IU Indianapolis ScholarWorks :: Browsing by Author "Li, Min"

Browsing by Author "Li, Min"

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A high-throughput FRET-based assay for determination of Atg4 activity
(Taylor & Francis, 2012) Li, Min; Chen, Xi; Ye, Qi-Zhuang; Vogt, Andreas; Yin, Xiao-Ming; Pathology and Laboratory Medicine, School of Medicine
Atg4 is required for cleaving Atg8, allowing it to be conjugated to phosphatidylethanolamine on phagophore membranes, a key step in autophagosome biogenesis. Deconjugation of Atg8 from autophagosomal membranes could be also a regulatory step in controlling autophagy. Therefore, the activity of Atg4 is important for autophagy and could be a target for therapeutic intervention. In this study, a sensitive and specific method to measure the activity of two Atg4 homologs in mammalian cells, Atg4A and Atg4B, was developed using a fluorescence resonance energy transfer (FRET)-based approach. Thus LC3B and GATE-16, two substrates that could be differentially cleaved by Atg4A and Atg4B, were fused with CFP and YFP at the N- and C-terminus, respectively, allowing FRET to occur. The FRET signals decreased in proportion to the Atg4-mediated cleavage, which separated the two fluorescent proteins. This method is highly efficient for measuring the enzymatic activity and kinetics of Atg4A and Atg4B under in vitro conditions. Applications of the assay indicated that the activity of Atg4B was dependent on its catalytic cysteine and expression level, but showed little changes under several common autophagy conditions. In addition, the assays displayed excellent performance in high throughput format and are suitable for screening and analysis of potential modulators. In summary, the FRET-based assay is simple and easy to use, is sensitive and specific, and is suitable for both routine measurement of Atg4 activity and high-throughput screening.
AMDE-1 is a dual function chemical for autophagy activation and inhibition
(PLoS, 2015-04-20) Li, Min; Yang, Zuolong; Vollmer, Laura L.; Gao, Ying; Fu, Yuanyuan; Lui, Cui; Chen, Xiaoyun; Liu, Peiqing; Vogt, Andreas; Yin, Xiao-Ming; Department of Pathology and Laboratory Medicine, IU School of Medicine
Autophagy is the process by which cytosolic components and organelles are delivered to the lysosome for degradation. Autophagy plays important roles in cellular homeostasis and disease pathogenesis. Small chemical molecules that can modulate autophagy activity may have pharmacological value for treating diseases. Using a GFP-LC3-based high content screening assay we identified a novel chemical that is able to modulate autophagy at both initiation and degradation levels. This molecule, termed as Autophagy Modulator with Dual Effect-1 (AMDE-1), triggered autophagy in an Atg5-dependent manner, recruiting Atg16 to the pre-autophagosomal site and causing LC3 lipidation. AMDE-1 induced autophagy through the activation of AMPK, which inactivated mTORC1 and activated ULK1. AMDE-1did not affect MAP kinase, JNK or oxidative stress signaling for autophagy induction. Surprisingly, treatment with AMDE-1 resulted in impairment in autophagic flux and inhibition of long-lived protein degradation. This inhibition was correlated with a reduction in lysosomal degradation capacity but not with autophagosome-lysosome fusion. Further analysis indicated that AMDE-1 caused a reduction in lysosome acidity and lysosomal proteolytic activity, suggesting that it suppressed general lysosome function. AMDE-1 thus also impaired endocytosis-mediated EGF receptor degradation. The dual effects of AMDE-1 on autophagy induction and lysosomal degradation suggested that its net effect would likely lead to autophagic stress and lysosome dysfunction, and therefore cell death. Indeed, AMDE-1 triggered necroptosis and was preferentially cytotoxic to cancer cells. In conclusion, this study identified a new class of autophagy modulators with dual effects, which can be explored for potential uses in cancer therapy.
The ATP-Dependent Protease ClpP Inhibits Biofilm Formation by Regulating Agr and Cell Wall Hydrolase Sle1 in Staphylococcus aureus
(Frontiers, 2017-05-15) Liu, Qian; Wang, Xing; Qin, Juanxiu; Cheng, Sen; Yeo, Won-Sik; He, Lei; Ma, Xiaowei; Liu, Xiaoyun; Li, Min; Bae, Taeok; Microbiology and Immunology, School of Medicine
Biofilm causes hospital-associated infections on indwelling medical devices. In Staphylococcus aureus, Biofilm formation is controlled by intricately coordinated network of regulating systems, of which the ATP-dependent protease ClpP shows an inhibitory effect. Here, we demonstrate that the inhibitory effect of ClpP on biofilm formation is through Agr and the cell wall hydrolase Sle1. Biofilm formed by clpP mutant consists of proteins and extracellular DNA (eDNA). The increase of the protein was, at least in part, due to the reduced protease activity of the mutant, which was caused by the decreased activity of agr. On the other hand, the increase of eDNA was due to increased cell lysis caused by the higher level of Sle1. Indeed, as compared with wild type, the clpP mutant excreted an increased level of eDNA, and showed higher sensitivity to Triton-induced autolysis. The deletion of sle1 in the clpP mutant decreased the biofilm formation, the level of eDNA, and the Triton-induced autolysis to wild-type levels. Despite the increased biofilm formation capability, however, the clpP mutant showed significantly reduced virulence in a murine model of subcutaneous foreign body infection, indicating that the increased biofilm formation capability cannot compensate for the intrinsic functions of ClpP during infection.
Autophagy Induced by Calcium Phosphate Precipitates Involves Endoplasmic Reticulum Membranes in Autophagosome Biogenesis
(Public Library of Science, 2012) Chen, Xi; Li, Min; Chen, Daohong; Gao, Wentao; Guan, Jun-Lin; Komatsu, Massaki; Yin, Xiao-Ming; Pathology and Laboratory Medicine, School of Medicine
Calcium can play an important role in the regulation of autophagy. We previously reported that exogenously introduced calcium in the form of calcium phosphate precipitates (CPP) induces autophagy. Here we showed that CPP-induced autophagy required the classical autophagic machinery, including the autophagosome initiating molecules FIP200 and Beclin 1, as well as molecules involved in the autophagosome membrane extension, Atg4, Atg5 and Atg3. On the other hand, Atg9 seemed to place a restriction on CPP-induced autophagy. Loss of Atg9 led to enhanced LC3 punctation and enhanced p62 degradation. CPP-induced autophagy was independent of mTOR and reactive oxygen species. It also did not affect MAP kinase activation and ER stress. DFCP1 is an ER-resident molecule that binds to phosphatidylinositol 3-phosphate. CPP activated DFCP1 punctation in a class III phosphatidylinositol-3-kinase and calcium dependent manner, and caused the association of DFCP1 puncta with the autophagosomes. Consistently, ER membranes, but not Golgi or mitochondrial membranes, colocalized with CPP-induced LC3 positive autophagosomes. These data suggest that CPP-induced autophagosome formation involves the interaction with the ER membrane.
Autophagy induced by calcium phosphate precipitates targets damaged endosomes
(ASBMB, 2014-04-18) Chen, Xi; Khambu, Bilon; Zhang, Hao; Gao, Wentao; Li, Min; Chen, Xiaoyun; Yoshimori, Tamotsu; Yin, Xiao-Ming; Department of Pathology & Laboratory Medicine, IU School of Medicine
Calcium phosphate precipitates (CPPs) form complexes with DNA, which enter cells via endocytosis. Under this condition CPPs induce autophagy via the canonic autophagy machinery. Here we showed that CPP-induced autophagy was also dependent on endocytosis as the process was significantly inhibited by methyl-β-cyclodextrin and dynasore, which suppress clathrin-dependent endocytosis. Consistently, CPP treatment triggered the formation of filipin-positive intracellular vesicles whose membranes are rich in cholesterol. Unexpectedly, these vesicles were also positive for galectin 3, suggesting that they were damaged and the membrane glycans became accessible to galectins to bind. Endosome damage was caused by endocytosis of CPPs and was reversed by calcium chelators or by endocytosis inhibitors. Notably, CPP-induced LC3-positive autophagosomes were colocalized with galectin 3, ubiquitin, and p62/SQSTM1. Inhibition of galectin 3 reduced p62 puncta and autophagosome formation. Knockdown of p62 additionally inhibited the colocalization of autophagosomes with galectins. Furthermore, most of the galectin 3-positive vesicles were colocalized with Rab7 or LAMP1. Agents that affect endosome/lysosome maturation and function, such as bafilomycin A1, also significantly affected CPP-induced tubulovesicular autophagosome formation. These findings thus indicate that endocytosed CPPs caused endosome damage and recruitment of galectins, particularly at the later endosome stage, which led to the interaction of the autophagosomal membranes with the damaged endosome in the presence of p62.
A C-X-C Chemokine Receptor Type 2–Dominated Cross-talk between Tumor Cells and Macrophages Drives Gastric Cancer Metastasis
(AACR, 2019-06) Zhou, Zhijun; Xia, Guanggai; Xiang, Zhen; Liu, Mingyang; Wei, Zhewei; Yan, Jie; Chen, Wei; Zhu, Jintao; Awasthi, Niranjan; Sun, Xiaotian; Fung, Kar-Ming; He, Yulong; Li, Min; Zhang, Changhua; Surgery, School of Medicine
Purpose: C-X-C chemokine receptor type 2 (CXCR2) is a key regulator that drives immune suppression and inflammation in tumor microenvironment. CXCR2-targeted therapy has shown promising results in several solid tumors. However, the underlying mechanism of CXCR2-mediated cross-talk between gastric cancer cells and macrophages still remains unclear. Experimental Design: The expression of CXCR2 and its ligands in 155 human gastric cancer tissues was analyzed via immunohistochemistry, and the correlations with clinical characteristics were evaluated. A coculture system was established, and functional assays, including ELISA, transwell, cell viability assay, and qPCR, were performed to determine the role of the CXCR2 signaling axis in promoting gastric cancer growth and metastasis. A xenograft gastric cancer model and a lymph node metastasis model were established to study the function of CXCR2 in vivo. Results: CXCR2 expression is associated with the prognosis of patients with gastric cancer (P = 0.002). Of all the CXCR2 ligands, CXCL1 and CXCL5 can significantly promote migration of gastric cancer cells. Macrophages are the major sources of CXCL1 and CXCL5 in the gastric cancer microenvironment, and promote migration of gastric cancer cells through activating a CXCR2/STAT3 feed-forward loop. Gastric cancer cells secrete TNF-α to induce release of CXCL1 and CXCL5 from macrophages. Inhibiting CXCR2 pathway of gastric cancer cells can suppress migration and metastasis of gastric cancer in vitro and in vivo. Conclusions: Our study suggested a previously uncharacterized mechanism through which gastric cancer cells interact with macrophages to promote tumor growth and metastasis, suggesting that CXCR2 may serve as a promising therapeutic target to treat gastric cancer.
CCCP-Induced LC3 Lipidation Depends on Atg9 Whereas FIP200/Atg13 and Beclin 1/Atg14 are Dispensable
(Elsevier, 2013) Chen, Daohong; Chen, Xi; Li, Min; Zhang, Hao; Ding, Wen-Xing; Yin, Xiao-Ming; Pathology and Laboratory Medicine, School of Medicine
Treatment of cells with carbonyl cyanide m-chlorophenylhydrazone (CCCP), a mitochondrial proton gradient uncoupler, can result in mitochondrial damage and autophagy activation, which in turn eliminates the injured mitochondria in a Parkin-dependent way. How CCCP mobilizes the autophagy machinery is not fully understood. By analyzing a key autophagy step, LC3 lipidation, we examined the roles of two kinase complexes typically involved in the initiation and nucleation phases of autophagy, namely the ULK kinase complex (UKC) and the Beclin 1/Atg14 complex. We found that CCCP-induced LC3 lipidation could be independent of Beclin 1 and Atg14. In addition, deletion or knockdown of the UKC component FIP200 or Atg13 only led to a partial reduction in LC3 lipidation, indicating that UKC could be also dispensable for this step during CCCP treatment. In contrast, Atg9, which is important for transporting vesicles to early autophagosomal structure, was required for CCCP-induced LC3 lipidation. Taken together, these data suggest that CCCP-induced autophagy and mitophagy depends more critically on Atg9 vesicles than on UKC and Beclin 1/Atg14 complex.
Diabetes mellitus promotes the nasal colonization of high virulent Staphylococcus aureus through the regulation of SaeRS two-component system
(Taylor & Francis, 2023) Wang, Qichen; Nurxat, Nadira; Zhang, Lei; Liu, Yao; Wang, Yanan; Zhang, Lei; Zhao, Na; Dai, Yingxin; Jian, Ying; He, Lei; Wang, Hua; Bae, Taeok; Li, Min; Liu, Qian; Microbiology and Immunology, School of Medicine
Diabetic foot infections are a common complication of diabetes. Staphylococcus aureus is frequently isolated from diabetic foot infections and commonly colonizes human nares. According to the study, the nasal microbiome analysis revealed that diabetic patients had a significantly altered nasal microbial composition and diversity. Typically, the fasting blood glucose (FBG) level had an impact on the abundance and sequence type (ST) of S. aureus in diabetic patients. We observed that highly virulent S. aureus ST7 strains were more frequently colonized in diabetic patients, especially those with poorly controlled FBG, while ST59 was dominant in healthy individuals. S. aureus ST7 strains were more resistant to human antimicrobial peptides and formed stronger biofilms than ST59 strains. Critically, S. aureus ST7 strains displayed higher virulence compared to ST59 strains in vivo. The dominance of S. aureus ST7 strains in hyperglycemic environment is due to the higher activity of the SaeRS two-component system (TCS). S. aureus ST7 strains outcompeted ST59 both in vitro, and in nasal colonization model in diabetic mice, which was abolished by the deletion of the SaeRS TCS. Our data indicated that highly virulent S. aureus strains preferentially colonize diabetic patients with poorly controlled FBG through SaeRS TCS. Detection of S. aureus colonization and elimination of colonizing S. aureus are critical in the care of diabetic patients with high FBG.
Discovery of a small molecule targeting autophagy via ATG4B inhibition and cell death of colorectal cancer cells in vitro and in vivo
(Taylor & Francis, 2019-02) Fu, Yuanyuan; Hong, Liang; Xu, Jiecheng; Zhong, Guoping; Gu, Qiong; Gu, Qianqian; Guan, Yanping; Zheng, Xueping; Dai, Qi; Luo, Xia; Liu, Cui; Huang, Zhiying; Yin, Xiao-Ming; Liu, Peiqing; Li, Min; Pathology and Laboratory Medicine, School of Medicine
Human Atg4 homologs are cysteine proteases, which play key roles in the macroautophagy/autophagy process by cleaving Atg8 homologs for conjugation to lipid membranes and for deconjugation of Atg8 homologs from membranes. Expression of ATG4B is significantly increased in colorectal cancer cells compared to normal cells, suggesting that ATG4B may be important for cancer biology. Inhibition of ATG4B may reduce the autophagy activity, thereby sensitizing cancer cells to therapeutic agents. Thus, developing specific and potent ATG4B inhibitors for research as well as for potential therapeutic uses is highly needed. In this study, we integrated in silico screening and in vitro assays to discover a potent ATG4B inhibitor, named S130, from a noncommercial library. This chemical binds to ATG4B with strong affinity and specifically suppresses the activity of ATG4B but not other proteases. S130 did not cause the impairment of autophagosome fusion, nor did it result in the dysfunction of lysosomes. Instead, S130 might attenuate the delipidation of LC3-II on the autolysosomes to suppress the recycling of LC3-I, which normally occurs after LC3-II cleavage by ATG4B. Intriguingly, S130 induced cell death, which was accompanied with autophagy stress and could be further exacerbated by nutrient deprivation. Such cytotoxicity could be partially reversed by enhancing ATG4B activity. Finally, we found that S130 was distributed in tumor tissues in vivo and was also effective in arresting the growth of colorectal cancer cells. Thus, this study indicates that ATG4B is a potential anticancer target and S130 might be a novel small-molecule candidate for future cancer therapy.
Golgi-associated LC3 lipidation requires V-ATPase in noncanonical autophagy
(Nature Publishing Group, 2016-08-11) Gao, Ying; Liu, Yajun; Hong, Liang; Yang, Zuolong; Cai, Xinran; Chen, Xiaoyun; Fu, Yuanyuan; Lin, Yujie; Wen, Weijie; Li, Sitong; Liu, Xingguo; Huang, Heqing; Vogt, Andreas; Liu, Peiqing; Yin, Xiao-Ming; Li, Min; Department of Pathology and Laboratory Medicine, School of Medicine
Autophagy is an evolutionarily conserved catabolic process by which cells degrade intracellular proteins and organelles in the lysosomes. Canonical autophagy requires all autophagy proteins (ATGs), whereas noncanonical autophagy is activated by diverse agents in which some of the essential autophagy proteins are dispensable. How noncanonical autophagy is induced and/or inhibited is still largely unclear. In this study, we demonstrated that AMDE-1, a recently identified chemical that can induce canonical autophagy, was able to elicit noncanonical autophagy that is independent of the ULK1 (unc-51-like kinase 1) complex and the Beclin1 complex. AMDE-1-induced noncanonical autophagy could be specifically suppressed by various V-ATPase (vacuolar-type H(+)-ATPase) inhibitors, but not by disturbance of the lysosome function or the intracellular ion redistribution. Similar findings were applicable to a diverse group of stimuli that can induce noncanonical autophagy in a FIP200-independent manner. AMDE-1-induced LC3 lipidation was colocalized with the Golgi complex, and was inhibited by the disturbance of Golgi complex. The integrity of the Golgi complex was also required for multiple other agents to stimulate noncanonical LC3 lipidation. These results suggest that the Golgi complex may serve as a membrane platform for noncanonical autophagy where V-ATPase is a key player. V-ATPase inhibitors could be useful tools for studying noncanonical autophagy.

Browsing by Author "Li, Min"

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