Regulation of MAPK Signaling Pathways by the Large HERC Ubiquitin Ligases.

Protein ubiquitylation acts as a complex cell signaling mechanism since the formation of different mono- and polyubiquitin chains determines the substrate's fate in the cell. E3 ligases define the specificity of this reaction by catalyzing the attachment of ubiquitin to the substrate protein. Thus, they represent an important regulatory component of this process. Large HERC ubiquitin ligases belong to the HECT E3 protein family and comprise HERC1 and HERC2 proteins. The physiological relevance of the Large HERCs is illustrated by their involvement in different pathologies, with a notable implication in cancer and neurological diseases. Understanding how cell signaling is altered in these different pathologies is important for uncovering novel therapeutic targets. To this end, this review summarizes the recent advances in how the Large HERCs regulate the MAPK signaling pathways. In addition, we emphasize the potential therapeutic strategies that could be followed to ameliorate the alterations in MAPK signaling caused by Large HERC deficiencies, focusing on the use of specific inhibitors and proteolysis-targeting chimeras.

HERC1 deficiency causes osteopenia through transcriptional program dysregulation during bone remodeling.

Bone remodeling is a continuous process between bone-forming osteoblasts and bone-resorbing osteoclasts, with any imbalance resulting in metabolic bone disease, including osteopenia. The HERC1 gene encodes an E3 ubiquitin ligase that affects cellular processes by regulating the ubiquitination of target proteins, such as C-RAF. Of interest, an association exists between biallelic pathogenic sequence variants in the HERC1 gene and the neurodevelopmental disorder MDFPMR syndrome (macrocephaly, dysmorphic facies, and psychomotor retardation). Most pathogenic variants cause loss of HERC1 function, and the affected individuals present with features related to altered bone homeostasis. Herc1-knockout mice offer an excellent model in which to study the role of HERC1 in bone remodeling and to understand its role in disease. In this study, we show that HERC1 regulates osteoblastogenesis and osteoclastogenesis, proving that its depletion increases gene expression of osteoblastic makers during the osteogenic differentiation of mesenchymal stem cells. During this process, HERC1 deficiency increases the levels of C-RAF and of phosphorylated ERK and p38. The Herc1-knockout adult mice developed imbalanced bone homeostasis that presented as osteopenia in both sexes of the adult mice. By contrast, only young female knockout mice had osteopenia and increased number of osteoclasts, with the changes associated with reductions in testosterone and dihydrotestosterone levels. Finally, osteocytes isolated from knockout mice showed a higher expression of osteocytic genes and an increase in the Rankl/Opg ratio, indicating a relevant cell-autonomous role of HERC1 when regulating the transcriptional program of bone formation. Overall, these findings present HERC1 as a modulator of bone homeostasis and highlight potential therapeutic targets for individuals affected by pathological HERC1 variants.

HERC2 deficiency activates C-RAF/MKK3/p38 signalling pathway altering the cellular response to oxidative stress.

HERC2 gene encodes an E3 ubiquitin ligase involved in several cellular processes by regulating the ubiquitylation of different protein substrates. Biallelic pathogenic sequence variants in the HERC2 gene are associated with HERC2 Angelman-like syndrome. In pathogenic HERC2 variants, complete absence or marked reduction in HERC2 protein levels are observed. The most common pathological variant, c.1781C > T (p.Pro594Leu), encodes an unstable HERC2 protein. A better understanding of how pathologic HERC2 variants affect intracellular signalling may aid definition of potential new therapies for these disorders. For this purpose, we studied patient-derived cells with the HERC2 Pro594Leu variant. We observed alteration of mitogen-activated protein kinase signalling pathways, reflected by increased levels of C-RAF protein and p38 phosphorylation. HERC2 knockdown experiments reproduced the same effects in other human and mouse cells. Moreover, we demonstrated that HERC2 and RAF proteins form molecular complexes, pull-down and proteomic experiments showed that HERC2 regulates C-RAF ubiquitylation and we found out that the p38 activation due to HERC2 depletion occurs in a RAF/MKK3-dependent manner. The displayed cellular response was that patient-derived and other human cells with HERC2 deficiency showed higher resistance to oxidative stress with an increase in the master regulator of the antioxidant response NRF2 and its target genes. This resistance was independent of p53 and abolished by RAF or p38 inhibitors. Altogether, these findings identify the activation of C-RAF/MKK3/p38 signalling pathway in HERC2 Angelman-like syndrome and highlight the inhibition of RAF activity as a potential therapeutic option for individuals affected with these rare diseases.

Gestational stress alters maternal behavior and inflammatory markers in the olfactory bulb of lactating mice.

Inflammatory markers represent important candidates responsible for the altered behavior and physiology observed after stressful experiences. In the maternal brain, the olfactory bulb (OB) is a key constituent of the neural circuit that mediates the reciprocal interaction between mother and infant. This study aimed to investigate the effects of stress during pregnancy on maternal behavior and inflammatory changes in the olfactory bulb of lactating mice. Female Balb/c mice were divided into two groups: control (CT) and restraint stress (RS). Maternal behavior was performed during the first 8 days of life of the offspring. On the 10th day after parturition, corticosterone, gene, and protein expression were assessed. Stress during pregnancy decreased the maternal index at postnatal day 4 and the nuclear factor-κB 1 (NFκB1) gene expression in the OB. Moreover, females from the RS group showed increased interleukin (IL-1ß) protein expression. In contrast, stressed females exhibited a decreased tumor necrosis factor (TNF-α) protein expression in the OB. In conclusion, exposure to stress during pregnancy was able to induce specific postnatal effects on maternal behavior and balance of inflammatory mediators in the OB.

Octyl gallate decrease lymphocyte activation and regulates neutrophil extracellular traps release.

BACKGROUND: Inflammation is a complex mechanism with an objective to destroy and eliminate the invading microorganisms. During acute inflammation, the neutrophils are the major cells involved in this process and, although they defend the organism, must die to not generate damage. The two major mechanisms that drive neutrophils to death are: apoptosis and a novel mechanism recently discovered denominated NETosis. This process is a "suicidal mechanism", in which the cells release "neutrophil extracellular traps" (NETs) during the inflammatory response. Octyl gallate (OG) is one of the gallic acid derivates, with several protective effects, such as antioxidant and anti-inflammatory in cancer models. Thus, this study aimed to investigate the action of OG on the proliferation of lymphocytes, neutrophils activation, and its effectiveness in an experimental sepsis model. METHODS: Lymphocytes and neutrophils were obtained from healthy donors. Cell viability, apoptosis, NETs release and antioxidant capacity of OG were observed. In addition, survival was evaluated in an experimental model of sepsis in C57BL/6 mice. RESULTS: Our study demonstrated, for the first time, that the OG can act as an inhibitor of reactive oxygen species (ROS) release, NETs formation in primary human neutrophils and, modulates the lipopolysaccharide (LPS) effect in neutrophil apoptosis. The OG also inhibited peripheral blood mononuclear cells (PBMCs) proliferation in vitro. Despite the positive results, we did not observe an increase in the survival of septic animals. CONCLUSIONS: The pharmacological potential of OG, modulating activation of neutrophils and lymphocytes, suggests the use as an adjuvant therapeutic strategy in inflammatory diseases.

HERC Ubiquitin Ligases in Cancer.

HERC proteins are ubiquitin E3 ligases of the HECT family. The HERC subfamily is composed of six members classified by size into large (HERC1 and HERC2) and small (HERC3-HERC6). HERC family ubiquitin ligases regulate important cellular processes, such as neurodevelopment, DNA damage response, cell proliferation, cell migration, and immune responses. Accumulating evidence also shows that this family plays critical roles in cancer. In this review, we provide an integrated view of the role of these ligases in cancer, highlighting their bivalent functions as either oncogenes or tumor suppressors, depending on the tumor type. We include a discussion of both the molecular mechanisms involved and the potential therapeutic strategies.

CPBMF65, a synthetic human uridine phosphorylase-1 inhibitor, reduces HepG2 cell proliferation through cell cycle arrest and senescence.

Hepatocellular carcinoma (HCC) is the most prevalent type of tumor among primary liver tumors and is the second highest cause of cancer-related deaths worldwide. Current therapies are controversial, and more research is needed to identify effective treatments. A new synthetic compound, potassium 5-cyano-4-methyl-6-oxo-1,6-dihydropyridine-2-olate (CPBMF65), is a potent inhibitor of the human uridine phosphorylase-1 (hUP1) enzyme, which controls the cell concentration of uridine (Urd). Urd is a natural pyrimidine nucleoside involved in cellular processes, such as RNA synthesis. In addition, it is considered a promising biochemical modulator, as it may reduce the toxicity caused by chemotherapeutics without impairing its anti-tumor activity. Thus, the objective of this study is to evaluate the effects of CPBMF65 on the proliferation of the human hepatocellular carcinoma cell line (HepG2). Cell proliferation, cytotoxicity, apoptosis, senescence, autophagy, intracellular Urd levels, cell cycle arrest, and drug resistance were analyzed. Results demonstrate that, after incubation with CPBMF65, HepG2 cell proliferation decreased, mainly through cell cycle arrest and senescence, increasing the levels of intracellular Urd and maintaining cell proliferation reduced during chronic treatment. In conclusion, results show, for the first time, the ability of a hUP1 inhibitor (CPBMF65) to reduce HepG2 cell proliferation through cell cycle arrest and senescence.

The ubiquitin ligase HERC1 regulates cell migration via RAF-dependent regulation of MKK3/p38 signaling.

Protein modifications by phosphorylation or ubiquitylation have been selected throughout evolution as efficient regulatory mechanisms of cellular processes. Cell migration is a complex, highly coordinated process where these mechanisms must participate in an integrated manner to transmit signaling during migration. In this study, we show that the ubiquitin ligase HERC1 regulates the p38 signaling pathway, and that this regulation is mediated by the MAPK kinase MKK3. Moreover, we demonstrate a crosstalk between RAF and MKK3/p38 pathways where RAF acts upstream of MKK3. Mechanistically, HERC1 regulates the protein levels of C-RAF and MKK3. Thus, HERC1 ubiquitylates C-RAF, targeting it for proteasomal degradation, and RAF proteins regulate MKK3 mRNA levels. Accordingly, HERC1 knockdown induces C-RAF stabilization and activation of RAF proteins; in turn, this activation increases MKK3, which phosphorylates and activates p38. The importance of these observations is demonstrated by HERC1 regulation of cell migration through regulation of p38 signaling via a RAF-dependent mechanism. Thus, HERC1 plays an essential role as a regulator of crosstalk between RAF/MKK3/p38 signaling pathways during cell migration.

Exenatide induces autophagy and prevents the cell regrowth in HepG2 cells.

The incidence of hepatocellular carcinoma (HCC) keeps rising year by year, and became the second leading cause of cancer-related death. Some studies have found that liraglutide, a GLP-1 analog, may decrease the tumor cells proliferation. Due to this, the aim of this work is to investigate the antiproliferative potential of exenatide, another GLP-1 analog. Cell proliferation was assessed by direct count with Trypan blue dye exclusion. Flow cytometry was used to determinate autophagy and nuclear staining. Morphometric analysis was used to verify senescence and apoptosis. The mechanism that induced cell growth inhibition was analyzed by Western Blot. Treatment with exenatide significantly decreases cell proliferation and increases autophagy, both in relation to control and liraglutide. In addition, mTOR inhibition was greater in cells treated with exenatide. In relation to chronic treatment, exenatide does not allow cellular regrowth by preventing some resistance mechanism that the cells can acquire. These results suggest that exenatide has a potent anti-proliferative activity via mTOR modulation and, among the GLP-1 analogs tested, could be in the future an alternative for HCC treatment.

HERCing: Structural and Functional Relevance of the Large HERC Ubiquitin Ligases.

Homologous to the E6AP carboxyl terminus (HECT) and regulator of chromosome condensation 1 (RCC1)-like domain-containing proteins (HERCs) belong to the superfamily of ubiquitin ligases. HERC proteins are divided into two subfamilies, Large and Small HERCs. Despite their similarities in terms of both structure and domains, these subfamilies are evolutionarily very distant and result from a convergence phenomenon rather than from a common origin. Large HERC genes, HERC1 and HERC2, are present in most metazoan taxa. They encode very large proteins (approximately 5,000 amino acid residues in a single polypeptide chain) that contain more than one RCC1-like domain as a structural characteristic. Accumulating evidences show that these unusually large proteins play key roles in a wide range of cellular functions which include neurodevelopment, DNA damage repair, and cell proliferation. To better understand the origin, evolution, and function of the Large HERC family, this minireview provides with an integrated overview of their structure and function and details their physiological implications. This study also highlights and discusses how dysregulation of these proteins is associated with severe human diseases such as neurological disorders and cancer.

Association of IL-10 to coronary disease severity in patients with metabolic syndrome.

BACKGROUND: Metabolic syndrome (MetS) is a group of risk factors that increase the risk for heart disease. Little is known about the role of IL-10 in the severity of coronary artery disease (CAD) in patients with MetS. We investigated plasma levels of IL-10 and other pro-inflammatory cytokines in patients with MetS with or without severe CAD. METHODS: Cross-sectional study with healthy and MetS individuals. IL-10 and other pro-inflammatory interleukins were analyzed in 90 subjects divided into 3 groups: group 1 (n = 30), patients with MetS without severe CAD; group 2 (n = 30), patients with MetS and severe CAD (history of myocardial infarction or revascularization performed through surgery or percutaneous transluminal coronary angioplasty with or without stent placement); and group 3 (n = 30), healthy individuals. RESULTS: Levels of IL-12 (p = .018), TNF-α (p = .007) and IL-6 (p = .010) were significantly higher in group 1 when compared to group 3 (p = .003; p = .002; p = .001, respectively). In addition, group 1 presented significantly higher levels of IL-12 (p = .019), TNF-α (p = .026) and IL-6 (p = .020) when compared to group 2. IL-10 levels were significantly higher in group 1 (p = .003) when compared to group 2 (p = .014) and group 3 (p < .001). Only the level of IL-10 was significant to explain the presence of severe CAD, as a protective factor (OR: 0.896; 95%CI: 0.818-0.981) in the logistic regression model. CONCLUSIONS: Higher IL-10 levels in patients with MetS are associated with lower incidence of severe CAD, suggesting a protective effect through its anti-inflammatory activity even in the presence of higher levels of pro-inflammatory cytokines.

Octyl gallate reduces ATP levels and Ki67 expression leading HepG2 cells to cell cycle arrest and mitochondria-mediated apoptosis.

Octyl gallate (OG) is an antioxidant that has shown anti-tumor, anti-diabetic and anti-amyloidogenic activities. Mitochondria play an important role in hepatocellular carcinoma, mainly by maintaining accelerated cellular proliferation through the production of ATP. Thus, the mitochondria may be a target for antitumor therapies. Here, we investigated the effects of OG in the hepatocarcinoma cell line (HepG2) and the mechanisms involved. We report, for the first time, that treatment with OG for 24h inhibited HepG2 cell growth by decreasing mitochondrial activity and mass, which led to the reduction of ATP levels. This reduction in the energy supply triggered a decrease in Ki67 protein expression, leading cells to cycle arrest. In addition, treatment with two doses of OG for 48h induced loss of mitochondrial functionality, mitochondrial swelling and apoptosis. Finally, we report that HepG2 cells had no resistance to treatment after multiple doses. Collectively, our findings indicate that metabolic dysregulation and Ki67 protein reduction are key events in the initial anti-proliferative action of OG, whereas mitochondrial swelling and apoptosis induction are involved in the action mechanism of OG after prolonged exposure. This suggests that OG targets mitochondria, thus representing a candidate for further research on therapies for hepatocarcinoma.

Mesenchymal stem cells decrease lung inflammation during sepsis, acting through inhibition of the MAPK pathway.

BACKGROUND: Sepsis is a severe medical condition that ranks among the top 10 causes of death worldwide and which has permanently high incidence rates. Mesenchymal stem cells (MSCs) have been found to be potent modulators of immune responses. More importantly, there is evidence that MSCs have a beneficial effect on preclinical models of polymicrobial sepsis. However, the changes caused by the MSCs in the effector cells of the host immune system remain unclear. METHODS: A mouse model of sepsis (male C57BL/6 mice) with three experimental groups was used for experiments in vivo: a control group, an untreated septic group, and a septic group treated with MSCs. In vitro experiments were performed using a cell line of pulmonary macrophages (RAW 264.7) co-cultured with MSCs and stimulated with lipopolysaccharide (LPS). RESULTS: In vivo we demonstrated that treatment with MSCs was able to reduce the expression of cyclooxygenase-2 (COX-2) and nuclear factor kappa B (NF-κB), and thereby decrease the production of inflammatory cytokines. In vitro experiments using a co-culture of macrophages with MSCs showed a decrease in COX-2 and NF-κB, and showed that this reduction was directly related to the ability of MSCs to inhibit phosphorylation of ERK, RSK, and p38, enzymes that belong to the family of mitogen-activated protein kinases (MAPKs). CONCLUSIONS: This study demonstrated that MSCs are able to inhibit the MAPK pathway activation, modulating the inflammatory response during sepsis. This understanding that MSCs can remodel the response of host cells and improve the course of sepsis is essential for developing new treatments for this pathology.

Fructose-1,6-bisphosphate reverts iron-induced phenotype of hepatic stellate cells by chelating ferrous ions.

Hepatic fibrosis is an extracellular matrix deposition by hepatic stellate cells (HSC). Fibrosis can be caused by iron, which will lead to hydroxyl radical production and cell damage. Fructose-1,6-bisphosphate (FBP) has been shown to deliver therapeutic effects in many pathological situations. In this work, we aimed to test the effects of FBP in HSC cell line, GRX, exposed to an excess of iron (Fe). The Fe-treatment increased cell proliferation and FBP reversed this effect, which was not due to increased necrosis, apoptosis or changes in cell cycle. Oil Red-O staining showed that FBP successfully increased lipid content and lead GRX cells to present characteristics of quiescent HSC. Fe-treatment decreased PPAR-γ expression and increased Col-1 expression. Both effects were reversed by FBP which also decreased TGF-ß1 levels in comparison to both control and Fe groups. FBP, also, did not present scavenger activity in the DPPH assay. The treatment with FBP resulted in decreased proliferation rate, Col-1 expression and TGF-ß1 release by HSC cells. Furthermore, activated PPAR-γ and increased lipid droplets induce cells to become quiescent, which is a key event to reversion of hepatic fibrosis. FBP also chelates iron showing potential to improve Cell redox state.

Mesenchymal stem cells cannot affect mRNA expression of toll-like receptors in different tissues during sepsis.

OBJECTIVE AND DESIGN: Experimental animal models and human clinical studies support a crucial role for TLRs in infectious diseases. The aim of this study was to test the ability of MSCs, which have immunomodulatory effects, of altering the mRNA expression of toll-like receptors during a experimental model of sepsis in different tissues. MATERIALS AND METHODS: Three experimental groups (male C57BL/6 mice) were formed for the test: control group, untreated septic group and septic group treated with MSCs (1 × 106 cells/animal). Lungs, cortex, kidney, liver and colon tissue were dissected after 12 h of sepsis induction and TLR2/3/4/9 mRNA were evaluated by RT-qPCR. RESULTS: We observed a decrease of TLR2 and 9 mRNA expression in the liver of the sepsis group, while TLR3 was decreased in the lung and liver. No change was found between the sepsis group and the sepsis + MSC group. CONCLUSIONS: In this model of experimental sepsis the MSCs were unable to modify the mRNA expression of the different toll-like receptors evaluated.

Fructose-1,6-bisphosphate decreases IL-8 levels and increases the activity of pro-apoptotic proteins in HepG2 cells.

Hepatocellular carcinoma (HCC) is the most prevalent primary liver tumor that affects the world population. Liver cancer inevitably causes great harms and its treatment is extremely difficult. Its development is related to the existence of chronic liver injury, such as in cirrhosis. Cancer is a disease related to the process of inflammation so, research with anti-inflammatory agents has been performed for the development of anti-tumor drugs. Fructose-1,6-bisphosphate (FBP), a metabolite of the glycolytic route, has shown anti-inflammatory actions. The purpose of this study is to investigate the effect of FBP on HepG2 cells growth and inflammatory parameters. Results showed that FBP decreased the proliferation of HepG2 cells through trypan blue assay, without causing necrosis, shown by the intracellular release of LDH. By flow cytometry, we observed a significant IL-8 decrease which is closely related to the tumoral progression and chemotherapeutic resistance, especially in HCC. Then, we found, by RT-PCR, a high expression level of pro-apoptotic protein, such as Bax and p53, and decreased the expression levels of anti-apoptotic proteins, like Bcl-2 suggesting apoptosis. Finally, our results showed that FBP can be a potential therapeutic agent to slow the progress of HCC.

Mesenchymal stem cells improves survival in LPS-induced acute lung injury acting through inhibition of NETs formation.

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are syndromes of acute hypoxemic respiratory failure resulting from a variety of direct and indirect injuries to the gas exchange parenchyma of the lungs. During the ALI, we have an increase release of proinflammatory cytokines and high reactive oxygen species (ROS) formation. These factors are responsible for the release and activation of neutrophil-derived proteases and the formation of neutrophil extracellular traps (NETs). The excessive increase in the release of NETs cause damage to lung tissue. Recent studies have studies involving the administration of mesenchymal stem cells (MSCs) for the treatment of experimental ALI has shown promising results. In this way, the objective of our study is to evaluate the ability of MSCs, in a lipopolysaccharide (LPS)-induced ALI model, to reduce inflammation, oxidative damage, and consequently decrease the release of NETs. Mice were submitted lung injury induced by intratracheal instillation of LPS and subsequently treated or not with MSCs. Treatment with MSCs was able to modulate pulmonary inflammation, decrease oxidative damage, and reduce the release of NETs. These benefits from treatment are evident when we observe a significant increase in the survival curve in the treated animals. Our results demonstrate that MSCs treatment is effective for the treatment of ALI. For the first time, it is described that MSCs can reduce the formation of NETs and an experimental model of ALI. This finding is directly related to these cells modulate the inflammatory response and oxidative damage in the course of the pathology.

Gallic acid reduces cell growth by induction of apoptosis and reduction of IL-8 in HepG2 cells.

Hepatocellular carcinoma is the most prevalent primary liver tumor and is among the top ten cancer that affect the world population. Its development is related, in most cases, to the existence of chronic liver injury, such as in cirrhosis. The knowledge about the correlation between chronic inflammation and cancer has driven new researches with anti-inflammatory agents that have potential for the development of antitumor drugs. Gallic acid is a phenolic acid found in many natural products and have shown anti-inflammatory, anti-tumor, anti-mutagenic and antioxidant actions. The purpose of this study was to investigate the effect of gallic acid on acute and chronic cell proliferation and inflammatory parameters of hepatocellular carcinoma cells (HepG2), as well as to investigate the mechanisms involved. Results showed that the gallic acid decreased the proliferation of HepG2 cells in a dose-dependent manner (Trypan blue exclusion assay), without causing necrosis (LDH assay). We observed a significant increase in the percentage of small and regular nuclei (Nuclear Morphometric Analysis assay), a significant induction of apoptosis by Annexin V-FITC and PI assay and no interference with the cell cycle using the FITC BrdU Flow Kit. We observed a significant reduction in the levels of IL-8 and increased levels of IL-10 and IL-12 (Cytometric Bead Array Human Inflammation Assay). Furthermore, gallic acid caused no cancer cells regrowth at a long term (Cumulative Population Doubling assay). According to these results, gallic acid showed a strong potential as an anti-tumor agent in hepatocellular carcinoma cells.

Rapamycin and fructose-1,6-bisphosphate reduce the HEPG2 cell proliferation via increase of free radicals and apoptosis.

Hepatocellular carcinoma is the most prevalent type of tumor among primary tumors affecting the liver. Rapamycin is currently used as a basis for chemotherapy in the treatment of cancers, including the liver. Because it shows several adverse effects, minimizing these effects without compromising efficacy is important. In this sense other drugs may be used concomitantly. One of these drugs is fructose-1,6-bisphosphate (FBP), which has shown therapeutic effect in various pathological situations, having antioxidant and anti-inflammatory proprieties. The objective of the present study was to evaluate the activity of rapamycin in combination with the FBP in HepG2 cell proliferation and the mechanisms involved. HepG2 cells were analyzed after 72 h of treatment with both drugs. Cell proliferation, cytotoxicity, cytokines, apoptosis, senescence, autophagy and oxidative stress were accessed. Ιt was demonstrated that the combination is more efficient than the single use of substances, because subtherapeutic doses of rapamycin, when associated to FBP become effective, reducing cell proliferation, through a significant increase in the production of tiobarbituric acid reactive substances (TBARS), suggesting that this might be the cause of death by apoptosis. According to these results, we believe that the association of both drugs may be a promising choice for the treatment of hepatocarcinoma.