Endocytosis in the adaptation to cellular stress

Cellular life is challenged by a multitude of stress conditions, triggered for example by alterations in osmolarity, oxygen or nutrient supply. Hence, cells have developed sophisticated stress responses to cope with these challenges. Some of these stress programs such as the heat shock response are understood in great detail, while other aspects remain largely elusive including potential stress-dependent adaptations of the plasma membrane proteome. The plasma membrane is not only the first point of encounter for many types of environmental stress, but given the diversity of receptor proteins and their associated molecules also represents the site at which many cellular signal cascades originate. Since these signaling pathways affect virtually all aspects of cellular life, changes in the plasma membrane proteome appear ideally suited to contribute to the cellular adaptation to stress. The most rapid means to alter the cell surface proteome in response to stress is by alterations in endocytosis. Changes in the overall endocytic flux or in the endocytic regulation of select proteins conceivably can help to counteract adverse environmental conditions. In this review we summarize recent data regarding stress-induced changes in endocytosis and discuss how these changes might contribute to the cellular adaptation to stress in different systems. Future studies will be needed to uncover the underlying mechanisms in detail and to arrive at a coherent picture

Stonin1 mediates endocytosis of the proteoglycan NG2 and regulates focal adhesion dynamics and cell motility

Cellular functions, ranging from focal adhesion (FA) dynamics and cell motility to tumour growth, are orchestrated by signals cells receive from outside via cell surface receptors. Signalling is fine-tuned by the exo-endocytic cycling of these receptors to control cellular responses such as FA dynamics, which determine cell motility. How precisely endocytosis regulates turnover of the various cell surface receptors remains unclear. Here we identify Stonin1, an endocytic adaptor of unknown function, as a regulator of FA dynamics and cell motility, and demonstrate that it facilitates the internalization of the oncogenic proteoglycan NG2, a co-receptor of integrins and platelet-derived growth factor receptor. Embryonic fibroblasts obtained from Stonin1-deficient mice display a marked surface accumulation of NG2, increased cellular signalling and defective FA disassembly as well as altered cellular motility. These data establish Stonin1 as a specific adaptor for the endocytosis of NG2 and as an important factor for FA dynamics and cell migration

Stonin1 mediates endocytosis of the proteoglycan NG2 and regulates focal adhesion dynamics and cell motility

Cellular functions, ranging from focal adhesion (FA) dynamics and cell motility to tumour growth, are orchestrated by signals cells receive from outside via cell surface receptors. Signalling is fine-tuned by the exo-endocytic cycling of these receptors to control cellular responses such as FA dynamics, which determine cell motility. How precisely endocytosis regulates turnover of the various cell surface receptors remains unclear. Here we identify Stonin1, an endocytic adaptor of unknown function, as a regulator of FA dynamics and cell motility, and demonstrate that it facilitates the internalization of the oncogenic proteoglycan NG2, a co-receptor of integrins and platelet-derived growth factor receptor. Embryonic fibroblasts obtained from Stonin1-deficient mice display a marked surface accumulation of NG2, increased cellular signalling and defective FA disassembly as well as altered cellular motility. These data establish Stonin1 as a specific adaptor for the endocytosis of NG2 and as an important factor for FA dynamics and cell migration

Pharmacologically diverse antidepressants facilitate TRKB receptor activation by disrupting its interaction with the endocytic adaptor complex AP-2

Several antidepressant drugs activate tropomyosin-related kinase B (TRKB) receptor, but it remains unclear whether these compounds employ a common mechanism for TRKB activation. Here, using MS, we found that a single intraperitoneal injection of fluoxetine disrupts the interaction of several proteins with TRKB in the hippocampus of mice. These proteins included members of adaptor protein complex-2 (AP-2) involved in vesicular endocytosis. The interaction of TRKB with the cargo-docking ? subunit of the AP-2 complex (AP2M) was confirmed to be disrupted by both acute and repeated fluoxetine treatments. Of note, fluoxetine disrupted the coupling between full-length TRKB and AP2M, but not the interaction between AP2M and the TRKB C-terminal region, indicating that the fluoxetine-binding site in TRKB lies outside the TRKB:AP2M interface. ELISA experiments revealed that in addition to fluoxetine, other chemically diverse antidepressants, such as imipramine, rolipram, phenelzine, ketamine, and its metabolite 2R,6R-hydroxynorketamine, also decreased the interaction between TRKB and AP2M in vitro. Silencing the expression of AP2M in a TRKB-expressing mouse fibroblast cell line (MG87.TRKB) increased cell-surface expression of TRKB and facilitated its activation by brain-derived neurotrophic factor (BDNF), observed as levels of phosphorylated TRKB. Moreover, animals haploinsufficient for the Ap2m1 gene displayed increased levels of active TRKB, along with enhanced cell-surface expression of the receptor in cultured hippocampal neurons. Taken together, our results suggest that disruption of the TRKB:AP2M interaction is a common mechanism underlying TRKB activation by several chemically diverse antidepressants.Peer reviewe

Endophilin-A coordinates priming and fusion of neurosecretory vesicles via intersectin

Endophilins-A are conserved endocytic adaptors with membrane curvature-sensing and -inducing properties. We show here that, independently of their role in endocytosis, endophilin-A1 and endophilin-A2 regulate exocytosis of neurosecretory vesicles. The number and distribution of neurosecretory vesicles were not changed in chromaffin cells lacking endophilin-A, yet fast capacitance and amperometry measurements revealed reduced exocytosis, smaller vesicle pools and altered fusion kinetics. The levels and distributions of the main exocytic and endocytic factors were unchanged, and slow compensatory endocytosis was not robustly affected. Endophilin-A’s role in exocytosis is mediated through its SH3-domain, specifically via a direct interaction with intersectin-1, a coordinator of exocytic and endocytic traffic. Endophilin-A not able to bind intersectin-1, and intersectin-1 not able to bind endophilin-A, resulted in similar exocytic defects in chromaffin cells. Altogether, we report that two endocytic proteins, endophilin-A and intersectin-1, are enriched on neurosecretory vesicles and regulate exocytosis by coordinating neurosecretory vesicle priming and fusion

Molecularly Distinct Clathrin-Coated Pits Differentially Impact EGFR Fate and Signaling

International audienc

Die Endozytose — ein zellulärer Aufnahmeweg mit vielfältigen Funktionen

The plasma membrane harbors a specific set of transmembrane proteins which enable diverse cellular functions such as nutrient uptake, ion homeostasis and cellular signaling. The surface levels of these proteins need to be dynamically regulated to allow for plastic changes in cellular behaviour e. g. upon cell stress or during neuronal communication. Endocytosis is a powerful mechanism for quickly adapting the surface proteome via protein internalization. Here, I discuss how endocytosis contributes to brain function and counteracts cell stress

Safeguards of Neurotransmission: Endocytic Adaptors as Regulators of Synaptic Vesicle Composition and Function

Communication between neurons relies on neurotransmitters which are released from synaptic vesicles (SVs) upon Ca2+ stimuli. To efficiently load neurotransmitters, sense the rise in intracellular Ca2+ and fuse with the presynaptic membrane, SVs need to be equipped with a stringently controlled set of transmembrane proteins. In fact, changes in SV protein composition quickly compromise neurotransmission and most prominently give rise to epileptic seizures. During exocytosis SVs fully collapse into the presynaptic membrane and consequently have to be replenished to sustain neurotransmission. Therefore, surface-stranded SV proteins have to be efficiently retrieved post-fusion to be used for the generation of a new set of fully functional SVs, a process in which dedicated endocytic sorting adaptors play a crucial role. The question of how the precise reformation of SVs is achieved is intimately linked to how SV membranes are retrieved. For a long time both processes were believed to be two sides of the same coin since Clathrin-mediated endocytosis (CME), the proposed predominant SV recycling mode, will jointly retrieve SV membranes and proteins. However, with the recent proposal of Clathrin-independent SV recycling pathways SV membrane retrieval and SV reformation turn into separable events. This review highlights the progress made in unraveling the molecular mechanisms mediating the high-fidelity retrieval of SV proteins and discusses how the gathered knowledge about SV protein recycling fits in with the new notions of SV membrane endocytosis

Gadkin: A novel link between endosomal vesicles and microtubule tracks

Different types of endosomal vesicles show distinct distribution patterns within cells. While early endosomes can be found throughout the cell, recycling endosomal vesicles and tubules tend to cluster near the microtubule organizing center in the perinuclear region in most cell types. The molecular mechanisms underlying the steady-state distribution and dynamics of various types of endosomal vesicles has long remained enigmatic. However, during the past decade it has become evident that microtubule-based motor proteins of the kinesin family play a pivotal role in the positioning of endosomes. Early endosomes were shown to cluster in the perinuclear area in the absence of KIF16B,1 KIF3A is required for the steady-state distribution of late endosomes/lysosomes,2,and KIF13A directs M6PR-containing vesicles from the TGN to the plasma membrane3 to name only a few examples. In the case of Tf-containing recycling endosomes antibody-injection experiments implicated kinesin-1, a heteromer comprised of KIF5 heavy and KLC light chains, as a motor for their transport towards the cell periphery.4 Indeed, KIF5B knockdown experiments confirmed that kinesin-1 is necessary to maintain the peripheral pool of recycling endosomes.5 But how is kinesin-1 linked to endosomal vesicles? Work from our own laboratory has identified the AP-1-binding protein Gadkin as a molecular link between AP-1-mediated traffic and kinesin-1-based transport along microtubules.5 This work as well as hypothetical models for kinesin-dependent endosomal membrane traffic will be discussed here

On the move : endocytic trafficking in cell migration

Directed cell migration is a fundamental process underlying diverse physiological and pathophysiological phenomena ranging from wound healing and induction of immune responses to cancer metastasis. Recent advances reveal that endocytic trafficking contributes to cell migration in multiple ways. (1) At the level of chemokines and chemokine receptors: internalization of chemokines by scavenger receptors is essential for shaping chemotactic gradients in tissue, whereas endocytosis of chemokine receptors and their subsequent recycling is key for maintaining a high responsiveness of migrating cells. (2) At the level of integrin trafficking and focal adhesion dynamics: endosomal pathways do not only modulate adhesion by delivering integrins to their site of action, but also by supplying factors for focal adhesion disassembly. (3) At the level of extracellular matrix reorganization: endosomal transport contributes to tumor cell migration not only by targeting integrins to invadosomes but also by delivering membrane type 1 matrix metalloprotease to the leading edge facilitating proteolysis-dependent chemotaxis. Consequently, numerous endocytic and endosomal factors have been shown to modulate cell migration. In fact key modulators of endocytic trafficking turn out to be also key regulators of cell migration. This review will highlight the recent progress in unraveling the contribution of cellular trafficking pathways to cell migration