Characterization of a polyclonal antibody to human thymidylate synthase suitable for the study of colorectal cancer specimens

A synbiotic combination of Lactobacillus gasseri 505 and Cudrania tricuspidata leaf extract prevents hepatic toxicity induced by colorectal cancer in mice

Colorectal cancer (CRC) is known to be a life-threatening disease and commonly leads to metastasis in the liver. Fermented milk acts as an effective carrier for probiotic strains, whose consumption improves host health. Our previous study indicated that fermented milk that included a synbiotic combination of Lactobacillus gasseri 505 (505) and Cudrania tricuspidata leaf extract (CT) resulted in significantly greater anti-oxidative effects than fermented milk without CT. Therefore, we hypothesized that fermented milk containing CT and 505 (FCT) could result in hepatoprotective effects against CRC-induced liver metastasis. Liver inflammation and CRC were induced in male C57BL/6J mice, using azoxymethane/dextran sodium sulfate, and 505, CT, and FCT were administered to the 3 sample-treated 505, CT, and FCT groups, respectively, for 10 wk. The results showed that FCT treatment significantly reduced serum aspartate aminotransferase and alanine aminotransferase concentrations and elevated albumin concentrations. Moreover, the results of histological analysis showed that hepatic steatosis was notably reduced in the FCT group. Among the 3 sample-treated groups, the expression of mRNA associated with enzymes showing anti-oxidative activities, such as superoxide dismutase, catalase, and glutathione reductase, was the highest in the FCT-treated mice. In addition, FCT administration resulted in the greatest anti-inflammatory activity, as inflammatory marker levels (i.e., tumor necrosis factor-α, cyclooxygenase-2, myeloperoxidase, and nuclear factor kappa-light-chain enhancer of activated B cells) were significantly downregulated at the mRNA level and the expression of proteins associated with the nuclear factor kappa-light-chain enhancer of activated B cells and mitogen-activated protein kinase signaling pathways was suppressed by FCT. Therefore, this study demonstrated that fermented milk containing novel synbiotics has the potential to prevent hepatic toxicity induced because of CRC owing to its enhanced anti-oxidative and anti-inflammatory activities.

Prognostic significance of 5-fluorouracil metabolism-relating enzymes and enhanced chemosensitivity to 5-fluorouracil by 5-chloro 2,4-dihydroxy-pyridine in urothelial carcinoma

Background

Recently, S-1, a novel 5-fluorouracil (5-FU)-based agent containing the strong dihydropyrimidine dehydrogenase (DPD) inhibitor, 5-chloro-2,4-dihydropyrimidine (CDHP) has been clinically used to treat various non-urothelial carcinomas (UC). High levels of thymidylate synthase (TS), the target enzyme of 5-FU and DPD which degrades the majority of 5-FU, are associated with poor prognosis in some cancers. However, only a few reports have dealt with this in UC. The aim of this study was to investigate the clinical significance of TS and DPD in upper tract urothelial carcinoma (UTUC) and evaluate the role of TS and DPD on the sensitivity of 5-FU in UC cell lines and the anti-tumor effect of S-1 in UC xenograft model.

Methods

Firstly, we evaluated the immunohistochemical expression of TS and DPD in 176 patients with UTUC to determine their prognostic significance. Secondly, the levels of TS and DPD in UC cell lines were measured by ELISA and real-time PCR. Furthermore, the association between their levels and the sensitivity to 5-FU was examined using the small interfering RNA (siRNA) specific for TS and DPD. Thirdly, the anti-tumor effect of S-1 was evaluated in UC xenograft model.

Results

Immunohistochemical evaluation of TS and DPD in UTUC human samples revealed that TS expression was significantly associated with stage, grade, and lymphovascular invasion and DPD expression was significantly associated with grade. Multivariate analysis revealed that high TS expression was an independent predictor of disease-specific survival in them. In in vitro study using UC cell lines, high levels of TS and DPD were associated with low response to 5-FU and these associations were confirmed with siRNA specific for TS and DPD. In in vivo study using UC xenograft model, S-1 treatment dramatically inhibited tumor growth compared to controls, tegafur, or UFT in UC tumor with a high level of DPD.

Conclusions

TS plays an important role in the prognosis of UTUC and S-1 may be a key agent for UC tumor, especially with a high level of DPD.

Expression of thymidylate synthase in human cells is an early G(1) event regulated by CDK4 and p16INK4A but not E2F

Thymidylate synthase (TS) is the enzyme that catalyses the last step in de novo thymidylate synthesis. It is of interest clinically because it is an effective target for drugs such as 5-fluorouracil, often used in combination therapy. Despite a number of earlier reports indicating that TS is a cell cycle-dependent enzyme, this remains equivocal. Here, we show that in HCT116 cells synchronised by serum starvation, there is a clear dissociation between the expression of cyclin E (a well-characterised cell-cycle protein) and TS. Although both cyclin E and TS mRNA and protein increased during G₁, TS upregulation was delayed. Moreover, TS levels did not decrease following S-phase completion while cyclin E decreased sharply. Similarly, clear differences were seen between cyclin E and TS as asynchronously growing HCT116 cells were growth-inhibited by low-serum treatment. In contrast to previous reports using rodent cells, adenovirus-mediated over-expression of E2F1 and cyclin E in three human cell lines had no effect on TS. Cell-cycle progression was blocked by treatment of cells with pharmacological inhibitors of CDK2 and CDK4 and by ectopic expression of p16INK4A. Whereas CDK2 inhibition had no effect on TS levels, inhibition of CDK4 was associated with decreased TS protein levels. These results provide the first evidence that drugs targeting CDK4 may be useful with anti-TS drugs as combination therapy for cancer.

Nuclear expression of thymidylate synthase in colorectal cancer cell lines and clinical samples

Thymidylate synthase (TS) [TYMS; OMIM reference number (188,350)] is normally considered to be a cytoplasmic enzyme. However, a few reports have suggested it may also be present in the nucleus. To explore this in more detail, we used a highly specific polyclonal antibody to TS and a combination of techniques, including immunocytochemistry, confocal microscopy, cell fractionation, and Western blotting. We developed cell line HeLa-55, a HeLa derivative that grossly overexpresses TS. Although the vast majority of TS was in the cytoplasm, some TS also was seen in the nucleus. TS in parental HeLa cells and in normal human fibroblasts was seen exclusively in the cytoplasm. HeLa-55 cells exposed to 5-fluorodeoxyuridine were fractionated and examined by Western blotting. Interestingly, both free TS and the ternary complex of TS were seen in the cytoplasmic fraction but only free TS was detected in the nuclear fraction. Amongst different cell lines examined, HCT-15 and normal fibroblasts showed no nuclear TS, HCC-2998 and SW-620 showed a small amount of nuclear TS, and HT-29, RKO, and HCT-116 showed a strong nuclear TS signal. Nuclear staining was clearly evident in some clinical colorectal specimens, both normal and malignant. This staining was definitively shown to be TS by competition with recombinant TS protein. A putative leucine-rich nuclear export sequence was identified but its function could not be confirmed. We conclude that small amounts of TS protein is present in the nucleus of some cell types but further work is needed to determine the significance of this observation.

Selective expression of Kir6.1 protein in different vascular and non-vascular tissues

K(ATP) channels are composed of pore-forming subunits Kir6.x and auxiliary subunits SURx. These channels play important roles in modulating the contractility of vascular smooth muscle cells (SMCs) by altering membrane potentials. The molecular basis of K(ATP) channels in vascular SMCs is unclear and the expression of different K(ATP) channel subunits at protein level in various tissues still undetermined. In this study, using an anti-Kir6.1 antibody, we detected the expression of Kir6.1 proteins in rat vascular tissues including mesenteric artery, pulmonary artery, aorta, and tail artery. Kir6.1 proteins were also identified in heart and other non-vascular tissues including spleen and brain, but they were undetectable in liver and kidney. Immunocytochemical study revealed the expression of Kir6.1 proteins in cultured rat thoracic aortic SMCs. Using the whole-cell patch-clamp technique, it was found that the intracellularly applied anti-Kir6.1 antibody significantly inhibited K(ATP) channel currents in HEK-293 cells that were stably transfected with Kir6.1 cDNA. A better understanding of differential expression of Kir6.1 proteins in various vascular and non-vascular tissues may help discern different molecular basis and functions of K(ATP) channel complexes in these tissues.

Selective nitration of histone tyrosine residues in vivo in mutatect tumors

Nitric oxide-derived reactive species have been implicated in many disorders. Protein nitrotyrosine is often used as a stable marker of these reactive species. Using immunohistochemistry, we have previously detected nitrotyrosine in murine Mutatect tumors, where neutrophils are the principal source of nitric oxide. We now report on the identification of several prominent nitrotyrosine-containing proteins. Using Western blot analysis, nitrotyrosine in higher molecular mass proteins (>20 kDa) was detected in tumors containing a high number of neutrophils but not in tumors with fewer neutrophils. Staining for nitrotyrosine was consistently seen in low molecular mass proteins (< or =15 kDa), regardless of the level of neutrophils. Protein nitrotyrosine was not seen in Mutatect cells growing in vitro. Treatment with nitric oxide donors produced nitration of < or =15-kDa proteins, but only after extended periods. These small proteins, both from tumors and cultured cells, were identified by mass spectrometry to be histones. Only a subset of tyrosine residues was nitrated. Selective nitration may reflect differential accessibility of different tyrosine residues and the influence of neighboring residues within the nucleosome. The prominence of histone nitration may reflect its relative stability, making this post-translational modification a potentially useful marker of extended exposure of cells or tissues to nitric oxide-derived reactive species.