GABARAP proteins as scaffolds in localized TIAM1-RAC1 signaling.
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ABSTRACT:
SUBMITTER: Genau HM
PROVIDER: S-EPMC4845176 | biostudies-other | 2016 Jan
REPOSITORIES: biostudies-other
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Project description:Metastasis is the key cause of failure of cancer therapy or mortality, but targeting metastatic seeding and colonization remains an unresolved challenge. Here, we report a novel molecular event in cancer metastasis mediated by NSD2/Rac1 signaling and provide a detailed mechanistic investigation of cancer metastasis. We found that NSD2, a histone methyltransferase responsible for di-methylating histone 3 at lysine 36, was overexpressed in metastatic tumors, and overexpressed NSD2 enhanced tumor metastasis both in vitro and in vivo. We further investigated that NSD2 promoted tumor metastasis by activating the Rac1 signaling pathway. Mechanistically, NSD2 methylated Tiam1, a guanine nucleotide exchange factor that facilitates GDP-Rac1 to GTP-Rac1 transition at K724. We demonstrated that Tiam1 K724 methylation plays a crucial role in Tiam1 activation and GDP-Rac1 to GTP-Rac1 transition. Specifically, we identified that Tiam1 K724 methylation could be a predictive factor in cancer prognosis, and we demonstrated that pharmacological blocking of Tiam1 K724 methylation by employing a transmembrane peptide inhibited tumor metastasis both in vitro and in vivo. Thus, NSD2-methylated Tiam1 promoted Rac1 signaling activation and cancer metastasis, which might provide novel insights into tumor metastasis inhibition.
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Project description:Glucose-stimulated insulin secretion [GSIS] from the islet β-cell involves a well-orchestrated interplay between metabolic and cationic events. It is well established that intracellular generation of adenine and guanine nucleotide triphosphates [e.g., ATP and GTP] represents one of the requisite signaling steps in GSIS. The small molecular mass GTP-binding proteins [G-proteins; e.g., Rac1 and Cdc42] have been shown to regulate islet β-cell function including actin cytoskeletal remodeling and fusion of insulin granules with the plasma membrane for GSIS to occur. In this context, several regulatory factors for these G-proteins have been identified in the pancreatic β-cell; these include guanine nucleotide exchange factors [GEFs] and guanine nucleotide dissociation inhibitors [GDI]. Recent pharmacological and molecular biological evidence identified Tiam1 and Vav2 as GEFs for Rac1 in promoting physiological insulin secretion. Paradoxically, emerging evidence in multiple cell types, including the islet β-cell, suggests key roles for Rac1 in the onset of cellular dysfunction under conditions of metabolic stress and diabetes. Furthermore, functional inactivation of either Tiam1 or Vav2 appears to attenuate sustained activation of Rac1 and its downstream signaling events [activation of stress kinases] under conditions of metabolic stress. Together, these findings suggest both "friendly" and "non-friendly" roles for Tiam1/Vav2-Rac1 signaling axis in islet β-cell in health and diabetes. Our current understanding of the field and the knowledge gaps that exist in this area of islet biology are heighted herein. Furthermore, potential caveats in the specificity and selectivity of pharmacological inhibitors that are available currently are discussed in this Commentary.
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Project description:Background/aimsType 1 diabetes (T1D) is characterized by absolute insulin deficiency due to destruction of pancreatic β-cells by cytokines (e.g., interleukin-1β; IL-1β) released by invading immune cells. The mechanisms by which these cytokines induce β-cell dysfunction remain poorly understood. Recent evidence suggests that excessive generation of reactive oxygen species (ROS) by the phagocyte-like NADPH oxidase2 (Nox2), along with significantly low levels of antioxidants in β-cells, drive them toward oxidative damage. Rac1, a small G-protein, is one of the members of Nox2 holoenzyme. We recently reported that NSC23766, a known inhibitor of Rac1, significantly attenuated cytokine-induced Nox2 activation and ROS generation in pancreatic islet β-cells in vitro. Herein, we determined the effects of NSC23766 (2.5 mg/kg/day, i.p/daily) on the development of diabetes in the NOD mouse, a model for T1D.MethodsTwo groups of experimental animals (Balb/c and NOD mice) received NSC23766, while the two control groups received equal volume of saline. Body weights and blood glucose were measured every week for 34 weeks. Rac1 activation in pancreatic islets was measured by GLISA activation assay. Rac1 and CHOP expression was determined by Western Blotting.ResultsOur findings indicate that administration of NSC23766 significantly prevented the development of spontaneous diabetes in the NOD mice. Furthermore, NSC23766 markedly suppressed Rac1 expression and activity and the endoplasmic reticulum stress (CHOP expression) in NOD islets.ConclusionsOur findings provide the first evidence implicating the role of Tiam1-Rac1-Nox2 signaling pathway in the onset of spontaneous diabetes in the NOD mouse model.
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Project description:Tiam1 methylation by NSD2 promotes Rac1 signaling activation and cancer metastasis
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