Cytochrome cM Is Probably a Membrane Protein Similar to the C Subunit of the Bacterial Nitric Oxide Reductase

Cytochrome cM was first described in 1994 and its sequence has been found in the genome of manifold cyanobacterial species ever since. Numerous studies have been carried out with the purpose of determining its function, but none of them has given place to conclusive results so far. Many of these studies are based on the assumption that cytochrome cM is a soluble protein located in the thylakoid lumen of cyanobacteria. In this work, we have reevaluated the sequence of cytochrome cM, with our results showing that its most probable 3D structure is strongly similar to that of the C subunit of the bacterial nitric oxide reductase. The potential presence of an α-helix tail, which could locate this protein in the thylakoid membrane, further supports this hypothesis, thus providing a new, unexpected role for this redox protein.

Demyristoylation of the Cytoplasmic Redox Protein Trx-h2 Is Critical for Inducing a Rapid Cold Stress Response in Plants

In Arabidopsis, the cytosolic redox protein thioredoxin h2 (Trx-h2) is anchored to the cytoplasmic endomembrane through the myristoylated second glycine residue (Gly2). However, under cold stress, the cytosolic Trx-h2 is rapidly translocated to the nucleus, where it interacts with and reduces the cold-responsive C-repeat-binding factors (CBFs), thus activating cold-responsive (COR) genes. In this study, we investigated the significance of fatty acid modification of Trx-h2 under cold conditions by generating transgenic Arabidopsis lines in the trx-h2 mutant background, overexpressing Trx-h2 (Trx-h2OE/trx-h2) and its point mutation variant Trx-h2(G/A) [Trx-h2(G/A)OE/trx-h2], in which the Gly2 was replaced by alanine (Ala). Due to the lack of Gly2, Trx-h2(G/A) was incapable of myristoylation, and a part of Trx-h2(G/A) localized to the nucleus even under warm temperature. As no time is spent on the demyristoylation and subsequent nuclear translocation of Trx-h2(G/A) under a cold snap, the ability of Trx-h2(G/A) to protect plants from cold stress was greater than that of Trx-h2. Additionally, COR genes were up-regulated earlier in Trx-h2(G/A)2OE/trx-h2 plants than in Trx-h2OE/trx-h2 plants under cold stress. Consequently, Trx-h2(G/A)2OE/trx-h2 plants showed greater cold tolerance than Col-0 (wild type) and Trx-h2OE/trx-h2 plants. Overall, our results clearly demonstrate the significance of the demyristoylation of Trx-h2 in enhancing plant cold/freezing tolerance.

ENOX2 NADH Oxidase: A BCR-ABL1-dependent cell surface and secreted redox protein in chronic myeloid leukemia (CML)

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm caused by the acquisition of BCR-ABL1 fusion in a hematopoietic stem cell. We identified the ENOX2 gene as up-regulated in BCR-ABL1-expressing UT-7 cell lines through a transcriptome assay. The oncofoetal ENOX2 protein (Ecto-Nicotinamide Adenine Dinucleotide Oxidase Disulfide Thiol Exchanger 2) is expressed on the external plasma membrane surface of cancer cells and can be released in cancer patients’ serum. Considering these data, we studied ENOX2 expression in CML cell lines and patients using quantitative RT-PCR, western-blots, the ELISA method, and transcriptomic dataset reanalysis. We confirmed increased ENOX2 mRNA expression in the BCR-ABL1-expressing UT-7 cell line. Comparable results were obtained in CML patients at diagnosis. Western-blot analyses on UT-7 and TET-inducible Ba/F3 cell lines established the up-regulation of ENOX2 protein. BCR-ABL1 has been found to induce ENOX2 overexpression in a kinase-dependent manner. In a series of 41 patients with CML, ELISA assays showed a highly significant increase of ENOX2 protein levels in the plasma of patients with CML (p < 0.0001) as compared to controls (n=28). Transcriptomic dataset (GSE4170) reanalyzes have shown specific ENOX2 mRNA overexpression in the chronic phase of the disease. Bioinformatic analyses identified several genes whose mRNA expression was positively correlated to ENOX2. Some of them encode proteins involved in cellular functions compatible with the growth deregulation observed in CML. All in all, our results demonstrate for the first time the upregulation of a secreted Redox protein in a BCR-ABL1-dependent manner in CML. Our data suggest that ENOX2 (through its transcriptional program) plays a significant role in the BCR-ABL1 leukemogenesis. Further studies are required to clarify the relationship between BCR-ABL1 and ENOX2.

Redox protein Memo1 coordinates FGF23-driven signaling and small Rho-GTPases in the mouse kidney

Memo promotes receptor tyrosine kinase (RTK) signaling by unknown mechanisms. Memo1 deletion in mice causes premature aging and unbalanced metabolism partially resembling Fgf23 and Klotho loss-of-function animals. Here, we report a role for Memo’s redox function in FGF23-driven RTK signaling in the kidney. Postnatally Memo-deficient (cKO) and floxed controls were treated with FGF23 or vehicle, followed by molecular and biochemical analyses. Findings were validated using cell culture and recombinant proteins. Memo cKO mice showed impaired renal ERK phosphorylation and transcriptional responses to FGF23. Redox proteomics revealed excessive thiols of Rho-GDP dissociation inhibitor 1 (Rho-GDI1). Renal RhoA abundance and activity were increased in Memo cKO. Immunoprecipitation analysis showed an association between Memo and Rho-GDI1. We confirmed an interaction between the two proteins, with Memo-dependent irreversible oxidation at Rho-GDI1 Cys79 in cell-free conditions. Collectively, our findings reveal that redox protein Memo promotes renal FGF23 signaling together with oxidative modulation of the Rho-GTPase network.