Molecular Regulation of Transforming Growth Factor-ß1-induced Thioredoxin-interacting Protein Ubiquitination and Proteasomal Degradation in Lung Fibroblasts: Implication in Pulmonary Fibrosis.

Thioredoxin-interacting protein (TXNIP) plays a critical role in regulation of cellular redox reactions and inflammatory responses by interacting with thioredoxin (TRX) or the inflammasome. The role of TXNIP in lung fibrosis and molecular regulation of its stability have not been well studied. Therefore, here we investigated the molecular regulation of TXNIP stability and its role in TGF-ß1-mediated signaling in lung fibroblasts. TXNIP protein levels were significantly decreased in lung tissues from bleomycin-challenged mice. Overexpression of TXNIP attenuated transforming growth factor-ß1 (TGF-ß1)-induced phosphorylation of Smad2/3 and fibronectin expression in lung fibroblasts, suggesting that decrease in TXNIP may contribute to the pathogenesis of lung fibrosis. Further, we observed that TGF-ß1 lowered TXNIP protein levels, while TXNIP mRNA levels were unaltered by TGF-ß1 exposure. TGF-ß1 induced TXNIP degradation via the ubiquitin-proteasome system. A serine residue mutant (TNXIP-S308A) was resistant to TGF-ß1-induced degradation. Furthermore, downregulationof ubiquitin-specific protease-13 (USP13) promoted the TGF-ß1-induced TXNIP ubiquitination and degradation. Mechanistic studies revealed that USP13 targeted and deubiquitinated TXNIP. The results of this study revealed that the decrease of TXNIP in lungs apparently contributes to the pathogenesis of pulmonary fibrosis and that USP13 can target TXNP for deubiquitination and regulate its stability.

The deubiquitinase USP40 preserves endothelial integrity by targeting the heat shock protein HSP90ß.

Endothelial cell (EC) barrier disruption and inflammation are the pathological hallmarks of vascular disorders and acute infectious diseases and related conditions, including the coronavirus disease 2019 (COVID-19) and sepsis. Ubiquitination plays a critical role in regulating the stability, intracellular trafficking, and enzymatic activity of proteins and is reversed by deubiquitinating enzymes (DUBs). The role of DUBs in endothelial biology is largely unknown. In this study, we report that USP40, a poorly characterized DUB, prevents EC barrier disruption through reductions in the activation of RhoA and phosphorylation of myosin light chain (MLC) and cofilin. Furthermore, USP40 reduces EC inflammation through the attenuation of NF-ĸB activation, ICAM1 expression, and leukocyte-EC adhesion. We further show that USP40 activity and expression are reduced in response to endotoxin challenge. Global depletion of USP40 and EC-targeted USP40 depletion in mice exacerbated experimental lung injury, whereas lentiviral gene transfer of USP40 protected against endotoxin-induced lung injury. Using an unbiased approach, we discovered that the protective effect of USP40 occurs through the targeting of heat shock protein 90ß (HSP90ß) for its deubiquitination and inactivation. Together, these data reveal a critical protective role of USP40 in vascular injury, identifying a unique mechanistic pathway that profoundly impacts endothelial function via DUBs.

USP13 regulates cell senescence through mediating MDM2 stability.

AIMS: Lung aging results in altered lung function, reduced lung remodeling and regenerative capacity, and increased susceptibility to acute and chronic lung diseases. The molecular and physiological underlying mechanisms of lung aging remain unclear. Mounting evidence suggests that deubiquitinating enzymes (DUBs) play a critical role in tissue aging and diseases through regulation of cellular signaling pathways. Here we investigate the role of Ubiquitin-Specific Protease 13 (USP13) in cell senescence and lung aging and its underlying mechanisms. MAIN METHODS: Protein levels of USP13 and MDM2 in lung tissues from aged and young mice were compared. Gene silencing and overexpression of USP13 in human cell lines were performed. MDM2 levels were examined by Quantitative Real-Time PCR and Western blotting analysis. The cell senescence levels of human cells were checked by the ß-galactosidase staining. KEY FINDINGS: Lung tissues from aged mice showed higher levels of USP13 compared to younger mice. We found a negative correlation between USP13 and MDM2 expression in lung tissues of aged mice. The increased protein levels of MDM2 were detected in lung tissues of USP13 deficient mice. Furthermore, overexpression of USP13 promoted cell senescence. Knockdown of USP13 increased MDM2 levels in lung cells, while overexpression of USP13 reduced it. The degradation of MDM2 caused by USP13 was prevented by the proteasome inhibitor MG132. Furthermore, we showed that USP13 targeted and reduced K63-linked polyubiquitination of MDM2. These results demonstrate that USP13 is involved in the aging signaling pathway in lungs through regulation of MDM2.

ISGylation of NF-κBp65 by SCFFBXL19 E3 Ligase Diminishes Endothelial Inflammation.

BACKGROUND: NF-κB (nuclear factor kappa B) plays a pivotal role in endothelial cell (EC) inflammation. Protein ISGylation is regulated by E3 ISG15 (interferon-stimulated gene 15) ligases; however, ISGylation of NF-κBp65 and its role in EC functions have not been investigated. Here, we investigate whether p65 is ISGylated and the role of its ISGylation in endothelial functions. METHODS: In vitro ISGylation assay and EC inflammation were performed. EC-specific transgenic mice were utilized in a murine model of acute lung injury. RESULTS: We find that NF-κBp65 is ISGylated in resting ECs and that the posttranslational modification is reversible. TNFα (tumor necrosis factor alpha) and endotoxin stimulation of EC reduce p65 ISGylation, promoting its serine phosphorylation through reducing its association with a phosphatase WIP1 (wild-type p53-induced phosphatase 1). Mechanistically, an SCF (Skp1-Cul1-F-box) protein E3 ligase SCFFBXL19 is identified as a new ISG15 E3 ligase that targets and catalyzes ISGylation of p65. Depletion of FBXL19 (F-box and leucine-rich repeat protein 19) increases p65 phosphorylation and EC inflammation, suggesting a negative correlation between p65 ISGylation and phosphorylation. Moreover, EC-specific FBXL19 overexpressing humanized transgenic mice exhibit reduced lung inflammation and severity of experimental acute lung injury. CONCLUSIONS: Together, our data reveal a new posttranslational modification of p65 catalyzed by a previously unrecognized role of SCFFBXL19 as an ISG15 E3 ligase that modulates EC inflammation.

Nedd4L suppression in lung fibroblasts facilitates pathogenesis of lung fibrosis.

Ubiquitination-mediated protein degradation is associated with the development of pulmonary fibrosis. We and others have shown that Nedd4L plays anti-inflammatory and anti-fibrotic roles by targeting lysophosphatidic acid receptor 1 (LPAR1), p-Smad2/3, and ß-catenin, and other molecules for their degradation in lung epithelial cells and fibroblasts. However, the molecular regulation of Nedd4L expression in lung fibroblasts has not been studied. In this study, we find that Nedd4L levels are significantly suppressed in lung myofibroblasts in IPF patients and in experimental pulmonary fibrosis, and in TGF-ß1-treated lung fibroblasts. Nedd4L knockdown promotes TGF-ß1-mediated phosphorylation of Smad2/3 and lung myofibroblast differentiation. Mechanistically, Nedd4L targets TGF-ß receptor II (TßRII), the first key enzyme of TGF-ß1-mediated signaling, for its ubiquitination and degradation. Further, we show that inhibition of transcriptional factor E2F rescues Nedd4L levels and mitigates experimental pulmonary fibrosis. Together, our data reveal insight into mechanisms by which E2F-mediated Nedd4L suppression contributes to the pathogenesis of lung fibrosis. This study provides evidence showing that upregulation of Nedd4L is a potential therapeutic strategy to treat fibrotic disorders including lung fibrosis.

Molecular Regulation of Heme Oxygenase-1 Expression by E2F Transcription Factor 2 in Lung Fibroblast Cells: Relevance to Idiopathic Pulmonary Fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a fatal chronic lung disease. Heme oxygenase-1 (HMOX1/HO-1) is an enzyme that catalyzes the degradation of heme. The role of HO-1 in the pathogenesis of IPF has been studied; however, the molecular regulation of HO-1 and its role in IPF are still unclear. In this study, we found that HO-1 protein levels significantly increased in lung myofibroblasts in IPF patients and in lungs in a murine model of bleomycin-induced lung fibrosis. In addition, we observed that administration of a E2F transcription factor inhibitor elevated HO-1 mRNA and protein levels in lung fibroblasts. Downregulation of E2F2 by siRNA transfection increased HO-1 mRNA and protein levels, while overexpression of E2F2 reduced HO-1 levels. However, overexpression of E2F2 did not alter hemin-induced HO-1 protein levels. Furthermore, modulation of HO-1 levels regulated TGF-ß1-induced myofibroblast differentiation without altering the phosphorylation of Smad2/3 in lung fibroblast cells. Moreover, the phosphorylation of protein kinase B (Akt) was significantly upregulated in HO-1-depleted lung fibroblast cells. In summary, this study demonstrated that E2F2 regulates the baseline expression of HO-1, but has no effect on modulating HO-1 expression by hemin. Finally, elevated HO-1 expression contributes to the TGF-ß1-induced lung myofibroblast differentiation through the activation of the serine/threonine kinase AKT pathway. Overall, our findings suggest that targeting E2F2/HO-1 might be a new therapeutic strategy to treat fibrotic diseases such as IPF.

A blocking peptide stabilizes lysophosphatidic acid receptor 1 and promotes lysophosphatidic acid-induced cellular responses.

G protein-coupled receptors regulate a variety of cellular responses and have been considered as therapeutic targets for human diseases. Lysophosphatidic acid receptor 1 (LPA1) is a receptor for bioactive lysophospholipid, LPA. LPA/LPA1-mediated signaling contributes to inflammatory and fibrotic responses in lung diseases; thus understanding regulation of LPA1 stability is important for modulating LPA/LPA1 signaling. Our previous study has shown that LPA1 is degraded in the Nedd4 like (Nedd4L) E3 ubiquitin ligase-mediated ubiquitin-proteasome system. In the current study, we attempt to identify a peptide that stabilizes LPA1 through disrupting LPA1 association with Nedd4L. LPA treatment induces both endogenous and overexpressed LPA1 degradation, which is attenuated by a proteasome inhibitor, suggesting that LPA1 is degraded in the proteasome. LPA increases phosphorylation of extracellular signal-regulated kinase 1/2 (Erk1/2) and I-κB kinase in lung epithelial cells, and this effect is promoted by overexpression of a peptide (P1) that mimics C-terminal of LPA1. P1, not a control peptide, attenuates LPA-induced LPA1 ubiquitination and degradation, suggesting that P1 stabilizes LPA1. Further, P1 diminishes Nedd4L-mediated degradation of LPA1 and Nedd4L/LPA1 association. In addition to increasing LPA1 signaling, P1 enhances LPA-induced cell migration and gene expression of Elafin, matrix metallopeptidase 1, and serpin family B member 2 in lung epithelial cells. These data suggest that disruption of LPA1 interaction with Nedd4L by P1 increases LPA1 stability and LPA/LPA1 signaling.

IL-37-induced activation of glycogen synthase kinase 3ß promotes IL-1R8/Sigirr phosphorylation, internalization, and degradation in lung epithelial cells.

Interleukin (IL)-37 diminishes a variety of inflammatory responses through ligation to its receptor IL-1R8/Sigirr. Sigirr is a Toll like receptor/IL-1R family member. We have shown that Sigirr is not stable in response to IL-37 treatment. IL-37-induced Sigirr degradation is mediated by the ubiquitin-proteasome system, and the process is reversed by a deubiquitinase, USP13. However, the molecular mechanisms by which USP13 regulates Sigirr stability have not been revealed. In this study, we investigate the roles of glycogen synthesis kinase 3ß (GSK3ß) in Sigirr phosphorylation and stability. IL-37 stimulation induced Sigirr phosphorylation and degradation, as well as activation of GSK3ß. Inhibition of GSK3ß attenuated IL-37-induced Sigirr phosphorylation, while exogenous expressed GSK3ß promoted Sigirr phosphorylation at threonine (T)372 residue. Sigirr association with GSK3ß was detected. Amino acid residues 51-101 in GSK3ß were identified as the Sigirr binding domain. These data indicate that GSK3ß mediates IL-37-induced threonine phosphorylation of Sigirr. Further, we investigated the role of GSK3ß-mediated phosphorylation of Sigirr in Sigirr degradation. Inhibition of GSK3ß attenuated IL-37-induced Sigirr degradation, while T372 mutant of Sigirr was resistant to IL-37-mediated degradation. Furthermore, inhibition of Sigirr phosphorylation prevented Sigirr internalization and association with USP13, suggesting GSK3ß promotes Sigirr degradation through disrupting Sigirr association with USP13.

Lipopolysaccharide reduces USP13 stability through c-Jun N-terminal kinase activation in Kupffer cells.

Protein ubiquitination regulates protein stability, cellular localization, and enzyme activity. Deubiquitinases catalyze the removal of ubiquitin from target proteins and reverse ubiquitination. USP13, a deubiquitinase, has been shown to regulate a variety of cellular responses including inflammation; however, the molecular regulation of USP13 has not been demonstrated. In this study, we revealed that USP13 is degraded in response to lipopolysaccharide (LPS) in Kupffer cells. USP13 levels are significantly decreased in inflamed organs, including liver tissues from septic mice. LPS reduces USP13 protein stability, not transcription, in Kupffer cells. Furthermore, LPS increases USP13 polyubiquitination. Inhibition of proteasome, but not lysosome or immunoproteasome, attenuates LPS-induced USP13 degradation, suggesting USP13 degradation is mediated by the ubiquitin-proteasome system. A catalytically inactive form of USP13 exhibits similar degree of degradation compared with USP13 wild-type, suggesting that USP13 degradation is not dependent on its activity. Furthermore, USP13 degradation is dependent on new protein synthesis. Inhibition of c-Jun N-terminal kinase (JNK) attenuates USP13 degradation, indicating that JNK-dependent new protein synthesis is necessary for USP13 degradation. This study reveals a molecular mechanism of regulation of USP13 degradation in Kupffer cells in response to bacterial endotoxin.

Traditional Chinese Medicine as Potential Therapy for COVID-19.

In December 2019, a novel coronavirus SARS-CoV-2, causing the disease COVID-19, spread from Wuhan throughout China and has infected people over 200 countries. Thus far, more than 3,400,000 cases and 240,000 deaths have occurred worldwide, and the coronavirus pandemic continues to grip the globe. While numbers of cases in China have been steadying, the number of infections outside China is increasing at a worrying pace. We face an urgent need to control the spread of the COVID-19 epidemic, which is currently expanding to a global pandemic. Efforts have focused on testing antiviral drugs and vaccines, but there is currently no treatment specifically approved. Traditional Chinese medicine (TCM) is grounded in empirical observations and the Chinese people use TCM to overcome these sorts of plagues many times in thousands of years of history. Currently, the Chinese National Health Commission recommended a TCM prescription of Qing-Fei-Pai-Du-Tang (QFPDT) in the latest version of the "Diagnosis and Treatment guidelines of COVID-19" which has been reported to provide reliable effects for COVID-19. While doubts about TCM still exist today, this review paper will describe the rationalities that QFPDT is likely to bring a safe and effective treatment of COVID-19.