Measuring transcription factor function with cell type-specific somatic transgenesis in chicken embryos.

Retroviral-mediated misexpression in chicken embryos has been a powerful research tool for developmental biologists in the last two decades. In the RCASBP retroviral vectors that are widely used for in vivo somatic transgenesis, a coding sequence of interest is under the transcriptional control of a strong viral promoter in the long terminal repeat. While this has proven to be effective for studying secreted signalling proteins, interpretation of the mechanisms of action of nuclear factors is more difficult using this system since it is not clear whether phenotypic effects are cell-autonomous or not, and therefore whether they represent a function of the endogenous protein. Here, we report the consequences of retroviral expression using the RCANBP backbone, in which the transcription factor Dlx5 is expressed under the control of chondrocyte-specific regulatory sequences from the Col2a1 gene. To our knowledge, this is the first demonstration of a tissue-specific phenotype in the chicken embryo.

RCAN family member 3 deficiency contributes to noncompaction of the ventricular myocardium.

Noncompaction of the ventricular myocardium (NVM), the third most diagnosed cardiomyopathy, is characterized by prominent trabeculae and intratrabecular recesses. However, the genetic etiology of 40%-60% of NVM cases remains unknown. Here, we identify two infants with NVM, in a nonconsanguineous family, with a typical clinical presentation of persistent bradycardia since the prenatal period. A homozygous missense variant (R223L) of RCAN family member 3 (RCAN3) is detected in both infants using whole-exome sequencing. In the zebrafish model, marked cardiac dysfunction is detected in rcan3 deficiency (MO-rcan3ATG-injected) and rcan-/- embryos. Developmental dysplasia of both endocardial and myocardial layers is also detected in rcan3-deficient embryos. RCAN3 R223L variant mRNAs can not rescue heart defects caused by rcan3 knockdown or knockout; however, hRCAN3 mRNAs rescue these phenotypes. RNA-seq experiments show that several genes involved in cardiomyopathies are significantly regulated through multiple signaling pathways in the rcan3-knockdown zebrafish model. In human cardiomyocytes, RCAN3 deficiency results in reduced proliferation and increased apoptosis, together with an abnormal mitochondrial ultrastructure. Thus, we suggest that RCAN3 is a susceptibility gene for cardiomyopathies, especially NVM and that the R223L mutation is a potential loss-of-function variant.

Nsp1 facilitates SARS-CoV-2 replication through calcineurin-NFAT signaling.

SARS-CoV-2, the causative agent of COVID-19, has been intensely studied in search of effective antiviral treatments. The immunosuppressant cyclosporine A (CsA) has been suggested to be a pan-coronavirus inhibitor, yet its underlying mechanism remained largely unknown. Here, we found that non-structural protein 1 (Nsp1) of SARS-CoV-2 usurped CsA-suppressed nuclear factor of activated T cells (NFAT) signaling to drive the expression of cellular DEAD-box helicase 5 (DDX5), which facilitates viral replication. Nsp1 interacted with calcineurin A (CnA) to displace the regulatory protein regulator of calcineurin 3 (RCAN3) of CnA for NFAT activation. The influence of NFAT activation on SARS-CoV-2 replication was also validated by using the Nsp1-deficient mutant virus. Calcineurin inhibitors, such as CsA and VIVIT, inhibited SARS-CoV-2 replication and exhibited synergistic antiviral effects when used in combination with nirmatrelvir. Our study delineated the molecular mechanism of CsA-mediated inhibition of SARS-CoV-2 replication and the anti-SARS-CoV-2 action of calcineurin inhibitors. IMPORTANCE: Cyclosporine A (CsA), commonly used to inhibit immune responses, is also known to have anti-SARS-CoV-2 activity, but its mode of action remains elusive. Here, we provide a model to explain how CsA antagonizes SARS-CoV-2 through three critical proteins: DDX5, NFAT1, and Nsp1. DDX5 is a cellular facilitator of SARS-CoV-2 replication, and NFAT1 controls the production of DDX5. Nsp1 is a viral protein absent from the mature viral particle and capable of activating the function of NFAT1 and DDX5. CsA and similar agents suppress Nsp1, NFAT1, and DDX5 to exert their anti-SARS-CoV-2 activity either alone or in combination with Paxlovid.

Suppression of RCAN1 alleviated lipid accumulation and mitochondrial fission in diabetic cardiomyopathy.

BACKGROUND: Although metabolic disturbance is a characteristic of diabetic cardiomyopathy (DbCM), the detailed pathogenesis of DbCM remains unknown. METHODS: We used a heart transplantation (HTx) cohort to explore the effect of diabetes mellitus on heart failure (HF) progression dependent of myocardium. Microscopic and ultramicroscopic pathology were used to depict the pathological features of human myocardium of DbCM. We performed targeted metabolomics to characterize the metabolic phenotype of human DbCM. Transcriptomics data were analyzed and weighted gene co-expression network analysis was performed to explore the potential upstream regulator for metabolic remodeling of DbCM. In vivo and in vitro experiments were further conducted to demonstrate the therapeutic effects and molecular mechanisms. RESULTS: DbCM promoted the progression of HF and increased death or HF-rehospitalization after HTx. Lipid accumulation and mitochondrial fission were the obvious pathological features of DbCM myocardium. The concentrations of C14:0-CoA and C16:1-CoA were significantly increased in the myocardium, and they were positively correlated with the accelerated HF progression and RCAN1 expression in DbCM patients. Knockdown of RCAN1 improved cardiac dysfunction, lipid accumulation, and mitochondrial fission in db/db mice. In vitro studies showed that RCAN1 knockdown improved mitochondrial dysfunction in DbCM cardiomyocytes via the RCAN1-p-Drp1 Ser616 axis. CONCLUSIONS: Diabetes is associated with faster progression of HF and causes poor prognosis after HTx, accompanied by metabolic remodeling in the myocardium. Accumulation of long chain acyl-CoA in the myocardium is the metabolic hallmark of human DbCM and is associated with more rapid disease progression for DbCM patients. Upregulation of RCAN1 in the myocardium is associated with the metabolic signatures of DbCM and RCAN1 is a potential therapeutic target for DbCM.

TMB Signature-Related RCAN2 Promotes Apoptosis by Upregulating EHF/DR5 Pathway in Hepatocellular Carcinoma.

BACKGROUND: The tumour mutation burden (TMB) is a valuable indicator of the accumulation of somatic mutations, and is thought to be associated with the biological behaviour and prognosis of tumours. However, the related genetic mechanism for these association is still unclear. The aim of the present study was to identify the key gene(s) associated with TMB in hepatocellular carcinoma (HCC) and to investigate its biological functions, downstream transcription factors, and mechanism of action. METHODS: Patients in The Cancer Genome Atlas-Liver Hepatocellular Carcinoma (TCGA-LIHC) database were classified according to TMB signature-related genes. Key genes related to the TMB signature and tumour prognosis were identified. Immunohistochemistry and Quantitative Real-Time Polymerase Chain Reaction (qPCR) were then used to assess gene expression in clinical HCC tissues and HCC cells. Cells with altered gene expression were evaluated for the effect on cell proliferation and apoptosis, both in vitro and in vivo. Three independent databases and cell sequencing data were used to identify the mechanisms involved and the downstream transcription factors. The mechanism was also studied by altering the expression of downstream transcription factors in vitro. RESULT: The integrated cluster (IC) 2 group, characterized by 99 TMB signature-related genes, showed a significant different TMB score compared to the IC1 group (p < 0.001), as well as more favourable tumour prognosis (p = 0.031). We identified five key prognostic genes that were differentially expressed between IC2 and IC1 and were associated with overall survival. The expression of one of these key prognostic genes, RCAN2, was negatively correlated with TMB in 18 out of 33 tumour types examined. A high level of RCAN2 was correlated with better overall survival in HCC (p = 0.0009). Overexpression of RCAN2 enhanced apoptosis in vitro and in vivo, whereas knockdown of RCAN2 attenuated apoptosis. The mechanism by which RCAN2 promotes apoptosis may involve upregulation of the expression of ETS homologous factor (EHF) and of death receptor 5 (DR5). CONCLUSIONS: Downregulation of RCAN2 expression was found to correlate with elevated TMB in multiple cancer types. RCAN2 was also found to be a biomarker of HCC prognosis, and to promote the apoptosis of HCC cells through the EHF/DR5 pathway. These findings provide a new perspective on systemic treatment for advanced HCC with a high TMB.

Calcineurin-NFAT dynamics correspond to cardiac remodeling during aortic banding and debanding, mimicking aortic valve replacement.

Aortic valve stenosis (AS) is a major health problem. Extensive myocardial remodeling increases operative risk and might lead to incomplete reverse remodeling with persistent symptoms after aortic valve replacement (AVR); this makes the optimal timing of AVR a clinical challenge. The pathogenesis behind incomplete reverse remodeling is unclear. Central among signaling pathways in the remodeling heart is the pro-hypertrophic Ca2+-activated calcineurin and its downstream nuclear factor of activated T-cell (NFATc1-c4) transcription factors. We investigated calcineurin-NFATc dynamics in patient and mouse hearts during remodeling and reverse remodeling. Myocardial biopsies were obtained from AS patients during AVR and left ventricles harvested from mice subjected to aortic banding (AB) and debanding (DB). The transcript and protein of the NFATc-responsive gene regulator of calcineurin 1-4 (RCAN1-4) and luciferase activity in NFAT-luciferase mice were used as read-outs for calcineurin-NFATc activity. Calcineurin-NFATc activation was sustained through AB 24 h to 18 weeks and elevated in AS patients. All four NFATc isoforms were elevated in AS, while NFATc4 was persistently elevated during chronic remodeling after AB in mice. NFAT activation remained reversible when 1 week's AB was followed by 1 week's DB and accompanied functional improvement. However, when DB for 1 week followed AB for 4 weeks, NFAT activation was not reversed. In conclusion, calcineurin-NFAT dynamics correspond with cardiac remodeling and reverse remodeling during experimental AB and DB. Our data suggest that calcineurin-NFATc attenuation is important for reverse remodeling and outcomes after AVR for AS.