Identification of Structural Domains of ESX Required for Breast Cell Transformation

摘要

ESX encodes an Ets family transcription factor gene that is potentially important in breast cancer because the ESX genomic region (chromosome lq32.l) is amplified in 50% of early breast cancers and ESX mRNA is over-expressed in human breast ductal carcinoma in situ (DCIS). However, the precise molecular mechanism by which ESX mediates breast cell transformation remains unknown. We have now completed the key milestones originally proposed. Specifically, we have demonstrated that stable expression of HA-tagged or GFP- tagged ESX transforms the human, non-transformed MCF-12A cell line (which fails to express endogenous ESX). Moreover, we have documented that the subcellular localization of ESX is cytoplasmic, and that it is this subcellular localization that is required for transformation. Indeed, nuclear localization appears to mediate apoptosis. We have excluded the key transcriptional motifs as being required for transformation, and have mapped the transforming Esx subdomain to a small, acidic region. Taken together, these data reveal that Esx is not functioning as a transcription factor to transform MCF-l2A mammary cells, but rather that ESX functions primarily via cytoplasmic mechanisms. Finally we demonstrate that endogenous Esx protein is localized in the cytoplasm in human breast cancer specimens. In summary, these are extremely novel results and challenge dogma that Eta factors must always a function in the nucleus as transcription regulators.