PAK Kinases Target Sortilin and Modulate Its Sorting.

The multifunctional type 1 receptor sortilin is involved in endocytosis and intracellular transport of ligands. The short intracellular domain of sortilin binds several cytoplasmic adaptor proteins (e.g.

Acidic Environment Induces Dimerization and Ligand Binding Site Collapse in the Vps10p Domain of Sortilin.

Sortilin is a neuronal receptor involved in transmembrane signaling, endocytosis, and intracellular sorting of proteins. It cycles through a number of cellular compartments where it encounters various acidic conditions. The crystal structure of the sortilin ectodomain has previously been determined at neutral pH.

SorLA in Interleukin-6 Signaling and Turnover.

Interleukin-6 (IL-6) is a multifunctional cytokine with important functions in various physiologic processes. Mice lacking IL-6 exhibit multiple phenotypic abnormalities, such as an inadequate immune and acute-phase response, and elevated levels of circulating IL-6 have been found to accompany several pathological conditions. IL-6 binds the nonsignaling IL-6 receptor (IL-6R), which is expressed as a transmembrane, as well as a secreted circulating protein, before it engages homodimeric gp130 for signaling.

SorLA and CLC:CLF-1-dependent Downregulation of CNTFRα as Demonstrated by Western Blotting, Inhibition of Lysosomal Enzymes, and Immunocytochemistry.

The heterodimeric cytokine Cardiotrophin-like Cytokine:Cytokine-like Factor-1 (CLC:CLF-1) targets the glycosylphosphatidylinositol (GPI)-anchored CNTFRα to form a trimeric complex that subsequently recruits glycoprotein 130/Leukemia Inhibitory Factor Receptor-β (gp130/LIFRβ) for signaling. Both CLC and CNTFRα are necessary for signaling but so far CLF-1 has only been known as a putative facilitator of CLC secretion. However, it has recently been shown that CLF-1 contains three binding sites: one for CLC; one for CNTFRα (that may promote assembly of the trimeric complex); and one for the endocytic receptor sorLA.

Soluble sortilin is present in excess and positively correlates with progranulin in CSF of aging individuals.

Mutations in progranulin are a major cause of frontotemporal lobe degeneration (FTLD). Hence, plasma progranulin is an attractive biomarker in FTLD but poorly reflects levels in cerebrospinal fluid (CSF), suggesting tissue-specific regulation of progranulin levels. Sortilin was recently identified as a progranulin scavenger receptor that destines it for lysosomal degradation.

Cytokine-Like Factor 1, an Essential Facilitator of Cardiotrophin-Like Cytokine:Ciliary Neurotrophic Factor Receptor α Signaling and sorLA-Mediated Turnover.

Cardiotrophin-like cytokine:cytokine-like factor-1 (CLC:CLF-1) is a heterodimeric neurotropic cytokine that plays a crucial role during neuronal development. Mice lacking CLC:CLF-1 die soon after birth due to a suckling defect and show reduced numbers of motor neurons. Humans carrying mutations in CLC:CLF-1 develop similar disorders, known as Sohar-Crisponi or cold-induced sweating syndrome, and have a high risk of early death.

ABSENCE OF A THYROID PHENOTYPE IN SORTILIN-DEFICIENT MICE.

Objective: The Vps10p family member sortilin is expressed in thyroid epithelial cells where it contributes to recycling of the thyroid hormone precursor thyroglobulin (Tg), a process that is thought to render hormone release more effective. Here we investigated the functional impact of sortilin in the thyroid gland using sortilin-deficient mice.

Methods: We measured free T4, thyroid-stimulating hormone (TSH) and Tg serum levels and studied thyroid morphology in 14 sortilin-deficient (Sort1)(-/-)and 12 wildtype (WT) mice.

Sortilin, encoded by the cardiovascular risk gene SORT1, and its suggested functions in cardiovascular disease.

Several genome-wide association studies have linked novel loci to a wide range of cardiovascular phenotypes including low-density lipoprotein (LDL)-cholesterol, early onset myocardial infarction, coronary artery calcification, coronary artery stenosis, and abdominal aorta aneurysm. Especially, one locus, namely, 1p13.3, has attracted much attention.

Revisiting the structure of the Vps10 domain of human sortilin and its interaction with neurotensin.

Sortilin is a multifunctional receptor involved in sorting and apoptosis. We have previously reported a 2.0-Å structure of the Vps10 ectodomain in complex with one of its ligands, the tridecapeptide neurotensin.

σ1B adaptin regulates adipogenesis by mediating the sorting of sortilin in adipose tissue.

Here, we describe altered sorting of sortilin in adipocytes deficient for the σ1B-containing AP-1 complex, leading to the inhibition of adipogenesis. The AP-1 complex mediates protein sorting between the trans-Golgi network and endosomes. Vertebrates express three AP1 σ1 subunit isoforms - σ1A, σ1B and σ1C (also known as AP1S1, AP1S2 and AP1S3, respectively).

SorCS2 regulates dopaminergic wiring and is processed into an apoptotic two-chain receptor in peripheral glia.

Balancing trophic and apoptotic cues is critical for development and regeneration of neuronal circuits. Here we identify SorCS2 as a proneurotrophin (proNT) receptor, mediating both trophic and apoptotic signals in conjunction with p75(NTR). CNS neurons, but not glia, express SorCS2 as a single-chain protein that is essential for proBDNF-induced growth cone collapse in developing dopaminergic processes.

Human sorCS1 binds sortilin and hampers its cellular functions.

Sortilin and sorCS1 [sortilin-related Vps10p (vacuolar protein sorting/targeting protein 10) domain-containing receptor 1], both members of the Vps10p-D (Vps10p-domain) receptor family, are synthesized as precursor proteins and are converted into their mature form by enzymatic cleavage of a short N-terminal propeptide. SorCS1 does not bind its propeptide, but sortilin is able to bind not just its own propeptide, but also that of sorCS1. In the present study we show that the propeptide region of sorCS1 contains two separate sites for binding to sortilin and that only one of these sites is removed from human (as opposed to mouse) sorCS1 during processing.

SorLA controls neurotrophic activity by sorting of GDNF and its receptors GFRα1 and RET.

Glial cell-line-derived neurotrophic factor (GDNF) is a potent neurotrophic factor that has reached clinical trials for Parkinson's disease. GDNF binds to its coreceptor GFRα1 and signals through the transmembrane receptor tyrosine kinase RET, or RET independently through NCAM or syndecan-3. Whereas the GDNF signaling cascades are well described, cellular turnover and trafficking of GDNF and its receptors remain poorly characterized.

The pro-neurotrophin receptor sortilin is a major neuronal apolipoprotein E receptor for catabolism of amyloid-β peptide in the brain.

Apolipoprotein E (APOE) is the major risk factor for sporadic Alzheimer's disease. Among other functions, APOE is proposed to sequester neurotoxic amyloid-β (Aβ) peptides in the brain, delivering them to cellular catabolism via neuronal APOE receptors. Still, the receptors involved in this process remain controversial.

Sortilin and SorLA display distinct roles in processing and trafficking of amyloid precursor protein.

The development and progression of Alzheimer's disease is linked to excessive production of toxic amyloid-β peptide, initiated by β-secretase cleavage of the amyloid precursor protein (APP). In contrast, soluble APPα (sAPPα) generated by the α-secretase is known to stimulate dendritic branching and enhance synaptic function. Regulation of APP processing, and the shift from neurotrophic to neurotoxic APP metabolism remains poorly understood, but the cellular localization of APP and its interaction with various receptors is considered important.

Quantitative modelling of amyloidogenic processing and its influence by SORLA in Alzheimer's disease.

The extent of proteolytic processing of the amyloid precursor protein (APP) into neurotoxic amyloid-β (Aβ) peptides is central to the pathology of Alzheimer's disease (AD). Accordingly, modifiers that increase Aβ production rates are risk factors in the sporadic form of AD. In a novel systems biology approach, we combined quantitative biochemical studies with mathematical modelling to establish a kinetic model of amyloidogenic processing, and to evaluate the influence by SORLA/SORL1, an inhibitor of APP processing and important genetic risk factor.

Receptor-mediated endocytosis of α-galactosidase A in human podocytes in Fabry disease.

Injury to the glomerular podocyte is a key mechanism in human glomerular disease and podocyte repair is an important therapeutic target. In Fabry disease, podocyte injury is caused by the intracellular accumulation of globotriaosylceramide. This study identifies in the human podocyte three endocytic receptors, mannose 6-phosphate/insulin-like growth II receptor, megalin, and sortilin and demonstrates their drug delivery capabilities for enzyme replacement therapy.

SorLA regulates the activity of lipoprotein lipase by intracellular trafficking.

Many different tissues and cell types exhibit regulated secretion of lipoprotein lipase (LPL). However, the sorting of LPL in the trans Golgi network has not, hitherto, been understood in detail. Here, we characterize the role of SorLA (officially known as SorLA-1 or sortilin-related receptor) in the intracellular trafficking of LPL.

Proneurotrophin-3 may induce Sortilin-dependent death in inner ear neurons.

The precursor of the neurotrophin (NT) nerve growth factor (NGF) (proNGF) serves physiological functions distinct from its mature counterpart as it induces neuronal apoptosis through activation of a p75 NT receptor (p75(NTR) ) and Sortilin death-signalling complex. The NTs brain-derived nerve growth factor (BDNF) and NT3 provide essential trophic support to auditory neurons. Injury to the NT-secreting cells in the inner ear is followed by irreversible degeneration of spiral ganglion neurons with consequences such as impaired hearing or deafness.

Sortilin facilitates signaling of ciliary neurotrophic factor and related helical type 1 cytokines targeting the gp130/leukemia inhibitory factor receptor beta heterodimer.

Sortilin is a member of the Vps10p domain family of neuropeptide and neurotrophin binding neuronal receptors. The family members interact with and partly share a variety of ligands and partake in intracellular sorting and protein transport as well as in transmembrane signal transduction. Thus, sortilin mediates the transport of both neurotensin and nerve growth factor and interacts with their respective receptors to facilitate ligand-induced signaling.

GGA autoinhibition revisited.

The cytosolic adaptors GGA1-3 mediate sorting of transmembrane proteins displaying a C-terminal acidic dileucine motif (DXXLL) in their cytosolic domain. GGA1 and GGA3 contain similar but intrinsic motifs that are believed to serve as autoinhibitory sites activated by the phosphorylation of a serine positioned three residues upstream of the DXXLL motif. In the present study, we have subjected the widely acknowledged concept of GGA1 autoinhibition to a thorough structural and functional examination.

Cubilin and megalin co-localize in the neonatal inner ear.

Cubilin and megalin are multifunctional endocytotic receptors expressed in many absorptive epithelia. The receptors have separate functions but may act in concert in several tissues including the small intestine, the visceral yolk sac and the renal proximal tubule to perform significant physiological functions essential to homeostasis in the extracellular fluid compartments. Because of the importance of fluid homeostasis in the inner ear, we investigated the expression of cubilin and megalin in this structure.

Ligands bind to Sortilin in the tunnel of a ten-bladed beta-propeller domain.

The structure of the Sortilin ectodomain in complex with neurotensin has been determined at 2-A resolution, revealing that the C-terminal part of neurotensin binds in the tunnel of a ten-bladed beta-propeller domain. Binding competition studies suggest that additional binding sites, for example, for the prodomain of nerve growth factor-beta, are present in the tunnel and that competition for binding relates to the restricted space inside the propeller.

VPS10P-domain receptors - regulators of neuronal viability and function.

VPS10P-domain receptors, such as SORLA and sortilin, constitute a recently identified class of type-1 receptors that are expressed in neurons. Family members are multifunctional proteins that target a range of ligands, including trophic factors and neuropeptides but also other transmembrane proteins. New findings have revealed unexpected roles for VPS10P-domain receptors as regulators of neuronal viability and function through the regulation of both protein transport and signal transduction.

Sortilin is a putative postendocytic receptor of thyroglobulin.

The Vps10p family member sortilin is involved in various cell processes, including protein trafficking. Here we found that sortilin is expressed in thyroid epithelial cells (thyrocytes) in a TSH-dependent manner, that the hormone precursor thyroglobulin (Tg) is a high-affinity sortilin ligand, and that binding to sortilin occurs after Tg endocytosis, resulting in Tg recycling. Sortilin was found to be expressed intracellularly in thyrocytes, as observed in mouse, human, and rat thyroid as well as in FRTL-5 cells.