Emerging Role of the Ubiquitin Proteasome System in the Control of Shoot Apical Meristem Function

The shoot apical meristem （SAM） is a population of undifferentiated cells at the tip of the shoot axis that establishes early during plant embryogenesis and gives rise to all shoot organs throughout the plant＇s life. A plethora of different families of transcription factors （TFs） play a key role in establishing the equilibrium between cell differentiation and stem cell maintenance in the SAM. Fine tuning of these regulatory proteins is crucial for a proper and fast SAM response to environmental and hormonal cues, and for development progression. One effective way to rapidly inactivate TFs involves regulated proteolysis by the ubiquitin/26S proteasome system （UPS）. However, a possible role of UPS-dependent protein degradation in the regulation of key SAM TFs has not been thoroughly investigated. Here, we summarize recent evidence supporting a role for the UPS in SAM maintenance and function. We integrate this survey with an in silico analysis of publicly-available microarray databases which identified ubiquitin ligases that are expressed in specific areas within the SAM, suggesting that they may regulate or act downstream of meristem-specific factors.

FBW7-mediated ubiquitination and degradation of KLF5

Krüppel-like factor(KLF) family proteins are transcription factors that regulate numerous cellular functions, such as cell proliferation, differentiation, and cell death. Posttranslational modification of KLF proteins is important for their transcriptional activities and biological functions. One KLF family member with important roles in cell proliferation and tumorigenesis is KLF5. The function of KLF5 is tightly controlled by post-translational modifications, including SUMOylation, phosphorylation, and ubiquitination. Recent studies from our lab and others' have demonstrated that the tumor suppressor FBW7 is an essential E3 ubiquitin ligase that targets KLF5 for ubiquitination and degradation. KLF5 contains functional Cdc4 phospho-degrons(CPDs), which are required for its interaction with FBW7. Mutation of CPDs in KLF5 blocks the ubiquitination and degradation of KLF5 by FBW7. The protein kinase Glycogen synthase kinase 3β is involved in the phosphorylation of KLF5 CPDs. In both cancer cell lines and mousemodels, it has been shown that FBW7 regulates the expression of KLF5 target genes through the modulation of KLF5 stability. In this review, we summarize the current progress on delineating FBW7-mediated KLF5 ubiquitination and degradation.

Modification of ubiquitin C-terminal hydrolase L1 by reactive lipid species: role in neural regeneration and diseases of aging

Role of ubiquitin C-terminal hydrolase L1（UCHL1）in brain function：Ubiquitin is used by a variety of cellular systems to tag proteins for transport to various organelles.There are a number of enzymes in the ubiquitin-proteasome pathway（UPP）that tag abnormally folded proteins with ubiquitin for transport to the proteasome for degradation.

Neuroprotective effect of the Chinese medicine Tiantai No.1 and its molecular mechanism in the senescence-accelerated mouse prone 8

Tiantai No.1, a Chinese medicine predominantly composed of powdered Rhizoma Gastrodiae, Radix Ginseng, and Ginkgo leaf at a ratio of 2：1：2 and dissolved in pure water, is neuroprotective in animal models of various cognitive disorders, but its molecular mechanism remains unclear. We administered Tiantai No.1 intragastrically to senescence-accelerated mouse prone 8（SAMP8） mice（a model of Alzheimer＇s disease） at doses of 50, 100 or 150 mg/kg per day for 8 weeks and evaluated their behavior in the Morris water maze and expression of Alzheimer＇s disease-related proteins in the brain. Tiantai No.1 shortened the escape latency in the water maze training trials, and increased swimming time in the target quadrant during the spatial probe test, indicating that Tiantai No.1 improved learning and memory in SAMP8 mice. Immunohistochemistry revealed that Tiantai No.1 restored the proliferation potential of Ki67-positive cells in the hippocampus. In addition, mice that had received Tiantai No.1 had fewer astrocytes, and less accumulation of amyloid-beta and phosphorylated tau. These results suggest that Tiantai No.1 is neuroprotective in the SAMP8 mouse model of Alzheimer＇s disease and acts by restoring neuronal number and proliferation potential in the hippocampus, decreasing astrocyte infiltration, and reducing the accumulation of amyloid-beta and phosphorylated tau.

The dichotomous role of immunoproteasome in cancer:Friend or foe?

Immunoproteasome is a variant of proteasome with structural differences in 20S subunits optimizing them for the production of antigenic peptides with higher binding affinity to major histocompatibility complex(MHC)-I molecules.Apart from this primary function in antigen presentation,immunoproteasome is also responsible for the degradation of proteins,both unfolded proteins for the maintenance of protein homeostasis and tumor suppressor proteins contributing to tumor progression.The altered expression of immunoproteasome is frequently observed in cancers;however,its expression levels and effects vary among different cancer types exhibiting antagonistic roles in tumor development.This review focuses on the dichotomous role of immunoproteasome in different cancer types,as well as summarizes the current progression in immunoproteasome activators and inhibitors.Specifically targeting immunoproteasome may be a beneficial therapeutic intervention in cancer treatment and understanding the role of immunoproteasome in cancers will provide a significant therapeutic insight for the prevention and treatment of cancers.

Targeting BPOZ-2 in Lewy body disease

Formation of Lewy body inclusions（LBs）in the substantia nigra（SN）is a very well-characterized pathological hallmark of Parkinson’s disease（PD）.LBs are aggregates of many biologically inactive proteins including structural elements,alpha-synuclein（asyn）-binding proteins,synphilin-1-binding proteins,and components of the ubiquitin-proteasome system.

HMMR alleviates endoplasmic reticulum stress by promoting autophagolysosomal activity during endoplasmic reticulum stress-driven hepatocellular carcinoma progression

Background The mechanism of hepatitis B virus(HBV)-induced carcinogenesis remains an area of interest.The accumulation of hepatitis B surface antigen in the endoplasmic reticulum(ER)of hepatocytes stimulates persistent ER stress.Activity of the unfolded protein response(UPR)pathway of ER stress may play an important role in inflammatory cancer transformation.How the protective UPR pathway is hijacked by cells as a tool for malignant transformation in HBV-related hepatocellular carcinoma(HCC)is still unclear.Here,we aimed to define the key molecule hyaluronan-mediated motility receptor(HMMR)in this process and explore its role under ER stress in HCC development.Methods An HBV-transgenic mouse model was used to characterize the pathological changes during the tumor progression.Proteomics and transcriptomics analyses were performed to identify the potential key molecule,screen the E3 ligase,and define the activation pathway.Quantitative real-time PCR and Western blotting were conducted to detect the expression of genes in tissues and cell lines.Luciferase reporter assay,chromatin immunoprecipitation,coimmunoprecipitation,immunoprecipitation,and immunofluorescence were employed to investigate the molecular mechanisms of HMMR under ER stress.Immunohistochemistry was used to clarify the expression patterns of HMMR and related molecules in human tissues.Results We found sustained activation of ER stress in the HBV-transgenic mouse model of hepatitis-fibrosis-HCC.HMMR was transcribed by c/EBP homologous protein(CHOP)and degraded by tripartite motif containing 29(TRIM29)after ubiquitination under ER stress,which caused the inconsistent expression of mRNA and protein.Dynamic expression of TRIM29 in the HCC progression regulated the dynamic expression of HMMR.HMMR could alleviate ER stress by increasing autophagic lysosome activity.The negative correlation between HMMR and ER stress,positive correlation between HMMR and autophagy,and negative correlation between ER stress and autophagy were verified in human tissues.Conclusions This study identified the complicated role of HMMR in autophagy and ER stress,that HMMR controls the intensity of ER stress by regulating autophagy in HCC progression,which could be a novel explanation for HBV-related carcinogenesis.

Plant E3 Ligases： Flexible Enzymes in a Sessile World

Since its discovery in the late 1970s, the ubiquitin proteasome pathway appears to be omnipresent in many research fields. Although originally discovered in animals, the pathway has a very central role in plants, which may be correlated to their sessile lifestyle. E3 ligases function as flexible and highly diverse key regulators within the path- way by targeting substrate proteins for ubiquitylation, and often proteolytic degradation via the 26S proteasome. This review provides a concise overview on the most common classes of E3 ligases so far described in plants, and emphasizes recent findings regarding these interesting and flexible enzymes and their diverse functions in plant biology.

Natural compounds in the regulation of proteostatic pathways: An invincible artillery against stress, ageing, and diseases

Cells have different sets of molecules for performing an array of physiological functions.Nucleic acids have stored and carried the information throughout evolution,whereas proteins have been attributed to performing most of the cellular functions.To perform these functions,proteins need to have a unique conformation and a definite lifespan.These attributes are achieved by a highly coordinated protein quality control(PQC)system comprising chaperones to fold the proteins in a proper threedimensional structure,ubiquitin-proteasome system for selective degradation of proteins,and autophagy for bulk clearance of cell debris.Many kinds of stresses and perturbations may lead to the weakening of these protective cellular machinery,leading to the unfolding and aggregation of cellular proteins and the occurrence of numerous pathological conditions.However,modulating the expression and functional efficiency of molecular chaperones,E3 ubiquitin ligases,and autophagic proteins may diminish cellular proteotoxic load and mitigate various pathological effects.Natural medicine and small molecule-based therapies have been well-documented for their effectiveness in modulating these pathways and reestablishing the lost proteostasis inside the cells to combat disease conditions.The present article summarizes various similar reports and highlights the importance of the molecules obtained from natural sources in disease therapeutics.

Discovery of the first potent proteolysis targeting chimera(PROTAC) degrader of indoleamine 2,3-dioxygenase 1

Cancer immunotherapy is revolutionizing oncology and has emerged as a promising strategy for the treatment of multiple cancers.Indoleamine 2,3-dioxygenase 1(IDO1),an immune checkpoint,plays an important role in tumor immune escape through the regulation of multiple immune cells and has been regarded as an attractive target for cancer immunotherapy.Proteolysis Targeting Chimeras(PROTAC)technology has emerged as a new model for drug research and development for its advantageous mechanism.Herein,we reported the application of PROTAC technology in targeted degradation of IDO 1,leading to the discovery of the first IDO1 PROTAC degrader 2 c,which induced significant and persistent degradation of IDO1 with maximum degradation(Dmax)of 93%in HeLa cells.Western-blot based mechanistic studies indicated that IDO 1 was degraded by 2 c through the ubiquitin proteasome system(UPS).Label-free real-time cell analysis(RTCA)indicated that 2 c moderately improved tumorkilling activity of chimeric antigen receptor-modified T(CAR-T)cells.Collectively,these data provide a new insight for the application of PROTAC technology in tumor immune-related proteins and a promising tool to study the function of IDO1.

Chaperone-assisted E3 ligase CHIP:A double agent in cancer

The carboxy-terminus of Hsp70-interacting protein(CHIP)is a ubiquitin ligase and co-chaperone belonging to Ubox family that plays a crucial role in the maintenance of cellular homeostasis by switching the equilibrium of the folding-refolding mechanism towards the proteasomal or lysosomal degradation pathway.It links molecular chaperones viz.HSC70,HSP70 and HSP90 with ubiquitin proteasome system(UPS),acting as a quality control system.CHIP contains charged domain in between N-terminal tetratricopeptide repeat(TPR)and C-terminal Ubox domain.TPR domain interacts with the aberrant client proteins via chaperones while Ubox domain facilitates the ubiquitin transfer to the client proteins for ubiquitination.Thus,CHIP is a classic molecule that executes ubiquitination for degradation of client proteins.Further,CHIP has been found to be indulged in cellular differentiation,proliferation,metastasis and tumorigenesis.Additionally,CHIP can play its dual role as a tumor suppressor as well as an oncogene in numerous malignancies,thus acting as a double agent.Here,in this review,we have reported almost all substrates of CHIP established till date and classified them according to the hallmarks of cancer.In addition,we discussed about its architectural alignment,tissue specific expression,sub-cellular localization,folding-refolding mechanisms of client proteins,E4 ligase activity,normal physiological roles,as well as involvement in various diseases and tumor biology.Further,we aim to discuss its importance in HSP90 inhibitors mediated cancer therapy.Thus,this report concludes that CHIP may be a promising and worthy drug target towards pharmaceutical industry for drug development.

Curcumin inhibits the replication of enterovirus 71 in vitro

Human enterovirus 71(EV71)is the main causative pathogen of hand,foot,and mouth disease(HFMD)in children.The epidemic of HFMD has been a public health problem in Asia-Pacific region for decades,and no vaccine and effective antiviral medicine are available.Curcumin has been used as a traditional medicine for centuries to treat a diversity of disorders including viral infections.In this study,we demonstrated that curcumin showed potent antiviral effect again EV71.In Vero cells infected with EV71,the addition of curcumin significantly suppressed the synthesis of viral RNA,the expression of viral protein,and the overall production of viral progeny.Similar with the previous reports,curcumin reduced the production of ROS induced by viral infection.However,the antioxidant property of curcumin did not contribute to its antiviral activity,since N-acetyl-L-cysteine,the potent antioxidant failed to suppress viral replication.This study also showed that extracellular signal-regulated kinase(ERK)was activated by either viral infection or curcumin treatment,but the activated ERK did not interfere with the antiviral effect of curcumin,indicating ERK is not involved in the antiviral mechanism of curcumin.Unlike the previous reports that curcumin inhibited protein degradation through ubiquitin–proteasome system(UPS),we found that curcumin had no impact on UPS in control cells.However,curcumin did reduce the activity of proteasomes which was increased by viral infection.In addition,the accumulation of the short-lived proteins,p53 and p21,was increased by the treatment of curcumin in EV71-infected cells.We further probed the antiviral mechanism of curcumin by examining the expression of GBF1 and PI4KB,both of which are required for the formation of viral replication complex.We found that curcumin significantly reduced the level of both proteins.Moreover,the decreased expression of either GBF1 or PI4KB by the application of siRNAs was sufficient to suppress viral replication.We also demonstrated that curcumin showed anti-apoptotic activity at the early stage of viral infection.The results of this study provide solid evidence that curcumin has potent anti-EV71 activity.Whether or not the down-regulated GBF1 and PI4KB by curcumin contribute to its antiviral effect needs further studies.