The ETS Transcription Factor ESE-1 Transforms MCF-12A Human Mammary Epithelial Cells via a Novel Cytoplasmic Mechanism

Abstract

Several different transcription factors, including estrogen receptor, progesterone receptor, and ETS family members, have been implicated in human breast cancer, indicating that transcription factor-induced alterations in gene expression underlie mammary cell transformation. ESE-1 is an epithelium-specific ETS transcription factor that contains two distinguishing domains, a serine- and aspartic acid-rich (SAR) domain and an AT hook domain. ESE-1 is abundantly expressed in human breast cancer and trans-activates epithelium-specific gene promoters in transient transfection assays. While it has been presumed that ETS factors transform mammary epithelial cells via their nuclear transcriptional functions, here we show (i) that ESE-1 protein is cytoplasmic in human breast cancer cells; (ii) that stably expressed green fluorescent protein-ESE-1 transforms MCF-12A human mammary epithelial cells; and (iii) that the ESE-1 SAR domain, acting in the cytoplasm, is necessary and sufficient to mediate this transformation. Deletion of transcriptional regulatory or nuclear localization domains does not impair ESE-1-mediated transformation, whereas fusing the simian virus 40 T-antigen nuclear localization signal to various ESE-1 constructs, including the SAR domain alone, inhibits their transforming capacity. Finally, we show that the nuclear localization of ESE-1 protein induces apoptosis in nontransformed mammary epithelial cells via a transcription-dependent mechanism. Together, our studies reveal two distinct ESE-1 functions, apoptosis and transformation, where the ESE-1 transcription activation domain contributes to apoptosis and the SAR domain mediates transformation via a novel nonnuclear, nontranscriptional mechanism. These studies not only describe a unique ETS factor transformation mechanism but also establish a new paradigm for cell transformation in general.

We are grateful to David M. Prescott, Heide Ford, and Pepper Schedin for critical review of the manuscript. We thank the members of the Gutierrez-Hartmann laboratory for their helpful comments and suggestions. We also thank Audrey Brumback and Steven Fadul for providing FM 4-64 vital dye and technical assistance with confocal microscopy. Digital deconvolution confocal fluorescence microscopy equipment was provided by the UCHSC Light Microscopy Facility.

DNA sequencing and FACS analysis were provided by Core Facilities of the University of Colorado Comprehensive Cancer Center (supported by grant NIH P30 CA 46934). This work was supported by grants DOD DAMD17-02-1-0352 and DOD DAMD17-00-1-0474 to J.D.P. and by grant DOD DAMD17-00-1-0476 to A.G.-H.