P16INK4a is required for hSNF5 chromatin remodeler-induced cellular senescence in malignant rhabdoid tumor cells.
ABSTRACT The hSNF5 chromatin-remodeling factor is a tumor suppressor that is inactivated in malignant rhabdoid tumors (MRTs). A number of studies have shown that hSNF5 re-expression blocks MRT cell proliferation. However, the pathway through which hSNF5 acts remains unknown. To address this question, we generated MRT-derived cell lines in which restoration of hSNF5 expression leads to an accumulation in G(0)/G(1), induces cellular senescence and increased apoptosis. Following hSNF5 expression, we observed transcriptional activation of the tumor suppressor p16(INK4a) but not of p14(ARF), repression of several cyclins and CD44, a cell surface glycoprotein implicated in metastasis. Chromatin immunoprecipitations indicated that hSNF5 activates p16(INK4a) transcription and CD44 down-regulation by mediating recruitment of the SWI/SNF complex. Thus, hSNF5 acts as a dualistic co-regulator that, depending on the promoter context, can either mediate activation or repression. Three lines of evidence established that p16(INK4a) is an essential effector of hSNF5-induced cell cycle arrest. 1) Overexpression of p16(INK4a) mimics the effect of hSNF5 induction and leads to cellular senescence. 2) Expression of a p16(INK4a)-insensitive form of CDK4 obstructs hSNF5-induced cell cycle arrest. 3) Inhibition of p16(INK4a) activation by siRNA blocks hSNF5-mediated cellular senescence. Collectively, these results indicate that in human MRT cells, the p16(INK4a)/pRb, rather than the p14(ARF)/p53 pathway, mediates hSNF5-induced cellular senescence.
- SourceAvailable from: Vincent Romanet[Show abstract] [Hide abstract]
ABSTRACT: Malignant rhabdoid tumors (MRTs) are aggressive pediatric cancers arising in brain, kidney and soft tissues, which are characterized by loss of the tumor suppressor SNF5/SMARCB1. MRTs are poorly responsive to chemotherapy and thus a high unmet clinical need exists for novel therapies for MRT patients. SNF5 is a core subunit of the SWI/SNF chromatin remodeling complex which affects gene expression by nucleosome remodeling. Here, we report that loss of SNF5 function correlates with increased expression of fibroblast growth factor receptors (FGFRs) in MRT cell lines and primary tumors and that re-expression of SNF5 in MRT cells causes a marked repression of FGFR expression. Conversely, siRNA-mediated impairment of SWI/SNF function leads to elevated levels of FGFR2 in human fibroblasts. In vivo, treatment with NVP-BGJ398, a selective FGFR inhibitor, blocks progression of a murine MRT model. Hence, we identify FGFR signaling as an aberrantly activated oncogenic pathway in MRTs and propose pharmacological inhibition of FGFRs as a potential novel clinical therapy for MRTs.PLoS ONE 01/2013; 8(10):e77652. · 3.53 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Epigenetic alterations are associated with all aspects of cancer, from tumor initiation to cancer progression and metastasis. It is now well understood that both losses and gains of DNA methylation as well as altered chromatin organization contribute significantly to cancer-associated phenotypes. More recently, new sequencing technologies have allowed the identification of driver mutations in epigenetic regulators, providing a mechanistic link between the cancer epigenome and genetic alterations. Oncogenic activating mutations are now known to occur in a number of epigenetic modifiers (i.e. IDH1/2, EZH2, DNMT3A), pinpointing epigenetic pathways that are involved in tumorigenesis. Similarly, investigations into the role of inactivating mutations in chromatin modifiers (i.e. KDM6A, CREBBP/EP300, SMARCB1) implicate many of these genes as tumor suppressors. Intriguingly, a number of neoplasms are defined by a plethora of mutations in epigenetic regulators, including renal, bladder, and adenoid cystic carcinomas. Particularly striking is the discovery of frequent histone H3.3 mutations in pediatric glioma, a particularly aggressive neoplasm that has long remained poorly understood. Cancer epigenetics is a relatively new, promising frontier with much potential for improving cancer outcomes. Already, therapies such as 5-azacytidine and decitabine have proven that targeting epigenetic alterations in cancer can lead to tangible benefits. Understanding how genetic alterations give rise to the cancer epigenome will offer new possibilities for developing better prognostic and therapeutic strategies.Protein & Cell 03/2014; · 3.22 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: SMARCB1 (Snf5/Ini1/Baf47) is a potent tumor suppressor, the loss of which serves as the diagnostic feature in malignant rhabdoid tumors (MRT) and atypical teratoid/rhabdoid tumors (AT/RT), two highly aggressive forms of pediatric neoplasms. SMARCB1 is a core subunit of Swi/Snf chromatin remodeling complexes, and loss of SMARCB1 or other subunits of these complexes has been observed in a variety of tumor types. Here, we restore Smarcb1 expression in cells derived from Smarcb1-deficient tumors, which developed in Smarcb1 heterozygous p53(-/-) mice. We find that while re-introduction of Smarcb1 does not induce growth arrest, it restores sensitivity to programmed cell death and completely abolishes the ability of the tumor cells to grow as xenografts. We describe persistent activation of AKT signaling in Smarcb1-deficient cells, which stems from PI3K (phosphatidylinositol 3'-kinase)-mediated signaling and which contributes to the survival and proliferation of the tumor cells. We further demonstrate that inhibition of AKT is effective in preventing proliferation of Smarcb1-deficient cells in vitro and inhibits the development of xenografted tumors in vivo. Profiling Smarcb1-dependent gene expression, we find genes that require Smarcb1 and Swi/Snf for their expression to be enriched for extracellular matrix and cell adhesion functions. We find that Smarcb1 is required for transcriptional activation of Igfbp7, a member of the insulin-like growth factor-binding proteins family and a tumor suppressor in itself, and show that re-introduction of Igfbp7 alone can hinder tumor development. Our results define a novel mechanism for Smarcb1-mediated tumorigenesis and highlight potential therapeutic targets.Oncogene advance online publication, 15 July 2013; doi:10.1038/onc.2013.261.Oncogene 07/2013; · 8.56 Impact Factor