Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.1.21 (thymidine kinase)
 7,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The connexin 26 (Cx26) gene suppresses the growth of HeLa cells in vitro and in vivo. We explored the possibility that the Cx26 gene not only suppresses growth but can also mediate the bystander effect that is observed in some gene therapy. In gene therapy mediated by the herpes simplex virus thymidine kinase, the toxicity of ganciclovir affects not only the cells transduced with the gene but also affects neighboring tumor cells; it has been suggested that gap junctional intercellular communication (GJIC) may play a role in such a bystander effect. HeLa cells expressing the Cx26 gene (Cx26+) or not expressing the Cx26 gene were transfected with the herpes simplex virus thymidine kinase (tk+) gene, producing Cx26(-)-tk-, Cx26(-)-tk+, Cx26+-tk-, and Cx26+-tk+ cells. By making different kinds of cocultures of these cells, we observed a clear bystander killing effect, assessed by the neutral red toxicity test, in the coculture of Cx26+-tk-/Cx26+-tk+ cells. The bystander effect was markedly prevented by a long-term inhibitor of GJIC, 18-alpha-glycyrrhetinic acid, demonstrating that a major part of the bystander effect seen occurred through Cx-mediated GJIC. These data suggest the possibility of using of Cxs as both tumor suppressor genes and as diffusers of ganciclovir toxicity in therapeutic approaches.
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PMID:A tumor suppressor gene, Cx26, also mediates the bystander effect in HeLa cells. 923 Feb 3

A bystander effect is described when nontransduced or genetically unmodified cells are killed during death of genetically modified tumor cells transduced with a suicide gene. The "bystander effect" greatly enhances the efficacy of the herpes simplex virus-thymidine kinase/ganciclovir (HSV-TK/GCV) gene therapy approach for cancer. The mechanism of the bystander effect is controversial. In this study, we examined the role of intercellular gap junction communication (GJIC) for the bystander effect in human gastrointestinal tumor cells. Our results show that the extent of the bystander effect varied amongst the tumor cell lines; pancreatic cancer cells BXPC-3 exhibited excellent bystander effects in vitro and in vivo studies whereas other gastrointestinal tumor cell lines such as pancreatic cancer cells MIAPACA-2, and colon cancer cells HT-29 showed poor bystander effects. Bystander effects were only found in the presence of cell-to-cell contact. The extent of the bystander effect was independent of the level of HSV-TK activity in the transduced tumor cells and was correlated with GJIC as demonstrated by an in vitro dye-transfer assay. Expression of the mRNA levels of gap junction protein connexin 43 was 8- to 26-fold or greater and connexin 26 gene expression was 2- to 229-fold greater in BXPC-3 cells compared to HT-29, MIAPACA-2, and PANC3 cells. Our results suggest that intercellular communication is essential for the bystander effect. The correlation between GJIC and the extent of the bystander effect suggest a role for GJIC in mediating the bystander effect. Analysis of tumors for GJIC or expression of gap junction proteins may identify the subset of patients suitable for gene therapy with the HSV-TK/GCV approach.
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PMID:Intercellular communication mediates the bystander effect during herpes simplex thymidine kinase/ganciclovir-based gene therapy of human gastrointestinal tumor cells. 955 19

Currently, there is no effective treatment for pancreatic cancer and prodrug-activating gene therapy with the herpes simplex virus thymidine kinase gene (HSV-tk) in combination with ganciclovir (GCV) has been suggested as a candidate approach against this disease. In the present study, we have evaluated the efficacy of the HSV-tk/GCV treatment in a panel of pancreatic tumor cells (NP-9, NP-18, NP-31) and the potentiation of the cytotoxic effect in combination with the overexpression of the connexin 26 gene (Cx26). Pancreatic cells transduced with a retrovirus containing the HSV-tk gene showed different sensitivities to GCV that seemed to be independent of HSV-tk expression levels. The extent of the bystander effect also varied among the pancreatic tumor cells and correlated with the level of gap junction intercellular communication (GJIC). Transduction of the pancreatic tumor cells with a retrovirus carrying the connexin 26 gene resulted in high levels of connexin 26 expression and in an increase in the GJIC that correlated to an extent in the bystander effect in both NP-9Cx26 and NP-18Cx26 cells. Neither an increment in GJIC nor an increase in the bystander killing was detected in NP-31Cx26. The bystander effect in NP-18 Cx26 cells was also prevented by the long term inhibitor of GJIC, 18-alpha-glycyrrhetinic acid (AGA). Together, these results demonstrate that pancreatic tumor cells are highly different as regards the susceptibility to HSV-tk/GCV treatment. Moreover, they indicate that overexpression of the Cx26 gene does not always correspond to an increase in GJIC although they clearly suggest the role of GJIC in mediating the bystander effect.
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PMID:Retrovirus-mediated transfer of the herpes simplex virus thymidine kinase and connexin26 genes in pancreatic cells results in variable efficiency on the bystander killing: implications for gene therapy. 1166 82

Gap junctional intercellular communication (GJIC) has been shown to be involved in the bystander effect through herpes simplex virus thymidine kinase/ganciclovir (HSV-tk/GCV) gene therapy. In this study, we examined the expression of connexins, the components of gap junction, and the degree of GJIC in esophageal cancer cell lines and compared the bystander effect in cells with different capacities of GJIC. We found loss in connexin 26 expression and reduced connexin 43 in esophageal cancer. GJIC capacity varied among cell lines and was dependent on the connexin 43 expression in the cell-cell contact areas. In mixing assay, the extent of the bystander effect was tightly correlated with the degree of GJIC capacity. The effects of retinoic acid and cAMP on the bystander effect were also investigated. Treatment with retinoic acid, but not with cAMP, was associated with augmented bystander killing by increase in GJIC in some esophageal cancer cell lines. Our results indicated that the degree of GJIC was predictive to identify a tumor as suitable for gene therapy with the HSV-tk/GCV system. Also GJIC chemically-enhanced with retinoic acid might be useful to improve response in suicide gene therapy.
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PMID:Bystander effect in suicide gene therapy is directly proportional to the degree of gap junctional intercellular communication in esophageal cancer. 1453 70