Nuclear and mitochondrial DNA microsatellite instability in Chinese hepatocellular carcinoma

Mitochondria in cancer: in the aspects of tumorigenesis and targeted therapy

Mitochondria play pivotal roles in most eukaryotic cells, ranging from energy production to regulation of apoptosis. As sites of cellular respiration, mitochondria experience accumulation of reactive oxygen species (ROS) due to damage in electron transport chain carriers. Mutations in mitochondrial DNA (mtDNA) as well as nuclear DNA are reported in various cancers. Mitochondria have a dual role in cancer: the development of tumors due to mutations in mitochondrial genome and the generation of ROS. Impairment in the mitochondria-regulated apoptosis pathway accelerates tumorigenesis. Numerous strategies targeting mitochondria have been developed to induce the mitochondrial (i.e. intrinsic) apoptosis pathway in cancer cells. This review elaborates the roles of mitochondria in cancer with respect to mutations and apoptosis and discusses mitochondria-targeting strategies as cancer therapies to enhance the killing of cancer cells.

Novel DNA mismatch-repair activity involving YB-1 in human mitochondria

Maintenance of the mitochondrial genome (mtDNA) is essential for proper cellular function. The accumulation of damage and mutations in the mtDNA leads to diseases, cancer, and aging. Mammalian mitochondria have proficient base excision repair, but the existence of other DNA repair pathways is still unclear. Deficiencies in DNA mismatch repair (MMR), which corrects base mismatches and small loops, are associated with DNA microsatellite instability, accumulation of mutations, and cancer. MMR proteins have been identified in yeast and coral mitochondria; however, MMR proteins and function have not yet been detected in human mitochondria. Here we show that human mitochondria have a robust mismatch-repair activity, which is distinct from nuclear MMR. Key nuclear MMR factors were not detected in mitochondria, and similar mismatch-binding activity was observed in mitochondrial extracts from cells lacking MSH2, suggesting distinctive pathways for nuclear and mitochondrial MMR. We identified the repair factor YB-1 as a key candidate for a mitochondrial mismatch-binding protein. This protein localizes to mitochondria in human cells, and contributes significantly to the mismatch-binding and mismatch-repair activity detected in HeLa mitochondrial extracts, which are significantly decreased when the intracellular levels of YB-1 are diminished. Moreover, YB-1 depletion in cells increases mitochondrial DNA mutagenesis. Our results show that human mitochondria contain a functional MMR repair pathway in which YB-1 participates, likely in the mismatch-binding and recognition steps.

Nuclear and mitochondrial DNA microsatellite instability in gastrointestinal stromal tumors

OBJECTIVE

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the digestive tract. Nuclear (nMSI) and mitochondrial microsatellite instability (mtMSI) play important roles in tumorigenesis in various organs. The aim of this study was to evaluate the role of nMSI and mtMSI in GISTs.

METHODS

Samples from 74 mesenchymal tumors were collected. nMSI and mtMSI were examined by microsatellite assay at BAT26 and D310 mononucleotide repeats in mtDNA, respectively. We compared nMSI, mtMSI and clinicopathologic features, including patient age and sex, tumor location, tumor size, presence of tumor ulceration and presence of distant metastasis, for 51 GISTs for which these data were available.

RESULTS

nMSI and mtMSI were detected in 3 (5%) and 10 (16%) of the 62 GISTs, respectively. There was no significant relationship between nMSI, mtMSI and clinicopathologic features.

CONCLUSION

These results suggest that mtMSI may play a role, but that nMSI may play little role in the development of GISTs.

Alterations of p53, Bcl-2, and hMSH2 protein expression in the cirrhotic, macroregenerative, dysplastic nodules and hepatocellular carcinomas in Upper Egypt

BACKGROUND

Hepatocarcinogenesis involves alterations in p53, Bcl-2 and human Mut S homologue-2 (hMSH2) genes. In Upper Egypt, the clinicopathologic and genetic changes during hepatocarcinogensis (cirrhotic nodules (CN); macroregenerative nodules (MRN) and dysplastic nodules (DN) are unknown.

METHODS

To examine these issues, 48 hepatic resection specimens entailing 25 CN, 16 MRN, 23 DN and 48 hepatocellular carcinoma (HCC) were immunohistochemically evaluated for p53, Bcl-2 and hMSH2 protein expression.

RESULTS

HCC was common in males than in females (2.6:1, P<0.05) and with hepatitis C virus than hepatitis B virus infection (77.1% vs. 18.7%, P=0.001). p53 expression was found in DN (3/23) and HCC (12/48). Its average weighted scores were high in DN/HCC as compared with CN (1.60+/-0.40 and 7.20+/-1.20, P=0.0001). Bcl-2 expression was seen in CN, MRN, DN and HCC (7/48). Its average weighted scores were high in DN (7.60+/-1.60), HCC (6.86+/-0.85) as compared with CN (6.14+/-0.42) and MRN (6.50+/-0.50, P=0.22). hMSH2 average weighted scores were reduced in HCC (7.94+/-1.06) as compared with CN (8.47+/-0.52), MRN (8.00+/-1.00) and DN (8.20+/-0.80, P>0.05).

CONCLUSION

In Upper Egypt: (1) HCC had similar clinicopathologic features to those in the high-risk regions, and (2) alterations of the p53, Bcl-2 and hMSH2 proteins occur during hepatocarcinogensis.