Single nucleotide variants of succinate dehydrogenase A gene in renal cell carcinoma

Tricarboxylic Acid Cycle Relationships with Non-Metabolic Processes: A Short Story with DNA Repair and Its Consequences on Cancer Therapy Resistance

Metabolic changes involving the tricarboxylic acid (TCA) cycle have been linked to different non-metabolic cell processes. Among them, apart from cancer and immunity, emerges the DNA damage response (DDR) and specifically DNA damage repair. The oncometabolites succinate, fumarate and 2-hydroxyglutarate (2HG) increase reactive oxygen species levels and create pseudohypoxia conditions that induce DNA damage and/or inhibit DNA repair. Additionally, by influencing DDR modulation, they establish direct relationships with DNA repair on at least four different pathways. The AlkB pathway deals with the removal of N-alkylation DNA and RNA damage that is inhibited by fumarate and 2HG. The MGMT pathway acts in the removal of O-alkylation DNA damage, and it is inhibited by the silencing of the MGMT gene promoter by 2HG and succinate. The other two pathways deal with the repair of double-strand breaks (DSBs) but with opposite effects: the FH pathway, which uses fumarate to help with the repair of this damage, and the chromatin remodeling pathway, in which oncometabolites inhibit its repair by impairing the homologous recombination repair (HRR) system. Since oncometabolites inhibit DNA repair, their removal from tumor cells will not always generate a positive response in cancer therapy. In fact, their presence contributes to longer survival and/or sensitization against tumor therapy in some cancer patients.

A highly malignant succinate dehydrogenase A‑deficient renal cell carcinoma with bone metastasis misdiagnosed as hereditary leiomyomatosis and renal cell carcinoma: A case report

Succinate dehydrogenase (SDH)-deficient renal cell carcinoma (RCC) is an autosomal dominant syndrome caused by heterozygous pathogenic germline variants of the SDH gene. SDH mutations are associated with an increased risk of developing RCC, although studies describing SDH-deficient RCC are currently limited. The present study reported a case of SDH-deficient RCC with high malignancy and rare bone metastasis. The patient was diagnosed with a right renal mass through B-mode ultrasound imaging and showed a carcinoma embolus in the right renal vein and inferior vena cava through kidney contrast-enhanced computed tomography. A whole-body bone scan showed radionuclide accumulation in the upper end of the left humerus, which indicated possible pathological bone destruction. As a result, surgical resection was performed. The postoperative pathology indicated a high-grade RCC and although the specific classification remained uncertain, hereditary leiomyomatosis and RCC was suspected. Subsequently, a germline mutation of the succinate dehydrogenase complex flavoprotein subunit A gene was identified through high-throughput sequencing (c.1A>G, p. Met1?) and immunohistochemistry demonstrated the loss of succinate dehydrogenase complex flavoprotein subunit B expression. Postoperatively, the patient underwent radiotherapy and targeted therapy. After 6 months of follow-up treatment, there was no indication of recurrence or metastasis on thoracoabdominal CT and whole-body bone scintigraphy. Based on the present report, germline screening should potentially be encouraged in early-onset patients as family history or pathological results may not provide sufficient information for the early, differential diagnosis of SDH-deficient RCC.

Succinate dehydrogenase complex subunit C: Role in cellular physiology and disease

Succinate dehydrogenase complex subunit C (SDHC) is a subunit of mitochondrial complex II (MCII), which is also known as succinate dehydrogenase (SDH) or succinate: ubiquinone oxidoreductase. Mitochondrial complex II is the smallest respiratory complex in the respiratory chain and contains four subunits. SDHC is a membrane-anchored subunit of SDH, which connects the tricarboxylic acid cycle and the electron transport chain. SDH regulates several physiological processes within cells, plays an important role in generating energy to maintain normal cell growth, and is involved in apoptosis. Currently, SDHC is generally recognized as a tumor-suppressor gene. SDHC mutations can cause oxidative damage in the body. It is closely related to the occurrence and development of cancer, neurodegenerative diseases, and aging-related diseases. Here, we review studies on the structure, biological function, related diseases of SDHC, and the mev-1 Animal Model of SDHC Mutation and its potential use as a therapeutic target of certain human diseases.

Succinate dehydrogenase B-deficient renal cell carcinoma with a germline variant in a Japanese patient: a case report

Succinate dehydrogenase (SDH)-deficient renal cell carcinoma (RCC) is a rare renal cancer. A 75-year-old Japanese female presented with gross hematuria. Computed tomography revealed two tumors in the left kidney, which were resected. Immunohistochemistry indicated negative staining for the B subunit of SDH (SDHB) in the resected specimen, leading to a final diagnosis of SDHB-deficient RCC. Genetic testing for SDHB showed a RCC germline variant in exon 6 (NM_003000.3:c.642 G > C) that was previously reported but associated with a novel phenotype (i.e., RCC). Twenty-six years prior, her daughter, who was 25 years old at the time, had undergone radical nephrectomy for a pathologic diagnosis of renal oncocytoma of the right kidney; SDHB immunostaining of her daughter's tumor was also negative retrospectively. We confirmed that her daughter carried the germline variant in SDHB exon 6, similar to the patient. The patient had no evidence of disease progression at 15 months after surgery.

Association of Nrf2 expression and mutation with Weiss and Helsinki scores in adrenocortical carcinoma

Adrenocortical carcinoma (ACC) is a rare malignant tumor. Genetic abnormalities that may represent therapeutic targets and prognostic factors in ACC remain unclear. Besides being one of the main cellular defense mechanisms that regulates antioxidant pathways for detoxifying reactive oxygen species (ROS), the transcription factor nuclear factor erythroid 2–related factor 2 (Nrf2) promotes tumor proliferation by increasing metabolic activity. In surgical specimens from 12 cases of nonmetastatic ACCs and nine cases of benign adrenocortical adenoma (ACA), we investigated gene mutation and protein expressions for Nrf2 and the preoperative maximum standard glucose uptake (SUVmax) on [¹⁸F]fluorodeoxy‐glucose positron emission tomography. Three of five ACCs with a Weiss score of 7 to 9 were Nrf2 mutants; these ACCs had higher expression of Nrf2 and higher preoperative SUVmax. The other seven ACCs had a Weiss score of 3 to 6; these seven ACCs and all the ACAs were non‐Nrf2 gene mutants. Patients with a Weiss score of 7 to 9 and Nrf2 mutant ACC had shorter overall survival. Based on Helsinki scoring, three ACCs with a Helsinki score greater than 17 had Nrf2 mutants, higher expression of Nrf2, higher preoperative SUVmax, and shorter overall survival. Our findings indicate that Nrf2 activation and the associated increase in metabolism play roles in ACC, in particular in ACC with a Weiss score of 7 to 9 and a Helsinki score of greater than 17.

Increased expression of Nrf2 and elevated glucose uptake in pheochromocytoma and paraganglioma with SDHB gene mutation

Background

Pheochromocytomas (PCC) and paragangliomas (PGL) are catecholamine-producing neuroendocrine tumors. According to the World Health Organization Classification 2017, all PCC/PGL are considered to have malignant potential. There is growing evidence that PCC/PGL represent a metabolic disease that leads to aerobic glycolysis. Cellular energy metabolism involves both transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) and succinate dehydrogenase (SDH) subtypes, but the association of these substances with PCC/PGL is largely unknown.

Methods

We investigated SDHB gene mutation and protein expressions for SDHB and Nrf2 in surgical specimens from 29 PCC/PGL. We also assessed preoperative maximum standard glucose uptake (SUVmax) on [¹⁸F]fluorodeoxy-glucose positron emission tomography and mRNA levels for Nrf2.

Results

Among 5 PCC/PGL with a PASS Score ≥ 4 or with a moderately to poorly differentiated type in the GAPP Score, 4 were metastatic and found to be SDHB mutants with homogeneous deletion of SDHB protein. SDHB mutants showed a higher expression of Nrf2 protein and a higher preoperative SUVmax than non-SDHB mutants with a PASS < 4 or a well-differentiated GAPP type. Furthermore, protein expression of Nrf2 was positively associated with preoperative SUVmax. The Nrf2 mRNA level positively correlated with malignant phenotype, higher expression for Nrf2 protein and SDHB gene mutant, but negatively correlated with expression for SDHB protein. There was also a positive correlation between Nrf2 mRNA level and SUVmax.

Conclusion

These results suggest that activation of Nrf2 and elevated metabolism play roles in PCC/PGL with malignant potential that have SDHB gene mutation and SDHB deficiency.

The Role of Ferric Nitrilotriacetate in Renal Carcinogenesis and Cell Death: From Animal Models to Clinical Implications

Iron is essential for cellular growth, and various ferroproteins and heme-containing proteins are involved in a myriad of cellular functions, such as DNA synthesis, oxygen transport, and catalytic reactions. As a consequence, iron deficiency causes pleiotropic effects, such as hypochromic microcytic anemia and growth disturbance, while iron overload is also deleterious by oxidative injury. To prevent the generation of iron-mediated reactive oxygen species (ROS), ferritin is synthesized to store excess iron in cells that are consistent with the clinical utility of the serum ferritin concentration to monitor the therapeutic effect of iron-chelation. Among the animal models exploring iron-induced oxidative stress, ferric nitrilotriacetate (Fe-NTA) was shown to initiate hepatic and renal lipid peroxidation and the development of renal cell carcinoma (RCC) after repeated intraperitoneal injections of Fe-NTA. Here, current understanding of Fe-NTA-induced oxidative stress mediated by glutathione-cycle-dependent iron reduction and the molecular mechanisms of renal carcinogenesis are summarized in combination with a summary of the relationship between the pathogenesis of human RCC and iron metabolism. In addition to iron-mediated carcinogenesis, the ferroptosis that is triggered by the iron-dependent accumulation of lipid peroxidation and is implicated in the carcinogenesis is discussed.

Transcriptional Changes after Enniatins A, A1, B and B1 Ingestion in Rat Stomach, Liver, Kidney and Lower Intestine

Enniatins (ENs) are depsipeptide mycotoxins produced by Fusarium fungi. They are known for their capacity to modulate cell membrane permeability and disruption of ionic gradients, affecting cell homeostasis and initiating oxidative stress mechanisms. The effect of the acute toxicity of ENs A, A1, B and B1 at two different concentrations after 8 h of exposure was analysed in Wistar rats by a transcriptional approach. The following key mitochondrial and nuclear codified genes related to the electron transport chain were considered for gene expression analysis in stomach, liver, kidney and lower intestine by quantitative Real-Time PCR: mitochondrially encoded NADH dehydrogenase 1 (MT-ND1), mitochondrially encoded cytochrome c oxidase 1 (MT-COX1), succinate dehydrogenase flavoprotein subunit A and ATP synthase F1 subunit alpha, respectively. Moreover, the expression of markers involved in oxidative stresssuperoxide dismutase 1 (SOD1), glutathione peroxidase 1 (Gpx1), heme oxygenase 1, apoptosis B-cell lymphoma 2, Bcl2 Associated protein X (Bax), tumor suppressor protein (p53), inhibition of apoptosis nuclear factor kappa of activated B cells, immune system interleukin 1β and intestinal tight junction Occludin merely in lower intestine tissues have been investigated. For mitochondrial genes, the main differences were observed for MT-ND1 and MT-COX1, showing its deficiency in all selected organs. With regard to the intestinal barrier’s cellular response to oxidative stress, the activity of the antioxidant gene SOD1 was decreased in a dose-dependent manner. Similarly, the catalytic enzyme GPx1 was also downregulated though merely at medium dose employed. On the contrary, the pro-apoptotic Bax and p53 regulators were activated after ENs exposure, reporting a significant increase in their expression. Furthermore, the alteration of intestinal permeability was assessed by the abnormal activity of the tight junction protein occludin. In summary, ENs may generate mitochondrial disorders and induce oxidative stress in intestinal barrier function.

Single nucleotide variants of succinate dehydrogenase A gene in renal cell carcinoma

Succinate dehydrogenase (SDH)-deficient renal cell carcinoma (RCC) is mainly associated with a mutation in the SDHB gene and sometimes with mutations in the SDHC or SDHD genes. However, only three cases of succinate dehydrogenase A (SDHA)-deficient RCC have been reported, and the relation between SDHA mutations and RCC has not been clarified. This study assessed the role of SDHA gene mutations in human RCC. We investigated SDHA/B/C/D gene mutations in 129 human RCCs. Targeted next-generation sequencing and direct Sanger sequencing revealed single nucleotide variants (SNVs) of the SDHA gene with amino acid sequence variations in 11/129 tumors, while no SDHB/C/D gene mutations were found. Tumor cells with SNVs of the SDHA gene were characterized by eosinophilic cytoplasm and various patterns of proliferation. Immunohistochemistry examination found that the 11 tumors with SNVs of the SDHA gene showed significant reduction of SDHA protein and SDHB protein expression compared to the 19 tumors without SDHA or SDHB mutations (both P < .0001). Western blotting showed a greater decrease in the expression of SDHA and SDHB proteins in the 11 tumors with SNVs of the SDHA gene than in the 19 tumors without (both P < .0001). There was a positive correlation between SDHA and SDHB protein levels (P < .0001). On immunohistochemistry and Western blotting, the 11 tumors with SNVs of the SDHA gene had higher protein expression for nuclear factor E2-related factor 2 (Nrf2) compared to the 19 tumors without the mutation (P < .01). These observations suggest that SDHA gene mutations might be associated with a subset of RCC.