RUSC2 and WDR47 oppositely regulate kinesin-1–dependent distribution of ATG9A to the cell periphery

Autophagy-related protein 9 (ATG9) is a transmembrane protein component of the autophagy machinery that cycles between the trans-Golgi network (TGN) in the perinuclear area and other compartments in the peripheral area of the cell. In mammalian cells, export of the ATG9A isoform from the TGN into ATG9A-containing vesicles is mediated by the adaptor protein 4 (AP-4) complex. However, the mechanisms responsible for the subsequent distribution of these vesicles to the cell periphery is unclear. Herein we show that the AP-4–accessory protein RUSC2 couples ATG9A-containing vesicles to the plus-end-directed microtubule motor kinesin-1 via an interaction between a disordered region of RUSC2 and the kinesin-1 light chain (KLC). This interaction is counteracted by the microtubule-associated WD40-repeat domain 47 protein (WDR47). These findings uncover a mechanism for the peripheral distribution of ATG9A-containing vesicles, involving the function of RUSC2 as a kinesin-1 adaptor and WDR47 as a negative regulator of this function.

SNX19 restricts endolysosome motility through contacts with the endoplasmic reticulum

The ability of endolysosomal organelles to move within the cytoplasm is essential for the performance of their functions. Long-range movement involves coupling of the endolysosomes to motor proteins that carry them along microtubule tracks. This movement is influenced by interactions with other organelles, but the mechanisms involved are incompletely understood. Herein we show that the sorting nexin SNX19 tethers endolysosomes to the endoplasmic reticulum (ER), decreasing their motility and contributing to their concentration in the perinuclear area of the cell. Tethering depends on two N-terminal transmembrane domains that anchor SNX19 to the ER, and a PX domain that binds to phosphatidylinositol 3-phosphate on the endolysosomal membrane. Two other domains named PXA and PXC negatively regulate the interaction of SNX19 with endolysosomes. These studies thus identify a mechanism for controlling the motility and positioning of endolysosomes that involves tethering to the ER by a sorting nexin.

Effect of Space Flight on the Behavior of Human Retinal Pigment Epithelial ARPE-19 Cells and Evaluation of Coenzyme Q10 Treatment

Astronauts on board the International Space Station (ISS) are exposed to the damaging effects of microgravity and cosmic radiation. One of the most critical and sensitive districts of their organism is the eye, and in particular the retina, so that more than half of them develops a complex of alterations designated as Spaceflight Associated Neuro-ocular Syndrome. We explored the cellular and molecular effects induced on human retinal pigment ARPE-19 cell line by their transfer to and three days stay on board the ISS in the context of an experiment funded by the Agenzia Spaziale Italiana (ASI). Treatment of cells on board ISS with the well-known bioenergetic, antioxidant and antiapoptotic coenzyme Q10 was also evaluated. In the ground control experiment the cells were exposed to the same conditions as on the ISS, except for microgravity and radiation. Transfer of ARPE-19 retinal cells to the ISS and their living on board for three days did not impact on cell viability or apoptosis but induced cytoskeleton remodeling consisting in vimentin redistribution from the cellular boundaries to the perinuclear area, underlining the collapse of the network of intermediate vimentin filaments under unloading conditions. Morphological changes endured by ARPE-19 cells grown on board the ISS were associated with changes in the transcriptomic profile related to cellular response to space environment, and were consistent with cell dysfunction adaptations. In addition, results obtained from ARPE-19 cells treated on board ISS with coenzyme Q10 showed its potential ability to increase cell resistance to damaging insults.

p27 controls autophagic vesicle trafficking in glucose-deprived cells via the regulation of ATAT1-mediated microtubule acetylation

The cyclin-dependent kinase inhibitor p27Kip1 (p27) has been involved in promoting autophagy and survival in conditions of metabolic stress. While the signaling cascade upstream of p27 leading to its cytoplasmic localization and autophagy induction has been extensively studied, how p27 stimulates the autophagic process remains unclear. Here, we investigated the mechanism by which p27 promotes autophagy upon glucose deprivation. Mouse embryo fibroblasts (MEFs) lacking p27 exhibit a decreased autophagy flux compared to wild-type cells and this is correlated with an abnormal distribution of autophagosomes. Indeed, while autophagosomes are mainly located in the perinuclear area in wild-type cells, they are distributed throughout the cytoplasm in p27-null MEFs. Autophagosome trafficking towards the perinuclear area, where most lysosomes reside, is critical for autophagosome–lysosome fusion and cargo degradation. Vesicle trafficking is mediated by motor proteins, themselves recruited preferentially to acetylated microtubules, and autophagy flux is directly correlated to microtubule acetylation levels. p27−/− MEFs exhibit a marked reduction in microtubule acetylation levels and restoring microtubule acetylation in these cells, either by re-expressing p27 or with deacetylase inhibitors, restores perinuclear positioning of autophagosomes and autophagy flux. Finally, we find that p27 promotes microtubule acetylation by binding to and stabilizing α-tubulin acetyltransferase (ATAT1) in glucose-deprived cells. ATAT1 knockdown results in random distribution of autophagosomes in p27+/+ MEFs and impaired autophagy flux, similar to that observed in p27−/− cells. Overall, in response to glucose starvation, p27 promotes autophagy by facilitating autophagosome trafficking along microtubule tracks by maintaining elevated microtubule acetylation via an ATAT1-dependent mechanism.

Membrane targeting activates Leucine-rich repeat kinase 2 with differential effects on downstream Rab activation

ABSTRACTGenetic variation at the Leucine-rich repeat kinase 2 (LRRK2) locus contributes to risk of familial and sporadic Parkinson’s disease. Recent data have shown a robust association between localization to various membranes of the endolysosomal system and LRRK2 activation. However, the mechanism(s) underlying LRRK2 activation at endolysosomal membranes are still poorly understood. Here we artificially direct LRRK2 to six different membranes within the endolysosomal system. We demonstrate that LRRK2 is activated and able to phosphorylate three of its Rab substrates (Rab10, Rab12 and Rab29) at each compartment. However, we report differing localization of pRab10 and pRab12 at the lysosomal and Golgi membranes. Specifically, we found that pRab10 colocalizes with a sub-population of perinuclear LRRK2-positive Golgi/lysosomal compartments whereas pRab12 localized to all LRRK2-positive Golgi/lysosomal membranes across the cell. When organelle positioning is manipulated by sequestering lysosomes to the perinuclear area, pRab10 colocalization with LRRK2 significantly increases. We also show recruitment of JIP4, a pRab10 effector that we have recently linked to LYTL, after trapping LRRK2 at various membranes. Taken together, we demonstrate that the association of LRRK2 to membranous compartments is sufficient for its activation and Rab phosphorylation independent of membrane identity. Our system also identifies a potential mechanism underlying the distinct relationships between LRRK2 and its substrates Rab10 and Rab12.

The FTS-Hook-FHIP (FHF) complex interacts with AP-4 to mediate perinuclear distribution of AP-4 and its cargo ATG9A

In this study, we identify the dynein–dynactin adaptor FTS-Hook-FHIP (FHF) complex as an accessory factor for the TGN-associated adaptor protein 4 (AP-4) coat. We show that FHF is required for distribution of AP-4 and its cargo ATG9A to the perinuclear area, highlighting a novel mechanism for coupling of transport vesicles to microtubule motors.

S1P-S1PR1 activity controls VEGF-A signaling during lymphatic vessel development

Sphingosine-1-phosphate (S1P), a lipid signaling molecule produced by endothelial cells, is required for development and homeostasis of blood vessels. However, its role during lymphatic vessel development is unclear. We show in murine newborns that pharmacologically enhanced S1P signaling increases VEGF-A-dependent LEC proliferation. In contrast, S1PR1 inhibition, mediated by the antagonist NIBR0213 or LEC-specific genetic deletion of S1pr1, promotes filopodia formation and vessel branching, independent of VEGF-A. To investigate the S1P and VEGF-A signaling crosstalk observed in vivo, we used LECs cultured in vitro. We demonstrate that S1P activates endogenous S1PR1 in a constitutive, autocrine manner. Importantly, S1P-S1PR1 activity was required for VEGF-A-induced LEC proliferation and strongly supported ERK1/2 activation and VEGFR-2 trafficking to the perinuclear area. In conclusion, S1P-S1PR1 signaling promotes VEGF-A-dependent LEC proliferation and limits migratory and filopodia-forming responses. Hence, S1P-S1PR1 signaling is required for balanced growth factor-induced lymphangiogenesis and correctly patterned lymphatic vessels during postnatal development.

Nonmuscle myosin IIA and IIB differentially modulate migration and alter gene expression in primary mouse tumorigenic cells

Though many cancers are known to show up-regulation of nonmuscle myosin (NM) IIA and IIB, the mechanism by which NMIIs aid in cancer development remains unexplored. Here we demonstrate that tumor-generating, fibroblast-like cells isolated from 3-methylcholanthrene (3MC)-induced murine tumor exhibit distinct phospho-dependent localization of NMIIA and NMIIB at the perinuclear area and tip of the filopodia and affect cell migration differentially. While NMIIA-KD affects protrusion dynamics and increases cell directionality, NMIIB-KD lowers migration speed and increases filopodial branching. Strategically located NMIIs at the perinuclear area colocalize with the linker of nucleoskeleton and cytoskeleton (LINC) protein Nesprin2 and maintain the integrity of the nuclear-actin cap. Interestingly, knockdown of NMIIs results in altered expression of genes involved in epithelial-to-mesenchymal transition, angiogenesis, and cellular senescence. NMIIB-KD cells display down-regulation of Gsc and Serpinb2, which is strikingly similar to Nesprin2-KD cells as assessed by quantitative PCR analysis. Further gene network analysis predicts that NMIIA and NMIIB may act on similar pathways but through different regulators. Concomitantly, knockdown of NMIIA or NMIIB lowers the growth rate and tumor volume of 3MC-induced tumor in vivo. Altogether, these results open a new window to further investigate the effect of LINC-associated perinuclear actomyosin complex on mechanoresponsive gene expression in the growing tumor.

Molecular determinants of ER–Golgi contacts identified through a new FRET–FLIM system

ER–TGN contact sites (ERTGoCS) have been visualized by electron microscopy, but their location in the crowded perinuclear area has hampered their analysis via optical microscopy as well as their mechanistic study. To overcome these limits we developed a FRET-based approach and screened several candidates to search for molecular determinants of the ERTGoCS. These included the ER membrane proteins VAPA and VAPB and lipid transfer proteins possessing dual (ER and TGN) targeting motifs that have been hypothesized to contribute to the maintenance of ERTGoCS, such as the ceramide transfer protein CERT and several members of the oxysterol binding proteins. We found that VAP proteins, OSBP1, ORP9, and ORP10 are required, with OSBP1 playing a redundant role with ORP9, which does not involve its lipid transfer activity, and ORP10 being required due to its ability to transfer phosphatidylserine to the TGN. Our results indicate that both structural tethers and a proper lipid composition are needed for ERTGoCS integrity.

Combining autophagy-inducing peptides and brefeldin A delivered by perinuclear-localized mesoporous silica nanoparticles: a manipulation strategy for ER-phagy

A small molecule was screened and delivered to the perinuclear area by mesoporous silica nanoparticles for regulating ER-phagy.