1: Pediatr Blood Cancer. 2005 Aug 5; [Epub ahead of print] p53 pathway dysfunction in primary childhood ependymomas. Gaspar N, Grill J, Geoerger B, Lellouch-Tubiana A, Michalowski MB, Vassal G. Pharmacology and New Treatments in Cancer UPRES EA 3535, Institut Gustave Roussy, Villejuif, France. BACKGROUND: Childhood ependymoma remains a major therapeutic challenge despite surgery, chemotherapy, and irradiation. We hypothesized that p53 function might be abrogated in ependymomas and implicated in their resistance to anti-cancer therapy. PROCEDURE: Primary ependymomas at diagnosis or relapse from 24 children were analyzed for p53 pathway, using a functional assay in yeast, RT-PCR, Western blot analysis, and/or immunohistochemistry for TP53 mutation, p14(ARF) deletion and promoter hypermethylation, MDM2 and PAX5 expression, respectively. p53-mediated response to radiation-induced DNA damage was evaluated using Western blot and flow cytometry analysis in two ependymoma xenograft models, IGREP37 and IGREP83, derived from primary anaplastic childhood ependymomas. RESULTS: No TP53, MDM2, p14(ARF), PAX5 gene abnormalities were detected in the primary ependymomas tumors and xenografts tested. Interestingly, despite the lack of these abnormalities, p53 induced p21-mediated G(1) growth arrest in response to irradiation was altered in the IGREP37 xenograft tumors. Although irradiation induced necrosis and apoptotic cell death, IGREP37 tumors were moderately sensitive to radiation therapy in vivo. In contrast, irradiation yielded significant tumor growth delays and tumor regressions in the p53 functional IGREP83 xenografts. CONCLUSION: Alterations in p53-mediated growth arrest in ependymomas might be implicated in the radio-resistance of these tumors and demand further evaluation. (c) 2005 Wiley-Liss, Inc. PMID: 16086408 [PubMed - as supplied by publisher] --------------------------------------------------------------- 2: Int Urol Nephrol. 2002-2003;34(4):495-501. The expression of PAX5, p53 immunohistochemistry and p53 mutation analysis in superficial bladder carcinoma tissue. Correlation with pathological findings and clinical outcome. Babjuk M, Soukup V, Mares J, Duskova J, Sedlacek Z, Trkova M, Pecen L, Dvoracek J, Hanus T, Kocvara R, Novak J, Povysil C. Dept. of Urology, General Faculty Hospital, 1st Medical Faculty Charles University, Postgraduate Institute, Praha, Czech Republic. marko.babjuk@lf1.cuni.cz OBJECTIVES: The expression pattern of PAX5 in the tissue of superficial bladder transitional cell carcinoma (TCC), its prognostic value and its correlation with p53 immunohistochemistry and p53 mutation analysis were evaluated. METHODS: Study comprised 61 patients with histologically confirmed superficial bladder TCC. Expression level of PAX5 mRNA was investigated using reverse transcriptase-polymerase chain reaction (RT-PCR) and determined semiquantitatively. The presence of p53 mutations was determined by SSCP and confirmed by direct sequencing. The p53 immunohistochemistry was performed with DO1 antibody and semiquantitatively evaluated using HSCORE (HS) method. As the control group for the evaluation of the PAX5 expression served 8 men with benign prostatic hyperplasia. RESULTS: PAX5 expression was found in 50 patients with bladder TCC but in no patient from the control group. Its quantity however correlated neither with the stage nor with the grade of the tumor. P53 mutation was confirmed only in 1 patient with pTaG2 tumor in exon 5 (deletion of proline 128). On the contrary, positive immunohistochemical staining of p53 was detected in most patients. Using the cutoff value of HS 200, 56.9% of patients showed p53 overexpression. Quantity of p53 immunochistochemical positivity did not correlate with the quantity of PAX5 expression. Using the cutoff values of HS 200 for p53 and of 0.2 for PAX5, 7 of 8 patients with future progression had p53 and 4 had PAX5 overexpression respectively. CONCLUSION: The expression of gene PAX5 is a frequent event in superficial TCC of the bladder. PMID: 14577491 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 3: EMBO J. 1995 Nov 15;14(22):5638-45. Loss of p53 function through PAX-mediated transcriptional repression. Stuart ET, Haffner R, Oren M, Gruss P. Department of Molecular Cell Biology, Max-Planck Institute for Biophysical Chemistry, Gottingen, Germany. Direct interactions between the genes that regulate development and those which regulate the cell cycle would provide a mechanism by which numerous biological events could be better understood. We have identified a direct role for PAX5 in the control of p53 transcription. In primary human diffuse astrocytomas, PAX5 expression inversely correlated with p53 expression. The human p53 gene harbours a PAX binding site within its untranslated first exon that is conserved throughout evolution. PAX5 and its paralogues PAX2 and PAX8 are capable of inhibiting both the p53 promoter and transactivation of a p53-responsive reporter in cell culture. Mutation of the identified binding site eliminates PAX protein binding in vitro and renders the promoter inactive in cells. These data suggest that PAX proteins might regulate p53 expression during development and propose a novel alternative mechanism for tumour initiation or progression, by which loss of p53 function occurs at the transcriptional level. PMID: 8521821 [PubMed - indexed for MEDLINE] ---------------------------------------------------------------