RESUMO
Renal cell carcinoma of the clear cell type (ccRCC) is associated with loss of functional von Hippel-Lindau (VHL) protein and high, homogeneous expression of the G250MN protein, an isoenzyme of the carbonic anhydrase family. High expression of G250MN is found in all ccRCCs, but not in most normal tissues, including normal human kidney. We specifically studied the mechanism of transcriptional regulation of the CAIXG250 gene in RCC. Previous studies identified Sp1 and hypoxia-inducible factor (HIF) as main regulatory transcription factors of G250MN in various non-RCC backgrounds. However, G250MN regulation in RCC has not been studied and may be differently regulated in view of the HIF accumulation under normoxic conditions due to VHL mutations. Transient transfection of different G250MN promoter constructs revealed strong promoter activity in G250MN -positive RCC cell lines, but no activity in G250MN -negative cell lines. DNase-I footprint and band-shift analysis demonstrated that Sp1 and HIF-1alpha proteins in nuclear extracts of RCC cells bind to the CAIX promoter and mutations in the most proximal Sp1 binding element or HIF binding element completely abolished CAIX promoter activity, indicating their critical importance for the activation of G250 expression in RCC. A close correlation between HIF-1alpha expression and G250MN expression was observed. In contrast, no relationship between HIF-2alpha expression and G250MN was seen. The participation of cofactor CBP/p300 in the regulation of G250 transcription was shown. In conclusion, HIF-1alpha and Sp1, in combination with CBP/p300, are crucial elements for G250MN expression in ccRCC, and CAIXG250 can be regarded as a unique HIF-1alpha target gene in ccRCC.
Assuntos
Adenocarcinoma de Células Claras/genética , Antígenos de Neoplasias/genética , Anidrases Carbônicas/genética , Carcinoma de Células Renais/genética , Regulação Neoplásica da Expressão Gênica , Neoplasias Renais/genética , Fatores de Transcrição/metabolismo , Sequência de Bases , Anidrase Carbônica IX , DNA de Neoplasias/metabolismo , Histona Acetiltransferases , Humanos , Subunidade alfa do Fator 1 Induzível por Hipóxia , Dados de Sequência Molecular , Coativador 3 de Receptor Nuclear , Ligação Proteica , Mapeamento por Restrição , Fator de Transcrição Sp1/metabolismo , Transativadores/metabolismo , Transcrição Gênica , Transfecção , Células Tumorais CultivadasRESUMO
OBJECTIVES: In renal cell carcinoma (RCC) cell lines, expression of the RCC-associated antigen G250 correlates with hypomethylation of the investigated CpG dinucleotides in the G250 promoter region, despite the absence of a CpG island. To gain insight into the molecular mechanism leading to G250 expression in vivo, we ascertained whether this correlation between G250 gene expression and the methylation status of the G250 gene also existed in primary RCC and normal kidney tissue. METHODS: G250 mRNA and protein expression was determined by reverse transcriptase-polymerase chain reaction, fluorescence activated cell sorting analysis, and immunohistochemistry in 15 RCC cell lines and 13 paired primary RCC/normal kidney tissue specimens. The methylation status of the G250 gene was determined by bisulfite genomic sequencing. RESULTS: RCC cell lines revealed a clear correlation between G250 expression and hypomethylation. In contrast, no hypomethylation was observed in primary RCC compared with normal kidney tissue. The CpG dinucleotides investigated were generally completely methylated in RCC, as well as in normal kidney tissue. Furthermore, a primary culture of RCC tissue revealed increasing hypomethylation of the G250 gene in successive passages, suggesting that the G250 hypomethylation observed in vitro is tissue culture induced. CONCLUSIONS: The methylation status of the G250 gene correlated with G250 expression in vitro but not in vivo.