Genetic changes in mitochondrial DNA (mtDNA) have been hypothesized more widely to play important roles in senescence, autoimmune disease and malignancy because of a paucity of introns and limited repair mechanisms. Malfunction of mismatch repair genes produces genome instability which plays an important role in the development of human cancers. The mtDNA markers for mitochondrial genome instability (mtGI) were point mutations, insertions, deletions and length changes in homopolymeric nucleotide tracts. We investigated the mtGI in AML cells and its effect to alteration in mtDNA copy number. Forty-eight matched AML bone marrow and buccal mucosa samples, and blood samples from 57 control subjects were collected after receiving Institutional Review Board approval and informed consent. We directly sequenced the control region, the tRNA leucine 1 gene plus a part of NADH dehydrogenase (ND)1 and cytochrome b (CYTB) of mtDNA. In an attempt to investigate mtGI, we carried out a qualitative and quantitative profiling mtDNA length heteroplasmies of six mtGIs (np 303–315 poly C, np 16184–16193 poly C, np 514–511 CA repeats, np 3566–3572 poly C, np 12385–12391 poly C and np 12418–12426 poly A) using a size-based PCR product separation by capillary electrophoresis (ABI Prism Genotyper version 3.1). Length heteroplasmy was further confirmed by cloning and sequencing. Quantitative analysis of mtDNA molecules was performed using the QuantiTect SYBR Green PCR kit (Qiagen). In the current study, we detected a large number of polymorphisms as well as new mtDNA variants. A total of 606 mtDNA sequence variants were identified. Among these, 15 mtDNA variants were identified as novel mutations that were absent from corresponding buccal mucosa, control subjects and established mtDNA polymorphism databases. In the control region, we found two types of mtDNA alterations - base substitutions and small deletions/insertions as well as the length heteroplasmies in the np 303 to 315 poly-C, np 16184 to 16193 poly-C and 514–515 CA repeats. Seven patients (15%) had leukemia cell-specific mtDNA substitution mutations in the ND1 and CYTB genes. Somatic mtDNA control region mutations found in this study preferentially altered known mtDNA regulatory elements. AML cells had about a two-fold decrease in mtDNA copy number compared with the results from control subjects (63 x 106 molecules/ul ± 23 x 106 vs 122 x 106 molecules/ul ± 73 x 106). Our results are consistent with a recent observation that carcinogenesis in the liver, kidney and lung involves a decrease of the cellular mitochondrial content and decreased mtDNA copy number (

Mutat Res 2004;547:71–78
). In conclusion, mtGI including point mutations, length changes (insertions or deletions) in homopolymeric tracts commonly occurred in AML cells and reduction in mtDNA copy number may result from either mtDNA control region mutations or impairment of mitochondrial biogenesis. These findings suggest that biogenesis of mitochondria is repressed in the leukemogenesis process of the human hematopoietic tissue.

Topics:
genomic instability, mitochondria, dna, mitochondrial, poly c, molecule, cancer, polymerase chain reaction, autoimmune diseases, carcinogenesis, cloning

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2005, The American Society of Hematology
2005
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