Posttranslational modifications of GLUT4 affect its subcellular localization and translocation

The facilitative glucose transporter type 4 (GLUT4) is expressed in adipose and muscle and plays a vital role in whole body glucose homeostasis. In the absence of insulin, only ~1% of cellular GLUT4 is present at the plasma membrane, with the vast majority localizing to intracellular organelles. GLUT4 is retained intracellularly by continuous trafficking through two inter-related cycles. GLUT4 passes through recycling endosomes, the trans Golgi network and an insulin-sensitive intracellular compartment, termed GLUT4-storage vesicles or GSVs. It is from GSVs that GLUT4 is mobilized to the cell surface in response to insulin, where it increases the rate of glucose uptake into the cell. As with many physiological responses to external stimuli, this regulated trafficking event involves multiple posttranslational modifications. This review outlines the roles of posttranslational modifications of GLUT4 on its function and insulin-regulated trafficking

Exo70-Mediated Recruitment of Nucleoporin Nup62 at the Leading Edge of Migrating Cells is Required for Cell Migration

Nucleoporin Nup62 localizes at the central channel of the nuclear pore complex and is essential for nucleocytoplasmic transport. Through its FG-repeat domain, Nup62 regulates nuclear pore permeability and binds nuclear transport receptors. Here, we report that Nup62 interacts directly with Exo70 and colocalizes with Exo70 at the leading edge of migrating cells. Nup62 binds the N-terminal domain of Exo70 through its coiled-coil domain but not through its FG-repeat domain. Selective inhibition of leading edge Nup62 using RNA interference significantly reduces cell migration. Furthermore, Exo70 recruits Nup62 at the plasma membrane and at filopodia. Removal of the Exo70-binding domain of Nup62 prevents leading edge localization of Nup62. Analogous to Exo70, Nup62 cycles between the plasma membrane and the perinuclear recycling compartment. Altogether, we propose that Nup62 not solely regulates access to the cell nucleus, but additionally functions in conjunction with Exo70, a key regulator of exocytosis and actin dynamics, at the leading edge of migrating cells

Increased cortical surface area and gyrification following long-term survival from early monocular enucleation

AbstractPurposeRetinoblastoma is typically diagnosed before 5 years of age and is often treated by enucleation (surgical removal) of the cancerous eye. Here, we sought to characterize morphological changes of the cortex following long-term survival from early monocular enucleation.MethodsNine adults with early right-eye enucleation (≤48 months of age) due to retinoblastoma were compared to 18 binocularly intact controls. Surface area, cortical thickness, and gyrification estimates were obtained from T1 weighted images and group differences were examined.ResultsEarly monocular enucleation was associated with increased surface area and/or gyrification in visual (i.e., V1, inferior temporal), auditory (i.e., supramarginal), and multisensory (i.e., superior temporal, inferior parietal, superior parietal) cortices compared with controls. Visual cortex increases were restricted to the right hemisphere contralateral to the remaining eye, consistent with previous subcortical data showing asymmetrical lateral geniculate nucleus volume following early monocular enucleation.ConclusionsAltered morphological development of visual, auditory, and multisensory regions occurs subsequent to long-time survival from early eye loss

SUMO Modification Regulates BLM and RAD51 Interaction at Damaged Replication Forks

SUMO modification of BLM controls the switch between BLM's pro- and anti-recombinogenic roles in homologous recombination following DNA damage during replication

The disruption of proteostasis in neurodegenerative diseases

Cells count on surveillance systems to monitor and protect the cellular proteome which, besides being highly heterogeneous, is constantly being challenged by intrinsic and environmental factors. In this context, the proteostasis network (PN) is essential to achieve a stable and functional proteome. Disruption of the PN is associated with aging and can lead to and/or potentiate the occurrence of many neurodegenerative diseases (ND). This not only emphasizes the importance of the PN in health span and aging but also how its modulation can be a potential target for intervention and treatment of human diseases.info:eu-repo/semantics/publishedVersio

SUMO Modification Regulates BLM and RAD51 Interaction at Damaged Replication Forks

The gene mutated in Bloom's syndrome, BLM, is important in the repair of damaged replication forks, and it has both pro- and anti-recombinogenic roles in homologous recombination (HR). At damaged forks, BLM interacts with RAD51 recombinase, the essential enzyme in HR that catalyzes homology-dependent strand invasion. We have previously shown that defects in BLM modification by the small ubiquitin-related modifier (SUMO) cause increased γ-H2AX foci. Because the increased γ-H2AX could result from defective repair of spontaneous DNA damage, we hypothesized that SUMO modification regulates BLM's function in HR repair at damaged forks. To test this hypothesis, we treated cells that stably expressed a normal BLM (BLM+) or a SUMO-mutant BLM (SM-BLM) with hydroxyurea (HU) and examined the effects of stalled replication forks on RAD51 and its DNA repair functions. HU treatment generated excess γ-H2AX in SM-BLM compared to BLM+ cells, consistent with a defect in replication-fork repair. SM-BLM cells accumulated increased numbers of DNA breaks and were hypersensitive to DNA damage. Importantly, HU treatment failed to induce sister-chromatid exchanges in SM-BLM cells compared to BLM+ cells, indicating a specific defect in HR repair and suggesting that RAD51 function could be compromised. Consistent with this hypothesis, RAD51 localization to HU-induced repair foci was impaired in SM-BLM cells. These data suggested that RAD51 might interact noncovalently with SUMO. We found that in vitro RAD51 interacts noncovalently with SUMO and that it interacts more efficiently with SUMO-modified BLM compared to unmodified BLM. These data suggest that SUMOylation controls the switch between BLM's pro- and anti-recombinogenic roles in HR. In the absence of BLM SUMOylation, BLM perturbs RAD51 localization at damaged replication forks and inhibits fork repair by HR. Conversely, BLM SUMOylation relieves its inhibitory effects on HR, and it promotes RAD51 function.</p

Proteomic analysis of the mammalian nuclear pore complex

As the sole site of nucleocytoplasmic transport, the nuclear pore complex (NPC) has a vital cellular role. Nonetheless, much remains to be learned about many fundamental aspects of NPC function. To further understand the structure and function of the mammalian NPC, we have completed a proteomic analysis to identify and classify all of its protein components. We used mass spectrometry to identify all proteins present in a biochemically purified NPC fraction. Based on previous characterization, sequence homology, and subcellular localization, 29 of these proteins were classified as nucleoporins, and a further 18 were classified as NPC-associated proteins. Among the 29 nucleoporins were six previously undiscovered nucleoporins and a novel family of WD repeat nucleoporins. One of these WD repeat nucleoporins is ALADIN, the gene mutated in triple-A (or Allgrove) syndrome. Our analysis defines the proteome of the mammalian NPC for the first time and paves the way for a more detailed characterization of NPC structure and function