A comprehensive test system to identify suitable antibodies against p53 for immunohistochemical analysis of canine tissues

The tumour suppressor p53 is commonly detected in tissues of companion animals by means of antibodies raised against the human protein. The following three-step procedure was devised to test the suitability of such antibodies for immunohistochemistry on canine tissues. (1) Western blot and immunohistochemical analyses on bacterially expressed recombinant canine protein to assess human-to-canine cross-reactivity. (2) Immunohistochemistry of cultured, UVB-irradiated canine keratinocytes to evaluate suitability for detection of endogenous p53. (3) Immunohistochemistry on tissue arrays to further substantiate suitability of the antibodies on a panel of normal and neoplastic human and canine tissues. Five of six antibodies cross-reacted with recombinant canine p53. Three of these (PAb122, PAb240, CM-1) also immunolabelled stabilized wild type p53 in cell cultures and elicited a consistent, characteristic labelling pattern in a subset of tumours. However, two alternative batches of polyclonal antibody CM-1 failed to detect p53 in cell cultures, while showing a characteristic labelling pattern of a completely different subset of tumours and unspecific labelling of normal tissues. The test system described is well suited to the selection of antibodies for immunohistochemical p53 detection. The results emphasize the need to include appropriate controls, especially for polyclonal antibodies.

The mitochondrial uncoupling protein-2 promotes chemoresistance in cancer cells

Cancer cells acquire drug resistance as a result of selection pressure dictated by unfavorable microenvironments. This survival process is facilitated through efficient control of oxidative stress originating from mitochondria that typically initiates programmed cell death. We show this critical adaptive response in cancer cells to be linked to uncoupling protein-2 (UCP2), a mitochondrial suppressor of reactive oxygen species (ROS). UCP2 is present in drug-resistant lines of various cancer cells and in human colon cancer. Overexpression of UCP2 in HCT116 human colon cancer cells inhibits ROS accumulation and apoptosis after exposure to chemotherapeutic agents. Tumor xenografts of UCP2-overexpressing HCT116 cells retain growth in nude mice receiving chemotherapy. Augmented cancer cell survival is accompanied by altered NH(2)-terminal phosphorylation of the pivotal tumor suppressor p53 and induction of the glycolytic phenotype (Warburg effect). These findings link UCP2 with molecular mechanisms of chemoresistance. Targeting UCP2 may be considered a novel treatment strategy for cancer.

Combined alpha-methylacyl coenzyme A racemase/p53 analysis to identify dysplasia in inflammatory bowel disease

Identification of dysplasia in inflammatory bowel disease represents a major challenge for both clinicians and pathologists. Clear diagnosis of dysplasia in inflammatory bowel disease is sometimes not possible with biopsies remaining "indefinite for dysplasia." Recent studies have identified molecular alterations in colitis-associated cancers, including increased protein levels of alpha-methylacyl coenzyme A racemase, p53, p16 and bcl-2. In order to analyze the potential diagnostic use of these parameters in biopsies from inflammatory bowel disease, a tissue microarray was manufactured from colons of 54 patients with inflammatory bowel disease composed of 622 samples with normal mucosa, 78 samples with inflammatory activity, 6 samples with low-grade dysplasia, 12 samples with high-grade dysplasia, and 66 samples with carcinoma. In addition, 69 colonoscopic biopsies from 36 patients with inflammatory bowel disease (28 low-grade dysplasia, 8 high-grade dysplasia, and 33 indefinite for dysplasia) were included in this study. Immunohistochemistry for alpha-methylacyl coenzyme A racemase, p53, p16 and bcl-2 was performed on both tissue microarray and biopsies. p53 and alpha-methylacyl coenzyme A racemase showed the most discriminating results, being positive in most cancers (77.3% and 80.3%) and dysplasias (94.4% and 94.4%) but only rarely in nonneoplastic epithelium (1.6% and 9.4%; P < .001). Through combining the best discriminators, p53 and alpha-methylacyl coenzyme A racemase, a stronger distinction between neoplastic tissues was possible. Of all neoplastic lesions, 75.8% showed a coexpression of alpha-methylacyl coenzyme A racemase and p53, whereas this was found in only 4 of 700 nonneoplastic samples (0.6%). alpha-methylacyl coenzyme A racemase/p53 coexpression was also found in 10 of 33 indefinite for dysplasia biopsies (30.3 %), suggesting a possible neoplastic transformation in these cases. Progression to dysplasia or carcinoma was observed in 3 of 10 p53/alpha-methylacyl coenzyme A racemase-positive, indefinite-for-dysplasia cases, including 1 of 7 cases without and 2 of 3 cases with p53 mutation. It is concluded that combined alpha-methylacyl coenzyme A racemase/p53 analysis may represent a helpful tool to confirm dysplasia in inflammatory bowel disease.

Increased cytotoxicity of cisplatin in SK-MEL 28 melanoma cells upon down-regulation of melanoma inhibitor of apoptosis protein

BACKGROUND: Malignant melanoma is a highly metastatic cutaneous cancer and typically refractory to chemotherapy. Deregulated apoptosis has been identified as a major cause of cancer drug resistance, and upregulated expression of the inhibitor of apoptosis protein melanom, an inhibitor of apoptosis (ML-IAP) is frequent in melanoma. METHODS: Based on the conclusion that ML-IAP expression contributes to a malignant phenotype, we down-regulated the ML-IAP mRNA using sequence optimized antisense oligonucleotides. RESULTS: As measured by real-time PCR, oligonucleotides M706 and M711 inhibited ML-IAP mRNA expression by 47% and 52%, respectively in the highly metastatic and drug resistant SK-MEL28 cell line. Oligonucleotide M706, which was previously evaluated in G361 cells as the most efficient inhibitor of ML-IAP expression, was chosen to compare cell viability and drug sensitivity of these two melanoma cell lines with different p53 functionality. Protein expression was reduced by oligonucleotide M706 to 49% of the normal level and resulted in a dose-dependent specific reduction of cell viability with a maximum of 39% at 600 nM. Typical morphological changes showed that loss of viability was mainly due to cell death. In combination experiments, the use of oligonucleotide M706 resulted in a two-fold increase of cisplatin cytotoxicity at different concentrations of oligonucleotide and cisplatin (P<0.05). This is in line with our previous findings in G361 melanoma cell line, in which oligonucleotide M706 caused a 3-fold increase in cisplatin cytotoxicity. CONCLUSION: Our data suggest the use of ML-IAP antisense oligonucleotides to overcome drug resistance in metastatic melanoma, in spite of its p53 status.

Inactivation of the p53-KLF4-CEBPA Axis in Acute Myeloid Leukemia.

PURPOSE In acute myeloid leukemia (AML), the transcription factors CEBPA and KLF4 as well as the universal tumor suppressor p53 are frequently deregulated. Here, we investigated the extent of dysregulation, the molecular interactions, and the mechanisms involved. EXPERIMENTAL DESIGN One hundred ten AML patient samples were analyzed for protein levels of CEBPA, KLF4, p53, and p53 modulators. Regulation of CEBPA gene expression by KLF4 and p53 or by chemical p53 activators was characterized in AML cell lines. RESULTS We found that CEBPA gene transcription can be directly activated by p53 and KLF4, suggesting a p53-KLF4-CEBPA axis. In AML patient cells, we observed a prominent loss of p53 function and concomitant reduction of KLF4 and CEBPA protein levels. Assessment of cellular p53 modulator proteins indicated that p53 inactivation in leukemic cells correlated with elevated levels of the nuclear export protein XPO1/CRM1 and increase of the p53 inhibitors MDM2 and CUL9/PARC in the cytoplasm. Finally, restoring p53 function following treatment with cytotoxic chemotherapy compounds and p53 restoring non-genotoxic agents induced CEBPA gene expression, myeloid differentiation, and cell-cycle arrest in AML cells. CONCLUSIONS The p53-KLF4-CEBPA axis is deregulated in AML but can be functionally restored by conventional chemotherapy and novel p53 activating treatments. Clin Cancer Res; 22(3); 746-56. ©2015 AACR.