Ryouji Fujii

Regulation of Lef-mediated Transcription and p53-dependent Pathway by Associating β-Catenin with CBP/p300

CBP and its homologue p300 play significant roles in cell differentiation, cell cycle, and anti-oncogenesis. We demonstrated that β-catenin, recently known as a potent oncogene, and CBP/p300 are associated through its CH3 region, which is a primary target of adenoviral oncoprotein E1A and various nuclear proteins, such as p53, cyclin E, and AP-1, and both are colocalized in the nuclear bodies. CBP/p300 potentiated Lef-mediated transactivation of β-catenin, and E1A, a potent inhibitor of CBP/p300, repressed its transactivation. Furthermore, overexpression of stable β-catenin mutant competitively suppressed the p53-dependent pathway. These may be a key mechanism of β-catenin involved in oncogenic events underlying disruption of tumor suppressor function through CBP/p300.

Dual roles of RNA helicase A in CREB-dependent transcription.

ABSTRACT RNA helicase A (RHA) is a member of an ATPase/DNA and RNA helicase family and is a homologue of Drosophila maleless protein (MLE), which regulates X-linked gene expression. RHA is also a component of holo-RNA polymerase II (Pol II) complexes and recruits Pol II to the CREB binding protein (CBP). The ATPase and/or helicase activity of RHA is required for CREB-dependent transcription. To further understand the role of RHA on gene expression, we have identified a 50-amino-acid transactivation domain that interacts with Pol II and termed it the minimal transactivation domain (MTAD). The protein sequence of this region contains six hydrophobic residues and is unique to RHA homologues and well conserved. A mutant with this region deleted from full-length RHA decreased transcriptional activity in CREB-dependent transcription. In addition, mutational analyses revealed that several tryptophan residues in MTAD are important for the interaction with Pol II and transactivation. These mutants had ATP binding and ATPase activities comparable to those of wild-type RHA. A mutant lacking ATP binding activity was still able to interact with Pol II. In CREB-dependent transcription, the transcriptional activity of each of these mutants was less than that of wild-type RHA. The activity of the double mutant lacking both functions was significantly lower than that of each mutant alone, and the double mutant had a dominant negative effect. These results suggest that RHA could independently regulate CREB-dependent transcription either through recruitment of Pol II or by ATP-dependent mechanisms.

Antithetic Effects of MBD2a on Gene Regulation

ABSTRACT DNA methylation is essential for epigenetic gene regulation during development. The cyclic AMP (cAMP)-responsive element (CRE) is found in the promoter of many cAMP-regulated genes and plays important roles in their gene expression. Methylation occurs on the CRE site and results in transcriptional repression via a direct mechanism, that is, prevention by the methyl group of binding of the cAMP-responsive factor CREB to this site. A recent study indicated that the nucleosome is also important in repressing transcription. In this study, we investigated the regulation of transcriptional repression on methylated CRE. We focused on methyl-CpG binding domain protein 2 (MBD2). MBD2 consists of two forms, MBD2a and MBD2b, the latter lacking the N-terminal extension of MBD2a. Unexpectedly, we found that MBD2a, but not MBD2b, promoted activation of the unmethylated cAMP-responsive genes. An in vivo binding assay revealed that MBD2a selectively interacted with RNA helicase A (RHA), a component of CREB transcriptional coactivator complexes. MBD2a and RHA cooperatively enhanced CREB-dependent gene expression. Interestingly, coimmunoprecipitation assays demonstrated that MBD2a binding to RHA was not associated with histone deacetylase 1. Our results indicate a novel role for MBD2a in gene regulation.

Isolation and partial characterization of carotenoid underproducing and overproducing mutants from an extremely thermophilic Thermus thermophilus HB27

Abstract Twenty-two carotenoid underproducing and thirteen overproducing mutants were obtained from Thermus thermophilus HB27. The strain HB27 was found to produce at least seven colored carotenoids, believed to be identical to those produced by Thermus aquaticus YT1. Based on the results of the genetic analyses performed on twelve carotenoid underproducing mutants, they were classified into three groups; groups 1, 2 and 3. No colored carotenoid was extracted from the cells of mutants belonging to groups 2 and 3, although the accumulation of phytoene, a colorless carotenoid, was observed in group 2 strains. Group 1 was subdivided into groups 1-a and 1-b, where 1-a strains produced neither colored carotenoids nor phytoene and 1-b strains produced two polar colored carotenoids. All of the overproducing mutants produced about twelve times as much seven colored carotenoid mixtures as the parental strain. The mutation loci among all the overproducing mutants were very close to one another, possibly in the same gene. Carotenoid overproducing mutants showed an extensive resistancy to UV-irradiation and showed poorer growth at higher temperatures. Carotenoid underproducing mutants were slightly more UV-sensitive but they grew almost normally at higher temperatures. These results suggest that carotenoids are secondary metabolites which are not essential for growth of T. thermophilus .

Overproduction of carotenoids in Thermus thermophilus

Phytoene synthase encoded by the crtB gene is one of the rate-limiting enzymes for carotenoid production in Thermus thermophilus. We introduced a multicopy recombinant plasmid, pCOP1, in which the Thermus crtB gene was cloned, into carotenoid overproducing mutants of T. thermophilus. The overproducing mutants carrying a pCOP1 produced about twenty times as much carotenoids as the parental strain did.

Cell type-dependent transactivation or repression of mesoderm-restricted basic helix-loop-helix protein, POD-1/Capsulin.

A family of basic-helix-loop-helix (bHLH) nuclear factors play important roles in controlling cell growth and differentiation as critical regulatory components in transcription. Here we describe molecular characterization of mesoderm-specific bHLH protein, POD-1/Capsulin. Transactivation property of POD-1/Capsulin was analyzed by the Gal4 fusion system in six mammalian cell lines. The results indicated that an activation property was shown in HT1080 and HeLa cells, but a repression activity in HepG2 cells. Mapping analysis for the transactivation and repression activities revealed that the C-terminal domain of POD-1/Capsulin is essential for the transactivation and both the N-terminal and C-terminal domains are contributed to the repression activities. Furthermore, in order to identify possible interactants of the POD-1/Capsulin, we performed yeast two-hybrid screen in a human kidney cDNA library, and identified a class A bHLH protein, ITF-2 as potential heterodimeric partner of the bHLH protein.