ABSTRACT
Autophagy is an intracellular degradation process that delivers cytoplasmic constituents to the lysosome. Abnormality of autophagy is related to many human diseases, which provides a new clue to the pathophysiology of human cancer. However, the role of autophagy in normal liver physiology and the pathogenesis of liver diseases need to be further clarified. This article reviews the role of autophagy in the occurrence and development of hepatocellular carcinoma and the molecular mechanisms.
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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.
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Previous studies suggest that the reduction of SMAD3 (mothers against decapentaplegic homolog 3) has a great impact on tumor development, but its exact pathological function remains unclear. In this study, we found that the protein level of SMAD3 was greatly reduced in human-grade IV glioblastoma tissues, in which LAMP2A (lysosome-associated membrane protein type 2A) was significantly up-regulated. LAMP2A is a key rate-limiting protein of chaperone-mediated autophagy (CMA), a lysosome pathway of protein degradation that is activated in glioma. We carefully analyzed the amino-acid sequence of SMAD3 and found that it contained a pentapeptide motif biochemically related to KFERQ, which has been proposed to be a targeting sequence for CMA. In vitro, we confirmed that SMAD3 was degraded in either serum-free or KFERQ motif deleted condition, which was regulated by LAMP2A and interacted with HSC70 (heat shock cognate 71 kDa protein). Using isolated lysosomes, amino-acid residues 75 and 128 of SMAD3 were found to be of importance for this process, which affected the CMA pathway in which SMAD3 was involved. Similarly, down-regulating SMAD3 or up-regulating LAMP2A in cultured glioma cells enhanced their proliferation and invasion. Taken together, these results suggest that excessive activation of CMA regulates glioma cell growth by promoting the degradation of SMAD3. Therefore, targeting the SMAD3-LAMP2A-mediated CMA-lysosome pathway may be a promising approach in anti-cancer therapy.
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Objective:To observe the expression of molecular chaperone-mediated autophagy in hippocampal neurons and its relationship with brain injury after recurrent-status seizures.Methods:Seven-day-old SD rats were divided into two groups according to simple randomization: the control group (NS group, 6 rats) and the recurrent-seizure group (RS group, 39 rats). Rats in the RS group were subjected to recurrent seizures after repeated inhalation of flurothyl, with 30 minutes once each day for consecutive 7 days.A total of 30 convulsive models were successfully established (9 rats that failed to establish models were discarded), and they were further divided into 0 h, 1.5 h, 3 h, 12 h and 24 h after the last seizure according to simple randomization, with 6 rats in each group.Western blot and reverse transcription-polymerase chain reaction (RT-PCR) were adopted for the observation of the expression of molecular chaperone-mediated autophagy markers [heat shock cognate protein 70 (Hsc70), lysosome-associated membrane protein type 2a (LAMP-2a), heat shock protein 40(HSP40) and heat shock protein 90(HSP90)] in hip-pocampal neurons, and apoptosis was detected by TdT-mediated dUTP nick-end labeling (TUNEL).Results:(1) RT-PCR and Western blot showed that, compared with the NS group, the expression of Hsc70, as a molecular chape-rone, started to increase at 1.5 h and continued until 24 h after the last seizure in the RS group ( P<0.05). HSP90 increased immediately after the last seizure and lasted until 24 h after the seizure ( P<0.01); the expression of HSP40 and LAMP-2a also showed high expression after the last seizure episode ( P<0.05). (2) The TUNEL method showed that the number of apoptotic cells in the hippocampal CA1 region increased significantly at 3 h (36.33±5.16)/40 field, 12 h (44.83±4.83)/40 field and 24 h (54.83±7.16)/40 field after the last seizure compared with NS group(15.16±2.48)/40 field ( P<0.01). (3) Pearson correlation analysis showed that the level of apoptosis in hippocampal CA1 region of rats after recurrent seizures was positively correlated with the expression of molecular chaperone marker molecules (Hsc70: r=0.734, P=0.001; LAMP2a: r=0.790, P<0.001). Conclusions:After recurrent seizures in developmental rats, the presence of increased expression of multiple molecular chaperone-mediated autophagy, which may positively correlate with apoptosis, may be involved in the process of brain injury.
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Chaperone-mediated autophagy (CMA) is a lysosome-dependent selective degradation pathway implicated in the pathogenesis of cancer and neurodegenerative diseases. However, the mechanisms that regulate CMA are not fully understood. Here, using unbiased drug screening approaches, we discover Metformin, a drug that is commonly the first medication prescribed for type 2 diabetes, can induce CMA. We delineate the mechanism of CMA induction by Metformin to be via activation of TAK1-IKKα/β signaling that leads to phosphorylation of Ser85 of the key mediator of CMA, Hsc70, and its activation. Notably, we find that amyloid-beta precursor protein (APP) is a CMA substrate and that it binds to Hsc70 in an IKKα/β-dependent manner. The inhibition of CMA-mediated degradation of APP enhances its cytotoxicity. Importantly, we find that in the APP/PS1 mouse model of Alzheimer's disease (AD), activation of CMA by Hsc70 overexpression or Metformin potently reduces the accumulated brain Aβ plaque levels and reverses the molecular and behavioral AD phenotypes. Our study elucidates a novel mechanism of CMA regulation via Metformin-TAK1-IKKα/β-Hsc70 signaling and suggests Metformin as a new activator of CMA for diseases, such as AD, where such therapeutic intervention could be beneficial.
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In this study, the effect of benzo[α]pyrene (BaP) on chaperone-mediated autophagy (CMA) in a simulated hypoxia environment was observed and the relationship to heat shock protein 90 (HSP90) was clarified. With HSP90 inhibitor geldanamycin (GA) and HSP90α silenced, the mRNA and protein expression of hypoxia-inducible factor-1α (HIF-1α), HSP90, heat shock cognate protein 70 (HSC70), and lysosomal associated protein 2A (LAMP-2A) of A549 cells on hypoxic environment by BaP were tested. Alkaline comet experiment, immunofluorescence γ-H2AX focus experiment, quantitative real-time PCR (qPCR), and Western blot analyses were used to clarify the relationship between the DNA damage of different concentrations of BaP in A549 cells and the mRNA and protein expression of CMA-related factors. The results show that hypoxia can promote the expression of mRNA and protein of CMA-related factors in A549 cells. This study found that BaP has an inhibitory effect on CMA under the hypoxic environment. The inhibition or silencing of HSP90 will enhance the inhibitory effect of BaP on CMA. In a normoxic environment, BaP causes DNA damage and promotes CMA.
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Aim To research the cross-talk and conversion between macroautophagy and chaperone-media-ted autophagy ( CMA) in cultured Burkitt lymphoma Raji cells induced by starvation. Methods The autophagic vacuoles were observed by fluorescence microscopy and confocal laser-scanning microscopy with monodansylcadaverine staining. The expression of autophagy associated-proteins were determined by West-em blot. Results Both macroautophagy and CMA were activated sequentially instead of simultaneously in starvation-induced Raji cells, and macroautophagy was quickly activated and peaked during the first hours of near baseline. With starvation persisted, CM A progressively increased along with the decline of macroautoph- A gy. Conclusions Macroautophagy and CMA are maximally activated during different stages of starvation. Activation of these two pathways is often sequential. The sequential switch from macroautophagy to CMA might be conducive to the adaption of cancer cells to miscellaneous intracellular or extracellular changes, maintaining their own growth and proliferation.
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Objective • To investigate the effects of chaperone-mediated autophagy (CMA) on α-synuclein oligomers level in the Parkinson's disease (PD) cell model with impaired ubiquitin proteasome system (UPS). Methods • The PD cell model was established by adding the proteasome inhibitor lactacystin in the SK-N-SH cell line stably transfected with wild type α-synuclein. The levels of α-synuclein oligomers, lysosome-associated membrane protein type 2A (LAMP2A) and 70 kDa heat shock homologous protein (HSC70) were detected using Western blotting. CMA function was inhibited with LAMP2A siRNA, and its effects on α-synuclein oligomers and cell viability were detected. Furthermore, the interaction of LAMP2A with α-synuclein oligomers was detected by immunoprecipitation. Results • In the PD cell model, the levels of α-synuclein oligomers, and CMA related proteins, i.e. LAMP2A and HSC70, were increased. Inhibiting the expression of LAMP2A further increased α-synuclein oligomers level, while it decreased cell viability. Furthermore, LAMP2A could interact with α-synuclein oligomers. Conclusion • In the PD cell model, CMA is one of the pathways regulating α-synuclein oligomers level. Inhibiting CMA function can further increase the α-synuclein oligomers level and deteriorate cell survival.
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Objective@#To investigate the role of lysosome-associated membrane protein type 2A (LAMP-2A) for immune-mediated liver injury of primary biliary cholangitis (PBC).@*Methods@#The association between LAMP-2A expression and PBC was examined by immunohistochemistry and electron microscopy in liver tissue samples from patients with PBC. Furthermore, the immunological damage of LAMP-2A overexpression on mouse liver was observed by adeno-associated virus (AAV) overexpression technique. The expression level of mRNA was analyzed by Student's t-test. The data were graphed and analyzed statistically using graphpad prism 5 (GraphPad Software).A value of p < 0.05 was considered statistically significant.@*Results@#The expression of LAMP-2A in liver tissue of PBC patients was increased, and the autophagosome formation was observed in hepatocytes. C57BL/6 mice were injected into the caudal vein with LAMP-2A AAV for 6 weeks. The formation of autophagosomes in mouse hepatocytes was increased significantly. The expression of related molecules was abnormal; simultaneously, the degree of lymphocyte infiltration in the liver tissue of mice was significantly higher than the control group.@*Conclusion@#An overexpression of LAMP-2A in the liver of patients with PBC may induce and/or promote the hepatic inflammatory response, especially the portal inflammatory infiltrate.