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Newly formed chromosome-like structures in independent mouse P388 sublines with developed in vivo mdr1 gene
N S Demidova1, O B Chernova, E Y Siyanova
1Institute of Chemical Physics, Academy of Sciences of the USSR, Chernogolovka.
Abstract:
Mouse leukemia P388 sublines that acquired the resistance to multiple drugs as a result of treatment in vivo with anthracyclines (rubomycin, ruboxyl) and/or vincristine were studied. The mdr gene amplification was found in all tested cell lines: in four of five sublines all three members of the mdr gene family showed increased copy numbers, and in one cell line, developed after treatment with ruboxyl, mdr1a and mdr1b genes were amplified to the same degree, whereas the mdr2 gene was not amplified at all. The levels of amplification of mdr genes varied in different cell lines from 30-fold to 50-fold. Unusual cytological manifestations--relatively large newly formed chromosomelike structures, were revealed in four of five long-term independent sublines. Some of these structures did not contained C blocks; the others, in contrast, were enriched by C-heterochromatin. In situ hybridization showed the presence of mdr genes in newly formed bodies. In the majority of cases, the formation of chromosomelike structures was preceded by the appearance of other, smaller size, structures: the so-called "small chromatin bodies" (minichromosomes) and/or homogeneously G-positive small ring chromosomes.
Insights
Multidrug resistance in mouse leukemia involves mdr gene amplification and the formation of unique chromosomelike structures. These structures, containing mdr genes, arise from smaller chromatin bodies and ring chromosomes.
Area of Science:
- Molecular Biology
- Genetics
- Cancer Research
Background:
- Studied mouse leukemia P388 sublines resistant to anthracyclines and vincristine.
- Investigated the genetic basis of multidrug resistance (MDR).
Purpose of the Study:
- To analyze mdr gene amplification in drug-resistant mouse leukemia.
- To identify cytological changes associated with MDR development.
Main Methods:
- In vivo drug treatment of mouse leukemia P388 sublines.
- Analysis of mdr gene copy number using molecular techniques.
- Cytological examination including in situ hybridization.
- Chromosomal banding analysis (C-banding, G-banding).
Main Results:
- All tested cell lines exhibited mdr gene amplification (30-50 fold).
- Four of five sublines showed amplification of all three mdr genes; one amplified mdr1a and mdr1b only.
- Unusual chromosomelike structures containing mdr genes were observed in four sublines.
- These structures originated from smaller chromatin bodies and ring chromosomes.
Conclusions:
- mdr gene amplification is a key mechanism for multidrug resistance in this model.
- Novel chromosomelike structures are associated with MDR and mdr gene amplification.
- The formation of these structures may involve chromosomal instability and rearrangement.