Ectopic expression of the TERE1 (UBIAD1) protein inhibits growth of renal clear cell carcinoma cells: altered metabolic phenotype associated with reactive oxygen species, nitric oxide and SXR target genes involved in cholesterol and lipid metabolism

In adult X-CGD patients, regulatory T cells are expanded while activated T cells display a NOX2-independent ROS increase

The X-linked chronic granulomatous disease (X-CGD), a rare genetic disease characterised by recurrent infections, is caused by mutations of NOX2. Significant proportions of X-CGD patients display signs of immune dysregulation. Regulatory T cells (Tregs) are CD4+T lymphocytes that expand in active inflammation and prevent autoimmune disorders. Here we asked whether X-CGD is associated to Treg dysfunctions in adult patients. To this aim, the frequency of Tregs was analysed through intracellular flow cytometry in a cohort of adult X-CGD patients, carriers and controls. We found that Tregs were significantly expanded and activated in blood of adult X-CGD patients, and this was associated with activation of conventional CD4+T cells (Tconvs). T cell activation was characterised by accumulation of intracellular ROS, not derived from NOX2 but likely produced by cellular metabolism. The higher TNF production by Tconvs in X-CGD patients might contribute to the expansion of Tregs through the TNFR2 receptor. In summary, our data indicate that Tregs expand in adult X-CGD in response to immune activation, and that the increase of NOX2-independent ROS content is a feature of activated T cells.

Effect of asciminib and vitamin K2 on Abelson tyrosine-kinase-inhibitor-resistant chronic myelogenous leukemia cells

BACKGROUND

Abelson (ABL) tyrosine kinase inhibitors (TKIs) are effective against chronic myeloid leukemia (CML); however, many patients develop resistance during ABL TKI therapy. Vitamin K2 (VK2) is a crucial fat-soluble vitamin used to activate hepatic coagulation factors and treat osteoporosis. Although VK2 has demonstrated impressive anticancer activity in various cancer cell lines, it is not known whether VK2 enhances the effects of asciminib, which specifically targets the ABL myristoyl pocket (STAMP) inhibitor.

METHOD

In this work, we investigated whether VK2 contributed to the development of CML cell lines. We also investigated the efficacy of asciminib and VK2 by using K562, ponatinib-resistant K562 (K562 PR), Ba/F3 BCR-ABL, and T315I point mutant Ba/F3 (Ba/F3 T315I) cells.

RESULTS

Based on data from the Gene Expression Omnibus (GEO) database, gamma-glutamyl carboxylase (GGCX) and vitamin K epoxide reductase complex subunit 1 (VKORC1) were elevated in imatinib-resistant patients (GSE130404). UBIA Prenyltransferase Domain Containing 1 (UBIAD1) was decreased, and K562 PR cells were resistant to ponatinib. In contrast, asciminib inhibited CML cells and ponatinib resistance in a dose-dependent manner. CML cells were suppressed by VK2. Caspase 3/7 activity was also elevated, as was cellular cytotoxicity. Asciminib plus VK2 therapy induced a significantly higher level of cytotoxicity than use of each drug alone. Asciminib and VK2 therapy altered the mitochondrial membrane potential.

CONCLUSIONS

Asciminib and VK2 are suggested as a novel treatment for ABL-TKI-resistant cells since they increase treatment efficacy. Additionally, this treatment option has intriguing clinical relevance for patients who are resistant to ABL TKIs.

Oxidative Stress and Mitochondrial Dysfunction in Chronic Kidney Disease

The kidney contains many mitochondria that generate ATP to provide energy for cellular processes. Oxidative stress injury can be caused by impaired mitochondria with excessive levels of reactive oxygen species. Accumulating evidence has indicated a relationship between oxidative stress and kidney diseases, and revealed new insights into mitochondria-targeted therapeutics for renal injury. Improving mitochondrial homeostasis, increasing mitochondrial biogenesis, and balancing mitochondrial turnover has the potential to protect renal function against oxidative stress. Although there are some reviews that addressed this issue, the articles summarizing the relationship between mitochondria-targeted effects and the risk factors of renal failure are still few. In this review, we integrate recent studies on oxidative stress and mitochondrial function in kidney diseases, especially chronic kidney disease. We organized the causes and risk factors of oxidative stress in the kidneys based in their mitochondria-targeted effects. This review also listed the possible candidates for clinical therapeutics of kidney diseases by modulating mitochondrial function.

New insights into vitamin K biology with relevance to cancer

Phylloquinone (vitamin K1) and menaquinones (vitamin K2 family) are essential for post-translational γ-carboxylation of a small number of proteins, including clotting factors. These modified proteins have now been implicated in diverse physiological and pathological processes including cancer. Vitamin K intake has been inversely associated with cancer incidence and mortality in observational studies. Newly discovered functions of vitamin K in cancer cells include activation of the steroid and xenobiotic receptor (SXR) and regulation of oxidative stress, apoptosis, and autophagy. We provide an update of vitamin K biology, non-canonical mechanisms of vitamin K actions, the potential functions of vitamin K-dependent proteins in cancer, and observational trials on vitamin K intake and cancer.

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.

Olfactory Mucosa Mesenchymal Stem Cells Ameliorate Cerebral Ischemic/Reperfusion Injury Through Modulation of UBIAD1 Expression

Mesenchymal stem cells (MSCs) have presented a promising neuroprotective effect in cerebral ischemia/reperfusion (I/R). Olfactory mucosa MSCs (OM-MSCs), a novel source of MSCs located in the human nasal cavity, are easy to obtain and situated for autologous transplantation. The present study was designed to evaluate the neuroprotective effects of OM-MSCs on cerebral I/R injury and the possible mechanisms. In the transient middle cerebral artery occlusion (t-MCAO) model, excessive oxidative stress and increased swollen mitochondria were observed in the peri-infarct cortex. Intravenous injection of OM-MSCs ameliorated mitochondrial damage and restored oxidant/antioxidant imbalance. Using the oxygen glucose deprivation/reperfusion (OGD/R) model in vitro, we discovered that the exposure of mouse neuroblastoma N2a cells to OGD/R triggers excessive reactive oxygen species (ROS) generation and induces mitochondrial deterioration with decreased mitochondrial membrane potential and reduces ATP content. OM-MSC transwell coculture attenuated the above perturbations accompanied with increased UbiA prenyltransferase domain-containing 1 (UBIAD1) expression, whereas these protective effects of OM-MSCs were blocked when UBIAD1 was knocked down. UBIAD1-specific small interfering RNA (siRNA) reversed the increased membrane potential and ATP content promoted by OM-MSCs. Additionally, UBIAD1-specific siRNA blocked the oxidant/antioxidant balance treated by OM-MSCs. Overall, our results suggested that OM-MSCs exert neuroprotective effects in cerebral I/R injury by attenuating mitochondrial dysfunction and enhancing antioxidation via upregulation of UBIAD1.

Divergent effects of vitamins K1 and K2 on triple negative breast cancer cells

Vitamin K serves as an essential co-factor in the γ-carboxylation of glutamate to γ-carboxyglutamate (GLA), a post-translational modification mediated by gamma-glutamyl carboxylase (GGCX) and vitamin K oxidoreductases (VKORC1 or VKORC1L1). While both phylloquinone (K1) and menaquinone (K2) support the synthesis of GLA-modified proteins, studies assessing K1 and/or K2 effects in cancer cells have reported minimal effects of K1 and anti-proliferative or pro-apoptotic effects of K2. qPCR results indicated highest expression of GGCX, VKORC1, and VKORC1L1 in triple negative breast cancer (TNBC) cell lines, Hs578T, MDA-MB-231 and SUM159PT, and in advanced stage disease. To assess differential effects of vitamin K, TNBC cells were cultured in media supplemented with K1 or K2. K1 treatment increased cell growth, and enhanced stemness and GLA-modified protein expression in TNBC lysates. Alternatively, lysates from cells exposed to vehicle, K2, or the VKOR antagonist, warfarin, did not express GLA-modified proteins. Further, K2 exposure reduced stemness and elicited anti-proliferative effects. These studies show that TNBC cells express a functional vitamin K pathway and that K1 and K2 exert distinct phenotypic effects. Clarification of the mechanisms by which K1 and K2 induce these effects may lead to relevant therapeutic strategies for manipulating this pathway in TNBC patients.

Nitric oxide inhibits autophagy and promotes apoptosis in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the second most common cause of cancer-related mortality worldwide. The expression of nitric oxide synthase (NOS) and the inhibition of autophagy have been linked to cancer cell death. However, the involvement of serum nitric oxide (NO), the expression of NOS and autophagy have not been investigated in HCC. In the present study, we first established that the NO level was significantly higher in hepatitis B virus-related HCC than in the liver cirrhosis control (53.60 ± 19.74 vs 8.09 ± 4.17 μmol/L, t = 15.13, P < 0.0001). Using immunohistochemistry, we found that the source of NO was at least partially attributed to the expression of inducible NOS and endothelial NOS but not neuronal NOS in the liver tissue. Furthermore, in human liver cancer cells, NO-induced apoptosis and inhibited autophagy. Pharmacological inhibition of autophagy also induced apoptosis, whereas the induction of autophagy could ameliorate NO-induced apoptosis. We also found that NO regulates the switch between apoptosis and autophagy by disrupting the Beclin 1/Vps34 association and by increasing the Bcl-2/Beclin 1 interaction. Overall, the present findings suggest that increased NOS/NO promotes apoptosis through the inhibition of autophagy in liver cancer cells, which may provide a novel strategy for the treatment of HCC.

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.

PLIN3 is up-regulated and correlates with poor prognosis in clear cell renal cell carcinoma

BACKGROUND

PLIN3, one of the members of the perilipin family, has been reported to be involved in the formation and accumulation of lipid droplets. However, the expression levels and diagnostic and prognostic value of PLIN3 in renal cell carcinoma (RCC) remain unclear.

METHODS

Bioinformatic analysis was used to assess the levels of PLIN3 and the correlation between PLIN3 levels and clinicopathological parameters in renal cancer. The expression levels of PLIN3 were determined in human RCC tissues and cell lines by western blot, immunofluorescence and immunohistochemistry assays. Receiver operating characteristic curves and Kaplan-Meier curves were used to analyze the diagnostic and prognostic significance of PLIN3 in RCC.

RESULTS

The expression level of PLIN3 was elevated in RCC tissues and cell lines, which was consistent with the analysis of the TCGA and Oncomine cancer database. The receiver operating characteristic curve indicated that high PLIN3 expression can distinguish cancer tissues from normal kidney tissues (area under the curve = 0.7270, P<0.0001). Kaplan-Meier curves revealed that elevated PLIN3 predicted poor disease-free survival and overall survival.

CONCLUSIONS

PLIN3 is highly expressed in kidney cancer, and high expression of PLIN3 can serve as a useful diagnostic and prognostic biomarker. PLIN3 functional inhibition can be used as a new clinical treatment option.

Clinical diversity in patients with Schnyder corneal dystrophy-a novel and known UBIAD1 pathogenic variants

PURPOSE

Schnyder corneal dystrophy (SCD) is a rare inherited disease that leads to gradual vision loss by the deposition of lipids in the corneal stroma. The aim of this study is to report a novel pathogenic variant in the UBIAD1 gene and present clinical and molecular findings in Polish patients with SCD.

METHODS

Individuals (n = 37) originating from four Polish SCD families were subjected for a complete ophthalmological check-up and genetic testing. Corneal changes were visualized by slit-lamp examination, anterior segment optical coherent tomography (AS-OCT), and in vivo confocal microscopy (IVCM).

RESULTS

In a proband with primarily mild SCD that progressed rapidly at the end of the fifth decade of life, a novel missense pathogenic variant in UBIAD1 (p.Thr120Arg) was identified. The other studied SCD family represents the second family reported worldwide with the UBIAD1 p.Asp112Asn variant. SCD in the remaining two families resulted from a frequently identified p.Asn102Ser pathogenic variant. All affected subjects presented a crystalline form of SCD. The severity of corneal changes was age-dependent, and their morphology and localization are described in detail.

CONCLUSION

The novel p.Thr120Arg is the fourth SCD-causing variant lying within the FARM motif of the UBIAD1 protein, which underlines a high importance of this motif for SCD pathogenesis. The current study provides independent evidence for the pathogenic potential of UBIAD1 p.Asp112Asn and new information useful for clinicians.

A Mouse Model of Schnyder Corneal Dystrophy with the N100S Point Mutation

Schnyder corneal dystrophy (SCD) is a rare autosomal dominant disease in humans, characterized by abnormal deposition of cholesterol and phospholipids in cornea caused by mutations in the UbiA prenyltransferase domain containing 1 (UBIAD1) gene. In this study, we generated a mouse line carrying Ubiad1 N100S point mutation using the CRISPR/Cas9 technique to investigate the pathogenesis of SCD. In vivo confocal microscopy revealed hyper-reflective dot-like deposits in the anterior cornea in heterozygotes and homozygotes. No significant change was found in corneal epithelial barrier function or wound healing. Electron microscopy revealed abnormal mitochondrial morphology in corneal epithelial, stromal, and endothelial cells. Mitochondrial DNA copy number assay showed 1.27 ± 0.07 fold change in homozygotes versus 0.98 ± 0.05 variation in wild type mice (P < 0.05). Lipidomic analysis indicated abnormal metabolism of glycerophosphoglycerols, a lipid class found in mitochondria. Four (34:1, 34:2, 36:2, and 44:8) of the 11 glycerophosphoglycerols species identified by mass spectrometry showed a significant increase in homozygous corneas compared with heterozygous and wild-type mouse corneas. Unexpectedly, we did not find a difference in the corneal cholesterol level between different genotypes by filipin staining or lipidomic analysis. The Ubiad1^N100S mouse provides a promising animal model of SCD revealing that mitochondrial dysfunction is a prominent component of the disease. The different phenotype in human and mouse may due to difference in cholesterol metabolism between species.

Molecular alterations associated with chronic exposure to cigarette smoke and chewing tobacco in normal oral keratinocytes

Tobacco usage is a known risk factor associated with development of oral cancer. It is mainly consumed in two different forms (smoking and chewing) that vary in their composition and methods of intake. Despite being the leading cause of oral cancer, molecular alterations induced by tobacco are poorly understood. We therefore sought to investigate the adverse effects of cigarette smoke/chewing tobacco exposure in oral keratinocytes (OKF6/TERT1). OKF6/TERT1 cells acquired oncogenic phenotype after treating with cigarette smoke/chewing tobacco for a period of 8 months. We employed whole exome sequencing (WES) and quantitative proteomics to investigate the molecular alterations in oral keratinocytes chronically exposed to smoke/ chewing tobacco. Exome sequencing revealed distinct mutational spectrum and copy number alterations in smoke/ chewing tobacco treated cells. We also observed differences in proteomic alterations. Proteins downstream of MAPK1 and EGFR were dysregulated in smoke and chewing tobacco exposed cells, respectively. This study can serve as a reference for fundamental damages on oral cells as a consequence of exposure to different forms of tobacco.

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.

UbiA prenyltransferase domain-containing protein-1 modulates HMG-CoA reductase degradation to coordinate synthesis of sterol and nonsterol isoprenoids

UBIAD1 (UbiA prenyltransferase domain-containing protein-1) utilizes geranylgeranyl pyrophosphate (GGpp) to synthesize vitamin K₂ We previously reported that sterols stimulate binding of UBIAD1 to endoplasmic reticulum (ER)-localized 3-hydroxy-3-methylglutaryl (HMG) CoA reductase. UBIAD1 binding inhibits sterol-accelerated, ER-associated degradation (ERAD) of reductase, one of several mechanisms for feedback control of this rate-limiting enzyme in the branched pathway that produces cholesterol and nonsterol isoprenoids such as GGpp. Accumulation of GGpp in ER membranes triggers release of UBIAD1 from reductase, permitting its maximal ERAD and ER-to-Golgi transport of UBIAD1. Mutant UBIAD1 variants associated with Schnyder corneal dystrophy (SCD), a human disorder characterized by corneal accumulation of cholesterol, resist GGpp-induced release from reductase and remain sequestered in the ER to block reductase ERAD. Using lines of genetically manipulated cells, we now examine consequences of UBIAD1 deficiency and SCD-associated UBIAD1 on reductase ERAD and cholesterol synthesis. Our results indicated that reductase becomes destabilized in the absence of UBIAD1, resulting in reduced cholesterol synthesis and intracellular accumulation. In contrast, an SCD-associated UBIAD1 variant inhibited reductase ERAD, thereby stabilizing the enzyme and contributing to enhanced synthesis and intracellular accumulation of cholesterol. Finally, we present evidence that GGpp-regulated, ER-to-Golgi transport enables UBIAD1 to modulate reductase ERAD such that synthesis of nonsterol isoprenoids is maintained in sterol-replete cells. These findings further establish UBIAD1 as a central player in the reductase ERAD pathway and regulation of isoprenoid synthesis. They also indicate that UBIAD1-mediated inhibition of reductase ERAD underlies cholesterol accumulation associated with SCD.

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.

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 tumor suppressor TERE1 (UBIAD1) prenyltransferase regulates the elevated cholesterol phenotype in castration resistant prostate cancer by controlling a program of ligand dependent SXR target genes

Castrate-Resistant Prostate Cancer (CRPC) is characterized by persistent androgen receptor-driven tumor growth in the apparent absence of systemic androgens. Current evidence suggests that CRPC cells can produce their own androgens from endogenous sterol precursors that act in an intracrine manner to stimulate tumor growth. The mechanisms by which CRPC cells become steroidogenic during tumor progression are not well defined. Herein we describe a novel link between the elevated cholesterol phenotype of CRPC and the TERE1 tumor suppressor protein, a prenyltransferase that synthesizes vitamin K-2, which is a potent endogenous ligand for the SXR nuclear hormone receptor. We show that 50% of primary and metastatic prostate cancer specimens exhibit a loss of TERE1 expression and we establish a correlation between TERE1 expression and cholesterol in the LnCaP-C81 steroidogenic cell model of the CRPC. LnCaP-C81 cells also lack TERE1 protein, and show elevated cholesterol synthetic rates, higher steady state levels of cholesterol, and increased expression of enzymes in the de novo cholesterol biosynthetic pathways than the non-steroidogenic prostate cancer cells. C81 cells also show decreased expression of the SXR nuclear hormone receptor and a panel of directly regulated SXR target genes that govern cholesterol efflux and steroid catabolism. Thus, a combination of increased synthesis, along with decreased efflux and catabolism likely underlies the CRPC phenotype: SXR might coordinately regulate this phenotype. Moreover, TERE1 controls synthesis of vitamin K-2, which is a potent endogenous ligand for SXR activation, strongly suggesting a link between TERE1 levels, K-2 synthesis and SXR target gene regulation. We demonstrate that following ectopic TERE1 expression or induction of endogenous TERE1, the elevated cholesterol levels in C81 cells are reduced. Moreover, reconstitution of TERE1 expression in C81 cells reactivates SXR and switches on a suite of SXR target genes that coordinately promote both cholesterol efflux and androgen catabolism. Thus, loss of TERE1 during tumor progression reduces K-2 levels resulting in reduced transcription of SXR target genes. We propose that TERE1 controls the CPRC phenotype by regulating the endogenous levels of Vitamin K-2 and hence the transcriptional control of a suite of steroidogenic genes via the SXR receptor. These data implicate the TERE1 protein as a previously unrecognized link affecting cholesterol and androgen accumulation that could govern acquisition of the CRPC phenotype.

The molecular genetics of coenzyme Q biosynthesis in health and disease

Coenzyme Q, or ubiquinone, is an endogenously synthesized lipid-soluble antioxidant that plays a major role in the mitochondrial respiratory chain. Although extensively studied for decades, recent data on coenzyme Q have painted an exciting albeit incomplete picture of the multiple facets of this molecule's function. In humans, mutations in the genes involved in the biosynthesis of coenzyme Q lead to a heterogeneous group of rare disorders, with most often severe and debilitating symptoms. In this review, we describe the current understanding of coenzyme Q biosynthesis, provide a detailed overview of human coenzyme Q deficiencies and discuss the existing mouse models for coenzyme Q deficiency. Furthermore, we briefly examine the current state of affairs in non-mitochondrial coenzyme Q functions and the latter's link to statin.