Aim: To investigate the expression of DNA repair genes and the impact of the breast cancer 1, early onset (BRCA1) protein on chemoresistance of hepatocellular carcinoma (HCC).
Methods: Microarray gene expression datasets were analyzed using the gene set enrichment analysis method. BRCA1 protein was tested by Western blotting. Response of HCC cells to interstrand cross-links was investigated by cell viability assay following exposure to mitomycin C, cisplatin, and melphalan. Effects of BRCA1 ectopic expression were studied in HepG2 cells with BRCA1-expression plasmids. Effects of BRCA1 downregulation were studied in SNU449 cells with BRCA1-specific siRNAs. Response of transfected SNU449 cells to mitomycin C was analyzed by cell viability tests and cell cycle analysis using flow cytometry.
Results: Expression of Fanconi anemia and double-stranded DNA break repair genes was significantly upregulated in HCC tumors. This upregulation displayed a gradual amplification during tumor progression. BRCA1 and BRCA2 genes were among consistently upregulated genes. Epithelial-like HCC cells had low BRCA1 expression and low chemoresistance, whereas mesenchymal-like HCC cells had high BRCA1 expression and increased chemoresistance. Ectopic expression of BRCA1 increased the chemoresistance of epithelial-like HepG2 cells. Conversely, BRCA1 knockdown chemosensitized mesenchymal-like SNU449 cells. Chemosensitization of SNU449 cells was due to cell cycle arrest at 4N stage.
Conclusion: Increased expression of Fanconi anemia and double-stranded DNA repair genes such as BRCA1 is a novel mechanism of HCC chemoresistance. However, functional inactivation of BRCA1 expression is sufficient to reverse such chemoresistance.
Keywords: BRCA1; DSB DNA repair; Fanconi anemia; chemosensitization; hepatocellular cancer; interstrand cross-linker drugs.
© 2016 The Japan Society of Hepatology.