Squalene-epoxidase-catalyzed 24(S),25-epoxycholesterol synthesis promotes trained-immunity-mediated antitumor activity

The importance of trained immunity in antitumor immunity has been increasingly recognized, but the underlying metabolic regulation mechanisms remain incompletely understood. In this study, we find that squalene epoxidase (SQLE), a key enzyme in cholesterol synthesis, is required for β-glucan-induced trained immunity in macrophages and ensuing antitumor activity. Unexpectedly, the shunt pathway, but not the classical cholesterol synthesis pathway, catalyzed by SQLE, is required for trained immunity induction. Specifically, 24(S),25-epoxycholesterol (24(S),25-EC), the shunt pathway metabolite, activates liver X receptor and increases chromatin accessibility to evoke innate immune memory. Meanwhile, SQLE-induced reactive oxygen species accumulation stabilizes hypoxia-inducible factor 1α protein for metabolic switching into glycolysis. Hence, our findings identify 24(S),25-EC as a key metabolite for trained immunity and provide important insights into how SQLE regulates trained-immunity-mediated antitumor activity.

Age-related cholesterol and colorectal cancer progression: Validating squalene epoxidase for high-risk cases

As people age, the risk and progression of colorectal cancer (CRC), along with cholesterol levels, tend to increase. Nevertheless, epidemiological studies on serum lipids and CRC have produced conflicting results. We previously demonstrated that the reduction of squalene epoxidase (SQLE) due to accumulated cholesterol within cells accelerates CRC progression through the activation of the β-catenin pathway. This study aimed to investigate the mechanism by which age-related cholesterol accumulation within tissue accelerates CRC progression and to assess the clinical significance of SQLE in older individuals with elevated CRC risk. Using machine learning-based digital image analysis with fluorescence-immunohistochemistry, we assessed SQLE, GSK3βpS9 (GSK3β activity inhibition through serine 9 phosphorylation at GSK3β), p53 wild-type (p53WT), and p53 mutant (p53MT) levels in CRC tissues. Our analysis revealed a significant reduction in SQLE, p53WT, and p53MT and increase in GSK3βpS9 levels, all associated with the substantial accumulation of intra-tissue cholesterol in aged CRCs. Cox analysis underscored the significant influence of SQLE on overall survival and progression-free survival in grade 2-3 CRC patients aged over 50. SQLE and GSK3βpS9 consistently exhibited outstanding prognostic and diagnostic performance, particularly in older individuals. Furthermore, combining SQLE with p53WT, p53MT, and GSK3βpS9 demonstrated a robust diagnostic ability in the older population. In conclusion, we have identified that individuals aged over 50 face an increased risk of CRC progression due to aging-linked cholesterol accumulation within tissue and the subsequent reduction in SQLE levels. This study also provides valuable biomarkers, including SQLE and GSK3βpS9, for older patients at elevated risk of CRC.

SQLE is a promising prognostic and immunological biomarker and correlated with immune Infiltration in Sarcoma

Squalene epoxidase (SQLE) is an essential enzyme involved in cholesterol biosynthesis. However, its role in sarcoma and its correlation with immune infiltration remains unclear. All original data were downloaded from The Cancer Genome Atlas (TCGA). SQLE expression was explored using the TCGA database, and correlations between SQLE and cancer immune characteristics were analyzed via the TISIDB databases. Generally, SQLE is predominantly overexpressed and has diagnostic and prognostic value in sarcoma. Upregulated SQLE was associated with poorer overall survival, poorer disease-specific survival, and tumor multifocality in sarcoma. Mechanistically, we identified a hub gene that included a total of 82 SQLE-related genes, which were tightly associated with histone modification pathways in sarcoma patients. SQLE expression was negatively correlated with infiltrating levels of dendritic cells and plasmacytoid dendritic cells and positively correlated with Th2 cells. SQLE expression was negatively correlated with the expression of chemokines (CCL19 and CX3CL1) and chemokine receptors (CCR2 and CCR7) in sarcoma. In conclusion, SQLE may be used as a prognostic biomarker for determining prognosis and immune infiltration in sarcoma.

Identifying squalene epoxidase as a metabolic vulnerability in high-risk osteosarcoma using an artificial intelligence-derived prognostic index

BACKGROUND

Osteosarcoma (OSA) presents a clinical challenge and has a low 5-year survival rate. Currently, the lack of advanced stratification models makes personalized therapy difficult. This study aims to identify novel biomarkers to stratify high-risk OSA patients and guide treatment.

METHODS

We combined 10 machine-learning algorithms into 101 combinations, from which the optimal model was established for predicting overall survival based on transcriptomic profiles for 254 samples. Alterations in transcriptomic, genomic and epigenomic landscapes were assessed to elucidate mechanisms driving poor prognosis. Single-cell RNA sequencing (scRNA-seq) unveiled genes overexpressed in OSA cells as potential therapeutic targets, one of which was validated via tissue staining, knockdown and pharmacological inhibition. We characterized changes in multiple phenotypes, including proliferation, colony formation, migration, invasion, apoptosis, chemosensitivity and in vivo tumourigenicity. RNA-seq and Western blotting elucidated the impact of squalene epoxidase (SQLE) suppression on signalling pathways.

RESULTS

The artificial intelligence-derived prognostic index (AIDPI), generated by our model, was an independent prognostic biomarker, outperforming clinicopathological factors and previously published signatures. Incorporating the AIDPI with clinical factors into a nomogram improved predictive accuracy. For user convenience, both the model and nomogram are accessible online. Patients in the high-AIDPI group exhibited chemoresistance, coupled with overexpression of MYC and SQLE, increased mTORC1 signalling, disrupted PI3K-Akt signalling, and diminished immune infiltration. ScRNA-seq revealed high expression of MYC and SQLE in OSA cells. Elevated SQLE expression correlated with chemoresistance and worse outcomes in OSA patients. Therapeutically, silencing SQLE suppressed OSA malignancy and enhanced chemosensitivity, mediated by cholesterol depletion and suppression of the FAK/PI3K/Akt/mTOR pathway. Furthermore, the SQLE-specific inhibitor FR194738 demonstrated anti-OSA effects in vivo and exhibited synergistic effects with chemotherapeutic agents.

CONCLUSIONS

AIDPI is a robust biomarker for identifying the high-risk subset of OSA patients. The SQLE protein emerges as a metabolic vulnerability in these patients, providing a target with translational potential.

Terbinafine resistance in Trichophyton mentagrophytes and Trichophyton rubrum in the Czech Republic: A prospective multicentric study

BACKGROUND

Terbinafine, an allylamine antifungal, is crucial for treating dermatophytosis by inhibiting squalene epoxidase (SQLE) in the ergosterol biosynthetic pathway. However, resistance is emerging, particularly in India and Southeast Asia, but reports of resistance spread worldwide. Despite this, comprehensive studies on terbinafine resistance in Trichophyton are still limited.

OBJECTIVES

This research aimed to determine the prevalence of terbinafine resistance in the Czech Republic, with a focus on Trichophyton rubrum and Trichophyton mentagrophytes, and investigate the underlying molecular mechanisms.

PATIENTS/METHODS

A total of 514 clinical strains of T. rubrum and 240 T. mentagrophytes collected from four Czech clinical institutions were screened for terbinafine resistance. Molecular investigations included DNA sequencing, specifically the ITS rDNA region and SQLE gene, as well as antifungal susceptibility testing following EUCAST guidelines.

RESULTS

While no resistance was observed in T. rubrum, 2.5% of T. mentagrophytes strains exhibited resistance, marked by the F397L mutation in SQLE. Notably, resistance surged from 1.2% in 2019 to 9.3% in 2020 but reverted to 0% in 2021. All resistant strains were identified as T. mentagrophytes var. indotineae. Resistant strains exhibited high MICs for terbinafine (≥4 mg L-1 ) but low MICs to the other seven antifungals tested except for fluconazole.

CONCLUSIONS

This study highlights the emergence of terbinafine-resistant T. mentagrophytes strains in the Czech Republic, with the F397L mutation being pivotal. Due to the relatively low resistance level, the current guidelines for dermatomycosis treatment in the Czech Republic remain effective, but ongoing surveillance is essential for timely adaptations if resistance patterns change.

A New Genotype of Trichophyton quinckeanum with Point Mutations in Erg11A Encoding Sterol 14-α Demethylase Exhibits Increased Itraconazole Resistance

Trichophyton quinckeanum, the causative agent of mouse favus, has been responsible for several infections of animal owners in recent years and showed an infection peak around 2020 in Jena, Thuringia. The isolated T. quinckeanum strains from Thuringia differ in some positions of the ITS region compared to strains from the IHEM collection as well as to Trichophyton schoenleinii. All T. quinckeanum strains of the new genotype show up to a 100-fold increased itraconazole resistance as measured by microplate laser nephelometry (MLN) assays. Analysis of genes involved in Trichophyton indotineae azole resistance, such as Erg1, which encodes squalene epoxidase, and Erg11B, one of two copies of the sterol 14-α demethylase gene, show a 100% identity between the two T. quinckeanum genotypes. In contrast, Erg11A fragments differ in 15-nucleotide positions between both T. quinckeanum genotypes, resulting in the unique amino acid substitution Ala256Ser in resistant strains. The new T. quinckeanum genotype may have evolved through interspecies mating. Mating type analysis showed a nearly 100% identity of the minus type MAT1-1-1 fragment for all T. quinckeanum isolates. The closely related Trichophyton schoenleinii belongs to the plus mating type and has 100% identical fragments of Erg1 and Erg11B. Erg11A protein sequences of T. schoenleinii and T. quinckeanum showed increased diversity.

Targeting Squalene Epoxidase Confers Metabolic Vulnerability and Overcomes Chemoresistance in HNSCC

Cisplatin resistance poses a substantial hurdle in effectively treating head and neck squamous cell carcinoma (HNSCC). Utilizing multiple tumor models and examining an internal HNSCC cohort, squalene epoxidase (SQLE) is pinpointed as a key driver of chemoresistance and tumorigenesis, operating through a cholesterol-dependent pathway. Comprehensive transcriptomic analysis reveals that SQLE is essential for maintaining c-Myc transcriptional activity by stabilizing the c-Myc protein and averting its ubiquitin-mediated degradation. Mechanistic investigation demonstrates that SQLE inhibition diminishes Akt's binding affinity to lipid rafts via a cholesterol-dependent process, subsequently deactivating lipid raft-localized Akt, reducing GSK-3β phosphorylation at S9, and increasing c-Myc phosphorylation at T58, ultimately leading to c-Myc destabilization. Importantly, employing an Sqle conditional knockout mouse model, SQLE's critical role in HNSCC initiation and progression is established. The preclinical findings demonstrate the potent synergistic effects of combining terbinafine and cisplatin in arresting tumor growth. These discoveries not only provide novel insights into the underlying mechanisms of SQLE-mediated cisplatin resistance and tumorigenesis in HNSCC but also propose a promising therapeutic avenue for HNSCC patients unresponsive to conventional cisplatin-based chemotherapy.

Therapeutic Updates on the Management of Tinea Corporis or Cruris in the Era of Trichophyton Indotineae: Separating Evidence from Hype-A Narrative Review

The emergence and spread of Trichophyton indotineae (T. indotineae) has led to a sea change in the prescription practices of clinicians regarding the management of dermatophytic skin infections. An infection easily managed with a few weeks of antifungals, tinea corporis or cruris, is now often chronic and recurrent and requires prolonged treatment. Rising resistance to terbinafine, with documented squalene epoxidase (SQLE) gene mutations, and slow clinical response to itraconazole leave clinicians with limited treatment choices. However, in these testing times, it is essential that the tenets of antifungal stewardship be followed in making therapeutic decisions, and that the existing armamentarium of antifungals be used in rationale ways to counter this extremely common cutaneous infection, while keeping the growing drug resistance among dermatophytes in check. This review provides updated evidence on the use of various systemic antifungals for dermatophytic infection of the glabrous skin, especially with respect to the emerging T. indotineae species, which is gradually becoming a worldwide concern.

Squalene epoxidase promotes hepatocellular carcinoma development by activating STRAP transcription and TGF-β/SMAD signalling

BACKGROUND AND PURPOSE

Squalene epoxidase (SQLE) is a key enzyme involved in cholesterol biosynthesis, but growing evidence also reveals that SQLE is abnormally expressed in some types of malignant tumours, even though the underlying mechanism remains poorly understood.

EXPERIMENTAL APPROACH

Bioinformatics analysis and RNA sequencing were applied to detect differentially expressed genes in clinical hepatocellular carcinoma (HCC). MTT, colony formation, AnnexinV-FITC/PI, EdU, wound healing, transwell, western blot, qRT-PCR, IHC, F-actin, RNA-sequencing, dual-luciferase reporters, and H&E staining were used to investigate the pharmacological effects and possible mechanisms of SQLE.

KEY RESULTS

SQLE expression was specifically elevated in HCC, correlating with poor clinical outcomes. SQLE significantly promoted HCC growth, epithelial-mesenchymal transition, and metastasis both in vitro and in vivo. RNA sequencing and functional experiments revealed that the protumourigenic effect of SQLE on HCC was closely related to the activation of TGF-β/SMAD signalling, but the stimulatory effect of SQLE on TGF-β/SMAD signalling and HCC development is critically dependent on STRAP. SQLE expression is well correlated with STRAP in HCC, and further, to amplify TGF-β/SMAD signalling, SQLE even transcriptionally increased STRAP gene expression mediated by AP-2α. Finally, as a chemical inhibitor of SQLE, NB-598 markedly inhibited HCC cell growth and tumour development.

CONCLUSIONS AND IMPLICATIONS

Taken together, SQLE serves as a novel oncogene in HCC development by activating TGF-β/SMAD signalling. Targeting SQLE could be useful in drug development and therapy for HCC.

Overexpression of TwSQS, TwSE, and TwOSC Regulates Celastrol Accumulation in Cambial Meristematic Cells and Dedifferentiated Cells

Squalene synthase (SQS), squalene epoxidase (SE), and oxidosqualene cyclase (OSC) are encoding enzymes in downstream biosynthetic pathway of triterpenoid in plants, but the relationship between three genes and celastrol accumulation in Tripterygium wilfordii still remains unknown. Gene transformation system in plant can be used for studying gene function rapidly. However, there is no report on the application of cambial meristematic cells (CMCs) and dedifferentiated cells (DDCs) in genetic transformation systems. Our aim was to study the effects of individual overexpression of TwSQS, TwSE, and TwOSC on terpenoid accumulation and biosynthetic pathway related gene expression through CMCs and DDCs systems. Overexpression vectors of TwSQS, TwSE, and TwOSC were constructed by Gateway technology and transferred into CMCs and DDCs by gene gun. After overexpression, the content of celastrol was significantly increased in CMCs compared with the control group. However, there was no significant increment of celastrol in DDCs. Meanwhile, the relative expression levels of TwSQS, TwSE, TwOSC, and terpenoid biosynthetic pathway related genes were detected. The relative expression levels of TwSQS, TwSE, and TwOSC were increased compared with the control group in both CMCs and DDCs, while the pathway-related genes displayed different expression trends. Therefore, it was verified in T. wilfordii CMCs that overexpression of TwSQS, TwSE, and TwOSC increased celastrol accumulation and had different effects on the expression of related genes in terpenoid biosynthetic pathway, laying a foundation for further elucidating the downstream biosynthetic pathway of celastrol through T. wilfordii CMCs system.

Targeting Squalene Epoxidase Interrupts Homologous Recombination via the ER Stress Response and Promotes Radiotherapy Efficacy

Over 50% of all patients with cancer are treated with radiotherapy. However, radiotherapy is often insufficient as a monotherapy and requires a nontoxic radiosensitizer. Squalene epoxidase (SQLE) controls cholesterol biosynthesis by converting squalene to 2,3-oxidosqualene. Given that SQLE is frequently overexpressed in human cancer, this study investigated the importance of SQLE in breast cancer and non-small cell lung cancer (NSCLC), two cancers often treated with radiotherapy. SQLE-positive IHC staining was observed in 68% of breast cancer and 56% of NSCLC specimens versus 15% and 25% in normal breast and lung tissue, respectively. Importantly, SQLE expression was an independent predictor of poor prognosis, and pharmacologic inhibition of SQLE enhanced breast and lung cancer cell radiosensitivity. In addition, SQLE inhibition enhanced sensitivity to PARP inhibition. Inhibition of SQLE interrupted homologous recombination by suppressing ataxia-telangiectasia mutated (ATM) activity via the translational upregulation of wild-type p53-induced phosphatase (WIP1), regardless of the p53 status. SQLE inhibition and subsequent squalene accumulation promoted this upregulation by triggering the endoplasmic reticulum (ER) stress response. Collectively, these results identify a novel tumor-specific radiosensitizer by revealing unrecognized cross-talk between squalene metabolites, ER stress, and the DNA damage response. Although SQLE inhibitors have been used as antifungal agents in the clinic, they have not yet been used as antitumor agents. Repurposing existing SQLE-inhibiting drugs may provide new cancer treatments.

SIGNIFICANCE

Squalene epoxidase inhibitors are novel tumor-specific radiosensitizers that promote ER stress and suppress homologous recombination, providing a new potential therapeutic approach to enhance radiotherapy efficacy.

2-Aminoselenazoles and 2-aminothiazoles: One-pot synthesis and control of the fungus Colletotrichum lindemuthianum in common beans

BACKGROUND

Anthracnose, caused by the fungus Colletotrichum lindemuthianum, increases losses in the production of common beans. As 1,3-diazoles can act against fungi by inhibiting the enzyme squalene epoxidase (SE), 2-aminoselenazoles and 2-aminothiazoles were synthesized and subjected to tests with the fungus. In addition, the interactions of the most promising substances with the enzyme SE were investigated in silico.

RESULTS

Seventeen compounds (eight new) were prepared by a one-pot methodology. In vitro antifungal activities of these compounds against C. lindemuthianum were determined by the minimum inhibitory concentration (MIC) method. Most treatments differed from the control (water), and six azoles with the lowest MIC values underwent an assay employing common bean plants inoculated with the fungus. Among the best results were those from 2-(3-fluorophenyl)amino-4-phenyl-1,3-thiazole (16; 2857 μg mL^-1 ), which reduced the severity of anthracnose in common beans to values statistically comparable to the commercial fungicide thiophanate-methyl (700 μg mL^-1 ). The in silico affinity of compound 16 for SE was statistically equal to those calculated for several inhibitors of this enzyme.

CONCLUSIONS

The results suggested that 2-(3-fluorophenyl)amino-4-phenyl-1,3-thiazole (16) could be considered a potential fungicidal lead compound for further structural optimization, which according to the in silico study acts via SE inhibition. © 2022 Society of Chemical Industry.

Clinical Isolate of a Multi-Antifungal-Resistant Trichophyton rubrum

The multi-antifungal drug-resistant strain (NUBS21012) of Trichophyton rubrum was isolated from a patient with recurrent tinea corporis. The resistant strain encoded Phe at codon 393 instead of Leu (L393F) in the squalene epoxidase (SQLE) gene. The expression of genes encoding ATP-binding cassette transporter proteins increased in the strain compared to that of other strains. This result provides evidence that ATP-binding cassette transporter proteins are closely associated with azole resistance.

Extensive Dermatophytosis Caused by Terbinafine-Resistant Trichophyton indotineae, France

Extensive dermatophytosis caused by terbinafine-resistant Trichophyton indotineae harboring Phe397Leu and Leu393Ser substitutions in the squalene epoxidase enzyme was diagnosed in France. Analysis of internal transcribed spacer sequences revealed the wide spread of this species in Asia and Europe. Detection of T. indotineae in animals suggests their possible role as reservoirs.

Emergence of Difficult-to-Treat Tinea Corporis Caused by Trichophyton mentagrophytes Complex Isolates, Paris, France

We describe 7 cases of extensive tinea corporis since 2018 in a hospital in Paris, France, after failure to cure with terbinafine. Molecular analysis indicated Trichophyton mentagrophytes internal transcribed spacer type VIII (T. indotineae). This strain, which has mutations in the squalene epoxidase gene, is spreading on the Indian subcontinent.

FDFT1 predicts poor prognosis in stage I-III colon adenocarcinoma and synergizes SQLE to promote tumor progression

Colon adenocarcinoma (COAD) is one of the most prevalent malignancies, with poor prognosis and lack of effective treatment targets. Squalene synthase (FDFT1) is an upstream enzyme of squalene epoxidase (SQLE) in cholesterol biosynthesis. In a previous study, we revealed that SQLE promotes colon cancer cell proliferation in vitro and in vivo. Here, we investigate the prognostic value of FDFT1 in stage I‐III COAD and explore the potential underlying mechanisms. Squalene synthase was significantly upregulated in stage I‐III COAD and positively correlated with poor differentiation and advanced tumor stage. High expression of FDFT1 was an independent predictor of overall and relapse‐free survival, and the nomograms based on FDFT1 could effectively identify patients at high risk of poor outcome. Squalene synthase accelerated colon cancer cell proliferation and promoted tumor growth. Lack of FDFT1 resulted in accumulating NAT8 and D‐pantethine to lower reactive oxygen species levels and inhibit colon cancer cell proliferation. Moreover, the combined inhibition of FDFT1 and SQLE induced a greater suppressive effect on cell proliferation and tumor growth than single inhibition. Taken together, these results indicate that FDFT1 predicts poor prognosis in stage I‐III COAD and has the tumor‐promoting effect on COAD through regulating NAT8 and D‐pantethine. Targeting both FDFT1 and SQLE is a more promising therapy than their single inhibition for stage I‐III COAD.

ATP-binding Cassette (ABC) Transporter Proteins in Highly Terbinafine-resistant Strains of Trichophyton indotineae (Former Species Name: Trichophyton interdigitale)

To clarify the terbinafine (TRF) resistance mechanism in highly TRF-resistant [minimum inhibitory concentration (MIC) >32 μg/mL] strains of Trichophyton indotineae (NUBS19006^T and NUBS19007), we investigated the expression of squalene epoxidase (SQLE), pleiotropic drug resistance 1 (PDR1), multidrug resistance 2 (MDR2), and MDR4 genes by real-time quantitative PCR analysis, given the known interaction of the corresponding proteins with antifungals and the efflux blocker tacrolimus (FK506). SQLE, PDR1, MDR2, and MDR4 transcript levels in TRF-resistant strains cultured in SDB were not significantly higher than those of the respective genes in TRF-susceptible strains (1 and 10). By contrast, PDR1, MDR2, and MDR4 transcript levels in TRF-resistant and TRF-susceptible strains cultured in SDB containing 10 μg/mL TRF were 5-100 times higher than those of the respective genes in strains grown in the absence of TRF. However, no differences in PDR1, MDR2, and MDR4 transcript levels were found between TRF-resistant (NUBS19006^T and NUBS19007) and TRF-susceptible strains cultured in SDB containing 10 μg/mL TRF. The interaction between TRF and FK506 on antifungal activity was not detected in TRF-resistant strains. These results indicate that ATP-dependent efflux pumps do not confer TRF-resistance mechanisms in TRF-resistant strains.

Squalene epoxidase promotes colorectal cancer cell proliferation through accumulating calcitriol and activating CYP24A1-mediated MAPK signaling

Background

Colorectal cancer (CRC) is one of the most malignant tumors with high incidence, yet its molecular mechanism is not fully understood, hindering the development of targeted therapy. Metabolic abnormalities are a hallmark of cancer. Targeting dysregulated metabolic features has become an important direction for modern anticancer therapy. In this study, we aimed to identify a new metabolic enzyme that promotes proliferation of CRC and to examine the related molecular mechanisms.

Methods

We performed RNA sequencing and tissue microarray analyses of human CRC samples to identify new genes involved in CRC. Squalene epoxidase (SQLE) was identified to be highly upregulated in CRC patients. The regulatory function of SQLE in CRC progression and the therapeutic effect of SQLE inhibitors were determined by measuring CRC cell viability, colony and organoid formation, intracellular cholesterol concentration and xenograft tumor growth. The molecular mechanism of SQLE function was explored by combining transcriptome and untargeted metabolomics analysis. Western blotting and real‐time PCR were used to assess MAPK signaling activation by SQLE.

Results

SQLE‐related control of cholesterol biosynthesis was highly upregulated in CRC patients and associated with poor prognosis. SQLE promoted CRC growth in vitro and in vivo. Inhibition of SQLE reduced the levels of calcitriol (active form of vitamin D3) and CYP24A1, followed by an increase in intracellular Ca²⁺ concentration. Subsequently, MAPK signaling was suppressed, resulting in the inhibition of CRC cell growth. Consistently, terbinafine, an SQLE inhibitor, suppressed CRC cell proliferation and organoid and xenograft tumor growth.

Conclusions

Our findings demonstrate that SQLE promotes CRC through the accumulation of calcitriol and stimulation of CYP24A1‐mediated MAPK signaling, highlighting SQLE as a potential therapeutic target for CRC treatment.

[Construction and optimization of squalene epoxide synthetic pathway in Escherichia coli]

Triterpenoids are a class of natural products of great commercial value that are widely used in pharmaceutical, health care and cosmetic industries. The biosynthesis of triterpenoids relies on the efficient synthesis of squalene epoxide, which is synthesized from the NADPH dependent oxidation of squalene catalyzed by squalene epoxidase. We screened squalene epoxidases derived from different species, and found the truncated squalene epoxidase from Rattus norvegicus (RnSETC) showed the highest activity in engineered Escherichia coli. Further examination of the effect of endogenous cytochrome P450 reductase like (CPRL) proteins showed that overexpression of NADH: quinone oxidoreductase (WrbA) under Lac promoter in a medium-copy number plasmid increased the production of squalene epoxide by nearly 2.5 folds. These results demonstrated that the constructed pathway led to the production of squalene epoxide, an important precursor for the biosynthesis of triterpenoids.

Potential anti-alopecia constituents from Theobroma cacao: An in silico study

Tinea capitis is local alopecia caused by a dermatophyte infection of the scalp. Trichophyton rubrum produces the squalene epoxidase enzyme, which has a crucial role in prolonged dermatophyte infection, as well as in synthesizing fatty acids in this dermatophyte group. This study analyzes Trichophyton cacao compounds as anti-alopecia by inhibiting the squalene epoxidase enzyme formation, in silico. The structure of T. cacao compounds was prepared using the MolView Web application. The compound docked to squalene epoxidase using AutoDock Vina in PyRx 0.8, followed by PyMOL for visualization, and the Proteins Plus program to analyze the complexity. The binding affinity value of catechin, epicatechin (−8.0 kcal/mol), and anthocyanin (−7.8 kcal/mol) compounds was higher than the positive control (terbinafine, −6.7 kcal/mol). Pre-ADMET demonstrated that catechin and epicatechin had moderate Human Intestinal Absorption (66.71%), but anthocyanin was very good (100%). Caco-2 parameters for catechin and epicatechin were relatively low (<4 nm s ^{− 1}), while anthocyanin, theobromine, and terbinafine were within 4–70 nm s ^{− 1}. Plasma protein binding shows catechin, epicatechin, and anthocyanin diffuse through the plasma membrane and interact with plasma proteins. The toxicity results for all compounds are mutagenic, and only terbinafine is carcinogenic. Based on the Lipinski's “Rule of Five,” compounds from T. Cacao can be given orally. Catechin and epicatechin compounds have the potential to act as anti-alopecia. These two compounds can diffuse and interact with plasma proteins so they are directly on the target when given orally.

High SQLE Expression and Gene Amplification Correlates with Poor Prognosis in Head and Neck Squamous Cell Carcinoma

Objective

Squalene epoxidase (SQLE) is considered a metabolic oncogene, but its biological function and prognostic value in head and neck squamous cell carcinoma (HNSCC) remain unclear. We aimed to evaluate the role of SQLE in the occurrence and development of HNSCC through bioinformatics analysis, and validation experiments.

Methods

Transcriptomic, genomic, and clinical data from The Cancer Genome Atlas were used for pan-cancer analysis. SQLE expression in HNSCC was evaluated using Gene Expression Omnibus datasets and immunohistochemistry. The biological significance of SQLE in the tumor microenvironment (TME) of HNSCC was determined using TISCH, HuRI, LinkedOmics, and TIMER 2.0. The prognostic value of SQLE in HNSCC was analyzed using univariate Cox regression and Kaplan–Meier survival curves. Effect of SQLE on the Cal27 HNSCC cell line was evaluated using cell counting kit 8, wound healing, and EdU assays.

Results

SQLE was overexpressed and amplified in various cancers, including HNSCC. High SQLE expression promoted cell proliferation, associated with T stage in HNSCC patients. Copy number amplification and DNA demethylation contributed to high SQLE expression in HNSCC, which was associated with poor prognosis. SQLE was related to HNSCC TME, and its mRNA expression/copy number alterations were negatively correlated with the infiltration of CD8+ T cells, follicular helper T cells, and regulatory T cell infiltration and mast cell activation and positively correlated with the infiltration of M0 macrophages and resting mast cells in HNSCC.

Conclusion

SQLE was identified as a prognostic biomarker and a potential pharmaceutical target for HNSCC.

Squalene epoxidase expression is associated with breast tumor progression and with a poor prognosis in breast cancer

Differentially expressed genes (DEGs) have been previously identified using massive parallel RNA sequencing in matched normal, breast cancer (BC) and nodal metastatic tissues. Squalene epoxidase (SQLE), one of these DEGs, is a key enzyme in cholesterol synthesis. The aim of the present study was to investigate the potential involvement of SQLE in the tumorigenic process of BC and to determine its association with the clinical outcome of BC. SQLE mRNA expression was measured using reverse transcription-quantitative PCR in 10 pairs of ductal carcinoma in situ (DCIS) and BC tissues and their adjacent normal tissues. Immunohistochemical staining of SQLE on tissue microarray was performed in 26 normal breast, 79 DCIS and 198 BC samples. The role of SQLE as a prognostic biomarker in patients with BC has been verified using BreastMark. SQLE mRNA expression was significantly increased in DCIS and BC tissues compared with that in their adjacent normal tissues. High SQLE expression was detected in 0, 48.1 and 40.4% of normal breast, DCIS and BC tissues, respectively. SQLE expression in DCIS and BC tissues was significantly higher than that in normal breast tissues. High SQLE expression was observed in DCIS with higher nuclear grade, comedo-type necrosis and HER2 positivity. High SQLE expression in BC was associated with larger tumor size, nodal metastases, higher stage, HER2 subtype and distant metastatic relapse. High SQLE expression was associated with poor disease-free and overall survival, and independently predicted poor disease-free survival in patients with BC. Following BreastMark analysis, high SQLE mRNA expression in BC was significantly associated with a poor prognosis in the ‘all’, lymph node negative, lymph node positive, luminal A subtype and luminal B subtype groups. Therefore, SQLE expression may be upregulated during the tumorigenic process of BC, and high SQLE expression may be a useful biomarker for predicting a poor prognosis in patients with BC.

Complementary effect of mechanism of multidrug resistance in Trichophyton mentagrophytes isolated from human dermatophytoses of animal origin

BACKGROUND

Dermatophytoses have gained interest worldwide due to the increased resistance to terbinafine and azoles and difficulty in management of these refractory diseases.

OBJECTIVES

In this study, we identified and analysed Trichophyton mentagrophytes clinical isolates obtained from humans with infections of animal origin.

METHODS

We used quantitative real-time PCR (qRT-PCR) to examine the transcriptional modulation of three MDR genes (PDR1, MDR2 and MDR4) and analysed squalene epoxidase (SQLE) gene sequences from multidrug-resistant Trichophyton mentagrophytes isolates.

RESULTS

The expression profile revealed a 2- to 12-fold increase in mRNA accumulation in the presence of any of the antifungals, compared to cells incubated without drugs. A statistically significant relationship between the isolates exposed to itraconazole and increased expression of the tested genes was revealed. Substantially lower transcription levels were noted for cells exposed to luliconazole, that is, a third-generation azole. Additionally, in the case of 50% of terbinafine-resistant strains, Leu397Phe substitution in the SQLE gene was detected. Furthermore, the reduced susceptibility to itraconazole and voriconazole was overcome by milbemycin oxime.

CONCLUSIONS

In conclusion, our study shed more light on the role of the ABC transporter family in T. mentagrophytes, which, if overexpressed, can confer resistance to single azole drugs and even cross-resistance. Finally, milbemycin oxime could be an interesting compound supporting treatment with azole drugs in the case of refractory dermatomycoses.

Indian Trichophyton mentagrophytes squalene epoxidase erg1 double mutants show high proportion of combined fluconazole and terbinafine resistance

BACKGROUND

The Indian ITS genotype VIII Trichophyton mentagrophytes population shows a high amount of different erg1 (ergosterol) mutants encoding for squalene epoxidase, which catalyses the first step of ergosterol biosynthesis.

OBJECTIVES

Illumination of the implication of point mutations at position Ala448Thr in single and double erg1 T mentagrophytes mutants because mutants of this type were abundantly found within the Indian fungal population.

METHODS

Growth in fluconazole or terbinafine containing medium was analysed using a microplate-laser-nephelometry (MLN)-based growth assay.

RESULTS

Ala 448 Thr erg1 single mutants were terbinafine sensitive, but about 50% of isolates showed an increased fluconazole resistance, whereas 95% of the double mutants (Phe 397 Leu, Ala 448Thr) demonstrated combined terbinafine and increased fluconazole resistance.

CONCLUSION

The new Indian T mentagrophytes populations show several point mutations in erg1. Point mutations at position 397 were previously described and cause terbinafine resistance. A large part of the double mutants exhibit resistance to terbinafine and fluconazole, demonstrating a selective advantage of the combination of both mutations.

High Squalene Epoxidase in Tumors Predicts Worse Survival in Patients With Hepatocellular Carcinoma: Integrated Bioinformatic Analysis on NAFLD and HCC

This study aimed to identify candidate biomarkers for predicting outcomes in nonalcoholic fatty liver disease (NAFLD) and hepatocellular carcinoma (HCC). Using Gene Expression Omnibus and The Cancer Genome Atlas (TCGA) databases, we identified common upregulated differential expressed genes (DEGs) in patients with NAFLD/nonalcoholic steatohepatitis (NASH) and HCC and conducted survival analysis of these upregulated DEGs with HCC outcomes. Two common upregulated DEGs including squalene epoxidase (SQLE) and EPPK1 messenger RNA (mRNA) were significantly upregulated in NAFLD, NASH, and HCC tissues, both in GSE45436 (P < .001) and TCGA profile (P < .001). Both SQLE and EPPK1 mRNA were upregulated in 15.56% and 8.06% patients with HCC in TCGA profile. Overexpression of SQLE in tumors was significantly associated with worse overall survival (OS) and disease-free survival (DFS) in patients with HCC (log-rank P = .027 and log-rank P = .048, respectively), while no statistical significances of OS and DFS were found in EPPK1 groups (both log-rank P > .05). For validation, SQLE upregulation contributed to significantly worse OS in patients wih HCC using Kaplan-Meier plotter analysis (hazard ratio = 1.43, 95% confidence interval: 1.01-2.02, log-rank P = .043). In addition, high level of SQLE significantly associated with advanced neoplasm histologic grade, advanced AJCC stage, and α-fetoprotein elevation (P = .036, .045, and .029, respectively). Squalene epoxidase is associated with OS and DFS and serves as a novel prognostic biomarker for patients with HCC.

Spread of Terbinafine-Resistant Trichophyton mentagrophytes Type VIII (India) in Germany-"The Tip of the Iceberg?"

Chronic recalcitrant dermatophytoses, due to Trichophyton (T.) mentagrophytes Type VIII are on the rise in India and are noteworthy for their predominance. It would not be wrong to assume that travel and migration would be responsible for the spread of T. mentagrophytes Type VIII from India, with many strains resistant to terbinafine, to other parts of the world. From September 2016 until March 2020, a total of 29 strains of T. mentagrophytes Type VIII (India) were isolated. All patients were residents of Germany: 12 females, 15 males and the gender of the remaining two was not assignable. Patients originated from India (11), Pakistan (two), Bangladesh (one), Iraq (two), Bahrain (one), Libya (one) and other unspecified countries (10). At least two patients were German-born residents. Most samples (21) were collected in 2019 and 2020. All 29 T. mentagrophytes isolates were sequenced (internal transcribed spacer (ITS) and translation elongation factor 1-α gene (TEF1-α)). All were identified as genotype VIII (India) of T. mentagrophytes. In vitro resistance testing revealed 13/29 strains (45%) to be terbinafine-resistant with minimum inhibitory concentration (MIC) breakpoints ≥0.2 µg/mL. The remaining 16 strains (55%) were terbinafine-sensitive. Point mutation analysis revealed that 10/13 resistant strains exhibited Phe³⁹⁷Leu amino acid substitution of squalene epoxidase (SQLE), indicative for in vitro resistance to terbinafine. Two resistant strains showed combined Phe³⁹⁷Leu and Ala⁴⁴⁸Thr amino acid substitutions, and one strain a single Leu³⁹³Phe amino acid substitution. Out of 16 terbinafine-sensitive strains, in eight Ala⁴⁴⁸Thr, and in one Ala⁴⁴⁸Thr +, new Val⁴⁴⁴ Ile amino acid substitutions were detected. Resistance to both itraconazole and voriconazole was observed in three out of 13 analyzed strains. Treatment included topical ciclopirox olamine plus topical miconazole or sertaconazole. Oral itraconazole 200 mg twice daily for four to eight weeks was found to be adequate. Terbinafine-resistant T. mentagrophytes Type VIII are being increasingly isolated. In Germany, transmission of T. mentagrophytes Type VIII from the Indian subcontinent to Europe should be viewed as a significant public health issue.

Genome-Scale CRISPR/Cas9 Screening Reveals Squalene Epoxidase as a Susceptibility Factor for Cytotoxicity of Malformin A1

Malformin A1 (MA1) is a fungus-produced cyclic pentapeptide. MA1 exhibits teratogenicity to plants, fibrinolysis-enhancing activity, and cytotoxicity to mammalian cells. To clarify the cytotoxic mechanism of MA1, we screened for the genes involved in the cytotoxicity of MA1 in monocytoid U937 cells by using a CRISPR/Cas9-based genome-wide knockout library. Screening was performed by positive selection for cells that were resistant to MA1 treatment, and single guide RNAs (sgRNAs) integrated into MA1-resistant cells were analyzed by high-throughput sequencing. As a result of the evaluation of sgRNAs that were enriched in MA1-resistant cells, SQLE, which encodes squalene epoxidase, was identified as a candidate gene. SQLE-depleted U937 cells were viable in the presence of MA1, and squalene epoxidase inhibitor conferred MA1 resistance to wild-type cells. These results indicate that squalene epoxidase is implicated in the cytotoxicity of MA1. This finding represents a new insight into applications of MA1 for treating ischemic diseases.

Antifungal Agents: Design, Synthesis, Antifungal Activity and Molecular Docking of Phloroglucinol Derivatives

Pseudoaspidinol is a phloroglucinol derivative with Antifungal activity and is a major active component of Dryopteris fragrans. In our previous work, we studied the total synthesis of pseudoaspidinol belonging to a phloroglucinol derivative and investigated its antifungal activity as well as its intermediates. However, the results showed these compounds have low antifungal activity. In this study, in order to increase antifungal activities of phloroglucinol derivatives, we introduced antifungal pharmacophore allylamine into the methylphloroglucinol. Meanwhile, we remained C1⁻C4 acyl group in C-6 position of methylphloroglucinol using pseudoaspidinol as the lead compound to obtain novel phloroglucinol derivatives, synthesized 17 compounds, and evaluated antifungal activities on Trichophyton rubrum and Trichophyton mentagrophytes in vitro. Molecular docking verified their ability to combine the protein binding site. The results indicated that most of the compounds had strong antifungal activity, in which compound 17 were found to be the most active on Trichophyton rubrum with Minimum Inhibitory Concentration (MIC) of 3.05 μg/mL and of Trichophyton mentagrophytes with MIC of 5.13 μg/mL. Docking results showed that compounds had a nice combination with the protein binding site. These researches could lay the foundation for developing antifungal agents of clinical value.

[Cloning and expression analysis of squalene epoxidase genes from Siraitia grosvenorii]

Siraitia grosvenorii, vine plant of Cucurbitaceae family, has been used as natural sweetener and folk medicine. The major components and sweet substances are both known as mogrosides which are cucurbitane-type tetra-triterpenoids. Squalene epoxidase (SQE) has been generally recognized as the common rate-limiting enzyme in triterpenes and phytosterols, catalyzing into their common precursor 2,3-oxidosqualene (OS); however, in the biosynthesis of mogrosides, the precursor was 2,3,22,23-dioxidosqualene (DOS) instead of OS. To explore the specific SQE in S. grosvenorii, we cloned two full-length SQEs (SgSQE1, SgSQE2), performed bioinformatic analysis, analyzed the expression patterns in different periods of fruits by Real-time PCR, and induced the prokaryotic expressions. Finally, the interactive sites between SQE and substrate were predicted by docking, which would provide evidence for SQE gene function study of mogrosides and also lay foundation for triterpene biosynthesis in other plants. SgSQE1 and SgSQE2 both encoded predicted proteins of 524 amino acids, and shared 84% identity to each other at residues level, but had high specificity at N-terminal region. They both accumulated in fruits, but with different patterns, SgSQE1 increased rapidly and reached the highest level at 15 d, which had identical co-expression pattern with cucurbitadienol synthase (CS). SgSQE2 had a relatively constant level. The docking results showed that predicted proteins of SgSQE1 and SgSQE2 can interact with OS, with different contact sites (R348 for SgSQE1, H349 for SgSQE2). The recombinant proteins had no activities by prokaryotic expression, which were caused by transmembrane regions. However, all the results strongly suggested that SgSQEs were both involved in secondary metabolites biosynthesis in S. grosvenorii. SgSQE1 might be involved in mogrosides biosynthesis and SgSQE2 might participate in other cucurbitane-type triterpenes or phytosterols biosynthesis.

Functional characterization of squalene synthase and squalene epoxidase in Taraxacum koksaghyz

The Russian dandelion Taraxacum koksaghyz produces high-value isoprenoids such as pentacyclic triterpenes and natural rubber in the latex of specialized cells known as laticifers. Squalene synthase (SQS) and squalene epoxidase (SQE) catalyze key steps in the biosynthesis of cyclic terpenoids, but neither enzyme has yet been characterized in T. koksaghyz. Genomic analysis revealed the presence of two genes (TkSQS1 and TkSQS2) encoding isoforms of SQS, and four genes (TkSQE1-4) encoding isoforms of SQE. Spatial expression analysis in different T. koksaghyz tissues confirmed that TkSQS1 and TkSQE1 are the latex-predominant isoforms, with highly similar mRNA expression profiles. The TkSQS1 and TkSQE1 proteins colocalized in the endoplasmic reticulum membrane and their enzymatic functions were confirmed by in vitro activity assays and yeast complementation studies, respectively. The functions of TkSQS1 and TkSQE1 were further characterized in the latex of T. koksaghyz plants with depleted TkSQS1 or TkSQE1 mRNA levels, produced by RNA interference. Comprehensive expression analysis revealed the coregulation of TkSQS1 and TkSQE1, along with a downstream gene in the triterpene biosynthesis pathway encoding the oxidosqualene cyclase TkOSC1. This indicates that the coregulation of TkSQS1, TkSQE1, and TkOSC1 could be used to optimize the flux toward specific terpenoids during development.

Terbinafine Resistance of Trichophyton Clinical Isolates Caused by Specific Point Mutations in the Squalene Epoxidase Gene

Terbinafine is one of the allylamine antifungal agents whose target is squalene epoxidase (SQLE). This agent has been extensively used in the therapy of dermatophyte infections. The incidence of patients with tinea pedis or unguium tolerant to terbinafine treatment prompted us to screen the terbinafine resistance of all Trichophyton clinical isolates from the laboratory of the Centre Hospitalier Universitaire Vaudois collected over a 3-year period and to identify their mechanism of resistance. Among 2,056 tested isolates, 17 (≈1%) showed reduced terbinafine susceptibility, and all of these were found to harbor SQLE gene alleles with different single point mutations, leading to single amino acid substitutions at one of four positions (Leu³⁹³, Phe³⁹⁷, Phe⁴¹⁵, and His⁴⁴⁰) of the SQLE protein. Point mutations leading to the corresponding amino acid substitutions were introduced into the endogenous SQLE gene of a terbinafine-sensitive Arthroderma vanbreuseghemii (formerly Trichophyton mentagrophytes) strain. All of the generated A. vanbreuseghemii transformants expressing mutated SQLE proteins exhibited obvious terbinafine-resistant phenotypes compared to the phenotypes of the parent strain and of transformants expressing wild-type SQLE proteins. Nearly identical phenotypes were also observed in A. vanbreuseghemii transformants expressing mutant forms of Trichophyton rubrum SQLE proteins. Considering that the genome size of dermatophytes is about 22 Mb, the frequency of terbinafine-resistant clinical isolates was strikingly high. Increased exposure to antifungal drugs could favor the generation of resistant strains.

Overexpression of the Squalene Epoxidase Gene Alone and in Combination with the 3-Hydroxy-3-methylglutaryl Coenzyme A Gene Increases Ganoderic Acid Production in Ganoderma lingzhi

The squalene epoxidase (SE) gene from the biosynthetic pathway of ganoderic acid (GA) was cloned and overexpressed in Ganoderma lingzhi. The strain that overexpressed the SE produced approximately 2 times more GA molecules than the wild-type (WT) strain. Moreover, SE overexpression upregulated lanosterol synthase gene expression in the biosynthetic pathway. These results indicated that SE stimulates GA accumulation. Then, the SE and 3-hydroxy-3-methylglutaryl coenzyme A (HMGR) genes were simultaneously overexpressed in G. lingzhi. Compared with the individual overexpression of SE or HMGR, the combined overexpression of the two genes further enhanced individual GA production. The overexpressing strain produced maximum GA-T, GA-S, GA-Mk, and GA-Me contents of 90.4 ± 7.5, 35.9 ± 5.4, 6.2 ± 0.5, and 61.8 ± 5.8 μg/100 mg dry weight, respectively. These values were 5.9, 4.5, 2.4, and 5.8 times higher than those produced by the WT strain. This is the first example of the successful manipulation of multiple biosynthetic genes to improve GA content in G. lingzhi.

Sterol Synthesis in Diverse Bacteria

Sterols are essential components of eukaryotic cells whose biosynthesis and function has been studied extensively. Sterols are also recognized as the diagenetic precursors of steranes preserved in sedimentary rocks where they can function as geological proxies for eukaryotic organisms and/or aerobic metabolisms and environments. However, production of these lipids is not restricted to the eukaryotic domain as a few bacterial species also synthesize sterols. Phylogenomic studies have identified genes encoding homologs of sterol biosynthesis proteins in the genomes of several additional species, indicating that sterol production may be more widespread in the bacterial domain than previously thought. Although the occurrence of sterol synthesis genes in a genome indicates the potential for sterol production, it provides neither conclusive evidence of sterol synthesis nor information about the composition and abundance of basic and modified sterols that are actually being produced. Here, we coupled bioinformatics with lipid analyses to investigate the scope of bacterial sterol production. We identified oxidosqualene cyclase (Osc), which catalyzes the initial cyclization of oxidosqualene to the basic sterol structure, in 34 bacterial genomes from five phyla (Bacteroidetes, Cyanobacteria, Planctomycetes, Proteobacteria, and Verrucomicrobia) and in 176 metagenomes. Our data indicate that bacterial sterol synthesis likely occurs in diverse organisms and environments and also provides evidence that there are as yet uncultured groups of bacterial sterol producers. Phylogenetic analysis of bacterial and eukaryotic Osc sequences confirmed a complex evolutionary history of sterol synthesis in this domain. Finally, we characterized the lipids produced by Osc-containing bacteria and found that we could generally predict the ability to synthesize sterols. However, predicting the final modified sterol based on our current knowledge of sterol synthesis was difficult. Some bacteria produced demethylated and saturated sterol products even though they lacked homologs of the eukaryotic proteins required for these modifications emphasizing that several aspects of bacterial sterol synthesis are still completely unknown.

Arabidopsis Squalene Epoxidase 3 (SQE3) Complements SQE1 and Is Important for Embryo Development and Bulk Squalene Epoxidase Activity

The existence of multigenic families in the mevalonate pathway suggests divergent functional roles for pathway components involved in the biosynthesis of plant sterols. Squalene epoxidases (SQEs) are key components of this pathway, and Squalene Epoxidase 1 (SQE1) has been identified as a fundamental enzyme in this biosynthetic step. In the present work, we extended the characterization of the remaining SQE family members, phylogenetically resolving between true SQEs and a subfamily of SQE-like proteins that is exclusive to Brassicaceae. Functional characterization of true SQE family members, Squalene Epoxidase 2 (SQE2) and Squalene Epoxidase 3 (SQE3), indicates that SQE3, but not SQE2, contributes to the bulk SQE activity in Arabidopsis, with sqe3-1 mutants accumulating squalene and displaying sensitivity to terbinafine. We genetically demonstrated that SQE3 seems to play a particularly significant role in embryo development. Also, SQE1 and SQE3 both localize in the endoplasmic reticulum, and SQE3 can functionally complement SQE1. Thus, SQE1 and SQE3 seem to be two functionally unequal redundant genes in the promotion of plant SQE activity in Arabidopsis.

Tracking the sterol biosynthesis pathway of the diatom Phaeodactylum tricornutum

Diatoms are unicellular photosynthetic microalgae that play a major role in global primary production and aquatic biogeochemical cycling. Endosymbiotic events and recurrent gene transfers uniquely shaped the genome of diatoms, which contains features from several domains of life. The biosynthesis pathways of sterols, essential compounds in all eukaryotic cells, and many of the enzymes involved are evolutionarily conserved in eukaryotes. Although well characterized in most eukaryotes, the pathway leading to sterol biosynthesis in diatoms has remained hitherto unidentified. Through the DiatomCyc database we reconstructed the mevalonate and sterol biosynthetic pathways of the model diatom Phaeodactylum tricornutum in silico. We experimentally verified the predicted pathways using enzyme inhibitor, gene silencing and heterologous gene expression approaches. Our analysis revealed a peculiar, chimeric organization of the diatom sterol biosynthesis pathway, which possesses features of both plant and fungal pathways. Strikingly, it lacks a conventional squalene epoxidase and utilizes an extended oxidosqualene cyclase and a multifunctional isopentenyl diphosphate isomerase/squalene synthase enzyme. The reconstruction of the P. tricornutum sterol pathway underscores the metabolic plasticity of diatoms and offers important insights for the engineering of diatoms for sustainable production of biofuels and high-value chemicals.

Knockout of mouse Cyp3a gene enhances synthesis of cholesterol and bile acid in the liver

Here, we studied the effects of cytochrome P450 (CYP)3A deficiency on the mRNA expression of genes encoding regulators of hepatic cholesterol levels using Cyp3a-knockout (Cyp3a(-/-)) mice. The mRNA expression levels of genes encoding enzymes involved in cholesterol biosynthesis in the livers of Cyp3a(-/-) mice were higher than those of wild-type (WT) mice. Nuclear levels of sterol regulatory element-binding protein-2 (SREBP-2), which enhances cholesterol biosynthesis, were also higher in the livers of Cyp3a(-/-) mice. Binding of SREBP-2 to the Hmgcs1 gene promoter was more abundant in the livers of Cyp3a(-/-) mice. These results suggest that deficiency of CYP3A enzymes enhances transcription of genes encoding enzymes involved in cholesterol biosynthesis via activation of SREBP-2. On the other hand, hepatic cholesterol levels in Cyp3a(-/-) mice were 20% lower than those in WT mice. The mRNA expression levels of genes encoding enzymes involved in bile acid synthesis, plasma levels of 7α-hydroxy-4-cholesten-3-one and hepatic levels of total bile acid were significantly higher in Cyp3a(-/-) mice than in WT mice. These findings suggest that reduction of hepatic total cholesterol in Cyp3a(-/-) mice would be the consequence of enhanced bile acid synthesis. Therefore, CYP3A enzymes appear to play roles in the synthesis of cholesterol and bile acid in vivo.

Analysis of the arabidopsis dry2/sqe1-5 mutant suggests a role for sterols in signaling

Sterols play multi-faceted roles in all eukaryotes. In plants, there are mounting evidences pointing to sterols, other than BRs, can act as signaling molecules. The Arabidopsis dry2/sqe1-5 mutant has multiple developmental defects caused by a point mutation in the SQE1 gene that generates a hypomorphic allele. SQE1 encodes a squalene epoxidase, which converts squalene into 2,3-oxidosqualene the precursor of plant sterols. Genetic, molecular and biochemical analyses suggest that dry2/sqe1-5 defective phenotypes cannot be simply explained by a depletion of bulk sterols but rather by altered ROS. It remains to be elucidated whether the altered ROS production of the mutant is caused by membrane composition, which in turn affect the lipid rafts composition and/or an altered signaling.