RESUMO
The insulin-like growth factor (IGF) system plays an important role in the biology of breast cancer. Most of the biological actions of IGF-I and IGF-II are mediated by the IGF-I receptor (IGF-IR), a membrane-bound heterotetramer with potent antiapoptotic and cell survival activities. Caveolin-1 (Cav-1) is one of the main components of caveolae, and it has been shown to interact with multiple signaling molecules. In view of the important roles of IGF-IR and Cav-1 in oncogenically transformed mammary gland cells, in the present study we addressed the potential regulation of IGF-IR gene expression by Cav-1. The results obtained showed that MCF7/Cav-1 cells, expressing the Cav-1 gene in a stable manner, contain significantly higher levels of IGF-IR protein and mRNA than native MCF7 cells. These elevated levels of expression are mediated at the level of transcription, as shown by the results of experiments showing that the activity of the proximal IGF-IR promoter was higher in Cav-1-expressing MCF7 cells than in untransfected MCF7 cells. Furthermore, in subcellular localization studies, intensive IGF-IR staining in membrane ruffles and projections in MCF7/Cav-1 cells were noted, in contrast to typical membrane staining in MCF7 cells. In addition, we demonstrated that transcriptional activation of the IGF-IR gene by Cav-1 requires an intact p53 signaling pathway, since Cav-1 was unable to elevate IGF-IR levels in p53-null cells. Finally, the effect of Cav-1 was associated with an elevation in the levels of Sp1, a zinc-finger protein with important roles in IGF-IR gene transactivation. In summary, we identified the IGF-IR gene as a downstream target for Cav-1 action in breast cancer cells.
Assuntos
Neoplasias da Mama/genética , Neoplasias da Mama/metabolismo , Caveolina 1/metabolismo , Receptor IGF Tipo 1/genética , Fator de Transcrição Sp1/metabolismo , Proteína Supressora de Tumor p53/metabolismo , Caveolina 1/genética , Linhagem Celular Tumoral , Feminino , Humanos , Regiões Promotoras Genéticas , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , RNA Neoplásico/genética , RNA Neoplásico/metabolismo , Receptor IGF Tipo 1/metabolismo , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Transdução de Sinais , Ativação Transcricional , Transfecção , Regulação para CimaRESUMO
The role of caveolae and the caveolin proteins in cancer has been the subject of extensive research. BRCA1 participates in multiple biological pathways including DNA damage repair, transcriptional control, cell growth, apoptosis, and others. Little information, however, is available regarding the cellular mechanisms that control BRCA1 gene expression. The present study examined the potential regulation of BRCA1 gene expression and subcellular localization by Cav-1. Results of Western blots, RT-PCR, and transfection experiments showed that Cav-1 enhances BRCA1 protein and mRNA levels via a mechanism that involves transactivation of the BRCA1 promoter and which is p53-dependent. In addition, immunostaining experiments demonstrate that Cav-1 induced the cytoplasmic sequestration of BRCA1.
