p53 Binds Preferentially to Non-B DNA Structures Formed by the Pyrimidine-Rich Strands of GAA·TTC Trinucleotide Repeats Associated with Friedreich's Ataxia

Expansions of trinucleotide repeats (TNRs) are associated with genetic disorders such as Friedreich's ataxia. The tumor suppressor p53 is a central regulator of cell fate in response to different types of insults. Sequence and structure-selective modes of DNA recognition are among the main attributes of p53 protein. The focus of this work was analysis of the p53 structure-selective recognition of TNRs associated with human neurodegenerative diseases. Here, we studied binding of full length p53 and several deletion variants to TNRs folded into DNA hairpins or loops. We demonstrate that p53 binds to all studied non-B DNA structures, with a preference for non-B DNA structures formed by pyrimidine (Py) rich strands. Using deletion mutants, we determined the C-terminal DNA binding domain of p53 to be crucial for recognition of such non-B DNA structures. We also observed that p53 in vitro prefers binding to the Py-rich strand over the purine (Pu) rich strand in non-B DNA substrates formed by sequence derived from the first intron of the frataxin gene. The binding of p53 to this region was confirmed using chromatin immunoprecipitation in human Friedreich's ataxia fibroblast and adenocarcinoma cells. Altogether these observations provide further evidence that p53 binds to TNRs' non-B DNA structures.

RMS roughness-independent tuning of surface wettability by tailoring silver nanoparticles with a fluorocarbon plasma polymer

A layer of 14 nm-sized Ag nanoparticles undergoes complex transformation when overcoated by thin films of a fluorocarbon plasma polymer. Two regimes of surface evolution are identified, both with invariable RMS roughness. In the early regime, the plasma polymer penetrates between and beneath the nanoparticles, raising them above the substrate and maintaining the multivalued character of the surface roughness. The growth (β) and the dynamic (1/z) exponents are close to zero and the interface bears the features of self-affinity. The presence of inter-particle voids leads to heterogeneous wetting with an apparent water contact angle θ_a = 135°. The multivalued nanotopography results in two possible positions for the water droplet meniscus, yet strong water adhesion indicates that the meniscus is located at the lower part of the spherical nanofeatures. In the late regime, the inter-particle voids become filled and the interface acquires a single valued character. The plasma polymer proceeds to grow on the thus-roughened surface whereas the nanoparticles keep emerging away from the substrate. The RMS roughness remains invariable and lateral correlations propagate with 1/z = 0.27. The surface features multiaffinity which is given by different evolution of length scales associated with the nanoparticles and with the plasma polymer. The wettability turns to the homogeneous wetting state.

p53 binds human telomeric G-quadruplex in vitro

The tumor suppressor protein p53 is a key factor in genome stability and one of the most studied of DNA binding proteins. This is the first study on the interaction of wild-type p53 with guanine quadruplexes formed by the human telomere sequence. Using electromobility shift assay and ELISA, we show that p53 binding to telomeric G-quadruplexes increases with the number of telomeric repeats. Further, p53 strongly favors G-quadruplexes folded in potassium over those formed in sodium, thus indicating the telomeric G-quadruplex conformational selectivity of p53. The presence of the quadruplex-stabilizing ligand, N-methyl mesoporphyrin IX (NMM), increases p53 recognition of G-quadruplexes in potassium. Using deletion mutants and selective p53 core domain oxidation, both p53 DNA binding domains are shown to be crucial for telomeric G-quadruplex recognition.

Assessment of Diagnostics Tools for Sarcopenia Severity Using the Item Response Theory (IRT)

OBJECTIVE

To use the item response theory (IRT) methods to examine the degree to which the four selected tools reflect sarcopenia and to arrange them according to their ability to estimate sarcopenia severity.

DESIGN

A cross-sectional study aimed at verifying the possibilities of using diagnostic tools for sarcopenia.

SETTING AND PARTICIPANTS

The study included residents living in an assisted living unit at the Senior Centre in Blansko (South Moravia, Czech Republic) (n=77). Sarcopenia was estimated according to the proposals of the European Working Group on Sarcopenia in Older People (EWGSOP) using calf circumference, the EWGSOP algorithm, hand grip strength, and the Short Physical Performance Battery (SPPB).

RESULTS

The results from the IRT model showed that these four methods indicate strong unidimensionality so that they measure the same latent variable. The methods ranked according to the discrimination level ranging from high to low discrimination where the calf circumference was the most discriminatory (Hi = 0.86) and the SPPB together with hand grip strength were the least discriminatory (both Hi = 0.44).

CONCLUSION

We are recommending to identify mild sarcopenia by SPPB or hand grip strength, moderate sarcopenia by the EWGSOP algorithm and severe sarcopenia by the calf circumference.

Effect of the MTHFR 677C/T polymorphism on homocysteinemia in response to creatine supplementation: a case study

Creatine (Cr) is recommended as a dietary supplement especially for athletes but its therapeutic potential is also discussed. It is assumed that human body uses Cr for the formation of phosphocreatine, which is necessary for muscular work as a source of energy. Production of Cr in a body is closely connected to methionine cycle where guanidinoacetate (GAA) is in a final step methylated from S-adenosylmethionine (SAM). Increased availability of SAM for phosphatidylcholine (PC) and sarcosine synthesis can potentially stimulate endogenous production of betaine a thus methylation of homocysteine (HCy) to form methionine. Our subject who was methylenetetrahydrofolate reductase (MTHFR) 677TT homozygote lowered plasma HCy from 33.3 micromol/l to 17.1 micromol/l following one-month Cr supplementation (5 g/day) opposite to 677CC and CT genotypes whose HCy levels tended to increase (but still in normal ranges). We suppose that Cr supplementation stimulates pathways leading to production of sarcosine which can serve to regenerate tetrahydrofolate (THF) to form 5,10-methylene-THF. This could potentially increase MTHFR enzyme activity which may later result in increased HCy methylation. Cr supplementation significantly effects metabolism of one carbon unit and potentially lower body´s demands for methyl groups. This could be beneficial as in the case of reduced enzyme activity such as MTHFR 677C/T polymorphism.

Supplemented creatine induces changes in human metabolism of thiocompounds and one- and two-carbon units

The administration of creatine (5 g/day for one month) to 11 young active sportsmen affected their urinary excretion of creatine, creatinine, and thiodiglycolic acid (TDGA) as well as blood levels of homocysteine, vitamin B12 and folates. The probands were divided into four groups, according to the amount of creatine found in urine, and of folates and vitamin B12 determined in blood. The changes of folates and vitamin B12 were mutually reciprocal. Each group utilized CR as donor of one- and two-carbon (1C and 2C) units by means of homocysteine (HoCySH), folates, and vitamin B12, in different metabolic pathways. In 10 men the creatine administration was accompanied by an increase of HoCySH level in blood, while in the last man, with accidentally discovered hyperhomocysteinemia, the HoCySH level dropped by 50%. Differences between initial and terminal TDGA levels indicate that creatine affects equilibria of redox processes. Creatinine excretion into urine changed in the dependence on the extent of metabolic disturbances.

Diagnostic significance of urinary thiodiglycolic acid as a possible tool for studying the role of vitamins B12 and folates in the metabolism of thiolic substances

We have found that the determination of thiodiglycolic acid (TDGA) in urine may help to characterize metabolic imbalance of substances participating in methionine synthesis, which leads to hyperhomocystinuria. From the metabolic scheme, based on a proper combination of known facts, we attempted to theoretically explain and to demonstrate the possibilities of TDGA formation via different ways of homocysteine transformation. This scheme was used in evaluating the results obtained by testing urine of a woman suffering from impaired function of methionine synthase reductase (CblE type of homocystinuria). The amount of TDGA excreted in her morning urine was very sensitive to the changes in her treatment based upon a combination of N5-formyl tetrahydrofolate, betaine and vitamin B12. Vitamin B12 given in the evening either alone or together with betaine increased the TDGA excretion in the morning urine up to ten times. On the other hand, in the absence of vitamin B12, betaine in combination with N5-formyl tetrahydrofolate hindered the appearance of TDGA in the morning urine. Generally, the determination of TDGA in urine of an appropriately pretreated patient may indicate the degree of success of the treatment.

Calcium channel antagonist effect on in vitro meningioma signal transduction pathways after growth factor stimulation

OBJECTIVE

We have previously demonstrated that calcium channel antagonists inhibit the growth of human meningiomas in culture after stimulation with growth factors. This study examined the effects of these drugs on signaling transduction pathways in an attempt to elucidate potential mechanisms by which this growth inhibition is mediated.

METHODS

Primary cell cultures from patients with intracranial meningiomas were established. Cell growth studies were performed with inhibitors and stimulators of tyrosine kinase signal transduction. Intracellular calcium changes and inositol phosphate production were measured after growth factor exposure, with or without pretreatment by calcium channel antagonists.

RESULTS

The growth of meningiomas in culture can be inhibited by tyrosine kinase receptor inhibitors. Inhibitors and stimulators of phospholipase C can stimulate or inhibit the growth of in vitro meningiomas, respectively. Calcium channel antagonists inhibit intracellular calcium changes induced by serum and epidermal growth factor. Inositol phosphate production is increased after growth factor stimulation, and calcium channel antagonists potentiate this effect.

CONCLUSION

Calcium channel antagonists interfere with intracellular signaling pathways of cultured meningioma cells. This inhibition is unrelated to voltage-sensitive calcium channels. The findings of this project may aid in the understanding of the signal transduction mechanisms involved in growth factor-mediated meningioma proliferation and may lead to clinically relevant strategies for growth inhibition.

The use of mechanically elicited electromyograms to protect nerve roots during surgery for spinal degeneration

STUDY DESIGN

This study investigated the use of mechanically elicited electromyograms during the placement of pedicle screws in 89 patients undergoing surgery for spinal stenosis.

SUMMARY OF BACKGROUND DATA

Several methods for monitoring nerve roots are available. However, mechanically elicited electromyograms may be more sensitive to mechanical irritation of nerve roots by pedicle screws than by other methods.

METHODS

Mechanically elicited electromyograms were recorded in muscle groups innervated by cervical or lumbar nerve roots. Confirmation of surgical activity with the level of the electromyogram was correlated.

RESULTS

Results indicated that mechanically elicited electromyograms are extremely sensitive to nerve root irritation. Compared to other methods, electromyograms are a viable alternative.

CONCLUSIONS

Results from this study indicated that mechanically elicited electromyograms are sensitive and specific to nerve root firings and should be considered for use during the dynamic phases of surgery.