ARTICLES SATB1 reprogrammes gene expression to promote breast tumour growth and metastasis Hye-Jung Han 1 , Jose Russo 2 , Yoshinori Kohwi 1 * & Terumi Kohwi-Shigematsu 1 * Mechanisms underlying global changes in gene expression during tumour progression are poorly understood. SATB1 is a genome organizer that tethers multiple genomic loci and recruits chromatin-remodelling enzymes to regulate chromatin structure and gene expression. Here we show that SATB1 is expressed by aggressive breast cancer cells and its expression level has high prognostic significance (P , 0.0001), independent of lymph-node status. RNA-interference-mediated knockdown of SATB1 in highly aggressive (MDA-MB-231) cancer cells altered the expression of .1,000 genes, reversing tumorigenesis by restoring breast-like acinar polarity and inhibiting tumour growth and metastasis in vivo. Conversely, ectopic SATB1 expression in non-aggressive (SKBR3) cells led to gene expression patterns consistent with aggressive-tumour phenotypes, acquiring metastatic activity in vivo. SATB1 delineates specific epigenetic modifications at target gene loci, directly upregulating metastasis-associated genes while downregulating tumour-suppressor genes. SATB1 reprogrammes chromatin organization and the transcription profiles of breast tumours to promote growth and metastasis; this is a new mechanism of tumour progression. Metastasis is the final step in solid tumour progression and is the most common cause of death in cancer patients 1 . Metastasis is a multi-step process: invasion of tumour cells into the adjacent tissues, entry of tumour cells in the systemic circulation (intravasation), survival in circulation, extravasation to distant organs, and finally growth of cancer cells to produce secondary tumours 2,3 . How tumour cells become metastatic is largely unknown. It was widely believed that metastatic cells are rare and evolve during late stages of tumour progression from a series of genetic changes that enable the cells to progress through the sequential steps that finally result in growth in distant organ microenvironments. Recently, however, gene expres- sion analysis of human breast carcinomas with known clinical outcomes has revealed profiles that are associated with disease pro- gression and has identified groups of genes whose characteristic expression pattern can predict the risk of metastatic recurrence 4–9 . The detection in some primary tumours of such poor-prognosis gene ‘signatures’ indicates that a large number of cells in the primary tumours already have such a gene expression pattern. Therefore, in addition to the traditional view of metastasis as an evolving process of rare variant clones, the poor-prognosis signatures suggest that cells in some primary tumours are predisposed to metastasis 10 . In fact, there might be an active molecular mechanism underlying such events. How gene expression profiles are established in these tumour cells such that they acquire metastatic properties is unknown. Here we show that the protein SATB1 is necessary for breast cancer cells to become metastatic, and when ectopically expressed in non- metastatic cells, can induce invasive activity in vivo. We also show that SATB1 expression in breast cancer cells establishes gene expres- sion profiles consistent with invasive tumours. SATB1 is a nuclear protein that functions as a ‘genome organizer’ essential for proper T-cell development 11 . SATB1 constitutes a functional nuclear architecture that has a ‘cage-like’ protein distribution surrounding heterochromatin. This architecture is referred to as ‘the SATB1 regu- latory network’, as SATB1 regulates gene expression 11–14 by recruiting chromatin remodelling/modifying enzymes and transcription fac- tors 13,14 to genomic DNA, which it tethers via specialized DNA sequences highly potentiated for unpairing (base unpairing regions, or BURs) 15–17 . On T-helper 2 cell activation, SATB1 becomes expressed and folds the cytokine-gene locus into dense loops for rapid induction of multiple cytokine genes 18 . In breast cancer cells, we find that once SATB1 is expressed, it coordinates expression of a large number of genes to induce metastasis. Removal of SATB1 from aggressive breast cancer cells not only reverses metastatic phenotypes but also inhibits tumour growth, indicating its key role in breast cancer progression. SATB1 expression correlates with poor prognosis We examined SATB1 expression in 24 breast epithelial cell lines, including normal human mammary epithelial cells (HMECs), 5 immortalized derivatives, 13 non-metastatic cancer cell lines and 5 metastatic cancer cell lines. Both SATB1 messenger RNA and protein were detected only in metastatic cancer cell lines, correlating SATB1 expression with aggressive tumour phenotypes (results from repre- sentative cell lines shown in Fig. 1a). SATB2, a close homologue of SATB1, was expressed in both malignant and non-malignant cell lines (Supplementary Fig. 1a). Among 28 human primary breast tumours, SATB1 protein was detected in all 16 poorly differentiated infiltrating ductal carcinomas (P , 0.0001). Low-level SATB1 expression was found in some mode- rately differentiated tumour samples (7 out of 12), and no SATB1 was detected in control samples taken from adjacent non-malignant tis- sues (representative data shown in Fig. 1b and Supplementary Table *These authors contributed equally to this work. 1 Life Sciences Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720, USA. 2 Breast Cancer Research Laboratory, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA. Vol 452 | 13 March 2008 | doi:10.1038/nature06781 187 Nature Publishing Group ©2008