Localization of the oxaloacetate-binding site in the iron-flavoprotein subunit of the inhibitor-succinate dehydrogenase complex

The Use of circRNAs as Biomarkers of Cancer

CircRNAs are a subclass of lncRNAs that have been found to be abundantly present in a wide range of species, including humans. CircRNAs are generally produced by a noncanonical splicing event called backsplicing that is dependent on the canonical splicing machinery, giving rise to circRNAs classified into three main categories: exonic circRNA, circular intronic RNA, and exon-intron circular RNA. Notably, circRNAs possess functional importance and display their functions through different mechanisms of action including sponging miRNAs, or even being translated into functional proteins. In addition, circRNAs also have great potential as biomarkers, particularly in cancer, thanks to their high stability, tissue type and developmental stage specificity, and their presence in biological fluids, which make them promising candidates as noninvasive biomarkers. In this chapter, we describe the most commonly used techniques for the study of circRNAs as cancer biomarkers, including high-throughput techniques such as RNA-Seq and microarrays, and other methods to analyze the presence of specific circRNAs in patient samples.

CircRNA-vgll3 promotes osteogenic differentiation of adipose-derived mesenchymal stem cells via modulating miRNA-dependent integrin α5 expression

Adipose-derived mesenchymal stem cells (ADSCs) are promising candidate for regenerative medicine to repair non-healing bone defects due to their high and easy availability. However, the limited osteogenic differentiation potential greatly hinders the clinical application of ADSCs in bone repair. Accumulating evidences demonstrate that circular RNAs (circRNAs) are involved in stem/progenitor cell fate determination, but their specific role in stem/progenitor cell osteogenesis, remains mostly undescribed. Here, we show that circRNA-vgll3 originating from the vgll3 locus markedly enhances osteogenic differentiation of ADSCs; nevertheless, silencing of circRNA-vgll3 dramatically attenuates ADSC osteogenesis. Furthermore, we validate that circRNA-vgll3 functions in ADSC osteogenesis through a circRNA-vgll3/miR-326-5p/integrin α5 (Itga5) pathway. Itga5 promotes ADSC osteogenic differentiation and miR-326-5p suppresses Itga5 translation. CircRNA-vgll3 directly sequesters miR-326-5p in the cytoplasm and inhibits its activity to promote osteogenic differentiation. Moreover, the therapeutic potential of circRNA-vgll3-modified ADSCs with calcium phosphate cement (CPC) scaffolds was systematically evaluated in a critical-sized defect model in rats. Our results demonstrate that circRNA-vgll3 markedly enhances new bone formation with upregulated bone mineral density, bone volume/tissue volume, trabeculae number, and increased new bone generation. This study reveals the important role of circRNA-vgll3 during new bone biogenesis. Thus, circRNA-vgll3 engineered ADSCs may be effective potential therapeutic targets for bone regenerative medicine.

Reactivity of the sulfhydryl groups of soluble succinate dehydrogenase

Soluble succinate dehydrogenase prepared by butanol extraction reacts with N-ethylmaleimide according to first-order kinetics with respect to both remaining active enzyme and the inhibitor concentration. Binding of the sulfhydryl groups of the enzyme prevents its alkylation by N-ethylmaleimide and inhibition by oxaloacetate. A kinetic analysis of the inactivation of alkylating reagent in the presence of succinate or malonate suggests that N-ethylmaleimide acts as a site-directed inhibitor. The apparent first-order rate constant of alkylation increases between pH 5.8 and 7.8 indicating a pKa value for the enzyme sulfhydryl group equal to 7.0 at 22 degrees C in 50 mM Tris-sufate buffer. Certain anions (phosphate, citrate, maleate and acetate) decrease the reactivity of the enzyme towards the alkylating reagent. Succinate/phenazine methosulfate reductase activity measured in the presence of a saturating concentration of succinate shows the same pH-dependence as the alkylation rate by N-ethylmaleimide. The mechanism of the first step of succinate oxidation, including a nucleophilic attack of substrate by the active-site sulfhydryl group, is discussed.

Affinity chromatography of succinate dehydrogenase from the membranes of Micrococcus lysodeikticus

Isolated plasma membranes of Micrococcus lysodeikticus were subjected to extraction with n-butanol in a two-phase system. Succinate dehydrogenase obtained in the soluble aqueous phase after high-speed centrifugation was resolved by separation on calcium phosphate gel and affinity chromatography. The affinity ligand used was oxaloacetate and elution from the column was achieved with 0.5 M succinate. In the final product there was an eleven-fold reduction in the 32P-lipid to protein ratio and a fourteen-fold increase in specific activity relative to the high speed supernatant fraction following n-butanol extraction.