Glucose-mediated N-glycosylation of RPTPα affects its subcellular localization and Src activation

Regulation of N-Glycosylation of CDNF on Its Protein Stability and Function in Hypoxia/Reoxygenation Model of H9C2 Cells

Myocardial ischemia-reperfusion (I/R) injury is a cause of high post-interventional mortality in patients with acute myocardial infarction (MI). Cerebral dopamine neurotrophic factor (CDNF) is an endoplasmic reticulum (ER) resident protein, and its expression and secretion are induced when tissues and cells are subjected to hypoxia, ischemia, or traumatic injury. As a novel cardiomyokine, CDNF plays a crucial role in the progression of myocardial I/R injury. In our previous study, we reported that the overexpression of CDNF inhibited tunicamycin-induced H9C2 cell apoptosis. Moreover, there is a unique N-glycosylation site at Asn57 in the CDNF protein, which likely affects its function in H9C2 cells. However, the detailed impact remains unexplored. In our current study, we observed elevated levels of CDNF in the serum of acute MI patients, myocardial tissue of I/R model mice, and H/R model H9C2 cells. To detect the effect of N-glycosylation on the CDNF protein, we constructed an Asn57 mutant (N57A) plasmid and found that the N57A protein presented similar intracellular localization to those of the wild-type CDNF protein. However, the N57A protein demonstrated reduced stability, and the mutant protein could not protect H/R-induced H9C2 cells from apoptosis. Moreover, this process may occur through the downregulation of the PI3K/Akt pathway. Therefore, N-glycosylation of CDNF may be essential for protein stability and its protective role in H/R injury in H9C2 cells.

Targeting site-specific N-glycosylated B7H3 induces potent antitumor immunity

B7H3, an immune checkpoint molecule, is a highly N-glycosylated membrane protein. However, the key glycosylated asparagine residues that mediate the function of the B7H3 protein are still unclear. Here we identify that N-glycans attached to asparagine residues N91/309 and N104/322 are required for proper B7H3 localization on the cell surface membrane. We demonstrate that mutations in these two pairs of N-glycosylation sites induce ER accumulation of B7H3 by blocking its ER-to-Golgi translocation and subsequently promote its degradation via the endoplasmic reticulum-associated protein degradation pathway. Additional evidence suggests that N-glycosylation at N91/309 and N104/322 of B7H3 is essential for its inhibition of T-cell proliferation and activation. More importantly, a monoclonal antibody, Ab-82, preferentially targeting B7H3 glycosylated at N91/309 and N104/322 is developed, which exhibits the ability to elicit cytotoxic T lymphocyte-mediated antitumor immunity via B7H3 internalization. Together, these findings offer a rationale for targeting glycosylated B7H3 as a potential strategy for immunotherapy.

Investigation of adipocyte differentiation based on proteomics and intact N-glycopeptide modificationomics

OBJECTIVE

To investigate the role of N-glycosylation modification of proteins in adipocyte differentiation during the adipogenic process.

METHODS

SVF cells and adipocytes were analyzed for proteomics and intact N-glycopeptide modificationomics.Differential expression of proteins, glycoforms, and sites between the two groups was screened and subjected to Gene Ontology (GO) functional enrichment analysis, KEGG pathway enrichment analysis, and protein-protein interaction (PPI) network analysis. The top 20 most significantly differentially expressed adipogenic differentiation-related proteins were identified, and the most pronouncedly altered proteins were analyzed for glycoforms, glycan chains, and sites.

RESULTS

Proteomics analysis identified 39,392 peptides and 5208 proteins, while intact N-glycopeptide modification profiling identified 3293 intact glycopeptides, 426 proteins, and 161 glycan chains. Proteomics identified 2510 differentially expressed proteins, with CD36 (Cluster of Differentiation 36, CD36) significantly upregulated. In adipocytes, CD36 had 4 N-glycosylation sites: N79, N220, N320, N417, with N320 being a newly identified site. GO enrichment results indicated that CD36 is associated with fatty acid oxidation, lipid oxidation, and fatty acid uptake into cells.

CONCLUSION

Multiple proteins undergo N-glycosylation modification during adipocyte differentiation, with CD36, a fatty acid translocase, being significantly expressed in adipocytes. This suggests that N-glycosylation modification of CD36 may play a crucial role in adipocyte differentiation, providing a foundation for further investigation into the function of CD36 N-glycosylation in adipocyte differentiation.

Analysis of Receptor-Type Protein Tyrosine Phosphatase Extracellular Regions with Insights from AlphaFold

The receptor-type protein tyrosine phosphatases (RPTPs) are involved in a wide variety of physiological functions which are mediated via their diverse extracellular regions. They play key roles in cell-cell contacts, bind various ligands and are regulated by dimerization and other processes. Depending on the subgroup, they have been described as everything from 'rigid rods' to 'floppy tentacles'. Here, we review current experimental structural knowledge on the extracellular region of RPTPs and draw on AlphaFold structural predictions to provide further insights into structure and function of these cellular signalling molecules, which are often mutated in disease and are recognised as drug targets. In agreement with experimental data, AlphaFold predicted structures for extracellular regions of R1, and R2B subgroup RPTPs have an extended conformation, whereas R2B RPTPs are twisted, reflecting their high flexibility. For the R3 PTPs, AlphaFold predicts that members of this subgroup adopt an extended conformation while others are twisted, and that certain members, such as CD148, have one or more large, disordered loop regions in place of fibronectin type 3 domains suggested by sequence analysis.