Dr. Gutierrez-Hartmann’s laboratory focuses on two main projects: (1) elucidating the molecular mechanisms governing pituitary-specific gene expression; and, (2) determining the role of Ets transcription factors in breast cancer.
In the first project, they study how the unique combination of Pit-1/GHF-1, a pituitary-specific POU-homeodomain transcription factor, and Ets-1, a ubiquitous proto-oncogene transcription factor, govern the activity of the pituitary-specific prolactin (PRL) gene promoter. Pit-1 not only regulates the pituitary cell-type specific expression of the PRL, growth hormone (GH) and TSHß genes, but also specifies the somatotroph, lactotroph and thyrotroph pituitary cell lineages. To date, they have defined the precise combination of transcription factors and DNA sequences that are required for optimal lactotroph-specific and Ras-responsive activity of the rPRL promoter. These results show that the physical and functional interactions of Pit-1 with Ets-1, acting at a composite DNA element containing vicinal Ets-1 and Pit-1 binding sites, are critical for pituitary-specific rPRL gene expression. They have mapped the Ets-1/Pit-1 physical interaction surfaces, showing that the Pit-1 homeodomain interacts with the Ets-1 RIII region, present just upstream of the ETS DNA binding domain, and collaborative NMR studies have identified the precise Pit-1 residues that interact with Ets-1. Moreover, they have found that the Ets-1/Pit-1 composite element in the rPRL promoter also functions as a Ras response unit, such that the MAP kinase-mediated phosphorylation of Ets-1 increases the transcription potency of the Ets-1/Pit-1 combination on the rPRL composite element. By contrast, the rGH promoter fails to respond to Ras because none of the Ets and Pit-1 sites are arranged in a composite manner. They have performed dominant-negative and siRNA expression studies and confirmed that Ets factors in general, and GABP in particular, are required for endogenous PRL gene expression in GH3 and GH4 pituitary cells. A splice-variant, Pit-1ß/ GHF-2, contains a 26-amino acid insertion in the transcription activation domain (TAD) at the amino terminus. The Pit-1ß isoform is nearly identical to Pit-1, yet displays unique positive and negative transcriptional properties that have been conferred on this isoform by the 26AA ß-domain. The Pit-1/Pit-1ß duo have overlapping DNA binding specificities and are expressed in the same cell, thus raising the question as to how these two proteins effect differential gene activation and signaling responses. They have shown that the ß-domain functions as an active repressor domain via two hydrophobic patches, which serve to modulate the activity of an N-CoR/Sin3 histone deacetylase complex. Moreover, the ß-domain is a portable and dominant, pituitary-specific repressor domain. Thus, the unique transcriptional properties of Pit-1 and Pit-1ß may be attributable to isoform-specific interactions or recruitment of cofactors by the ß-domain, resulting in the formation of functionally distinct complexes. Taken together, these results provide an experimental paradigm for further study of the molecular mechanisms by which ubiquitous hormone and oncogene signaling cascades are interpreted in a cell-specific manner. Furthermore, these model systems allow us to elucidate the molecular details by which related transcription factors with similar DNA binding specificities result in distinct responses.
In the second project, they study the role of the epithelial-specific Ets transcription factor, Esx, in human breast tumorigenesis. The Esx gene is an Ets member that is particularly relevant to breast cancer. Esx is located on chromosome 1q32.1, in a region that is amplified in 50% of early breast cancers. Esx mRNA is over-expressed in human breast ductal carcinoma in situ (DCIS). Finally, HER2/neu and Esx expression levels are positively correlated in human breast cancer cell lines. They have shown that Esx confers a transformed phenotype to immortalized, but nontransformed MCF-12A epithelial mammary cells. These Esx-transformed cells display increased motility, invasiveness, growth factor-independent growth and MAPK activation, colonies in soft agar, and that they form tumor-like colonies in a 3D organoid assay. They are now pursuing biochemical, molecular and transgenic approaches to elucidate the mechanism of Esx-mediated mammary cell transformation.