ABSTRACT
Cisplatin (CDDP) is a widely used potent chemotherapeutic agent for many malignancies. However, the mechanism of resistance to CDDP remains unclear. To investigate the molecular mechanism, we established a CDDP-resistant cell line (H-1R) from a CDDP-sensitive cell line (H-1) which was derived from moderately differentiated squamous cell carcinoma of the lower gingiva. The 3-(3,4-dimethyl-thiazol-2-yl) 2,5-diphenyltetrazolium bromide (MTT) assay indicated that H-1R had a 10-fold greater resistance to CDDP than H-1. When we compared gene expression levels in the cell lines using an in-house cDNA microarray, which represented 2,201 genes originating from normal oral tissue, primary oral cancer, and oral cancer cell lines, 12 genes showing elevated mRNA expression in H-1R compared with H-1 were identified. Among them, the up-regulated expression of ATP-binding cassette transporter genes (MDR1, MRP1, and MRP2), CD55, and PGK1 and down-regulated expression of Caveolin 1 were further confirmed by semiquantitative reverse transcriptase-polymerase chain reaction (PCR) or real-time PCR. Our results suggest that H-1 and H-1R cell lines could be useful for elucidating the candidate genes responsible for CDDP resistance, including the genes found in this study.
Subject(s)
Antineoplastic Agents/pharmacology , Carcinoma, Squamous Cell/pathology , Cisplatin/pharmacology , Mouth Neoplasms/pathology , Tumor Cells, Cultured , ATP-Binding Cassette Transporters/biosynthesis , ATP-Binding Cassette Transporters/genetics , Drug Resistance, Neoplasm , Gene Expression Profiling , Humans , Male , Oligonucleotide Array Sequence AnalysisABSTRACT
The adenomatous polyposis coli gene (APC gene) originally was identified as a tumor suppressor gene in colon cancer. We reported previously that APC is mutated and/or deleted in primary oral squamous cell carcinoma (OSCC) tissues and suggested that loss of APC function contributes to carcinogenesis in the oral region. In this study, we examined 50 OSCC tissue samples, which had been fixed in 10% buffered formaldehyde solution and embedded in paraffin, and eight cell lines, which were derived from OSCC, to analyze the expression level of the APC gene. Significant down-regulation of APC was detected by immunohistochemistry in 15 (30.0%) of 50 tissue samples and by the reverse transcriptase-polymerase chain reaction in five (62.5%) of eight cell lines. We then investigated the status of APC gene promoter methylation and restoration of the APC gene mRNA. Hypermethylation of the APC promoter CpG island was detected in two of eight (25%) OSCC-derived cell lines, and APC gene mRNA was restored in all OSCC-derived cell lines showing down-regulation of gene expression (n=5) after treatment with 5-aza-2'-deoxycytidine, a DNA demethylating agent. Thus, the contribution of down-regulated APC expression to the development of human OSCC was about 30%, and hypermethylation of the gene promoter CpG island was confirmed to be a significant mechanism of inactivation of the APC gene in oral carcinogenesis.
