Amyloid beta (Aβ) precursor protein (APP) is a key protein in the pathogenesis of Alzheimer's disease (AD). Both APP and its paralogue APLP1 (amyloid beta precursor-like protein 1) have multiple functions in cell adhesion and proliferation. Previously it was thought that autophagy is a novel beta-amyloid peptide (Aβ)-generating pathway activated in AD. However, the protein proteolysis of APLP1 is still largely unknown. The present study shows that APLP1 is rapidly degraded in neuronal cells in response to stresses, such as proteasome inhibition. Activation of the endoplasmic reticulum (ER) stress by proteasome inhibitors induces autophagy, causing reduction of mature APLP1/APP. Blocking autophagy or JNK stress kinase rescues the protein expression for both APP and APLP1. Therefore, our results suggest that APP/APLP1 is degraded through autophagy and the APLP1 proteolysis is mainly mediated by autophagy-lysosome pathway.
Amyloid beta-Protein Precursor ; genetics ; metabolism ; Animals ; Autophagy ; Cell Line ; Endoplasmic Reticulum ; metabolism ; JNK Mitogen-Activated Protein Kinases ; antagonists & inhibitors ; metabolism ; Leupeptins ; pharmacology ; Mice ; Neurons ; cytology ; metabolism ; Proteasome Endopeptidase Complex ; metabolism ; Proteasome Inhibitors ; Protein Stability ; Rats

Recent researches indicate that ubiquitin-protea some pathway plays an important role in apoptosis regulation. Proteasome inhibitors induce apoptosis in many kinds of neoplastic cells, thus provide a great opportunity for exploring synergy of proteasome inhibitors and other apoptosis-inducing agents. In this study, the effect of the proteasome inhibitor Z-LLL-CHO combined with etoposide (VP16) on leukemic cell lines M-07e and TF-1 was investigated by MTT assay, trypan blue exclusion, flow cytometry and Western blot. The results showed that the combination of Z-LLL-CHO and VP16 was much more effective than either agents alone in promoting cytotoxicity in both cell lines evaluated. Accumulation of cells in S + G2/M phase of the cell cycle was observed in the cells treated with VP16 and Z-LLL-CHO alone, while apparent increase of sub-G0/G1 fraction was detected in cells treated with combination of the agents. The cleavage of Bcl-2 into a shortened 22 kD fragment was detected in M-07e cells exposed to either agents alone, and the fraction of 22 kD fragment was increased in the cells treated with combination of the agents. In conclusion, the combination of Z-LLL-CHO and VP16 enhanced their individual cytotoxic effect by inducing apoptosis, in which increase of S + G2/M fraction in cell cycle as well as the enhanced cleavage of Bcl-2 are the possible mechanism of the additive effect on leukemic cells by Z-LLL-CHO and VP16.
Apoptosis ; drug effects ; Cell Cycle ; drug effects ; Cell Line, Tumor ; Cysteine Endopeptidases ; Etoposide ; pharmacology ; Humans ; Leukemia ; pathology ; Multienzyme Complexes ; antagonists & inhibitors ; Oligopeptides ; pharmacology ; Proteasome Endopeptidase Complex ; Proto-Oncogene Proteins c-bcl-2 ; analysis

The inhibition of protein degradation through the ubiquitin-proteasome pathway is a recently developed approach to cancer treatment which extends the range of cellular target for chemotherapy. This therapeutic strategy is very interesting since the proteasomes carry out the regulated degradation of unnecessary or damaged cellular proteins, a process that is dysregulated in many cancer cells. Based on this hypothesis, the proteasome complex inhibitor Bortezomib was approved for use in multiple myeloma patients by FDA in 2003. Drug discovery programs in academy and the pharmaceutical industry have developed a range of synthetic and natural inhibitors of the 20S proteasome core particle that have entered human clinical trials as significant anti-cancer leads. The main results from the use of proteasome inhibition in cancer chemotherapy, the structure of several proteasome inhibitors and their synthesis is going to be reviewed in this paper.
Acetylcysteine ; analogs & derivatives ; chemical synthesis ; chemistry ; Antineoplastic Agents ; chemical synthesis ; classification ; therapeutic use ; Boronic Acids ; chemical synthesis ; chemistry ; therapeutic use ; Bortezomib ; Cysteine Proteinase Inhibitors ; chemical synthesis ; classification ; Dipeptides ; chemical synthesis ; chemistry ; Humans ; Multiple Myeloma ; drug therapy ; enzymology ; Peptides, Cyclic ; chemical synthesis ; chemistry ; Proteasome Endopeptidase Complex ; metabolism ; Proteasome Inhibitors ; Pyrazines ; chemical synthesis ; chemistry ; therapeutic use ; Ubiquitin ; antagonists & inhibitors ; metabolism

Glucosamine, a naturally occurring amino monosaccharide, has been reported to play a role in the regulation of apoptosis more than half century. However the effect of glucosamine on tumor cells and the involved molecular mechanisms have not been thoroughly investigated. Glucosamine enters the hexosamine biosynthetic pathway (HBP) downstream of the rate-limiting step catalyzed by the GFAT (glutamine:fluctose-6-phosphate amidotransferase), providing UDP-GlcNAc substrates for O-linked beta-N-acetylglucosamine (O-GlcNAc) protein modification. Considering that O-GlcNAc modification of proteasome subunits inhibits its activity, we examined whether glucosamine induces growth inhibition via affecting proteasomal activity. In the present study, we found glucosamine inhibited proteasomal activity and the proliferation of ALVA41 prostate cancer cells. The inhibition of proteasomal activity results in the accumulation of ubiquitinated proteins, followed by induction of apoptosis. In addition, we demonstrated that glucosamine downregulated proteasome activator PA28gamma and overexpression of PA28gamma rescued the proteasomal activity and growth inhibition mediated by glucosamine. We further demonstrated that inhibition of O-GlcNAc abrogated PA28gamma suppression induced by glucosamine. These findings suggest that glucosamine may inhibit growth of ALVA41 cancer cells through downregulation of PA28gamma and inhibition of proteasomal activity via O-GlcNAc modification.
Acetylglucosamine/chemistry/metabolism ; Alloxan/pharmacology ; Apoptosis/*drug effects ; Autoantigens/genetics/*metabolism ; Cell Line, Tumor ; Cell Proliferation/*drug effects ; Gene Expression Regulation, Neoplastic ; Glucosamine/*pharmacology ; Humans ; Male ; Phosphorylation ; Prostatic Neoplasms/*enzymology ; Proteasome Endopeptidase Complex/*antagonists & inhibitors/genetics/metabolism ; RNA, Small Interfering/genetics ; Ubiquitinated Proteins/metabolism

PURPOSE: To investigate the effects of resveratrol on the expression of hypoxia-inducible factor 1alpha (HIF-1alpha) and vascular endothelial growth factor (VEGF) in human adult retinal pigment epithelial (ARPE-19) cells, and on experimental choroidal neovascularization (CNV) in mice. MATERIALS AND METHODS: ARPE-19 cells were treated with different concentrations of resveratrol and then incubated under hypoxic conditions with subsequent evaluation of cell viability, expression of HIF-1alpha, and expression of VEGF. The effects of resveratrol on the synthesis and degradation of hypoxia-induced HIF-1alpha were evaluated using inhibitors of the PI3K/Akt/mTOR and the ubiquitin proteasome pathways. In animal studies, CNV lesions were induced in C57BL/6 mice by laser photocoagulation. After 7 days of oral administration of resveratrol or vehicle, which began one day after CNV induction, image analysis was used to measure CNV areas on choroidal flat mounts stained with isolectin IB4. RESULTS: In ARPE-19 cells, resveratrol significantly inhibited HIF-1alpha and VEGF in a dose-dependent manner, by blocking the PI3K/Akt/mTOR signaling pathway and by promoting proteasomal HIF-1alpha degradation. In mice experiments, orally administered resveratrol significantly inhibited CNV growth in a dose-dependent manner. CONCLUSION: Resveratrol may have therapeutic value in the management of diseases involving pathological neovascularization.
Adult ; Animals ; Anoxia/metabolism/physiopathology ; Cell Survival/drug effects ; Choroidal Neovascularization/*metabolism/pathology ; Humans ; Hypoxia-Inducible Factor 1, alpha Subunit/*drug effects/metabolism ; Mice ; Mice, Inbred C57BL ; Phosphatidylinositol 3-Kinases/antagonists & inhibitors/*physiology ; Proteasome Endopeptidase Complex ; Proto-Oncogene Proteins c-akt/antagonists & inhibitors/*physiology ; Retinal Pigment Epithelium/*drug effects/metabolism ; Signal Transduction ; Stilbenes/administration & dosage/*pharmacology ; TOR Serine-Threonine Kinases/antagonists & inhibitors/*physiology ; Ubiquitin ; Vascular Endothelial Growth Factor A/*drug effects/metabolism

17β-estradiol (E2) treatment of cells results in an upregulation of SIRT1 and a down-regulation of PPARγ. The decrease in PPARγ expression is mediated by increased degradation of PPARγ. Here we report that PPARγ is ubiquitinated by HECT E3 ubiquitin ligase NEDD4-1 and degraded, along with PPARγ, in response to E2 stimulation. The PPARγ interacts with ubiquitin ligase NEDD4-1 through a conserved PPXY-WW binding motif. The WW3 domain in NEDD4-1 is critical for binding to PPARΓ. NEDD4-1 overexpression leads to PPARγ ubiquitination and reduced expression of PPARγ. Conversely, knockdown of NEDD4-1 by specific siRNAs abolishes PPARΓ ubiquitination. These data indicate that NEDD4-1 is the E3 ubiquitin ligase responsible for PPARγ ubiquitination. Here, we show that NEDD4-1 delays cellular senescence by degrading PPARΓ expression. Taken together, our data show that E2 could upregulate SIRT1 expression via promoting the PPARΓ ubiquitination-proteasome degradation pathway to delay the process of cell senescence.
Amino Acid Motifs ; Animals ; Cellular Senescence ; Down-Regulation ; drug effects ; Endosomal Sorting Complexes Required for Transport ; antagonists & inhibitors ; genetics ; metabolism ; Estradiol ; pharmacology ; Female ; HeLa Cells ; Humans ; Mice ; Mice, Inbred BALB C ; Nedd4 Ubiquitin Protein Ligases ; PPAR gamma ; genetics ; metabolism ; Proteasome Endopeptidase Complex ; metabolism ; Protein Structure, Tertiary ; RNA Interference ; RNA, Small Interfering ; metabolism ; Sirtuin 1 ; genetics ; metabolism ; Ubiquitin ; metabolism ; Ubiquitin-Protein Ligases ; antagonists & inhibitors ; genetics ; metabolism ; Ubiquitination ; drug effects ; Up-Regulation ; drug effects