Metastatic sweat gland adenocarcinoma: A clinico-pathological dilemma

Background  

Sweat gland adenocarcinoma is a rare malignancy with high metastatic potential seen more commonly in later years of life. Scalp is the most common site of occurrence and it usually spreads to lymph nodes. Liver, lung and bones are the distant sites of metastasis with fatal results. The differentiation between apocrine and eccrine metastatic sweat gland carcinoma is often difficult. The criteria's are inadequate to be of any practical utility.     

Selective inhibition of selenocysteine tRNA maturation and selenoprotein synthesis in transgenic mice expressing isopentenyladenosine-deficient selenocysteine tRNA

Selenocysteine (Sec) tRNA (tRNA([Ser]Sec)) serves as both the site of Sec biosynthesis and the adapter molecule for donation of this amino acid to protein. The consequences on selenoprotein biosynthesis of overexpressing either the wild type or a mutant tRNA([Ser]Sec) lacking the modified base, isopentenyladenosine, in its anticodon loop were examined by introducing multiple copies of the corresponding tRNA([Ser]Sec) genes into the mouse genome. Overexpression of wild-type tRNA([Ser]Sec) did not affect selenoprotein synthesis. In contrast, the levels of numerous selenoproteins decreased in mice expressing isopentenyladenosine-deficient (i(6)A(-)) tRNA([Ser]Sec) in a protein- and tissue-specific manner. Cytosolic glutathione peroxidase and mitochondrial thioredoxin reductase 3 were the most and least affected selenoproteins, while selenoprotein expression was most and least affected in the liver and testes, respectively. The defect in selenoprotein expression occurred at translation, since selenoprotein mRNA levels were largely unaffected. Analysis of the tRNA([Ser]Sec) population showed that expression of i(6)A(-) tRNA([Ser]Sec) altered the distribution of the two major isoforms, whereby the maturation of tRNA([Ser]Sec) by methylation of the nucleoside in the wobble position was repressed. The data suggest that the levels of i(6)A(-) tRNA([Ser]Sec) and wild-type tRNA([Ser]Sec) are regulated independently and that the amount of wild-type tRNA([Ser]Sec) is determined, at least in part, by a feedback mechanism governed by the level of the tRNA([Ser]Sec) population. This study marks the first example of transgenic mice engineered to contain functional tRNA transgenes and suggests that i(6)A(-) tRNA([Ser]Sec) transgenic mice will be useful in assessing the biological roles of selenoproteins.     

Critical test of some computational methods for prediction of NMR <Superscript>1</Superscript>H and <Superscript>13</Superscript>C chemical shifts

Performance of 18 DFT functionals (B1B95, B3LYP, B3PW91, B97D, BHandHLYP, BMK, CAM-B3LYP, HSEh1PBE, M06-L, mPW1PW91, O3LYP, OLYP, OPBE, PBE1PBE, tHCTHhyb, TPSSh, wB97xD, VSXC) in combinations with six basis sets (cc-pVDZ, aug-cc-pVDZ, cc-pVTZ, aug-cc-pVTZ, IGLO-II, and IGLO-III) and three methods for calculating magnetic shieldings (GIAO, CSGT, IGAIM) was tested for predicting ¹H and ¹³C chemical shifts for 25 organic compounds, for altogether 86 H and 88 C atoms. Proton shifts varied between 1.03 ppm to 12.00 ppm and carbon shifts between 7.87 ppm to 209.28 ppm. It was found that the best method for calculating ¹³C shifts is PBE1PBE/aug-cc-pVDZ with CSGT or IGAIM approaches (mae?=?1.66 ppm), for ¹H the best results were obtained with HSEh1PBE, mPW1PW91, PBE1PBE, CAM-B3LYP, and B3PW91 functionals with cc-pVTZ basis set and with CSGT or IGAIM approaches (mae?=?0.28 ppm). We found that often larger basis sets do not give better results for chemical shifts. The best basis sets for calculating ¹H and ¹³C chemical shifts were cc-pVTZ and aug-cc-pVDZ, respectively. CSGT and IGAIM NMR approaches can perform really well and are in most cases better than popular GIAO approach.

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Graphical Abstract Mean absolute errors for ¹H and ¹³C chemical shifts and computational times of neutral toluene molecule with aug-cc-pVDZ basis set and CSGT approach

     

Structural studies of the final enzyme in the alpha-aminoadipate pathway-saccharopine dehydrogenase from Saccharomyces cerevisiae

The 1.64 A structure of the apoenzyme form of saccharopine dehydrogenase (SDH) from Saccharomyces cerevisiae shows the enzyme to be composed of two domains with similar dinucleotide binding folds with a deep cleft at the interface. The structure reveals homology to alanine dehydrogenase, despite low primary sequence similarity. A model of the ternary complex of SDH, NAD, and saccharopine identifies residues Lys77 and Glu122 as potentially important for substrate binding and/or catalysis, consistent with a proton shuttle mechanism. Furthermore, the model suggests that a conformational change is required for catalysis and that residues Lys99 and Asp281 may be instrumental in mediating this change. Analysis of the crystal structure in the context of other homologous enzymes from pathogenic fungi and human sources sheds light into the suitability of SDH as a target for antimicrobial drug development.     

A simple rapid immunoassay for S-adenosylhomocysteine in plasma

The measurement of plasma S-adenosylhomocysteine is a more sensitive indicator of the risk for vascular disease than is plasma homocysteine. Because the level of S-adenosylhomocysteine is normally in the nanomolar range, it has been difficult to measure and necessitated the development of complex fluorometric and mass-spectrophotometric methods. We have now adapted an existing immunoassay used for the measurement of homocysteine to the measurement of S-adenosylhomocysteine in plasma. This assay is sensitive down to the level of less than 0.1 pmol, and there is no interference by S-adenosylmethionine. The assay is carried out in microplates, allows the measurement of 12 samples per plate and can easily be carried out in a 4-h period. The method is applicable to plasma samples having S-adenosylhomocysteine concentrations ranging from 10 to 150 nM without dilution. The mean value for 16 normal subjects by this method was 18.9±1.4 nM (S.E.M.), compared with 17.8±1.4 nM obtained by a previously described method using two high-performance liquid chromatography columns with fluorescence derivatization. Mean values for seven cirrhotic patients were 46.5±3.3 nM by this new method compared with 44.6±5.3 by the former method. The ease and speed of this method should allow the widespread measurement of this important metabolite in laboratories without access to sophisticated equipment.     

Variability of serum levels of tumor necrosis factor-alpha, interleukin 6, and soluble interleukin 6 receptor over 2 years in young women

Serum levels of tumor necrosis factor-alpha (TNF-alpha), interleukin 6 (IL-6), and soluble interleukin 6 receptor (sIL-6R) have been studied as risk factors of cardiovascular disease in longitudinal studies. However, it is unknown about their long-term intra-individual variations and whether single measurements of these cytokines and receptor are reliable biomarkers in epidemiological studies. In this study, serum levels of TNF-alpha, IL-6, and sIL-6R were assayed by ELISAs in 36 young, healthy women from whom three blood samples were collected at 12-month intervals over 2 years, and the intraclass correlation coefficients (ICC) were estimated. The ICC of 0.73 (95% CI=0.49-0.79) for TNF-alpha was comparable to those of other commonly used biomarkers, justifying its use in epidemiological studies. The ICC of 0.48 (95% CI=0.25-0.58) for IL-6 was not optimal. However, IL-6 has been demonstrated as a consistent risk factor for cardiovascular disease, suggesting it could still be a useful biomarker if its disease association is substantial. The ICC of 0.36 (95% CI=0.10-0.47) for sIL-6R was relatively low, and multiple samples would need to be collected in prospective studies for this receptor.     

Selenoprotein P is required for mouse sperm development

Selenoprotein P (SEPP1), an extracellular glycoprotein of unknown function, is a unique member of the selenoprotein family that, depending on species, contains 10-17 selenocysteines in its primary structure; in contrast, all other family members contain a single selenocysteine residue. The SEPP1-null (Sepp1(-/-)) male but not the female mice are infertile, but the cellular basis of this male phenotype has not been defined. In this study, we demonstrate that mature spermatozoa of Sepp1(-/-) males display a specific set of flagellar structural defects that develop temporally during spermiogenesis and after testicular maturation in the epididymis. The flagellar defects include a development of a truncated mitochondrial sheath, an extrusion of a specific set of axonemal microtubules and outer dense fibers from the principal piece, and ultimately a hairpin-like bend formation at the midpiece-principal piece junction. The sperm defects found in Sepp1(-/-) males appear to be the same as those observed in wild-type (Sepp1(+/+)) males fed a low selenium diet. Supplementation of dietary selenium levels for Sepp1(-/-) males neither reverses the development of sperm defects nor restores fertility. These data demonstrate that SEPP1 is required for development of functional spermatozoa and indicate that it is an essential component of the selenium delivery pathway for developing germ cells.     

Roles of the equatorial tyrosyl iron ligand of protocatechuate 3,4-dioxygenase in catalysis

The active site Fe(III) of protocatechuate 3,4-dioxygenase (3,4-PCD) from Pseudomonas putida is ligated axially by Tyr447 and His462 and equatorially by Tyr408, His460, and OH(-). Tyr447 and OH(-) are displaced as protocatechuate (3,4-dihydroxybenzoate, PCA) chelates the iron and appear to serve as in situ bases to promote this process. The role(s) of Tyr408 is (are) explored here using mutant enzymes that exhibit less than 0.1% wild-type activity. The X-ray crystal structures of the mutants and their PCA complexes show that the new shorter residues in the 408 position cannot ligate the iron and instead interact with the iron through solvents. Moreover, PCA binds as a monodentate rather than a bidentate ligand, and Tyr447 fails to dissociate. Although the new residues at position 408 do not directly bind to the iron, large changes in the spectroscopic and catalytic properties are noted among the mutant enzymes. Resonance Raman features show that the Fe-O bond of the monodentate 4-hydroxybenzoate (4HB) inhibitor complex is significantly stronger in the mutants than in wild-type 3,4-PCD. Transient kinetic studies show that PCA and 4HB bind to 3,4-PCD in a fast, reversible step followed by a step in which coordination to the metal occurs; the latter process is at least 50-fold slower in the mutant enzymes. It is proposed that, in wild-type 3,4-PCD, the Lewis base strength of Tyr408 lowers the Lewis acidity of the iron to foster the rapid exchange of anionic ligands during the catalytic cycle. Accordingly, the increase in Lewis acidity of the iron caused by substitution of this residue by solvent tends to make the iron substitution inert. Tyr447 cannot be released to allow formation of the usual dianionic PCA chelate complex with the active site iron, and the rate of electrophilic attack by O(2) becomes rate limiting overall. The structures of the PCA complexes of these mutant enzymes show that hydrogen-bonding interactions between the new solvent ligand and the new second-sphere residue in position 408 allow this residue to significantly influence the spectroscopic and kinetic properties of the enzymes.