No abstract

We have examined several types of tumor cell lines and shown that they invariably expressed little or no Egr-1, in contrast to their normal counterparts. We have previously shown that the expression of exogenous Egr-1 in human breast and other tumor cells markedly reduces transformed growth and tumorigenicity. We therefore hypothesized that the loss of Egr-1 expression plays a role in transformation. All human and mouse breast cancer cell lines and tumors examined had reduced Egr-1 expression compared with their normal counterparts. Reduced Egr-1 expression was also observed in 7,12-dimethylbenz(a)anthracene (DMBA)-induced rat mammary tumors, and this level increased to normal levels in tumors that regressed after tamoxifen treatment. We concluded, therefore, that loss of Egr-1 expression may play a role in the deregulation of normal growth in the tumorigenic process and that Egr-1 acts as a tumor suppressor gene. The early growth response gene, Egr-1 (Sukhatme et al., 1988) (zfp-6 in Standardized Genetic Nomenclature for Mice), also known as NGF1A, Krox 24, zif268 and T1S-8, encodes a protein with 3 adjacent zinc-finger motifs, structures that are present in many DNA-binding transcription factors. The Egr family of proteins consists of 4 members that all bind to the same DNA element: GCGGGGGCG or GCGT/GGGGCG (Christy and Nathans, 1989;LeMaire et al., 1988) because of the remarkable conservation of their zinc-finger DNA binding domains. The Egr family is a highly evolutionarily conserved set of genes but it has proved difficult to define a precise role. One member of the family, WT1, has a homologous zinc-finger domain with 4 fingers that bind to the same DNA motif. WT1 has been categorized as a tumor suppressor gene that is mutant in Wilms' tumor disease in children (Rauscher, 1993).We have shown that Egr-1 has tumor suppressor properties and that the DNA-binding domain is necessary for this activity (Huang et al., 1994a;. The over-expression of Egr-1 in transformed cells suppressed their growth in soft agar and their growth as tumors in athymic mice. In contrast, further inhibition of Egr-1 in mouse transformed cells using antisense-expression vectors increased the transformed character of the cells (Huang et al., 1994b). During the analysis of a range of tumor cell lines, we observed that the expression of Egr-1 was often anomalously low. We have shown that the over-expression of Egr-1 can restore normal growth patterns to these tumor cells, which suggested that the loss of this transcription factor might be either a cause of, or may accompany, the loss of growth control leading to tumor production. Some of this growth down-regulation is due to the induction of Transforming Growth Factor-b expression (Liu et al., 1996). This factor is a growth inhibitor of epithelial cells that express the receptor and accounts for reduced growth rates in some cell types.We have examined here the expression of Egr-1 in human breast tissues and mammary cell lines and tissues. The data strongly support the hypothesis that Egr-1 ...

Stable re-expression of connexin 43 (cx43) in human glioblastoma suppresses transformation and tumorigenicity. The present study was designed to examine the role of cx43 in chemotherapy-induced apoptosis. Expression of cx43 in human glioblastoma cells significantly increased sensitivity to several common chemotherapeutic agents, including etoposide, paclitaxel (Taxol) and doxorubicin, compared with control-transfected cells. The increased sensitivity to chemotherapeutic agents resulted from apoptosis as evidenced by Hoechst dye staining, TUNEL assay and annexin V assay. These cx43-mediated effects were coupled with decreased expression of the specific apoptosis inhibitor bcl-2. Over-expression of bcl-2 in cx43-transfected cells partially confers the resistance to apoptosis induced by etoposide, suggesting that the cx43-mediated apoptosis to chemotherapeutic agents is regulated in part through the down-regulation of bcl-2 expression. Furthermore, the cx43-mediated apoptosis in response to chemotherapeutic drugs may not be linked to increased gap junctional communication in cx43-transfected cells. Our results demonstrate a new role of cx43 in the mediation of apoptosis during chemotherapy.

Nitric oxide (NO) is produced from the conversion of L-arginine by NO synthase (NOS) and regulates a variety of processes in the gastrointestinal tract. Considering the increased activity of arginase in colitis tissue, it is speculated that arginase could inhibit NO synthesis by competing for the same L-arginine substrate, resulting in the exacerbation of colitis. We examined the role of arginase and its relationship to NO metabolism in dextran sulfate sodium (DSS)-induced colitis. Experimental colitis was induced in mice by administration of 2.5% DSS in drinking water for 8 days. Treatment for arginase inhibition was done by once daily intraperitoneal injection of N(ω)-hydroxy-nor- arginine (nor-NOHA). On day 8, we evaluated clinical parameters (body weight, disease activity index, and colon length), histological features, the activity and expression of arginase, L-arginine content, the expression of NO synthase (NOS), and the concentration of NO end-product (NOx: nitrite + nitrate). Administration of nor-NOHA improved the worsened clinical parameters and histological features in DSS-induced colitis. Treatment with nor-NOHA attenuated the increased activity of arginase, upregulation of arginase Ι at both mRNA and protein levels, and decreased the content of L-arginine in colonic tissue in the DSS-treated mice. Conversely, despite the decreased expression of NOS2 mRNA, the decreased concentration of NOx in colonic tissues was restored to almost normal levels. The consumption of L-arginine by arginase could lead to decreased production of NO from NOS, contributing to the pathogenesis of the colonic inflammation; thus, arginase inhibition might be effective for improving colitis.