Tristetraprolin Posttranscriptionally Downregulates TRAIL Death Receptors

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) has attracted attention as a potential candidate for cancer therapy. However, many primary cancers are resistant to TRAIL, even when combined with standard chemotherapy. The mechanism of TRAIL resistance in cancer cells has not been fully elucidated. The TRAIL death receptor (DR) 3′-untranslated region (3′-UTR) is reported to contain AU-rich elements (AREs) that are important for regulating DR mRNA stability. However, the mechanisms by which DR mRNA stability is determined by its 3′-UTR are unknown. We demonstrate that tristetraprolin (TTP), an ARE-binding protein, has a critical function of regulating DR mRNA stability. DR4 mRNA contains three AREs and DR5 mRNA contains four AREs in 3′-UTR. TTP bound to all three AREs in DR4 and ARE3 in DR5 and enhanced decay of DR4/5 mRNA. TTP overexpression in colon cancer cells changed the TRAIL-sensitive cancer cells to TRAIL-resistant cells, and down-regulation of TTP increased TRAIL sensitivity via DR4/5 expression. Therefore, this study provides a molecular mechanism for enhanced levels of TRAIL DRs in cancer cells and a biological basis for posttranscriptional modification of TRAIL DRs. In addition, TTP status might be a biomarker for predicting TRAIL response when a TRAIL-based treatment is used for cancer.

Paternal age as an independent factor does not affect embryo quality and pregnancy outcomes of testicular sperm extraction-intracytoplasmic sperm injection in azoospermia

This study was performed to evaluate the independent influence of paternal age affecting embryo development and pregnancy using testicular sperm extraction (TESE)-intracytoplasmic sperm injection (ICSI) in obstructive azoospermia (OA) and nonobstructive azoospermia (NOA). Paternal patients were divided into the following groups: ≤30 years, 31-35 years, 36-40 years, 41-45 years and ≥46 years. There were no differences in the rates of fertilisation or embryo quality according to paternal and maternal age. However, clinical pregnancy and implantation rates were significantly lower between those ≥46 years of paternal age compared with other age groups. Fertilisation rate was higher in the OA than the NOA, while embryo quality, pregnancy and delivery results were similar. Clinical pregnancy and implantation rates were significantly lower for patients ≥46 years of paternal age compared with younger age groups. In conclusion, fertilisation using TESE in azoospermia was not affected by the independent influence of paternal age; however, as maternal age increased concomitantly with paternal age, rates of pregnancy and delivery differed between those with paternal age <41 years and ≥46 years. Therefore, paternal age ≥46 years old should be considered when applying TESE-ICSI in cases of azoospermia, and patients should be advised of the associated low pregnancy rates.

Endpoints for screening thyroid cancer in the Republic of Korea: thyroid specialists' perspectives

Cancer screening is aimed primarily at reducing deaths from the specific cancer. Thyroid-specific cancer mortality may be the most ambitious endpoint for obtaining estimates of screening effect. Numerous observations have accumulated over the years, indicating that thyroid cancer mortality endpoint has been difficult to study and is confounded by population heterogeneity, provision of randomization, and requirement of large cohorts with sufficiently long follow-up due to the excellent prognosis of the cancer. Accordingly, it may be important to reconsider how to best measure thyroid cancer screening efficacy. Recommendations against thyroid cancer screening should be based upon trials designed to evaluate its effectiveness not only in significant reduction in cancer mortality, but also of other distinct endpoints. It is desirable to evaluate derivative endpoints that can reliably predict reductions in mortality. The term "derivative" means a variable that is related to the true endpoint and is likely to be observable before the primary endpoint. Derivative endpoints may include thyroid cancer incidence, the proportion of early-stage tumors detected, more treatable stage, the identification of small tumors (to maintain in observation), decrease in the number of people who develop metastatic disease, the increased chance of lesser extent surgery, and the application of minimally invasive approaches, as well as no need for lifelong thyroid replacement therapy, a consistent follow-up, low-dose or no RAI administration and risk factor assessments where case findings should be continuous. The Korean guidelines for thyroid cancer national-level screening were published by a relevant group of multidisciplinary thyroid experts. It was concluded that the evidence is insufficient to balance the benefits and harms of thyroid cancer screening. However, the paper seems to raise the necessary investments in future research and demand a complete analysis for derivative endpoints, and offer screening participants with complete information necessary to make decisions that will provide them with the most value when a small thyroid cancer is screen-identified.

Outcome of percutaneous transluminal angioplasty in diabetic patients with critical limb ischaemia

OBJECTIVE

We investigated the clinical outcome of percutaneous transluminal angioplasty (PTA) which has not been fully established in diabetic patients with critical limb Ischaemia (CLI) compared with non-diabetics.

DESIGN AND PATIENTS

A total of 73 limbs of 52 patients (50 limbs of 34 diabetic patients and 23 limbs of 18 non-diabetics) who underwent PTA for CLI (Rutherford-Becker category 4, 5 or 6) were enrolled. Rates of amputation and restenosis, and ankle brachial index (ABI), were assessed before and after PTA during a 36-month follow-up period.

RESULTS

Diabetic patients had a higher rate of major amputations after PTA (10 vs. 0%, P<0.05); however, total amputation (12.0 vs. 8.7%, P=0.62) and restenosis rates (4.0 vs. 8.7%, P=0.38) were not significantly different compared with non-diabetic patients. ABI at 3 months after PTA was significantly improved in both diabetic and non-diabetic patients (0.70±0.20 vs. 0.93±0.19, P<0.01 in diabetic patients; 0.69±0.25 vs. 0.92±0.17, P<0.01 in non-diabetics). Improved ABI was maintained for 36 months in both groups and did not show a significant difference (0.88±0.21 vs. 0.89±0.20, P=0.89).

CONCLUSION

Our results, showing that the outcome of PTA in diabetic patients is not inferior to that in non-diabetics, suggest the potential benefit of primary PTA, instead of bypass surgery, for CLI in diabetic patients who are at high risk of perioperative complications.

Identification and characterization of a novel transcriptional regulator, MatR, for malonate metabolism in Rhizobium leguminosarum bv. trifolii

A novel gene, matR, located upstream of matABC, transcribed in the opposite direction, and encoding a putative regulatory protein by sequence analysis was discovered from Rhizobium leguminosarum bv. trifolii. The matA, matB, and matC genes encode malonyl-CoA decarboxylase, malonyl-CoA synthetase, and a presumed malonate transporter, respectively. Together, these enzymes catalyze the uptake and conversion of malonate to acetyl-CoA. The deduced amino-acid sequence of matR showed sequence similarity with GntR from Bacillus subtilis in the N-terminal region encoding a helix-turn-helix domain. Electrophoretic mobility shift assay indicated that MatR bound to a fragment of DNA corresponding to the mat promoter region. The addition of malonate or methylmalonate increased the association of MatR and DNA fragment. DNase I footprinting assays identified a MatR binding site encompassing 66 nucleotides near the mat promoter. The mat operator region included an inverted repeat (TCTTGTA/TACACGA) centered -46.5 relative to the transcription start site. Transcriptional assays, using the luciferase gene, revealed that MatR represses transcription from the mat promoter and malonate alleviates MatR-mediated repression effect on the expression of Pmat-luc+ reporter fusion.

The active site and substrates binding mode of malonyl-CoA synthetase determined by transferred nuclear Overhauser effect spectroscopy, site-directed mutagenesis, and comparative modeling studies

The active sites and substrate bindings of Rhizobium trifolii molonyl-CoA synthetase (MCS) catalyzing the malonyl-CoA formation from malonate and CoA have been determined based on NMR spectroscopy, site-directed mutagenesis, and comparative modeling methods. The MCS-bound conformation of malonyl-CoA was determined from two-dimensional-transferred nuclear Overhauser effect spectroscopy data. MCS protein folds into two structural domains and consists of 16 alpha-helices, 24 beta-strands, and several long loops. The core active site was determined as a wide cleft close to the end of the small C-terminal domain. The catalytic substrate malonate is placed between ATP and His206 in the MCS enzyme, supporting His206 in its catalytic role as it generates reaction intermediate, malonyl-AMP. These findings are strongly supported by previous biochemical data, as well as by the site-directed mutagenesis data reported here. This structure reveals the biochemical role as well as the substrate specificity that conservative residues of adenylate-forming enzymes have.

Identification of residues essential for a two-step reaction by malonyl-CoA synthetase from Rhizobium trifolii

Malonyl-CoA synthetase (MCS) catalyses the formation of malonyl-CoA in a two-step reaction consisting of the adenylation of malonate with ATP followed by malonyl transfer from malonyl-AMP to CoA. In order to identify amino acid residues essential for each step of the enzyme, catalysis based on chemical modification and database analysis, Arg-168, Lys-170, and His-206 were selected for site-directed mutagenesis. Glutathione-S-transferase-fused enzyme (GST-MCS) was constructed and mutagenized to make R168G, K170M, R168G/K170M and H206L mutants, respectively. The MCS activity of soluble form GST-MCS was the same as that of wild-type MCS. Circular dichroism spectra for the four mutant enzymes were nearly identical to that for the GST-MCS, indicating that Arg-168, Lys-170 and His-206 are not important for conformation but presumably for substrate binding and/or catalysis. HPLC analysis of products revealed that the intermediate malonyl-AMP is not accumulated during MCS catalysis and that none of the mutant enzymes accumulated it either. Kinetic analysis of the mutants revealed that Lys-170 and His-206 play a critical role for ATP binding and the formation of malonyl-AMP, whereas Arg-168 is critical for formation of malonyl-CoA and specificity for malonyl-AMP. Molecular modelling based on the crystal structures of luciferase and gramicidin S synthetase 1 provided MCS structure which could fully explain all these biochemical data even though the MCS model was generated by comparative modelling.

A gene cluster encoding malonyl-CoA decarboxylase (MatA), malonyl-CoA synthetase (MatB) and a putative dicarboxylate carrier protein (MatC) in Rhizobium trifolii--cloning, sequencing, and expression of the enzymes in Escherichia coli

A gene cluster consisting of three consecutive genes, matABC, was isolated using a probe prepared from amino acid sequence information of Rhizobium trifolii malonyl-CoA synthetase, and was subsequently sequenced. The sequences of matA and matB were overlapped by four base pairs, whereas the intergenic region between matB and matC had 95 base pairs. The upstream region contained DNA sequences which are typical for an Escherichia coli sigma70 promoter, and no other open reading frame was found within 400 bp downstream of matC. The ribosome-binding sites were found 7 to 12 base pairs upstream of each gene. MatA gene encoded a polypeptide of 462 amino acid residues, with deduced molecular mass of 51414 Da. A glutathione-S-transferase-MatA fusion protein has been purified and MatA was shown to have an intrinsic malonyl-CoA decarboxylase activity (Km = 0.47 mM; Vmax = 52 micromol x min(-1) x mg(-1)). MatB encoded a polypeptide of 504 amino acid residues with deduced molecular mass of 54612 Da. MatB was also purified from E. coli transformant carrying the gene cluster. The enzyme was essentially indistinguishable from the wild-type malonyl-CoA synthetase of R. trifolii by the criteria of polyacrylamide gel electrophoresis and biochemical properties. MatC encoded a 46453-Da protein with a high content of hydrophobic residues. The deduced amino acid sequences of matC showed identity to some extent with anaerobic C4-dicarboxylate carrier proteins from E. coli (25%) and Haemophilus influenzae (17%). MatC protein appears to be an integral membrane protein that could function as a malonate carrier. The formation of acetyl-CoA and malonyl-CoA from malonate was confirmed by thin-layer chromatographic analysis. These results strongly suggest that the gene cluster encodes proteins involved in the malonate-metabolizing system, malonate-->malonyl-CoA-->acetyl-CoA, in R. trifolii and that the metabolic pathway in the malonate-rich clover nodule might play an important role in symbiosis.

High-performance reversed-phase chromatographic mapping of 2-pyridylamino derivatives of xyloglucan oligosaccharides

Xyloglucan oligosaccharides from cotton cell walls and tamarind seeds were derivatized with 2-aminopyridine and subsequently separated by reversed-phase chromatography (r.p.c.) using an octadecylsilyl silica stationary phase and aqueous-organic eluents with 0.01% (v/v) trifluoroacetic acid. The chromatographic behavior of the 2-pyridylamino derivatives of xyloglucan oligosaccharides was examined under a wide range of elution conditions, including gradient steepness and shape, initial acetonitrile concentration in the eluent, and pore size of the r.p.c. packings. Relatively steep acetonitrile gradients resulted in poor resolution of the different xyloglucan fragments, which is believed to be the result of acetonitrile-induced conformational changes. Under these circumstances the elution order of the derivatized xyloglucan oligosaccharides was such that the smaller fragments eluted from the column before the larger ones. R.p.c. packing with a 70-A pore size necessitated relatively high acetonitrile concentration in the eluent when compared with 300-A stationary phase. The r.p.c. mapping of 2-pyridylamino derivatives of xyloglucan oligosaccharides was best achieved when both a wide-pore octadecyl-silyl silica stationary phase and a shallow gradient with consecutive linear segments of increasing acetonitrile concentration in the eluent were employed. This combination yielded rapid r.p.c. maps of the xyloglucan fragments from different sources with high separation efficiencies and concomitantly high resolution. The effects of the nature of the sugar residues in the xyloglucan oligomers and their degree of branching on r.p.c. retention and selectivity are also highlighted.