Kegg Pathway: Ubiquitin mediated proteolysis

Cell Cycle. 2009 Dec 17; 8(24):
Xu C, Kim NG, Gumbiner BM

Glycogen synthase kinase-3 (GSK3) plays important roles in numerous signaling pathways that regulate a variety of cellular processes including cell proliferation, differentiation, apoptosis and embryonic development. In the canonical Wnt signaling pathway, GSK3 phosphorylation mediates proteasomal targeting and degradation of beta-catenin via the destruction complex. We recently reported a biochemical screen that discovered multiple additional protein substrates whose stability is regulated by Wnt signaling and/or GSK3 and these have important implications for Wnt/GSK3 regulation of different cellular processes.(1) In this article, we also present a bio-informatics based screen for proteins whose stability may be controlled by GSK3 and beta-Trcp, the SCF E3 Ubiquitin ligase that is responsible for beta-catenin degradation in the Wnt signaling pathway. Furthermore, we review various GSK3 regulated proteolysis substrates described in the literature. We propose that GSK3 phosphorylation dependent proteolysis is a widespread mechanism that the cell employs to regulate a variety of cell processes in response to signals.

Cell Death Differ. 2009 Nov 13;
Nihira K, Ando Y, Yamaguchi T, Kagami Y, Miki Y, Yoshida K

Post-translational modification and degradation of proteins by the Ubiquitin-proteasome system are key regulatory mechanisms in cellular responses to various stimuli. The NF-kappaB signaling pathway is controlled by the Ubiquitin-mediated proteolysis. RelA/p65, which is a main subunit of NF-kappaB, is Ubiquitinated for degradation by SOCS-1, but the functional mechanism of its Ubiquitination remains poorly understood. In this study we show that phosphorylation of RelA/p65 at Ser276 prevents its degradation by Ubiquitin-mediated proteolysis. In contrast, impairment of Ser276 phosphorylation affects constitutive degradation of RelA/p65. Importantly, we identify Pim-1 as a further kinase responsible for the phosphorylation of RelA/p65 at Ser276. Depletion of Pim-1 hinders not only Ser276 phosphorylation but also transactivation of RelA/p65 target genes. We also show that Pim-1 contributes to recruitment of RelA/p65 to kappaB-elements to activate NF-kappaB signalling after TNF-alpha stimulation. In concert with these results, the knockdown of Pim-1 impairs IL-6 production and augments apoptosis by interfering RelA/p65 activation. These findings provide a model in which Pim-1 phosphorylation of RelA/p65 at Ser276 allows defense against Ubiquitin-mediated degradation and whereby exerts activation of NF-kappaB signalling.Cell Death and Differentiation advance online publication, 13 November 2009; doi:10.1038/cdd.2009.174.

Development. 2009 Nov 11;
Chen D, Wang Q, Huang H, Xia L, Jiang X, Kan L, Sun Q, Chen D

Increasing evidence supports the idea that the regulation of stem cells requires both extrinsic and intrinsic mechanisms. However, much less is known about how intrinsic signals regulate the fate of stem cells. Studies on germline stem cells (GSCs) in the Drosophila ovary have provided novel insights into the regulatory mechanisms of stem cell maintenance. In this study, we demonstrate that a Ubiquitin-dependent pathway mediated by the Drosophila eff gene, which encodes the E2 Ubiquitin-conjugating enzyme Effete (Eff), plays an essential role in GSC maintenance. We show that Eff both physically and genetically interacts with dAPC2, a key component of the anaphase-promoting complex (APC), which acts as a multisubunit E3 ligase and plays an essential role in targeting mitotic regulators for degradation during exit from mitosis. This interaction indicates that Eff regulates the APC/C-mediated proteolysis pathway in GSCs. Moreover, we show that expression of a stable form of Cyclin A, but not full-length Cyclin A, results in GSC loss. Finally we show that, in common with APC2, Eff is required for the ubiquitylation of Cyclin A, and overexpression of full-length Cyclin A accelerates the loss of GSCs in the eff mutant background. Collectively, our data support the idea that Effete/APC-mediated degradation of Cyclin A is essential for the maintenance of germline stem cells in Drosophila. Given that the regulation of mitotic Cyclins is evolutionarily conserved between flies and mammals, our study also implies that a similar mechanism may be conserved in mammals.

Curr Hypertens Rep. 2009 Dec; 11(6): 389-95
Ranek MJ, Wang X

Doxorubicin (Dox) is a very potent anticancer agent, but its use is limited by its dose-dependent, irreversible cardiotoxicity. Despite intensive research efforts, the mechanism of Dox cardiotoxicity remains poorly understood, so very limited means are available for its prevention or effective management. Recent studies have revealed that a therapeutic dose of Dox can activate proteolysis in cardiomyocytes that is mediated by the Ubiquitin-proteasome system (UPS), and that the UPS-mediated degradation of a number of pivotal cardiac transcription factors and/or survival factors is enhanced by Dox treatment. These findings suggest that Dox-induced UPS activation may represent a new mechanism underlying Dox cardiotoxicity. Notably, recent experimental studies suggest that proteasome activation promotes cardiac remodeling during hypertension. This review surveys the current literature on the impact of Dox on the UPS and the potential mechanisms by which UPS activation may compromise the heart during Dox therapy.

Biochem Pharmacol. 2009 Oct 29;
Bourgoin-Voillard S, Gallo D, Laïos I, Cleeren A, Bali LE, Jacquot Y, Nonclercq D, Laurent G, Tabet JC, Leclercq G

Estrogen receptor alpha (ERalpha) belongs to the superfamily of nuclear receptors and as such acts as a ligand-modulated transcription factor. Ligands elicit in ERalpha conformational changes leading to the recruitment of coactivators required for the transactivation of target genes via cognate response elements. In many cells, activated ERalpha also undergoes downregulation by proteolysis mediated by the Ubiquitin/proteasome system. Although these various molecular processes have been well characterized, little is known as to which extent they are interrelated. In the present study, we used a panel of type I (estradiol derivatives and "linear", non-steroidal ligands) and type II ("angular" ligands) estrogens, in order to identify possible relationships between ligand binding affinity, recruitment of LxxLL-containing coactivators, ERalpha downregulation in MCF-7 cells and related transactivation activity of ligand-bound ERalpha. For type I estrogens, there was a clear-cut relationship between ligand binding affinity, hydrophobicity around C-11 of estradiol and ability of ERalpha to associate with LxxLL motifs, both in cell-free condition and in vivo (MCF-7 cells). Moreover, LxxLL motif recruitment by ERalpha seemed to be a prerequisite for the downregulation of the receptor. By contrast, type II ligands, as well as estradiol derivatives bearing a bulky side chain at 11beta, had much less tendency to promote ERalpha-LxxLL interaction or even behaved as antagonists in this respect, in agreement with the well known partial estrogenicity/antiestrogenicity of some of these compounds. Interestingly, some type II ligands which antagonized LxxLL motif recruitment were nonetheless able to enhance ERalpha-mediated gene transactivation.

Mol Cell Biol. 2009 Oct 26;
Kile AC, Koepp DM

A stable genome is critical to cell viability and proliferation. During DNA replication, the S-phase checkpoint pathway responds to replication stress. In budding yeast, the chromatin-bound F-box protein Dia2 is required to maintain genomic stability and may help replication complexes overcome sites of damaged DNA and natural fragile regions. SCF (Skp1/Cul1/F-box protein) complexes are modular Ubiquitin ligases. We show here that Dia2 is itself targeted for Ubiquitin-mediated proteolysis and activation of the S-phase checkpoint pathway inhibits Dia2 protein degradation. S-phase checkpoint mutants fail to stabilize Dia2 in response to replication stress. Deletion of DIA2 from these checkpoint mutants exacerbates their sensitivity to hydroxyurea and MMS, suggesting that stabilization of Dia2 contributes to the replication stress response. Unlike other F-box proteins, deletion of the F-box domain in Dia2 does not stabilize the protein. Rather, an N-terminal domain that is also required for nuclear localization is necessary for degradation. When a strong NLS is added to dia2 mutants lacking this domain, the Dia2 protein is both stable and nuclear. Together, our results suggest that Dia2 protein turnover does not involve an autocatalytic mechanism and that Dia2 proteolysis is inhibited by activation of the replication stress response.

Nucleic Acids Res. 2009 Oct 6;
Liu S, Wang H, Wang X, Lu L, Gao N, Rowe PS, Hu B, Wang Y

Matrix extracellular phosphoglycoprotein/osteoblast factor 45 (MEPE/OF45) was cloned in 2000 with functions related to bone metabolism. We identified MEPE/OF45 for the first time as a new co-factor of CHK1 in mammalian cells to protect cells from DNA damage induced killing. We demonstrate here that MEPE/OF45 directly interacts with CHK1. Knocking down MEPE/OF45 decreases CHK1 levels and sensitizes the cells to DNA damage inducers such as ionizing radiation (IR) or camptothicin (CPT)-induced killing. Over-expressing wild-type MEPE/OF45, but not the mutant MEPE/OF45 (depleted the key domain to interact with CHK1) increases CHK1 levels in the cells and increases the resistance of the cells to IR or CPT. MEPE/OF45, interacting with CHK1, increases CHK1 half-life and decreases CHK1 degradation through the Ubiquitine-mediated pathway. In addition, the interaction of MEPE/OF45 with CHK1 decreases CHK1 levels in the Ubiquitin E3 ligases (Cul1 and Cul4A) complex, which suggests that MEPE/OF45 competes with the Ubiquitin E3 ligases binding to CHK1 and thus decreases CHK1 from Ubiquitin-mediated proteolysis. These findings reveal an important role of MEPE/OF45 in protecting cells from DNA damage induced killing through stabilizing CHK1, which would provide MEPE/OF45 as a new target for sensitizing tumor cells to radiotherapy or chemotherapy.

Proc Natl Acad Sci U S A. 2009 Oct 13; 106(41): 17493-8
Li DQ, Ohshiro K, Reddy SD, Pakala SB, Lee MH, Zhang Y, Rayala SK, Kumar R

Metastasis-associated protein 1 (MTA1), a component of the nucleosome remodeling and histone deacetylation (NuRD) complex, is widely upregulated in human cancers. However, the mechanism for regulating its protein stability remains unknown. Here we report that MTA1 is an Ubiquitinated protein and targeted by the RING-finger E3 Ubiquitin-protein ligase constitutive photomorphogenesis protein 1 (COP1) for degradation via the Ubiquitin-proteasome pathway. Induced expression of wild-type COP1 but not its RING motif mutants promotes the Ubiquitination and degradation of MTA1, indicating that the ligase activity is required for the COP1-mediated proteolysis of MTA1. Conversely, depletion of endogenous COP1 resulted in a marked decrease in MTA1 Ubiquitination, accompanied by a pronounced accumulation of MTA1 protein. MTA1, in turn, destabilizes COP1 by promoting its autoUbiquitination, thus creating a tight feedback loop that regulates both MTA1 and COP1 protein stability. Accordingly, disruption of the COP1-mediated proteolysis by ionizing radiation leads to MTA1 stabilization, accompanied by an increased coregulatory function of MTA1 on its target. Furthermore, we discovered that MTA1 is required for optimum DNA double-strand break repair after ionizing radiation. These findings provide novel insights into the regulation of MTA1 protein and reveal a novel function of MTA1 in DNA damage response.

PLoS One. 2009; 4(10): e7332
van de Sluis B, Groot AJ, Vermeulen J, van der Wall E, van Diest PJ, Wijmenga C, Klomp LW, Vooijs M

BACKGROUND: The Copper Metabolism MURR1 Domain containing 1 protein COMMD1 has been associated with copper homeostasis, NF-kappaB signaling, and sodium transport. Recently, we identified COMMD1 as a novel protein in HIF-1 signaling. Mouse embryos deficient for Commd1 have increased expression of hypoxia/HIF-regulated genes i.e. VEGF, PGK and Bnip3. Hypoxia-inducible factors (HIFs) are master regulators of oxygen homeostasis, which control angiogenesis, erythropoiesis, glycolysis and cell survival/proliferation under normal and pathologic conditions. Although HIF activity is mainly controlled by Ubiquitination and protein degradation by the von Hippel Lindau (pVHL) tumor suppressor gene other mechanisms have recently been identified that regulate HIF signaling independently of pVHL. PRINCIPAL FINDINGS: Here we characterized the mechanism by which COMMD1 regulates HIF-1alpha protein degradation. We show that COMMD1 competes with the chaperone heat shock protein HSP90beta for binding to the NH(2)-terminal DNA-binding and heterodimerization domain of HIF-1alpha to regulate HIF-1alpha stability together with HSP70. Inhibition of HSP90 activity with 17-Allylamino-17-demethoxygeldanamycin (17-AAG) increased COMMD1-mediated HIF-1alpha degradation independent of Ubiquitin and pVHL. CONCLUSION/SIGNIFICANCE: These data reveal a novel role for COMMD1 in conjunction with HSP90beta/HSP70 in the Ubiquitin and O(2)-independent regulation of HIF-1alpha.

Am J Physiol Endocrinol Metab. 2009 Sep 22;
Sundaram P, Pang Z, Miao M, Yu L, Wing S

The Ubiquitin-proteasome system plays an important role in the degradation of myofibrillar proteins that occurs in muscle wasting. Many studies have demonstrated the importance of enzymes mediating conjugation of Ubiquitin. However, little is known about the role of deUbiquitinating enzymes. We previously showed that the USP19 deUbiquitinating enzyme is induced in atrophying skeletal muscle (Combaret et al. Amer. J. Physiol. 2005; 288: E693-E700). To further explore the role of USP19, we used siRNA in L6 muscle cells. Lowering USP19 by 70-90% in myotubes resulted in a 20% decrease in the rate of proteolysis and an 18% decrease in the rate of protein synthesis with no net change in protein content. Despite the decrease in overall synthesis, there were ~1.5 fold increases in protein levels of myosin heavy chain (MHC), actin, troponin T and a ~2.5 fold increase in tropomyosin. USP19 depletion also increased MHC and tropomyosin mRNA levels suggesting that this effect is due to increased transcription. Consistent with this, USP19 depletion increased myogenin protein and mRNA levels by ~2 fold. Lowering myogenin using siRNA prevented the increase in MHC and tropomyosin upon USP19 depletion indicating that myogenin mediated the increase in myofibrillar proteins. Dexamethasone treatment lowered MHC and increased USP19. Depletion of USP19 reversed the dexamethasone suppression of MHC. These studies demonstrate that USP19 modulates transcription of major myofibrillar proteins and indicate that the Ubiquitin system not only mediates the increased protein breakdown but is also involved in the decreased protein synthesis in atrophying skeletal muscle.

J Cell Sci. 2009 Oct 15; 122(Pt 20): 3663-72
Sasagawa Y, Otani M, Higashitani N, Higashitani A, Sato K, Ogura T, Yamanaka K

p97 (CDC-48 in Caenorhabditis elegans) is a Ubiquitin-selective AAA (ATPases associated with diverse cellular activities) chaperone and its key function is to disassemble protein complexes. p97 functions in diverse cellular processes including endoplasmic reticulum (ER)-associated degradation, membrane fusion, and meiotic and mitotic progression. However, its cellular functions in development have not yet been clarified. Here, we present data that p97 is involved in the switch from spermatogenesis to oogenesis in the germline of the C. elegans hermaphrodite. We found that the cdc-48.1 deletion mutant produced less sperm than the wild type and thus showed a decreased brood size. The cdc-48.1 mutation suppressed the sperm-overproducing phenotypes of fbf-1 and fem-3(gf) mutants. In addition, the p97/CDC-48-UFD-1-NPL-4 complex interacted with the E3 Ubiquitin ligase CUL-2 complex via NPL-4 binding to Elongin C. Furthermore, TRA-1A, which is the terminal effector of the sex determination pathway and is regulated by CUL-2-mediated proteolysis, accumulated in the cdc-48.1 mutant. Proteasome activity was also required for the brood size determination and sperm-oocyte switch. Our results demonstrate that the C. elegans p97/CDC-48-UFD-1-NPL-4 complex controls the sperm-oocyte switch by regulating CUL-2-mediated TRA-1A proteasome degradation.

Arch Virol. 2009; 154(9): 1417-31
Durand SV, Hulst MM, de Wit AA, Mastebroek L, Loeffen WL

The immune response to CSFV and the strategies of this virus to evade and suppress the pigs' immune system are still poorly understood. Therefore, we investigated the transcriptional response in the tonsils, median retropharyngeal lymph node (MRLN), and spleen of pigs infected with CSFV strains of similar origin with high, moderate, and low virulence. Using a porcine spleen/intestinal cDNA microarray, expression levels in RNA pools prepared from infected tissue at 3 dpi (three pigs per virus strain) were compared to levels in pools prepared from uninfected homologue tissues (nine pigs). A total of 44 genes were found to be differentially expressed. The genes were functionally clustered in six groups: innate and adaptive immune response, interferon-regulated genes, apoptosis, Ubiquitin-mediated proteolysis, oxidative phosphorylation and cytoskeleton. Significant up-regulation of three IFN-gamma-induced genes in the MRLNs of pigs infected with the low virulence strain was the only clear qualitative difference in gene expression observed between the strains with high, moderate and low virulence. Real-time PCR analysis of four response genes in all individual samples largely confirmed the microarray data at 3 dpi. Additional PCR analysis of infected tonsil, MRLN, and spleen samples collected at 7 and 10 dpi indicated that the strong induction of expression of the antiviral response genes chemokine CXCL10 and 2'-5' oligoadenylate synthetase 2, and of the TNF-related apoptosis-inducing ligand (TRAIL) gene at 3 dpi, decreased to lower levels at 7 and 10 dpi. For the highly and moderately virulent strains, this decrease in antiviral and apoptotic gene expression coincided with higher levels of virus in these immune tissues.

PLoS One. 2009; 4(7): e6155
Cinnamon Y, Feine O, Hochegger H, Bershadsky A, Brandeis M

BACKGROUND: Cellular contractility, essential for cell movement and proliferation, is regulated by microtubules, RhoA and actomyosin. The RhoA dependent kinase ROCK ensures the phosphorylation of the regulatory Myosin II Light Chain (MLC) Ser19, thereby activating actomyosin contractions. Microtubules are upstream inhibitors of contractility and their depolymerization or depletion cause cells to contract by activating RhoA. How microtubule dynamics regulates RhoA remains, a major missing link in understanding contractility. PRINCIPAL FINDINGS: We observed that contractility is inhibited by microtubules not only, as previously reported, in adherent cells, but also in non-adhering interphase and mitotic cells. Strikingly we observed that contractility requires Ubiquitin mediated proteolysis by a Cullin-RING Ubiquitin ligase. Inhibition of proteolysis, Ubiquitination and neddylation all led to complete cessation of contractility and considerably reduced MLC Ser19 phosphorylation. CONCLUSIONS: Our results imply that cells express a contractility inhibitor that is degraded by Ubiquitin mediated proteolysis, either constitutively or in response to microtubule depolymerization. This degradation seems to depend on a Cullin-RING Ubiquitin ligase and is required for cellular contractions.

Mol Cell Biol. 2009 Sep; 29(18): 4959-70
Chu Z, Eshaghi M, Poon SY, Liu J

Transcription of the MluI cell cycle box (MCB) motif-containing genes at G(1) phase is regulated by the MCB-binding factors (MBF) (also called DSC1) in Schizosaccharomyces pombe. Upon S-phase arrest, the MBF transcriptional activity is induced through the accumulation of the MBF activator Rep2. In this study, we show that the turnover of Rep2 is attributable to Ubiquitin-mediated proteolysis. Levels of Rep2 oscillate during the cell cycle, with a peak at G(1) phase, coincident with the MBF activity. Furthermore, we show that Rep2 Ubiquitination requires the function of the E3 ligase anaphase-promoting complex/cyclosome (APC/C). Ste9 can be phosphorylated by the checkpoint kinase Cds1 in vitro, and its inhibition/phosphorylation at S-phase arrest is dependent on the function of Cds1. Our data indicate that the Cds1-dependent stabilization of Rep2 is achieved through the inhibition/phosphorylation of APC/C-Ste9 at the onset of S-phase arrest. Stabilization of Rep2 is important for stimulating transcription of the MBF-dependent genes to ensure a sufficient supply of proteins essential for cell recovery from S-phase arrest. We propose that oscillation of Rep2 plays a role in regulation of periodic transcription of the MBF-dependent genes during cell cycle progression.

Int J Cancer. 2009 Nov 1; 125(9): 2029-35
Ikeuchi K, Marusawa H, Fujiwara M, Matsumoto Y, Endo Y, Watanabe T, Iwai A, Sakai Y, Takahashi R, Chiba T

Parkin has a critical role in the Ubiquitin-proteasome system as an E3-ligase targeting several substrates. Our recent finding that Parkin-deficient mice are susceptible to tumorigenesis provided evidence that Parkin is a tumor suppressor gene. Dysfunction of the Parkin gene is frequently observed in various human cancers, but the mechanism underlying the cell cycle disruption induced by Parkin dysfunction that leads to carcinogenesis is not known. Here, we demonstrated that Parkin expression in colonic epithelial cells is regulated in a cell cycle-associated manner. Epidermal growth factor (EGF) stimulation upregulated Parkin gene expression in human colon cells. Inhibition of the phosphoinositide 3-kinase [PI(3)K]-Akt-dependent pathways suppressed growth factor-induced Parkin expression. The expression of alternatively spliced Parkin isoforms with various deletions spanning exons 3-6 was detected in 18 of 43 (42%) human colorectal cancer tissues. Wild-type Parkin induced the degradation of cyclin E protein, but the alternatively spliced Parkin identified in colon cancers showed defective proteolysis of cyclin E. These findings indicate that Parkin expression is induced by growth factor stimulation and is involved in the cell cycle regulation of colon cells. Tumor-specific expression of alternatively spliced Parkin isoforms might contribute to enhanced cell proliferation through the attenuation of proteolysis-mediated cyclin E regulation in human colorectal cancers.

J Mol Biol. 2009 Aug 28; 391(4): 691-702
Huang X, Langelotz C, Hetfeld-Pechoc BK, Schwenk W, Dubiel W

The Wnt/beta-catenin signalling pathway has important roles in normal cellular proliferation, development and angiogenesis. Many malignant transformations, including sporadic colorectal tumours, are caused by constitutive activation of the Wnt route due to mutations in the tumour suppressor protein adenomatous polyposis coli (APC) or the beta-catenin oncogene, ultimately resulting in reduced beta-catenin degradation by the Ubiquitin (Ub) proteasome system (UPS). The COP9 signalosome (CSN) regulates the UPS by controlling cullin-RING Ub ligases (CRLs). We show here that the CSN and the beta-catenin destruction complex cooperate in targeting beta-catenin for degradation by the UPS. Together with the CRL that Ubiquitinates beta-catenin, they form a supercomplex responsible for beta-catenin degradation. Wnt3A, glycogen synthase kinase 3beta inhibitors or mutation of CSN-mediated deneddylation induce the disassembly of the supercomplex and the accumulation of beta-catenin. Likewise, downregulation of the CSN in HeLa cells leads to retarded degradation of beta-catenin. Additionally, we found that the knockdown of the CSN causes accelerated proteolysis of APC, an essential component of the beta-catenin destruction complex, which is degraded by the UPS as beta-catenin. We show here that APC is stabilised by the Ub-specific protease 15 (USP15) associated with the CSN. This is demonstrated by over-expression of siRNA oligonucleotides against USP15 or by over-expression of an USP15 mutant, which is unable to degrade poly-Ub chains. Thus, the CSN controls the Wnt/beta-catenin signalling by assisting the assembly of beta-catenin-degrading supercomplexes by deneddylation and, simultaneously, by stabilising APC via CSN-associated USP15. The CSN regulates the balance between beta-catenin and APC. Disturbance of this balance can cause cancer by driving cell transformation, tumour angiogenesis and metastasis. A model is provided that proposes a role of CSN-mediated deneddylation in the formation of the beta-catenin-degrading supercomplex and the protection of complex-bound APC via CSN-associated USP15.

J Vis Exp. 2009;
Ciechanover A

Aaron Ciechanover was born in Haifa, Israel in October 1947. He shared the Nobel Prize in Chemistry in 2004 with Avram Hershko and Irwin Rose for their discovery of Ubiquitin-mediated protein degradation. When Ciechanover began his work on proteolysis, the field was outside the realm of scientific mainstream as many thought that the fundamental secrets relating to sequence specificity were relevant to the synthetic side, or code side. The notion that specific sequences could selectively guide a destructive process did not naturally occur to scientists including Ciechanover himself. The emergence of controversial evidence demonstrating a requirement for metabollic energy in intracellular protein degradation, refuted the idea that cellular proteolysis was an entirely exergonic process occuring in the lysosme and prompted Ciechanover, Hershko, and Rose to "launch an attack" on the system, in order to uncover true pathway. Later findings of Ciechanover and subsequent groups showed that not only was the process energy-dependent, but that 8% of the human genome is remarkabley one large Ubiquitin system. Following the recapitulation and reflection of his work, Ciechanover shares insights into his principal and philosophical approach to science and life alltogether. The life and work of Aaron Ciechanover are deeply rooted and influenced by Judaism and Israel and it is therefore that with only brief intermission, Ciechanover spent his scientific career in Israel as he is--through his presence and work--able to contribute and shape presence and future of the State of Israel.

J Virol. 2009 Sep; 83(17): 8885-92
Vos RM, Altreuter J, White EA, Howley PM

Proteomic identification of human papillomavirus type 16 (HPV16) E6-interacting proteins revealed several proteins involved in Ubiquitin-mediated proteolysis. In addition to the well-characterized E6AP Ubiquitin-protein ligase, a second HECT domain protein (HERC2) and a deubiquitylating enzyme (USP15) were identified by tandem affinity purification of HPV16 E6-associated proteins. This study focuses on the functional consequences of the interaction of E6 with USP15. Overexpression of USP15 resulted in increased levels of the E6 protein, and the small interfering RNA-mediated knockdown of USP15 decreased E6 protein levels. These results implicate USP15 directly in the regulation of E6 protein stability and suggest that ubiquitylated E6 could be a substrate for USP15 Ubiquitin peptidase activity. It remains possible that E6 could affect the activity of USP15 on specific cellular substrates, a hypothesis that can be tested as more is learned about the substrates and pathways controlled by USP15.

Int J Hyperthermia. 2009 Jun 15; 1-9
Udono H, Ichiyanagi T, Mizukami S, Imai T

Heat shock proteins (HSP) are molecular chaperones implicated in facilitation of protein folding and translocation between distinct compartments, and hence in preventing protein from aggregation. In terms of proteolysis, HSP act as a double-edged sword, stimulating proteasome-dependent proteolysis while preventing the degradation of the same proteins, even though in both cases association of unfolded proteins with HSP is the initial step. The proteasomal degradation products are utilised as ligands of major histocompatibility complex (MHC) class I molecules to be recognised by CD8(+) T cells, leading to activation of cytotoxic T cell immunity indispensable in fighting virus infections and cancers. In this context, HSP-mediated antigen traffic towards proteasomal degradation is coupled with acquired T cell immunity. In addition, exogenous antigens internalised by dendritic cells (DC) are also forwarded to the proteasome, possibly through the ER-associated degradation (ERAD) system, based on the fusion of the ER-membrane to the endosome containing the antigens. Thus, antigens within endosomes might be translocated to the cytosol, possibly through the Sec61 complex recruited from ER and degraded by the proteasome, rendering their peptides presentable by MHC class I molecules, a process known as cross-presentation. Since binding protein (Bip) facilitates degradation of most ER luminal soluble proteins in yeast, it is possible that endosomal HSP in DC, mimicking the action of Bip, facilitate the degradation of internalised soluble antigens. This may explain why the HSP-peptide/protein complex is extremely efficient in terms of cross-presentation ability. In this review, we discuss how HSP are linked to the Ubiquitin-dependent proteasome system to generate peptides presentable by MHC molecules.

Mol Cell Biol. 2009 Sep; 29(17): 4798-811
Nakao R, Hirasaka K, Goto J, Ishidoh K, Yamada C, Ohno A, Okumura Y, Nonaka I, Yasutomo K, Baldwin KM, Kominami E, Higashibata A, Nagano K, Tanaka K, Yasui N, Mills EM, Takeda S, Nikawa T

Skeletal muscle atrophy caused by unloading is characterized by both decreased responsiveness to myogenic growth factors (e.g., insulin-like growth factor 1 [IGF-1] and insulin) and increased proteolysis. Here, we show that unloading stress resulted in skeletal muscle atrophy through the induction and activation of the Ubiquitin ligase Cbl-b. Upon induction, Cbl-b interacted with and degraded the IGF-1 signaling intermediate IRS-1. In turn, the loss of IRS-1 activated the FOXO3-dependent induction of atrogin-1/MAFbx, a dominant mediator of proteolysis in atrophic muscle. Cbl-b-deficient mice were resistant to unloading-induced atrophy and the loss of muscle function. Furthermore, a pentapeptide mimetic of tyrosine(608)-phosphorylated IRS-1 inhibited Cbl-b-mediated IRS-1 Ubiquitination and strongly decreased the Cbl-b-mediated induction of atrogin-1/MAFbx. Our results indicate that the Cbl-b-dependent destruction of IRS-1 is a critical dual mediator of both increased protein degradation and reduced protein synthesis observed in unloading-induced muscle atrophy. The inhibition of Cbl-b-mediated Ubiquitination may be a new therapeutic strategy for unloading-mediated muscle atrophy.