How to Inactivate Human Ubiquitin E3 Ligases by Mutation.

E3 ubiquitin ligases are the ultimate enzymes involved in the transfer of ubiquitin to substrate proteins, a process that determines the fate of the modified protein. Numerous diseases are caused by defects in the ubiquitin-proteasome machinery, including when the activity of a given E3 ligase is hampered. Thus, inactivation of E3 ligases and the resulting effects at molecular or cellular level have been the focus of many studies during the last few years. For this purpose, site-specific mutation of key residues involved in either protein interaction, substrate recognition or ubiquitin transfer have been reported to successfully inactivate E3 ligases. Nevertheless, it is not always trivial to predict which mutation(s) will block the catalytic activity of a ligase. Here we review over 250 site-specific inactivating mutations that have been carried out in 120 human E3 ubiquitin ligases. We foresee that the information gathered here will be helpful for the design of future experimental strategies.

CD5L is a pleiotropic player in liver fibrosis controlling damage, fibrosis and immune cell content.

BACKGROUND: Chronic hepatic inflammation leads to liver fibrosis, which may progress to cirrhosis, a condition with high morbidity. Our aim was to assess the as yet unknown role of innate immunity protein CD5L in liver fibrosis. METHODS: CD5L was measured by ELISA in plasma samples from cirrhotic (n = 63) and hepatitis (n = 39) patients, and healthy controls (n = 7), by immunohistochemistry in cirrhotic tissue (n = 12), and by quantitative RT-PCR in mouse liver cell subsets isolated by cell sorting. Recombinant CD5L (rCD5L) was administered into a murine model of CCl4-induced fibrosis, and damage, fibrosis and hepatic immune cell infiltration, including the LyC6hi (pro-fibrotic)-LyC6low (pro-resolutive) monocyte ratio were determined. Moreover, rCD5L was added into primary human hepatic stellate cells to study transforming growth factor ß (TGFß) activation responses. FINDINGS: Cirrhotic patients showed elevated plasma CD5L concentrations as compared to patients with hepatitis and healthy controls (Mann-Whitney test p < 0·0001). Moreover, plasma CD5L correlated with disease progression, FIB4 fibrosis score (r:0·25, p < 0·0001) and tissue expression (r = 0·649; p = 0·022). Accordingly, CCl4-induced damage increased CD5L levels in total liver, particularly in hepatocytes and macrophages. rCD5L administration attenuated CCl4-induced injury and fibrosis as determined by reduced serum transaminase and collagen content. Moreover, rCD5L inhibited immune cell infiltration and promoted a phenotypic shift in monocytes from LyC6hi to LyC6low. Interestingly, rCD5L also had a direct effect on primary human hepatic stellate cells promoting SMAD7 expression, thus repressing TGFß signalling. INTERPRETATION: Our study identifies CD5L as a key pleiotropic inhibitor of chronic liver injury. FUND: Fundació Marató TV3, AGAUR and the ISCIII-EDRF.

Fibre-type-specific and Mitochondrial Biomarkers of Muscle Damage after Mountain Races.

Consequences of running mountain races on muscle damage were investigated by analysing serum muscle enzymes and fibre-type-specific sarcomere proteins. We studied 10 trained amateur and 6 highly trained runners who ran a 35 km and 55 km mountain trail race (MTR), respectively. Levels of creatine kinase (CK), CK-MB isoform (CK-MB), sarcomeric mitochondrial CK (sMtCK), transaminases (AST and ALT), cardiac troponin I (cTnI) and fast (FM) and slow myosin (SM) isoforms, were assessed before, 1 h, 24 h and 48 h after the beginning of MTR. Significant SM increases were found at 24 h in the 55 km group. Levels of CK, CK-MB, AST and cTnI were significantly elevated in both groups following MTR, but in the 55 km group they tended to stabilize in at 48 h. Using pooled data, time-independent serum peaks of SM and CK-MB were significantly correlated. Moreover, concentration of sMtCK was significantly elevated at 1 and 24 h after the race in the 35 km group. Although training volume could confer protection on the mitochondria, the increase in serum CK-MB and SM in the 55 km group might be related to damage to the contractile apparatus type I fibres. Competing in long-distance MTRs might be related to deeper type I muscle fibre damage, even in highly trained individuals.

CD5L is upregulated in hepatocellular carcinoma and promotes liver cancer cell proliferation and antiapoptotic responses by binding to HSPA5 (GRP78).

CD5-like (CD5L) is a soluble scavenger cysteine-rich protein that modulates inflammatory responses. We studied the involvement of CD5L in liver cancer. Immunohistochemistry (IHC) of CD5L in 60 hepatocellular carcinomas and 34 adjacent nontumor livers, showed that CD5L staining was higher in tumor than in nontumor tissue (Mann-Whitney test; P = 0.0039). High CD5L correlated with elevated proliferation (Ki67, linear regression; P < 0.0001) and lower patient event-free survival (log-rank; P = 0.0185). Accordingly, CD5L expression was detected in the liver cancer cell lines Huh7, HepG2, and SNU-398. In vitro technologies using these cell lines, including small interfering RNA (siRNA) and cDNA transfection, showed that CD5L promoted colony formation and cell proliferation and protected against cisplatin-induced apoptosis. To find a molecular explanation for these roles, novel CD5L-interacting protein ligands in liver cancer cells were identified by immunoprecipitation followed by mass spectrometry. Among these, the molecular chaperone of the unfolded protein response (UPR), heat shock protein (HSP)-A5, was selected for validation. The interaction was confirmed by confocal microscopy in the Huh7 and HepG2 cell lines. Furthermore, functional experiments revealed that CD5L activates the UPR and autophagy mechanisms in Huh7 cells, thereby providing a novel molecular link between the UPR and autophagy in liver cancer.-Aran, G., Sanjurjo, L., Bárcena, C., Simon-Coma, M., Téllez, É., Vázquez-Vitali, M., Garrido, M., Guerra, L., Díaz, E., Ojanguren, I., Elortza, F., Planas, R., Sala, M., Armengol, C., Sarrias, M.-R. CD5L is upregulated in hepatocellular carcinoma and promotes liver cancer cell proliferation and antiapoptotic responses by binding to HSPA5 (GRP78).

Targeting glucosylceramide synthase upregulation reverts sorafenib resistance in experimental hepatocellular carcinoma.

Evasive mechanisms triggered by the tyrosine kinase inhibitor sorafenib reduce its efficacy in hepatocellular carcinoma (HCC) treatment. Drug-resistant cancer cells frequently exhibit sphingolipid dysregulation, reducing chemotherapeutic cytotoxicity via the induction of ceramide-degrading enzymes. However, the role of ceramide in sorafenib therapy and resistance in HCC has not been clearly established. Our data reveals that ceramide-modifying enzymes, particularly glucosylceramide synthase (GCS), are upregulated during sorafenib treatment in hepatoma cells (HepG2 and Hep3B), and more importantly, in sorafenib-resistant cell lines. GCS silencing or pharmacological GCS inhibition sensitized hepatoma cells to sorafenib exposure. GCS inhibition, combined with sorafenib, triggered cytochrome c release and ATP depletion in sorafenib-treated hepatoma cells, leading to mitochondrial cell death after energetic collapse. Conversely, genetic GCS overexpression increased sorafenib resistance. Of interest, GCS inhibition improved sorafenib effectiveness in a xenograft mouse model, recovering drug sensitivity of sorafenib-resistant tumors in mice. In conclusion, our results reveal GCS induction as a mechanism of sorafenib resistance, suggesting that GCS targeting may be a novel strategy to increase sorafenib efficacy in HCC management, and point to target the mitochondria as the subcellular location where sorafenib therapy could be potentiated.

Gas6/Axl pathway is activated in chronic liver disease and its targeting reduces fibrosis via hepatic stellate cell inactivation.

BACKGROUND & AIMS: Liver fibrosis, an important health concern associated to chronic liver injury that provides a permissive environment for cancer development, is characterized by accumulation of extracellular matrix components mainly derived from activated hepatic stellate cells (HSCs). Axl, a receptor tyrosine kinase and its ligand Gas6, are involved in cell differentiation, immune response and carcinogenesis. METHODS: HSCs were obtained from WT and Axl(-/-) mice, treated with recombinant Gas6 protein (rGas6), Axl siRNAs or the Axl inhibitor BGB324, and analyzed by western blot and real-time PCR. Experimental fibrosis was studied in CCl4-treated WT and Axl(-/-) mice, and in combination with Axl inhibitor. Gas6 and Axl serum levels were measured in alcoholic liver disease (ALD) and hepatitis C virus (HCV) patients. RESULTS: In primary mouse HSCs, Gas6 and Axl levels paralleled HSC activation. rGas6 phosphorylated Axl and AKT prior to HSC phenotypic changes, while Axl siRNA silencing reduced HSC activation. Moreover, BGB324 blocked Axl/AKT phosphorylation and diminished HSC activation. In addition, Axl(-/-) mice displayed decreased HSC activation in vitro and liver fibrogenesis after chronic damage by CCl4 administration. Similarly, BGB324 reduced collagen deposition and CCl4-induced liver fibrosis in mice. Importantly, Gas6 and Axl serum levels increased in ALD and HCV patients, inversely correlating with liver functionality. CONCLUSIONS: The Gas6/Axl axis is required for full HSC activation. Gas6 and Axl serum levels increase in parallel to chronic liver disease progression. Axl targeting may be a therapeutic strategy for liver fibrosis management.

Angiogenin secretion from hepatoma cells activates hepatic stellate cells to amplify a self-sustained cycle promoting liver cancer.

Hepatocellular carcinoma (HCC) frequently develops in a pro-inflammatory and pro-fibrogenic environment with hepatic stellate cells (HSCs) remodeling the extracellular matrix composition. Molecules secreted by liver tumors contributing to HSC activation and peritumoral stromal transformation remain to be fully identified. Here we show that conditioned medium from HCC cell lines, Hep3B and HepG2, induced primary mouse HSCs transdifferentiation, characterized by profibrotic properties and collagen modification, with similar results seen in the human HSC cell line LX2. Moreover, tumor growth was enhanced by coinjection of HepG2/LX2 cells in a xenograft murine model, supporting a HCC-HSC crosstalk in liver tumor progression. Protein microarray secretome analyses revealed angiogenin as the most robust and selective protein released by HCC compared to LX2 secreted molecules. In fact, recombinant angiogenin induced in vitro HSC activation requiring its nuclear translocation and rRNA transcriptional stimulation. Moreover, angiogenin antagonism by blocking antibodies or angiogenin inhibitor neomycin decreased in vitro HSC activation by conditioned media or recombinant angiogenin. Finally, neomycin administration reduced tumor growth of HepG2-LX2 cells coinjected in mice. In conclusion, angiogenin secretion by HCCs favors tumor development by inducing HSC activation and ECM remodeling. These findings indicate that targeting angiogenin signaling may be of potential relevance in HCC management.

Growth arrest-specific protein 6 is hepatoprotective against murine ischemia/reperfusion injury.

UNLABELLED: Growth arrest-specific gene 6 (GAS6) promotes growth and cell survival during tissue repair and development in different organs, including the liver. However, the specific role of GAS6 in liver ischemia/reperfusion (I/R) injury has not been previously addressed. Here we report an early increase in serum GAS6 levels after I/R exposure. Moreover, unlike wild-type (WT) mice, Gas6(-/-) mice were highly sensitive to partial hepatic I/R, with 90% of the mice dying within 12 hours of reperfusion because of massive hepatocellular injury. I/R induced early hepatic protein kinase B (AKT) phosphorylation in WT mice but not in Gas6(-/-) mice without significant changes in c-Jun N-terminal kinase phosphorylation or nuclear factor kappa B translocation, whereas hepatic interleukin-1ß (IL-1ß) and tumor necrosis factor (TNF) messenger RNA levels were higher in Gas6(-/-) mice versus WT mice. In line with the in vivo data, in vitro studies indicated that GAS6 induced AKT phosphorylation in primary mouse hepatocytes and thus protected them from hypoxia-induced cell death, whereas GAS6 diminished lipopolysaccharide-induced cytokine expression (IL-1ß and TNF) in murine macrophages. Finally, recombinant GAS6 treatment in vivo not only rescued GAS6 knockout mice from severe I/R-induced liver damage but also attenuated hepatic damage in WT mice after I/R. CONCLUSION: Our data have revealed GAS6 to be a new player in liver I/R injury that is emerging as a potential therapeutic target for reducing postischemic hepatic damage.

GD3 synthase overexpression sensitizes hepatocarcinoma cells to hypoxia and reduces tumor growth by suppressing the cSrc/NF-kappaB survival pathway.

BACKGROUND: Hypoxia-mediated HIF-1alpha stabilization and NF-kappaB activation play a key role in carcinogenesis by fostering cancer cell survival, angiogenesis and tumor invasion. Gangliosides are integral components of biological membranes with an increasingly recognized role as signaling intermediates. In particular, ganglioside GD3 has been characterized as a proapoptotic lipid effector by promoting cell death signaling and suppression of survival pathways. Thus, our aim was to analyze the role of GD3 in hypoxia susceptibility of hepatocarcinoma cells and in vivo tumor growth. METHODOLOGY/PRINCIPAL FINDINGS: We generated and characterized a human hepatocarcinoma cell line stably expressing GD3 synthase (Hep3B-GD3), which catalyzes the synthesis of GD3 from GM3. Despite increased GD3 levels (2-3 fold), no significant changes in cell morphology or growth were observed in Hep3B-GD3 cells compared to wild type Hep3B cells under normoxia. However, exposure of Hep3B-GD3 cells to hypoxia (2% O(2)) enhanced reactive oxygen species (ROS) generation, resulting in decreased cell survival, with similar findings observed in Hep3B cells exposed to increasing doses of exogenous GD3. In addition, hypoxia-induced c-Src phosphorylation at tyrosine residues, NF-kappaB activation and subsequent expression of Mn-SOD were observed in Hep3B cells but not in Hep3B-GD3 cells. Moreover, MnTBAP, an antioxidant with predominant SOD mimetic activity, reduced ROS generation, protecting Hep3B-GD3 cells from hypoxia-induced death. Finally, lower tumor growth, higher cell death and reduced Mn-SOD expression were observed in Hep3B-GD3 compared to Hep3B tumor xenografts. CONCLUSION: These findings underscore a role for GD3 in hypoxia susceptibility by disabling the c-Src/NF-kappaB survival pathway resulting in lower Mn-SOD expression, which may be of relevance in hepatocellular carcinoma therapy.