Propeptide glycosylation and galectin-3 binding decrease proteolytic activation of human proMMP-9/progelatinase B

Truncated O-glycosylation in metastatic triple-negative breast cancer reveals a gene expression signature associated with extracellular matrix and proteolysis

Breast cancer (BC) is the leading cause of death by cancer in women worldwide. Triple-negative (TN) BC constitutes aggressive and highly metastatic tumors associated with shorter overall survival of patients compared to other BC subtypes. The Tn antigen, a glycoconjugated structure resulting from an incomplete O-glycosylation process, is highly expressed in different adenocarcinomas, including BC. It also favors cancer growth, immunoregulation, and metastasis in TNBC. This work describes the differentially expressed genes (DEGs) associated with BC aggressiveness and metastasis in an incomplete O-glycosylated TNBC cell model. We studied the transcriptome of a TNBC model constituted by the metastatic murine 4T1 cell line that overexpresses the Tn antigen due to a mutation in one of the steps of the O-glycosylation pathway. We analyzed and compared the results with the parental wild-type cell line and with a Tn-negative cell clone that was poorly metastatic and less aggressive than the 4T1 parental cell line. To gain insight into the generated expression data, we performed a gene set analysis. Biological processes associated with cancer development and metastasis, immune evasion, and leukocyte recruitment were highly enriched among functional terms of DEGs. Furthermore, different highly O-glycosylated protein-coding genes, such as mmp9, ecm1 and ankyrin-2, were upregulated in 4T1/Tn+ tumor cells. The altered biological processes and DEGs that promote tumor growth, invasion and immunomodulation might explain the aggressive properties of 4T1/Tn+ tumor cells. These results support the hypothesis that incomplete O-glycosylation that leads to the expression of the Tn antigen, which might regulate activity or interaction of different molecules, promotes cancer development and immunoregulation.

Glycosylation in breast cancer progression and mammary development: Molecular connections and malignant transformations

INTRODUCTION

The cellular behavior in normal mammary gland development and the progression of breast cancer is like the relationship between an object and its mirror image: they may appear similar, but their essence is completely different. Breast cancer can be considered as temporal and spatial aberrations of normal development in mammary gland. Glycans have been shown to regulate key pathophysiological steps during mammary development and breast cancer progression, and the glycoproteins that play a key role in both processes can affect the normal differentiation and development of mammary cells, and even cause malignant transformation or accelerate tumorigenesis due to differences in their type and level of glycosylation.

KEY FINDINGS

In this review, we summarize the roles of glycan alterations in essential cellular behaviors during breast cancer progression and mammary development, and also highlight the importance of key glycan-binding proteins such as epidermal growth factor receptor, transforming growth factor β receptors and other proteins, which are pivotal in the modulation of cellular signaling in mammary gland. Our review takes an overall view of the molecular interplay, signal transduction and cellular behaviors in mammary gland development and breast cancer progression from a glycobiological perspective.

SIGNIFICANCE

This review will give a better understanding of the similarities and differences in glycosylation between mammary gland development and breast cancer progression, laying the foundation for elucidating the key molecular mechanisms of glycobiology underlying the malignant transformation of mammary cells.

Glycosylation site Asn168 is important for slow in vivo clearance of recombinant human diamine oxidase heparin-binding motif mutants

Elevated plasma and tissues histamine concentrations can cause severe symptoms in mast cell activation syndrome, mastocytosis or anaphylaxis. Endogenous and recombinant human diamine oxidase (rhDAO) can rapidly and completely degrade histamine, and administration of rhDAO represents a promising new treatment approach for diseases with excess histamine release from activated mast cells. We recently generated heparin-binding motif mutants of rhDAO with considerably increased in vivo half-lives in rodents compared with the rapidly cleared wildtype protein. Herein, we characterize the role of an evolutionary recently added glycosylation site asparagine 168 in the in vivo clearance and the influence of an unusually solvent accessible free cysteine 123 on the oligomerization of diamine oxidase (DAO). Mutation of the unpaired cysteine 123 strongly reduced oligomerization without influence on enzymatic DAO activity and in vivo clearance. Recombinant hDAO produced in ExpiCHO-S™ cells showed a 15-fold reduction in the percentage of glycans with terminal sialic acid at Asn168 compared with Chinese hamster ovary (CHO)-K1 cells. Capping with sialic acid was also strongly reduced at the other glycosylation sites. The high abundance of terminal mannose and N-acetylglucosamine residues in the four glycans expressed in ExpiCHO-S™ cells compared with CHO-K1 cells resulted in rapid in vivo clearance. Mutation of Asn168 or sialidase treatment also significantly increased clearance. Intact N-glycans at Asn168 seem to protect DAO from rapid clearance in rodents. Full processing of all glycoforms is critical for preserving the improved in vivo half-life characteristics of the rhDAO heparin-binding motif mutants.

Protease-dependent defects in N-cadherin processing drive PMM2-CDG pathogenesis

The genetic bases for the congenital disorders of glycosylation (CDG) continue to expand, but how glycosylation defects cause patient phenotypes remains largely unknown. Here, we combined developmental phenotyping and biochemical studies in a potentially new zebrafish model (pmm2^sa10150) of PMM2-CDG to uncover a protease-mediated pathogenic mechanism relevant to craniofacial and motility phenotypes in mutant embryos. Mutant embryos had reduced phosphomannomutase activity and modest decreases in N-glycan occupancy as detected by matrix-assisted laser desorption ionization mass spectrometry imaging. Cellular analyses of cartilage defects in pmm2^sa10150 embryos revealed a block in chondrogenesis that was associated with defective proteolytic processing, but seemingly normal N-glycosylation, of the cell adhesion molecule N-cadherin. The activities of the proconvertases and matrix metalloproteinases responsible for N-cadherin maturation were significantly altered in pmm2^sa10150 mutant embryos. Importantly, pharmacologic and genetic manipulation of proconvertase activity restored matrix metalloproteinase activity, N-cadherin processing, and cartilage pathology in pmm2^sa10150 embryos. Collectively, these studies demonstrate in CDG that targeted alterations in protease activity create a pathogenic cascade that affects the maturation of cell adhesion proteins critical for tissue development.

Citrullination as a novel posttranslational modification of matrix metalloproteinases

Matrix metalloproteinases (MMPs) are enzymes with critical roles in biology and pathology. Glycosylation, nitrosylation and proteolysis are known posttranslational modifications (PTMs) regulating intrinsically the activities of MMPs. We discovered MMP citrullination by peptidyl arginine deiminases (PADs) as a new PTM. Upon hypercitrullination, MMP-9 acquired a higher affinity for gelatin than control MMP-9. Furthermore, hypercitrullinated proMMP-9 was more efficiently activated by MMP-3 compared to control MMP-9. JNJ0966, a specific therapeutic inhibitor of MMP-9 activation, inhibited the activation of hypercitrullinated proMMP-9 by MMP-3 significantly less in comparison with control proMMP-9. The presence of citrullinated/homocitrullinated MMP-9 was detected in vivo in neutrophil-rich sputum samples of cystic fibrosis patients. In addition to citrullination of MMP-9, we report efficient citrullination of MMP-1 and lower citrullination levels of MMP-3 and MMP-13 by PAD2 in vitro. In conclusion, citrullination of MMPs is a new PTM worthy of additional biochemical and biological studies.

Protease propeptide structures, mechanisms of activation, and functions

Proteases are a diverse group of hydrolytic enzymes, ranging from single-domain catalytic molecules to sophisticated multi-functional macromolecules. Human proteases are divided into five mechanistic classes: aspartate, cysteine, metallo, serine and threonine proteases, based on the catalytic mechanism of hydrolysis. As a protective mechanism against uncontrolled proteolysis, proteases are often produced and secreted as inactive precursors, called zymogens, containing inhibitory N-terminal propeptides. Protease propeptide structures vary considerably in length, ranging from dipeptides and propeptides of about 10 amino acids to complex multifunctional prodomains with hundreds of residues. Interestingly, sequence analysis of the different protease domains has demonstrated that propeptide sequences present higher heterogeneity compared with their catalytic domains. Therefore, we suggest that protease inhibition targeting propeptides might be more specific and have less off-target effects than classical inhibitors. The roles of propeptides, besides keeping protease latency, include correct folding of proteases, compartmentalization, liganding, and functional modulation. Changes in the propeptide sequence, thus, have a tremendous impact on the cognate enzymes. Small modifications of the propeptide sequences modulate the activity of the enzymes, which may be useful as a therapeutic strategy. This review provides an overview of known human proteases, with a focus on the role of their propeptides. We review propeptide functions, activation mechanisms, and possible therapeutic applications.

Post-Translational Modification-Dependent Activity of Matrix Metalloproteinases

Due to their capacity to process different proteins of the extracellular matrix (ECM), matrix metalloproteinases (MMPs) were initially described as a family of secreted proteases, functioning as main ECM regulators. However, through proteolytic processing of various biomolecules, MMPs also modulate intra- and extracellular pathways and networks. Thereby, they are functionally implicated in the regulation of multiple physiological and pathological processes. Consequently, MMP activity is tightly regulated through a combination of epigenetic, transcriptional, and post-transcriptional control of gene expression, proteolytic activation, post-translational modifications (PTMs), and extracellular inhibition. In addition, MMPs, their substrates and ECM binding partners are frequently modified by PTMs, which suggests an important role of PTMs in modulating the pleiotropic activities of these proteases. This review summarizes the recent progress towards understanding the role of PTMs (glycosylation, phosphorylation, glycosaminoglycans) on the activity of several members of the MMP family.