ABSTRACT
BACKGROUND: Scaffold Attachment Factor B1 (SAFB1) is a multifunctional protein which has been implicated in breast cancer previously. We recently generated SAFB1 knockout mice (SAFB1-/-), but pleiotropic phenotypes including high lethality, dwarfism associated with low IGF-I levels, and infertility and subfertility in male and female mice, respectively, do not allow for straightforward tumorigenesis studies in these mice. Therefore, we asked whether SAFB1 heterozygosity would influence tumor development and progression in MMTV-Wnt-1 oncomice or DMBA induced tumorigenicity, in a manner consistent with haploinsufficiency of the remaining allele. METHODS: We crossed female SAFB1+/- (C57B6/129) mice with male MMTV-Wnt-1 (C57B6/SJL) mice to obtain SAFB1+/+/Wnt-1, SAFB1+/-/Wnt-1, and SAFB1+/- mice. For the chemical induced tumorigenesis study we treated 8 weeks old SAFB1+/- and SAFB+/+ BALB/c mice with 1 mg DMBA once per week for 6 weeks. Animals were monitored for tumor incidence and tumor growth. Tumors were characterized by performing H&E, and by staining for markers of proliferation and apoptosis. RESULTS: We did not detect significant differences in tumor incidence and growth between SAFB1+/+/Wnt-1 and SAFB1+/-/Wnt-1 mice, and between DMBA-treated SAFB1+/+ and SAFB1+/-mice. Histological evaluation of tumors showed that SAFB1 heterozygosity did not lead to changes in proliferation or apoptosis. There were, however, significant differences in the distribution of tumor histologies with an increase in papillary and cribriform tumors, and a decrease in squamous tumors in the SAFB1+/-/Wnt-1 compared to the SAFB1+/+/Wnt-1 tumors. Of note, DMBA treatment resulted in shortened survival of SAFB1+/- mice compared to their wildtype littermates, however this trend did not reach statistical significance. CONCLUSION: Our data show that SAFB1 heterozygosity does not influence Wnt-1 or DMBA-induced mammary tumorigenesis.
Subject(s)
DNA-Binding Proteins/genetics , Heterozygote , RNA-Binding Proteins/genetics , Wnt1 Protein/genetics , 9,10-Dimethyl-1,2-benzanthracene , Animals , Carcinogens , DNA-Binding Proteins/metabolism , Female , Insulin-Like Growth Factor I/metabolism , Male , Mice , Mice, Knockout , Neoplasms, Experimental/chemically induced , Neoplasms, Experimental/genetics , Neoplasms, Experimental/pathology , RNA-Binding Proteins/metabolism , Wnt1 Protein/metabolismABSTRACT
Scaffold attachment factor B1 (SAFB1) is a multifunctional protein, which has previously been implicated in breast cancer. Here, we show that genetic deletion of SAFB1 in mouse embryonic fibroblasts (MEF) leads to spontaneous immortalization and altered expression of two proteins involved in immortalization and escape from senescence: low levels of p19(ARF) and high levels of TBX2. Inactivation of TBX2 using a dominant-negative TBX2 resulted in up-regulation of p19(ARF) in SAFB1 knockout MEFs. SAFB1 loss also caused lack of contact inhibition, increased foci formation, and increased oncogene-induced anchorage-independent growth. These findings suggest that SAFB1 is a novel player in cellular immortalization and transformation.
Subject(s)
Cellular Senescence/genetics , Cyclin-Dependent Kinase Inhibitor p16/genetics , DNA-Binding Proteins/genetics , Fibroblasts/physiology , RNA-Binding Proteins/genetics , T-Box Domain Proteins/genetics , Animals , DNA-Binding Proteins/deficiency , Embryo, Mammalian , Female , Fibroblasts/cytology , Mice , Mice, Knockout , RNA/genetics , RNA/isolation & purification , Reverse Transcriptase Polymerase Chain ReactionABSTRACT
Scaffold attachment factor B1 (SAFB1) is a multifunctional protein that can bind both DNA and RNA and is involved in RNA processing and stress response. In addition, SAFB1 contains a transcriptional repression domain and can bind certain hormone receptors and repress their activity. To assess the role of SAFB1 in vivo, we generated SAFB1 mutant mice through targeted deletion in embryonic stem cells. While viable homozygous mutant (SAFB1-/-) mice were obtained, genotypic distribution indicated that homozygous deficiency resulted in both prenatal and neonatal lethality. Mice lacking SAFB1 exhibited dwarfism, as a result of in utero growth retardation, and had low serum insulin-like growth factor 1 (IGF1) levels. In agreement with the previous characterization of SAFB1 as a corepressor for hormone receptors, we found that SAFB1-/- mice displayed dramatic defects in the development and function of the reproductive system. Male SAFB1 null mice were infertile, apparently because of low circulating levels of testosterone. SAFB1-/- testes were small and showed progressive degeneration of the germinal epithelium, increased apoptosis of germ cells, and Leydig cell hyperplasia. SAFB-/- female mice were subfertile and showed progressive infertility, in part because of defects in oviductal transport and reduced numbers of follicles. Immortalized SAFB1-/- mouse embryonic fibroblasts showed cell-intrinsic defects including increased transcriptional estrogen receptor alpha activity and enhanced responsiveness to IGF1. Together, these in vivo findings establish a critical role for SAFB1 in development, growth regulation, and reproduction.
Subject(s)
DNA-Binding Proteins/physiology , Dwarfism/genetics , Embryonic Development/genetics , Genes, Lethal , RNA-Binding Proteins/physiology , Reproduction/genetics , Animals , Apoptosis , Cell Line, Transformed , DNA-Binding Proteins/genetics , Estrogen Receptor alpha/genetics , Estrogen Receptor alpha/physiology , Female , Fetal Growth Retardation/genetics , Fibroblasts/metabolism , Gonadal Steroid Hormones/blood , Infertility, Female/genetics , Infertility, Male/genetics , Insulin-Like Growth Factor I/analysis , Insulin-Like Growth Factor I/metabolism , Leydig Cells/pathology , Male , Mice , Mice, Knockout , Pregnancy , RNA-Binding Proteins/genetics , Transcription, GeneticABSTRACT
We have characterized previously the nuclear matrix protein/scaffold attachment factor (SAFB) as an estrogen receptor corepressor and as a potential tumor suppressor gene in breast cancer. A search of the human genome for other potential SAFB family members revealed that KIAA00138 (now designated as SAFB2) has high homology to SAFB (now designated as SAFB1). SAFB1 and SAFB2 are mapped adjacent to each other on chromosome 19p13.3 and are arranged in a bidirectional divergent configuration (head to head), being separated by a short (<500 bp) GC-rich intergenic region that can function as a bidirectional promoter. SAFB1 and SAFB2 share common functions but also have unique properties. As shown previously for SAFB1, SAFB2 functions as an estrogen receptor corepressor, and its overexpression results in inhibition of proliferation. SAFB1 and SAFB2 interact directly through a C-terminal domain, resulting in additive repression activity. They are coexpressed in a number of tissues, but unlike SAFB1, which is exclusively nuclear, SAFB2 is found in the cytoplasm as well as the nucleus. Consistent with its cytoplasmic localization, we detected an interaction between SAFB2 and vinexin, a protein involved in linking signaling to the cytoskeleton. Our findings suggest that evolutionary duplication of the SAFB gene has allowed it to retain crucial functions, but also to gain novel functions in the cytoplasm and/or nucleus.
