Epigenetic control is critical for regulation of gene transcription in mammalian cells. Among the... more Epigenetic control is critical for regulation of gene transcription in mammalian cells. Among the most important epigenetic mechanisms are those associated with post-translational modifications of chromosomal histone proteins, which modulate chromatin structure and increased accessibility of promoter regulatory elements for competency to support transcription. A critical histone mark is trimethylation of histone H3 at lysine residue 27 (H3K27me3) that is mediated by Ezh2, the catalytic subunit of the Polycomb Group Complex PRC2 to repress transcription. Treatment of cells with the active vitamin D metabolite 1,25(OH) 2 D 3 , results in transcriptional activation of the CYP24A1 gene, which encodes a 24-hydroxylase enzyme that is essential for physiological control of vitamin D3 levels. We report that the Ezh2-mediated deposition of H3K27me3 at the CYP24A1 gene promoter is a requisite regulatory component during transcriptional silencing of this gene in osteoblastic cells in the absence of 1,25(OH) 2 D 3. 1,25(OH) 2 D 3 dependent transcriptional activation of the CYP24A1 gene is accompanied by a rapid release of Ezh2 from the promoter, together with binding of the H3K27me3-specific demethylase Utx/Kdm6a and thereby subsequent erasing of the H3K27me3 mark. Importantly, we find that these changes in H3K27me3 enrichment at the CYP24A1 gene promoter are highly dynamic, as this modification is rapidly reacquired following withdrawal of 1,25(OH) 2 D 3 .
In bone cells vitamin D dependent regulation of gene expression principally occurs through modula... more In bone cells vitamin D dependent regulation of gene expression principally occurs through modulation of gene transcription. Binding of the active vitamin D metabolite 1,25(OH) 2 D 3 to the vitamin D receptor (VDR) induces conformational changes in its C-terminal domain enabling competency for interaction with physiologically relevant co-activators, including SRC-1. Consequently, regulatory complexes can be assembled that support intrinsic enzymatic activities with competency to post-translationally modify chromatin histones at target genomic sequences to epigenetically alter transcription. Here we examine specific transitions in representation and/or enrichment of epigenetic histone marks during 1,25(OH) 2 D 3 mediated upregulation of CYP24A1 gene expression in osteoblastic cells. This gene encodes the 24-Hydroxylase enzyme, essential for biological control of vitamin D levels. We demonstrate that as the CYP24A1 gene promoter remains transcriptionally silent, there is enrichment of H4R3me2s together with its "writing" enzyme PRMT5 and decreased abundance of the H3ac/H4ac, H3R17me2a, and H4R3me2a marks as well as of their corresponding "writers". Exposure of osteoblastic cells to 1,25(OH) 2 D 3 stimulates the recruitment of a VDR/SRC-1 containing complex to the CYP24A1 promoter to mediate increased H3/H4 acetylation. VDR/SRC-1 binding occurs concomitant with the release of PRMT5 and the recruitment of the arginine methyltransferases CARM1 and PRMT1 to catalyze the deposition of the H3R17me2a and H4R3me2a marks, respectively. Our results indicate that these dynamic transitions of histone marks at the CYP24A1 promoter, provide a "chromatin
Renal transplantation (RTx) is an effective therapy to improve clinical outcomes in paediatric pa... more Renal transplantation (RTx) is an effective therapy to improve clinical outcomes in paediatric patients with terminal chronic kidney disease. However, chronic immunosuppression with glucocorticoids (GC) reduces bone growth and mineral density. The mechanisms causing GC-induced growth impairment have not been fully clarified. Fibroblast growth factor 23 (FGF23) is a peptide hormone that regulates phosphate homeostasis and bone growth. In pathological conditions, FGF23 excess or abnormal FGF receptors (FGFR) activity leads to bone growth impairment. Experimental data indicates that FGF23 expression is induced by chronic GC exposure. Therefore, we hypothesize that GC impairs bone growth by increasing FGF23 expression, which has direct effects on bone growth plate. In a post-hoc analysis of a multicentric randomized clinical trial of prepubertal RTx children treated with early GC withdrawal or chronic GC treatment, we observed that GC withdrawal was associated with improvement in longitudinal growth and bone mineral This article is protected by copyright. All rights reserved. Accepted Article density, and lower plasma FGF23 levels as compared to chronic GC group. In prepubertal rats, GC-induced bone growth retardation correlated with increased plasma FGF23 and bone FGF23 expression. Additionally, GC treatment decreased FGFR1 expression while increased FGFR3 expression in mouse tibiae explants. Blockage of FGF23 receptors using a pan-FGFR antagonist (PD173074), C-terminal FGF23 (FGF23 180-205) which blocks the binding of FGF23 with FGFR-Klotho complex or a specific FGFR3 antagonist (P3), prevented GC-induced growth impairment in vitro. Finally, local administration of PD173074 into tibiae growth plate of GC-treated rats ameliorated cartilage growth impairment. These results show that GC treatment partially reduces longitudinal bone growth via upregulation of FGF23 and FGFR3 expression, thus suggesting that the FGF23/Klotho/FGFR3 axis at the growth plate could be a potential therapeutic target for the management of GC-induced growth impairment in children.
The Journal of Steroid Biochemistry and Molecular Biology, 2010
The architectural organization of the genome and regulatory proteins within the nucleus supports ... more The architectural organization of the genome and regulatory proteins within the nucleus supports gene expression in a physiologically-regulated manner. In osteoblastic cells ligand activation induces a nuclear punctate distribution of the 1α,25-dihydroxy vitamin D3 (1α,25(OH) 2 D 3) receptor (VDR) and promotes its interaction with transcriptional coactivators such as SRC-1, NCoA-62/Skip, and DRIP205. Here, we discuss evidence demonstrating that in osteoblastic cells VDR binds to the nuclear matrix fraction in a 1α,25(OH) 2 D 3-dependent manner. This interaction occurs rapidly after exposure to 1α,25(OH) 2 D 3 and does not require a functional VDR DNA binding domain. The nuclear matrix-bound VDR molecules colocalize with the also nuclear matrix-associated coactivator DRIP205. We propose a model where the rapid association of VDR with the nuclear matrix fraction represents an event that follows 1α,25(OH) 2 D 3-dependent nuclear localization of VDR, but that precedes 1α,25(OH) 2 D 3-dependent transcriptional upregulation at target genes.
El objetivo esta investigación es caracterizar el perfil de ingreso de los estudiantes al bachill... more El objetivo esta investigación es caracterizar el perfil de ingreso de los estudiantes al bachillerato en ciencias de la Universidad Andrés Bello (UNAB) entre los años 2016 y 2020, dentro del contexto nacional chileno, utilizando las bases de datos del Sistema Único de Admisión, del Servicio de Información de Educación Superior y del Consejo Nacional de Educación chileno. Los resultados muestran que a nivel nacional existen bachilleratos generales como también específicos para una carrera determinada, con duraciones de dos a cuatro semestres. En el caso de UNAB, el ingreso es mayoritariamente femenino. Los puntajes de selección universitaria con los que ingresan los estudiantes al programa de la UNAB se distribuyen entre los 450 y 700 puntos, observándose un aumento en los puntajes más altos en los últimos años. Se concluye que el bachillerato se ha transformado en una vía alternativa de ingreso a carreras con mayor demanda, siendo una alternativa propedéutica para los jóvenes con puntajes menores.
Epigenetic control is critical for regulation of gene transcription in mammalian cells. Among the... more Epigenetic control is critical for regulation of gene transcription in mammalian cells. Among the most important epigenetic mechanisms are those associated with post-translational modifications of chromosomal histone proteins, which modulate chromatin structure and increased accessibility of promoter regulatory elements for competency to support transcription. A critical histone mark is trimethylation of histone H3 at lysine residue 27 (H3K27me3) that is mediated by Ezh2, the catalytic subunit of the Polycomb Group Complex PRC2 to repress transcription. Treatment of cells with the active vitamin D metabolite 1,25(OH) 2 D 3 , results in transcriptional activation of the CYP24A1 gene, which encodes a 24-hydroxylase enzyme that is essential for physiological control of vitamin D3 levels. We report that the Ezh2-mediated deposition of H3K27me3 at the CYP24A1 gene promoter is a requisite regulatory component during transcriptional silencing of this gene in osteoblastic cells in the absence of 1,25(OH) 2 D 3. 1,25(OH) 2 D 3 dependent transcriptional activation of the CYP24A1 gene is accompanied by a rapid release of Ezh2 from the promoter, together with binding of the H3K27me3-specific demethylase Utx/Kdm6a and thereby subsequent erasing of the H3K27me3 mark. Importantly, we find that these changes in H3K27me3 enrichment at the CYP24A1 gene promoter are highly dynamic, as this modification is rapidly reacquired following withdrawal of 1,25(OH) 2 D 3 .
In bone cells vitamin D dependent regulation of gene expression principally occurs through modula... more In bone cells vitamin D dependent regulation of gene expression principally occurs through modulation of gene transcription. Binding of the active vitamin D metabolite 1,25(OH) 2 D 3 to the vitamin D receptor (VDR) induces conformational changes in its C-terminal domain enabling competency for interaction with physiologically relevant co-activators, including SRC-1. Consequently, regulatory complexes can be assembled that support intrinsic enzymatic activities with competency to post-translationally modify chromatin histones at target genomic sequences to epigenetically alter transcription. Here we examine specific transitions in representation and/or enrichment of epigenetic histone marks during 1,25(OH) 2 D 3 mediated upregulation of CYP24A1 gene expression in osteoblastic cells. This gene encodes the 24-Hydroxylase enzyme, essential for biological control of vitamin D levels. We demonstrate that as the CYP24A1 gene promoter remains transcriptionally silent, there is enrichment of H4R3me2s together with its "writing" enzyme PRMT5 and decreased abundance of the H3ac/H4ac, H3R17me2a, and H4R3me2a marks as well as of their corresponding "writers". Exposure of osteoblastic cells to 1,25(OH) 2 D 3 stimulates the recruitment of a VDR/SRC-1 containing complex to the CYP24A1 promoter to mediate increased H3/H4 acetylation. VDR/SRC-1 binding occurs concomitant with the release of PRMT5 and the recruitment of the arginine methyltransferases CARM1 and PRMT1 to catalyze the deposition of the H3R17me2a and H4R3me2a marks, respectively. Our results indicate that these dynamic transitions of histone marks at the CYP24A1 promoter, provide a "chromatin
Renal transplantation (RTx) is an effective therapy to improve clinical outcomes in paediatric pa... more Renal transplantation (RTx) is an effective therapy to improve clinical outcomes in paediatric patients with terminal chronic kidney disease. However, chronic immunosuppression with glucocorticoids (GC) reduces bone growth and mineral density. The mechanisms causing GC-induced growth impairment have not been fully clarified. Fibroblast growth factor 23 (FGF23) is a peptide hormone that regulates phosphate homeostasis and bone growth. In pathological conditions, FGF23 excess or abnormal FGF receptors (FGFR) activity leads to bone growth impairment. Experimental data indicates that FGF23 expression is induced by chronic GC exposure. Therefore, we hypothesize that GC impairs bone growth by increasing FGF23 expression, which has direct effects on bone growth plate. In a post-hoc analysis of a multicentric randomized clinical trial of prepubertal RTx children treated with early GC withdrawal or chronic GC treatment, we observed that GC withdrawal was associated with improvement in longitudinal growth and bone mineral This article is protected by copyright. All rights reserved. Accepted Article density, and lower plasma FGF23 levels as compared to chronic GC group. In prepubertal rats, GC-induced bone growth retardation correlated with increased plasma FGF23 and bone FGF23 expression. Additionally, GC treatment decreased FGFR1 expression while increased FGFR3 expression in mouse tibiae explants. Blockage of FGF23 receptors using a pan-FGFR antagonist (PD173074), C-terminal FGF23 (FGF23 180-205) which blocks the binding of FGF23 with FGFR-Klotho complex or a specific FGFR3 antagonist (P3), prevented GC-induced growth impairment in vitro. Finally, local administration of PD173074 into tibiae growth plate of GC-treated rats ameliorated cartilage growth impairment. These results show that GC treatment partially reduces longitudinal bone growth via upregulation of FGF23 and FGFR3 expression, thus suggesting that the FGF23/Klotho/FGFR3 axis at the growth plate could be a potential therapeutic target for the management of GC-induced growth impairment in children.
The Journal of Steroid Biochemistry and Molecular Biology, 2010
The architectural organization of the genome and regulatory proteins within the nucleus supports ... more The architectural organization of the genome and regulatory proteins within the nucleus supports gene expression in a physiologically-regulated manner. In osteoblastic cells ligand activation induces a nuclear punctate distribution of the 1α,25-dihydroxy vitamin D3 (1α,25(OH) 2 D 3) receptor (VDR) and promotes its interaction with transcriptional coactivators such as SRC-1, NCoA-62/Skip, and DRIP205. Here, we discuss evidence demonstrating that in osteoblastic cells VDR binds to the nuclear matrix fraction in a 1α,25(OH) 2 D 3-dependent manner. This interaction occurs rapidly after exposure to 1α,25(OH) 2 D 3 and does not require a functional VDR DNA binding domain. The nuclear matrix-bound VDR molecules colocalize with the also nuclear matrix-associated coactivator DRIP205. We propose a model where the rapid association of VDR with the nuclear matrix fraction represents an event that follows 1α,25(OH) 2 D 3-dependent nuclear localization of VDR, but that precedes 1α,25(OH) 2 D 3-dependent transcriptional upregulation at target genes.
El objetivo esta investigación es caracterizar el perfil de ingreso de los estudiantes al bachill... more El objetivo esta investigación es caracterizar el perfil de ingreso de los estudiantes al bachillerato en ciencias de la Universidad Andrés Bello (UNAB) entre los años 2016 y 2020, dentro del contexto nacional chileno, utilizando las bases de datos del Sistema Único de Admisión, del Servicio de Información de Educación Superior y del Consejo Nacional de Educación chileno. Los resultados muestran que a nivel nacional existen bachilleratos generales como también específicos para una carrera determinada, con duraciones de dos a cuatro semestres. En el caso de UNAB, el ingreso es mayoritariamente femenino. Los puntajes de selección universitaria con los que ingresan los estudiantes al programa de la UNAB se distribuyen entre los 450 y 700 puntos, observándose un aumento en los puntajes más altos en los últimos años. Se concluye que el bachillerato se ha transformado en una vía alternativa de ingreso a carreras con mayor demanda, siendo una alternativa propedéutica para los jóvenes con puntajes menores.
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