The complex II resistance mutation H258Y in succinate dehydrogenase subunit B causes fitness penalties associated with mitochondrial respiratory deficiency

BACKGROUND

The acaricides cyflumetofen, cyenopyrafen and pyflubumide inhibit the mitochondrial electron transport chain at complex II [succinate dehydrogenase (SDH) complex]. A target site mutation H258Y was recently discovered in a resistant strain of the spider mite pest Tetranychus urticae. H258Y causes strong cross-resistance between cyenopyrafen and pyflubumide, but not cyflumetofen. In fungal pests, fitness costs associated with substitutions at the corresponding H258 position that confer resistance to fungicidal SDH inhibitors have not been uncovered. Here, we used H258 and Y258 near-isogenic lines of T. urticae to quantify potential pleiotropic fitness effects on mite physiology.

RESULTS

The H258Y mutation was not associated with consistent significant changes of single generation life history traits and fertility life table parameters. In contrast, proportional Sanger sequencing and droplet digital polymerase chain reaction showed that the frequency of the resistant Y258 allele decreased when replicated 50:50 Y258:H258 experimentally evolving populations were maintained in an acaricide-free environment for approximately 12 generations. Using in vitro assays with mitochondrial extracts from resistant (Y258) and susceptible (H258) lines, we identified a significantly reduced SDH activity (48% lower activity) and a slightly enhanced combined complex I and III activity (18% higher activity) in the Y258 lines.

CONCLUSION

Our findings suggest that the H258Y mutation is associated with a high fitness cost in the spider mite T. urticae. Importantly, while it is the most common approach, it is clear that only comparing life history traits and life table fecundity does not allow to reliably estimate fitness costs of target site mutations in natural pest populations. © 2023 Society of Chemical Industry.

Th17 cells target the metabolic miR-142-5p-succinate dehydrogenase subunit C/D (SDHC/SDHD) axis, promoting invasiveness and progression of cervical cancers

During cervical carcinogenesis, T-helper (Th)-17 cells accumulate in the peripheral blood and tumor tissues of cancer patients. We previously demonstrated that Th17 cells are associated with therapy resistance as well as cervical cancer metastases and relapse; however, the underlying Th17-driven mechanisms are not fully understood. Here, using microarrays, we found that Th17 cells induced an epithelial-to-mesenchymal transition (EMT) phenotype of cervical cancer cells and promoted migration and invasion of 2D cultures and 3D spheroids via induction of microRNA miR-142-5p. As the responsible mechanism, we identified the subunits C and D of the succinate dehydrogenase (SDH) complex as new targets of miR-142-5p and provided evidence that Th17-miR-142-5p-dependent reduced expression of SDHC and SDHD mediated enhanced migration and invasion of cancer cells using small interfering RNAs (siRNAs) for SDHC and SDHD, and miR-142-5p inhibitors. Consistently, patients exhibited high levels of succinate in their serum associated with lymph node metastases and diminished expression of SDHD in patient biopsies correlated with increased numbers of Th17 cells. Correspondingly, a combination of weak or negative SDHD expression and a ratio of Th17/CD4+ T cells > 43.90% in situ was associated with reduced recurrence-free survival. In summary, we unraveled a previously unknown molecular mechanism by which Th17 cells promote cervical cancer progression and suggest evaluation of Th17 cells as a potential target for immunotherapy in cervical cancer.

Molecular imaging and radionuclide therapy of pheochromocytoma and paraganglioma in the era of genomic characterization of disease subgroups

In recent years, advancement in genetics has profoundly helped to gain a more comprehensive molecular, pathogenic, and prognostic picture of pheochromocytomas and paragangliomas (PPGLs). Newly discovered molecular targets, particularly those that target cell membranes or signaling pathways have helped move nuclear medicine in the forefront of PPGL precision medicine. This is mainly based on the introduction and increasing experience of various PET radiopharmaceuticals across PPGL genotypes quickly followed by implementation of novel radiotherapies and revised imaging algorithms. Particularly, 68Ga-labeled-SSAs have shown excellent results in the diagnosis and staging of PPGLs and in selecting patients for PRRT as a potential alternative to 123/131I-MIBG theranostics. PRRT using 90Y/177Lu-DOTA-SSAs has shown promise for treatment of PPGLs with improvement of clinical symptoms and/or disease control. However, more well-designed prospective studies are required to confirm these findings, in order to fully exploit PRRT's antitumoral properties to obtain the final FDA approval. Such an approval has recently been obtained for high-specific-activity 131I-MIBG for inoperable/metastatic PPGL. The increasing experience and encouraging preliminary results of these radiotherapeutic approaches in PPGLs now raises an important question of how to further integrate them into PPGL management (e.g. monotherapy or in combination with other systemic therapies), carefully taking into account the PPGLs locations, genotypes, and growth rate. Thus, targeted radionuclide therapy (TRT) should preferably be performed at specialized centers with an experienced interdisciplinary team. Future perspectives include the introduction of dosimetry and biomarkers for therapeutic responses for more individualized treatment plans, α-emitting isotopes, and the combination of TRT with other systemic therapies.

Pheochromocytoma and paraganglioma: implications of germline mutation investigation for treatment, screening, and surveillance

OBJECTIVE

Paraganglioma (PGL) and pheochromocytoma (PCC) are rare neuroendocrine tumors that were considered to be predominantly sporadic. However, with the identification of novel susceptibility genes over the last decade, it is currently estimated that up to 40% of cases can occur in the context of a hereditary syndrome. We aimed to characterize PGL/PCC families to exemplify the different scenarios in which hereditary syndromes can be suspected and to emphasize the importance for patients and their families of making an opportune genetic diagnosis.

MATERIALS AND METHODS

Retrospective analysis of patients diagnosed with PGL/PCC. Germline mutations were studied using next-generation sequencing panels including SDHA, SDHB, SDHC and SDHD. Clinical data were collected from clinical records, and all patients received genetic counseling.

RESULTS

We describe 4 families with PGL/PCC and germline mutations in SDH complex genes. 2 families have SDHB mutations and 2 SDHD mutations. The clinical presentation of the patients and their families was heterogeneous, with some being atypical according to the literature.

CONCLUSIONS

PGL/PCC are more commonly associated with a germline mutation than any other cancer type, therefore, all individuals with these types of tumors should undergo genetic risk evaluation. NGS multigene panel testing is a cost-effective approach given the overlapping phenotypes. Individuals with germline mutations associated with PGL/PCC should undergo lifelong clinical, biochemical and imaging surveillance and their families should undergo genetic counseling. For all these reasons, it is critical that all medical staff can suspect and diagnose these inherited cancer predisposition syndromes.

Interaction of germline variants in a family with a history of early-onset clear cell renal cell carcinoma

Background

Identification of genetic factors causing predisposition to renal cell carcinoma has helped improve screening, early detection, and patient survival.

Methods

We report the characterization of a proband with renal and thyroid cancers and a family history of renal and other cancers by whole‐exome sequencing (WES), coupled with WES analysis of germline DNA from additional affected and unaffected family members.

Results

This work identified multiple predicted protein‐damaging variants relevant to the pattern of inherited cancer risk. Among these, the proband and an affected brother each had a heterozygous Ala45Thr variant in SDHA, a component of the succinate dehydrogenase (SDH) complex. SDH defects are associated with mitochondrial disorders and risk for various cancers; immunochemical analysis indicated loss of SDHB protein expression in the patient’s tumor, compatible with SDH deficiency. Integrated analysis of public databases and structural predictions indicated that the two affected individuals also had additional variants in genes including TGFB2, TRAP1, PARP1, and EGF, each potentially relevant to cancer risk alone or in conjunction with the SDHA variant. In addition, allelic imbalances of PARP1 and TGFB2 were detected in the tumor of the proband.

Conclusion

Together, these data suggest the possibility of risk associated with interaction of two or more variants.

Alternative splicing isoform in succinate dehydrogenase complex, subunit C causes downregulation of succinate-coenzyme Q oxidoreductase activity in mitochondria

Mitochondrial succinate dehydrogenase (SDH) is localized to the inner mitochondrial membrane and is responsible for the redox of succinic acid. SDH is a tetrameric iron-sulfur flavoprotein of the tricarboxylic acid cycle and respiratory chain. The SDH complex, subunit C (SDHC) transcript has deletion-type alternative splicing sites. Generally, alternative splicing produces variant proteins and expression patterns, as products of different genes. In certain cases, specific alternative splicing variants (ASVs) have been associated with human disease. Due to a frameshift mutation causing loss of the heme binding region, the SDHC Δ5 isoform (lacking exon 5) exhibits no SDHC activity. To investigate whether the SDHC splicing variants can function as dominant-negative inhibitors, SDHC ASVs were overexpressed in HCT-15 human colorectal cancer cells. Using real-time reverse transcription-polymerase chain reaction, a dominant-negative effect of the Δ5 isoform on SDHC mRNA was shown. In addition, Δ5 overexpression increased the levels of reactive oxygen species. Furthermore, in the Δ5 isoform-overexpressing cells, SDH activity was reduced. SDHC activation is a significant event during the electron transport chain, and the function of the SDHC Δ5 variant may be significant for the differentiation of tumor cells.