Golgi membrane protein Erd1 Is essential for recycling a subset of Golgi glycosyltransferases

Protein glycosylation in the Golgi is a sequential process that requires proper distribution of transmembrane glycosyltransferase enzymes in the appropriate Golgi compartments. Some of the cytosolic machinery required for the steady-state localization of some Golgi enzymes are known but existing models do not explain how many of these enzymes are localized. Here, we uncover the role of an integral membrane protein in yeast, Erd1, as a key facilitator of Golgi glycosyltransferase recycling by directly interacting with both the Golgi enzymes and the cytosolic receptor, Vps74. Loss of Erd1 function results in mislocalization of Golgi enzymes to the vacuole/lysosome. We present evidence that Erd1 forms an integral part of the recycling machinery and ensures productive recycling of several early Golgi enzymes. Our work provides new insights on how the localization of Golgi glycosyltransferases is spatially and temporally regulated, and is finely tuned to the cues of Golgi maturation.

MTCL2 promotes asymmetric microtubule organization by crosslinking microtubules on the Golgi membrane

The Golgi complex plays an active role in organizing asymmetric microtubule arrays essential for polarized vesicle transport. The coiled-coil protein MTCL1 stabilizes microtubules nucleated from the Golgi membrane. Here, we report an MTCL1 paralog, MTCL2, which preferentially acts on the perinuclear microtubules accumulated around the Golgi. MTCL2 associates with the Golgi membrane through the N-terminal coiled-coil region and directly binds microtubules through the conserved C-terminal domain without promoting microtubule stabilization. Knockdown of MTCL2 significantly impaired microtubule accumulation around the Golgi as well as the compactness of the Golgi ribbon assembly structure. Given that MTCL2 forms parallel oligomers through homo-interaction of the central coiled-coil motifs, our results indicate that MTCL2 promotes asymmetric microtubule organization by crosslinking microtubules on the Golgi membrane. Results of in vitro wound healing assays further suggest that this function of MTCL2 enables integration of the centrosomal and Golgi-associated microtubules on the Golgi membrane, supporting directional migration. Additionally, the results demonstrated the involvement of CLASPs and giantin in mediating the Golgi association of MTCL2.

Mutation of an arabidopsis golgi membrane protein ELMO1 reduces cell adhesion

Plant growth, morphogenesis and development involves cellular adhesion, a process dependent on the composition and structure of the extracellular matrix (ECM) or cell wall. Pectin in the cell wall is thought to play an essential role in adhesion, and its modification and cleavage are suggested to be highly regulated so as to change adhesive properties. To increase our understanding of plant cell adhesion a population of EMS mutagenized Arabidopsis were screened for hypocotyl adhesion defects using the pectin binding dye Ruthenium Red that penetrates defective but not WT hypocotyl cell walls. Genomic sequencing was used to identify a mutant allele of ELMO1 which encodes a 20 kDa Golgi membrane protein that has no predicted enzymatic domains. ELMO1 colocalizes with several Golgi markers and elmo1−/- plants can be rescued by an ELMO1-GFP fusion. elmo1−/- exhibits reduced mannose content relative to WT but no other cell wall changes and can be rescued to WT phenotype by mutants in ESMERALDA1 that also suppresses other adhesion mutants. elmo1 describes a previously unidentified role for the ELMO1 protein in plant cell adhesion.

Regulation of Golgi turnover by CALCOCO1-mediated selective autophagy

The Golgi complex is essential for the processing, sorting, and trafficking of newly synthesized proteins and lipids. Golgi turnover is regulated to meet different cellular physiological demands. The role of autophagy in the turnover of Golgi, however, has not been clarified. Here we show that CALCOCO1 binds the Golgi-resident palmitoyltransferase ZDHHC17 to facilitate Golgi degradation by autophagy during starvation. Depletion of CALCOCO1 in cells causes expansion of the Golgi and accumulation of its structural and membrane proteins. ZDHHC17 itself is degraded by autophagy together with other Golgi membrane proteins such as TMEM165. Taken together, our data suggest a model in which CALCOCO1 mediates selective Golgiphagy to control Golgi size and morphology in eukaryotic cells via its interaction with ZDHHC17.

Combined Serum Golgi Membrane Glycoprotein 73 Improves the Accuracy of Transient Elastography for Significant Fibrosis Detection in Patients with Chronic HBV Infections

Background: Golgi membrane glycoprotein 73 (GP73) serum level is a potential biomarker for diagnosing significant fibrosis and cirrhosis in chronic liver diseases. Objectives: The current study aimed to evaluate the accuracy of GP73 serum levels as a biomarker in the diagnosis of significant liver fibrosis in patients with hepatitis B virus (HBV). A new promising algorithm was developed by combining LSM and GP73 to predict significant liver fibrosis. Methods: Information on the following parameters were obtained from 165 patients with HBV: liver stiffness measurement (LSM), serum GP73 level, and some other fibrosis criteria approved for clinical practice. The area under the curve (AUC) and sensitivity and specificity of GP73 were compared with LSM, aminotransferase-to-platelet ratio index (APRI), and 4-factor based fibrosis index (FIB-4) for diagnosing significant fibrosis. Results: Compared to the non-significant liver fibrosis patients, the HBV infected patients with significant fibrosis showed a higher level of serum GP73 [64.05 (24.41 - 144.39) versus 91.30 (31.81 - 200.05) ng/mL, P < 0.001]. Concerning significant fibrosis diagnosis, GP73 exhibited advantages regarding the AUC (0.702), sensitivity (69.3%), and specificity (66.0%). Besides, GP73 did not show any advantage over LSM and APRI, but it had a better performance than FIB-4 in significant fibrosis detection. For the newly developed algorithm combining GP73 with LSM, the AUC, sensitivity, and specificity were 0.848, 77.4%, and 83.5%, respectively; hence, it's superior to LSM (0.832, 72.6%, and 83.5%, respectively; P = 0.016) for diagnosing significant fibrosis. Conclusions: This study demonstrated that GP73 can be considered as a new effective biomarker for diagnosing liver fibrosis. The accuracy of significant fibrosis detection in patients with HBV infection can be improved by the new algorithm that contains GP73 and LSM.

The functional landscape of Golgi membrane protein 1 (GOLM1) phosphoproteome reveal GOLM1 regulating P53 that promotes malignancy

Golgi membrane protein 1 (GOLM1) was implicated in carcinogenesis of multiple types of cancer. However, Phosphoproteome landscapes of GOLM1 overexpression in lung cancer remain largely unknown. In this study, using data from the Cancer Genome Atlas (TCGA) and phosphoproteome, we systematically evaluated the feature of GOLM1 and studied its prognostic value in non-small cell lung cancer (NSCLC). The proliferation, migration, and invasion capacities in PC9 cell with GOLM1 overexpression were determined using Trans-well system assay. Tumor engrafts was visualized in mice models and confirmed by ex vivo. An increased expression of GOLM1 had shorter overall survival (OS) in patients with NSCLC in TCGA database. GOLM1 in single gene set enrichment analysis (GSEA) related to adherent’s junction, cell cycle, and pathway in cancer. Overexpression of GOLM1 in GOLM1OE PC9 cells promoted cell proliferation, migration, and invasion. Decreased migration and invasion potential were also observed in knockdown of GOLM1 in GOLM1KD PC9 cells in migration assay. An increased expression of GOLM1 could significantly increase the growth of tumor in xenograft mice models. phosphoproteome analysis showed 239 upregulated and 331 downregulated Phosphorylated proteins in GOLM1OE PC9 cells. Overexpression of GOLM1 in GSEA was significantly related to P53 in MAPK signaling pathway. Overexpression of GOLM1enhanced the phosphorylation of P53 protein at site S315 but inhibited the formation of P53 tetramers. These results indicate that overexpression GOLM1 enhances non-small-cell carcinoma aggressiveness through inhibited the formation of P53 tetramer.