Fluorescence energy transfer in tryptophanase

Excitation of apotryptophanase from Escherichia coli$\text{B}\text{lt7-A}$ at 290 nm yielded a fluorescence emission centered at 340 nm. Binding of pyridoxal phosphate to apoenzyme induced quenching of protein fluorescence concomitant with an appearance of another peak at 510 nm by way of energy transfer from tryptophan. Based on the results, an approximate distance between the coenzyme and tryptophan was estimated to be 18–24 Å according to the Förster's theory. The ozone-inactivated enzyme yielded only the 340 nm-peak upon excitation at 290 nm following reconstitution with the coenzyme. The fluorescence decay time of the tryptophyl residue was somewhat increased by ozone-inactivation. These results suggest that the tryptophyl residue essential for the activity is involved in a direct interaction with the coenzyme.     

Effects of phenytoin on cell-mediated immunity

Summary The effects of phenytoin on cellular immunity were examined in murine models. Fresh splenocytes were obtained from mice which had received 1 mg/day of phenytoin i.p. for 28 days. The serum concentration of phenytoin in these animals was 10–10 g/ml. The proliferative response of splenocytes to mitogens was assessed by ³H-thymidine incorporation. The cytotoxic activities of cells such as natural killer (NK) cells, cytotoxic T lymphocytes (CTL), and lymphokine-activated killer (LAK) cells were estimated by a 4-h ⁵¹Cr release assay. The ³H-thymidine incorporation of splenocytes was reduced significantly (P<0.01) in phenytoin-treated mice. The NK and CTL activities of splenocytes from phenytoin-treated mice were significantly suppressed. However, the LAK activity of phenytoin-treated mice was equal to that of control mice.     

The IGF‐I regulatory system and its impact on skeletal and energy homeostasis

Insulin‐like growth factor (IGF)‐I is important in the acquisition and maintenance of both soft and hard tissues. Skeletal remodeling requires energy and recent work has demonstrated that bone can influence insulin sensitivity and thereby regulate metabolic processes. New insights from mouse models into the role of IGF‐binding proteins (IGFBPs) as more than mere depots for the IGFs has reignited investigations into the metabolic targets influenced by the IGF regulatory system and the pathways that link bone to adipose tissue. Although there remains continued uncertainty about the relative balance between the effects of circulating versus tissue IGF‐I actions, the role of the IGFBPs has been redefined both as modulators of IGF‐I action and as independent signaling factors. This review highlights several recent findings that shed new light on the physiologic role of the IGF regulatory system and its influence on skeletal and fat metabolism. J. Cell. Biochem. 111: 14–19, 2010. © 2010 Wiley‐Liss, Inc.     

Cutting Edge: Brucella abortus Exploits a Cellular Prion Protein on Intestinal M Cells as an Invasive Receptor

Brucella abortus is a Gram-negative bacterium causing brucellosis. Although B. abortus is known to infect via the oral route, the entry site in the gastrointestinal tract has been unclear. We found that B. abortus was selectively internalized by microfold cells (M cells), a subset of epithelial cells specialized for mucosal Ag uptake. During this process, colocalization of cellular prion protein (PrP(C)) and B. abortus was evident on the apical surface as well as in subapical vacuolar structures in M cells. Internalization of B. abortus by M cells of PrP(C)-deficient (Prnp(-/-)) mice was greatly reduced compared with that in wild-type mice. Furthermore, an oral infection study revealed that translocation of B. abortus into the Peyer's patch was significantly lower in Prnp(-/-) than in wild-type mice. These observations suggest that orally infected B. abortus invades the host through M cells by using PrP(C) on the apical surface of M cells as an uptake receptor.     

An ultrasensitive enzymatic method for measuring mevalonic acid in serum

We have developed a simple, precise, and ultrasensitive enzymatic method for measuring serum mevalonic acid (MVA) concentration, which is thought to be a good indicator of the in vivo cholesterol biosynthesis rate. This assay is based on an enzyme cycling reaction and makes use of HMG-CoA reductase (HMGR), thio-NAD, NADH, and CoA. MVA participates in the HMGR cycling reaction, and its level is measured based on the production of thio-NADH, which is determined from the change in absorbance at 405 nm. To achieve high specificity, we used mevalonate kinase (MVK) in addition to HMGR. Only substrates able to participate in both the HMGR cycling reaction and the MVK reaction are measured as MVA. The detection limit for MVA is 0.4 ng/ml (2.7 nmol/l), and the calibration curve for MVA is linear up to 44 ng/ml (300 nmol/l). Regression analysis with 40 serum samples showed the accuracy of quantifying MVA with this enzymatic assay to be comparable to that using LC-MS/MS (correlation: y = 0.83x + 0.24; r = 0.97). This procedure is simple, precise, and robust. It is also rapid and has a high throughput, making it potentially useful for clinical applications.     

Identification of small molecule proliferating cell nuclear antigen (PCNA) inhibitor that disrupts interactions with PIP-box proteins and inhibits DNA replication

We have discovered that 3,3′,5-triiodothyronine (T3) inhibits binding of a PIP-box sequence peptide to proliferating cell nuclear antigen (PCNA) protein by competing for the same binding site, as evidenced by the co-crystal structure of the PCNA-T3 complex at 2.1 Å resolution. Based on this observation, we have designed a novel, non-peptide small molecule PCNA inhibitor, T2 amino alcohol (T2AA), a T3 derivative that lacks thyroid hormone activity. T2AA inhibited interaction of PCNA/PIP-box peptide with an IC₅₀ of ∼1 μm and also PCNA and full-length p21 protein, the tightest PCNA ligand protein known to date. T2AA abolished interaction of PCNA and DNA polymerase δ in cellular chromatin. De novo DNA synthesis was inhibited by T2AA, and the cells were arrested in S-phase. T2AA inhibited growth of cancer cells with induction of early apoptosis. Concurrently, Chk1 and RPA32 in the chromatin are phosphorylated, suggesting that T2AA causes DNA replication stress by stalling DNA replication forks. T2AA significantly inhibited translesion DNA synthesis on a cisplatin-cross-linked template in cells. When cells were treated with a combination of cisplatin and T2AA, a significant increase in phospho(Ser¹³⁹)histone H2AX induction and cell growth inhibition was observed.     

Destruction of pancreatic beta-cells by transgenic induction of prostaglandin E2 in the islets

Type 2 diabetes mellitus is characterized by insulin resistance of peripheral tissues and dysfunction of pancreatic beta-cells. Furthermore, the number of pancreatic beta-cells decreases as a secondary effect of advanced type 2 diabetes, although the molecular mechanism has not been elucidated. Recently, it has been shown that hyperglycemic conditions induce the expression of cyclooxygenase-2 in pancreatic islets and increase the downstream product prostaglandin E(2) (PGE(2)). To investigate whether high glucose-induced PGE(2) has an adverse effect on pancreatic beta-cells, we generated transgenic mice (RIP-C2mE) that express cyclooxygenase-2 and microsomal prostaglandin E synthase-1 in their beta-cells using the rat insulin-2 gene promoter (RIP). The homozygous RIP-C2mE (Tg/Tg) mice showed severe hyperglycemia from six weeks of age. Although the heterozygous RIP-C2mE (Tg/-) mice showed normal blood glucose levels throughout their lifetime, this level increased significantly compared with that of wild-type mice when glucose was loaded. The relative number of beta-cells to the total islet cell number was reduced to 54 and 14% in the RIP-C2mE (Tg/-) and (Tg/Tg) mice, respectively, whereas that in the wild-type mice was 84%. Importantly, the proliferation rate in the islets of the RIP-C2mE (Tg/Tg) mice at four weeks of age decreased significantly in comparison to that in the wild-type mice. Because beta-cells replicate not only during the postnatal period but also in the adult pancreas at a basal level, it is possible that increased PGE(2) signaling thus contributes to the reduction of the pancreatic beta-cell mass through inhibition of proliferation, thereby aggravating diabetes further.     

Disturbance of cerebellar synaptic maturation in mutant mice lacking BSRPs, a novel brain-specific receptor-like protein family

By DNA cloning, we have identified the BSRP (brain-specific receptor-like proteins) family of three members in mammalian genomes. BSRPs were predominantly expressed in the soma and dendrites of neurons and localized in the endoplasmic reticulum (ER). Expression levels of BSRPs seemed to fluctuate greatly during postnatal cerebellar maturation. Triple-knockout mice lacking BSRP members exhibited motor discoordination, and Purkinje cells (PCs) were often innervated by multiple climbing fibers with different neuronal origins in the mutant cerebellum. Moreover, the phosphorylation levels of protein kinase Calpha (PKCalpha) were significantly downregulated in the mutant cerebellum. Because cerebellar maturation and plasticity require metabotropic glutamate receptor signaling and resulting PKC activation, BSRPs are likely involved in ER functions supporting PKCalpha activation in PCs.