy to interrogate the role of oncogenes in the initiation, maintenance, and regression of tumors through both spatial and temporal control of expression. This approach has several potential advantages over conventional methods to generate genetically engineered mouse models. First, continuous constitutive overexpression of an oncogene can be lethal to the host impeding further study. Second, constitutive overexpression fails to model adult onset of disease. Third, constitutive deletion does not permit, whereas conditional overexpression of an oncogene enables the study of the consequences of restoring expression of an oncogene back to endogenous levels. Fourth, the conditional activation of oncogenes enables examination of specific and/or developmental state-specific consequences.Hence, by allowing precise control of when and where a gene is expressed, the tetracycline regulatory system provides an ideal approach for the study of putative oncogenes in the initiation as well as the maintenance of tumorigenesis and the examination of the mechanisms of oncogene addiction. In this protocol, we describe the methods involved in the development of a conditional mouse model of MYC-induced T-cell acute lymphoblastic leukemia.

Topics: Animals; Animals, Genetically Modified; Apoptosis; Carcinogenesis; Cell Line, Tumor; Cell Transformation, Neoplastic; Disease Models, Animal; DNA; Gene Expression Regulation; Genes, myc; Genetic Engineering; Humans; Mice; Oncogenes; Precursor T-Cell Lymphoblastic Leukemia-Lymphoma; Protein Synthesis Inhibitors; Proto-Oncogene Proteins c-myc; T-Lymphocytes; Tetracycline

Dysregulation of hypoxia-inducible transcription factors HIF-1α and HIF-2α correlates with poor prognosis in human cancers; yet, divergent and sometimes opposing activities of these factors in cancer biology have been observed. Adding to this complexity is that HIF-1α apparently possesses tumor-suppressing activities, as indicated by the loss-of-function mutations or even homozygous deletion of HIF1A in certain human cancers. As a step towards understanding this complexity, we employed 8-week intermittent induction of a stable HIF-1α variant, HIF1α(PP), in various cancer cell lines and examined the effects on malignant progression in xenografts of immunocompromised mice in comparison to those of HIF2α(PP). Although 8-week treatment led to eventual loss of HIF1α(PP) expression, treated osteosarcoma U-2 OS cells acquired tumorigenicity in the subcutaneous tissue. Furthermore, the prior treatment resulted in widespread invasion of malignant glioma U-87 MG cells in the mouse brain and sustained growth of U-118 MG glioma cells. The lasting effects of HIF-1α on malignant progression are specific because neither HIF2α(PP) nor β-galactosidase yielded similar effects. By contrast, transient expression of HIF1α(PP) in U-87 MG cells or constitutive expression of HIF1α(PP) but not HIF2α(PP) in a patient-derived glioma sphere culture inhibited tumor growth and spread. Our results indicate that intermittent induction of HIF-1α produces lasting effects on malignant progression even at its own expense.

Topics: Animals; Basic Helix-Loop-Helix Transcription Factors; Brain; Carcinogenesis; Cell Line, Tumor; Cell Transformation, Neoplastic; Disease Progression; Gene Expression Regulation, Neoplastic; Humans; Hypoxia-Inducible Factor 1, alpha Subunit; Male; Mice; Mutation; Neoplasm Invasiveness; Tetracycline; Transgenes

High levels of S100A6 have been associated with poor outcome in some types of human cancers, but the role of S100A6 in the molecular pathogenesis of these cancers is largely unknown. This study was performed to explore the expression and functional roles of S100A6 in hepatocellular carcinoma (HCC). The expression level of S100A6 in HCC tumor and corresponding peritumoral tissues were determined by immunohistochemistry analysis. The potential functions of S100A6 in tumorigenesis and metastasis were analyzed by cell proliferation, migration, and invasion assays in human liver cancer cells. Moreover, through expression and purification of S100A6 recombinant protein tagged with cell-penetrating peptide, we analyzed its complex extracellular/intracellular effects in a S100A6-silenced cellular model. As a result, the expression of S100A6 was up-regulated in human HCC compared with adjacent peritumoral tissues. S100A6 silencing inhibited the growth and motility of HCC cells, while intracellular re-expression of S100A6 could rescue the proliferation and migration defects. Intracellular over-expression of S100A6 resulted in down-regulation of E-cadherin expression and promoted nuclear accumulation of β-catenin. Moreover, we found that the enhanced cell proliferation and motility after S100A6 stimulation were dependent on the activation of PI3K/AKT pathway. These results suggest that S100A6 may be involved in promotion and progression of human liver cancer.. S100A6 is overexpressed in human hepatocellular carcinoma clinical specimens. S100A6 promotes proliferation and migration of human hepatoma cells. Overexpression of S100A6 results in alteration of E-cadherin and β-catenin. The multi-effects of S100A6 may be mediated in part by PI3K/AKT pathway activation.

Topics: Animals; beta Catenin; Cadherins; Carcinogenesis; Carcinoma, Hepatocellular; Cell Cycle Proteins; Cell Movement; Cell Nucleus; Cell Proliferation; Cell Shape; Cholangiocarcinoma; Down-Regulation; G1 Phase Cell Cycle Checkpoints; Gene Silencing; Hep G2 Cells; Humans; Immunohistochemistry; Liver Neoplasms; Mice; Phosphatidylinositol 3-Kinases; Protein Transport; Proto-Oncogene Proteins c-akt; Pseudopodia; S100 Calcium Binding Protein A6; S100 Proteins; Signal Transduction; Tetracycline