Tiwari A, Jung JJ, Inamdar SM, Nihalani D, Choudhury A. The myosin motor Myo1c is required for VEGFR2 delivery to the cell surface and for angiogenic signaling.

The ␣5␤1 integrin heterodimer regulates many processes that contribute to embryonic development and angiogenesis, in both physiological and pathological contexts. As one of the major adhesion complexes on endothelial cells, it plays a vital role in adhesion and migration along the extracellular matrix. We recently showed that angiogenesis is modulated by syntaxin 6, a Golgi-and endosome-localized t-SNARE, and that it does so by regulating the post-Golgi trafficking of VEGFR2. Here we show that syntaxin 6 is also required for ␣5␤1 integrin-mediated adhesion of endothelial cells to, and migration along, fibronectin. We demonstrate that syntaxin 6 and ␣5␤1 integrin colocalize in EEA1-containing early endosomes, and that functional inhibition of syntaxin 6 leads to misrouting of ␤1 integrin to the degradation pathway (late endosomes and lysosomes) rather transport along recycling pathway from early endosomes; an increase in the pool of ubiquitinylated ␣5 integrin and its lysosome-dependent degradation; reduced cell spreading on fibronectin; decreased Rac1 activation; and altered Rac1 localization. Collectively, our data show that functional syntaxin 6 is required for the regulation of ␣5␤1-mediated endothelial cell movement on fibronectin. These syntaxin 6-regulated membrane trafficking events control outside-in signaling via haptotactic and chemotactic mechanisms.Adhesion molecules present on the endothelial cell (EC) 2 surface are vital regulators of vascular homeostasis and angiogenesis. Integrins are heterodimeric cell-adhesion receptors for extracellular matrix proteins, and are composed of noncovalently bound ␣ and ␤ subunits (1). During embryonic vascular development, as well as during tumor angiogenesis, the extracellular matrix protein fibronectin serves as an adhesive support and signals through ␣5␤1 integrin to regulate the spreading, migration, and contractility of ECs (1-3). Integrins do not have intrinsic enzymatic activity; their ability to transduce signals depends on recruitment of cytoplasmic linker and signaling proteins, and on the assembly of focal adhesions. Hence the processes that regulate integrin turnover at the cell surface may have implications for the regulation of angiogenesis in the context of therapies.The levels of ␣5␤1 integrin on the cell surface are maintained by recycling of endocytosed complexes back to the plasma membrane (PM). Internalization of the ␣5␤1 integrin complexes occurs via both clathrin-dependent and clathrin-independent endocytic pathways (4). Subsequently, these complexes traffic to early endosomes (EEs) and then to the perinuclear recycling compartment, from which they are recycled to the PM (5-7). This transport requires Rab11 and the activity of PKB/GSK3b (5). Binding of fibronectin to the ␣5␤1 integrin triggers endocytosis that does not involve integrin recycling; in this case the integrin complexes move from the EEs into the multivesicular endosomes for degradation (8). This phenomenon highlights the importance of ␣5␤1 integrin trafficking at the EE compartme...

Intracellular membrane trafficking along endocytic and secretory transport pathways plays a critical role in diverse cellular functions including both developmental and pathological processes. Briefly, proteins and lipids destined for transport to distinct locations are collectively assembled into vesicles and delivered to their target site by vesicular fusion. SNARE (soluble N-ethylmaleimide-sensitive factor-attachment protein receptor) proteins are required for these events, during which v-SNAREs (vesicle SNAREs) interact with t-SNAREs (target SNAREs) to allow transfer of cargo from donor vesicle to target membrane. Recently, the t-SNARE family member, syntaxin-6, has been shown to play an important role in the transport of proteins that are key to diverse cellular dynamic processes. In this paper, we briefly discuss the specific role of SNAREs in various mammalian cell types and comprehensively review the various roles of the Golgi- and endosome-localized t-SNARE, syntaxin-6, in membrane trafficking during physiological as well as pathological conditions.

The soluble form of vascular endothelial growth factor receptor 1 (sVEGFR-1/sFlt1) is generated by alternative splicing of the FLT1 gene. Secretion of sFlt1 from endothelial cells plays an important role in blood vessel sprouting and morphogenesis. However, excess sFlt1 secretion is associated with diseases such as preeclampsia and chronic kidney disease. To date, the secretory transport process involved in the secretion of sFlt1 is poorly understood. In the present study, we investigated the itinerary of sFlt1 trafficking along the secretory pathway. To understand the timecourse of sFlt1 secretion, endothelial cells stably expressing sFlt1 were metabolically radiolabeled with [35S]-methionine and cysteine. Our results indicate that after initial synthesis the levels of secreted [35S]-sFlt1 in the extracellular medium peaks at 8 hours. Treatment with brefeldin A (BFA), a drug which blocks trafficking between the endoplasmic reticulum (ER) and the Golgi complex, inhibited extracellular release of sFlt1 suggesting that ER to Golgi and intra-Golgi trafficking of sFlt1 are essential for its secretion. Furthermore, we show that ectopic expression of dominant-negative mutant forms of Arf1, Arf6, and Rab11 as well as siRNA-mediated knockdown of these GTPases block secretion of sFlt1 during normoxic and hypoxic conditions suggesting role for these small GTPases. This work is the first to report role of regulatory proteins involved in sFlt1 trafficking along the secretory pathway and may provide insights and new molecular targets for the modulation of sFlt-1 release during physiological and pathological conditions.

Vision, hearing, smell, taste, and touch are the tools used to perceive and navigate the world. They enable us to obtain essential resources such as food and highly desired resources such as mates. Thanks to the investments in biomedical research the molecular unpinning's of human sensation are rivaled only by our knowledge of sensation in the laboratory mouse. Humans rely heavily on vision whereas mice use smell as their dominant sense. Both modalities have many features in common, starting with signal detection by highly specialized primary sensory neurons-rod and cone photoreceptors (PR) for vision, and olfactory sensory neurons (OSN) for the smell. In this chapter, we provide an overview of how these two types of primary sensory neurons operate while highlighting the similarities and distinctions.