Identification of a novel suppressive vitamin D response sequence in the 5'-flanking region of the murine Id1 gene

Tumor Autonomous Effects of Vitamin D Deficiency Promote Breast Cancer Metastasis

Patients with breast cancer (BCa) frequently have preexisting vitamin D deficiency (low serum 25-hydroxyvitamin D) when their cancer develops. A number of epidemiological studies show an inverse association between BCa risk and vitamin D status in humans, although some studies have failed to find an association. In addition, several studies have reported that BCa patients with vitamin D deficiency have a more aggressive molecular phenotype and worse prognostic indicators. However, it is unknown whether this association is mechanistically causative and, if so, whether it results from systemic or tumor autonomous effects of vitamin D signaling. We found that ablation of vitamin D receptor expression within BCa cells accelerates primary tumor growth and enables the development of metastases, demonstrating a tumor autonomous effect of vitamin D signaling to suppress BCa metastases. We show that vitamin D signaling inhibits the expression of the tumor progression gene Id1, and this pathway is abrogated in vitamin D deficiency in vivo in 2 murine models of BCa. These findings are relevant to humans, because we discovered that the mechanism of VDR regulation of Inhibitor of differentiation 1 (ID1) is conserved in human BCa cells, and there is a negative correlation between serum 25-hydroxyvitamin D levels and the level of ID1 in primary tumors from patients with BCa.

Vitamin D signaling in myogenesis: potential for treatment of sarcopenia

Muscle mass and strength progressively decrease with age, which results in a condition known as sarcopenia. Sarcopenia would lead to physical disability, poor quality of life, and death. Therefore, much is expected of an effective intervention for sarcopenia. Epidemiologic, clinical, and laboratory evidence suggest an effect of vitamin D on muscle function. However, the precise molecular and cellular mechanisms remain to be elucidated. Recent studies suggest that vitamin D receptor (VDR) might be expressed in muscle fibers and vitamin D signaling via VDR plays a role in the regulation of myoblast proliferation and differentiation. Understanding how vitamin D signaling contributes to myogenesis will provide a valuable insight into an effective nutritional strategy to moderate sarcopenia. Here we will summarize the current knowledge about the effect of vitamin D on skeletal muscle and myogenic cells and discuss the potential for treatment of sarcopenia.

1alpha,25-Dihydroxyvitamin D3 regulates the expression of Id1 and Id2 genes and the angiogenic phenotype of human colon carcinoma cells

1alpha,25-Dihydroxyvitamin D3 (1alpha,25(OH)2D3) has antitumor activity in addition to its classical action on calcium metabolism and bone tissue biology. It is thought to regulate the expression of multiple target genes and thus modulate processes critical for tumor growth and metastases. Here we show that 1alpha,25(OH)2D3 differentially regulates the expression of Id1 and Id2 genes, members of a family of transcriptional regulators of cell proliferation and differentiation. 1alpha,25(OH)2D3 induced epithelial differentiation in SW480-ADH human colon carcinoma cell line by promoting expression of the proteins implicated in adherent junction formation, including E-cadherin, and by inhibiting beta-catenin transcriptional activity. 1alpha,25(OH)2D3 activated the human Id1 gene promoter and rapidly induced Id1 RNA and protein. Ectopic overexpression of Id1 was not sufficient to induce E-cadherin, which was critical for the morphological changes induced by 1alpha,25(OH)2D3 in SW480-ADH cells. Conversely, Id2 transcription rate, RNA and protein levels were decreased by 1alpha,25(OH)2D3. Id2 downregulation by 1alpha,25(OH)2D3 mediated the antiproliferative effect of 1alpha,25(OH)2D3 on SW480-ADH cells. In addition, we showed that 1alpha,25(OH)2D3 changed the levels of the inducer of angiogenesis, vascular endothelial growth factor and the potent antiangiogenic factor thrombospondin-1, leading to a balanced change in the angiogenic potential of SW480-ADH human colon carcinoma cells.

Proteasome mediated degradation of Id-1 is associated with TNFalpha-induced apoptosis in prostate cancer cells

Overexpression of the helix-loop-helix protein Id-1 has been reported in over 20 types of cancer. While a number of factors have been demonstrated to regulate Id-1 gene transcription, little is known about the mechanisms responsible for its degradation. In this study, we have demonstrated that Id-1 protein stability was regulated by TNFalpha in prostate cancer cells. We found that exposure of prostate cancer cell lines, DU145 and PC-3, to TNFalpha resulted in a rapid and significant downregulation of the Id-1 protein level. The fact that neither the Id-1 promoter activity nor the Id-1 mRNA level was affected by the TNFalpha treatment suggested that the decrease in Id-1 protein was not due to the suppression of gene transcription. In addition, the half-life of the Id-1 protein was decreased in both cell lines in the presence of TNFalpha, and the addition of an ubiquitin/proteasome inhibitor (MG-132) prior to the TNFalpha treatment completely blocked the effect of the TNFalpha-induced Id-1 protein degradation. Furthermore, introduction of a Flag-tag sequence into the N-terminus region of the Id-1 protein, which has been shown to stabilize the protein, was able to protect the Id-1 protein from TNFalpha-induced degradation. These results suggest that TNFalpha downregulated Id-1 through activation of the ubiquitin/proteasome degradation pathway in prostate cancer cells. Interestingly, in both DU145 and PC-3 cells, the decrease of Id-1 protein was associated with the activation of apoptotic pathway, as evidenced by the increased expression of cleaved PARP and caspase 3. In addition, TNFalpha failed to downregulate Id-1 in a sub-line of LNCaP cells that was resistant to TNFalpha-induced apoptosis. These results further suggest that the downregulation of Id-1 may facilitate TNFalpha-induced apoptosis in prostate cancer cells. In conclusion, our findings indicate that Id-1 protein may be regulated by TNFalpha through the ubiquitin/proteasome degradation pathway and the stability of the Id-1 protein appears to correlate with the sensitivity of TNFalpha-induced apoptosis.

Global gene expression analysis in time series following N-acetyl L-cysteine induced epithelial differentiation of human normal and cancer cells in vitro

Background

Cancer prevention trials using different types of antioxidant supplements have been carried out at several occasions and one of the investigated compounds has been the antioxidant N-acetyl-L-cysteine (NAC). Studies at the cellular level have previously demonstrated that a single supplementation of NAC induces a ten-fold more rapid differentiation in normal primary human keratinocytes as well as a reversion of a colon carcinoma cell line from neoplastic proliferation to apical-basolateral differentiation [1]. The investigated cells showed an early change in the organization of the cytoskeleton, several newly established adherens junctions with E-cadherin/β-catenin complexes and increased focal adhesions, all features characterizing the differentiation process.

Methods

In order to investigate the molecular mechanisms underlying the proliferation arrest and accelerated differentiation induced by NAC treatment of NHEK and Caco-2 cells in vitro, we performed global gene expression analysis of NAC treated cells in a time series (1, 12 and 24 hours post NAC treatment) using the Affymetrix GeneChip™ Human Genome U95Av2 chip, which contains approximately 12,000 previously characterized sequences. The treated samples were compared to the corresponding untreated culture at the same time point.

Results

Microarray data analysis revealed an increasing number of differentially expressed transcripts over time upon NAC treatment. The early response (1 hour) was transient, while a constitutive trend was commonly found among genes differentially regulated at later time points (12 and 24 hours). Connections to the induction of differentiation and inhibition of growth were identified for a majority of up- and down-regulated genes. All of the observed transcriptional changes, except for seven genes, were unique to either cell line. Only one gene, ID-1, was mutually regulated at 1 hour post treatment and might represent a common mediator of early NAC action.

The detection of several genes that previously have been identified as stimulated or repressed during the differentiation of NHEK and Caco-2 provided validation of results. In addition, real-time kinetic PCR analysis of selected genes also verified the differential regulation as identified by the microarray platform.

Conclusion

NAC induces a limited and transient early response followed by a more consistent and extensively different expression at later time points in both the normal and cancer cell lines investigated. The responses are largely related to inhibition of proliferation and stimulation of differentiation in both cell types but are almost completely lineage specific. ID-1 is indicated as an early mediator of NAC action.

Id2 protein is selectively upregulated by UVB in primary, but not in immortalized human keratinocytes and inhibits differentiation

Solar ultraviolet B (UVB) acts as both an initiator and promoter in models of multistage skin carcinogenesis. We found that, whereas UVB induces apoptosis in human papillomavirus-16 E6/7-immortalized keratinocytes, it inhibits markers of differentiation in human foreskin keratinocytes (HFK). Potential mechanisms for this differential response were examined by DNA microarray, which revealed that UVB alters the expression of three of the four human inhibitor of differentiation/DNA binding (Id) proteins that comprise a class of helix-loop-helix family of transcription factors involved in proliferation, differentiation, apoptosis, and carcinogenesis. These results were verified by RT-PCR and immunoblot analysis of control and UVB-irradiated primary and immortalized keratinocytes. Whereas Id1 was downregulated in both cell types, Id2 expression was upregulated in primary HFK, but not immortalized cells. In contrast, Id3 expression was significantly increased only in immortalized cells. The differential expression pattern of Id2 in response to UVB was recapitulated in reporter constructs containing the 5' regulatory regions of this gene. Id2 promoter activity increased in response to UVB in HFK, but not in immortalized cells. To identify the regulatory elements in the Id2 promoter that mediate transcriptional activation by UVB in HFK, promoter deletion/mutation analysis was performed. Deletion analysis revealed that transactivation involves a 166 bp region immediately upstream to the Id2 transcriptional start site and is independent of c-Myc. The consensus E twenty-six (ETS) binding site at -120 appears to mediate UVB transcriptional activation of Id2 because point mutations at this site completely abrogated this response. Chromatin immunoprecipitation and electrophoretic mobility-shift assays verified that the Id2 promoter interacts with known Id2 promoter (ETS) binding factors Erg1/2 and Fli1, but not with c-Myc; and this interaction is enhanced after UVB exposure. Similar to the effects of UVB exposure, ectopic expression of Id2 protein in primary HFK resulted in inhibition of differentiation, as shown by decreased levels of the terminal differentiation marker keratin K1 and inhibition of involucrin crosslinking. Reduction of Id2 expression by small interfering RNAs attenuated the UVB-induced inhibition of differentiation in these cells. These results suggest that UVB-induced inhibition of differentiation of primary HFK is at least, in part, due to the upregulation of Id2, and that upregulation of Id2 by UVB might predispose keratinocytes to carcinogenesis by preventing their normal differentiation program.

1,25-dihydroxyvitamin D3 down-regulation of PHEX gene expression is mediated by apparent repression of a 110 kDa transfactor that binds to a polyadenine element in the promoter

The PHEX gene encodes an endopeptidase expressed in osteoblasts that inactivates an uncharacterized peptide hormone, phosphatonin, which suppresses bone mineralization as well as renal phosphate reabsorption and vitamin D bioactivation. We demonstrate that 1alpha-25-dihydroxyvitamin D (1,25(OH)2D3), the, active renal vitamin D metabolite, decreases PHEX mRNA in the rat osteoblastic cell line, UMR-106, as well as in mouse calvaria. Promoter/reporter construct analysis of the murine PHEX gene in transfected UMR-106 cells localized the repressive effect of 1,25(OH)2D3 to the -133 to -74 bp region, and gel mobility shift experiments revealed that 1,25(OH)2D3 treatment of the cells diminished the binding of a nuclear protein(s) to a stretch of 17 adenines from bp -116 to -100 in the proximal PHEX promoter. Either overexpression of a dominant-negative vitamin D receptor (VDR) or deletion of this sequence of 17 A-T base pairs abolished the repressive effect of 1,25(OH)2D3 by attenuating basal promoter activity, indicating that this region mediates the 1,25(OH)2D3 response and is involved in basal transcription. South-western blot analysis and DNA affinity purification show that an unidentified 110 kDa nuclear protein binds to the poly(A) element. Because 1,25(OH)2D3-liganded VDR neither binds to the polyadenine region of the PHEX promoter nor directly influences the association of the 110 kDa transfactor, we conclude that 1,25(OH)2D3 indirectly decreases PHEX expression via VDR-mediated repression (or modification) of this novel transactivator. Thus, we have identified a cis-element required for PHEX gene transcription that participates in negative feedback control of PHEX expression and thereby modulates the actions of phosphatonin.

AML1 interconnected pathways of leukemogenesis

The AML1 transcription factor, identified by the cloning of the translocation t(8;21) breakpoint, is one of the most frequent targets for chromosomal translocations in leukemia. Furthermore, polysomies and point mutations can also alter AML1 function. AML1, also called CBF alpha 2, PEBP alpha 2 or RUNX1, is thus implicated in a great number of acute leukemias via a variety of pathogenic mechanisms and seems to act either as an oncogene or a tumor suppressor gene. Characterization of AML1 knockout mice has shown that AML1 is necessary for normal development of all hematopoietic lineages and alterations in the overal functional level of AML1 can have a profound effect on hematopoiesis. Numerous studies have shown that AML1 plays a vital role in the regulation of expression of many genes involved in hematopoietic cell development, and the impairment of AML1 function disregulates the pathways leading to cellular proliferation and differentiation. However, heterozygous AML1 mutations alone may not be sufficient for the development of leukemia. A cumulative process of mutagenesis involving additional genetic events in functionally related molecules, may be necessary for the development of leukemia and may determine the leukemic phenotype. We review the known AML1 target genes, AML1 interacting proteins, AML1 gene alterations and their effects on AML1 function, and mutations in AML1-related genes associated with leukemia. We discuss the interconnections between all these genes in cell signaling pathways and their importance for future therapeutic developments.

Localization of a negative vitamin D response sequence in the human growth hormone gene

1,25-Dihydroxyvitamin D(3) [1,25(OH)(2) D(3)] exerts its biological effects by binding to the vitamin D receptor (VDR), which binds in turn to the vitamin D response elements located in the target gene's promoter. We have previously demonstrated that VDR binds in vitro with high affinity to the 5'-flanking sequence of the human growth hormone (hGH) gene. In this study, we analyzed the response to 1,25(OH)(2) D(3) of hGH-promoter constructs introduced by transfection into the MCF-7 human adenocarcinoma cell line. We found that the transcriptional activity of some of these constructs was markedly reduced by 1,25(OH)(2) D(3). Deletion analyses revealed that a 34-bp sequence located between positions -62 and -29 upstream of the transcription start site is sufficient for this repressive response. This conclusion was also confirmed by gel mobility shift assays. Our results indicate that vitamin D inhibits hGH gene transcription, directly or by interference with other transcription factors.

Sp1 and NF-Y synergistically mediate the effect of vitamin D(3) in the p27(Kip1) gene promoter that lacks vitamin D response elements

Vitamin D(3) promotes myeloid leukemic cell lines to differentiate terminally into monocytes/macrophages. It has been reported that overexpression of the cdk inhibitor p27(Kip1) results in the differentiation of the myelomonocytic U937 cell line and that this gene is the target of vitamin D(3). To identify the sequences required for the positive regulation of p27(Kip1) transcription by vitamin D(3), a 3.6-kilobase 5'-flanking region of the human p27(Kip1) gene was examined by transiently transfecting luciferase reporter constructs into U937 cells. The transcriptional activity of this construct was activated by vitamin D(3). Deletion and mutational analysis revealed that both a GGGCGG sequence (-545/-539) and a CCAAT sequence (-525/-520) were necessary to induce p27(Kip1) gene expression. Importantly, the region containing both of these elements conferred positive responsiveness to vitamin D(3) to a heterologous promoter. Gel shift assays showed that Sp1 binds to the GGGCGG sequence and that NF-Y binds to the CCAAT sequence. Consistent with the roles of these transcription factors, treatment with vitamin D(3) stimulated the DNA binding activities of these factors to each element and induced the change of one NF-Y subunit. We conclude that vitamin D(3) stimulates transcription of the p27(Kip1) gene by a novel mechanism involving Sp1 and NF-Y, but not the vitamin D receptor, during the early stages of U937 cell differentiation.

Genomic cloning, structure, and regulatory elements of the 1 alpha, 25(OH)2D3 down-regulated gene for cyclic AMP-dependent protein kinase inhibitor

The cyclic AMP-dependent protein kinase inhibitor (PKI) mRNA and protein are negatively and tissue-specifically regulated in the kidney by 1 alpha, 25(OH)2D3. A 17-kb PKI clone, isolated from a chick genomic library, revealed that the PKI gene consists of two exons separated by a 4.5-kb intron. A 411-bp upstream region (constituting 93 bp upstream and 318 bp downstream from the transcriptional start site) containing a putative negative VDRE (nVDRE) fused to the luciferase gene was used for transient transfections of primary cultures of chick kidney cells. Luciferase activity was significantly down-regulated in response to 1 alpha, 25(OH)2D3. This result suggests that the promoter region containing the putative nVDRE plays a pivotal role in the negative regulation of PKI gene transcription.

A two-hit mechanism for vitamin D3-mediated transcriptional repression of the granulocyte-macrophage colony-stimulating factor gene: vitamin D receptor competes for DNA binding with NFAT1 and stabilizes c-Jun

We previously described a control element in the granulocyte-macrophage colony-stimulating factor (GM-CSF) enhancer that is necessary and sufficient to mediate both transcriptional activation in response to T-cell stimuli and transcriptional repression by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] through the vitamin D3 receptor (VDR). This DNA element is a composite site that is recognized by both Fos-Jun and NFAT1; it is directly bound by VDR in the absence of a retinoid X receptor as an apparent monomer, and it is bound in a unique tertiary conformation. We describe here the mechanism by which VDR elicits its transcriptional inhibitory effect. Firstly, VDR outcompetes NFAT1 for binding to the composite site. Overexpression of NFAT1 in vivo by transient transfection is able to relieve the 1,25(OH)2D3-dependent repression. Secondly, VDR stabilizes the binding of a Jun-Fos heterodimer to the adjacent AP-1 portion of the element. This appears to occur through a direct interaction between VDR and c-Jun, as demonstrated in vitro by direct glutathione S-transferase coprecipitation assays. In vivo, overexpression of c-Jun, but not c-Fos, leads to a rescue of the 1, 25(OH)2D3-mediated repression. Transfected FLAG-VDR bound to the NFAT1-AP-1 DNA binding element can be selectively precipitated from nuclear extracts that are made from cells treated with activating agents in the presence of 1,25(OH)2D3. VDR is not detected in the complex in the absence of the ligand. Thus, VDR acts selectively on the two components required for activation of this promoter/enhancer: it competes with NFAT1 for binding to the composite site, positioning itself adjacent to Jun-Fos on the DNA. Co-occupancy apparently leads to an inhibitory effect on c-Jun's transactivation function. These two events mediated by VDR effectively block the NFAT1-AP-1 activation complex, resulting in an attenuation of activated GM-CSF transcription.

Vitamin D and regulation of gene expression

The function of 1,25-dihydroxyvitamin D3, the biologically active form of vitamin D, extends from bone and mineral homeostasis to the control of cell growth and differentiation in a variety of tissues. Most of these actions are mediated by activation of the nuclear vitamin D receptor, which regulates the transcription of vitamin D target genes. Considerable progress has been made in the understanding of vitamin D receptor function (especially regarding its interaction with coactivators), as well as in the identification of novel vitamin D responsive genes related to cell growth, differentiation and cytokine production.