RESUMO

Smac-α is a mitochondrial protein that, during apoptosis, is translocated to the cytoplasm, where it negatively regulates members of the inhibitor of apoptosis (IAP) family via the IAP-binding motif (IBM) contained within its amino-terminus. Here, we describe a new alternative splice variant from Smac gene, which we have named Smac-ε. Smac-ε lacks both an IBM and a mitochondrial-targeting signal (MTS) element. Smac-ε mRNA exhibits a tissue-specific expression pattern in healthy human tissues as well as in several cancer cell lines. The steady-state levels of endogenous Smac-ε protein is regulated by the proteasomal pathway. When ectopically expressed, this isoform presents a cytosolic localization and is unable to associate with or to regulate the expression of X-linked Inhibitor of apoptosis protein, the best-studied member of IAP family. Nevertheless, over-expression of Smac-ε increases mammosphere formation. Whole genome expression analyses from these mammospheres show activation of several pro-survival and growth pathways, including Estrogen-Receptor signaling. In conclusion, our results support the functionality of this new Smac isoform.

Assuntos

Neoplasias da Mama/metabolismo , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Proteínas Mitocondriais/metabolismo , Proteínas Reguladoras de Apoptose , Neoplasias da Mama/genética , Neoplasias da Mama/patologia , Citosol/metabolismo , Feminino , Perfilação da Expressão Gênica/métodos , Regulação Neoplásica da Expressão Gênica , Redes Reguladoras de Genes , Células HeLa , Humanos , Peptídeos e Proteínas de Sinalização Intracelular/genética , Células MCF-7 , Proteínas Mitocondriais/genética , Análise de Sequência com Séries de Oligonucleotídeos , Complexo de Endopeptidases do Proteassoma/metabolismo , Isoformas de Proteínas , Proteólise , Esferoides Celulares , Transcrição Gênica , Transfecção , Regulação para Cima