Drp1 overexpression induces desmin disassembling and drives kinesin-1 activation promoting mitochondrial trafficking in skeletal muscle

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Sgt1 is required for human kinetochore assembly

Budding yeast Sgt1 is required for kinetochore assembly, and its homologues have a role in cAMP signalling in fungi and pathogen resistance in plants. The function of mammalian Sgt1 is unknown. We report that RNA interference-mediated depletion of Sgt1 from HeLa cells causes dramatic alterations of the mitotic spindle and problems in chromosome alignment. Cells lacking Sgt1 undergo a mitotic delay due to activation of the spindle checkpoint. The checkpoint response, however, is significantly weakened in Sgt1-depleted cells, and this correlates with a dramatic reduction in kinetochore levels of Mad1, Mad2 and BubR1. These effects are explained by a problem in kinetochore assembly that prevents the localization of Hec1, CENP-E, CENP-F, CENP-I, but not CENP-C, to mitotic kinetochores. Our studies implicate Sgt1 as an essential protein and a critical assembly factor for the mammalian kinetochore, and lend credit to the hypothesis of a kinetochore assembly pathway that is conserved from yeast to man

VE-cadherin is a critical endothelial regulator of TGF-β signalling

VE-cadherin is an endothelial-specific transmembrane protein concentrated at cell-to-cell adherens junctions. Besides promoting cell adhesion and controlling vascular permeability, VE-cadherin transfers intracellular signals that contribute to vascular stabilization. However, the molecular mechanism by which VE-cadherin regulates vascular homoeostasis is still poorly understood. Here, we report that VE-cadherin expression and junctional clustering are required for optimal transforming growth factor-β (TGF-β) signalling in endothelial cells (ECs). TGF-β antiproliferative and antimigratory responses are increased in the presence of VE-cadherin. ECs lacking VE-cadherin are less responsive to TGF-β/ALK1- and TGF-β/ALK5-induced Smad phosphorylation and target gene transcription. VE-cadherin coimmunoprecipitates with all the components of the TGF-β receptor complex, TβRII, ALK1, ALK5 and endoglin. Clustered VE-cadherin recruits TβRII and may promote TGF-β signalling by enhancing TβRII/TβRI assembly into an active receptor complex. Taken together, our data indicate that VE-cadherin is a positive and EC-specific regulator of TGF-β signalling. This suggests that reduction or inactivation of VE-cadherin may contribute to progression of diseases where TGF-β signalling is impaired

The Primate-specific Protein TBC1D3 Is Required for Optimal Macropinocytosis in a Novel ARF6-dependent Pathway

The generation of novel genes and proteins throughout evolution has been proposed to occur as a result of whole genome and gene duplications, exon shuffling, and retrotransposition events. The analysis of such genes might thus shed light into the functional complexity associated with highly evolved species. One such case is represented by TBC1D3, a primate-specific gene, harboring a TBC domain. Because TBC domains encode Rab-specific GAP activities, TBC-containing proteins are predicted to play a major role in endocytosis and intracellular traffic. Here, we show that the TBC1D3 gene originated late in evolution, likely through a duplication of the RNTRE locus, and underwent gene amplification during primate speciation. Despite possessing a TBC domain, TBC1D3 is apparently devoid of Rab-GAP activity. However, TBC1D3 regulates the optimal rate of epidermal growth factor–mediated macropinocytosis by participating in a novel pathway involving ARF6 and RAB5. In addition, TBC1D3 binds and colocalize to GGA3, an ARF6-effector, in an ARF6-dependent manner, and synergize with it in promoting macropinocytosis, suggesting that the two proteins act together in this process. Accordingly, GGA3 siRNA-mediated ablation impaired TBC1D3-induced macropinocytosis. We thus uncover a novel signaling pathway that appeared after primate speciation. Within this pathway, a TBC1D3:GGA3 complex contributes to optimal propagation of signals, ultimately facilitating the macropinocytic process