The reversal effect of albiflorin on multidrug resistance of human ovarian cancer and its mechanism / 中国药理学通报

Aim To study the reversal effect of albiflorin(AL)on multidrug resistance of human ovarian cancer and the potential mechanism. Methods The drug resistance reversal effect of AL on SKOV3/DDP cells was detected by CCK-8 kit,and the effect of AL on P-glycoprotein(P-gp)function was detected by flow cytometry. The effects of AL on MYC,WWP1 and ABCB1 in SKOV3/DDP cells were detected by RT-qPCR and Western blot. The MYC-knockdown SKOV3/DDP cell line was constructed by RNA interference technology,and its drug resistance,P-gp function and related gene and protein expression changes were investigated. Results AL had a drug resistance reversal effect on SKOV3/DDP cells and a concentration-dependent inhibitory effect on P-gp function. The inhibitory effects of AL 25,50 and 100 μmol·L-1 on ABCB1/P-gp,MYC and WWP1 were gradually enhanced. The inhibitory effect of MYCi975,a MYC inhibitor,on ABCB1/P-gp,MYC and WWP1 was stronger than or equivalent to that of AL 100 μmol·L-1 group. After knockdown of MYC in SKOV3/DDP cells,cell drug resistance,P-gp function,and related gene and protein expression were inhibited. Conclusions The drug resistance reversal effect of AL on SKOV3/DDP cells may be related to the inhibition of P-gp function and the expression of ABCB1/P-gp,MYC and WWP1,which provides an experiment base for the development of AL as a drug resistance reversal agent for the clinical treatment of ovarian cancer.

The F-box-only protein 44 regulates pregnane X receptor protein level by ubiquitination and degradation

Pregnane X receptor (PXR) is a ligand-activated nuclear receptor that transcriptionally upregulates drug-metabolizing enzymes [e.g., cytochrome P450 3A4 (CYP3A4)] and transporters. Although the regulation of PXR target genes is well-characterized, less is known about the regulation of PXR protein level. By screening an RNAi library, we identified the F-box-only protein 44 (FBXO44) as a novel E3 ligase for PXR. PXR abundance increases upon knockdown of FBXO44, and, inversely, decreases upon overexpression of FBXO44. Further analysis revealed that FBXO44 interacts with PXR, leading to its ubiquitination and proteasomal degradation, and we determined that the F-box associated domain of FBXO44 and the ligand binding domain of PXR are required for the functional interaction. In summary, FBXO44 regulates PXR protein abundance, which has downstream consequences for CYP3A4 levels and drug-drug interactions. The results of this study provide new insight into the molecular mechanisms that regulate PXR protein level and activity and suggest the importance of considering how modulating E3 ubiquitin ligase activities will affect PXR-mediated drug metabolism.

TRIB3 promotes pulmonary fibrosis through inhibiting SLUG degradation by physically interacting with MDM2

Pulmonary fibrosis (PF) is the pathological structure of incurable fibroproliferative lung diseases that are attributed to the repeated lung injury-caused failure of lung alveolar regeneration (LAR). Here, we report that repetitive lung damage results in a progressive accumulation of the transcriptional repressor SLUG in alveolar epithelial type II cells (AEC2s). The abnormal increased SLUG inhibits AEC2s from self-renewal and differentiation into alveolar epithelial type I cells (AEC1s). We found that the elevated SLUG represses the expression of the phosphate transporter SLC34A2 in AEC2s, which reduces intracellular phosphate and represses the phosphorylation of JNK and P38 MAPK, two critical kinases supporting LAR, leading to LAR failure. TRIB3, a stress sensor, interacts with the E3 ligase MDM2 to suppress SLUG degradation in AEC2s by impeding MDM2-catalyzed SLUG ubiquitination. Targeting SLUG degradation by disturbing the TRIB3/MDM2 interaction using a new synthetic staple peptide restores LAR capacity and exhibits potent therapeutic efficacy against experimental PF. Our study reveals a mechanism of the TRIB3-MDM2-SLUG-SLC34A2 axis causing the LAR failure in PF, which confers a potential strategy for treating patients with fibroproliferative lung diseases.

Recent progress in targeting degradation of FAK based on PROTAC / 药学学报

Local focal adhesion kinase (FAK) is a non-receptor intracellular tyrosine kinase that plays an important role in tumor initiation, development, metastasis and invasion, and is considered to be an important target for the development of antineoplastic drugs. It has both kinase-dependent and non-kinase-dependent scaffolding functions. However, traditional small molecular inhibitors can only inhibit its kinase-dependent activity, so it is difficult to target the kinase-independent scaffolding function. Therefore, there is an urgent need for novel strategies to enhance FAK targeting to lay the foundation for determining the druggability and discovery of FAK inhibitors. Proteolysis targeting chimera (PROTAC) is a new drug development strategy that can recruit E3 ligase to specifically ubiquitinylate target proteins for degradation through the proteasome system. The unique mechanism of action of the PROTAC system could be used to target and degrade the FAK protein, thus eliminating the scaffolding function of FAK. In this review, FAK protein, the signaling pathway, and small molecule inhibitors are briefly described, and the latest research progress in targeting the degradation of FAK using PROTAC technology is summarized.

TRIB3‒GSK-3

Pulmonary fibrosis (PF) is a chronic, progressive, fatal interstitial lung disease with limited available therapeutic strategies. We recently reported that the protein kinase glycogen synthase kinase-3

Ubiquitin E3 Ligase Pellino-1 Inhibits IL-10-mediated M2c Polarization of Macrophages, Thereby Suppressing Tumor Growth

Pellino-1 is a ubiquitin (Ub) E3 ligase that plays a role in M1, but not M2a polarization of macrophages. However, it is unknown whether Pellino-1 regulates IL-10-mediated M2c polarization of macrophages. Here, we found that Pellino-1 attenuated tumor growth by inhibiting M2c polarization of macrophages. Upon IL-10 stimulation, Pellino-1-deificient bone marrow-derived macrophages (BMDMs) showed higher expression of M2c markers, but not M2a, and M2b markers than wild-type (WT) BMDMs, indicating that Pellino-1 inhibits M2c polarization of macrophages. Pellino-1-deficient BMDMs exhibited a defect in mitochondria respiration, but enhancement of glycolysis during M2c polarization. During M2c polarization of macrophages, Pellino-1 increased STAT1 phosphorylation via K63-linked ubiquitination of IL-1 receptor associated kinase 1 (IRAK1). Furthermore, Lysm-CrePellino-1(fl/fl) mice showed enhancement of tumor growth via regulating M2c polarization of tumor-associated macrophages. These results demonstrate that Pellino-1 inhibits IL-10-induced M2c macrophage polarization via K63-linked ubiquitination of IRAK1 and activation of STAT1, thereby inhibiting tumor growth in vivo.

Immune regulation by protein ubiquitination: roles of the E3 ligases VHL and Itch

Protein ubiquitination is an important means of post-translational modification which plays an essential role in the regulation of various aspects of leukocyte development and function. The specificity of ubiquitin tagging to a protein substrate is determined by E3 ubiquitin ligases via defined E3-substrate interactions. In this review, we will focus on two E3 ligases, VHL and Itch, to discuss the latest progress in understanding their roles in the differentiation and function of CD4 T helper cell subsets, the stability of regulatory T cells, effector function of CD8 T cells, as well as the development and maturation of innate lymphoid cells. The biological implications of these E3 ubiquitin ligases will be highlighted in the context of normal and dysregulated immune responses including the control of homeostasis, inflammation, auto-immune responses and anti-tumor immunity. Further elucidation of the ubiquitin system in immune cells will help in the design of new therapeutic interventions for human immunological diseases and cancer.

A miRNA-HERC4 pathway promotes breast tumorigenesis by inactivating tumor suppressor LATS1

The E3 ligase HERC4 is overexpressed in human breast cancer and its expression levels correlated with the prognosis of breast cancer patients. However, the roles of HERC4 in mammary tumorigenesis remain unclear. Here we demonstrate that the knockdown of HERC4 in human breast cancer cells dramatically suppressed their proliferation, survival, migration, and tumor growth in vivo, while the overexpression of HERC4 promoted their aggressive tumorigenic activities. HERC4 is a new E3 ligase for the tumor suppressor LATS1 and destabilizes LATS1 by promoting the ubiquitination of LATS1. miRNA-136-5p and miRNA-1285-5p, expression of which is decreased in human breast cancers and is inversely correlated with the prognosis of breast cancer patients, are directly involved in suppressing the expression of HERC4. In summary, we discover a miRNA-HERC4-LATS1 pathway that plays important roles in the pathogenesis of breast cancer and represents new therapeutic targets for human breast cancer.

The E3 ligase MuRF2 plays a key role in the functional capacity of skeletal muscle fibroblasts

Fibroblasts are a highly heterogeneous population of cells, being found in a large number of different tissues. These cells produce the extracellular matrix, which is essential to preserve structural integrity of connective tissues. Fibroblasts are frequently engaged in migration and remodeling, exerting traction forces in the extracellular matrix, which is crucial for matrix deposition and wound healing. In addition, previous studies performed on primary myoblasts suggest that the E3 ligase MuRF2 might function as a cytoskeleton adaptor. Here, we hypothesized that MuRF2 also plays a functional role in skeletal muscle fibroblasts. We found that skeletal muscle fibroblasts express MuRF2 and its siRNA knock-down promoted decreased fibroblast migration, cell border accumulation of polymerized actin, and down-regulation of the phospho-Akt expression. Our results indicated that MuRF2 was necessary to maintain the actin cytoskeleton functionality in skeletal muscle fibroblasts via Akt activity and exerted an important role in extracellular matrix remodeling in the skeletal muscle tissue.

Pja2 Inhibits Wnt/β-catenin Signaling by Reducing the Level of TCF/LEF1

Ubiquitination of proteins plays an essential role in various cellular processes, including protein degradation, DNA repair, and cell signaling pathways. Previous studies have shown that protein ubiquitination is implicated in regulating pluripotency as well as fate determination of stem cells. To identify how protein ubiquitination affects differentiation of embryonic stem cells, we analyzed microarray data, which are available in the public domain, of E3 ligases and deubiquitinases whose levels changed during stem cell differentiation. Expression of pja2, a member of the RING-type E3 ligase family, was up-regulated during differentiation of stem cells. Wnt/β-catenin signaling is one of the most important signaling pathways for regulation of the self-renewal and differentiation of embryonic stem cells. Pja2 was shown to bind to TCF/LEF1, which are transcriptional factors for Wnt/β-catenin signaling, and regulate protein levels by ubiquitination, leading to down-regulation of Wnt signaling activity. Based on these results, we suggest that E3 ligase Pja2 regulates stem cell differentiation by controlling the level of TCF/LEF1 by ubiquitination.

Protein degradation as an innovative strategy in drug discovery / 药学学报

The success rate of mechanism-based drug discovery depends on the drug targets. With the rapid development of genomics and proteomics, a lot of nonenzymic proteins have been identified as potential drug targets. However, these nonenzymic proteins cannot be regulated by occupying the active site, which were recognized as undruggable targets. Direct regulation of the concentration of these proteins in cells by the innate ubiquitin-proteasome is a potential approach to target these proteins. The ubiquitination of target protein by E3 ligase is the key step for ubiquitin-proteasome mediated protein degradation. Proteolysis targeting chimeras (PROTACs) can facilitate the assembly of complex that consists of the target protein and E3 ligase. The target protein will be ubiquitinated, leading to the degradation by proteasome. This type of regulation mechanism can expand the scope of potential drug targets, and the development of PROTACs may be an innovative strategy in drug discovery.

Role of ubiquitin E3 ligase TRIM10 in regulating cardiomyocyte hyper-trophy / 中国病理生理杂志

AIM:To explore the role of ubiquitin E3 ligase tripartite motif 10 (TRIM10) in the development of cardiomyocyte hypertrophy .METHODS: Primary cultured neonatal rat cardiomyocytes ( NRCMs ) were infected with siRNA-TRIM10, siRNA-control, Ad-TRIM10 or Ad-GFP for 24 h respectively, and then stimulated with phenylephrine ( PE) for additional 24 h.The protein levels of TRIM10, AKT and ERK1/2 were determined by Western blot .The size of the NRCMs was measured by immunofluorescence staining .The mRNA expression of atrial natriuretic peptide ( ANP) and brain natriuretic peptide ( BNP) was detected by RT-qPCR.RESULTS:Compared with the control , PE treatment signifi-cantly increased the protein expression of TRIM 10.Moreover, transfection of NRCMs with siRNA-TRIM10 markedly inhibi-ted cardiomyocyte size , the mRNA expression of ANP and BNP , and the phosphorylation levels of AKT and ERK as com-pared with siRNA-control after PE treatment.In contrast, overexpression of TRIM10 significantly enhanced PE-induced hy-pertrophic effect on NRCMs above .CONCLUSION:TRIM10 regulates cardiomyocyte hypertrophy partially through AKT and ERK signaling pathways .

Role of ubiquitin E3 ligase TRIM10 in regulating cardiomyocyte hyper-trophy / 中国病理生理杂志

AIM:To explore the role of ubiquitin E3 ligase tripartite motif 10 (TRIM10) in the development of cardiomyocyte hypertrophy .METHODS: Primary cultured neonatal rat cardiomyocytes ( NRCMs ) were infected with siRNA-TRIM10, siRNA-control, Ad-TRIM10 or Ad-GFP for 24 h respectively, and then stimulated with phenylephrine ( PE) for additional 24 h.The protein levels of TRIM10, AKT and ERK1/2 were determined by Western blot .The size of the NRCMs was measured by immunofluorescence staining .The mRNA expression of atrial natriuretic peptide ( ANP) and brain natriuretic peptide ( BNP) was detected by RT-qPCR.RESULTS:Compared with the control , PE treatment signifi-cantly increased the protein expression of TRIM 10.Moreover, transfection of NRCMs with siRNA-TRIM10 markedly inhibi-ted cardiomyocyte size , the mRNA expression of ANP and BNP , and the phosphorylation levels of AKT and ERK as com-pared with siRNA-control after PE treatment.In contrast, overexpression of TRIM10 significantly enhanced PE-induced hy-pertrophic effect on NRCMs above .CONCLUSION:TRIM10 regulates cardiomyocyte hypertrophy partially through AKT and ERK signaling pathways .

The Ubiquitin-Proteasome System and F-box Proteins in Pathogenic Fungi

The ubiquitin-proteasome system is one of the major protein turnover mechanisms that plays important roles in the regulation of a variety of cellular functions. It is composed of E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme), and E3 ubiquitin ligases that transfer ubiquitin to the substrates that are subjected to degradation in the 26S proteasome. The Skp1, Cullin, F-box protein (SCF) E3 ligases are the largest E3 gene family, in which the F-box protein is the key component to determine substrate specificity. Although the SCF E3 ligase and its F-box proteins have been extensively studied in the model yeast Saccharomyces cerevisiae, only limited studies have been reported on the role of F-box proteins in other fungi. Recently, a number of studies revealed that F-box proteins are required for fungal pathogenicity. In this communication, we review the current understanding of F-box proteins in pathogenic fungi.