Cloning and expression of mannosylphospho dolichol synthase from bovine adrenal medullary capillary endothelial cells

BIRTH OF A GLYCOTHERAPY FOR BREAST CANCER

Breast cancer is the most common malignant disease in women and is worldwide. The incidence rate of women's breast cancer in 2020 was 2,261,419 and 2022 estimates diagnosing 1,918,030 cases. The disease is heterogeneous and the pathogenesis of breast cancer still remains unclear. Much progress has been made in early detection and better treatment to improve survival. Unfortunately, the current treatment strategies destroy the patient's quality of life. The patients develop drug resistance, exhibit severe side effects, and not afford the cost creates anxiety among the patients, families, and friends. In addition, a considerable number of patients relapse as a result of organ metastasis, e.g., the triple-negative breast cancer (TNBC, ER-/PR-HER2-). The 5-year survival rate of patients who recurred with distant metastasis is less than 20%. More than half a million women worldwide still suffer from metastatic breast cancer annually, and 90% of their deaths could be attributed to metastasis. One of the reasons for the failure of cancer therapeutics is the approaches did not consider the cancer holistically. All breast cancer cells and their micro environmental capillary endothelial cells express asparagine-linked (N-linked) glycoproteins. We have tested a biologic and a small molecule, Tunicamycin-P (P = pure N-glycosylation inhibitor) to interfere with the protein N-glycosylation pathway in the endoplasmic reticulum (ER) by specifically blocking the catalytic activity of N-acetylglusosaminyl 1-phosphate transferase (GPT) activity. The outcome has been quantitative inhibition of in vitro and in vivo angiogenesis and the breast tumor progression of multiple subtypes in pre-clinical mouse models with "zero" toxicity. We have, therefore, concluded that Tunicamycin-P is expected to supersede the current therapeutics and become a Glycotherapy treating breast cancer of all subtypes.

Glycotherapy: A New Paradigm in Breast Cancer Research

Breast cancer is an ancient disease recognized first by the Egyptians as early as 1600 BC. The first cancer-causing gene in a chicken tumor virus was found in 1970. The United States signed the National Cancer Act in 1971, authorizing federal funding for cancer research. Irrespective of multi-disciplinary approaches, diverting a great deal of public and private resources, breast cancer remains at the forefront of human diseases, affecting as many as one in eight women during their lifetime. Because of overarching challenges and changes in the breast cancer landscape, five-year disease-free survival is no longer considered adequate. The absence of a cure, and the presence of drug resistance, severe side effects, and destruction of the patient’s quality of life, as well as the fact that therapy is often expensive, making it unaffordable to many, have created anxiety among patients, families, and friends. One of the reasons for the failure of cancer therapeutics is that the approaches do not consider cancer holistically. Characteristically, all breast cancer cells and their microenvironmental capillary endothelial cells express asparagine-linked (N-linked) glycoproteins with diverse structures. We tested a small biological molecule, Tunicamycin, that blocks a specific step of the protein N-glycosylation pathway in the endoplasmic reticulum (ER), i.e., the catalytic activity of N-acetylglusosaminyl 1-phosphate transferase (GPT). The outcome was overwhelmingly exciting. Tunicamycin quantitatively inhibits angiogenesis in vitro and in vivo, and inhibits the breast tumor progression of multiple subtypes in pre-clinical mouse models with “zero” toxicity. Mechanistic details support ER stress-induced unfolded protein response (upr) signaling as the cause for the apoptotic death of both cancer and the microvascular endothelial cells. Additionally, it interferes with Wnt signaling. We therefore conclude that Tunicamycin can be expected to supersede the current therapeutics to become a glycotherapy for treating breast cancer of all subtypes.

DPM1 expression as a potential prognostic tumor marker in hepatocellular carcinoma

Background

Altered glycosylation of proteins contributes to tumor progression. Dolichol phosphate mannose synthase (DPMS), an essential mannosyltransferase, plays a central role in post-translational modification of proteins, including N-linked glycoproteins, O-mannosylation, C-mannosylation and glycosylphosphatidylinositol anchors synthesis. Little is known about the function of DPMS in liver cancer.

Methods

The study explored the roles of DPMS in the prognosis of hepatocellular carcinoma using UALCAN, Human Protein Atlas, GEPIA, cBioPortal and Metascape databases. The mRNA expressions of DPM1/2/3 also were detected by quantitative real-time PCR experiments in vitro.

Results

The transcriptional and proteinic expressions of DPM1/2/3 were both over-expressed in patients with hepatocellular carcinoma. Over-expressions of DPMS were discovered to be dramatically associated with clinical cancer stages and pathological tumor grades in hepatocellular carcinoma patients. In addition, higher mRNA expressions of DPM1/2/3 were found to be significantly related to shorter overall survival in liver cancer patients. Futhermore, high genetic alteration rate of DPMS (41%) was also observed in patients with liver cancer, and genetic alteration in DPMS was associated with shorter overall survival in hepatocellular carcinoma patients. We also performed quantitative real-time PCR experiments in human normal hepatocytes and hepatoma cells to verify the expressions of DPM1/2/3 and results showed that the expression of DPM1 was significantly increased in hepatoma cells SMMC-7721 and HepG2.

Conclusions

Taken together, these results suggested that DPM1 could be a potential prognostic biomarker for survivals of hepatocellular carcinoma patients.

Structural basis for dolichylphosphate mannose biosynthesis

Protein glycosylation is a critical protein modification. In biogenic membranes of eukaryotes and archaea, these reactions require activated mannose in the form of the lipid conjugate dolichylphosphate mannose (Dol-P-Man). The membrane protein dolichylphosphate mannose synthase (DPMS) catalyzes the reaction whereby mannose is transferred from GDP-mannose to the dolichol carrier Dol-P, to yield Dol-P-Man. Failure to produce or utilize Dol-P-Man compromises organism viability, and in humans, several mutations in the human dpm1 gene lead to congenital disorders of glycosylation (CDG). Here, we report three high-resolution crystal structures of archaeal DPMS from Pyrococcus furiosus, in complex with nucleotide, donor, and glycolipid product. The structures offer snapshots along the catalytic cycle, and reveal how lipid binding couples to movements of interface helices, metal binding, and acceptor loop dynamics to control critical events leading to Dol-P-Man synthesis. The structures also rationalize the loss of dolichylphosphate mannose synthase function in dpm1-associated CDG.

The generation of glycolipid dolichylphosphate mannose (Dol-P-Man) is a critical step for protein glycosylation and GPI anchor synthesis. Here the authors report the structure of dolichylphosphate mannose synthase in complex with bound nucleotide and donor to provide insight into the mechanism of Dol-P-Man synthesis.

Dolichol phosphate mannose synthase: a Glycosyltransferase with Unity in molecular diversities

N-glycans provide structural and functional stability to asparagine-linked (N-linked) glycoproteins, and add flexibility. Glycan biosynthesis is elaborative, multi-compartmental and involves many glycosyltransferases. Failure to assemble N-glycans leads to phenotypic changes developing infection, cancer, congenital disorders of glycosylation (CDGs) among others. Biosynthesis of N-glycans begins at the endoplasmic reticulum (ER) with the assembly of dolichol-linked tetra-decasaccharide (Glc₃Man₉GlcNAc₂-PP-Dol) where dolichol phosphate mannose synthase (DPMS) plays a central role. DPMS is also essential for GPI anchor biosynthesis as well as for O- and C-mannosylation of proteins in yeast and in mammalian cells. DPMS has been purified from several sources and its gene has been cloned from 39 species (e.g., from protozoan parasite to human). It is an inverting GT-A folded enzyme and classified as GT2 by CAZy (carbohydrate active enZyme; http://www.cazy.org ). The sequence alignment detects the presence of a metal binding DAD signature in DPMS from all 39 species but finds cAMP-dependent protein phosphorylation motif (PKA motif) in only 38 species. DPMS also has hydrophobic region(s). Hydropathy analysis of amino acid sequences from bovine, human, S. crevisiae and A. thaliana DPMS show PKA motif is present between the hydrophobic domains. The location of PKA motif as well as the hydrophobic domain(s) in the DPMS sequence vary from species to species. For example, the domain(s) could be located at the center or more towards the C-terminus. Irrespective of their catalytic similarity, the DNA sequence, the amino acid identity, and the lack of a stretch of hydrophobic amino acid residues at the C-terminus, DPMS is still classified as Type I and Type II enzyme. Because of an apparent bio-sensing ability, extracellular signaling and microenvironment regulate DPMS catalytic activity. In this review, we highlight some important features and the molecular diversities of DPMS.

N-glycans in cell survival and death: cross-talk between glycosyltransferases

Asparagine-linked (N-linked) protein glycosylation is one of the most important protein modifications. N-glycans with "high mannose", "hybrid", or "complex" type sugar chains participate in a multitude of cellular processes. These include cell-cell/cell-matrix/receptor-ligand interaction, cell signaling/growth and differentiation, to name a few. Many diseases such as disorders of blood clotting, congenital disorder of glycosylation, diseases of blood vessels, cancer, neo-vascularization, i.e., angiogenesis essential for breast and other solid tumor progression and metastasis are associated with N-glycan expression. Biosynthesis of N-glycans requires multiple steps and multiple cellular compartments. Following transcription and translation the proteins migrate to the endoplasmic reticulum (ER) lumen to acquire glycan chain(s) with a defined glycoform, i.e., a tetradecasaccharide. These are further modified, i.e., edited in ER lumen and in Golgi prior to moving to their respective destinations. The tetradecasaccharide is pre-assembled on a poly-isoprenoid lipid called dolichol, and becomes an essential component of the supply chain. Therefore, dolichol cycle synthesizing the lipid-linked oligosaccharide (LLO) is a hallmark for all N-linked glycoproteins. It is expected that there is a great deal of cross-talk between the participating glycosyltransferases and any missed step would express defective N-glycans that could have fatal consequences. The positive impact of the structurally altered N-glycans could lead to discovery of an N-glycan signature for a disease and/or help developing glycotherapeutic treating cancer or other human diseases. The purpose of this review is to identify the gaps of N-glycan biology and help developing appropriate technology for biomedical applications. This article is part of a Special Issue entitled Glycoproteomics.

Mannosylphosphodolichol synthase overexpression supports angiogenesis

Mannosylphospho dolichol synthase (DPMS) plays a critical role in Glc(3)Man(9)GlcNAc(2)-PP-Dol (lipid-linked oligosaccharide, LLO) biosynthesis, an essential intermediate in asparagine-linked (N-linked) protein glycosylation. We have observed earlier that phosphorylation of DPMS increases the catalytic activity of the enzyme by increasing the V(max) as well as the enzyme turnover (k(cat)) without significantly changing the K(m) for GDP-mannose. As a result, LLO biosynthesis, turnover and protein N-glycosylation are increased. This is manifested in increased proliferation of capillary endothelial cells, i.e., angiogenesis. We have then asked if the phosphorylation event or the up-regulation of the DPMS due to over production of the enzyme is a key factor in up-regulating angiogenesis? This question has been answered by isolating a stable capillary endothelial cell clone overexpressing the DPMS gene. Our results indicate that the DPMS overexpressing clone has a high level DPMS mRNA judged by QRT-PCR. The clone also expresses nearly four-times higher DPMS protein over the clone transfected with pEGFP-N1 vector only (i.e., control) as analyzed by western blotting. Most importantly, the overexpressing DPMS clone has ~108% higher DPMS activity than that of the vector control. Immunofluorescence microscopy with Texas-Red conjugated WGA indicates a high level expression of GlcNAc-beta-(1,4)-GlcNAc)1-4-beta-GlcNAc-NeuAc glycans on the external surface of the capillary endothelial cells overexpressing DPMS. Increased cellular proliferation and accelerated healing of the wound induced by a mechanical stress of the DPMS overexpressing clone unequivocally supports DPMS for angiogenesis.