High copy number of mitochondrial DNA predicts poor prognosis in patients with advanced stage colon cancer

Mitochondrial DNA copy number and cancer risks: A comprehensive Mendelian randomization analysis

Mitochondrial DNA plays a critical role in the pathophysiology of cancer. However, the associations between mitochondrial DNA copy number (mtDNA-CN) and cancer risk are controversial. Mendelian randomization (MR) analyses were performed using three independent instrumental variables (IVs) to explore potential associations between mtDNA-CN and 20 types of cancer. The three sets of IVs were primarily obtained from participants in the UK Biobank and the Cohorts for Heart and Aging Research in Genomic Epidemiology consortium using different methods. The outcome data of cancers were investigated using summary statistics from the FinnGen cohort. The potential causal associations were evaluated using the MR-Egger regression, weighted median, inverse-variance weighted (IVW), and weighted mode methods. The robustness of IVW estimates was validated using leave-one-out sensitivity analysis. Additionally, a meta-analysis was conducted to pool results from three sets of IVs. The results revealed that genetically predicted mtDNA-CN was not associated with cancer risk (odds ratio = 1.02; 95% confidence interval: 0.95-1.10). Subgroup analyses indicated no causal association between mtDNA-CN and breast, lung, prostate, skin, colorectal, gastric, liver, cervical uteri, esophageal, thyroid, bladder, pancreas, kidney, corpus uteri, ovary, brain, larynx, and anus cancers. It was observed that mtDNA-CN was associated with lip, oral cavity, and testis cancers. However, these results should be interpreted with caution because a small number of patients with lip and oral cavity or testis cancers were included. The comprehensive MR analysis demonstrated that mtDNA-CN is not a suitable biomarker for tumor risk assessment.

Mitochondrial DNA copy number plays opposing roles in T-lymphocyte infiltration of colorectal cancer based on mismatch repair status: new directions for immunotherapy?

BACKGROUND

Researchers have previously reported that mitochondrial DNA copy number (mtDNA-CN) can play different roles in microsatellite instable/mismatch repair-deficient (MSI/dMMR) and microsatellite stable/mismatch repair-proficient (MSS/pMMR) colorectal cancer (CRC). To support malignancy, dMMR CRC relies on glycolysis, while pMMR CRC favors oxidative phosphorylation. However, it is unclear whether mtDNA-CN changes are related to T cell infiltration in CRC.

METHODS

The mtDNA-CN was detected by qRT-PCR in 532 patients, and the expression of CD3 and CD8 in 485 patients was detected by immunohistochemistry. The correlation between mtDNA-CN and the prognosis of CRC patients was further analyzed, and the correlation between mtDNA-CN and T lymphocyte infiltration was also analyzed. Biopsy specimens from the immune checkpoint inhibitors (ICIs) treatment cohort were obtained to verify the correlation between mtDNA-CN and the efficacy of ICIs. The effects of mtDNA-CN and MMR status on gene expression were analyzed by RNA-seq.

RESULTS

Our results show that mtDNA-CN has inverse relationships to CRC prognosis in cases with different MMR statuses, potentially inducing the U-shaped association in CRC. The opposing correlations between mtDNA-CN and T lymphocyte infiltration in cases of dMMR CRC and pMMR CRC further suggest that mtDNA-CN might play an important role in CRC development. More importantly, cases of pMMR CRC with lower mtDNA-CN and of dMMR CRC with higher mtDNA-CN can benefit more dramatically from ICIs. Furthermore, RNA-seq revealed a link between the level of mtDNA-CN and T lymphocyte infiltration in CRC cases with different MMR statuses.

CONCLUSION

Our study found a potential relationship between mtDNA-CN and CRC development that differs by MMR status, potentially providing a rationale for the use of mtDNA-CN as both a predictive biomarker and a therapeutic target for ICIs.

Oncotherapeutic Strategies in Early Onset Colorectal Cancer

Early onset colorectal cancer (EOCRC), defined as colorectal cancers in patients aged less than 50 years, is becoming an increasingly common issue, globally. Since 1994, the incidence of this condition has been rising by 2% annually. Approximately one in five patients under 50 years of age diagnosed with colorectal cancer have an underlying genetic predisposition syndrome. The detection of cancer among the other 80% of patients poses a considerable task, as there is no family history to advocate for commencing early screening in this group. Patients with EOCRC have distinct social, spiritual, fertility, and financial needs from their older counterparts that need to be addressed. This review discusses the risk factors associated with the development of EOCRC and current best practice for the management of this disease.

Mitochondrial DNA Copy Number: Linking Diabetes and Cancer

Recent Advances: Various studies have suggested that mitochondrial DNA copy number (mtDNA-CN), a surrogate biomarker of mitochondrial dysfunction, is an easily quantifiable biomarker for chronic diseases, including diabetes and cancer. However, current knowledge is limited, and the results are controversial. This has been attributed mainly to methodology and study design. Critical Issues: The incidence of diabetes and cancer has increased significantly in recent years. Moreover, type 2 diabetes (T2D) has been shown to be a risk factor for cancer. mtDNA-CN has been associated with both T2D and cancer. However, it is not known whether mtDNA-CN plays any role in the association between T2D and cancer. Significance: In this review, we have discussed mtDNA-CN in diabetes and cancer, and reviewed the literature and methodology used in published studies so far. Based on the literature review, we have speculated how mtDNA-CN may act as a link between diabetes and cancer. Furthermore, we have provided some recommendations for reliable translation of mtDNA-CN as a biomarker. Future Directions: Further research is required to elucidate the role of mtDNA-CN in the association between T2D and cancer. If established, early lifestyle interventions, such as physical activity and diet control that improve mitochondrial function, may help preventing cancer in patients with T2D. Antioxid. Redox Signal. 37, 1168-1190.

Copy Number Alterations as Novel Biomarkers and Therapeutic Targets in Colorectal Cancer

In colorectal cancer, somatic mutations have played an important role as prognostic and predictive biomarkers, with some also functioning as therapeutic targets. Another genetic aberration that has shown significance in colorectal cancer is copy number alterations (CNAs). CNAs occur when a change to the DNA structure propagates gain/amplification or loss/deletion in sections of DNA, which can often lead to changes in protein expression. Multiple techniques have been developed to detect CNAs, including comparative genomic hybridization with microarray, low pass whole genome sequencing, and digital droplet PCR. In this review, we summarize key findings in the literature regarding the role of CNAs in the pathogenesis of colorectal cancer, from adenoma to carcinoma to distant metastasis, and discuss the roles of CNAs as prognostic and predictive biomarkers in colorectal cancer.

Mitochondrial Function Differences between Tumor Tissue of Human Metastatic and Premetastatic CRC

Simple Summary

Metastasis is an important cause of death from colorectal cancer (CRC). Mitochondria, which are important organelles of cells, play a key role in the metastatic transformation of cancer cells. We aimed to evaluate the adaptations associated with mitochondrial function in tumor tissues from advanced stages of human CRC and whether they could ultimately be used as a therapeutic target in metastatic CRC. We have compared the mitochondrial functionality parameters in tumor tissue samples and the normal adjacent tissue of advanced CRC patients with no radio- or chemotherapy treatment before surgery. Notable differences in mitochondrial functionality were detected between the samples of adjacent tissue versus tumor tissue from metastatic CRC patients. These findings suggest a shift in the mitochondrial function profile occurring in tumor tissue once the metastatic stage has been reached. These changes contribute to promote and maintain the metastatic phenotype, with evidence of mitochondrial function impairment in tumor tissue in the metastatic stage samples.

Abstract

Most colorectal cancer (CRC) patients die as a consequence of metastasis. Mitochondrial dysfunction could enhance cancer development and metastatic progression. We aimed to evaluate the adaptations associated with mitochondrial function in tumor tissues from stages III and IV of human CRC and whether they could ultimately be used as a therapeutic target in metastatic colorectal cancer (mCRC). We analyzed the protein levels by Western blotting and the enzymatic activities of proteins involved in mitochondrial function, as well as the amount of mitochondrial DNA (mtDNA), by real-time PCR, analyzing samples of non-tumor adjacent tissue and tumor tissue from stages III and IV CRC patients without radio- or chemotherapy treatment prior to surgery. Our data indicate that the tumor tissue of pre-metastatic stage III CRC exhibited an oxidant metabolic profile very similar to the samples of non-tumor adjacent tissue of both stages. Notable differences in the protein expression levels of ATPase, IDH2, LDHA, and SIRT1, as well as mtDNA amount, were detected between the samples of non-tumor adjacent tissue and tumor tissue from metastatic CRC patients. These findings suggest a shift in the oxidative metabolic profile that takes place in the tumor tissue once the metastatic stage has been reached. Tumor tissue oxidative metabolism contributes to promote and maintain the metastatic phenotype, with evidence of mitochondrial function impairment in stage IV tumor tissue.

Mitochondrial DNA copy number as a prognostic marker is age-dependent in adult glioblastoma

BACKGROUND

Glioblastoma (GBM) is the most common and aggressive form of glioma. GBM frequently displays chromosome (chr) 7 gain, chr 10 loss and/or EGFR amplification (chr7+/chr10-/EGFRamp). Overall survival (OS) is 15 months after treatment. In young adults, IDH1/2 mutations are associated with longer survival. In children, histone H3 mutations portend a dismal prognosis. Novel reliable prognostic markers are needed in GBM. We assessed the prognostic value of mitochondrial DNA (mtDNA) copy number in adult GBM.

METHODS

mtDNA copy number was assessed using real-time quantitative PCR in 232 primary GBM. Methylation of POLG and TFAM genes, involved in mtDNA replication, was assessed by bisulfite-pyrosequencing in 44 and 51 cases, respectively.

RESULTS

Median age at diagnosis was 56.6 years-old and median OS, 13.3 months. 153/232 GBM (66 %) displayed chr7+/chr10-/EGFRamp, 23 (9.9 %) IDH1/2 mutation, 3 (1.3 %) H3 mutation and 53 (22.8 %) no key genetic alterations. GBM were divided into two groups, "Low" (n = 116) and "High" (n = 116), according to the median mtDNA/nuclear DNA ratio (237.7). There was no significant difference in OS between the two groups. By dividing the whole cohort according to the median age at diagnosis, OS was longer in the "High" vs "Low" subgroup (27.3 vs 15 months, P = .0203) in young adult GBM (n = 117) and longer in the "Low" vs "High" subgroup (14.5 vs 10.2 months, P = .0116) in older adult GBM (n = 115). POLG was highly methylated, whereas TFAM remained unmethylated.

CONCLUSION

mtDNA copy number may be a novel prognostic biomarker in GBM, its impact depending on age.

Quantification of mtDNA content in cultured cells by direct droplet digital PCR

Although alterations in cellular mitochondrial DNA (mtDNA) content have been linked to various pathological conditions, the mechanisms that govern mtDNA copy number (mtCN) control remain poorly understood. Moreover, techniques for mtDNA quantification do not allow for direct comparisons of absolute mtCNs between labs. Here we report the development of a direct droplet digital PCR technique for the determination of mtCNs in whole-cell lysates. Using this technique, we demonstrate that cellular mtDNA content can fluctuate in culture by as much as 50% and provide evidence for both cell proliferation-coupled and uncoupled mtDNA replication.

High mitochondrial content is associated with breast cancer aggressiveness

Mitochondria are relevant for cancer initiation and progression. Antibodies against mitochondrially encoded cytochrome c oxidase II (MTCO2), targeting a mitochondria specific epitope, can be used to quantitate the mitochondria content of tumor cells. The present study evaluated the impact of the cellular mitochondrial content on the prognosis of patients with breast cancer using immunohistochemical analysis on 2,197 arrayed breast cancer specimens. Results were compared with histological tumor parameters, patient overall survival, tumor cell proliferation using Ki67 labeling index (Ki67LI) and various other molecular features. Tumor cells exhibited stronger MTCO2 expression than normal breast epithelial cells. MTCO2 immunostaining was largely absent in normal breast epithelium, but was observed in 71.9% of 1,797 analyzable cancer specimens, including 34.6% tumors with weak expression, 22.3% with moderate expression and 15.0% with strong expression. High MTCO2 expression was significantly associated with advanced tumor stage, high Bloom-Richardson-Elston/Nottingham (BRE) grade, nodal metastasis and shorter overall survival (P<0.0001 each). In multivariate analysis, MTCO2 expression did not provide prognostic information independent of BRE grade, pathological tumor and pathological lymph node status. Additionally, significant associations were observed for high MTCO2 expression and various molecular features, including high Ki67LI, amplifications of HER2, MYC, CCND1 and MDM2, deletions of PTEN, 8p21 and 9p, low estrogen receptor expression (P<0.0001 each) and progesterone receptor expression (P<0.0001). The present study demonstrated that high MTCO2 expression was strongly associated with a poor prognosis and unfavorable phenotypical and molecular tumor features in patients with breast cancer. This suggests that the mitochondrial content may have a pivotal role in breast cancer progression.

Mitochondrial transcription factor A plays opposite roles in the initiation and progression of colitis-associated cancer

Background

Mitochondria are key regulators in cell proliferation and apoptosis. Alterations in mitochondrial function are closely associated with inflammation and tumorigenesis. This study aimed to investigate whether mitochondrial transcription factor A (TFAM), a key regulator of mitochondrial DNA transcription and replication, is involved in the initiation and progression of colitis‐associated cancer (CAC).

Methods

TFAM expression was examined in tissue samples of inflammatory bowel diseases (IBD) and CAC by immunohistochemistry. Intestinal epithelial cell (IEC)‐specific TFAM‐knockout mice (TFAM^△IEC) and colorectal cancer (CRC) cells with TFAM knockdown or overexpression were used to evaluate the role of TFAM in colitis and the initiation and progression of CAC. The underlying mechanisms of TFAM were also explored by analyzing mitochondrial respiration function and biogenesis.

Results

The expression of TFAM was downregulated in active IBD and negatively associated with the disease activity. The downregulation of TFAM in IECs was induced by interleukin‐6 in a signal transducer and activator of transcription 3 (STAT3)/miR‐23b‐dependent manner. In addition, TFAM knockout impaired IEC turnover to promote dextran sulfate sodium (DSS)‐induced colitis in mice. Of note, TFAM knockout increased the susceptibility of mice to azoxymethane/DSS‐induced CAC and TFAM overexpression protected mice from intestinal inflammation and colitis‐associated tumorigenesis. By contrast, TFAM expression was upregulated in CAC tissues and contributed to cell growth. Furthermore, it was demonstrated that β‐catenin induced the upregulation of TFAM through c‐Myc in CRC cells. Mechanistically, TFAM promoted the proliferation of both IECs and CRC cells by increasing mitochondrial biogenesis and activity.

Conclusions

TFAM plays a dual role in the initiation and progression of CAC, providing a novel understanding of CAC pathogenesis.

Extrachromosomal Circular DNAs: Origin, formation and emerging function in Cancer

The majority of cellular DNAs in eukaryotes are organized into linear chromosomes. In addition to chromosome DNAs, genes also reside on extrachromosomal elements. The extrachromosomal DNAs are commonly found to be circular, and they are referred to as extrachromosomal circular DNAs (eccDNAs). Recent technological advances have enriched our knowledge of eccDNA biology. There is currently increasing concern about the connection between eccDNA and cancer. Gene amplification on eccDNAs is prevalent in cancer. Moreover, eccDNAs commonly harbor oncogenes or drug resistance genes, hence providing a growth or survival advantage to cancer cells. eccDNAs play an important role in tumor heterogeneity and evolution, facilitating tumor adaptation to challenging circumstances. In addition, eccDNAs have recently been identified as cell-free DNAs in circulating system. The altered level of eccDNAs is observed in cancer patients relative to healthy controls. Particularly, eccDNAs are associated with cancer progression and poor outcomes. Thus, eccDNAs could be useful as novel biomarkers for the diagnosis and prognosis of cancer. In this review, we summarize current knowledge regarding the formation, characteristics and biological importance of eccDNAs, with a focus on the molecular mechanisms associated with their roles in cancer progression. We also discuss their potential applications in the detection and treatment of cancer. A better understanding of the functional role of eccDNAs in cancer would facilitate the comprehensive analysis of molecular mechanisms involved in cancer pathogenesis.

Identification of a prognostic gene signature of colon cancer using integrated bioinformatics analysis

Background

Colon cancer is a worldwide leading cause of cancer-related mortality, and the prognosis of colon cancer is still needed to be improved. This study aimed to construct a prognostic model for predicting the prognosis of colon cancer.

Methods

The gene expression profile data of colon cancer were obtained from the TCGA, GSE44861, and GSE44076 datasets. The WGCNA module genes and common differentially expressed genes (DEGs) were used to screen out the prognosis-associated DEGs, which were used to construct a prognostic model. The performance of the prognostic model was assessed and validated in the TCGA training and microarray validation sets (GSE38832 and GSE17538). At last, the model and prognosis-associated clinical factors were used for the construction of the nomogram.

Results

Five colon cancer-related WGCNA modules (including 1160 genes) and 1153 DEGs between tumor and normal tissues were identified, inclusive of 556 overlapping DEGs. Stepwise Cox regression analyses identified there were 14 prognosis-associated DEGs, of which 12 DEGs were included in the optimized prognostic gene signature. This prognostic model presented a high forecast ability for the prognosis of colon cancer both in the TCGA training dataset and the validation datasets (GSE38832 and GSE17538; AUC > 0.8). In addition, patients’ age, T classification, recurrence status, and prognostic risk score were associated with the prognosis of TCGA patients with colon cancer. The nomogram was constructed using the above factors, and the predictive 3- and 5-year survival probabilities had high compliance with the actual survival proportions.

Conclusions

The 12-gene signature prognostic model had a high predictive ability for the prognosis of colon cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12957-020-02116-y.

Dynamic Changes of Mitochondrial DNA Copy Number in Gastrointestinal Tract Cancers: A Systematic Review and Meta-Analysis

We have performed a systematic review and meta-analysis for evaluation of mitochondrial DNA copy number (mtDNA-CN) alterations in peripheral blood leukocytes (PBL), and tumor tissues of gastrointestinal tract (GIT) cancers. Analysis of the PBL demonstrated a significant decrease [OR: 0.6 (0.5, 0.8)] and increase [OR: 1.4 (1.1, 1.9)] prior to and following GIT cancer development, respectively. This trend was more evident in CRC, and GC subgroups. Analysis of tissue yielded high levels of heterogeneity. However, the mean difference for the CRC subgroup was statistically significant [1.5 (1.0, 2.2)]. Our analysis suggests mtDNA-CN deserves further investigations as a GIT-cancer screening tool.

Mitochondrial DNA copy number in human disease: the more the better?

Most of the genetic information has been lost or transferred to the nucleus during the evolution of mitochondria. Nevertheless, mitochondria have retained their own genome that is essential for oxidative phosphorylation (OXPHOS). In mammals, a gene‐dense circular mitochondrial DNA (mtDNA) of about 16.5 kb encodes 13 proteins, which constitute only 1% of the mitochondrial proteome. Mammalian mtDNA is present in thousands of copies per cell and mutations often affect only a fraction of them. Most pathogenic human mtDNA mutations are recessive and only cause OXPHOS defects if present above a certain critical threshold. However, emerging evidence strongly suggests that the proportion of mutated mtDNA copies is not the only determinant of disease but that also the absolute copy number matters. In this review, we critically discuss current knowledge of the role of mtDNA copy number regulation in various types of human diseases, including mitochondrial disorders, neurodegenerative disorders and cancer, and during ageing. We also provide an overview of new exciting therapeutic strategies to directly manipulate mtDNA to restore OXPHOS in mitochondrial diseases.

High Tumor Mitochondrial DNA Content Correlates With an Improved Patient's Outcome in WHO Grade III Meningioma

Background: Studies have shown mitochondrial genome content (mtDNA content) varies in many malignancies. However, its distribution and prognostic values in high-grade meningioma remain largely unknown. In this retrospective study, we sought to assess a putative correlation between the mtDNA content and clinical characteristics. Methods: Mitochondrial DNA was extracted from 87 World Health Organization grade III meningioma samples using a qPCR method. The distribution of mtDNA content in WHO grade III meningioma and its correlations with clinical variables were assessed. Furthermore, we prognostic values were also determined. Results: Mean mtDNA content was 617.7 (range, 0.8-3000). There was no mtDNA distribution difference based on the histological subtypes (P = 0.07). Tumors with preoperative radiation were associated with lower mtDNA content (P = 0.041), whereas no correlations with other clinical variables were observed. A high mtDNA content was associated with significantly better PFS (P = 0.044) and OS (P = 0.019). However, in patients who received postoperative radiotherapy, low mtDNA content was associated with better PFS (P = 0.028), while no difference in OS was observed (P = 0.272). Low mtDNA content was also associated with better OS and PFS in subgroups of patients with ER negative status (PFS, P = 0.002; OS, P = 0.002). Conclusions: Consistent with other tumors, high mtDNA content was associated with better outcome in WHO grade III meningioma in our cohort. However, for patients who received post-operative radiation therapy, low mtDNA content was associated with better PFS. These findings suggest that mtDNA content may further be explored as a potential biomarker for high-grade meningioma patients and for those who received postoperative radiation therapy.

Association between pre-diagnostic leukocyte mitochondrial DNA copy number and survival among colorectal cancer patients

BACKGROUND

Mitochondrial DNA copy number (mtDNAcn) is considered a biomarker for mitochondrial function and oxidative stress. Although previous studies have suggested a potential relationship between mtDNAcn at the time of colorectal cancer (CRC) diagnosis and CRC prognosis, findings have been inconsistent, and no study has specifically investigated the association of pre-diagnostic mtDNAcn with CRC survival.

METHODS

We examined the association of pre-diagnostic leukocyte mtDNAcn (measured by qPCR) with overall and CRC-specific survival among 587 patients in Nurses' Health Study and Health Professionals Follow-Up Study. Cox models were constructed to estimate hazard ratios (HRs) and 95 % confidence intervals (95 % CIs).

RESULTS

During a mean follow-up of 10.5 years, 395 deaths were identified; 180 were due to CRC. Overall, we did not observe significant associations between mtDNAcn and either overall or CRC-specific survival among all cases or by cancer location, grade, or stage. In an exploratory stratified analysis, a suggestive inverse association of mtDNAcn and overall death risk appeared among current smokers [HR (95 % CI) for 1 SD decrease in mtDNAcn = 1.50 (0.98, 2.32), P-trend = 0.06]. Reduced mtDNAcn and lower CRC-specific death risk was observed among patients aged ≤ 70.5 at diagnosis [HR (95 % CI) for 1 SD decrease of mtDNAcn = 0.71 (0.52, 0.97), P-trend = 0.03], ≤ 5 years from blood collection to diagnosis [HR (95 % CI) for 1 SD decrease in mtDNAcn = 0.65 (0.44, 0.96), P-trend = 0.03] and those consuming a low-inflammatory diet [HR (95 % CI) for 1 SD decrease in mtDNAcn = 0.61 (0.42, 0.88), P-trend = 0.009].

CONCLUSION

no significant associations between pre-diagnostic leukocyte mtDNAcn and either overall or CRC-specific survival appeared but exploratory analysis identified potential sub-group associations.

Identification of Prognostic Dosage-Sensitive Genes in Colorectal Cancer Based on Multi-Omics

Several studies have already identified the prognostic markers in colorectal cancer (CRC) based on somatic copy number alteration (SCNA). However, very little information is available regarding their value as a prognostic marker. Gene dosage effect is one important mechanism of copy number and dosage-sensitive genes are more likely to behave like driver genes. In this work, we propose a new pipeline to identify the dosage-sensitive prognostic genes in CRC. The RNAseq data, the somatic copy number of CRC from TCGA were assayed to screen out the SCNAs. Wilcoxon rank-sum test was used to identify the differentially expressed genes in alteration samples with |SCNA| > 0.3. Cox-regression was used to find the candidate prognostic genes. An iterative algorithm was built to identify the stable prognostic genes. Finally, the Pearson correlation coefficient was calculated between gene expression and SCNA as the dosage effect score. The cell line data from CCLE was used to test the consistency of the dosage effect. The differential co-expression network was built to discover their function in CRC. A total of six amplified genes (NDUFB4, WDR5B, IQCB1, KPNA1, GTF2E1, and SEC22A) were found to be associated with poor prognosis. They demonstrate a stable prognostic classification in more than 50% threshold of SCNA. The average dosage effect score was 0.5918 ± 0.066, 0.5978 ± 0.082 in TCGA and CCLE, respectively. They also show great stability in different data sets. In the differential co-expression network, these six genes have the top degree and are connected to the driver and tumor suppressor genes. Function enrichment analysis revealed that gene NDUFB4 and GTF2E1 affect cancer-related functions such as transmembrane transport and transformation factors. In conclusion, the pipeline for identifying the prognostic dosage-sensitive genes in CRC was proved to be stable and reliable.

Overexpression of miR-671-5p indicates a poor prognosis in colon cancer and accelerates proliferation, migration, and invasion of colon cancer cells

Purpose

Colon cancer is one of the common malignancies worldwide, and many genes, including microRNAs (miRNAs), have been demonstrated that associated with progression of various diseases, including cancers. The aim of this study is to investigate the potential role of miR-671-5p in colon cancer.

Patients and methods

Reverse transcription-quantitative polymerase chain reaction (qRT-PCR) was performed to detect the expression levels of miR-671-5p in 115 paired colon cancer tissues and adjacent normal tissues, as well as in colon cancer cells. Kaplan-Meier curve and Cox regression analyses were used to estimate the prognostic significance of miR-671-5p in colon cancer. CCK-8 assay, colony-formation assay, Transwell migration and invasion assays were used to evaluate the effects of miR-671-5p on cell proliferation, migration, and invasion in colon cancer.

Results

We found that miR-671-5p expression was increased in colon cancer tissues and cell lines. Overexpression of miR-671-5p was found associated with lymph node metastasis, TNM stage, and poor overall survival of patients with colon cancer. By exploiting miR-671-5p mimics and inhibitors, miR-671-5p overexpression significantly increased cell proliferation, migration, and invasion, while downregulation of miR-671-5p inhibited proliferation, migration, and invasion of colon cancer cells.

Conclusion

Taken together, miR-671-5p may act as an oncogene in colon cancer and promote proliferation, migration, and invasion of colon cancer cells by targeting TRIM67. And it may be a promising prognostic biomarker and therapeutic application for colon cancer treatment.

Upregulation of mtSSB by interleukin-6 promotes cell growth through mitochondrial biogenesis-mediated telomerase activation in colorectal cancer

It is now widely accepted that mitochondrial biogenesis is inhibited in most cancer cells. Interestingly, one of the possible exceptions is colorectal cancer (CRC), in which the content of mitochondria has been found to be higher than in normal colon mucosa. However, to date, the causes and effects of this phenomenon are still unclear. In the present study, we systematically investigated the functional role of mitochondrial single-strand DNA binding protein (mtSSB), a key molecule in the regulation of mitochondrial DNA (mtDNA) replication, in the mitochondrial biogenesis and CRC cell growth. Our results demonstrated that mtSSB was frequently upregulated in CRC tissues and that upregulated mtSSB was associated with poor prognosis in CRC patients. Furthermore, overexpression of mtSSB promoted CRC cell growth in vitro by regulating cell proliferation. The in vivo assay confirmed these results, indicating that the forced expression of mtSSB significantly increases the growth capacity of xenograft tumors. Mechanistically, the survival advantage conferred by mtSSB was primarily caused by increased mitochondrial biogenesis and subsequent ROS production, which induced telomerase reverse transcriptase (TERT) expression and telomere elongation via Akt/mTOR pathway in CRC cells. In addition, FOXP1, a member of the forkhead box family, was identified as a new transcription factor for mtSSB. Moreover, our results also demonstrate that proinflammatory IL-6/STAT3 signaling facilitates mtSSB expression and CRC cell proliferation via inducing FOXP1 expression. Collectively, our findings demonstrate that mtSSB induced by inflammation plays a critical role in the regulation of mitochondrial biogenesis, telomerase activation, and subsequent CRC proliferation, providing a strong evidence for mtSSB as drug target in CRC treatment.

Mitochondrial inheritance and cancer

Mitochondria are essential intracellular organelles that are responsible for energy metabolism, cell growth, and differentiation, redox homeostasis, oncogenic signaling, and apoptosis. These multifunctional organelles have been implicated in cancer initiation, progression, and metastasis, relapse, and acquired drug resistance due to metabolic alterations in transformed cells. Maternally inherited mitochondrial DNA (mtDNA) is thought to contribute to cancer development and prognosis and proposed as a therapeutic target for cancer treatment. In this review, we summarize the current knowledge of mtDNA alterations, with a specific focus on somatic changes, germline variants, haplogroups, large deletions, and mtDNA content changes associated with cancer susceptibility and prognosis. We also discuss the potential of mtDNA as biomarkers of cancer detection and targets of cancer treatment. Deeper understanding of the mechanisms underlying these associations requires further investigation.

Clinical application of plasma mitochondrial DNA content in patients with lung cancer

Alterations of mitochondrial DNA (mtDNA) have been identified in several types of solid tumor. However, to the best of our knowledge, the clinical significance of plasma mtDNA content in lung cancer remains unknown. Thus, the current study explored the diagnostic and prognostic value of plasma mtDNA quantification in patients with lung cancer. Plasma mtDNA copy numbers of patients with lung cancer (n=128) and healthy individuals (n=107) were quantified by quantitative polymerase chain reaction. Plasma mtDNA copy numbers in patients and healthy controls were 0.89×10⁴ and 1.37×10⁴ copies/µl, respectively (P<0.0001). Furthermore, lower plasma mtDNA content was associated with tumor size, lymph node metastases, distant metastases and serum carcinoembryonic antigen levels (P<0.05), but was not associated with pathological type, age, sex or main driver gene mutation status (P>0.05). Plasma mtDNA facilitated the detection of lung cancer at a threshold of 1.19×10⁴ copies/µl with a sensitivity of 71.1% and specificity of 70.1%, as determined by receiver operating characteristic curve analysis. Advanced stage (III and IV) patients with a lower mtDNA copy number (cutoff: 1.02×10⁴ copies/µl) tended to exhibit poorer prognosis (P<0.05). These results indicated that plasma mtDNA content is a promising and complementary candidate with tissue mtDNA for diagnosis and prognostic prediction for lung cancer.

PGC1α promotes cisplatin resistance in human ovarian carcinoma cells through upregulation of mitochondrial biogenesis

The induction of lesions in nuclear and mitochondrial DNA by cisplatin is only a small component of its cytostatic/cytotoxic activity. The signaling pathway network in the nucleus and cytoplasm may contribute to chemotherapeutic resistance. Peroxisome proliferator-activated receptor-coactivator 1α (PGC1α)-mediated mitochondrial biogenesis regulates mitochondrial structural and the functional adaptive response against chemotherapeutic stress, and may be a therapeutic target. However, this regulatory network is complex and depends upon tumor types and environments, which require further investigation. Our previous study found that cisplatin-resistant ovarian epithelial carcinoma was more dependent on mitochondrial aerobic oxidation to support their growth, suggesting the association between mitochondrial function and chemotherapeutic resistance. In the present study, it was demonstrated that the expression of PGC1α and level of mitochondrial biogenesis were higher in cisplatin-resistant SKOV3/DDP cells compared with cisplatin-sensitive SKOV3 cells. Furthermore, SKOV3/DDP cells upregulated the expression of PGC1α and maintained mitochondrial structural and functional integrity through mitochondrial biogenesis under cisplatin stress. Inhibiting the expression of PGC1α using short hairpin RNA led to the downregulation of mitochondrial biogenesis and high levels of apoptosis in the SKOV3/DDP cells, and cisplatin resistance was reversed in the PGC1α-deficient SKOV3/DDP cells. Collectively, the present study provided evidence that cisplatin stimulated the expression of PGC1α and the upregulation of mitochondrial biogenesis through PGC1α, promoting cell viability and inhibiting apoptosis in response to cisplatin treatment, thus triggering cisplatin resistance in ovarian cancer cells.

Mitochondrial DNA replication: a PrimPol perspective

PrimPol, (primase-polymerase), the most recently identified eukaryotic polymerase, has roles in both nuclear and mitochondrial DNA maintenance. PrimPol is capable of acting as a DNA polymerase, with the ability to extend primers and also bypass a variety of oxidative and photolesions. In addition, PrimPol also functions as a primase, catalysing the preferential formation of DNA primers in a zinc finger-dependent manner. Although PrimPol's catalytic activities have been uncovered in vitro, we still know little about how and why it is targeted to the mitochondrion and what its key roles are in the maintenance of this multicopy DNA molecule. Unlike nuclear DNA, the mammalian mitochondrial genome is circular and the organelle has many unique proteins essential for its maintenance, presenting a differing environment within which PrimPol must function. Here, we discuss what is currently known about the mechanisms of DNA replication in the mitochondrion, the proteins that carry out these processes and how PrimPol is likely to be involved in assisting this vital cellular process.

MtDNA As a Cancer Marker: A Finally Closed Chapter?

Sequence alterations of the mitochondrial DNA (mtDNA) have been identified in many tu-mor types. Their nature is not entirely clear. Somatic mutation or shifts of heteroplasmic mtDNA vari-ants may play a role. These sequence alterations exhibit a sufficient frequency in all tumor types investi-gated thus far to justify their use as a tumor marker. This statement is supported by the high copy num-ber of mtDNA, which facilitates the detection of aberrant tumor-derived DNA in bodily fluids. This will be of special interest in tumors, which release a relatively high number of cells into bodily fluids, which are easily accessible, most strikingly in urinary bladder carcinoma. Due to the wide distribution of the observed base substitutions, deletions or insertions within the mitochondrial genome, high efforts for whole mtDNA sequencing (16.5 kb) from bodily fluids would be required, if the method would be in-tended for initial tumor screening. However, the usage of mtDNA for sensitive surveillance of known tumor diseases is a meaningful option, which may allow an improved non-invasive follow-up for the urinary bladder carcinoma, as compared to the currently existing cytological or molecular methods. Fol-lowing a short general introduction into mtDNA, this review demonstrates that the scenario of a sensi-tive cancer follow-up by mtDNA-analysis deserves more attention. It would be most important to inves-tigate precisely in the most relevant tumor types, if sequencing approaches in combination with simple PCR-assays for deletions/insertions in homopolymeric tracts has sufficient sensitivity to find most tu-mor-derived mtDNAs in bodily fluids.

Can Mitochondria DNA Provide a Novel Biomarker for Evaluating the Risk and Prognosis of Colorectal Cancer?

Colorectal cancer (CRC) was one of the most frequent cancers worldwide. Accurate risk and prognosis evaluation could obtain better quality of life and longer survival time for the patients. Current research hotspot was focus on the gene biomarker to evaluate the risk and prognosis. Mitochondrion contains its own DNA and regulates self-replicating so that it can be as a candidate biomarker for evaluating the risk and prognosis of colorectal cancer. But there were already huge controversies on this issue. The review was to summarize current viewpoints of the controversial issues and described our understanding from the four aspects including mtDNA copy number, mitochondrial displacement loop, mtDNA variation, and mtDNA microsatellite instability, wishing the summary of the mtDNA in colorectal cancer could provide a meaningful reference or a valuable direction in the future studies.

Elevated Mitochondrial DNA Copy Number in Peripheral Blood and Tissue Predict the Opposite Outcome of Cancer: A Meta-Analysis

Previous studies have suggested that mitochondrial DNA (mtDNA) copy number was associated with cancer risk. However, no solid conclusion revealed the potential predictive value of mtDNA copy number for cancer prognosis. The present meta-analysis was performed to clarify the problem. Hence, we performed a systematic search in PubMed, EmBase, Web of Science databases independently and a total of eighteen studies comprising 3961 cases satisfied the criteria and finally enrolled. Our results didn’t show the association between them but significant heterogeneity in overall analysis (OS: HR = 0.923, 95% CI: 0.653–1.306, p = 0.652; DFS: HR = 0.997, 95% CI: 0.599–1.659, p = 0.99). However, subgroup analysis stratified by sample came to the opposite conclusion. High level mitochondrial DNA copy number in peripheral blood predicted a poor cancer prognosis (OS: HR = 1.624, 95% CI: 1.211–2.177, p = 0.001; DFS: HR = 1.582, 95% CI: 1.026–2.439, p = 0.038) while patients with high level mitochondrial DNA copy number in tumor tissue exhibited better outcomes (OS: HR = 0.604 95% CI: 0.406–0.899, p = 0.013; DFS: HR = 0.593, 95% CI: 0.411–0.857, p = 0.005). These findings were further proved in detailed analyses in blood or tissue subgroup. In conclusion, our study suggested the elevated mtDNA copy number in peripheral blood predicted a poor cancer prognosis while the better outcome was presented among patients with elevated mtDNA copy number in tumor tissue.