Epigenetic regulation of vitamin D metabolism in human lung adenocarcinoma

Association of DNA methylation of vitamin D metabolic pathway related genes with colorectal cancer risk

BACKGROUND

Vitamin D might have anti-tumor effect, which is affected by the genes related to vitamin D metabolic pathway. Epigenetic mechanism may affect the expression level of vitamin D metabolic pathway related genes, then plays an important role in the occurrence and development of colorectal cancer. To date, no study has reported on the association between blood-based DNA methylation level of vitamin D metabolic pathway related genes and colorectal cancer risk.

METHODS

A case-control study was conducted including 102 colorectal cancer cases and 102 sex- and age-frequency-matched controls in Guangzhou, China. CpG islands in the VDR, CYP24A1, CYP27B1 and CYP2R1 genes were chosen for DNA methylation analysis by MethylTarget sequencing. The receiver operating characteristic (ROC) curve was used to evaluate the diagnostic value of DNA methylation levels for colorectal cancer. Taking the point with the largest Youden index as the boundary value, the cumulative methylation levels of vitamin D metabolic pathway related genes were divided into hypomethylation and hypermethylation. Unconditional multivariable logistical regression model was used to calculate the adjusted odds ratio (aOR) and 95% confidence intervals (95% CIs) after adjusting for potential confounders.

RESULTS

Among 153 CpG sites, 8 CpG sites were significantly different between the cases and the controls. The cumulative methylation level of all CpG sites in CYP2R1 was inversely associated with the risk of colorectal cancer (aOR, 0.49; 95% CI, 0.26-0.91). However, no significant association was found between cumulative methylation levels of all CpG sites in VDR, CYP24A1 and CYP27B1 and colorectal cancer risk. Significant inverse association was observed between cumulative methylation level of significant CpG sites in VDR (aOR, 0.28; 95% CI, 0.16-0.51) and CYP24A1 (aOR, 0.19; 95% CI, 0.09-0.40) and colorectal cancer risk. There were no significant associations between cumulative methylation levels of significant CpG sites in CYP2R1 and CYP27B1 and colorectal cancer risk.

CONCLUSIONS

This study indicated that the cumulative methylation levels of significant CpG sites in VDR and CYP24A1 and all CpG sites in CYP2R1 were inversely associated with colorectal cancer risk.

The role of Lamin B2 in human diseases

Lamin B2 (LMNB2), on the inner side of the nuclear envelope, constitutes the nuclear skeleton by connecting with other nuclear proteins. LMNB2 is involved in a wide range of nuclear functions, including DNA replication and stability, regulation of chromatin, and nuclear stiffness. Moreover, LMNB2 regulates several cellular processes, such as tissue development, cell cycle, cellular proliferation and apoptosis, chromatin localization and stability, and DNA methylation. Besides, the influence of abnormal expression and mutations of LMNB2 has been gradually discovered in cancers and laminopathies. Therefore, this review summarizes the recent advances of LMNB2-associated biological roles in physiological or pathological conditions, with a particular emphasis on cancers and laminopathies, as well as the potential mechanism of LMNB2 in related cancers.

Interplay of Vitamin D and SIRT1 in Tissue-Specific Metabolism-Potential Roles in Prevention and Treatment of Non-Communicable Diseases Including Cancer

The importance of the prevention and control of non-communicable diseases, including obesity, metabolic syndrome, type 2 diabetes, cardiovascular diseases, and cancer, is increasing as a requirement of the aging population in developed countries and the sustainability of healthcare. Similarly, the 2013-2030 action plan of the WHO for the prevention and control of non-communicable diseases seeks these achievements. Adequate lifestyle changes, alone or with the necessary treatments, could reduce the risk of mortality or the deterioration of quality of life. In our recent work, we summarized the role of two central factors, i.e., appropriate levels of vitamin D and SIRT1, which are connected to adequate lifestyles with beneficial effects on the prevention and control of non-communicable diseases. Both of these factors have received increased attention in relation to the COVID-19 pandemic as they both take part in regulation of the main metabolic processes, i.e., lipid/glucose/energy homeostasis, oxidative stress, redox balance, and cell fate, as well as in the healthy regulation of the immune system. Vitamin D and SIRT1 have direct and indirect influence of the regulation of transcription and epigenetic changes and are related to cytoplasmic signaling pathways such as PLC/DAG/IP3/PKC/MAPK, MEK/Erk, insulin/mTOR/cell growth, proliferation; leptin/PI3K-Akt-mTORC1, Akt/NFĸB/COX-2, NFĸB/TNFα, IL-6, IL-8, IL-1β, and AMPK/PGC-1α/GLUT4, among others. Through their proper regulation, they maintain normal body weight, lipid profile, insulin secretion and sensitivity, balance between the pro- and anti-inflammatory processes under normal conditions and infections, maintain endothelial health; balance cell differentiation, proliferation, and fate; and balance the circadian rhythm of the cellular metabolism. The role of these two molecules is interconnected in the molecular network, and they regulate each other in several layers of the homeostasis of energy and the cellular metabolism. Both have a central role in the maintenance of healthy and balanced immune regulation and redox reactions; therefore, they could constitute promising targets either for prevention or as complementary therapies to achieve a better quality of life, at any age, for healthy people and patients under chronic conditions.

Polymorphisms in VDR, CYP27B1, CYP2R1, GC and CYP24A1 Genes as Biomarkers of Survival in Non-Small Cell Lung Cancer: A Systematic Review

The objective of this systematic review was to provide a compilation of all the literature available on the association between single-nucleotide polymorphisms (SNPs) in the genes involved in the metabolic pathway of vitamin D and overall survival (OS) and progression-free survival (PFS) in patients with non-small cell lung cancer (NSCLC). This systematic review was conducted in accordance with the PRISMA guidelines. It included all the literature published up to 1 November 2022 and was carried out in four databases (Medline [PubMed], Scopus, Web of Science, and Embase), using the PICO strategy, with relevant keywords related to the objective. The quality of the studies included was evaluated with an assessment tool derived from the Strengthening the Reporting of Genetic Association Studies (STREGA) statement. Six studies were included in this systematic review. Our findings showed that the BsmI (rs1544410), Cdx-2 (rs11568820), FokI (rs2228570), ApaI (rs7975232), TaqI (rs731236), rs4646536, rs6068816, rs7041, and rs10741657 SNPs in the genes that play a part in vitamin D synthesis (CYP2R1, CYP27B1), transport (GC), and metabolism (CYP24A1), as well as in the vitamin D receptor (VDR), are associated with OS and/or PFS in patients with NSCLC. The SNPs in VDR have been the most extensively analyzed. This systematic review summed up the available evidence concerning the association between 13 SNPs in the main genes involved in the vitamin D metabolic pathway and prognosis in NSCLC. It revealed that SNPs in the VDR, CYP27B1, CYP24A1, GC, and CYP2R1 genes could have an impact on survival in this disease. These findings suggest the identification of prognostic biomarkers in NSCLC patients. However, evidence remains sparse for each of the polymorphisms examined, so these findings should be treated with caution.

Vitamin D metabolism in cancer: potential feasibility of vitamin D metabolism blocking therapy

In this review, we discuss the possibility of the vitamin D metabolizing enzyme CYP24A1 being a therapeutic target for various tumors including breast, colorectal and prostate tumors. Given the pleiotropic cellular activity of vitamin D, its deficiency impairs its physiological function in target cells and results in various pathologies including cancer. In addition, accumulated data have shown that elevated expression of CYP24A1 promotes carcinogenesis in various cancer subtypes by decreasing the bioavailability of vitamin D metabolites. Thus, we propose the potential feasibility of vitamin D metabolism-blocking therapy in various types of human malignancies that express constitutive CYP24A1.

Association of CYP24A1 with survival and drug resistance in clinical cancer patients: a meta-analysis

BACKGROUND

Acquired chemo-drug resistance constantly led to the failure of chemotherapy for malignant cancers, consequently causing cancer relapse. Hence, identifying the biomarker of drug resistance is vital to improve the treatment efficacy in cancer. The clinical prognostic value of CYP24A1 remains inconclusive, hence we aim to evaluate the association between CYP24A1 and the drug resistance in cancer patients through a meta-analysis approach.

METHOD

Relevant studies detecting the expression or SNP of CYP24A1 in cancer patients up till May 2022 were systematically searched in four common scientific databases including PubMed, EMBASE, Cochrane library and ISI Web of Science. The pooled hazard ratios (HRs) indicating the ratio of hazard rate of survival time between CYP24A1^high population vs CYP24A1^low population were calculated. The pooled HRs and odds ratios (ORs) with 95% confidence intervals (CIs) were used to explore the association between CYP24A1's expression or SNP with survival, metastasis, recurrence, and drug resistance in cancer patients.

RESULT

Fifteen studies were included in the meta-analysis after an initial screening according to the inclusion and exclusion criteria. There was a total of 3784 patients pooled from all the included studies. Results indicated that higher expression or SNP of CYP24A1 was significantly correlated with shorter survival time with pooled HRs (95% CI) of 1.21 (1.12, 1.31), metastasis with pooled ORs (95% CI) of 1.81 (1.11, 2.96), recurrence with pooled ORs (95% CI) of 2.14 (1.45, 3.18) and drug resistance with pooled HRs (95% CI) of 1.42 (1.17, 1.68). In the subgroup analysis, cancer type, treatment, ethnicity, and detection approach for CYP24A1 did not affect the significance of the association between CYP24A1 expression and poor prognosis.

CONCLUSION

Findings from our meta-analysis demonstrated that CYP24A1's expression or SNP was correlated with cancer progression and drug resistance. Therefore, CYP24A1 could be a potential molecular marker for cancer resistance.

Vitamin D resistant genes - promising therapeutic targets of chronic diseases

Vitamin D is an essential vitamin indispensable for calcium and phosphate metabolism, and its deficiency has been implicated in several extra-skeletal pathologies, including cancer and chronic kidney disease. Synthesized endogenously in the layers of the skin by the action of UV-B radiation, the vitamin maintains the integrity of the bones, teeth, and muscles and is involved in cell proliferation, differentiation, and immunity. The deficiency of Vit-D is increasing at an alarming rate, with nearly 32% of children and adults being either deficient or having insufficient levels. This has been attributed to Vit-D resistant genes that cause a reduction in circulatory Vit-D levels through a set of signaling pathways. CYP24A1, SMRT, and SNAIL are three genes responsible for Vit-D resistance as their activity either lowers the circulatory levels of Vit-D or reduces its availability in target tissues. The hydroxylase CYP24A1 inactivates analogs and prohormonal and/or hormonal forms of calcitriol. Elevation of the expression of CYP24A1 is the major cause of exacerbation of several diseases. CYP24A1 is rate-limiting, and its induction has been correlated with increased prognosis of diseases, while loss of function mutations cause hypersensitivity to Vit-D. The silencing mediator of retinoic acid and thyroid hormone receptor (SMRT) and its corepressor are involved in the transcriptional repression of VDR-target genes. SNAIL1 (SNAIL), SNAIL2 (Slug), and SNAIL3 (Smuc) are involved in transcriptional repression and binding to histone deacetylases and methyltransferases in addition to recruiting polycomb repressive complexes to the target gene promoters. An inverse relationship between the levels of calcitriol and the epithelial-to-mesenchymal transition is reported. Studies have demonstrated a strong association between Vit-D deficiency and chronic diseases, including cardiovascular diseases, diabetes, cancers, autoimmune diseases, infectious diseases, etc. Vit-D resistant genes associated with the aforementioned chronic diseases could serve as potential therapeutic targets. This review focuses on the basic structures and mechanisms of the repression of Vit-D regulated genes and highlights the role of Vit-D resistant genes in chronic diseases.

Regulation of Butyrate-Induced Resistance through AMPK Signaling Pathway in Human Colon Cancer Cells

Butyrates inhibit cell growth in colon cancer cells by inhibiting histone deacetylases. However, chronic exposure to butyrates induces butyrate resistance in colon cancer cells. The mechanism underlying the acquisition of resistance is not yet fully understood. Here, butyrate-resistant (BR) colon cancer cells were developed in HCT116, HT29, and SW480 human colon cancer cells and were confirmed by the increase in the inhibitory concentrations of cell growth by 50% (IC₅₀) compared to their respective parental (PT) cells. Chronic exposure to butyrate induced autophagy via higher expression of Beclin-1 and LC3B-II. The AMP-activated protein kinase (AMPK) was downregulated along with the activation of Akt and mammalian target of rapamycin (mTOR) and decrease in acetyl-CoA carboxylase (ACC) in BR colon cancer cells compared to those in their respective PT cells. Activation of AMPK by AICAR treatment in BR colon cancer cells suppressed cell proliferation by inhibiting Akt and mTOR and activating ACC. Taken together, chronic exposure to butyrate increased butyrate resistance in human colon cancer by inducing protective autophagy through the downregulation of AMPK/ACC and activation of Akt/mTOR signaling. Activation of AMPK restored sensitivity to butyrate by the inhibition of Akt/mTOR, suggesting that AMPK could be a therapeutic target for BR colon cancers.

Redox modulation of vitagenes via plant polyphenols and vitamin D: Novel insights for chemoprevention and therapeutic interventions based on organoid technology

Polyphenols are chemopreventive through the induction of nuclear factor erythroid 2 related factor 2 (Nrf2)-mediated proteins and anti-inflammatory pathways. These pathways, encoding cytoprotective vitagenes, include heat shock proteins, such as heat shock protein 70 (Hsp70) and heme oxygenase-1 (HO-1), as well as glutathione redox system to protect against cancer initiation and progression. Phytochemicals exhibit biphasic dose responses on cancer cells, activating at low dose, signaling pathways resulting in upregulation of vitagenes, as in the case of the Nrf2 pathway upregulated by hydroxytyrosol (HT) or curcumin and NAD/NADH-sirtuin-1 activated by resveratrol. Here, the importance of vitagenes in redox stress response and autophagy mechanisms, as well as the potential use of dietary antioxidants in the prevention and treatment of multiple types of cancer are discussed. We also discuss the possible relationship between SARS-CoV-2, inflammation and cancer, exploiting innovative therapeutic approaches with HT-rich aqueous olive pulp extract (Hidrox®), a natural polyphenolic formulation, as well as the rationale of Vitamin D supplementation. Finally, we describe innovative approaches with organoids technology to study human carcinogenesis in preclinical models from basic cancer research to clinical practice, suggesting patient-derived organoids as an innovative tool to test drug toxicity and drive personalized therapy.

Epigenetic Regulation of Differentially Expressed Drug-Metabolizing Enzymes in Cancer

Drug metabolism is a biotransformation process of drugs, catalyzed by drug-metabolizing enzymes (DMEs), including phase I DMEs and phase II DMEs. The aberrant expression of DMEs occurs in the different stages of cancer. It can contribute to the development of cancer and lead to individual variations in drug response by affecting the metabolic process of carcinogen and anticancer drugs. Apart from genetic polymorphisms, which we know the most about, current evidence indicates that epigenetic regulation is also central to the expression of DMEs. This review summarizes differentially expressed DMEs in cancer and related epigenetic changes, including DNA methylation, histone modification, and noncoding RNAs. Exploring the epigenetic regulation of differentially expressed DMEs can provide a basis for implementing individualized and rationalized medication. Meanwhile, it can promote the development of new biomarkers and targets for the diagnosis, treatment, and prognosis of cancer. SIGNIFICANCE STATEMENT: This review summarizes the aberrant expression of DMEs in cancer and the related epigenetic regulation of differentially expressed DMEs. Exploring the epigenetic regulatory mechanism of DMEs in cancer can help us to understand the role of DMEs in cancer progression and chemoresistance. Also, it provides a basis for developing new biomarkers and targets for the diagnosis, treatment, and prognosis of cancer.

Gene polymorphism of cytochrome P450 significantly affects lung cancer susceptibility

BACKGROUND

Cytochrome P450 (CYPs) are heme proteins involved in the metabolism of a variety of endogenous and exogenous substances and play an important role in the carcinogenesis mechanisms of environmental and hereditary factors. The objective of this study was to investigate how polymorphisms of CYPs correlate with lung cancer (LC) susceptibility.

METHODS

Six single nucleotide polymorphisms (SNPs) were genotyped in this study. The chi-square test and unconditional logistic regression model were used to evaluate the correlation between SNPs and LC susceptibility. The expressions and survival data of genes in patients with LC were mined using Oncomine and Kaplan-Meier Plotter database.

RESULTS

Four SNPs were found to be significantly associated with the risk of LC development (P < 0.05). The most significant correlation was that the A allele and AA genotype of CYP2D6 rs1065852 were associated with increased risk of LC development (adjusted odds ratio [OR] = 1.35, 95% confidence interval [95%CI] = 1.13-1.60, P = 9.04e-4; OR = 1.83, 95%CI = 1.29-2.59, P = 0.001 respectively). Similar association of this variant was also found in the subgroups of male patients, cases in III-IV stages, positive lymph node, squamous cell carcinomas and adenocarcinomas. Whereas rs1065852 was considered as protective factor in females (adjusted OR = 0.33, 95% CI = 0.16-0.70, P = 0.004). In stratified analyses, the association of CYP24A1 rs2762934, CYP24A1 rs6068816, CYP20A1 rs2043449 polymorphism with LC risk appeared stronger in some subgroups. CYP2D6, CYP24A1 and CYP20A1 are overexpressed in some pathological types of LC (P < 0.05), and high levels of CYP2D6 and CYP20A1 indicate poor and good prognosis of LC, respectively.

CONCLUSION

This study revealed that rs1065852, rs2043449, rs2762s934, and rs6068816 of CYPs were associated with LC susceptibility in the Northwestern Chinese Han population; CYP2D6 and CYP20A1 were overexpressed and correlated with prognosis of LC.

Vitamin D Deficiency: Effects on Oxidative Stress, Epigenetics, Gene Regulation, and Aging

Recent advances in vitamin D research indicate that this vitamin, a secosteroid hormone, has beneficial effects on several body systems other than the musculoskeletal system. Both 25 dihydroxy vitamin D [25(OH)₂D] and its active hormonal form, 1,25-dihydroxyvitamin D [1,25(OH)₂D] are essential for human physiological functions, including damping down inflammation and the excessive intracellular oxidative stresses. Vitamin D is one of the key controllers of systemic inflammation, oxidative stress and mitochondrial respiratory function, and thus, the aging process in humans. In turn, molecular and cellular actions form 1,25(OH)₂D slow down oxidative stress, cell and tissue damage, and the aging process. On the other hand, hypovitaminosis D impairs mitochondrial functions, and enhances oxidative stress and systemic inflammation. The interaction of 1,25(OH)₂D with its intracellular receptors modulates vitamin D–dependent gene transcription and activation of vitamin D-responsive elements, which triggers multiple second messenger systems. Thus, it is not surprising that hypovitaminosis D increases the incidence and severity of several age-related common diseases, such as metabolic disorders that are linked to oxidative stress. These include obesity, insulin resistance, type 2 diabetes, hypertension, pregnancy complications, memory disorders, osteoporosis, autoimmune diseases, certain cancers, and systemic inflammatory diseases. Vitamin D adequacy leads to less oxidative stress and improves mitochondrial and endocrine functions, reducing the risks of disorders, such as autoimmunity, infections, metabolic derangements, and impairment of DNA repair; all of this aids a healthy, graceful aging process. Vitamin D is also a potent anti-oxidant that facilitates balanced mitochondrial activities, preventing oxidative stress-related protein oxidation, lipid peroxidation, and DNA damage. New understandings of vitamin D-related advances in metabolomics, transcriptomics, epigenetics, in relation to its ability to control oxidative stress in conjunction with micronutrients, vitamins, and antioxidants, following normalization of serum 25(OH)D and tissue 1,25(OH)₂D concentrations, likely to promise cost-effective better clinical outcomes in humans.

Polymorphism in CYP24A1 Is Associated with Lung Cancer Risk: A Case-Control Study in Chinese Female Nonsmokers

CYP24A1 plays important roles in antiproliferative effects, which have been proved in many human tumor cells. Polymorphisms in CYP24A1 may affect the risk of lung cancer, but the results remained inconclusive. To enhance the understanding of possible relationship between CYP24A1 polymorphism rs6068816 and lung cancer risks, we first carried out this case-control study among Chinese female nonsmokers, including 345 lung cancer patients and 351 noncancer controls. Our results revealed that individuals carrying CT and CC genotype were associated with decreasing lung cancer risk (adjusted odds ratios were 0.71 and 0.59, and 95% confidence intervals were 0.52-0.97 and 0.35-0.99, p-values were 0.031 and 0.048, respectively). Patients carrying allele-T showed lower hazard risks, especially in adenocarcinoma and advanced stage cancers. We also found that subjects with allele-T showed a relatively low risk of lung cancer when they were exposed to oil fume. But neither additive scale nor multiplicative scale revealed interactions between allele-T and environmental exposures, including oil fume, coal fuel fume, and passive smoking. Overall, these findings indicated that CYP24A1 polymorphism rs6068816 could be significantly associated with susceptibility of lung cancer in Chinese female nonsmokers.

Inverse association of vitamin D3 levels with lung cancer mediated by genetic variation

Vitamin D is an essential micronutrient required for normal physiological function and recognized for its role regulating calcium metabolism. Recent work is beginning to emerge demonstrating a role for vitamin D in chronic illnesses, such as cancer. Circulating serum levels of 25(OH)D_2/3 were quantitatively measured using sensitive ultraperformance liquid chromatography coupled to tandem mass spectrometry (UPLC‐MS/MS) in 406 lung cancer cases and 437 population controls, while 1,25(OH)₂D_2/3 levels were measured in a subset of 90 cases and 104 controls using the same method, from the NCI‐MD case–control cohort. 25(OH)D₃ levels were inversely associated with lung cancer status across quartiles (Q2 vs. Q1: OR_adjusted = 0.5, 95% CI = 0.3–0.8; Q3 vs. Q1: OR_adjusted = 0.5, 95% CI = 0.3–0.8; Q4 vs. Q1: OR_adjusted = 0.5, 95% CI = 0.2–0.9; P_trend = 0.004). Levels of 1,25(OH)₂D₃ were also inversely associated with lung cancer status (Q2 vs. Q1: OR_adjusted = 0.2, 95% CI = 0.03–0.7; Q3 vs. Q1: OR_adjusted = 0.1, 95% CI = 0.01–0.4; Q4 vs. Q1: OR_adjusted = 0.04, 95% CI = 0.01–0.3; P_trend<0.0001). Although the observed trends were similar for the 25(OH)D₂ (P_trend = 0.08), no significant associations were seen between vitamin D₂ and lung cancer status. Additionally, genotyping of 296 SNPs in the same subjects resulted in findings that 27 SNPs, predominantly in CYP24A1 and VDR genes, were significantly associated with lung cancer status, affected mRNA expression, and modulated vitamin D levels. These findings suggest a protective role for vitamin D₃ in lung cancer, with similar trends but insignificant findings for D₂. Vitamin D₃ levels appeared to be modulated by genetic variation in CYP24A1 and VDR genes. Additional research to illuminate the mechanism(s) through which vitamin D exacerbates effects against lung carcinogenesis is warranted.

Exploring vitamin D metabolism and function in cancer

Vitamin D, traditionally known as an essential nutrient, is a precursor of a potent steroid hormone that regulates a broad spectrum of physiological processes. In addition to its classical roles in bone metabolism, epidemiological, preclinical, and cellular research during the last decades, it revealed that vitamin D may play a key role in the prevention and treatment of many extra-skeletal diseases such as cancer. Vitamin D, as a prohormone, undergoes two-step metabolism in liver and kidney to produce a biologically active metabolite, calcitriol, which binds to the vitamin D receptor (VDR) for the regulation of expression of diverse genes. In addition, recent studies have revealed that vitamin D can also be metabolized and activated through a CYP11A1-driven non-canonical metabolic pathway. Numerous anticancer properties of vitamin D have been proposed, with diverse effects on cancer development and progression. However, accumulating data suggest that the metabolism and functions of vitamin D are dysregulated in many types of cancer, conferring resistance to the antitumorigenic effects of vitamin D and thereby contributing to the development and progression of cancer. Thus, understanding dysregulated vitamin D metabolism and function in cancer will be critical for the development of promising new strategies for successful vitamin D-based cancer therapy.

Vitamin D and cardiovascular diseases: Causality

Vitamin D regulates blood pressure, cardiac functions, and endothelial and smooth muscle cell functions, thus, playing an important role in cardiovascular health. Observational studies report associations between vitamin D deficiency with hypertension and cardiovascular-related deaths. Peer-reviewed papers were examined in several research databases as per the guidelines of the Preferred Reporting Items for Systematic Reviews, using key words that address the relationship between vitamin D and cardiovascular disease. Correlations and interpretations were made considering the risks-benefits, broader evidence, and implications. This review analyzed current knowledge regarding the effects of vitamin D on the cardiovascular system. 1,25(OH)₂D and related epigenetic modifications subdue cellular inflammation, improve overall endothelial functions, reduce age-related systolic hypertension and vascular rigidity, and attenuate the actions of the renin-angiotensin-aldosterone system. Most observational and ecological studies support 25(OH)vitamin D having protective effects on the cardiovascular system. However, the association of vitamin D deficiency with cardiovascular diseases is based primarily on observational and ecological studies and thus, is a matter of controversy. Adequately powered, randomized controlled clinical trial data are not available to confirm these associations. Thus, to test the hypothesis that correction of vitamin D deficiency protects the cardiovascular system, well-designed, statistically powered, longer-term clinical trials are needed in persons with vitamin D deficiency. Nevertheless, the available data support that adequate vitamin D supplementation and/or sensible sunlight exposure to achieve optimal vitamin D status are important in the prevention of cardiovascular disease and other chronic diseases.

Function of the vitamin D endocrine system in mammary gland and breast cancer

The nuclear receptor for 1α,25-dihydroxycholecalciferol (1,25D), the active form of vitamin D, has anti-tumor actions in many tissues. The vitamin D receptor (VDR) is expressed in normal mammary gland and in many human breast cancers suggesting it may represent an important tumor suppressor gene in this tissue. When activated by 1,25D, VDR modulates multiple cellular pathways including those related to energy metabolism, terminal differentiation and inflammation. There is compelling pre-clinical evidence that alterations in vitamin D status affect breast cancer development and progression, while clinical and epidemiological data are suggestive but not entirely consistent. The demonstration that breast cells express CYP27B1 (which converts the precursor vitamin D metabolite 25D to the active metabolite 1,25D) and CYP24A1 (which degrades both 25D and 1,25D) provides insight into the difficulties inherent in using dietary vitamin D, sun exposure and/or serum biomarkers of vitamin D status to predict disease outcomes. Emerging evidence suggests that the normally tight balance between CYP27B1 and CYP24A1 becomes deregulated during cancer development, leading to abrogation of the tumor suppressive effects triggered by VDR. Research aimed at understanding the mechanisms that govern uptake, storage, metabolism and actions of vitamin D steroids in normal and neoplastic breast tissue remain an urgent priority.

Oncogenic Potential of CYP24A1 in Lung Adenocarcinoma

INTRODUCTION

We have previously demonstrated that a subset of lung cancer cells express higher CYP24A1 mRNA, a metabolizing enzyme for 1,25-D3, compared to benign tumors or surrounding normal lung and that high CYP24A1 mRNA expression is associated with poor prognosis in resected lung adenocarcinoma (AC). We hypothesized that CYP24A1 has oncogenic potential and increased CYP24A1 expression may contribute to tumor growth, whereas, CYP24A1 targeting may reduce tumor burden.

METHODS

Two low CYP24A1 expressing human lung cancer cell lines (SK-LU-1 and Calu-6) were stably transfected either with an empty lentiviral vector or with the CYP24A1 expressing vector. Over-expression of mRNA and protein levels of CYP24A1 in SK-LU-1 and Calu-6 were confirmed using qRT-PCR and immunoblotting respectively. Next, effects of targeting CYP24A1 were examined in lung cancer cells (A549 and H441), which express higher basal levels of CYP24A1. Finally, we studied the effects of stable knockdown of CYP24A1 in xenograft models.

RESULTS

Over-expression of CYP24A1 correlated with accelerated cell growth and invasion compared to control vector-transfected cells. CYP24A1 over-expression also increased RAS protein expression. Knockdown of CYP24A1 using either si- or shRNA reduced CYP24A1 mRNA and protein expression and significantly decreased cell proliferation (30-60%) and reduced mitochondrial DNA content compared to non-targeting (NT) si-/shRNA transfected/transduced cells. Transfection with CYP24A1 siRNA also decreased total RAS protein, thus reducing phosphorylated AKT. Importantly, stable knockdown of CYP24A1 in A549 and H441 lung tumor xenograft models resulted in tumor growth delay and smaller tumor size as evident from tumor bioluminescence and tumor volume measurement studies. Such observations were correlated with decreased tumor cell proliferation as evidenced by reduced Ki67 and Cyclin D staining.

CONCLUSIONS

Our data suggest that CYP24A1 has oncogenic properties mediated by increasing RAS signaling, targeting of which may provide an alternate strategy to treat a subset of lung AC.

Vitamin D-Related Gene Polymorphisms, Plasma 25-Hydroxy-Vitamin D, Cigarette Smoke and Non-Small Cell Lung Cancer (NSCLC) Risk

Epidemiological studies regarding the relationship between vitamin D, genetic polymorphisms in the vitamin D metabolism, cigarette smoke and non-small cell lung cancer (NSCLC) risk have not been investigated comprehensively. To search for additional evidence, the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique and radioimmunoassay method were utilized to evaluate 5 single-nucleotide polymorphisms (SNPs) in vitamin D receptor (VDR), 6 SNPs in 24-hydroxylase (CYP24A1), 2 SNPs in 1α-hydroxylase (CYP27B1) and 2 SNPs in vitamin D-binding protein (group-specific component, GC) and plasma vitamin D levels in 426 NSCLC cases and 445 controls from China. Exposure to cigarette smoke was ascertained through questionnaire information. Multivariable linear regressions and mixed effects models were used in statistical analysis. The results showed that Reference SNP rs6068816 in CYP24A1, rs1544410 and rs731236 in VDR and rs7041 in GC were statistically significant in relation to reduction in NSCLC risk (p < 0.001-0.05). No significant connection was seen between NSCLC risk and overall plasma 25-hydroxyvitamin D [25(OH)D] concentrations, regardless of smoking status. However, the mutation genotype of CYP24A1 rs6068816 and VDR rs1544410 were also significantly associated with increased 25(OH)D levels only in both the smoker and non-smoker cases (p < 0.01-0.05). Meanwhile, smokers and non-smokers with mutated homozygous rs2181874 in CYP24A1 had significantly increased NSCLC risk (odds ratio (OR) = 2.14, 95% confidence interval (CI) 1.47-3.43; p = 0.031; OR = 3.57, 95% CI 2.66-4.74; p = 0.019, respectively). Smokers with mutated homozygous rs10735810 in VDR had significantly increased NSCLC risk (OR = 1.93, 95% CI 1.41-2.76; p = 0.015). However, smokers with mutated homozygous rs6068816 in CYP24A1 had significantly decreased NSCLC risk (OR = 0.43, 95% CI 0.27-1.02; p = 0.006); and smokers and non-smokers with mutated homozygous rs1544410 in VDR had significantly decreased NSCLC risk (OR = 0.51, 95% CI 0.34-1.17; p = 0.002; OR = 0.26, 95% CI 0.20-0.69; p = 0.001, respectively). There are significant joint effects between smoking and CYP24A1 rs2181874, CYP24A1 rs6068816, VDR rs10735810, and VDR rs1544410 (p < 0.01-0.05). Smokers with mutated homozygous rs10735810 in VDR had significantly increased NSCLC risk (OR = 1.93, 95% CI 1.41-2.76; p = 0.015). In summary, the results suggested that the lower the distribution of vitamin D concentration, the more the genetic variations in CYP24A1, VDR and GC genes may be associated with NSCLC risk. In addition, there are significant joint associations of cigarette smoking and vitamin D deficiency on NSCLC risk.

Vitamin D Signaling Modulators in Cancer Therapy

The antiproliferative and pro-apoptotic effects of 1α,25-dihydroxycholecalciferol (1,25(OH)2D3, 1,25D3, calcitriol) have been demonstrated in various tumor model systems in vitro and in vivo. However, limited antitumor effects of 1,25D3 have been observed in clinical trials. This may be attributed to a variety of factors including overexpression of the primary 1,25D3 degrading enzyme, CYP24A1, in tumors, which would lead to rapid local inactivation of 1,25D3. An alternative strategy for improving the antitumor activity of 1,25D3 involves the combination with a selective CYP24A1 inhibitor. The validity of this approach is supported by numerous preclinical investigations, which demonstrate that CYP24A1 inhibitors suppress 1,25D3 catabolism in tumor cells and increase the effects of 1,25D3 on gene expression and cell growth. Studies are now required to determine whether selective CYP24A1 inhibitors+1,25D3 can be used safely and effectively in patients. CYP24A1 inhibitors plus 1,25D3 can cause dose-limiting toxicity of vitamin D (hypercalcemia) in some patients. Dexamethasone significantly reduces 1,25D3-mediated hypercalcemia and enhances the antitumor activity of 1,25D3, increases VDR-ligand binding, and increases VDR protein expression. Efforts to dissect the mechanisms responsible for CYP24A1 overexpression and combinational effect of 1,25D3/dexamethasone in tumors are underway. Understanding the cross talk between vitamin D receptor (VDR) and glucocorticoid receptor (GR) signaling axes is of crucial importance to the design of new therapies that include 1,25D3 and dexamethasone. Insights gained from these studies are expected to yield novel strategies to improve the efficacy of 1,25D3 treatment.

Cytochrome P450 Vitamin D Hydroxylases in Inflammation and Cancer

Vitamin D insufficiency correlates with increased incidence of inflammatory disorders and cancer of the colon, breast, liver, and prostate. Preclinical studies demonstrated that the hormonally active form of vitamin D, 1,25(OH)2D3, has antiproliferative, proapoptotic, anti-inflammatory, and immunomodulatory effects. Tissue levels of 1,25(OH)2D3 are determined by expression and activity of specific vitamin D hydroxylases expressed at renal and extrarenal sites. In order to understand how perturbations in the vitamin D system affect human health, we need to understand the steps involved in the synthesis and catabolism of the active metabolite. This review provides an overview about recent findings on the altered vitamin D metabolism in inflammatory conditions and carcinogenesis. We will summarize existing data on the pathophysiological regulation of vitamin D hydroxylases and outline the role of adequate levels of 1,25(OH)2D3 on tissue homeostasis.

Role of Vitamin D Metabolism and Activity on Carcinogenesis

The vitamin D endocrine system regulates a broad variety of independent biological processes, and its deficiency is associated with rickets, bone diseases, diabetes, cardiovascular diseases, and tuberculosis. Cellular and molecular studies have also shown that it is implicated in the suppression of cancer cell invasion, angiogenesis, and metastasis. Sunlight exposure and consequent increased circulating levels of vitamin D are associated with reduced occurrence and a reduced mortality in different histological types of cancer, including those resident in the skin, prostate, breast, colon, ovary, kidney, and bladder. The vitamin D receptor (VDR) as a steroid hormone superfamily of nuclear receptors is highly expressed in epithelial cells at risk for carcinogenesis, providing a direct molecular link by which vitamin D status impacts on carcinogenesis. Because VDR expression is retained in many human tumors, vitamin D status may be an important modulator of cancer progression in persons living with cancer. The aim of this review is to highlight the relationship between vitamin D, VDR, and cancer, summarizing several mechanisms proposed to explain the potential protective effect of vitamin D against the development and progression of cancer.