Essential Trace Elements and Promoter DNA Methylation of Mineral Transporters Genes: Unravelling Novel Epigenetic Mechanisms in Human Hepatocarcinoma.

Objectives: Hepatocellular carcinoma (HCC) is the second most common cause of death from cancer, worldwide. The etiology and factors involved in its development remain, however, largely unknown. A marked decrease in mineral trace elements is related to the genesis of several diseases including cancer but their role in carcinogenesis, including that of HCC, is yet not fully defined. We investigated an ample set of trace elements amounts in serum, HCC tissues and homologous non-neoplastic liver tissues (N) from HCC patients. Gene expression and promoter DNA methylation of major element-transport proteins were also determined. We aimed at studying the possible involvement of DNA methylation in trace element-linked proteins dysregulation and eventually in HCC progression. Methods: Cu, Zn and Se, Cd, Co were measured in tissues and serum of HCC patients undergoing hepatic curative surgery by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analysis. Gene expression profiles and DNA methylation at promoter of zinc-transporter (ZIP8, ZIP14) and metallothioneins (MT1G, MT1H, MT2) genes were determined by a microarray genome-wide approach. Results: Serum levels of Cu, Zn, Se did not show differences and were within the reference limits among all the patients. Tissue levels of Zn, Cd, Se and Co were, instead, markedly decreased in HCC as compared to normal tissues; Cu levels did not differ significantly between HCC and N tissues. Moreover, ZIP8 and ZIP14, MT1G, MT1H, MT2 genes were repressed with a consensual promoter hypermethylation in HCC liver tissues as compared to N tissues. Conclusions: We show the novel finding of a significant reduction of Zn and Cd levels in HCC tissues, together with a gene repression of the metal-transporters ZIP8, ZIP14, MT1, MT2 linked to promoter gene hypermethylation suggesting an early, epigenetic-based dysregulation of Zn and Cd depletion in HCC. These evidences provide new insights into the role of trace elements in HCC carcinogenesis.