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Toxicol Sci. 2019 Mar 1;168(1):137-148. doi: 10.1093/toxsci/kfy280.

Exposure to 1,2-Dichloropropane Upregulates the Expression of Activation-Induced Cytidine Deaminase (AID) in Human Cholangiocytes Co-Cultured With Macrophages.

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Department of Occupational and Environmental Health, Faculty of Pharmaceutical Sciences, Tokyo University of Science, Noda 278-8510, Japan.
Evolutionary Medicine, Shiga Medical Center Research Institute, Moriyama 524-8524, Japan.
Aichi Cancer Center, Nagoya 464-8681, Japan.
Department of Environmental and Preventive Medicine, Jichi Medical University School of Medicine, Shimotsuke 329-0498, Japan.
Osaka Occupational Health Service Centre, Japan Industrial Safety and Health Association, Osaka 550-0001, Japan.


1,2-dichloropropane (1,2-DCP) was reclassified recently by IARC as a Group 1 carcinogen based on epidemiological studies on an outbreak of cholangiocarcinoma in offset-printing workers exposed to 1,2-DCP in Japan. However, the underlying mechanism of 1,2-DCP-induced cholangiocarcinoma remains obscure. A previous whole-genome mutation analysis of cholangiocarcinoma of 4 cases exposed to 1,2-DCP suggested the involvement of activation-induced cytidine deaminase (AID), based on specific signatures of mutation patterns. The objective of the present study is to determine whether exposure to 1,2-DCP induces expression of AID in human cholangiocytes. Human MMNK-1 cholangiocytes, differentiated THP-1 macrophages, and co-cultures of MMNK-1/THP-1 cells were exposed to 1,2-DCP at different concentrations and time intervals. The mRNA expression levels of AID and related genes were quantified by real-time PCR. Protein expression was measured by immunostaining. Alkaline Comet assay was performed to examine DNA damage. The results showed that 1,2-DCP alone did not change AID expression in MMNK-1 cholangiocytes. 1,2-DCP significantly increased pro-inflammatory cytokine TNF-α expression in THP-1 macrophages. TNF-α treatment upregulated expression of AID, NF-κB, and IκB in MMNK-1 cholangiocytes. SN50, a NF-κB inhibitor, significantly downregulated TNF-α-induced AID expression, suggesting the involvement of NF-κB pathway in TNF-α-induced AID expression. Exposure to 1,2-DCP significantly increased AID expression in MMNK-1 cholangiocytes co-cultured with THP-1 macrophages. Comet assay showed that 1,2-DCP-induced DNA damage in MMNK-1 cholangiocytes, as indicated by increased tail DNA% and tail moment, was enhanced when co-cultured with macrophages. The results suggest that inflammatory response of macrophages and consequent aberrant AID expression or DNA damage in the cholangiocytes underlie the mechanism of 1,2-DCP-induced cholangiocarcinoma in humans.


1,2-dichloropropane; AID; cholangiocarcinoma; co-culture; macrophage


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