Functional regulation of the DNA damage-recognition factor DDB2 by ubiquitination and interaction with xeroderma pigmentosum group C protein

In mammalian nucleotide excision repair, the DDB1–DDB2 complex recognizes UV-induced DNA photolesions and facilitates recruitment of the XPC complex. Upon binding to damaged DNA, the Cullin 4 ubiquitin ligase associated with DDB1–DDB2 is activated and ubiquitinates DDB2 and XPC. The structurally disordered N-terminal tail of DDB2 contains seven lysines identified as major sites for ubiquitination that target the protein for proteasomal degradation; however, the precise biological functions of these modifications remained unknown. By exogenous expression of mutant DDB2 proteins in normal human fibroblasts, here we show that the N-terminal tail of DDB2 is involved in regulation of cellular responses to UV. By striking contrast with behaviors of exogenous DDB2, the endogenous DDB2 protein was stabilized even after UV irradiation as a function of the XPC expression level. Furthermore, XPC competitively suppressed ubiquitination of DDB2 in vitro, and this effect was significantly promoted by centrin-2, which augments the DNA damage-recognition activity of XPC. Based on these findings, we propose that in cells exposed to UV, DDB2 is protected by XPC from ubiquitination and degradation in a stochastic manner; thus XPC allows DDB2 to initiate multiple rounds of repair events, thereby contributing to the persistence of cellular DNA repair capacity.     

Development of a new class of benzoylpyrrole-based PPARα/γ activators

Starting with a subtle blood glucose-lowering effect of a TGF-β inhibitor, we designed and synthesized a series of benzoylpyrrole-based carboxylic acids as PPARs activators. Among these compounds, 10sNa exhibited favorable blood glucose-lowering effect without body weight gain. We assume that the beneficial effect of 10sNa is attributed to not only its compound PPARα agonistic activity but also its PPARγ partial agonistic activity.     

Deposition gene transfection using bioconjugates of DNA and thermoresponsive cationic homopolymer

A poly(N,N-dimethylaminoethylmethacrylate) (PDMAEMA) homopolymer with both thermoresponsive and cationic characteristics was applied to a vector for use in deposition transfection. PDMAEMA with a molecular weight of 2.5 × 10(5) g mol(-1) was synthesized by photoinduced radical polymerization. Polyplexes approximately 750 nm in size were formed by mixing PDMAEMA with luciferase-encoding plasmid DNA. The polyplexes had a lower critical solution temperature (LCST) of approximately 30 °C. In addition, they exhibited excellent adsorption and durability on a polystyrene surface, as confirmed by a surface chemical compositional analysis. When HeLa cells and primary cells were cultured on a substrate coated with the polyplexes, high transgene expression and cell viability of more than 90% were obtained at low charge ratios (PDMAEMA/plasmid DNA ratio) ranging from 2 to 8. In addition, transgene expression was sustained for over 2 weeks post-transfection whereas decreased expression was observed 5 days post-transfection when the conventional solution-mediated transfection method was used. Thus, high and sustained transgene expression as well as high cell viability can be realized by using small amounts of PDMAEMA as a deposition transfection material.     

Mechanism of Photoregulated Carotenogenesis in Rhodotorula minuta IV. Effect of Light on the Production of Ergosterol and Phytoene and on the Composition of Carotenoid Pigments

The effect of light on the production of ergosterol and phytoeneand on the composition of carotenoids in Rhodotorula minutawas studied to determine which part of the pathway of carotenoidsynthesis regulated by light. The ergosterol content in the cells was in the range of 3.4–3.6mg/g dry cells regardless of the presence or absence of illuminationand the light intensity. The phytoene production in the cellswas markedly stimulated by light and was dependent on the lightintensity according to the amount of carotenoid pigments produced.In addition, the ratio of phytoene to carotenoid was in therange of 0.36–0.44, regardless of the presence or absenceof illumination and the light intensity. The fact that the ratio of carotenoid fractionated on the basisof the functional group involved in each carotenoid to the totalamount of carotenoid was almost constant regardless of the lightintensity suggested that the composition of the carotenoidssynthesized in the cells is not affected by light. It was deduced from these results that light induced the productionof enzyme(s) required for phytoene biosynthesis in Rhodotorulaminuta. (Received November 7, 1981; Accepted March 19, 1982)     

UV-induced ubiquitylation of XPC protein mediated by UV-DDB-ubiquitin ligase complex

The xeroderma pigmentosum group C (XPC) protein complex plays a key role in recognizing DNA damage throughout the genome for mammalian nucleotide excision repair (NER). Ultraviolet light (UV)-damaged DNA binding protein (UV-DDB) is another complex that appears to be involved in the recognition of NER-inducing damage, although the precise role it plays and its relationship to XPC remain to be elucidated. Here we show that XPC undergoes reversible ubiquitylation upon UV irradiation of cells and that this depends on the presence of functional UV-DDB activity. XPC and UV-DDB were demonstrated to interact physically, and both are polyubiquitylated by the recombinant UV-DDB-ubiquitin ligase complex. The polyubiquitylation altered the DNA binding properties of XPC and UV-DDB and appeared to be required for cell-free NER of UV-induced (6-4) photoproducts specifically when UV-DDB was bound to the lesion. Our results strongly suggest that ubiquitylation plays a critical role in the transfer of the UV-induced lesion from UV-DDB to XPC.     

Roles of the polymerase and BRCT domains of Rev1 protein in translesion DNA synthesis in yeast in vivo

Rev1p in yeast is essential for the translesion of abasic sites and 6-4 photoproducts. It plays a role as a translesion polymerase, but also supports translesion catalyzed by other polymerases. The protein has two domains, BRCT and Y-family polymerase. A point mutation in the BRCT domain is known to abolish the second function. In the present research, we have studied the effects of deletion of the BRCT domain and a point mutation at the two amino acids in the putative polymerase active center. We have introduced an abasic site, its tetrahydrofuran analog, and a 6-4 thymine-thymine photoproduct using the oligonucleotide transformation assay. Translesion efficiencies were estimated from the transforming activities of the oligonucleotides with a lesion, and the mutation spectra were analyzed by DNA sequencing of the transformants. Results showed that the lack of the BRCT domain reduced translesion efficiencies, but that substantial translesion synthesis took place. The mutation spectra of the lesions were not greatly affected. Therefore, the BRCT domain may be important, but dispensable for translesion synthesis. In contrast, the polymerase mutation, rev1AA, has only small effects on the translesion efficiencies, but the mutation spectra were greatly affected; the incorporation of dCMP opposite the lesions was specifically lost. This clearly shows that the polymerase domain is responsible for the dCMP incorporation. The effect of Poleta was also analyzed. From all the results DNA polymerases other than these two translesion polymerases, too, seem to initiate the translesion synthesis.     

Development of a sandwich ELISA assay for measuring bovine soluble type II IL-1 receptor (IL1R2) concentration in serum and milk

The IL1R is composed of two kinds of molecule, type I (IL1R I) and type II (IL1R2). IL1R1 contributes to IL-1 signaling, whereas the IL1R2 has no signaling property and acts as a decoy for IL-1. In this study, we developed a bovine IL1R2-specific sandwich ELISA to examine the sIL1R2 concentration in serum and milk from dairy cows. The concentration of colostral IL-1beta was examined to estimate the correlation to sIL1R2. The results showed that the sIL1R2 concentration in sera and milk changes with the stages of lactation. The serum sIL1R2 concentrations were 5.56+/-0.69 ng/ml (colostrum), 3.14+/-0.72 ng/ml (the early stage of lactation) and 5.76+/-1.25 ng/ml (the late stage of lactation). The milk sIL1R2 concentrations were 1.83+/-0.47 ng/ml (colostrum), 0.73+/-0.22 ng/ml (the early stage of lactation) and 2.92+/-0.56 ng/ml (the late stage of lactation). The concentrations of IL1R2 in sera and milk were significantly higher at the late stage of lactation and colostrum than that of the early stage of lactation. The reduction rates of sIL1R2 levels from the colostrum to the early stage of lactation were 43.6% (serum) and 61% (whey). IL-1beta was detected in all the colostrum (995.9+/-346.6 ng/ml). Significant correlation was observed between the levels of colostral IL-1beta and IL1R2 (r=0.75).     

Intein-based biosynthetic incorporation of unlabeled protein tags into isotopically labeled proteins for NMR studies

Segmental isotopic labeling of proteins using protein ligation is a recently established in vitro method for incorporating isotopes into one domain or region of a protein to reduce the complexity of NMR spectra, thereby facilitating the NMR analysis of larger proteins. Here we demonstrate that segmental isotopic labeling of proteins can be conveniently achieved in Escherichia coli using intein-based protein ligation. Our method is based on a dual expression system that allows sequential expression of two precursor fragments in media enriched with different isotopes. Using this in vivo approach, unlabeled protein tags can be incorporated into isotopically labeled target proteins to improve protein stability and solubility for study by solution NMR spectroscopy.