Biomedical subjects

Jiali Shen

Publications and source records attributed to Jiali Shen.

7 recordsLinked to original sources

PubMed2006

Identification of phosphatases for Smad in the BMP/DPP pathway.

Phosphorylation of the SSXS motif of Smads is critical in activating the transforming growth factor beta (TGF-beta) and bone morphogenetic protein (BMP) pathways. However, the phosphatase(s) involved in dephosphorylating and hence inactivating Smads remained elusive. Through RNA interference (RNAi)-based screening of serine/threonine phosphatases in Drosophila S2 cells, we identified pyruvate dehydrogenase phosphatase (PDP) to be required for dephosphorylation of Mothers against Decapentaplegic (MAD), a Drosophila Smad. Biochemical and genetic evidence suggest that PDP directly dephosphorylates MAD and inhibits signal transduction of Decapentaplegic (DPP). We show that the mammalian PDPs are important in dephosphorylation of BMP-activated Smad1 but not TGF-beta-activated Smad2 or Smad3. Thus, PDPs specifically inactivate Smads in the BMP/DPP pathway.

Animals↗

PubMed2003

Intranuclear trafficking of transcription factors: Requirements for vitamin D-mediated biological control of gene expression.

The architecturally associated subnuclear organization of nucleic acids and cognate regulatory factors suggest functional interrelationships between nuclear structure and gene expression. Mechanisms that contribute to the spatial distribution of transcription factors within the three-dimensional context of nuclear architecture control the sorting of regulatory information as well as the assembly and activities of sites within the nucleus that support gene expression. Vitamin D control of gene expression serves as a paradigm for experimentally addressing mechanisms that govern the intranuclear targeting of regulatory factors to nuclear domains where transcription of developmental and tissue-specific genes occur. We will present an overview of molecular, cellular, genetic, and biochemical approaches that provide insight into the trafficking of regulatory factors that mediate vitamin D control of gene expression to transcriptionally active subnuclear sites. Examples will be presented that suggest modifications in the intranuclear targeting of transcription factors abrogate competency for vitamin D control of skeletal gene expression during development and fidelity of gene expression in tumor cells.

Animals↗

PubMed2003

Transcriptional induction of the osteocalcin gene during osteoblast differentiation involves acetylation of histones h3 and h4.

The remodeling of chromatin is required for tissue-specific gene activation to permit interactions of transcription factors and coregulators with their cognate elements. Here, we investigate the chromatin-mediated mechanisms by which the bone-specific osteocalcin (OC) gene is transcriptionally activated during cessation of cell growth in ROS 17/2.8 osteosarcoma cells and during normal osteoblast differentiation. Acetylation of histones H3 and H4 at the OC gene promoter was assayed during the proliferative and postproliferative stages of cell growth by using chromatin immunoprecipitation assays with antibodies that recognize different acetylated forms of histones H3 or H4. The results show that the promoter and coding regions of the OC gene contain very low levels of acetylated histones H3 and H4 during the proliferative period of osteoblast differentiation when the OC gene is inactive. Active expression of the OC gene in mature osteoblasts and confluent ROS 17/2.8 cells is functionally linked to preferential acetylation of histone H4 and, to a lesser extent, to acetylation of histone H3. Histone acetylation at the loci for RUNX2 (CBFA1), alkaline phosphatase, bone sialoprotein, osteopontin, and the cell growth regulator p21, which are expressed throughout osteoblast differentiation, is not altered postproliferatively. We conclude that acetylation of histones H3 and H4 is functionally coupled to the chromatin remodeling events that mediate the developmental induction of OC gene transcription in bone cells.

Acetylation↗

PubMed2003

Nuclear microenvironments support physiological control of gene expression.

There is growing recognition that the organization of nucleic acids and regulatory proteins is functionally linked to the assembly, localization and activity of gene regulatory machinery. Cellular, molecular, biochemical and in-vivo genetic evidence support an obligatory relationship between nuclear microenvironments where regulatory complexes reside and fidelity of transcriptional control. Perturbations in mechanisms governing the intranuclear trafficking of transcription factors and the temporal/spatial organization of regulatory proteins within the nucleus occur with compromised gene expression that abrogates skeletal development and mediates leukemogenesis.

Cell Nucleus↗

PubMed2003

Runx2/Cbfa1 functions: diverse regulation of gene transcription by chromatin remodeling and co-regulatory protein interactions.

Development of the osteoblast phenotype requires transcriptional mechanisms that regulate induction of a program of temporally expressed genes. Key components of gene activation, repression, and responsiveness to physiologic mediators require remodeling of the chromatin structure of a gene that renders promoter elements competent for the assembly of macromolecular transcriptional complexes. Here we review evidence that the Runx transcription factors support tissue-specific gene expression and bone formation by contributing to promoter structure, chromatin remodeling, and the integration of independent signaling pathways. In addition, we discuss the role of Runx2 in both activation and negative regulation of gene promoters (osteocalcin, bone sialoprotein, and Runx2/Cbfa1) in relation to the interaction of Runx with co-regulatory proteins in distinct subnuclear foci. The modifications in chromatin organization and transcription of the osteocalcin gene that are influenced by the activities of Runx2/Cbfa1 mediated by interacting proteins (YAP, TLE, SMAD, C/EBP) are emphasized. These functional properties of Runx2 provide novel insights into the requirements for multiple levels of transcriptional control within the context of nuclear architecture to support the convergence of regulatory signals that control tissue-specific gene expression.

Animals↗

PubMed2002

Histone acetylation in vivo at the osteocalcin locus is functionally linked to vitamin D-dependent, bone tissue-specific transcription.

The accessibility of regulatory elements in chromatin represents a principal rate-limiting parameter of gene transcription and is modulated by enzymatic transcriptional co-factors that alter the topology of chromatin or covalently modify histones (e.g. by acetylation). The bone-specific activation and 1,25-dihydroxyvitamin D(3) enhancement of osteocalcin (OC) gene transcription are both functionally linked to modifications in nucleosomal organization. The initiation of tissue-specific basal transcription is accompanied by the induction of two DNase I hypersensitive sites, and this chromatin remodeling event requires binding of the key osteogenic factor RUNX2/CBFA1 to the OC promoter. Here, we analyzed the acetylation status of histones H3 and H4 when the OC gene is active (in osteoblastic ROS17/2.8 cells) or inactive (in fibroblastic ROS24/1 cells) using chromatin immunoprecipitation assays. We find that acetylated histone H3 and H4 proteins are associated with the OC promoter only when the gene is transcriptionally active and that the acetylation status is relatively uniform across the OC locus under basal conditions. Acetylation of H4 at the OC gene is selectively increased following vitamin D(3) enhancement of OC transcription, with the most prominent changes occurring in the region between the vitamin D(3) enhancer and basal promoter. Thus, our results suggest functional linkage of H3 and H4 acetylation in specific regions of the OC promoter to chromatin remodeling that accompanies tissue-specific transcriptional activation and vitamin D enhancement of OC gene expression. These findings provide mechanistic insights into bone-specific gene activation within a native genomic context in response to steroid hormone-related regulatory cues.

Acetylation↗

PubMedDate not supplied

Intranuclear organization of RUNX transcriptional regulatory machinery in biological control of skeletogenesis and cancer.

RUNX (AML/CBFA/PEBP2) transcription factors serve as paradigms for obligatory relationships between nuclear structure and physiological control of phenotypic gene expression. The RUNX proteins contribute to tissue restricted transcription by sequence-specific binding to promoter elements of target genes and serving as scaffolds for the assembly of coregulatory complexes that mediate biochemical and architectural control of activity. We will present an overview of approaches we are pursuing to address: (1) the involvement of RUNX proteins in governing competency for protein/DNA and protein/protein interactions at promoter regulatory sequences; (2) the recruitment of RUNX factors to subnuclear sites where the machinery for expression or repression of target genes is organized; and (3) the trafficking and integration of regulatory signals that control RUNX-mediated transcription.

Animals↗