We originally cloned SAFB1 as a transcriptional repressor, and it has since been implicated in a number of processes including hormone response, and transformation. The SAFB1 gene shows extremely high rates of loss of heterozygosity in breast cancer, and its loss is associated with high grade tumors, and reduced survival of breast cancer patients. Structure-function studies identified a transcriptional repression domain and overexpression of SAFB1 blunted estrogen-induction of gene expression and enhanced estrogen-mediated repression. Intriguingly, we found that sumoylation of SAFB1 was necessary for its co-repressor activity. We generated SAFB1-null mice which showed pre- and neonatal lethality, with surviving mice having dramatic defects in the reproductive system. To gain more insight into SAFB1's role in ER1 action, we performed an unbiased screen using SAFB1 siRNA knockdown followed by microarray analysis of estrogen-stimulated breast cancer cells. This experiment revealed a significant role for SAFB1 in estrogen-mediated repression of gene expression, and candidate genes were identified that showed a complete requirement for SAFB1 in estrogen-mediated downregulation. These candidates include proteins known to be involved in migration, invasion, and survival, such as NEDD9 and osteoprotegerin (OPG). Furthermore, we identified a novel role for HDAC7 in estrogen-mediated repression of some of the same candidate genes. We thus hypothesize that SAFB1 is an important and unique co-regulator that is critical for estrogen downregulation of genes, and that the repression is mediated through its posttranslational modification by sumoylation and, at least in part, through interaction with HDAC7. Finally, we hypothesize that SAFB1-mediated repression of its target genes is critical for its role in breast tumorigenesis, since loss of repression might result in increased migration, invasion, and survival of breast cancer cells. We will test these hypotheses by analyzing how SAFB1 mediates transcriptional repression of estrogen-responsive target genes, how is its co-repressor function modified by posttranslational modification, and we will test whether repression of its target genes contributes to SAFB1's role in breast tumorigenesis? This work is highly significant since it will provide insight into fundamental mechanisms of SAFB1 action which may contribute to a change in the paradigm of ER1 action. While ER1 has mainly been studied as a transcriptional activator, the equally frequent estrogen-mediated repression of gene expression, and in particular the role of co-repressors like SAFB1 in this repression, is an understudied area. Most importantly, we will also learn whether and how this repression activity of SAFB1 is critical for its role in breast tumorigenesis.

Public Health Relevance

SAFB1 is a transcriptional co-repressor, and it has since been implicated in a number of cellular processes including hormone, response, immortalization, apoptosis, and transformation. We have discovered that SAFB1 plays a significant role in estrogen- mediated repression of gene expression, which is an understudied yet critical process in estrogen receptor action. Here we propose to study the in-depth mechanism of this repression, and how this relates to SAFB1's role in breast tumorigenesis.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
7R01CA097213-08
Application #
8244698
Study Section
Molecular and Cellular Endocrinology Study Section (MCE)
Program Officer
Sathyamoorthy, Neeraja
Project Start
2002-08-01
Project End
2011-08-30
Budget Start
2011-02-01
Budget End
2011-08-30
Support Year
8
Fiscal Year
2010
Total Cost
$203,529
Indirect Cost
Name
University of Pittsburgh
Department
Pharmacology
Type
Schools of Medicine
DUNS #
004514360
City
Pittsburgh
State
PA
Country
United States
Zip Code
15213
Nayak, Shweta R; Harrington, Emily; Boone, David et al. (2015) A Role for Histone H2B Variants in Endocrine-Resistant Breast Cancer. Horm Cancer 6:214-24
Jiang, Shiming; Katz, Tiffany A; Garee, Jason P et al. (2015) Scaffold attachment factor B2 (SAFB2)-null mice reveal non-redundant functions of SAFB2 compared with its paralog, SAFB1. Dis Model Mech 8:1121-7
Pathiraja, Thushangi N; Nayak, Shweta R; Xi, Yuanxin et al. (2014) Epigenetic reprogramming of HOXC10 in endocrine-resistant breast cancer. Sci Transl Med 6:229ra41
Mukhopadhyay, N K; Kim, J; You, S et al. (2014) Scaffold attachment factor B1 regulates the androgen receptor in concert with the growth inhibitory kinase MST1 and the methyltransferase EZH2. Oncogene 33:3235-45
Hernandez-Hernandez, J Manuel; Mallappa, Chandrashekara; Nasipak, Brian T et al. (2013) The Scaffold attachment factor b1 (Safb1) regulates myogenic differentiation by facilitating the transition of myogenic gene chromatin from a repressed to an activated state. Nucleic Acids Res 41:5704-16
Oesterreich, Steffi; Brufsky, Adam M; Davidson, Nancy E (2013) Using mice to treat (wo)men: mining genetic changes in patient xenografts to attack breast cancer. Cell Rep 4:1061-2
Casa, Angelo J; Potter, Adam S; Malik, Simeen et al. (2012) Estrogen and insulin-like growth factor-I (IGF-I) independently down-regulate critical repressors of breast cancer growth. Breast Cancer Res Treat 132:61-73
Garee, Jason P; Meyer, Rene; Oesterreich, Steffi (2011) Co-repressor activity of scaffold attachment factor B1 requires sumoylation. Biochem Biophys Res Commun 408:516-22
Malik, Simeen; Jiang, Shiming; Garee, Jason P et al. (2010) Histone deacetylase 7 and FoxA1 in estrogen-mediated repression of RPRM. Mol Cell Biol 30:399-412
Hammerich-Hille, Stephanie; Kaipparettu, Benny A; Tsimelzon, Anna et al. (2010) SAFB1 mediates repression of immune regulators and apoptotic genes in breast cancer cells. J Biol Chem 285:3608-16

Showing the most recent 10 out of 18 publications