Biomedical subjects

Kenneth S Zaret

Publications and source records attributed to Kenneth S Zaret.

22 records · Page 2Linked to original sources

PubMed2003

The CBP bromodomain and nucleosome targeting are required for Zta-directed nucleosome acetylation and transcription activation.

The Epstein-Barr virus (EBV)-encoded lytic activator Zta is a bZIP protein that can stimulate nucleosomal histone acetyltransferase (HAT) activity of the CREB binding protein (CBP) in vitro. We now show that deletion of the CBP bromo- and C/H3 domains eliminates stimulation of nucleosomal HAT activity in vitro and transcriptional coactivation by Zta in transfected cells. In contrast, acetylation of free histones was not affected by the addition of Zta or by deletions in the bromo or C/H3 domain of CBP. Zta stimulated acetylation of oligonucleosomes assembled on supercoiled DNA and dinucleosomes assembled on linear DNA, but Zta-stimulated acetylation was significantly reduced for mononucleosomes. Western blotting and amino-terminal protein sequencing indicated that all lysine residues in the H3 and H4 amino-terminal tails were acetylated by CBP and enhanced by the addition of Zta. Histone acetylation was also dependent upon the Zta basic DNA binding domain, which could not be substituted with the homologous basic region of c-Fos, indicating specificity in the bZIP domain nucleosome binding function. Finally, we show that Zta and CBP colocalize to viral immediate-early promoters in vivo and that overexpression of Zta leads to a robust increase in H3 and H4 acetylation at various regions of the EBV genome in vivo. Furthermore, deletion of the CBP bromodomain reduced stable CBP-Zta complex formation and histone acetylation at Zta-responsive viral promoters in vivo. These results suggest that activator- and bromodomain-dependent targeting to oligonucleosomal chromatin is required for stable promoter-bound complex formation and transcription activity.

Acetylation↗

PubMed2002

Opening of compacted chromatin by early developmental transcription factors HNF3 (FoxA) and GATA-4.

The transcription factors HNF3 (FoxA) and GATA-4 are the earliest known to bind the albumin gene enhancer in liver precursor cells in embryos. To understand how they access sites in silent chromatin, we assembled nucleosome arrays containing albumin enhancer sequences and compacted them with linker histone. HNF3 and GATA-4, but not NF-1, C/EBP, and GAL4-AH, bound their sites in compacted chromatin and opened the local nucleosomal domain in the absence of ATP-dependent enzymes. The ability of HNF3 to open chromatin is mediated by a high affinity DNA binding site and by the C-terminal domain of the protein, which binds histones H3 and H4. Thus, factors that potentiate transcription in development are inherently capable of initiating chromatin opening events.

Amino Acid Motifs↗

PubMed2002

Regulatory phases of early liver development: paradigms of organogenesis.

Genetic analysis, embryonic tissue explantation and in vivo chromatin studies have together identified the distinct regulatory steps that are necessary for the development of endoderm into a bud of liver tissue and, subsequently, into an organ. In this review, I discuss the acquisition of competence to express liver-specific genes by the endoderm, the control of early hepatic growth, the coordination of hepatic and vascular development and the cell differentiation that is necessary to generate a functioning liver. The regulatory mechanisms that underlie these phases are common to the development of many organ systems and might be recapitulated or disrupted during stem-cell differentiation and adult tissue pathogenesis.

Animals↗

PubMed2002

Prenylcysteine carboxylmethyltransferase is essential for the earliest stages of liver development in mice.

BACKGROUND & AIMS: Liver development, regeneration, and oncogenesis involve signaling events mediated by a number of proteins, such as ras and the related small guanosine triphosphatases. Many of these signaling proteins carry unique CAAX motifs, which are processed by prenylcysteine carboxylmethyltransferase (PCCMT), among several other enzymes. We investigated the function of Pccmt during mouse liver development to better understand the embryonic lethality of the null mutation. METHODS: Generation of Pccmt-null mice by embryonic stem cell technology, molecular and histologic analysis of Pccmt-null embryos, and foregut endoderm cultures. RESULTS: Pccmt-null embryos die in utero with severe anemia and extensive apoptosis at embryonic day 10.5. We show that deletion of Pccmt leads to a dramatic delay in albumin induction, an early and definitive marker for hepatocyte development. In tissue explant cultures supplemented with fibroblast growth factor (FGF), albumin induction remained impaired. We found that hepatocyte precursors in Pccmt-null embryos failed to invade the septum transversum, resulting in liver agenesis. CONCLUSIONS: PCCMT is essential for several stages of hepatic induction, consistent with its role in modifying proteins required to transduce signals, such as FGF, that have been shown to promote liver specification and early growth.

Anemia↗