RESUMO
Cancer development involves changes driven by the epigenetic machinery, including nucleosome positioning. Recently, the concept that adenoviral replication may be driven by tumor specific promoters (TSPs) gained support, and several conditionally replicative adenoviruses (CRAd) exhibited therapeutic efficacy in clinical trials. Here, we show for the first time that placing a nucleosome positioning sequence (NPS) upstream of a TSP combined with Wnt-responsive motifs (pART enhancer) enhanced the TSP transcriptional activity and increased the lytic activity of a CRAd. pART enhanced the transcriptional activity of the gastrointestinal cancer (GIC)-specific REG1A promoter (REG1A-pr); moreover, pART also increased the in vitro lytic activity of a CRAd whose replication was driven by REG1A-Pr. The pART enhancer effect in vitro and in vivo was strictly dependent on the presence of the NPS. Indeed, deletion of the NPS was strongly deleterious for the in vivo antitumor efficacy of the CRAd on orthotopically established pancreatic xenografts. pART also enhanced the specific activity of other heterologous promoters; moreover, the NPS was also able to enhance the responsiveness of hypoxia- and NFκB-response elements. We conclude that NPS could be useful for gene therapy approaches in cancer as well as other diseases.
Assuntos
Adenoviridae/genética , Nucleossomos/genética , Animais , Linhagem Celular Tumoral , Feminino , Terapia Genética , Células HT29 , Humanos , Masculino , Camundongos Nus , Terapia Viral Oncolítica , Neoplasias Pancreáticas/terapia , Regiões Promotoras Genéticas/genética , Replicação Viral/genética , Replicação Viral/fisiologia , Ensaios Antitumorais Modelo de XenoenxertoRESUMO
The Runx2 transcription factor is essential for skeletal development as it regulates expression of several key bone-related genes. Multiple lines of evidence indicate that expression of the Runx2/p57 isoform in osteoblasts is controlled by the distal P1 promoter. Alterations of chromatin structure are often associated with transcription and can be mediated by members of the SWI/SNF family of chromatin remodeling complexes, or by transcriptional coactivators that possess enzymatic activities that covalently modify structural components of the chromatin. Here, we report that a specific chromatin remodeling process at the proximal region (residues -400 to 35) of the Runx2 gene P1 promoter accompanies transcriptional activity in osteoblasts. This altered chromatin organization is reflected by the presence of two DNase I hypersensitive sites that span key regulatory elements for Runx2/p57 transcription. Chromatin remodeling and transcription of the Runx2 gene are associated with elevated levels of histone acetylation at the P1 promoter region and binding of active RNA polymerase II and are independent of the activity of the SWI/SNF chromatin remodeling complex. Changes in chromatin organization at the P1 promoter are stimulated during differentiation of C2C12 mesenchymal cells to the osteoblastic lineage by treatment with BMP2. Together, our results support a model in which changes in chromatin organization occur at very early stages of mesenchymal differentiation to facilitate subsequent expression of the Runx2/p57 isoform in osteoblastic cells.
Assuntos
Proteínas Cromossômicas não Histona/metabolismo , Subunidade alfa 1 de Fator de Ligação ao Core/metabolismo , Desoxirribonucleases/metabolismo , Histonas/metabolismo , Regiões Promotoras Genéticas , Fatores de Transcrição/metabolismo , Transcrição Gênica , Acetilação , Animais , Proteína Morfogenética Óssea 2/genética , Proteína Morfogenética Óssea 2/metabolismo , Diferenciação Celular/fisiologia , Linhagem Celular , Montagem e Desmontagem da Cromatina , Proteínas Cromossômicas não Histona/genética , Subunidade alfa 1 de Fator de Ligação ao Core/genética , Regulação da Expressão Gênica , Histonas/genética , Camundongos , Osteoblastos/citologia , Osteoblastos/fisiologia , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Fatores de Transcrição/genéticaRESUMO
Calcium/calmodulin-dependent protein kinase IV (CaMKIV) plays a key role in the regulation of calcium-dependent gene expression. The expression of CaMKIV and the activation of CREB regulated genes are involved in memory and neuronal survival. We report here that: (a) a bioinformatic analysis of 15,476 promoters of the human genome predicted several Wnt target genes, being CaMKIV a very interesting candidate; (b) CaMKIV promoter contains TCF/LEF transcription motifs similar to those present in Wnt target genes; (c) biochemical studies indicate that lithium and the canonical ligand Wnt-3a induce CaMKIV mRNA and protein expression levels in rat hippocampal neurons as well as CaMKIV promoter activity; (d) treatment of hippocampal neurons with Wnt-3a increases the binding of beta-catenin to the CaMKIV promoter: (e) In vivo activation of the Wnt signaling improve spatial memory impairment and restores the expression of CaMKIV in a mice double transgenic model for Alzheimer's disease which shows decreased levels of the kinase. We conclude that CaMKIV is regulated by the Wnt signaling pathway and that its expression could play a role in the neuroprotective function of the Wnt signaling against the Alzheimer's amyloid peptide.
Assuntos
Proteína Quinase Tipo 4 Dependente de Cálcio-Calmodulina/metabolismo , Transdução de Sinais/fisiologia , Proteínas Wnt/metabolismo , beta Catenina/metabolismo , Doença de Alzheimer/tratamento farmacológico , Doença de Alzheimer/metabolismo , Doença de Alzheimer/patologia , Animais , Comportamento Animal/efeitos dos fármacos , Proteína Quinase Tipo 4 Dependente de Cálcio-Calmodulina/genética , Linhagem Celular , Biologia Computacional , Modelos Animais de Doenças , Elementos Facilitadores Genéticos/genética , Expressão Gênica/efeitos dos fármacos , Expressão Gênica/genética , Hipocampo/citologia , Hipocampo/efeitos dos fármacos , Hipocampo/patologia , Humanos , Cloreto de Lítio/farmacologia , Cloreto de Lítio/uso terapêutico , Camundongos , Camundongos Endogâmicos , Camundongos Transgênicos , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Testes Neuropsicológicos , Regiões Promotoras Genéticas/genética , Ligação Proteica/genética , Ratos , Ratos Endogâmicos , Fatores de Transcrição TCF/metabolismo , Transfecção , Proteínas Wnt/farmacologia , Proteína Wnt3 , Proteína Wnt3A , beta Catenina/genéticaRESUMO
Vitamin D is a principal modulator of skeletal gene expression, thus necessitating an understanding of interfaces between the activity of this steroid hormone and regulatory cascades that are functionally linked to the regulation of skeletal genes. Physiologic responsiveness requires combinatorial control, whereas co-regulatory proteins determine the specificity of biologic responsiveness to physiologic cues. It is becoming increasingly evident that regulatory complexes containing the vitamin D receptor are dynamic rather than static. Temporal and spatial modifications in the composition of these complexes provide a mechanism for integrating regulatory signals to support positive or negative control through synergism and antagonism. Compartmentalization of components of vitamin D control in nuclear microenvironments supports the integration of regulatory activities, perhaps by establishing thresholds for protein activity in time frames that are consistent with the execution of regulatory signaling.
Assuntos
Desenvolvimento Ósseo/genética , Regulação da Expressão Gênica no Desenvolvimento , Vitamina D/fisiologia , Animais , Núcleo Celular/metabolismo , Humanos , Modelos Biológicos , Complexos Multiproteicos/fisiologia , Fatores de Transcrição/fisiologiaRESUMO
Despite the advance of knowledge about the factors and potential mechanisms triggering the ichthyotoxicity in microalgae, these remain unclear or are controversial for several species (e.g. Heterosigma). Neither typical toxicity tests carried out with cell extracts nor direct exposure to harmful species were proved suitable to unravel the mechanism of harm. Ichthyotoxic species show a complex harmful effect on fish, which is mediated through various mechanisms depending on the species. In this work, we present a method to study sub-lethal effects triggered by reactive oxygen species of a population of harmful algae in vivo over a fish cell line. To that end, Transwell co-cultures in which causative and target species are separated by a 0.4 µm pore membrane were carried out. This allowed the evaluation of the effect of the released molecules by cells in a rapid and compact test. In our method, the harmful effect was sensed through the transcriptional activation of sub-lethal marker Hsp70b in the CHSE214 salmon cell line. The method was tested with the raphidophyte Heterosigma akashiwo and Dunaliella tertiolecta (as negative control). It was shown that superoxide intracellular content and its release are not linked in these species. The methodology allowed proving that reactive oxygen species produced by H. akashiwo are able to induce the transcriptional activation of sub-lethal marker Hsp70b. However, neither loss of viability nor apoptosis was observed in CHSE214 salmon cell line except when exposed to direct contact with the raphidophyte cells (or their extract). Consequently, ROS was not concluded to be the main cause of ichthyotoxicity in H. akashiwo.
Assuntos
Proteínas de Choque Térmico HSP70/biossíntese , Microalgas/crescimento & desenvolvimento , Espécies Reativas de Oxigênio/metabolismo , Estramenópilas/crescimento & desenvolvimento , Ativação Transcricional , Animais , Linhagem Celular , Técnicas de Cocultura , Proteínas de Choque Térmico HSP70/genética , Microalgas/genética , Salmão , Estramenópilas/genéticaRESUMO
Chilean waters are often affected by Alexandrium catenella, one of the leading organisms behind Harmful Algae Blooms (HABs). Genetic variability for this species are commonly carried out from cultured samples, approach that may not accurately quantify genetic variability of this organism in the water column. In this study, genetic variability of A. catenella was determined by sequencing the rDNA region, in water samples from the Canal Puyuhuapi (South Austral Ecosystem of Chile). A. catenella was detected in 8,8% of samples analysed. All sequences obtained were A. catenella (Tamara complex group I), with three highly frequent haplotypes (34%), and twenty new haplotypes. These haplotypes increase the genetic variability from 2.8% to 3.14% in this area. Through this new method, genetic determination of A. catenella can accurately be monitored and ecological studies of this species can be implemented.
Assuntos
Dinoflagellida/genética , Ecossistema , Água/parasitologia , Chile , Variação Genética , HaplótiposRESUMO
Bone-specific transcription of the osteocalcin (OC) gene is regulated principally by the Runx2 transcription factor and is further stimulated in response to 1alpha,25-dihydroxyvitamin D3 via its specific receptor (VDR). The rat OC gene promoter contains three recognition sites for Runx2 (sites A, B, and C). Mutation of sites A and B, which flank the 1alpha,25-dihydroxyvitamin D3-responsive element (VDRE), abolishes 1alpha,25-dihydroxyvitamin D3-dependent enhancement of OC transcription, indicating a tight functional relationship between the VDR and Runx2 factors. In contrast to most of the members of the nuclear receptor family, VDR possesses a very short N-terminal A/B domain, which has led to the suggestion that its N-terminal region does not contribute to transcriptional enhancement. Here, we have combined transient-overexpression, coimmunoprecipitation, in situ colocalization, chromatin immunoprecipitation, and glutathione S-transferase pull-down analyses to demonstrate that in osteoblastic cells expressing OC, VDR interacts directly with Runx2 bound to site B, which is located immediately adjacent to the VDRE. This interaction contributes significantly to 1alpha,25-dihydroxyvitamin D3-dependent enhancement of the OC promoter and requires a region located C terminal to the runt homology DNA binding domain of Runx2 and the N-terminal region of VDR. Together, our results indicate that Runx2 plays a key role in the 1alpha,25-dihydroxyvitamin D3-dependent stimulation of the OC promoter in osteoblastic cells by further stabilizing the interaction of the VDR with the VDRE. These studies demonstrate a novel mechanism for combinatorial control of bone tissue-specific gene expression. This mechanism involves the intersection of two major pathways: Runx2, a "master" transcriptional regulator of osteoblast differentiation, and 1alpha,25-dihydroxyvitamin D3, a hormone that promotes expression of genes associated with these terminally differentiated bone cells.
Assuntos
Proteínas de Ligação a DNA/metabolismo , Regulação da Expressão Gênica , Osteoblastos/fisiologia , Osteocalcina/genética , Osteocalcina/metabolismo , Receptores de Calcitriol/metabolismo , Fatores de Transcrição/metabolismo , Elemento de Resposta à Vitamina D , Animais , Sítios de Ligação , Linhagem Celular , Subunidade alfa 1 de Fator de Ligação ao Core , Proteínas de Ligação a DNA/genética , Genes Reporter , Substâncias Macromoleculares , Osteoblastos/citologia , Regiões Promotoras Genéticas , Estrutura Terciária de Proteína , Ratos , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Fator de Transcrição AP-2 , Fatores de Transcrição/genética , Transcrição Gênica , Regulação para CimaRESUMO
p300 is a multifunctional transcriptional coactivator that serves as an adapter for several transcription factors including nuclear steroid hormone receptors. p300 possesses an intrinsic histone acetyltransferase (HAT) activity that may be critical for promoting steroid-dependent transcriptional activation. In osteoblastic cells, transcription of the bone-specific osteocalcin (OC) gene is principally regulated by the Runx2/Cbfa1 transcription factor and is stimulated in response to vitamin D(3) via the vitamin D(3) receptor complex. Therefore, we addressed p300 control of basal and vitamin D(3)-enhanced activity of the OC promoter. We find that transient overexpression of p300 results in a significant dose-dependent increase of both basal and vitamin D(3)-stimulated OC gene activity. This stimulatory effect requires intact Runx2/Cbfa1 binding sites and the vitamin D-responsive element. In addition, by coimmunoprecipitation, we show that the endogenous Runx2/Cbfa1 and p300 proteins are components of the same complexes within osteoblastic cells under physiological concentrations. We also demonstrate by chromatin immunoprecipitation assays that p300, Runx2/Cbfa1, and 1alpha,25-dihydroxyvitamin D(3) receptor interact with the OC promoter in intact osteoblastic cells expressing this gene. The effect of p300 on the OC promoter is independent of its intrinsic HAT activity, as a HAT-deficient p300 mutant protein up-regulates expression and cooperates with P/CAF to the same extent as the wild-type p300. On the basis of these results, we propose that p300 interacts with key transcriptional regulators of the OC gene and bridges distal and proximal OC promoter sequences to facilitate responsiveness to vitamin D(3).
Assuntos
Acetiltransferases/metabolismo , Proteínas de Ciclo Celular/metabolismo , Regulação da Expressão Gênica/fisiologia , Proteínas de Neoplasias , Osteocalcina/genética , Receptores de Calcitriol/metabolismo , Fatores de Transcrição/metabolismo , Acetiltransferases/genética , Animais , Sítios de Ligação , Osso e Ossos/fisiologia , Proteínas de Ciclo Celular/genética , Células Cultivadas , Cromatina/imunologia , Cromatina/metabolismo , Subunidade alfa 1 de Fator de Ligação ao Core , Histona Acetiltransferases , Mutação , Osteoblastos/citologia , Osteoblastos/metabolismo , Osteocalcina/metabolismo , Testes de Precipitina , Regiões Promotoras Genéticas , Ratos , Receptores de Calcitriol/genética , Sequências Reguladoras de Ácido Nucleico , Proteínas de Saccharomyces cerevisiae/metabolismo , Especificidade da Espécie , Fatores de Transcrição/genética , Regulação para Cima , Elemento de Resposta à Vitamina D , Fatores de Transcrição de p300-CBPRESUMO
Bone-specific transcription of the osteocalcin (OC) gene is principally regulated by the Runx2 transcription factor and further stimulated in response to 1alpha,25-dihydroxy Vitamin D3 via its specific receptor (VDR). The rat OC gene promoter contains three recognition sites for Runx2 (sites A-C). Mutation of sites A and B, which flank the 1alpha,25-dihydroxy Vitamin D3-responsive element (VDRE), abolishes 1alpha,25-dihydroxy Vitamin D3-dependent enhancement of OC transcription, indicating a tight functional relationship between VDR and Runx2 factors. Additionally, the transcriptional co-activator p300 is recruited to the OC promoter by Runx2 where it up-regulates both basal and 1alpha,25-dihydroxy Vitamin D3-enhanced OC expression. Here, we present an overview of how in osteoblastic cells expressing OC, Runx2 modulates the 1alpha,25-dihydroxy Vitamin D3-dependent stimulation of the OC promoter by first recruiting transcriptional co-activators and then by further stabilizing the interaction of the VDR with the VDRE.
Assuntos
Calcitriol/farmacologia , Proteínas de Neoplasias/fisiologia , Osteoblastos/efeitos dos fármacos , Osteocalcina/genética , Fatores de Transcrição/fisiologia , Regulação para Cima/efeitos dos fármacos , Animais , Subunidade alfa 1 de Fator de Ligação ao Core , Osteoblastos/metabolismo , Ratos , Regulação para Cima/fisiologiaRESUMO
Self-renewal of human pluripotent embryonic stem cells proceeds via an abbreviated cell cycle with a shortened G(1) phase. We examined which genes are modulated in this abbreviated period and the epigenetic mechanisms that control their expression. Accelerated upregulation of genes encoding histone proteins that support DNA replication is the most prominent gene regulatory program at the G(1)/S-phase transition in pluripotent cells. Expedited expression of histone genes is mediated by a unique chromatin architecture reflected by major nuclease hypersensitive sites, atypical distribution of epigenetic histone marks, and a region devoid of histone octamers. We observed remarkable differences in chromatin structure--hypersensitivity and histone protein modifications--between human embryonic stem (hES) and normal diploid cells. Cell cycle-dependent transcription factor binding permits dynamic three-dimensional interactions between transcript initiating and processing factors at 5' and 3' regions of the gene. Thus, progression through the abbreviated G(1) phase involves cell cycle stage-specific chromatin-remodeling events and rapid assembly of subnuclear microenvironments that activate histone gene transcription to promote nucleosomal packaging of newly replicated DNA during stem cell renewal.
Assuntos
Células-Tronco Embrionárias/citologia , Epigênese Genética , Fase G1 , Histonas/genética , Células-Tronco Pluripotentes Induzidas/citologia , Fase S , Linhagem Celular , Cromatina/genética , Cromatina/metabolismo , Desoxirribonucleases/metabolismo , Células-Tronco Embrionárias/metabolismo , Histonas/metabolismo , Humanos , Células-Tronco Pluripotentes Induzidas/metabolismo , RNA Polimerase II/metabolismo , Proteínas Repressoras/metabolismo , Regulação para CimaRESUMO
BACKGROUND: Increased expression of the cyclooxygenase-2 enzyme (COX2) is one of the main characteristics of gastric cancer (GC), which is a leading cause of death in the world, particularly in Asia and South America. Although the Wnt/ß-catenin signaling pathway has been involved in the transcriptional activation of the COX2 gene, the precise mechanism modulating this response is still unknown. METHODOLOGY/PRINCIPAL FINDINGS: Here we studied the transcriptional regulation of the COX2 gene in GC cell lines and assessed whether this phenomenon is modulated by Wnt/ß-catenin signaling. We first examined the expression of COX2 mRNA in GC cells and found that there is a differential expression pattern consistent with high levels of nuclear-localized ß-catenin. Pharmacological treatment with either lithium or valproic acid and molecular induction with purified canonical Wnt3a significantly enhanced COX2 mRNA expression in a dose- and time-dependent manner. Serial deletion of a 1.6 Kbp COX2 promoter fragment and gain- or loss-of-function experiments allowed us to identify a minimal Wnt/ß-catenin responsive region consisting of 0.8 Kbp of the COX2 promoter (pCOX2-0.8), which showed maximal response in gene-reporter assays. The activity of this pCOX2-0.8 promoter region was further confirmed by site-directed mutagenesis and DNA-protein binding assays. CONCLUSIONS/SIGNIFICANCE: We conclude that the pCOX2-0.8 minimal promoter contains a novel functional T-cell factor/lymphoid enhancer factor (TCF/LEF)-response element (TBE Site II; -689/-684) that responds directly to enhanced Wnt/ß-catenin signaling and which may be important for the onset/progression of GC.
Assuntos
Ciclo-Oxigenase 2/genética , Transdução de Sinais/genética , Neoplasias Gástricas/enzimologia , Neoplasias Gástricas/genética , Transcrição Gênica , Proteínas Wnt/metabolismo , beta Catenina/metabolismo , Sítios de Ligação , Linhagem Celular Tumoral , Núcleo Celular/metabolismo , Ciclo-Oxigenase 2/metabolismo , Regulação Neoplásica da Expressão Gênica , Humanos , Regiões Promotoras Genéticas/genética , Ligação Proteica , Transporte Proteico , Neoplasias Gástricas/patologia , Regulação para Cima/genéticaRESUMO
Vitamin D serves as a principal modulator of skeletal gene transcription, thus necessitating an understanding of interfaces between the activity of this steroid hormone and regulatory cascades that are functionally linked to the regulation of skeletal genes. Physiological responsiveness requires combinatorial control where coregulatory proteins determine the specificity of biological responsiveness to physiological cues. It is becoming increasingly evident that the regulatory complexes containing the vitamin D receptor are dynamic rather than static. Temporal and spatial modifications in the composition of these complexes provide a mechanism for integrating regulatory signals to support positive or negative control through synergism and antagonism. Compartmentalization of components of vitamin D control in nuclear microenvironments supports the integration of regulatory activities, perhaps by establishing thresholds for protein activity in time frames that are consistent with the execution of regulatory signaling.
Assuntos
Núcleo Celular/metabolismo , Regulação da Expressão Gênica/fisiologia , Receptores de Calcitriol/metabolismo , Transdução de Sinais/fisiologia , Vitamina D/metabolismo , Transporte Ativo do Núcleo Celular/fisiologia , Animais , HumanosRESUMO
Changes in local chromatin structure accompany transcriptional activation of eukaryotic genes. In vivo these changes in chromatin organization can be catalyzed by ATP-dependent chromatin-remodeling complexes, such as SWI/SNF. These complexes alter the tight wrapping of DNA in the nucleosomes and can facilitate the mobilization of the histone octamer to adjacent DNA segments, leaving promoter regulatory elements exposed for transcription factor binding. To gain understanding of how the activity of SWI/SNF complexes may be modulated by the different DNA sequences within a natural promoter, we have reconstituted nucleosomes containing promoter segments of the transcriptionally active cell type-specific osteocalcin (OC) gene and determined how they affect the directional movements of the nucleosomes. Our results indicate that SWI/SNF complexes induce octamer sliding to preferential positions in the OC promoter, leading to a nucleosomal organization that resembles that described in intact cells expressing the OC gene. Our studies demonstrate that the position of the histone octamer is primarily determined by sequences within the OC promoter that include or exclude nucleosomes. We propose that these sequences are critical components of the regulatory mechanisms that mediate expression of this tissue-specific gene.
Assuntos
Montagem e Desmontagem da Cromatina/fisiologia , Proteínas Cromossômicas não Histona/química , Nucleossomos/metabolismo , Osteocalcina/genética , Osteocalcina/metabolismo , Regiões Promotoras Genéticas/fisiologia , Fatores de Transcrição/química , Animais , Linhagem Celular Tumoral , Proteínas Cromossômicas não Histona/fisiologia , Regulação da Expressão Gênica/genética , Nucleossomos/genética , Osteocalcina/biossíntese , Ratos , Fatores de Transcrição/fisiologiaRESUMO
Chromatin organization within the nuclear compartment is a fundamental mechanism to regulate the expression of eukaryotic genes. During the last decade, a number of nuclear protein complexes with the ability to remodel chromatin and regulate gene transcription have been reported. Among these complexes is the SWI/SNF family, which alters chromatin structure in an ATP-dependent manner. A considerable effort has been made to understand the molecular mechanisms by which SWI/SNF catalyzes nucleosome remodeling. However, limited attention has been dedicated to studying the role of the DNA sequence in this remodeling process. Therefore, in this minireview, we discuss the contribution of nucleosome positioning and nucleosome excluding sequences to the targeting and activity of SWI/SNF complexes. This discussion includes results from our group using the rat osteocalcin gene promoter as a model. Based on these results, we postulate a model for chromatin remodeling and transcriptional activation of this gene in osteoblastic cells.
Assuntos
Sequência de Bases , Montagem e Desmontagem da Cromatina , Proteínas Cromossômicas não Histona/metabolismo , DNA , Nucleossomos , Fatores de Transcrição/metabolismo , Animais , DNA/genética , DNA/metabolismo , Modelos Genéticos , Nucleossomos/metabolismo , Nucleossomos/ultraestrutura , Osteocalcina/genética , Regiões Promotoras Genéticas , Transcrição GênicaRESUMO
Tissue-specific activation of the osteocalcin (OC) gene is associated with changes in chromatin structure at the promoter region. Two nuclease-hypersensitive sites span the key regulatory elements that control basal tissue-specific and vitamin D3-enhanced OC gene transcription. To gain understanding of the molecular mechanisms involved in chromatin remodeling of the OC gene, we have examined the requirement for SWI/SNF activity. We inducibly expressed an ATPase-defective BRG1 catalytic subunit that forms inactive SWI/SNF complexes that bind to the OC promoter. This interaction results in inhibition of both basal and vitamin D3-enhanced OC gene transcription and a marked decrease in nuclease hypersensitivity. We find that SWI/SNF is recruited to the OC promoter via the transcription factor CCAAT/enhancer-binding protein beta, which together with Runx2 forms a stable complex to facilitate RNA polymerase II binding and activation of OC gene transcription. Together, our results indicate that the SWI/SNF complex is a key regulator of the chromatin-remodeling events that promote tissue-specific transcription in osteoblasts.