Asparagine endopeptidase (AEP), also called legumain, is currently the only known cysteine protease that specifically cleaves peptide bonds in asparaginyl residue in the mammalian genome. Since 2003, AEP has been reported to be widely expressed in a variety of carcinomas and is considered a potential therapeutic target. In the following years, researchers intensively investigated the substrates of AEP and the mechanism of AEP in partial tumors. With the identification of substrate proteins such as P53, integrin αvβ3, MMP-2, and MMP-9, the biochemical mechanism of AEP in carcinomas is also more precise. This review will clarify the probable mechanisms of AEP in the progression of breast carcinoma, glioblastoma, gastric carcinoma, and epithelial ovarian carcinoma. This review will also discuss the feasibility of targeted therapy with AEP inhibitor (AEPI) in these carcinomas.

Oxygen and nutrient deprivation are common features of solid tumors. Although abnormal alternative splicing (AS) has been found to be an important driving force in tumor pathogenesis and progression, the regulatory mechanisms of AS that underly the adaptation of cancer cells to harsh microenvironments remain unclear. Here, we found that hypoxia- and nutrient deprivation–induced asparagine endopeptidase (AEP) specifically cleaved DDX3X in a HIF1A-dependent manner. This cleavage yields truncated carboxyl-terminal DDX3X (tDDX3X-C), which translocates and aggregates in the nucleus. Unlike intact DDX3X, nuclear tDDX3X-C complexes with an array of splicing factors and induces AS events of many pre-mRNAs; for example, enhanced exon skipping (ES) in exon 2 of the classic tumor suppressor PRDM2 leads to a frameshift mutation of PRDM2. Intriguingly, the isoform ARRB1-Δexon 13 binds to glycolytic enzymes and regulates glycolysis. By utilizing in vitro assays, glioblastoma organoids, and animal models, we revealed that AEP/tDDX3X-C promoted tumor malignancy via these isoforms. More importantly, high AEP/tDDX3X-C/ARRB1-Δexon 13 in cancerous tissues was tightly associated with poor patient prognosis. Overall, our discovery of the effect of AEP-cleaved DDX3X switching on alternative RNA splicing events identifies a mechanism in which cancer cells adapt to oxygen and nutrient shortages and provides potential diagnostic and/or therapeutic targets.

Increasing evidence has demonstrated that ischemic preconditioning (IPC) increases cerebral tolerance to subsequent prolonged ischemic insults. However, the exact mechanisms underlying the process have not been fully explored. In the current study, we aim to investigate whether NLRP3 inflammasome and cell pyroptosis are involved in the neuroprotective mechanism of IPC after ischemic stroke. In vitro, IPC was set up by exposing BV-2 cells to 10 min of oxygen–glucose deprivation (OGD). In vivo, IPC was performed by a transient cerebral ischemia of 10 min occlusion of the middle cerebral artery (MCA) in mice. We found that the NLRP3 inflammasome was activated and cell pyroptosis was induced at 6 h and 24 h post-stroke in an ischemic brain. IPC treatment increased cell viability under OGD state, reduced the infarct size, and attenuated the neurological deficits of mice. However, the effects NLRP3 inflammasome activation and pyroptosis after stroke were attenuated by IPC, which decreased the expression of NLRP3, ASC, cleaved caspase 1, and GSDMD-N and reduced the production of IL-1β and IL-18. In addition, confocal immunofluorescence staining of Annexin V-mCherry and SYTOX green was inhibited by IPC. These findings suggest a more enhanced link between IPC and inflammatory signature and cell death, highlighting that the NLRP3 inflammasome may act as a promising target for the prevention and treatment of ischemic stroke.

Background. Legumain is related to carotid atherosclerotic plaques and may be a new biomarker of carotid atherosclerosis. However, the association between legumain and peripheral artery disease (PAD) of lower extremity has been less studied. This study is aimed at exploring the potential link between legumain and PAD in patients with type 2 diabetes mellitus (T2DM). Methods. A cross-sectional study was conducted on 483 hospitalized T2DM patients. The serum legumain level was measured by a sandwich enzyme-linked immunosorbent assay. PAD was evaluated by color Doppler sonography. The association between legumain and PAD was tested by logistic regression. The predictive power of legumain for PAD was evaluated with the receiver-operating-characteristic (ROC) curve. Results. Overall, 201 (41.6%) patients suffered from PAD. Patients with PAD had significantly higher serum legumain level than those without PAD [11.9 (6.3, 17.9) μg/L vs. 7.6 (3.2, 14.2) μg/L, ]. Logistic regression showed that a higher serum legumain level was independently associated with a greater risk of PAD in T2DM patients [adjusted odds ratio (aOR): 1.03; 95% confidence interval (CI): 1.01-1.06]. The area under the ROC curve was 0.634 (95% CI, 0.585 to 0.684). Conclusion. High serum legumain level was significantly correlated with an increased risk of PAD in T2DM patients.