Disease relevance of CYP24A1

• In this study, by using the Escherichia coli expression system for human CYP24A1, we identified 25,26,27-trinor-23-ene-D(3) and 25,26,27-trinor-23-ene-1alpha(OH)D(3) as novel metabolites of 25(OH)D(3) and 1alpha,25(OH)(2)D(3), respectively [1].
• We found that CYP24A1 mRNA was significantly up-regulated in colon, ovary and lung tumors, but down-regulated in breast tumor relative to the analogous normal tissues [2].
• Possible involvement of pregnane X receptor-enhanced CYP24 expression in drug-induced osteomalacia [3].
• Clinical significance of the overexpression of the candidate oncogene CYP24 in esophageal cancer [4].
• RNAi-mediated silencing of CYP27B1 abolishes 1,25(OH)(2)D(3) synthesis and reduces osteocalcin and CYP24 mRNA expression in human osteosarcoma (HOS) cells [5].

High impact information on CYP24A1

• The putative oncogene ZNF217 (ref. 5) mapped to one peak, and CYP24 (encoding vitamin D 24 hydroxylase), whose overexpression is likely to lead to abrogation of growth control mediated by vitamin D, mapped to the other [6].
• Quantitative mapping of amplicon structure by array CGH identifies CYP24 as a candidate oncogene [6].
• A recent report suggests that activation of steroid and xenobiotic receptor (SXR) also enhances the expression of CYP24, providing a new molecular mechanism of drug-induced osteomalacia [7].
• Combined with our previous findings that CYP3A4, not CYP24, plays the dominant role in hydroxylation of 1,25(OH)2D3 in human liver and intestine, our results indicate that SXR has a dual role in mediating vitamin D catabolism and drug-induced osteomalacia [7].
• Steroid and xenobiotic receptor and vitamin D receptor crosstalk mediates CYP24 expression and drug-induced osteomalacia [7].

Chemical compound and disease context of CYP24A1

• We induced CYP24 in seven esophageal cancer cell lines using 25-hydroxyvitamin D3 [25(OH)D3] and compared cell growth rate, measured using the 3-(4, 5-dimethylthiazol-2-y)-2, 5-diphenyltetrazolium bromide (MTT) assay system [4].
• Treatment of DU-145 prostatic cancer cells with genistein led to a time- and dose-dependent inhibition of CYP24 [8].
• The presence of 9-cis-RA increases induction of cyp24 transcripts and differentiation of colon cancer cells by vitamin D, confers significant agonistic activity to a VDR ligand with very low agonistic activity and can even restore transcriptional activity of an AF-2 mutant VDR that causes hereditary rickets [9].
• 5alpha-dihydrotestosterone inhibits 1alpha,25-dihydroxyvitamin D3-induced expression of CYP24 in human prostate cancer cells [10].
• Phase I and II trials of calcitriol, either alone or in combination with carboplatin, taxanes or dexamethasone, as well as the non-specific CYP24 inhibitor, ketoconazole, have been initiated in patients with androgen-dependent and -independent prostate cancer and other advanced cancers [11].

Biological context of CYP24A1

• These metabolites appear to be closely related to the C-23 hydroxylation pathway, because human CYP24A1 produces much more of these metabolites than does rat CYP24A1 [1].
• Homology model of 1alpha,25-dihydroxyvitamin D(3) 24-hydroxylase cytochrome P450 24A1 (CYP24A1): Active site architecture and ligand binding [12].
• The metabolism of 1alpha,25(OH)(2)D(3) (1alpha,3beta) and its A-ring diastereomers, 1beta,25(OH)(2)D(3) (1beta,3beta), 1alpha,25(OH)(2)-3-epi-D(3) (1alpha,3alpha), and 1beta,25(OH)(2)-3-epi-D(3) (1beta,3alpha), was examined to compare the substrate specificity and reaction specificity of CYP24A1 between humans and rats [13].
• In this study, we employed real-time reverse transcription PCR to examine the expression of VDR and CYP24A1 mRNA in a cohort of human breast, lung, colon and ovary tumor samples [2].
• We conclude from these experiments a constitutive gene expression of the vitamin D3 hydroxylases, whereas the catabolic enzyme CYP24A1 is markedly regulated by UVB, calcitriol, and perhaps cell proliferation [14].

Anatomical context of CYP24A1

• Treatment of two breast cancer cell lines, SW-620 and MCF-7, and one colon cancer cell line, HT-29, by 1,25(OH)2D3 for 48 h profoundly stimulated CYP24A1 mRNA expression (EC50=0.6, 0.8 and 29.5 nM in SW-620, HT-29 and MCF-7, respectively), but did not significantly affect VDR mRNA expression [2].
• MATERIALS AND METHODS: Using primary human keratinocytes, CYP24A1 expression was examined at the mRNA level by dot-blot and Northern blot hybridization, and at the enzyme activity level by analysing HPLC profiles from incubations with 3H-labelled VD metabolites [15].
• We therefore investigated basal and Vitamin D-regulated expression and activity of the synthesizing (CYP27B1) and metabolizing (CYP24A1) hydroxylase in three cell lines derived from the colon, and compared this to cells from the prostate and mammary gland [16].
• CYP24 mRNA is upregulated in vivo in mice by pregnenolone 16alpha-carbonitrile and dexamethasone, 2 murine PXR agonists, and in vitro in human hepatocytes by rifampicin and hyperforin, 2 human PXR agonists [3].
• The blocker of Ca(2+) channels, verapamil, impeded both rapid (calcium) and long term (24-hydroxylase activity, CYP24, and ferredoxin mRNAs) responses in patient and control fibroblasts [17].

Associations of CYP24A1 with chemical compounds

• A five-step inactivation pathway from 1alpha,25-(OH)(2)D(3) to calcitroic acid is attributed to a single multifunctional CYP, CYP24A1, which is transcriptionally induced in vitamin D target cells by the action of 1alpha,25-(OH)(2)D(3) [18].
• Co-expression of CYP2R1 with vitamin D 1alpha-hydroxylase (CYP27B1) elicited additive activation of vitamin D3, whereas co-expression with vitamin D 24-hydroxylase (CYP24A1) caused inactivation [19].
• Consistent with this observation, analysis of mRNA isolated from human intestine and liver (including samples from donors treated with phenytoin) revealed a general absence of CYP24A1 mRNA [20].
• Novel metabolism of 1 alpha,25-dihydroxyvitamin D3 with C24-C25 bond cleavage catalyzed by human CYP24A1 [1].
• The use of a selective inhibitor of PKA (H-89) prevented the effects of calcitriol on CYP27B1 gene and hCG secretion, but not on CYP24A1 transcription [21].

Physical interactions of CYP24A1

• We demonstrated that PXR binds to and transactivates the 2 proximal vitamin D-responsive elements of the human CYP24 promoter [3].

Regulatory relationships of CYP24A1

• The MEK 1/2 kinase inhibitor PD98059 also blocked the CYP24 mRNA response [17].
• It was previously suggested that the 25-Vitamin-D3-1alpha-hydroxylase (CYP27B1) is downregulated during human prostate tumor pathogenesis while the catabolic 25-Vitamin-D3-24-hydroxylase (CYP24) expression is increased [22].
• Calcitonin stimulates expression of the rat 25-hydroxyvitamin D3-24-hydroxylase (CYP24) promoter in HEK-293 cells expressing calcitonin receptor: identification of signaling pathways [23].

Other interactions of CYP24A1

• CYP3A4 exhibited opposite product stereochemical preference compared with that of CYP24A1, a known 1,25(OH)(2)D(3) hydroxylase [20].
• 1,25(OH)(2)D(3) and activators of the PKA signaling system decreased the expression of CYP27B1, whereas increased CYP24A1 gene transcription [21].
• However, here we showed that activation of SXR did not induce CYP24 expression in vitro and in vivo, nor did it transactivate the CYP24 promoter [7].
• Surprisingly, more than 70 % of the vitamin D metabolites observed in a living body were found to be the products formed by the activities of CYP27A1, CYP27B1 and CYP24A1 [24].
• CYP24 mRNA was inducible in all clones by 1,25-D3 but not by EGF [25].

Analytical, diagnostic and therapeutic context of CYP24A1

• Therefore, we monitored the spatio-temporal, 1alpha,25OH2D3-dependent chromatin acetylation status of the human CYP24 promoter by performing chromatin immunoprecipitation (ChIP) assays with antibodies against acetylated histone 4 [26].
• CYP24 leads to abrogate growth control mediated by vitamin D. MATERIALS AND METHODS: We examined CYP24 expression as well as VDR (vitamin D receptor) gene expression in 42 esophageal cancer cases using semi-quantitative RT-PCR assay [4].
• Structure-function analysis of vitamin D 24-hydroxylase (CYP24A1) by site-directed mutagenesis: amino acid residues responsible for species-based difference of CYP24A1 between humans and rats [27].
• The HPLC and LC-MS analyses of the metabolites revealed that rat CYP24 converted 1alpha,25(OH)(2)-20-epi-D(3) to 25,26,27-trinor-1alpha(OH)-24(COOH)-20-epi-D(3) through 1alpha,24,25(OH)(3)-20-epi-D(3) and 1alpha,25(OH)(2)-24-oxo-20-epi-D(3) [28].
• The CYP24 inducing activity in BM15766-pretreated UVB-irradiated CaCo-2 cells and THP-1 macrophages was identified as 1,25(OH)2D3 by combined high-performance liquid chromatography radioimmunoassay [29].

References