Activation of Galectin-1 gene in human hepatocellular carcinoma involves methylation-sensitive complex formations at the transcriptional upstream and downstream elements

The expression of Galectin-1 (Gal-1) mRNA was activated in primary hepatocellular carcinomas (HCCs) compared to matched non-tumorous liver tissues. To elucidate the mechanism of Gal-1 activation in HCC cells, DNA methylation encompassing the transcriptional start site (−165/+151) was examined. Among 12 CpG dinucleotides on both DNA strands, those at positions −116, −109, −52, −41, −36, +35 and +43 were preferentially methylated in non-tumorous liver tissue, while hypomethylated in the matched HCC tissue. Transient transfection of a series of deleted GAL-1 promoters revealed that both an upstream (−57/−31) and a downstream (+10/+57) elements accounted for efficient promoter activity. Electrophoretic mobility shift assay of the upstream element (−63/−30) using nuclear extracts from three HCC cell lines (HLF, HuH7 and HepG2) and normal liver cells revealed at least two complexes (α and (β) interacted with the upstream element in all of the nuclear extracts. Competition experiments revealed that the complex β preferentially attached to the upstream element harboring unmethylated CpGs. On the other hand, at least three complexes (I, II and III) interacted with the downstream element in all of the nuclear extracts. Competition experiments revealed that complex I specifically attached to the downstream element harboring unmethylated CpG at +35. Furthermore, a DNase I protection assay revealed that a methylation-associated conformational alteration occurred near the CpG site at +35 in HLF cells. Thus, the specific interaction of methylation-sensitive factors to the upstream and downstream elements may be essential for the activation of the Gal-1 gene in HCC cells.