| Human hepatocellular carcinoma (HCC) is one of the most common tumorsworldwide, in which the genetic mechanisms of oncogenesis are stillunclear. To investigate whether the genomic DNA copy number alterationsmay contribute to primary HCC, the cDNA microarray-based comparativegenomic hybridization (CGH) analysis was here performed in 41 primary HCCinfected by hepatitis B virus and 12 HCC cell lines. The resulting datashowed that, on average, 7.25% of genome-wide DNA copy numbers wassignificantly altered in those samples (4.61±2.49% gained and 2.64±1.78% lost). Gains involving 1q, 6p, 8q; and 9p were frequently observedin these cases; and whilst, losses involving 1p, 16q and 19p occurred inmost patients. To address the correlation between the alteration ofgenomic DNA copy numbers and transcriptional expression, the same cDNAmicroarray was further applied in 20 HCC specimens and all available celllines to figure out the gene expression profiles of those samples.Interestingly, the genomic DNA copy number alterations of most genesappeared not to be in generally parallel with the correspondingtranscriptional expression. However, the transcriptional deregulation ofa few genes, such as osteopontin (SPP1), transgelin 2 (TAGLN2) and PEG10,could be ascribed partially to their genomic aberrations, although themany alternative mechanisms could be involved in the deregulation of thesegenes. In general, this work would provide new insights into the geneticmechanisms in hepatocarcinogenesis associated with hepatitis B virusthrough the comprehensive survey on correlation between genomic DNA copynumber alterations and transcriptional expression.Dysregulation of a genomic imprinting gene can contribute to carcinogenesis.Here, delta-like 1 homolog (Drosophila) (DLK1), a paternally expressed gene, wasfound to be significantly up-regulated in 60 (73.2%) of a total of 82 hepatocellularcarcinoma (HCC) specimens using reverse transcription-PCR. In addition,immunohistochemistry staining was performed in another 88 HCC specimens, ofwhich 50/88 (56.8%) cancerous tissues were considered as positive. The expression ofDLK1 was obviously induced in HCC cells, Bel-7402 and MHCC-H, by ademethylation agent, 5-aza-2'-deoxycytidine (DAC). Furthermore, both demethylation of the DLK1 promoter (-565～-362) and hypermethylation of the imprinting controldomain in the region upstream of matemally expressed gene 3 (MEG3) wereidentified in a few HCC specimens. This implies that deregulation of genomic DNAmethylation of the imprinted domain could be attributed to the up-regulation of DLK1in HCC, although the undoubtedly complex mechanisms involved in the epigeneticevent should be further investigated in HCC. Surprisingly, the expression of DLK1 inHCC was confirmed to be monoallelic-specific, not bi-allelic, in three HCCspecimens with a single nucleotide polymorphism as at T852C (rs2295660).Importantly, the exogenous DLK1 can significantly promote the cell proliferation ofSMMC-7721 cells, a HCC cell line, whereas the suppression of endogenetic DLK1through RNA interference can markedly inhibit cell growth, colony formation andtumorigenicity of HepG2, Hep3B and HUH-7 cells. These data suggest that DLK1 asan imprinted gene could be significantly up-regulated in HCC due to certainepigenetic events and contribute to the oncogenesis of this tumor.
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