Work Package 10

Role of SWI/SNF complexes in the control of cell proliferation and disease.

Introduction
The precisely orchestrated expression of selective genes within eukaryotic genomes at the right time and place underlies cellular differentiation and the development of multicellular organisms. The genomes of eukaryotes are bound by histones and packaged into repressive chromatin. Consequently, factors that modulate chromatin structure form an integral part of the gene regulatory machinery. One important class of enzymes that regulate chromatin structure comprises proteins that utilize the energy derived from ATP-hydrolysis to modulate the contacts between histones and DNA, resulting in an increased DNA accessibility. These SWI/SNF ATP-dependent chromatin-remodeling factors play a crucial role in the regulation of gene expression during cellular differentiation and development. Aberrant gene control due to mutations in the human SWI/SNF chromatin-remodeling complex can lead to cancer, as illustrated by the observation that the hSNF5 subunit is a tumor suppressor that is consistently mutated in human malignant rhabdoid tumors (MRT). This view is enforced by the association of SWI/SNF with tumor suppressors such as Rb and BRCA1. Perhaps paradoxically, mouse studies have revealed that while loss of hSNF5 leads to a very strong predisposition to cancers, hSNF5 is also required for cell viability of virtually all cell types. SWI/SNF factors appear to play a critical role in the decision between proliferation and cell differentiation during development and have been implicated in the Wnt signaling pathway.

Objectives
The goal of this project is to thoroughly understand the role of the SWI/SNF complex in the control of (hematopoietic) stem cell differentiation and its function as a tumor-suppressor in human cancers. We will dissect the regulatory circuitry controlled by SWI/SNF, which determines the balance between cell proliferation and differentiation. We will investigate how signal transduction pathways impinge on the SWI/SNF gene control function during development. Finally, we will identify the key effectors for the SWI/SNF tumor suppression function, which may uncover potential targets for therapeutic intervention.

Approach
To investigate the role of hSNF5 in the control of cell proliferation, we have generated a series of human tumor-derived cell lines in which the expression of either wild type or tumor-associated mutant forms of hSNF5/INI1 can be induced. We found that re-expression of hSNF5 in these tumor cells leads to a strong block of cell proliferation, which is dependent on the p16/pRb tumor suppressor pathway. In other tumor cells we observed massive cell death upon re-expression of hSNF5. We will use our hSNF5 inducible cell-lines in gene-expression profiling experiments to uncover the key effectors of SWI/SNF tumor suppression function. Targets will be evaluated by inhibition by RNAi. We will utilize inducible RNAi knock down approaches in stem cells to study the cell survival and control of differentiation functions of SWI/SNF. We will also generate conditional knock out mice for a novel component of the SWI/SNF complex, containing signature hallmarks of a hormone receptor co-activator, which we recently identified. Finally, human cancer-associated mutants of hSNF5, containing single amino acid substitutions will be reintroduced in mice in order to generate mouse models for human diseases.

Links with other projects: This project has clear links with themes 1 and 2, in particular with WP2, 5, 6, 8 and 9.

Keywords: chromatin, SWI/SNF, cancer, (hematopoietic) stem cell differentiation

Participants: Verrijzer, Grosveld, Dzierzak