Department of Biomedical Sciences, University of Foggia, Foggia, Italy.
Free Radic Biol Med. 2012 Mar 1;52(5):916-27. doi: 10.1016/j.freeradbiomed.2011.12.018. Epub 2012 Jan 2.
Gap junctions play a central role in coordinating intercellular signal-transduction pathways to control tissue homeostasis. Deregulation of gap junctional intercellular communication is a common phenotype of cancer cells and supports its involvement in the carcinogenesis process. Many carcinogens, like environmental heavy-metal chemical pollutants, are known to activate various signal transduction mechanisms and modulate GJIC. They act as tumor promoters on preexisting "initiated" cells, rather than as genotoxic initiators, albeit their mode of action is often unknown. In this study we investigated the effect of Hg(II) (HgCl(2)) on GJIC in cultured human keratinocytes. It is shown that subcytotoxic concentrations of HgCl(2) as low as 10 nM cause inhibition of the GJIC, assessed by dye transfer assay, despite enhanced expression of connexins. In addition, HgCl(2)-treated keratinocytes exhibited a decrease of free thiols and accumulation of mitochondria-derived reactive oxygen species, albeit no effect on the respiratory chain activity was observed. Treatment of HgCl(2)-exposed keratinocytes with the PKC inhibitor calphostin C and with all-trans retinoic acid resulted in rescue of the mitochondrial ROS overproduction and full recovery of the GJIC. Similar results were obtained with the PKA activator db-cAMP. Overall, the presented results support a cross-talk between the altered intracellular redox tone and PKA- and PKC-mediated signaling in HgCl(2)-challenged keratinocytes. These events, although not cytotoxic, lead to inhibition of GJIC and possibly to carcinogenic priming.
间隙连接在协调细胞间信号转导途径以控制组织稳态方面发挥着核心作用。间隙连接细胞间通讯的失调是癌细胞的常见表型，并支持其参与致癌过程。许多致癌物质，如环境重金属化学污染物，已知可激活各种信号转导机制并调节 GJIC。它们作为肿瘤促进剂作用于预先存在的“起始”细胞，而不是作为遗传毒性起始剂，尽管其作用方式通常未知。在这项研究中，我们研究了 Hg(II)（HgCl2）对培养的人角质形成细胞中 GJIC 的影响。结果表明，亚细胞毒性浓度的 HgCl2（低至 10 nM）会抑制染料转移测定评估的 GJIC，尽管连接蛋白的表达增强。此外，HgCl2 处理的角质形成细胞表现出游离巯基减少和线粒体来源的活性氧物质积累，尽管未观察到对呼吸链活性的影响。用蛋白激酶 C 抑制剂 calphostin C 和全反式视黄酸处理暴露于 HgCl2 的角质形成细胞可挽救线粒体 ROS 的过度产生，并完全恢复 GJIC。用蛋白激酶 A 激活剂 db-cAMP 也得到了类似的结果。总体而言，所呈现的结果支持细胞内氧化还原调谐改变与 PKA 和 PKC 介导的信号转导之间的串扰在 HgCl2 挑战的角质形成细胞中。这些事件虽然没有细胞毒性，但会导致 GJIC 抑制，并可能导致致癌启动。
