Browsing by Subject "T-bet"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Crystal structure of the DNA binding domain of the transcription factor T-bet suggests simultaneous recognition of distant genome sites
    (Proceedings of the National Academy of Sciences, 2016-10-25) Liu, Ce Feng; Brandt, Gabriel S.; Hoang, Quyen Q.; Naumova, Natalia; Lazarevic, Vanja; Hwang, Eun Sook; Dekker, Job; Glimcher, Laurie H.; Ringe, Dagmar; Petsko, Gregory A.; Department of Biochemistry & Molecular Biology, IU School of Medicine
    The transcription factor T-bet (Tbox protein expressed in T cells) is one of the master regulators of both the innate and adaptive immune responses. It plays a central role in T-cell lineage commitment, where it controls the TH1 response, and in gene regulation in plasma B-cells and dendritic cells. T-bet is a member of the Tbox family of transcription factors; however, T-bet coordinately regulates the expression of many more genes than other Tbox proteins. A central unresolved question is how T-bet is able to simultaneously recognize distant Tbox binding sites, which may be located thousands of base pairs away. We have determined the crystal structure of the Tbox DNA binding domain (DBD) of T-bet in complex with a palindromic DNA. The structure shows a quaternary structure in which the T-bet dimer has its DNA binding regions splayed far apart, making it impossible for a single dimer to bind both sites of the DNA palindrome. In contrast to most other Tbox proteins, a single T-bet DBD dimer binds simultaneously to identical half-sites on two independent DNA. A fluorescence-based assay confirms that T-bet dimers are able to bring two independent DNA molecules into close juxtaposition. Furthermore, chromosome conformation capture assays confirm that T-bet functions in the direct formation of chromatin loops in vitro and in vivo. The data are consistent with a looping/synapsing model for transcriptional regulation by T-bet in which a single dimer of the transcription factor can recognize and coalesce distinct genetic elements, either a promoter plus a distant regulatory element, or promoters on two different genes.
  • Thumbnail Image
    Item
    Prognosis of hormone-dependent breast cancers: implications of the presence of dysfunctional transcriptional networks activated by insulin via the immune transcription factor T-bet
    (American Association for Cancer Research, 2010-01-15) McCune, Kasi; Bhat-Nakshatri, Poornima; Thorat, Mangesh A; Nephew, Kenneth P; Badve, Sunil; Nakshatri, Harikrishna
    Estrogen receptor alpha (ERα)-positive breast cancers that co-express trans cription factors GATA-3 and FOXA1 have a favorable prognosis. These transcription factors form an autoregulatory hormonal network that influences estrogen responsiveness and sensitivity to hormonal therapy. Disruption of this network may be a mechanism whereby ERα positive breast cancers become resistant to therapy. The transcription factor T-bet is a negative regulator of GATA-3 in the immune system. In this study, we report that insulin increases the expression of T-bet in breast cancer cells, which correlates with reduced expression of GATA-3, FOXA1 and the ERα:FOXA1:GATA-3 target gene GREB-1. The effects of insulin on GATA-3 and FOXA1 could be recapitulated through overexpression of T-bet in MCF-7 cells (MCF-7-T-bet). Chromatin immunoprecipitation assays revealed reduced ERα binding to GREB-1 enhancer regions in MCF-7-T-bet cells and in insulin treated MCF-7 cells. MCF-7-T-bet cells were resistant to tamoxifen in the presence of insulin and displayed prolonged ERK and AKT activation in response to epidermal growth factor treatment. ERα-positive cells with intrinsic tamoxifen resistance as well as MCF-7 cells with acquired tamoxifen and fulvestrant resistance expressed elevated levels of T-bet and/or reduced levels of FOXA1 and GATA-3. Analysis of publicly available databases revealed ERα-positive/T-bet-positive breast cancers expressing lower levels of FOXA1 (p=0.0137) and GATA-3 (p=0.0063) compared to ERα-positive/T-bet-negative breast cancers. Thus, T-bet expression in primary tumors and circulating insulin levels may serve as surrogate biomarkers to identify ERα-positive breast cancers with a dysfunctional hormonal network, enhanced growth factor signaling, and resistance to hormonal therapy.