Manganese-induced trafficking and turnover of GPP130 is mediated by sortilin

Diagnostic utility of sortilin & other biomarkers in the diagnosis of carotid & coronary atherosclerosis in individuals with arterial hypertension

Background & objectives Cardiovascular diseases (CVDs) are a leading cause of mortality worldwide. The aim of this investigation was to study the role of biological markers in predicting the risk of carotid and coronary artery atherosclerosis. Methods A total of 161 males in the age group of 30-65 yr were included in this study. All participants underwent biochemical analyses [cholesterol, low density lipoprotein cholesterol (LDL-C), triglycerides, glucose, (interleukin) IL-8, IL-10, (proprotein convertase inhibitors subtilisin/kexin type 9) PCSK9, sortilin, creatinine]; ECG; echocardiography; coronary angiography; ultrasound doppler of brachiocephalic arteries. Based on PCSK9 levels, participants were divided into four groups: group 1, n=41 individuals with PCSK9 level of 100-250 ng/ml; group 2, n=37 individuals with PCSK9 level of 251-400 ng/ml; group 3, n=51 individuals with PCSK9 level of 401-600 ng/ml and group 4, n=32 individuals with PCSK9 level of 601-900 ng/ml. Results Sortilin level was the highest in group 2. Group 3 individuals had the highest level of IL-8. Correlation analysis of the entire data set revealed the relationship of relative left ventricular thickness index with age, cardiovascular risk, body mass index, intima-media thickness and left ventricular mass index; sortilin had a negative relationship of weak strength with age and smoking, a direct relationship between the risk of cardiovascular complications and with IL-10. Interpretation & conclusions Sortilin is the innovative marker of CVDs. In the present investigation, we demonstrated the clear increase in the inflammatory markers (IL-8) in individuals with subclinical atherosclerosis. This fact can be explained by the oxygen stress activation. In individuals with coronary artery stenosis (50% and more), the increase in IL-10 levels demonstrates, to our opinion, the activation of antioxidant protection activation.

Chromosomal 3q amplicon encodes essential regulators of secretory vesicles that drive secretory addiction in cancer

Cancer cells exhibit heightened secretory states that drive tumor progression. Here, we identified a chromosome 3q amplicon that serves as a platform for secretory regulation in cancer. The 3q amplicon encodes multiple Golgi-resident proteins, including the scaffold Golgi integral membrane protein 4 (GOLIM4) and the ion channel ATPase secretory pathway Ca2+ transporting 1 (ATP2C1). We show that GOLIM4 recruited ATP2C1 and Golgi phosphoprotein 3 (GOLPH3) to coordinate Ca2+-dependent cargo loading, Golgi membrane bending, and vesicle scission. GOLIM4 depletion disrupted the protein complex, resulting in a secretory blockade that inhibited the progression of 3q-amplified malignancies. In addition to its role as a scaffold, GOLIM4 maintained intracellular manganese (Mn) homeostasis by binding excess Mn in the Golgi lumen, which initiated the routing of Mn-bound GOLIM4 to lysosomes for degradation. We show that Mn treatment inhibited the progression of multiple types of 3q-amplified malignancies by degrading GOLIM4, resulting in a secretory blockade that interrupted prosurvival autocrine loops and attenuated prometastatic processes in the tumor microenvironment. As it potentially underlies the selective activity of Mn against 3q-amplified malignancies, ATP2C1 coamplification increased Mn influx into the Golgi lumen, resulting in a more rapid degradation of GOLIM4. These findings show that functional cooperativity between coamplified genes underlies heightened secretion and a targetable secretory addiction in 3q-amplified malignancies.

Targeted Protein Unfolding at the Golgi Apparatus

Maintaining protein homeostasis (proteostasis) is vital to cellular and organismal health. How the Golgi apparatus, the central protein maturation and sorting station in the cell, manages misfolded proteins to maintain proteostasis is still poorly understood. Here we present a strategy for targeted protein unfolding at the Golgi that enables studying Golgi-related protein quality control and stress-signaling pathways. Targeted protein unfolding is induced by small molecule-based chemical biology approaches-hydrophobic tagging and the use of a destabilization domain. Imaging studies allow visualizing quality control (QC) phenotypes, such as the formation of QC carriers and Golgi-to-endoplasmic reticulum trafficking, and correlating these phenotypes with other trafficking processes.

Sorting through the extensive and confusing roles of sortilin in metabolic disease

Sortilin is a post-Golgi trafficking receptor homologous to the yeast vacuolar protein sorting receptor 10 (VPS10). The VPS10 motif on sortilin is a 10-bladed β-propeller structure capable of binding more than 50 proteins, covering a wide range of biological functions including lipid and lipoprotein metabolism, neuronal growth and death, inflammation, and lysosomal degradation. Sortilin has a complex cellular trafficking itinerary, where it functions as a receptor in the trans-Golgi network, endosomes, secretory vesicles, multivesicular bodies, and at the cell surface. In addition, sortilin is associated with hypercholesterolemia, Alzheimer's disease, prion diseases, Parkinson's disease, and inflammation syndromes. The 1p13.3 locus containing SORT1, the gene encoding sortilin, carries the strongest association with LDL-C of all loci in human genome-wide association studies. However, the mechanism by which sortilin influences LDL-C is unclear. Here, we review the role sortilin plays in cardiovascular and metabolic diseases and describe in detail the large and often contradictory literature on the role of sortilin in the regulation of LDL-C levels.

Biometals and glycosylation in humans: Congenital disorders of glycosylation shed lights into the crucial role of Golgi manganese homeostasis

About half of the eukaryotic proteins bind biometals that participate in their structure and functions in virtually all physiological processes, including glycosylation. After reviewing the biological roles and transport mechanisms of calcium, magnesium, manganese, zinc and cobalt acting as cofactors of the metalloproteins involved in sugar metabolism and/or glycosylation, the paper will outline the pathologies resulting from a dysregulation of these metals homeostasis and more particularly Congenital Disorders of Glycosylation (CDGs) caused by ion transporter defects. Highlighting of CDGs due to defects in SLC39A8 (ZIP8) and TMEM165, two proteins transporting manganese from the extracellular space to cytosol and from cytosol to the Golgi lumen, respectively, has emphasized the importance of manganese homeostasis for glycosylation. Based on our current knowledge of TMEM165 structure and functions, this review will draw a picture of known and putative mechanisms regulating manganese homeostasis in the secretory pathway.

HHV-7 U21 exploits Golgi quality control carriers to reroute class I MHC molecules to lysosomes

The human herpesvirus-7 (HHV-7) U21 glycoprotein binds to class I major histocompatibility complex (MHC) molecules in the endoplasmic reticulum (ER) and reroutes them to lysosomes. How this single viral glycoprotein efficiently redirects the U21/class I MHC complex to the lysosomal compartment is poorly understood. To investigate the trafficking of HHV-7 U21, we followed synchronous release of U21 from the ER as it traffics through the secretory system. Sorting of integral membrane proteins from the trans-Golgi network (TGN) has been shown to occur through tubular carriers that emanate from the TGN or through vesicular carriers that recruit GGA (Golgi-localized, γ-ear–containing, ARF-binding protein), clathrin adaptors, and clathrin. Here, we present evidence for the existence of a third type of Golgi-derived carrier that is vesicular, yet clathrin independent. This U21-containing carrier also carries a Golgi membrane protein engineered to form inducible oligomers. We propose that U21 employs the novel mechanism of forming oligomeric complexes with class I MHC molecules that result in sorting of the oligomeric U21/class I MHC complexes to Golgi-­derived quality control carriers destined for lysosomes.

Protein quality control in the secretory pathway

Protein folding is inherently error prone, especially in the endoplasmic reticulum (ER). Even with an elaborate network of molecular chaperones and protein folding facilitators, misfolding can occur quite frequently. To maintain protein homeostasis, eukaryotes have evolved a series of protein quality-control checkpoints. When secretory pathway quality-control pathways fail, stress response pathways, such as the unfolded protein response (UPR), are induced. In addition, the ER, which is the initial hub of protein biogenesis in the secretory pathway, triages misfolded proteins by delivering substrates to the proteasome or to the lysosome/vacuole through ER-associated degradation (ERAD) or ER-phagy. Some misfolded proteins escape the ER and are instead selected for Golgi quality control. These substrates are targeted for degradation after retrieval to the ER or delivery to the lysosome/vacuole. Here, we discuss how these guardian pathways function, how their activities intersect upon induction of the UPR, and how decisions are made to dispose of misfolded proteins in the secretory pathway.

Dissection of TMEM165 function in Golgi glycosylation and its Mn2+ sensitivity

Since 2012, the interest for TMEM165 increased due to its implication in a rare genetic human disease named TMEM165-CDG (Congenital Disorder(s) of Glycosylation). TMEM165 is a Golgi localized protein, highly conserved through evolution and belonging to the uncharacterized protein family 0016 (UPF0016). Although the precise function of TMEM165 in glycosylation is still controversial, our results highly suggest that TMEM165 would act as a Golgi Ca²⁺/Mn²⁺ transporter regulating both Ca²⁺ and Mn²⁺ Golgi homeostasis, the latter is required as a major cofactor of many Golgi glycosylation enzymes. Strikingly, we recently demonstrated that besides its role in regulating Golgi Mn²⁺ homeostasis and consequently Golgi glycosylation, TMEM165 is sensitive to high manganese exposure. Members of the UPF0016 family contain two particularly highly conserved consensus motifs E-φ-G-D-[KR]-[TS] predicted to be involved in the ion transport function of UPF0016 members. We investigate the contribution of these two specific motifs in the function of TMEM165 in Golgi glycosylation and in its Mn²⁺ sensitivity. Our results show the crucial importance of these two conserved motifs and underline the contribution of some specific amino acids in both Golgi glycosylation and Mn²⁺ sensitivity.

Golgi integral membrane protein 4 manipulates cellular proliferation, apoptosis, and cell cycle in human head and neck cancer

The incidence of global head and neck cancer has increased markedly in the last 10 years, and its prognosis is poor, which seriously endangers people’s life and health. At present, there are few studies on its pathogenesis. Golgi integral membrane protein 4 (GOLIM4) is a major member of the Golgi apparatus transporter complex, and its role in tumor is unclear. The present study found that GOLIM4 was the key target protein downstream of stromal interaction molecule 1 (STIM1), which can inhibit the proliferation of head and neck cancer cells FaDu (human pharyngeal squamous carcinoma cell) and Tca-8113 (human tongue squamous carcinoma cell) with knockdown of GOLIM4 by lentivirus. And the decreased expression of GOLIM4 induced cellular apoptosis. Further experiments revealed that FaDu cell cycle progression was changed after GOLIM4 silence, G₁ phase arrest and the number of G₂/M cells decreased significantly. It was also found that the cells in S-phase decreased markedly after GOLIM4 was knocked down compared with the control group by 5-bromo-2′-deoxyuridine (BrdU) incorporation experiment. In conclusion, we found that GOLIM4, as the target gene downstream of STIM1, inhibited the proliferation of head and neck cancer, promoted apoptosis, and regulated cell cycle progression, and GOLIM4 is a novel oncogene in head and neck cancer and might help in developing promising targetted therapies for head and neck cancer patients.

Role of the AP-5 adaptor protein complex in late endosome-to-Golgi retrieval

The AP-5 adaptor protein complex is presumed to function in membrane traffic, but so far nothing is known about its pathway or its cargo. We have used CRISPR-Cas9 to knock out the AP-5 ζ subunit gene, AP5Z1, in HeLa cells, and then analysed the phenotype by subcellular fractionation profiling and quantitative mass spectrometry. The retromer complex had an altered steady-state distribution in the knockout cells, and several Golgi proteins, including GOLIM4 and GOLM1, were depleted from vesicle-enriched fractions. Immunolocalisation showed that loss of AP-5 led to impaired retrieval of the cation-independent mannose 6-phosphate receptor (CIMPR), GOLIM4, and GOLM1 from endosomes back to the Golgi region. Knocking down the retromer complex exacerbated this phenotype. Both the CIMPR and sortilin interacted with the AP-5–associated protein SPG15 in pull-down assays, and we propose that sortilin may act as a link between Golgi proteins and the AP-5/SPG11/SPG15 complex. Together, our findings suggest that AP-5 functions in a novel sorting step out of late endosomes, acting as a backup pathway for retromer. This provides a mechanistic explanation for why mutations in AP-5/SPG11/SPG15 cause cells to accumulate aberrant endolysosomes, and highlights the role of endosome/lysosome dysfunction in the pathology of hereditary spastic paraplegia and other neurodegenerative disorders.

Eukaryotic cells contain multiple membrane-bound compartments, each with a distinct function and molecular composition. Proteins are transported from one compartment to another by vesicular carriers. Formation of these carriers requires coat proteins, which both shape the membrane into a vesicle and select the proteins that are to be included as cargo. In many cases, cargo selection is facilitated by an adaptor protein (AP) complex, of which 5 have been identified. The most recently identified complex, AP-5, localises to a late endosomal/lysosomal compartment, and patients with mutations in AP-5 have a form of hereditary spastic paraplegia characterised by aberrant lysosomes. However, the precise function of AP-5, including its cargo and its pathway, has until now been unclear. In the present study, we have used unbiased subcellular proteomics to look for changes in the localisation of thousands of different proteins in cells from which AP-5 has been deleted by gene editing. We found that there are defects in the retrieval of several proteins from late endosomes back to the Golgi apparatus. Thus, we propose that AP-5 facilitates a novel late-acting retrieval pathway, which contributes to normal lysosomal homeostasis.