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Sirtuin 3 (SIRT3) is the main mitochondrial deacetylase and targets several crucial enzymes against oxidative stress. Recent reports suggest that SIRT3 could also participate in the quality and quantity control of mitochondria. The aim of this study was to analyze whether SIRT3 silencing in colon cancer cells could affect mitochondrial biogenesis and impair mitochondrial function. For this purpose, metastatic colon cancer cell line SW620 was transfected with a specific shRNA against SIRT3 to obtain a stable knockdown. Gene expression and protein levels of several proteins related to mitochondrial biogenesis and function were determined by RT-qPCR and Western blotting. Mitochondrial function was studied by analyzing COX, ATPase, and LDH enzymatic activities, oxygen consumption, superoxide levels, and mitochondrial membrane potential. Confocal images were also taken to study mitochondrial morphology, and cell motility and clonogenicity were also studied. SIRT3 silencing resulted in a reduced mitochondrial biogenesis and function, as evidenced by the decrease in proteins such as PGC-1α and mitochondrial transcription factor A and lower levels of OXPHOS complexes. Furthermore, COX activity and oxygen consumption were also diminished after SIRT3 knockdown. Finally, SIRT3-silenced cells showed mitochondrial aggregation compared with control cells as well as reduced motility and colony formation ability. In conclusion, SIRT3 silencing in SW620 cancer cells leads to decreased mitochondrial biogenesis and mitochondrial dysfunction, ultimately affecting cell viability and could be a therapeutic strategy to render cells more sensitive to treatment.

Sirtuin 3 (SIRT3) is the major mitochondria deacetylase and regulates ROS levels by targeting several key proteins, such as those involved in mitochondrial function and antioxidant defenses. This way, SIRT3 balances ROS production and scavenging and promotes cell survival. The aim of this study was to analyze the effect of SIRT3 silencing on the antioxidant response in SW620 colon cancer cell line, and whether this intervention could improve efficacy of oxaliplatin, a common drug used to treat colon cancer. For this purpose, we obtained stable clones of SW620 with SIRT3 knockdown and determined parameters such as ROS levels and ROS production, levels of several antioxidant enzymes, cell viability, and apoptosis. Results showed that after SIRT3 silencing, both ROS levels and production were increased, and antioxidant enzymes gene expression was significantly reduced. Furthermore, manganese superoxide dismutase levels and enzymatic activity were reduced. Combination of SIRT3 knockdown with oxaliplatin treatment further increased ROS production and apoptosis, reducing cell viability. Finally, survival curves on colon cancer patients suggested that SIRT3 expression is related to a poorer prognosis. In conclusion, SIRT3 could be a target for colon cancer, since it regulates the antioxidant response and its knockdown improves the efficacy of oxaliplatin treatment.

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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.

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Chronic inflammation can induce malignant cell transformation, having an important role in all colorectal cancer (CRC) phases. Non-tumor adjacent tissue plays an important role in tumor progression, but its implication in CRC has not yet been fully elucidated. The aim was to analyze the expression of inflammatory, epithelial-mesenchymal transition (EMT), and metastasis-related proteins in both tumor and non-tumor adjacent tissues from CRC patients by western blot. Tumor tissue presented an increase in metastasis and EMT-related proteins compared to non-tumor adjacent tissue, especially in stage II. Tumor tissue stage II also presented an increase in inflammatory-related proteins compared to other stages, which was also seen in non-tumor adjacent tissue stage II. Additionally, the relapse-free survival study of Vimentin and VEGF-B expression levels in stage II patients showed that the higher the expression levels of each protein, the lower 10-year relapse-free survival. These could suggest that some metastasis-related signalling pathways may be activated in stage II in tumor tissue, accompanied by an increase in inflammation. Furthermore, non-tumor adjacent tissue presented an increase of the inflammatory status that could be the basis for future tumor progression. In conclusion, these proteins could be useful as biomarkers of diagnosis for CRC at early stages.