Double minutes arise from circular extrachromosomal DNA intermediates which integrate into chromosomal sites in human HL-60 leukemia cells.

Abstract

Amplification of oncogenes has been found to be an important prognostic factor in behavior of patients' malignancies. In this study we have used new gel electrophoresis techniques to follow the location of amplified c-myc oncogene sequences in HL-60 promyelocytic leukemia cells. In passages 46-62 of the cells, the cells contain amplified c-myc sequences on submicroscopic circular extrachromosomal DNA (episomes). With increased passages in culture (passages 63-72) the cells lose the episome c-myc sequences with a shift of those sequences to double minutes. With additional passage in culture, the c-myc shifts from the double minutes to a chromosomal site der(5)t(5; 17Xqll.2;q?11.2). Concomitant with the shift of the c-myc sequences into the chromosomal compartment is a phenotypic change of a shortened cell-doubling time. These studies provide the first molecular evidence of a progression from a submicroscopic location for amplified oncogene sequences to a chromosomal location for the amplified sequences. This molecularly documented model can now be used to test various strategies to prevent incorporation of extrachromosomally located oncogene sequences into chromosomal sites. Prevention of integration of the oncogene sequences into chromosomal sites could modulate progression of patients'

CYP2D6: novel genomic structures and alleles

“…This involves the excision and possible reinsertion of an episomal DNA intermediate analogous to the double minute model of extra-chromosomal and genomic gene amplification [22–24]. These episomes have been observed in developmental stages of insect [25–27], frog [28,29] and mouse cell lines [30], and in mammalian cancer cells [31–35]. Carroll et al [22] showed that mitotic gene amplification of the carbamoyl-phosphate synthetase/aspartate transcarbamoylase/dihydroorotase gene complex was mediated by episomal DNA circles in a Chinese Hamster Ovary cell line grown in the presence of the carbamoyl-phosphate synthetase/aspartate transcarbamoylase/dihydroorotase inhibitor N -phosphonacetyl- l -aspartate.…”

“…The episomes underwent amplification of their sequences to form larger episomes known as double minutes; these episomes were observed to reintegrate into the chromosome thereby amplifying the gene involved. Similarly, Von Hoff et al [31] studied the location of amplified c- myc oncogene sequences in HL-60 promyelocytic leukemia cells through several cell passages and were able to follow the presence of episomal DNA through a double minute stage before they integrated into a chromosomal site as an amplified sequence. Amplification of drug resistance genes through this mechanism has been associated with drug resistance of patients’ tumors to antineoplastic agent [36–39].…”

A Mechanism of Gene Amplification Driven by Small DNA Fragments

“…DMs segregate randomly during mitosis and are therefore very unstable, except when they provide a selective advantage to the cells by carrying extra copies of oncogenes or drug resistance genes [17].…”

Cellular exposure to muscle relaxants and propofol could lead to genomic instability in vitro

“…There were 5/20 metaphases with 78, 80, 80, 80, and 80 chromosomes all displaying endoreduplication. New aberrations were present, including double minute (Dmin) chromosome, 6/25 images, representing amplified gene specific DNA that vary in size and number, and were visualized by DAPI counterstaining[14],[15]. Extrachromosomal elements (ECE) were observed in 7/25 metaphases, which represent amplified chromosomal genes containing DNA visualized by both SKY and DAPI.…”