| Objectives: DNA polymerase beta plays an important role in repair of damaged DNA, especially in base excision repair (BER). DNA polymerase beta expresses at a constant low level throughout the cell cycle. Overexpression of DNA polymerase beta can compete with other DNA polymerases during replication of duplex DNA in vitro, when this DNA polymerase beta is added into human cell extracts. Since DNA polymerase beta posses the lowest repair- fidelity and error-prone during replication, overexpression of DNA polymerase beta found in some human tumors could confer mutagenic tolerance phenotype toward DNA cross-linking anticancer drugs, and result in increased spontaneous mutagenesis and mutator phenotype. Our study showed that the DNA polymerase beta gene expression in both human esophageal cancer tissues and the adjacent cancer tissues was higher than that of the "normal" tissues, suggesting that overexpression of DNA polymerase beta in adjacent cancer tissue may be an early event in carcinogenesis and may be considered as a functional mutation. So far there has been no report about its alternation during malignant cell differentiation. In this study the 8-Br-cAMP and quercetin were used as differentiation drugs, and PCNA, VEGF, EGFR and c-myc as a bio-marker for malignancy, to observe the express alternation of DNA polymerase beta, wtp53, involved in the regulation of BER and XRCC1 which forms a heterodimer with DNA polymerase beta in BER.Methods: The cultured Eca-109 cells were divided into 3 groups: (1) cocultured with 8-Br-cAMP (Br) group; (2) cocultured with quercetin (Q) group; (3) cultured with no any drug (C) group. Each group cells was cultured 48h simultaneously. The biotin-labeled cDNA probes, including DNA polymerase beta, EGFR, wtp53 and c-myc were prepared. The insitu hybridization technique and RNA dot blot array were carried out in 3 groups respectively. The immunocytochemistry and immuno-dot blot array for DNA polymerase beta, XRCC1, PCNA and VEGF were performed. Results: The voilin signals detected by Bio-labeled pol 3 cDNA probe were located in the cytoplasm of Eca-109 cells. And the signals in C group cells were stronger than those in Br or Q group cells(P<0. 05). While the Dig-labeled wtp53 probe signals appeared orange-yellow in color were also located in the cytoplasm of Eca-109 eel Is. And the yellow-colored signals were in C group weaker than those in Br and Q group cells(P<0. 05). The gene expressions of DNA polymerase beta, EGFR and c-myc which detected by RNA dot blot array in Br group were 5 folds, 6.5 folds and 2.5 folds down-regulated respectively, and the expression of wtp53 was 2.5 folds up-regulated; In Q group the gene expressions of DNA polymerase beta, EGFR and c-myc detected by RNA dot blot array were 6.5 folds, 7 folds and 2.2 folds down-regulated respectively, and the wtp53 was 2.5 folds up. The expressions of DNA polymerase beta and XRCC1 detected by immunochemistry were appeared in brown-yellow and both located in Nucleolus. The signals detected by immunochemistry in C group cells were stronger than those in Br or Q group cells (P<0. 05). The DNA polymerase beta-IR and XRCC1-IR, PCNA-IR and VEGF-IR which detected by immuno-dot blot in Br group were 4.5 folds, 4.5 folds, 5 folds and 4.5 folds down-regulated respectively; And those in Q group were were 4.0 folds, 4.5 folds, 5.5 folds and 3.5 folds down-regulated respectively. Conclusions:1. Both 8-Br-cAMP and quercetin can down-regulate the expression of DNA polymerase beta and XRCC1 in Eca-109 cells, suggesting that the DNA polymerase beta and XRCC1 in Eca-109 cells are overexpressed.2. The expression of PCNA ,VEGF and c-myc, as malignancy bio-markers, was attenuated, suggesting that both 8-Br-cAMP and quercetin could induce differentiation of Eca-109 cells in a certain extent.3. The overexpression of DNA polymerase beta and XRCC1 in Eca-109 cells could be down-regulated by both 8-Br-cAMP and quercetin, suggesting that the expression of DNA polymerase beta and XRCC1 m...
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