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Alu-associated interstitial deletions and chromosomal re-arrangement in 2 human multidrug-resistant cell lines
T Harada1, J Nagayama, K Kohno
1Department of Medical Biochemistry, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
Abstract:
Previous studies have shown that gene re-arrangements play a significant role in tumorigenesis. Gene re-arrangements involving the human multidrug resistance-1 (MDR1) gene have been identified as a mechanism for MDR1 over-expression in human malignant cells. In 2 multidrug-resistant human cancer sublines with high levels of MDR1 and P-glycoprotein (MCF7/TX400 and S48-3s/Adr10), hybrid mRNAs containing sequences from MDR1 and an unrelated gene have previously been identified. To characterize and determine the site of the re-arrangements resulting in generation of hybrid mRNAs, we first constructed a lambda phage library extending over a contiguous genomic region of 100 kb and containing the region upstream of MDR1. In MCF7/TX400 cells, homologous recombination was observed involving an Alu repeat 80 kb upstream of the MDR1 gene, with a 79 bp intra-Alu deletion flanked by chi-like sequences at the re-arrangement junction. By contrast, non-homologous recombination was observed in S48-3s/Adr10 cells with Alu repeats near the junction sequence. While the specific features of the breakpoints appear to be different, Alu repeats might be involved in both gene re-arrangements. The gene re-arrangements at or near the Alu sequence should be regarded as potentially involved in the transcriptional activation of human MDR1.
Insights
Gene re-arrangements near Alu repeats can activate human multidrug resistance-1 (MDR1) gene expression, contributing to multidrug resistance in cancer. These re-arrangements involve both homologous and non-homologous recombination mechanisms.
Area of Science:
- Molecular Biology
- Genetics
- Cancer Research
Background:
- Gene re-arrangements are implicated in cancer development.
- Over-expression of the human multidrug resistance-1 (MDR1) gene contributes to multidrug resistance in cancer cells.
- Hybrid mRNAs involving MDR1 have been observed in multidrug-resistant cancer sublines.
Purpose of the Study:
- To identify and characterize the genomic sites of re-arrangements leading to hybrid MDR1 mRNAs.
- To elucidate the mechanisms underlying MDR1 gene activation in multidrug-resistant cancer cells.
Main Methods:
- Construction of a lambda phage library covering a 100 kb genomic region upstream of the MDR1 gene.
- Analysis of gene re-arrangement breakpoints in two multidrug-resistant human cancer sublines (MCF7/TX400 and S48-3s/Adr10).
Main Results:
- Homologous recombination involving an Alu repeat 80 kb upstream of MDR1 was identified in MCF7/TX400 cells.
- Non-homologous recombination involving Alu repeats near the junction sequence was observed in S48-3s/Adr10 cells.
- Alu repeats appear to be involved in gene re-arrangements in both cell lines, despite differences in recombination type.
Conclusions:
- Gene re-arrangements occurring at or near Alu sequences may play a role in the transcriptional activation of the human MDR1 gene.
- Understanding these re-arrangements is crucial for comprehending multidrug resistance mechanisms in cancer.