Research progress in controllable proteolysis targeting chimeras / 药学学报

Proteolysis targeting chimeras (PROTACs) is an innovative technique in targeted protein degradation. PROTACs is a heterobifunctional molecule which can bind to the E3 ligase and target protein to form a ubiquitination complex, resulting in the ubiquitin-proteasome system dependent degradation of target protein. PROTACs has been regarded as the promising method in drug discovery campaign, for its high commonality, potent degradation activity and unique selectivity profile. However, the catalytic mechanism also induces the uncontrollable protein degradation risk. Controllable PROTACs contain the responsive element in the molecular entity. In certain conditions, the element can be triggered to activate or terminate the degradation event. In this review, we will briefly summarize the strategies in controllable PROTACs and describe the representative examples according to the responsive mechanism. We hope this review could provide some insight into the further development of controllable PROTACs.

Research progress of targeted degradation of Mycobacterium tuberculosis proteins / 药学学报

Tuberculosis (TB), an infectious disease caused by Mycobacterium tuberculosis (Mtb), is still one of the significant threats to human life. In recent years, the continuous exploration of small molecule inhibitors represented by bedaquinoline has brought new vitality into the field of tuberculosis. However, small molecule inhibitors will inevitably occur acquired drug resistance during clinical medication. As a new pharmacological mechanism, targeted protein degradation (TPD) achieves efficacy by destroying rather than inhibiting protein targets. It might be an excellent strategy to develop anti-tuberculosis drugs based on the TPD concept to solve drug resistance. This article reviews the protein degradation pathways of Mtb, such as the Pup proteasome system and the ClpP-ClpC1 complex enzyme system. The future development of these strategies into TPD drugs was prospected and summarized.

Advances and prospects in targeted protein degradation / 药学实践杂志

Targeted protein degradation (TPD) techniques eliminate pathogenic proteins by hijacking the intracellular proteolysis machinery which includes the ubiquitin-proteasome system (UPS) and the lysosomal degradation pathway, holding promise to overcome the limitations of traditional inhibitors and further broaden the target space including many “undruggable” targets, and provide new targeted treatments for drug discovery. In this review, recent advances in a variety of promising TPD strategies were summarized, such as proteolysis targeting chimera (PROTAC), molecular glue, lysosome-targeting chimaera (LYTAC), autophagosome-tethering compound (ATTEC), autophagy-targeting chimera AUTAC and AUTOTAC, particularly. The representative case studies, potential applications and challenges were analyzed.

Building bioorthogonal click-release capable artificial receptors on cancer cell surface for imaging, drug targeting and delivery

The current targeting drug delivery mainly relies on cancer cell surface receptors. However, in many cases, binding affinities between protein receptors and homing ligands is relatively low and the expression level between cancer and normal cells is not significant. Distinct from conventional targeting strategies, we have developed a general cancer targeting platform by building artificial receptor on cancer cell surface via a chemical remodeling of cell surface glycans. A new tetrazine (Tz) functionalized chemical receptor has been designed and efficiently installed on cancer cell surface as "overexpressed" biomarker through a metabolic glycan engineering. Different from the reported bioconjugation for drug targeting, the tetrazine labeled cancer cells not only locally activate TCO-caged prodrugs but also release active drugs via the unique bioorthogonal Tz-TCO click-release reaction. The studies have demonstrated that the new drug targeting strategy enables local activation of prodrug, which ultimately leads to effective and safe cancer therapy.

Ubiquitin-specific peptidase 22 (USP22) regulates the level and function of hepatitis B virus X protein / 中华微生物学和免疫学杂志

Objective:To investigate the effects of the interaction between ubiquitin-specific peptidase 22 (USP22) and hepatitis B virus X protein (HBx) on the protein level and the biological function of HBx.Methods:The interactions between HBx and USP22 were analyzed by GST pull-down, co-immunoprecipitation assay and confocal laser scanning assay. USP22 recombinant plasmids or specific siRNA were transiently co-transfected with HBx plasmids. Western blot were used to detect the protein level of HBx. The half-life and degradation pathway of HBx in the transfected cells treated with cycloheximide (CHX) or proteasome inhibitor MG132 were detected. In vivo ubiquitination assay was used to detect the ubiquitination of HBx with USP22 overexpression. Moreover, dual-luciferase reporter assay and colony formation assay were used to analyze the effects of USP22 on the biological function of HBx. Results:USP22 could interact with HBx in vivo and in vitro. USP22 significantly increased the stability of HBx and inhibited the proteasome-mediated degradation of HBx protein by reducing the ubiquitination of HBx, thereby enhancing the biological function of HBx. Conclusions:USP22 inhibited HBx protein degradation through ubiquitin-dependent proteasome pathway, thus enhancing the stability and biological function of HBx.

Non-small molecule PROTACs (NSM-PROTACs): Protein degradation kaleidoscope

The proteolysis targeting chimeras (PROTACs) technology has been rapidly developed since its birth in 2001, attracting rapidly growing attention of scientific institutes and pharmaceutical companies. At present, a variety of small molecule PROTACs have entered the clinical trial. However, as small molecule PROTACs flourish, non-small molecule PROTACs (NSM-PROTACs) such as peptide PROTACs, nucleic acid PROTACs and antibody PROTACs have also advanced considerably over recent years, exhibiting the unique characters beyond the small molecule PROTACs. Here, we briefly introduce the types of NSM-PROTACs, describe the advantages of NSM-PROTACs, and summarize the development of NSM-PROTACs so far in detail. We hope this article could not only provide useful insights into NSM-PROTACs, but also expand the research interest of NSM-PROTACs.

Research advances in new technologies in targeted protein degradation / 药学学报

In recent years, the targeted protein degradation technology has developed quickly, with proteolysis-targeting chimera (PROTAC) as the best-known strategy through exploring the ubiquitin-proteasome system. A number of new targeted protein degradation strategies have been emerging to expand the scope of protein degradation technology, including lysosome-targeting chimeras (LYTACs), autophagy-targeting chimeras (AUTACs), autophagosome-tethering compounds (ATTECs) and chimeras based on chaperone-mediated autophagy (CMA). The emerging methodologies have explored another important protein degradation system in eukaryotes-lysosomal systems, such as the endosome-lysosome pathway and the autophagy-lysosome pathway. This review summaries the mechanisms and features of different strategies for targeted protein degradation, with a special emphasis on the new targeted protein degradation technologies, such as their current status, advantages and limitations.

mTOR-targeted cancer therapy: great target but disappointing clinical outcomes, why? / 医学前沿

The mammalian target of rapamycin (mTOR) critically regulates several essential biological functions, such as cell growth, metabolism, survival, and immune response by forming two important complexes, namely, mTOR complex 1 (mTORC1) and complex 2 (mTORC2). mTOR signaling is often dysregulated in cancers and has been considered an attractive cancer therapeutic target. Great efforts have been made to develop efficacious mTOR inhibitors, particularly mTOR kinase inhibitors, which suppress mTORC1 and mTORC2; however, major success has not been achieved. With the strong scientific rationale, the intriguing question is why cancers are insensitive or not responsive to mTOR-targeted cancer therapy in clinics. Beyond early findings on induced activation of PI3K/Akt, MEK/ERK, and Mnk/eIF4E survival signaling pathways that compromise the efficacy of rapalog-based cancer therapy, recent findings on the essential role of GSK3 in mediating cancer cell response to mTOR inhibitors and mTORC1 inhibition-induced upregulation of PD-L1 in cancer cells may provide some explanations. These new findings may also offer us the opportunity to rationally utilize mTOR inhibitors in cancer therapy. Further elucidation of the biology of complicated mTOR networks may bring us the hope to develop effective therapeutic strategies with mTOR inhibitors against cancer.

Research progress of mitochondrial Lon protease and its related diseases / 上海交通大学学报（医学版）

Lon protease (LON) is a highly conserved ATP-dependent serine protease, which is responsible for the decomposition and elimination of abnormal proteins. As an important executor of intracellular environment stability, LON can degrade misfolded and damaged proteins together with proteasome to ensure the high quality of proteins in vivo, especially in the maintenance of mitochondrial function. At the same time, the physiological function of LON also has an important effect on cell survival under various stresses. Recent studies have shown that the abnormal expression or activity of LON is involved in the occurrence and development of many diseases such as neurodegenerative diseases, diabetes mellitus, myocardial ischemia, cerebral ischemia and tumors. This review focuses on the structure and the function of LON, the relationship between abnormal expression and diseases, and the research progress of LON activity intervention, in order to provide ideas for clinical diagnosis and treatment of related diseases.

TRIB3 promotes B-ALL progression by suppressing CTSZ-mediated BCR-ABL degradation / 药学学报

Philadelphia chromosome (Ph) positive (Ph+) B cell acute lymphoblastic leukemia (B-ALL) is the most common genetic abnormality associated with B-ALL and has been shown to confer the worst prognosis to both children and adults. Increasing evidence has revealed that high tribbles homologue 3 (TRIB3) expression contributes to multi-cancer development and progression, but the underlying role and molecular mechanisms of TRIB3 in Ph+ B-ALL remain unclear. Here, we report that TRIB3 expression was enhanced in Ph+ B-ALL patient samples and positively associated with the expression of breakpoint cluster region-Abelson tyrosine kinase (BCR-ABL). We further demonstrated that deletion of TRIB3 attenuated the progression of Ph+ B-ALL by reducing BCR-ABL expression. Mechanistically, TRIB3 interacted with lysosomal cysteine proteinase cathepsin Z (CTSZ) to suppress CTSZ-mediated BCR-ABL degradation, which enhanced BCR-ABL activity, causing high proliferation of Ph+ B-ALL cells. Thus, our study indicated that inhibiting the expression of TRIB3 to regulate BCR-ABL kinase activity may be exploited as an additional target therapy for Ph+ ALL. Procedures for animal study were performed with approval of the Animal Care and Use Committee of the Chinese Academy of Medical Sciences and Peking Union Medical College. The procedure of human leukemia sample was approved by the Ethics Committee of Chinese Academy of Medical Sciences and Peking Union Medical College (KT2019055-EC-1).

Improving proteolytic stability of Npu DnaE C-fragment in Escherichia coli expression system / 中国药科大学学报

@#Naturally split Npu DnaE intein can mediate rapid trans-splicing and C-cleavage, which is of great use in many aspects of protein engineering. However, the degradation of NpuC during expression and purification reduces the yield and purity of recombinant protein. N2C, an extended NpuN2-containing N-terminal NpuC fragment, was constructed to improve NpuC stability. N2C was expressed in BL21(DE3) and purified by affinity chromatography. The degradation ratio was calculated by ImageJ, and the factors affecting the C-terminal cleavage reaction of intein, such as temperature, DTT concentration and N/C ratio, were also investigated. The results showed that N2C lowered the proportion of degradation to 2.7%-7.2% and the yield of C-terminal cleavage reached 90% in 30 min at 37 °C with an N/C ratio of 5∶1 catalyzed by 1 mmol/L DTT. N2C can not only improve the stability of NpuC in Escherichia coli expression system, but also retain the activity of C-terminal cleavage reaction, which is of great significance for its application in protein purification.

Degradation of proteins by PROTACs and other strategies

Blocking the biological functions of scaffold proteins and aggregated proteins is a challenging goal. PROTAC proteolysis-targeting chimaera (PROTAC) technology may be the solution, considering its ability to selectively degrade target proteins. Recent progress in the PROTAC strategy include identification of the structure of the first ternary eutectic complex, extra-terminal domain-4-PROTAC-Von-Hippel-Lindau (BRD4-PROTAC-VHL), and PROTAC ARV-110 has entered clinical trials for the treatment of prostate cancer in 2019. These discoveries strongly proved the value of the PROTAC strategy. In this perspective, we summarized recent meaningful research of PROTAC, including the types of degradation proteins, preliminary biological data in vitro and in vivo, and new E3 ubiquitin ligases. Importantly, the molecular design, optimization strategy and clinical application of candidate molecules are highlighted in detail. Future perspectives for development of advanced PROTAC in medical fields have also been discussed systematically.

Short-term creatine supplementation changes protein metabolism signaling in hindlimb suspension

The effect of a short-term creatine supplementation on hindlimb suspension (HS)-induced muscle atrophy was investigated. Creatine monohydrate (5 g/kg b.w. per day) or placebo, divided in 2 daily doses, was given by oral gavage for 5 days. Rats were maintained in HS with dietary supplementation concomitantly for 5 days. Body weight, soleus and EDL muscle masses, and cross-sectional areas (CSA) of the muscle fibers were measured. Signaling pathways associated with skeletal muscle mass regulation (FST, MSTN, FAK, IGF-1, MGF, Akt, mTOR, atrogin-1, and MuRF1 expressions, and Akt, S6, GSK3B, and 4EBP1 proteins) were evaluated in the muscles. Soleus muscle exhibited more atrophy than the EDL muscle due to HS. Creatine supplementation attenuated the decrease of wet weight and increased p-4EBP1 protein in the EDL muscle of HS rats. Also, creatine increased mTOR and atrogin-1 expressions in the same muscle and condition. In the absence of HS, creatine supplementation increased FAK and decreased MGF expressions in the EDL muscle. Creatine attenuated the increase in FST expression due to HS in the soleus muscle. MuRF1 expression increased in the soleus muscle due to creatine supplementation in HS animals whereas atrogin-1 expression increased still further in this group compared with untreated HS rats. In conclusion, short-term creatine supplementation changed protein metabolism signaling in soleus and EDL muscles. However, creatine supplementation only slightly attenuated the mass loss of both muscles and did not prevent the CSA reduction and muscle strength decrease induced by HS for 5 days.

Regulation of Protein Degradation by Proteasomes in Cancer

Imbalance of protein homeostasis (proteostasis) is known to cause cellular malfunction, cell death, and diseases. Elaborate regulation of protein synthesis and degradation is one of the important processes in maintaining normal cellular functions. Protein degradation pathways in eukaryotes are largely divided into proteasome-mediated degradation and lysosome-mediated degradation. Proteasome is a multisubunit complex that selectively degrades 80% to 90% of cellular proteins. Proteasome-mediated degradation can be divided into 26S proteasome (20S proteasome + 19S regulatory particle) and free 20S proteasome degradation. In 1980, it was discovered that during ubiquitination process, wherein ubiquitin binds to a substrate protein in an ATP-dependent manner, ubiquitin acts as a degrading signal to degrade the substrate protein via proteasome. Conversely, 20S proteasome degrades the substrate protein without using ATP or ubiquitin because it recognizes the oxidized and structurally modified hydrophobic patch of the substrate protein. To date, most studies have focused on protein degradation via 26S proteasome. This review describes the 26S/20S proteasomal pathway of protein degradation and discusses the potential of proteasome as therapeutic targets for cancer treatment as well as against diseases caused by abnormalities in the proteolytic system.

Plant arginyltransferases (ATEs)

Abstract Regulation of protein stability and/or degradation of misfolded and damaged proteins are essential cellular processes. A part of this regulation is mediated by the so-called N-end rule proteolytic pathway, which, in concert with the ubiquitin proteasome system (UPS), drives protein degradation depending on the N-terminal amino acid sequence. One important enzyme involved in this process is arginyl-t-RNA transferase, known as ATE. This enzyme acts post-translationally by introducing an arginine residue at the N-terminus of specific protein targets to signal degradation via the UPS. However, the function of ATEs has only recently begun to be revealed. Nonetheless, the few studies to date investigating ATE activity in plants points to the great importance of the ATE/N-end rule pathway in regulating plant signaling. Plant development, seed germination, leaf morphology and responses to gas signaling in plants are among the processes affected by the ATE/N-end rule pathway. In this review, we present some of the known biological functions of plant ATE proteins, highlighting the need for more in-depth studies on this intriguing pathway.

Myostatin promotes distinct responses on protein metabolism of skeletal and cardiac muscle fibers of rodents

Myostatin is a novel negative regulator of skeletal muscle mass. Myostatin expression is also found in heart in a much less extent, but it can be upregulated in pathological conditions, such as heart failure. Myostatin may be involved in inhibiting protein synthesis and/or increasing protein degradation in skeletal and cardiac muscles. Herein, we used cell cultures and isolated muscles from rats to determine protein degradation and synthesis. Muscles incubated with myostatin exhibited an increase in proteolysis with an increase of Atrogin-1, MuRF1 and LC3 genes. Extensor digitorum longus muscles and C2C12 myotubes exhibited a reduction in protein turnover. Cardiomyocytes showed an increase in proteolysis by activating autophagy and the ubiquitin proteasome system, and a decrease in protein synthesis by decreasing P70S6K. The effect of myostatin on protein metabolism is related to fiber type composition, which may be associated to the extent of atrophy mediated effect of myostatin on muscle.

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.

Degradation of eNOS induced by TNF-α in human umbilical vein endothelial cells / 基础医学与临床

Objective To investigate does intracellular protein degradation pathway play an important role in decrease of endothelial nitric oxide synthase (eNOS) in human umbilical vein endothelial cells (HUVECs).MethodsTo establish a primary HUVECs culture methods,the HUVECs were incubated with concentration gradient group of TNF-α(0.01,0.1,1 and 10 ng/mL) in different time periods (24,48 and 72 h).The HUVECs were pretreated with NH4Cl or treated with caspase inhibitor or MG-132 1.5 h prior to incubation for an additional 24 h with TNF-α.The expression of eNOS was detected via Western blot assay.Results Treatment of the HUVECs with TNF-α(0.01-10 ng/mL) led to a dose-dependent reduction of eNOS expression.And treatment with TNF-α(1 ng/mL) reduced the eNOS expression in a time-depended manner.Compared with the TNF-α group,the protein expression level of eNOS was obviously increased in the co-working group of MG-123 and TNF-α.Conclusions TNF-α induces degradation of eNOS through a ubiquitin-proteasome pathway.

Autophagy alleviates neuronal toxicityinduced by abnormally phosphorylated tau protein / 中国药理学通报

Aim To observe the effects of rapamycin (Rapa) and starvation-induced autophagy on the morphology of neuronal cells, tau protein aggregation and expression of phosphorylated tau protein, to explore the possible mechanism of cytoprotective effect of these two classical autophagy inducers on phosphorylated tau expressing cells.Methods N2a cells were transfected with GFP-tau plasmid, and equal amount of empty vector was used as control.Then cells were incubated with or without okadaic acid(OA) for 12 h, followed by treatment with autophagy inducers rapamycin(Rapa) and EBSS, autophagy inhibitor Bafilomycin A1(Baf A1) for 6 h.DAB was used to observe tau expression and cell morphology.Confocal microscopy was used to observe the intracellular tau aggregation.TUNEL assay and cleaved caspase-3 level were used to detect cell apoptosis.Immunoblot was used to detect the expression of phosphorylated tau and autophagy-related proteins.Results Our study showed that the N2a cells treated with OA exhibited small cell body, retracted processes and increased tau aggregation, compared with only tau-expressing cells.Rapa and EBSS treatment significantly improved cell morphology, decreased tau aggregation and reduced cell apoptosis.On the contrary, Baf A1 treatment induced aberrant cell shape and increased tau aggregation and cell apoptosis.In addition, Rapa significantly decreased the high molecular weight, phosphorylated tau whereas EBSS especially decreased the low molecular weight phosphorylated tau.Conclusions Rapa and EBSS is alleviate hyperphosphorylated tau-induced cytotoxicity through different mechanism.Rapamycin mainly decreases phosphorylated tau oligomers, while EBSS liable to decrease the soluble phosphorylated tau.

Reversible phosphorylation of the 26S proteasome

The 26S proteasome at the center of the ubiquitin-proteasome system (UPS) is essential for virtually all cellular processes of eukaryotes. A common misconception about the proteasome is that, once made, it remains as a static and uniform complex with spontaneous and constitutive activity for protein degradation. Recent discoveries have provided compelling evidence to support the exact opposite insomuch as the 26S proteasome undergoes dynamic and reversible phosphorylation under a variety of physiopathological conditions. In this review, we summarize the history and current understanding of proteasome phosphorylation, and advocate the idea of targeting proteasome kinases/phosphatases as a new strategy for clinical interventions of several human diseases.