p53-independent WAF1 induction by ACNU in human glioblastoma cells

Ctenopharyngodon idella p53 mediates between NF-κB and PKR at the transcriptional level

p53, NF-κB and PKR are well-known to be involved in antiviral response. Although p53 has been reported in fish, its role in the regulation of NF-κB and PKR is not well understood. Here, we cloned and characterized the full length of cDNA sequence of grass carp (Ctenopharyngodon idella) p53 (Cip53) and its promoter sequence. The full length cDNA of Cip53 was 1879 bp with an ORF of 1116 bp encoding a polypeptide of 371 amino acids. Phylogenetic tree analysis revealed that Cip53 shares high homology with Dario rerio p53 (Drp53). Similar to those of Cip65 and CiPKR, the expression of Cip53 in CIK cells was significantly up-regulated after stimulation with poly I:C. To further understand the roles of fish p53 in the transcriptional control of NF-κB and PKR, Cip53 and Cip65 were expressed in E. coli BL21 and purified by affinity chromatography with the Ni-NTA His-Bind resin. In vitro, gel mobility shift assays demonstrated that the high affinity interaction between Cip65 and Cip53 promoter. Similarly, Cip53 bound to CiPKR promoter with high affinity. Dual-luciferase reporter assays showed that Cip65 activated Cip53 promoter and Cip53 activated CiPKR promoter, respectively. In addition, the role of p53 in p65-p53-PKR transcription pathway was explored. When Cip53 was knockdown in CIK cells, the mRNA levels of Cip65 and CiPKR were decreased. Taken together, p53 may play pivotal roles in transcription pathway of NF-κB and PKR in fish.

Chloroethylating nitrosoureas in cancer therapy: DNA damage, repair and cell death signaling

Chloroethylating nitrosoureas (CNU), such as lomustine, nimustine, semustine, carmustine and fotemustine are used for the treatment of malignant gliomas, brain metastases of different origin, melanomas and Hodgkin disease. They alkylate the DNA bases and give rise to the formation of monoadducts and subsequently interstrand crosslinks (ICL). ICL are critical cytotoxic DNA lesions that link the DNA strands covalently and block DNA replication and transcription. As a result, S phase progression is inhibited and cells are triggered to undergo apoptosis and necrosis, which both contribute to the effectiveness of CNU-based cancer therapy. However, tumor cells resist chemotherapy through the repair of CNU-induced DNA damage. The suicide enzyme O⁶-methylguanine-DNA methyltransferase (MGMT) removes the precursor DNA lesion O⁶-chloroethylguanine prior to its conversion into ICL. In cells lacking MGMT, the formed ICL evoke complex enzymatic networks to accomplish their removal. Here we discuss the mechanism of ICL repair as a survival strategy of healthy and cancer cells and DNA damage signaling as a mechanism contributing to CNU-induced cell death. We also discuss therapeutic implications and strategies based on sequential and simultaneous treatment with CNU and the methylating drug temozolomide.

Molecular signalling pathways in canine gliomas

In this study, we determined the expression of key signalling pathway proteins TP53, MDM2, P21, AKT, PTEN, RB1, P16, MTOR and MAPK in canine gliomas using western blotting. Protein expression was defined in three canine astrocytic glioma cell lines treated with CCNU, temozolamide or CPT-11 and was further evaluated in 22 spontaneous gliomas including high and low grade astrocytomas, high grade oligodendrogliomas and mixed oligoastrocytomas. Response to chemotherapeutic agents and cell survival were similar to that reported in human glioma cell lines. Alterations in expression of key human gliomagenesis pathway proteins were common in canine glioma tumour samples and segregated between oligodendroglial and astrocytic tumour types for some pathways. Both similarities and differences in protein expression were defined for canine gliomas compared to those reported in human tumour counterparts. The findings may inform more defined assessment of specific signalling pathways for targeted therapy of canine gliomas.

Prevention of colitis-associated carcinogenesis in a mouse model by diet supplementation with ursodeoxycholic acid

Bile acids in the intestinal lumen contribute to the homeostatic regulation of proliferation and death of the colonic epithelial cells: Deoxycholic acid (DCA) appears to enhance and ursodeoxycholic acid (UDCA) to attenuate the process of chemically induced carcinogenesis. We studied the effects of UDCA on colitis-related colorectal carcinogenesis. Three groups of 25 mice were given 0.7% dextran sulphate in drinking water for 7 days and pure water for 10 days and were fed a standard diet containing double iron concentration. In 2 groups, the diet was supplemented with 0.2% cholic acid (CA), the precursor of DCA, or with 0.4% UDCA. After 15 cycles, the histology, the expression of MUC2, beta-catenin, p27 and p16 and the fecal water concentration of DCA and UDCA were investigated. All animals showed colitis with similar severity and histologic as well as immunophenotypic alterations, resembling those of human colitis. Among the animals fed the nonsupplemented diet, 46% developed colorectal adenocarcinomas and 54% anal-rectal squamous cell carcinomas. The prevalence of dysplasia and carcinomas did not change significantly in the animals given CA. Among the mice fed with UDCA, none developed adenocarcinomas and 20% squamous carcinomas. Dysplastic lesions were found in 88%, 67% and 40% of each group, respectively. The prevalence of dysplasia as well as of carcinoma showed an inverse relationship to the UDCA concentration in the fecal water. These data indicate that UDCA suppresses colitis-associated carcinogenesis. This model is suitable for investigation of the mechanism of the anticarcinogenic effect of UDCA in vivo.