Manning F C, Xu J, Patierno S R
Department of Pharmacology, George Washington University Medical Center, Washington, District of Columbia, 20037.
Mol Carcinog. 1992;6(4):270-9. doi: 10.1002/mc.2940060409.
Hexavalent chromium compounds are carcinogenic to humans, are potent inducers of tumors in experimental animals, and can neoplastically transform cells in culture. In this study, the effects of sodium chromate on the expression of the 78-kDa glucose-regulated protein (GRP78) gene and on general transcription were investigated with respect to the DNA damage induced by this agent. DNA single-strand breaks, DNA-protein cross-links, and chromium-DNA adducts were present in CHO cells immediately after 2 h of treatment with sodium chromate. Subsequently, these types of damage were repaired at different rates. Single-strand breaks were essentially repaired after 8 h. By 24 h posttreatment, no cross-links remained in cells exposed to 30 or 150 microM chromate, although cells treated with the 300-microM concentration still contained cross-links at that time. DNA-chromium adducts remained unrepaired for at least 32 h. The moderate constitutive level of GRP78 mRNA was not affected by chromate. Chromate did, however, suppress induction of this gene by tunicamycin in a concentration-and time-dependent manner. Thirty micromolar sodium chromate (96% survival), which caused the least DNA damage, had no effect on GRP78 induction, general RNA synthesis, or mRNA synthesis. Induction of GRP78 was suppressed immediately and 12 h after treatment with 150 microM chromate (54% survival), although there was a partial recovery of induction at 24 h after treatment, which correlated with the repair of DNA-protein cross-links. In contrast, both total cytoplasmic RNA and mRNA synthesis were suppressed by approximately 60-75% for at least 32 h by 150 microM chromate. At the 300-microM concentration (8% survival), where DNA-protein cross-links persisted beyond 24 h, GRP78 induction was totally suppressed for at least 24 h, while total RNA and mRNA synthesis were suppressed by 80-90% for at least 32 h. Overall, the effects of chromate on GRP78 induction correlated most closely with the presence of DNA-protein cross-links, but suppression of total RNA and mRNA synthesis correlated with the presence of DNA-chromium adducts. These results indicate that chromate exerts differential effects on the induction of the GRP78 gene and on general transcription.
六价铬化合物对人类具有致癌性，是实验动物肿瘤的强效诱导剂，并且能够在培养物中使细胞发生肿瘤性转化。在本研究中，针对铬酸钠诱导的DNA损伤，研究了铬酸钠对78-kDa葡萄糖调节蛋白（GRP78）基因表达和一般转录的影响。在用铬酸钠处理2小时后，CHO细胞中立即出现了DNA单链断裂、DNA-蛋白质交联和铬-DNA加合物。随后，这些类型的损伤以不同的速率得到修复。单链断裂在8小时后基本得到修复。在处理后24小时，暴露于30或150μM铬酸盐的细胞中不再存在交联，尽管用300μM浓度处理的细胞在那时仍含有交联。DNA-铬加合物至少32小时未得到修复。GRP78 mRNA的适度组成水平不受铬酸盐的影响。然而，铬酸盐确实以浓度和时间依赖性方式抑制衣霉素对该基因的诱导。引起最少DNA损伤的30μM铬酸钠（存活率96%）对GRP78诱导、总RNA合成或mRNA合成没有影响。在用150μM铬酸盐处理后立即和12小时，GRP78的诱导受到抑制（存活率54%），尽管在处理后24小时诱导有部分恢复，这与DNA-蛋白质交联的修复相关。相比之下，150μM铬酸盐使总细胞质RNA和mRNA合成至少32小时被抑制约60-75%。在300μM浓度（存活率8%）下，DNA-蛋白质交联持续超过24小时，GRP78诱导至少24小时被完全抑制，而总RNA和mRNA合成至少32小时被抑制80-90%。总体而言，铬酸盐对GRP78诱导的影响与DNA-蛋白质交联的存在最密切相关，但总RNA和mRNA合成的抑制与DNA-铬加合物的存在相关。这些结果表明，铬酸盐对GRP78基因的诱导和一般转录具有不同的影响。
