Downregulation of p38 MAPK Activation and Radiation-Sensitive 52 Expression Enhances 5-Fluorouracil and Erlotinib-Induced Cytotoxicity in Human Lung Squamous Cells.

INTRODUCTION: 5-Fluorouracil (5-FU) is used to treat various cancers, including non-small-cell lung cancer (NSCLC). It inhibits nucleotide synthesis and induces single- and double-strand DNA breaks. In the homologous recombination pathway, radiation-sensitive 52 (Rad52) plays a crucial role in DNA repair by promoting the annealing of complementary single-stranded DNA and stimulating Rad51 recombinase activity. Erlotinib (Tarceva) is a selective epidermal growth factor receptor tyrosine kinase inhibitor with clinical activity against NSCLC cells. However, whether the combination of 5-FU and erlotinib has synergistic activity against NSCLC cells is unknown. METHODS: After the 5-FU and/or erlotinib treatment, the expressions of Rad52 mRNA were determined by quantitative real-time polymerase chain reaction analysis. Protein levels of Rad52 and phospho-p38 MAPK were determined by Western blot analysis. We used specific Rad52 or p38 MAPK small interfering RNA and p38 MAPK inhibitor (SB2023580) to examine the role of p38 MAPK-Rad52 signal in regulating the chemosensitivity of 5-FU and/or erlotinib. Cell viability was assessed by MTS assay and trypan blue exclusion assay. RESULTS: In 2 squamous cell carcinoma cell lines, namely, H520 and H1703, 5-FU reduced Rad52 expression in a p38 MAPK inactivation-dependent manner. Enhancement of p38 MAPK activity by transfection with MKK6E (a constitutively active form of MKK6) vector increased the Rad52 protein level and cell survival by 5-FU. However, in human lung bronchioloalveolar cell adenocarcinoma A549 cells, 5-FU reduced Rad52 expression and induced cytotoxicity independent of p38 MAPK. Moreover, 5-FU synergistically enhanced the cytotoxicity and cell growth inhibition of erlotinib in NSCLC cells; these effects were associated with Rad52 downregulation and p38 MAPK inactivation in H520 and H1703 cells. CONCLUSION: The results provide a rationale for combining 5-FU and erlotinib in lung cancer treatment.

Probiotic, Bacillus subtilis E20 alters the immunity of white shrimp, Litopenaeus vannamei via glutamine metabolism and hexosamine biosynthetic pathway.

The purpose of this study was to profile the mechanisms of action of probiotic, Bacillus subtilis E20 in activating the immunity of white shrimp, Litopenaeus vannamei. Two groups of shrimp were studied. One group was fed a control diet without probiotic supplementation and the other was fed a probiotic-containing diet at a level of 109 cfu kg diet-1. After the 8-week feeding regimen, the metabolite composition in the hepatopancreas of shrimp were investigated using 1H nuclear magnetic resonance (1H NMR) based metabolomic analysis. Results from the 1H NMR analysis revealed that 16 hepatopancreatic metabolites were matched and identified among groups, of which 2 metabolites, creatinine and glutamine were significantly higher in probiotic group than in the control group. This result was confirmed by the reverse-phase high-performance liquid chromatography (RP-HPLC) and spectrophotometric analysis. Transcriptome analysis indicated the expressions of 10 genes associated with antioxidant enzymes, pattern recognition proteins and antimicrobial molecules, more active expression in the shrimp fed a diet supplemented with probiotic as compared to that of shrimp in control. In addition, the expressions of 4 genes involved with hexosamine biosynthesis pathway (HBP) and UDP-N-acetylglucosamine-peptide N-acetylglucosaminyltransferase for protein O-glycosylation were also higher in hepatopancreas of probiotic-treated shrimp than in shrimp fed a control diet. Western blot and enzyme-linked immunosorbent assay showed that heat shock factor 1, heat shock protein 70, and protein O-glycosylation in hepatopancreas were higher in probiotic group than the control group. These findings suggest that probiotic, B. subtilis E20 promotes the digestibility of glutamine in the diet, and that the increased glutamine in shrimp can be used as fuel for immune cells or may be used to regulate immune molecule expressions and protein O-glycosylation via the HBP to increase protein O-glycosylation, thereby improving the health of shrimp.

Nitroglycerin-induced downregulation of AKT- and ERK1/2-mediated radiation-sensitive 52 expression to enhance pemetrexed-induced cytotoxicity in human lung cancer cells.

Nitroglycerin (NTG)-a nitric oxide-donating drug-is traditionally administered via the sublingual route to treat acute myocardial angina attacks. NTG also increases tumor blood flow and, consequently, cancer drug delivery to tumor cells. In the homologous recombination pathway, radiation-sensitive 52 (Rad52) plays a crucial role in DNA repair by promoting the annealing of complementary single-stranded DNA and stimulating radiation-sensitive 51 (Rad51) recombinase activity. Pemetrexed-a multitargeted antifolate agent-exhibits satisfactory clinical activity in wild-type nonsquamous non-small-cell lung cancer (NSCLC) cells. However, the synergistic activity of combination therapy with NTG and pemetrexed against NSCLC cells has not yet been clarified. In 2 NSCLC cell lines (i.e. lung squamous cell carcinoma H520 and lung adenocarcinoma H1975 cells), NTG reduced Rad52 expression; in addition, decreased phospho-AKT and phospho-ERK1/2 protein levels were observed. Enhancement of AKT or ERK1/2 activity through transfection with a constitutively active AKT (AKT-CA) vector or constitutively active mitogen-activated protein kinase kinase 1 (MKK1-CA) vector increased the Rad52 protein level and cell survival, which were suppressed by NTG. The knockdown of Rad52 expression by using small interfering RNA or by inhibiting AKT and ERK1/2 activity enhanced the cytotoxicity and cell growth inhibition induced by NTG. Moreover, NTG synergistically enhanced the cytotoxicity and cell growth inhibition induced by pemetrexed in NSCLC cells; these effects were associated with AKT and ERK1/2 inactivation and, consequently, Rad52 downregulation in H520 and H1975 cells. The results provide a rationale for combining NTG and pemetrexed in lung cancer treatment to improve lung cancer control.

Heat shock protein 90 inhibitor 17-AAG down-regulates thymidine phosphorylase expression and potentiates the cytotoxic effect of tamoxifen and erlotinib in human lung squamous carcinoma cells.

Elevated thymidine phosphorylase (TP) levels, a key enzyme in the pyrimidine nucleoside salvage pathway, in cancer cells, are related to a poor prognosis in a variety of cancers. Heat shock protein 90 (Hsp90) is a ubiquitous molecular chaperone that is involved in the stabilization and maturation of many oncogenic proteins. The aim of this study is to elucidate whether Hsp90 inhibitor 17-AAG could enhance tamoxifen- and erlotinib-induced cytotoxicity in nonsmall cell lung cancer (NSCLC) cells via modulating TP expression in two squamous NSCLC cell lines, H520 and H1703. We found that 17-AAG reduced TP expression via inactivating the MKK1/2-ERK1/2-mitogen-activated protein kinase (MAPK) pathway. TP knockdown with siRNA or ERK1/2 MAPK inactivation with the pharmacological inhibitor U0126 could enhance the cytotoxic and growth inhibitory effects of 17-AAG. In contrast, MKK1-CA or MKK2-CA (a constitutively active form of MKK1/2) vector-enforced expression could reduce the cytotoxic and cell growth inhibitory effects of 17-AAG. Furthermore, 17-AAG enhanced the cytotoxic and cell growth inhibitory effects of tamoxifen and erlotinib in NSCLC cells, which were associated with TP expression downregulation and MKK1/2-ERK1/2 signal inactivation. Taken together, Hsp90 inhibition downregulates TP, enhancing the tamoxifen- and erlotinib-induced cytotoxicity in H520 and H1703 cells.