A novel Golgi retention signal RPWS for tumor suppressor UBIAD1

Cancer cell stiffening via CoQ10 and UBIAD1 regulates ECM signaling and ferroptosis in breast cancer

CoQ10 (Coenzyme Q10) is an essential fat-soluble metabolite that plays a key role in cellular metabolism. A less-known function of CoQ10 is whether it may act as a plasma membrane-stabilizing agent and whether this property can affect cancer development and progression. Here, we show that CoQ10 and its biosynthetic enzyme UBIAD1 play a critical role in plasmamembrane mechanical properties that are of interest for breast cancer (BC) progression and treatment. CoQ10 and UBIAD1 increase membrane fluidity leading to increased cell stiffness in BC. Furthermore, CoQ10 and UBIAD1 states impair ECM (extracellular matrix)-mediated oncogenic signaling and reduce ferroptosis resistance in BC settings. Analyses on human patients and mouse models reveal that UBIAD1 loss is associated with BC development and progression and UBIAD1 expression in BC limits CTCs (circulating tumor cells) survival and lung metastasis formation. Overall, this study reveals that CoQ10 and UBIAD1 can be further investigated to develop therapeutic interventions to treat BC patients with poor prognosis.

UBIAD1 effectively alleviated myocardial ischemia reperfusion injury by activating SIRT1/PGC1α

BACKGROUND AND OBJECTIVES

Myocardial ischemia-reperfusion injury (MIRI) threatens global health and lowers people's sense of happiness. Till now, the mechanism of MIRI has not been well-understood. Therefore, this study was designed to explore the role of UBIAD1 in MIRI as well as its detailed reaction mechanism.

METHODS

The mRNA and protein expressions of UBIAD1 before or after transfection were measured using RT-qPCR and western blot. Western blot was also adopted to measure the expressions of signaling pathway-, mitochondrial damage- and apoptosis-related proteins. Moreover, mitochondrial membrane potential and ATP level were verified by JC-1 immunofluorescence and ATP kits, respectively. With the application of CCK-8, LDH and CK-MB assays, the cell viability, LDH and CK-MB levels were evaluated, respectively. In addition, the cell apoptosis was detected using TUNEL. Finally, the expressions of ROS, SOD, MDA and CAT were measured using DCFH-DA, SOD, MDA and CAT assays, respectively.

RESULTS

In the present study, we found that UBIAD1 was downregulated in hypoxia-reoxygenation (H/R) -induced H9C2 cells and its upregulation could activate SIRT1/PGC1α signaling pathway. It was also found that UBIAD1 regulated mitochondrial membrane potential and ATP level via activating SIRT1/PGC1α signaling pathway. In addition, the injury of H/R-induced H9C2 cells could be relieved by UBIAD1 through the activation of SIRT1/PGC1α signaling pathway. Moreover, UBIAD1 exhibited inhibitory effects on apoptosis and oxidative stress of H/R-induced H9C2 cells through activating SIRT1/PGC1α signaling pathway.

CONCLUSION

To sum up, UBIAD1 could alleviate apoptosis, oxidative stress and H9C2 cell injury by activating SIRT1/PGC1α, which laid experimental foundation for the clinical treatment of MIRI.

Critical Determinants in ER-Golgi Trafficking of Enzymes Involved in Glycosylation

All living cells generate structurally complex and compositionally diverse spectra of glycans and glycoconjugates, critical for organismal evolution, development, functioning, defense, and survival. Glycosyltransferases (GTs) catalyze the glycosylation reaction between activated sugar and acceptor substrate to synthesize a wide variety of glycans. GTs are distributed among more than 130 gene families and are involved in metabolic processes, signal pathways, cell wall polysaccharide biosynthesis, cell development, and growth. Glycosylation mainly takes place in the endoplasmic reticulum (ER) and Golgi, where GTs and glycosidases involved in this process are distributed to different locations of these compartments and sequentially add or cleave various sugars to synthesize the final products of glycosylation. Therefore, delivery of these enzymes to the proper locations, the glycosylation sites, in the cell is essential and involves numerous secretory pathway components. This review presents the current state of knowledge about the mechanisms of protein trafficking between ER and Golgi. It describes what is known about the primary components of protein sorting machinery and trafficking, which are recognition sites on the proteins that are important for their interaction with the critical components of this machinery.

Naturally occurring UBIAD1 mutations differentially affect menaquinone biosynthesis and vitamin K-dependent carboxylation

UbiA prenyltransferase domain-containing protein-1 (UBIAD1) is responsible for the biosynthesis of menaquinone-4 (MK-4), a cofactor for extrahepatic carboxylation of vitamin K-dependent (VKD) proteins. Genetic variations of UBIAD1 are mainly associated with Schnyder corneal dystrophy (SCD), a disease characterized by abnormal accumulation of cholesterol in the cornea. Results from in vitro studies demonstrate that SCD-associated UBIAD1 mutations are defective in MK-4 biosynthesis. However, SCD patients do not exhibit typical phenotypes associated with defects of MK-4 or VKD carboxylation. Here, we coupled UBIAD1's biosynthetic activity of MK-4 with VKD carboxylation in HEK293 cells that stably express a chimeric VKD reporter protein. The endogenous Ubiad1 gene in these cells was knocked out by CRISPR-Cas9-mediated genome editing. The effect of UBIAD1 mutations on MK-4 biosynthesis and VKD carboxylation was evaluated in Ubiad1-deficient reporter cells by determining the production of MK-4 or by measuring the efficiency of reporter-protein carboxylation. Our results show that the hot-spot mutation N102S has a moderate impact on MK-4 biosynthesis (retained ˜ 82% activity) but does not affect VKD carboxylation. However, the G186R mutation significantly affected both MK-4 biosynthesis and VKD carboxylation. Other mutations exhibit varying degrees of effects on MK-4 biosynthesis and VKD carboxylation. These results are consistent with in vivo results obtained from gene knock-in mice and SCD patients. Our findings suggest that UBIAD1's MK-4 biosynthetic activity does not directly correlate with the phenotypes of SCD patients. The established cell-based assays in this study provide a powerful tool for the functional studies of UBIAD1 in a cellular milieu.

Functional study of SCCD pathogenic gene UBIAD1 (Review)

Schnyder's crystalline corneal dystrophy (SCCD) is a rare autosomal dominant genetic disorder that is characterized by progressive corneal opacity, owing to aberrant accumulation of cholesterol and phospholipids in the cornea. A number of SCCD affected families have been reported in the world since 1924, when it was first described. In 2007, the molecular basis of SCCD was demonstrated to be associated with a tumor suppressor, UbiA prenyltransferase domain-containing 1 (UBIAD1), which was isolated from the bladder mucosa and demonstrated to be involved in vitamin K₂ and CoQ10 biosynthesis. This sterol triggers the binding of UBIAD1 to 3-hydroxy-3-methyl-glutaryl coenzyme A reductase (HMGCR) at endoplasmic reticulum (ER) membranes, which is regulated by an intracellular geranylgeranyl diphosphate (GGpp) molecule. The inability of SCCD-associated UBIAD1 to bind GGpp results in the consistent binding of UBIAD1 to HMGCR at ER membranes. This binding leads to HMGCRs being redundant. Therefore, they cannot be degraded through ER-associated degradation to synthesize abundant cholesterol in tissue cells. Excess corneal cholesterol accumulation thus leads to SCCD disease. After decades, the efforts of numerous ophthalmologists and scientists have helped clarify the molecular basis and pathogenesis of SCCD, which has guided the effective diagnosis and treatment of this genetic disorder. However, more studies need to be conducted to understand the pathogenesis of SCCD disease from a genetic basis by studying the defective gene, UBIAD1. Results would guide effective diagnosis and treatment of the inherited eye disease.

Posttranslational Regulation of HMG CoA Reductase, the Rate-Limiting Enzyme in Synthesis of Cholesterol

The polytopic, endoplasmic reticulum (ER) membrane protein 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase produces mevalonate, the key intermediate in the synthesis of cholesterol and many nonsterol isoprenoids including geranylgeranyl pyrophosphate (GGpp). Transcriptional, translational, and posttranslational feedback mechanisms converge on this reductase to ensure cells maintain a sufficient supply of essential nonsterol isoprenoids but avoid overaccumulation of cholesterol and other sterols. The focus of this review is mechanisms for the posttranslational regulation of HMG CoA reductase, which include sterol-accelerated ubiquitination and ER-associated degradation (ERAD) that is augmented by GGpp. We discuss how GGpp-induced ER-to-Golgi trafficking of the vitamin K₂ synthetic enzyme UbiA prenyltransferase domain-containing protein-1 (UBIAD1) modulates HMG CoA reductase ERAD to balance the synthesis of sterol and nonsterol isoprenoids. We also summarize the characterization of genetically manipulated mice, which established that sterol-accelerated, UBIAD1-modulated ERAD plays a major role in regulation of HMG CoA reductase and cholesterol metabolism in vivo.

Construction of a novel MK-4 biosynthetic pathway in Pichia pastoris through heterologous expression of HsUBIAD1

Background

With a variety of physiological and pharmacological functions, menaquinone is an essential prenylated product that can be endogenously converted from phylloquinone (VK₁) or menadione (VK₃) via the expression of Homo sapiens UBIAD1 (HsUBIAD1). The methylotrophic yeast, Pichia pastoris, is an attractive expression system that has been successfully applied to the efficient expression of heterologous proteins. However, the menaquinone biosynthetic pathway has not been discovered in P. pastoris.

Results

Firstly, we constructed a novel synthetic pathway in P. pastoris for the production of menaquinone-4 (MK-4) via heterologous expression of HsUBIAD1. Then, the glyceraldehyde-3-phosphate dehydrogenase constitutive promoter (P_GAP) appeared to be mostsuitable for the expression of HsUBIAD1 for various reasons. By optimizing the expression conditions of HsUBIAD1, its yield increased by 4.37 times after incubation at pH 7.0 and 24 °C for 36 h, when compared with that under the initial conditions. We found HsUBIAD1 expressed in recombinant GGU-23 has the ability to catalyze the biosynthesis of MK-4 when using VK₁ and VK₃ as the isopentenyl acceptor. In addition, we constructed a ribosomal DNA (rDNA)-mediated multi-copy expression vector for the fusion expression of SaGGPPS and PpIDI, and the recombinant GGU-GrIG afforded higher MK-4 production, so that it was selected as the high-yield strain. Finally, the yield of MK-4 was maximized at 0.24 mg/g DCW by improving the GGPP supply when VK₃ was the isopentenyl acceptor.

Conclusions

In this study, we constructed a novel synthetic pathway in P. pastoris for the biosynthesis of the high value-added prenylated product MK-4 through heterologous expression of HsUBIAD1 and strengthened accumulation of GGPP. This approach could be further developed and accomplished for the biosynthesis of other prenylated products, which has great significance for theoretical research and industrial application.

A GFP-tagged version of the pseudorabies virus protein UL56 localizes to the Golgi and trans-Golgi network through a predicted C-terminal leucine-rich helix in transfected cells

BACKGROUND

Pseudorabies virus (PRV) protein UL56 (pUL56) has been implicated in viral dissemination and virulence in vivo. However, the properties of PRV pUL56 remain largely unknown. In the present study, we aim to investigate the subcellular localization of pUL56 and the underlying molecular basis in transfected cells.

METHODS

Constructs of N-terminal green fluorescent protein (GFP) fused pUL56 and its truncations were employed for investigating subcellular localization and further identifying amino acids crucial for pUL56 localization in transfected Vero cells. Finally, the identified amino acids were replaced with alanine for confirming if these mutations could impair the specific localization of pUL56.

RESULTS

The pUL56 predominantly localized at the Golgi and trans-Golgi network (TGN) through its predicted C-terminal transmembrane helix in transfected Vero cells. A Golgi-associated protein Rab6a, independent of interaction with pUL56, was significantly downregulated by pUL56. Further, we found three truncated pUL56 C-terminal fragments (174-184, 175-185 and 191-195) could restrict GFP in the perinuclear region, respectively. Within these truncations, the ¹⁷⁴proline (P), ¹⁸¹leucine (L), ¹⁸⁵L and ¹⁹¹L were essential for maintaining perinuclear accumulation, thus suggesting an important role of leucine. Alanine (A) mutagenesis assays were employed to generate a series of pUL56 C-terminal mutants on the basis of leucine. Finally, a pUL56 mutant M10 (¹⁷⁴P/A-¹⁷⁷L/A-¹⁸¹L/A-¹⁸⁵L/A-¹⁹¹L/A-¹⁹⁴L/A-¹⁹⁵I/A-^196-197L/A-²⁰⁰L/A) lost Golgi-TGN localization. Thus, our data revealed that the leucine-rich transmembrane helix was responsible for pUL56 Golgi-TGN localization and retention, probably through specific intracellular membrane insertion.

CONCLUSION

Our data indicated that the C-terminal transmembrane helix was responsible for the Golgi-TGN localization of pUL56. In addition, the leucines within C-terminal transmembrane helix were essential for maintaining pUL56 Golgi-TGN retention in cells. Further, the pUL56 can induce downregulation of Golgi-associated protein Rab6a.

UBIAD1 suppresses the proliferation of bladder carcinoma cells by regulating H-Ras intracellular trafficking via interaction with the C-terminal domain of H-Ras

UbiA prenyltransferase domain-containing protein 1 (UBIAD1) plays a key role in biosynthesis of vitamin K2 and coenzyme Q10 using geranylgeranyl diphosphate (GGPP). However, the mechanism by which UBIAD1 participates in tumorigenesis remains unknown. This study show that UBIAD1 interacts with H-Ras, retains H-Ras in the Golgi apparatus, prevents H-Ras trafficking from the Golgi apparatus to the plasma membrane, blocks the aberrant activation of Ras/MAPK signaling, and inhibits the proliferation of bladder cancer cells. In addition, GGPP was required to maintain the function of UBIAD1 in regulating the Ras/ERK signaling pathway. A Drosophila model was employed to confirm the function of UBIAD1/HEIX in vivo. The activation of Ras/ERK signaling at the plasma membrane induced melanotic masses in Drosophila larvae. Our study suggests that UBIAD1 serves as a tumor suppressor in cancer and tentatively reveals the underlying mechanism of melanotic mass formation in Drosophila.

UBIAD1 expression is associated with cardiac hypertrophy in spontaneously hypertensive rats

The present study investigated the potential role of UbiA prenyltransferase domain-containing 1 (UBIAD1) in the pathogenesis of hypertensive cardiac hypertrophy. Spontaneously hypertensive rats (SHRs) and Wistar‑Kyoto (WKY) rats at 8, 16 and 28 weeks of age were used. Blood pressure was measured using a non‑invasive tail cut‑off system. Cardiac functional index was assessed by arterial catheterization. Myocardial structure and cell apoptosis were evaluated by hematoxylin and eosin staining, and terminal deoxynucleotidyl‑transferase‑mediated dUTP nick end labeling assays, respectively. Myocardial expression of UBIAD1, coenzyme Q10 (CoQ10), endothelial nitric oxide synthase (eNOS) and atrial natriuretic peptide were evaluated by immunohistochemistry, western blotting and reverse transcription‑quantitative polymerase chain reaction. Circulating and myocardial expression of nitric oxide (NO) were measured using the Griess method. SHRs exhibited increased blood pressure and cardiomyocyte apoptosis, as well as cardiac hypertrophy, compared with age‑matched WKY rats. Myocardial expression of UBIAD1 was significantly decreased in SHRs in an age‑dependent manner. Similarly, myocardial CoQ10 and eNOS expression were significantly reduced in SHR compared to age‑matched WKY rats, and these expression levels additionally decreased further with aging. Serum and myocardial NO expression was additionally decreased in SHRs. Decreased UBIAD1 expression in SHR hearts was associated with decreased levels of CoQ10, eNOS and NO. Given the well‑established role of UBIAD1 in the regulation of NO signaling, reduced expression of UBIAD1 in SHR hearts potentially contributed to the pathogenesis of hypertensive cardiac hypertrophy. Therefore, UBIAD1 may represent a potential therapeutic target for clinical treatment of hypertensive cardiac hypertrophy.

Clinical and para-clinical description of a novel mutation for Schnyder dystrophy in a French family

INTRODUCTION

The objective of this article is to describe the evolution of Schnyder dystrophy in 3 related patients of different ages and to highlight the discovery of a new mutation unidentified until now.

CASE REPORT

We present a series of 3 cases, all first-degree relatives with no suggestion of consanguinity, of different ages (30, 40 and 59 years) and two distinct generations (mother and children). Slit lamp examination revealed the same lesions in our three patients: an early-onset corneal arcus senilis, central corneal deposits, and a gray stromal haze in the two oldest subjects. The older the patient, the more numerous and dense were these lesions. The various anterior segment OCTs showed an increase in the number of hyperreflective opacities in the anterior stroma and, in the older subject, the appearance of many posterior shadows. Monitoring of pachymetry by Pentacam^® showed progressive age-related thickening. All three patients had dyslipidemia treated with statins or diet alone. In our case we proposed treatment only to subject A because of the significant impact on her visual acuity.

DISCUSSION

Numerous clinical, para-clinical and genetic descriptions of this disease are found in the literature. Schnyder dystrophy is rare but not unheard of and may be discovered fortuitously or in the setting of decreased visual acuity. Genetic analysis of our family revealed a mutation of the UBIAD1 gene not described in the literature. UBIAD1 encodes the protein domain-containing UbiA prenyltransferase 1 which converts vitamin K1 into K2 and is involved in the cholesterol synthesis pathway. In the case of a mutation, it is no longer functional, leading to the accumulation of cholesterol crystals. Given the clinical context and the presence of this variant of the reference sequence in all relatives, its pathogenesis is strongly suspected in our family. The originality of our article is to present the progression of the same pathology in 3 patients with the same mutation at different ages and degrees of severity. This notion of progressive worsening and the need to treat late in the majority of cases are found in literature.

CONCLUSION

The discovery of a new variant within the UBAID1 gene suggests its pathogenesis in view of the clinical features available to us. The dystrophy is initially asymptomatic before the high number of deposits becomes disabling.

UBIAD1 protects against oxygen-glucose deprivation/reperfusion-induced multiple subcellular organelles injury through PI3K/AKT pathway in N2A cells

Cerebral ischemia/reperfusion-induced injury plays a significant role in the development of multi-subcellular organelles injury after ischemic stroke. UBIAD1 was discovered originally as a potential tumor suppressor protein. Recently, analysis of UBIAD1 has indicated it is a prenyltransferase enzyme for both non-mitochondrial CoQ10 and vitamin K2 production. Further, UBIAD1 has been localized to multiple subcellular organelles. Particularly, UBIAD1 plays an important role in the regulation of oxidative stress, apoptosis and cell proliferation, cholesterol and lipid metabolism, which was closely associated with the cerebral ischemic/reperfusion mechanism. However, the mechanism underlying effects of UBIAD1 on cerebral ischemia/reperfusion-induced injury remains largely unknown. We aimed to investigate the effects of UBIAD1 on ischemia/reperfusion-induced multiple subcellular organelles injury in vitro, mouse N2A cells were subjected to a classical oxygen-glucose deprivation and reperfusion (OGD/R) insult. The expression of UBIAD1 was reduced in mouse N2A cells after OGD/R. UBIAD1 exhibits multi-subcellular organelles co-localization in N2a cells, including in the mitochondria, endoplasmic reticulum, and Golgi apparatus. The over-expression of UBIAD1 significantly protects against OGD/R-induced cell death. UBIAD1 over-expression also attenuated OGD/R-induced mitochondrial fragmentation and dysfunction and mediated the level of apoptosis-associated protein. Moreover, we observed that the over-expression of UBIAD1 ameliorated OGD/R-induced fragmentation and reduced the level of oxidative stress-related protein expression in both the endoplasmic reticulum and Golgi apparatus. Besides, the neuroprotective effect of UBIAD1 was correlated with the PI3K/AKT pathway, which was demonstrated using the PI3K inhibitor LY294002 and perifosion. Collectively, these findings identified that UBIAD1 protects against OGD/R-induced multiple subcellular organelles injury through PI3K/AKT Pathway.

A New Horizon in Vitamin K Research

Vitamin K is a cofactor for γ-glutamyl carboxylase, which catalyzes the posttranslational conversion of specific glutamyl residues to γ-carboxyglutamyl residues in a variety of vitamin K-dependent proteins (VKDPs) involved in blood coagulation, bone and cartilage metabolism, signal transduction, and cell proliferation. Despite the great advances in the genetic, structural, and functional studies of VKDPs as well as the enzymes identified as part of the vitamin K cycle which enable it to be repeatedly recycled within the cells, little is known of the identity and roles of key regulators of vitamin K metabolism in mammals and humans. This review focuses on new insights into the molecular mechanisms underlying the intestinal absorption and in vivo tissue conversion of vitamin K1 to menaquinone-4 (MK-4) with special emphasis on two major advances in the studies of intestinal vitamin K transporters in enterocytes and a tissue MK-4 biosynthetic enzyme UbiA prenyltransferase domain-containing protein 1 (UBIAD1), which participates in the in vivo conversion of a fraction of dietary vitamin K1 to MK-4 in mammals and humans, although it remains uncertain whether UBIAD1 functions as a key regulator of intracellular cholesterol metabolism, bladder and prostate tumor cell progression, vascular integrity, and protection from oxidative stress.

Identification of the First De Novo UBIAD1 Gene Mutation Associated with Schnyder Corneal Dystrophy

Purpose. To report the identification of the first de novo UBIAD1 missense mutation in an individual with Schnyder corneal dystrophy (SCD). Methods. A slit lamp examination was performed on a 47-year-old woman without a family history of corneal disorders. The proband's parents, two sisters, and son were also examined and genomic DNA from all six individuals was collected. The exons and exon-intron boundaries of UBIAD1 were screened using Sanger sequencing. Identified mutations were screened for in 200 control chromosomes. In silico analysis predicted the impact of identified mutations on protein function and structure. Results. Slit lamp examination of the proband revealed findings consistent with SCD. Corneas of the family members appeared unaffected. Screening of UBIAD1 in the proband identified a novel heterozygous c.308C>T mutation, predicted to encode the missense amino acid substitution p.(Thr103Ile). This mutation was not identified in any of the family members or in 200 control chromosomes and was predicted to be damaging to normal protein function and structure. Conclusions. We present a novel heterozygous de novo missense mutation in UBIAD1, p.(Thr103Ile), identified in a patient with classic clinical features of SCD. This highlights the value of genetic testing in clinical diagnostic settings, even in the absence of a positive family history.

Role of UBIAD1 in Intracellular Cholesterol Metabolism and Vascular Cell Calcification

Vascular calcification is an important risk factor associated with mortality among patients with chronic kidney disease. Intracellular cholesterol metabolism is involved in the process of vascular cell calcification. In this study, we investigated the role of UbiA prenyltransferase domain containing 1 (UBIAD1) in intracellular cholesterol metabolism and vascular cell calcification, and identified its subcellular location. Primary human umbilical vein smooth muscle cells (HUVSMCs) were incubated with either growth medium (1.4 mmol/L Pi) or calcification medium (CM) (3.0 mmol/L Pi). Under treatment with CM, HUVSMCs were further incubated with exogenous cholesterol, or menaquinone-4, a product of UBIAD1. The plasmid and small interfering RNA were transfected in HUVSMCs to alter the expression of UBIAD1. Matrix calcium quantitation, alkaline phosphatase activity, intracellular cholesterol level and menaquinone-4 level were measured. The expression of several genes involved in cholesterol metabolism were analyzed. Using an anti-UBIAD1 antibody, an endoplasmic reticulum marker and a Golgi marker, the subcellular location of UBIAD1 in HUVSMCs was analyzed. CM increased matrix calcium, alkaline phosphatase activity and intracellular cholesterol level, and reduced UBIAD1 expression and menaquinone-4 level. Addition of cholesterol contributed to increased matrix calcification and alkaline phosphatase activity in a dose-dependent manner. Elevated expression of UBIAD1 or menaquinone-4 in HUVSMCs treated with CM significantly reduced intracellular cholesterol level, matrix calcification and alkaline phosphatase activity, but increased menaquinone-4 level. Elevated expression of UBIAD1 or menaquinone-4 reduced the gene expression of sterol regulatory element-binding protein-2, and increased gene expression of ATP binding cassette transporters A1, which are in charge of cholesterol synthesis and efflux. UBIAD1 co-localized with the endoplasmic reticulum marker and the Golgi marker in HUVSMCs. In conclusion, high intracellular cholesterol content contributes to phosphate-induced vascular cell differentiation and calcification. UBIAD1 or menaquinone-4 could decrease vascular cell differentiation and calcification, probably via its potent role of inversely modulating cellular cholesterol.

Functional characterization of the vitamin K2 biosynthetic enzyme UBIAD1

UbiA prenyltransferase domain-containing protein 1 (UBIAD1) plays a significant role in vitamin K₂ (MK-4) synthesis. We investigated the enzymological properties of UBIAD1 using microsomal fractions from Sf9 cells expressing UBIAD1 by analysing MK-4 biosynthetic activity. With regard to UBIAD1 enzyme reaction conditions, highest MK-4 synthetic activity was demonstrated under basic conditions at a pH between 8.5 and 9.0, with a DTT ≥0.1 mM. In addition, we found that geranyl pyrophosphate and farnesyl pyrophosphate were also recognized as a side-chain source and served as a substrate for prenylation. Furthermore, lipophilic statins were found to directly inhibit the enzymatic activity of UBIAD1. We analysed the aminoacid sequences homologies across the menA and UbiA families to identify conserved structural features of UBIAD1 proteins and focused on four highly conserved domains. We prepared protein mutants deficient in the four conserved domains to evaluate enzyme activity. Because no enzyme activity was detected in the mutants deficient in the UBIAD1 conserved domains, these four domains were considered to play an essential role in enzymatic activity. We also measured enzyme activities using point mutants of the highly conserved aminoacids in these domains to elucidate their respective functions. We found that the conserved domain I is a substrate recognition site that undergoes a structural change after substrate binding. The conserved domain II is a redox domain site containing a CxxC motif. The conserved domain III is a hinge region important as a catalytic site for the UBIAD1 enzyme. The conserved domain IV is a binding site for Mg²⁺/isoprenyl side-chain. In this study, we provide a molecular mapping of the enzymological properties of UBIAD1.

The prenyltransferase UBIAD1 is the target of geranylgeraniol in degradation of HMG CoA reductase

Schnyder corneal dystrophy (SCD) is an autosomal dominant disorder in humans characterized by abnormal accumulation of cholesterol in the cornea. SCD-associated mutations have been identified in the gene encoding UBIAD1, a prenyltransferase that synthesizes vitamin K₂. Here, we show that sterols stimulate binding of UBIAD1 to the cholesterol biosynthetic enzyme HMG CoA reductase, which is subject to sterol-accelerated, endoplasmic reticulum (ER)-associated degradation augmented by the nonsterol isoprenoid geranylgeraniol through an unknown mechanism. Geranylgeraniol inhibits binding of UBIAD1 to reductase, allowing its degradation and promoting transport of UBIAD1 from the ER to the Golgi. CRISPR-CAS9-mediated knockout of UBIAD1 relieves the geranylgeraniol requirement for reductase degradation. SCD-associated mutations in UBIAD1 block its displacement from reductase in the presence of geranylgeraniol, thereby preventing degradation of reductase. The current results identify UBIAD1 as the elusive target of geranylgeraniol in reductase degradation, the inhibition of which may contribute to accumulation of cholesterol in SCD.

DOI:http://dx.doi.org/10.7554/eLife.05560.001

People with a rare genetic disorder called ‘Schnyder corneal dystrophy’ gradually lose their vision, because their corneas become increasingly cloudy. This cloudiness is caused by a build-up of excessive amounts of cholesterol, and the disorder itself is caused by mutations in a gene that encodes a protein called UBIAD1. Researchers have previously discovered that the UBIAD1 protein is involved in making vitamin K₂, but it is not clear how this protein also helps to control cholesterol levels in the cornea.

An enzyme called HMG CoA reductase makes a molecule that is used to make cholesterol and many other similar sterol molecules. A ‘feedback loop’ operates in cells to control the amount of the reductase and prevent cholesterol from becoming too high or too low. Sterol molecules, together with another molecule called geranylgeraniol, participate in this feedback loop by promoting the destruction of the reductase enzyme. Here, Schumacher et al. reveal a link between UBIAD1 and the reductase that may explain how UBIAD1 contributes to the production of excess cholesterol in patients with Schnyder corneal dystrophy.

The experiments show that, in the presence of sterol molecules, UBIAD1 can bind to HMG CoA reductase to protect the reductase from being destroyed by other proteins. Geranylgeraniol—which stops the UBIAD1 protein from binding to the enzyme—is required to completely destroy the reductase enzyme. However, when UBIAD1 is missing, the reductase enzyme is destroyed even in the absence of geranylgeraniol.

Furthermore, the experiments show that the genetic mutations linked to Schnyder corneal dystrophy lead to the production of versions of the UBIAD1 protein that bind to the reductase enzyme even when geranylgeraniol molecules are present. This prevents the normal breakdown of the reductase enzyme, which could lead to the build up of cholesterol in the cornea of individuals with the disorder.

Schumacher et al.'s findings show that the UBIAD1 protein helps to control the levels of cholesterol in cells by protecting the HMG CoA reductase enzyme from destruction. These findings may aid the development of new therapies to lower cholesterol levels in cells, which may help patients with Schnyder's corneal dystrophy and other conditions caused by high cholesterol levels.

DOI:http://dx.doi.org/10.7554/eLife.05560.002

Heixuedian (heix), a potential melanotic tumor suppressor gene, exhibits specific spatial and temporal expression pattern during Drosophila hematopoiesis

The Drosophila heixuedian (heix) is the ortholog of human UBIAD1 gene (a.k.a TERE1). The protein product of UBIAD1/heix has multiple enzymatic activities, including the vitamin K2 and the non-mitochondrial CoQ10 biosynthesis. However, the expression pattern of UBIAD1/Heix during metazoan development has not been systematically studied. In this paper, we found that loss of function of heix resulted in pathological changes of larval hematopoietic system, including lymph gland hypertrophy, hemocyte overproliferation and aberrant differentiation, and melanin mass formation. Overexpression of heix cDNA under the tubulin Gal4 driver rescued the above hematopoietic defects. Interestingly, Heix was specifically expressed in plasmatocyte/macrophage lineage in srp driven EGFP positive cells on the head mesoderm during embryogenesis, while it was highly expressed in crystal cells in the primary lobes of the third instar larval lymph gland. Using qRT-PCR analysis, loss of function of heix caused aberrant activation of multiple hemocyte proliferation-related as well as immune-related pathways, including JAK/STAT pathway, Ras/MAPK pathway, IMD pathway and Toll pathway. These data suggested that heix is a potential melanotic tumor suppressor gene and plays a pivotal role in both hemocytes proliferation and differentiation in Drosophila.

Mitochondrial damage and cholesterol storage in human hepatocellular carcinoma cells with silencing of UBIAD1 gene expression

Heterozygous mutations in the UBIAD1 gene cause Schnyder corneal dystrophy characterized by abnormal cholesterol and phospholipid deposits in the cornea. Ubiad1 protein was recently identified as Golgi prenyltransferase responsible for biosynthesis of vitamin K2 and CoQ10, a key protein in the mitochondrial electron transport chain. Our study shows that silencing UBIAD1 in cultured human hepatocellular carcinoma cells causes dramatic morphological changes and cholesterol storage in the mitochondria, emphasizing an important role of UBIAD1 in mitochondrial function.

Vitamin K2 biosynthetic enzyme, UBIAD1 is essential for embryonic development of mice

UbiA prenyltransferase domain containing 1 (UBIAD1) is a novel vitamin K₂ biosynthetic enzyme screened and identified from the human genome database. UBIAD1 has recently been shown to catalyse the biosynthesis of Coenzyme Q10 (CoQ10) in zebrafish and human cells. To investigate the function of UBIAD1 in vivo, we attempted to generate mice lacking Ubiad1, a homolog of human UBIAD1, by gene targeting. Ubiad1-deficient (Ubiad1^−/−) mouse embryos failed to survive beyond embryonic day 7.5, exhibiting small-sized body and gastrulation arrest. Ubiad1^−/− embryonic stem (ES) cells failed to synthesize vitamin K₂ but were able to synthesize CoQ9, similar to wild-type ES cells. Ubiad1^+/− mice developed normally, exhibiting normal growth and fertility. Vitamin K₂ tissue levels and synthesis activity were approximately half of those in the wild-type, whereas CoQ9 tissue levels and synthesis activity were similar to those in the wild-type. Similarly, UBIAD1 expression and vitamin K₂ synthesis activity of mouse embryonic fibroblasts prepared from Ubiad1^+/− E15.5 embryos were approximately half of those in the wild-type, whereas CoQ9 levels and synthesis activity were similar to those in the wild-type. Ubiad1^−/− mouse embryos failed to be rescued, but their embryonic lifespans were extended to term by oral administration of MK-4 or CoQ10 to pregnant Ubiad1^+/− mice. These results suggest that UBIAD1 is responsible for vitamin K₂ synthesis but may not be responsible for CoQ9 synthesis in mice. We propose that UBIAD1 plays a pivotal role in embryonic development by synthesizing vitamin K₂, but may have additional functions beyond the biosynthesis of vitamin K₂.

The effect of miRNA-122 in regulating fat deposition in a cell line model

Accumulating evidence supports the role of miR-122 in fatty liver disease. We investigated miR-122 expression in a steatotic hepatocyte model, the effect of miR-122 over-expression and inhibition in the pathogenesis. Human hepatic cell line L02 was induced with oleic acid to establish the steatotic hepatocyte model. Intracellular lipid content was observed with laser scanning confocal microscope (LSCM), and triglyceride content was determined with kits. Total RNA was extracted and reversely transcribed into cDNA. miR-122 expression was measured using qRT-PCR. Subsequently, miR-122 mimic and miR-122 inhibitor were transfected into steatotic hepatocytes to observe their effect on intracellular lipid content. The lipid fluorescence intensity and triglyceride content within the steatotic hepatocytes were significantly higher than those in normal control (860.01 ± 26.52 vs. 257.77 ± 29.69 and 3.47 ± 0.12 vs. 1.85 ± 0.02 at 24 h) (P < 0.01). miR-122 expression in steatotic hepatocytes was down-regulated compared with that in control (2-ΔCt value: 0.0286 ± 0.0078 vs. 0.0075 ± 0.0012) (P ≪ 0.01). After transfection, miR-122 expression (2-ΔCt value) in the miR-122 mimic group increased 2.96-fold compared with that in control, and its lipid fluorescence intensity was significantly lower than that in control (790.92 ± 46.72 vs. 1,022.16 ± 49.66) (P < 0.01). Nevertheless, miR-122 expression decreased 3.45-fold in the miR-122 inhibitor group compared with that in control, and its fluorescence intensity was significantly higher than that in control (1,386.49 ± 40.34 vs 1,022.16 ± 49.66)(P ≪ 0.01). We concluded that miR-122 was down-regulated in steatotic hepatocytes model. The pathogenesis of hepatocyte steatosis was enhanced by miR-122 mimic and reduced with miR-122 inhibitor.