Human DNA polymerase iota promiscuous mismatch extension

Human DNA polymerase iota is a low-fidelity template copier that preferentially catalyzes the incorporation of the wobble base G, rather than the Watson-Crick base A, opposite template T (Tissier, A., McDonald, J. P., Frank, E. G., and Woodgate, R. (2000) Genes Dev. 14, 1642-1650; Johnson, R. E., Washington, M. T., Haracska, L., Prakash, S., and Prakash, L. (2000) Nature 406, 1015-1019; Zhang, Y., Yuan, F., Wu, X., and Wang, Z. (2000) Mol. Cell. Biol. 20, 7099-7108). Here, we report on its ability to extend all 12 possible mispairs and 4 correct pairs in different sequence contexts. Extension from both matched and mismatched primer termini is generally most efficient and accurate when A is the next template base. In contrast, extension occurs less efficiently and accurately when T is the target template base. A striking exception occurs during extension of a G:T mispair, where the enzyme switches specificity, "preferring" to make a correct A:T base pair immediately downstream from an originally favored G:T mispair. Polymerase iota generates a variety of single and tandem mispairs with high frequency, implying that it may act as a strong mutator when copying undamaged DNA templates in vivo. Even so, its limited ability to catalyze extension from a relatively stable primer/template containing a "buried" mismatch suggests that polymerase iota-catalyzed errors are confined to short template regions.     

Translesion DNA polymerases in eukaryotes: what makes them tick?

Life as we know it, simply would not exist without DNA replication. All living organisms utilize a complex machinery to duplicate their genomes and the central role in this machinery belongs to replicative DNA polymerases, enzymes that are specifically designed to copy DNA. “Hassle-free” DNA duplication exists only in an ideal world, while in real life, it is constantly threatened by a myriad of diverse challenges. Among the most pressing obstacles that replicative polymerases often cannot overcome by themselves are lesions that distort the structure of DNA. Despite elaborate systems that cells utilize to cleanse their genomes of damaged DNA, repair is often incomplete. The persistence of DNA lesions obstructing the cellular replicases can have deleterious consequences. One of the mechanisms allowing cells to complete replication is “Translesion DNA Synthesis (TLS)”. TLS is intrinsically error-prone, but apparently, the potential downside of increased mutagenesis is a healthier outcome for the cell than incomplete replication. Although most of the currently identified eukaryotic DNA polymerases have been implicated in TLS, the best characterized are those belonging to the “Y-family” of DNA polymerases (pols η, ι, κ and Rev1), which are thought to play major roles in the TLS of persisting DNA lesions in coordination with the B-family polymerase, pol ζ. In this review, we summarize the unique features of these DNA polymerases by mainly focusing on their biochemical and structural characteristics, as well as potential protein–protein interactions with other critical factors affecting TLS regulation.     

Cell surface expression of CD147/EMMPRIN is regulated by cyclophilin 60

CD147, also known as extracellular matrix metalloproteinase inducer, is a regulator of matrix metalloproteinase production and also serves as a signaling receptor for extracellular cyclophilins. Previously, we demonstrated that cell surface expression of CD147 is sensitive to cyclophilin-binding drug cyclosporin A, suggesting involvement of a cyclophilin in the regulation of intracellular transport of CD147. In this report, we identify this cyclophilin as cyclophilin 60 (Cyp60), a distinct member of the cyclophilin family of proteins. CD147 co-immunoprecipitated with Cyp60, and confocal immunofluorescent microscopy revealed intracellular co-localization of Cyp60 and CD147. This interaction with Cyp60 involved proline 211 of CD147, which was shown previously to be critical for interaction between CD147 and another cyclophilin, cyclophilin A, in solution. Mutation of this proline residue abrogated co-immunoprecipitation of CD147 and Cyp60 and reduced surface expression of CD147 on the plasma membrane. Suppression of Cyp60 expression using RNA interference had an effect similar to that of cyclosporin A: reduction of cell surface expression of CD147. These results suggest that Cyp60 plays an important role in the translocation of CD147 to the cell surface. Therefore, Cyp60 may present a novel target for therapeutic interventions in diseases where CD147 functions as a pathogenic factor, such as cancer, human immunodeficiency virus infection, or rheumatoid arthritis.     

The Use of “Space” Electrical Myostimulation in Clinical Cardiology on Earth

Human Physiology - The article describes a series of studies of the efficacy of the method of electromyostimulation, developed under the leadership of Inesa Benediktovna Kozlovskaya for the system...     

Selective endothelial overexpression of arginase II induces endothelial dysfunction and hypertension and enhances atherosclerosis in mice

Background

Cardiovascular disorders associated with endothelial dysfunction, such as atherosclerosis, have decreased nitric oxide (NO) bioavailability. Arginase in the vasculature can compete with eNOS for L-arginine and has been implicated in atherosclerosis. The aim of this study was to evaluate the effect of endothelial-specific elevation of arginase II expression on endothelial function and the development of atherosclerosis.

Methodology/Principal Findings

Transgenic mice on a C57BL/6 background with endothelial-specific overexpression of human arginase II (hArgII) gene under the control of the Tie2 promoter were produced. The hArgII mice had elevated tissue arginase activity except in liver and in resident peritoneal macrophages, confirming endothelial specificity of the transgene. Using small-vessel myography, aorta from these mice exhibited endothelial dysfunction when compared to their non-transgenic littermate controls. The blood pressure of the hArgII mice was 17% higher than their littermate controls and, when crossed with apoE −/− mice, hArgII mice had increased aortic atherosclerotic lesions.

Conclusion

We conclude that overexpression of arginase II in the endothelium is detrimental to the cardiovascular system.     

The effect of a weight-reducing diet on the nitrogen metabolism of obese adolescents

Rates of whole body amino nitrogen flux were measured in 16 obese adolescents undergoing weight reduction with a high protein low energy diet. The subjects received approximately 2.5 g of animal protein per day per kilogram ideal body weight and maintained nitrogen balance throughout the 18 days on the diet. Flux rates were calculated separately from the cumulative excretion of 15N in urinary ammonia and urea following the administration of a single dose of [15N]glycine. The pattern of 15N label appearance in urinary ammonia and urea nitrogen was followed for 72 h after the administration of [15N]glycine. Significant amounts of label continued to be excreted in both urinary ammonia and nitrogen for 36-48 h after label administration. The weight-reducing diet accelerated 15N cumulative excretion in urinary urea, but not in ammonia nitrogen compared with the control diet. Whole body nitrogen flux rates increased rapidly and significantly on the diet. Using the urea end product, this increase was evident on the 4th diet day, but not by the 7th or subsequent days. On the other hand, using the ammonia end product, flux rate increased markedly (p less than 0.0001) and remained elevated throughout the whole study. Our results demonstrate adaptive changes in whole body amino-nitrogen metabolism in response to the reducing diet. Different patterns of change are seen depending upon whether an ammonia or a urea end product is used. Our data thus add to the evidence for compartmentation of the body's amino-nitrogen pools.     

Effect of growth hormone therapy on IGF-I, bone GLA-protein and bone mineral content in short children with and without chronic renal failure.

Chronic renal failure (CRF) in the young is complicated by, among other conditions, growth retardation, hyperparathyroidism and uremic osteodystrophy. Many children with CRF are now being treated with growth hormone (GH). Since GH has a direct mitogenic effect on osteoblasts in culture, we studied the effects of GH therapy on osteoblastic activity, such as serum alkaline phosphatase (AP), bone GLA-protein (BGP) and bone mass density (BMD) in poorly growing children with and without CRF. Fifteen (4 girls, 11 boys) healthy children with short stature (SS) and 10 (3 girls, 7 boys) children with end-stage renal failure (CRF) 4.5-12.4 years of age were treated with daily subcutaneous injections of GH in a dose of 0.1-0.125 IU/kg/day for 1 year. IGF-I, BGP and BMD of the spine were determined before and after the year of treatment. During GH therapy, a similar increase in height velocity and IGF-I were noted in SS and CRF groups: 3.8 +/- 0.77 to 8.38 +/- 1.25 (p < 0.001) vs. 4.0 +/- 0.6 to 7.14 +/- 1.3 cm/year (p < 0.001) and 7.8 +/- 2.6 to 21.8 +/- 7.5 (p < 0.01) vs. 7.9 +/- 1.3 to 21.5 +/- 5.6 nmol/l (p < 0.01), respectively. AP increased from 205 +/- 27 to 274 +/- 50 IU/l (p < 0.01) in the SS group but not in CRF patients (223 +/- 58 pre- 218 +/- 51 IU/l post-GH therapy).(ABSTRACT TRUNCATED AT 250 WORDS)