| Popis: |
TP53 does not fully comply with the Knudson’s two-hit model in that a reduction of constitutional expression of p53 may be sufficient for tumor predisposition. To determine whether the TP53 gene dosage affects the transcriptional regulation of target genes, we performed oligo-array gene expression analysis using isogenic cells with different TP53 gene dosage. We identified 35 genes whose expression is significantly correlated to the dosage of TP53. These genes are involved in a variety of cellular processes including signal transduction, cell adhesion, and transcription regulation. Among those genes, CSPG2 [chondroitin sulfate proteoglycan 2 (Versican)] was selected for further study because it contains a p53 binding site in its first intron and its expression highly correlates with TP53 dosage. Using in vitro and in vivo assays, we showed CSPG2 to be directly transactivated by p53. In search of tumor suppressor genes in Papillary Thyroid Cancer (PTC), we previously used gene expression profiling to identify genes underexpressed in tumor compared with paired unaffected tissue. While searching for loss of heterozygosity (LOH) in the genomic regions harboring candidate tumor suppressor genes, we detected LOH in a ~ 20 kb region around marker D9S176. Several ESTs flanking D9S176 were underexpressed in tumors, and for one of the ESTs, downregulation was highly associated with the activating BRAF mutation V600E, the most common genetic lesion in PTC. A putative novel gene, NAMA (noncoding RNA associated with MAP kinase pathway and growth arrest) containing the affected EST was cloned and characterized. Several characteristics of NAMA suggest that it might be a non-coding but functional RNA. NAMA is inducible by knockdown of BRAF, inhibition of the MAP kinase pathway, growth arrest, and DNA damage in cancer cell lines. We suggest that NAMA is a noncoding RNA (ncRNA) associated with growth arrest. Thus, this study identified a list of genes affected by TP53 gene dosage including a direct target, CSPG2. Further, a noncoding RNA, NAMA, associated with the activating mutation in the BRAF oncogene, was discovered. These results suggest that gene dosage variation in tumor suppressor genes or noncoding RNA may modify cancer risk and progression. |
