54971

BANP

BEND1|SMAR1|SMARBP1;BTG3 associated nuclear protein;BANP;BTG3 associated nuclear protein

BEN domain-containing protein 1|protein BANP|scaffold/matrix-associated region-1-binding protein

16q24

protein-coding

Matrix attachment region binding proteins have been shown to play an important role in gene regulation by altering chromatin in a stage- and tissue-specific manner. Our previous studies report that SMAR1, a matrix-associated protein, regresses B16-F1-induced tumors in mice. Here we show SMAR1 targets the cyclin D1 promoter, a gene product whose dysregulation is attributed to breast malignancies. Our studies reveal that SMAR1 represses cyclin D1 gene expression, which can be reversed by small interfering RNA specific to SMAR1. We demonstrate that SMAR1 interacts with histone deacetylation complex 1, SIN3, and pocket retinoblastomas to form a multiprotein repressor complex. This interaction is mediated by the SMAR1(160-350) domain. Our data suggest SMAR1 recruits a repressor complex to the cyclin D1 promoter that results in deacetylation of chromatin at that locus, which spreads to a distance of at least the 5 kb studied upstream of the cyclin D1 promoter. Interestingly, we find that the high induction of cyclin D1 in breast cancer cell lines can be correlated to the decreased levels of SMAR1 in these lines. Our results establish the molecular mechanism exhibited by SMAR1 to regulate cyclin D1 by modification of chromatin.

Intermediary filaments play a crucial role in transformation of cells to a malignant phenotype. Here, we report that tumor suppressor SMAR1 downregulates Cytokeratin 8 gene expression by modulating p53-mediated transactivation of this gene. Moreover, the cell surface cytokeratin expression was downregulated leading to a decreased migration and invasiveness of cells. We further validated these results using genotoxic stress agents that lead to an increase in the levels of SMAR1 protein. This subsequently represses the transcription of Cytokeratin 8 gene by local chromatin condensation mediated by histone methylation and deacetylation. Evaluation of SMAR1 and Cytokeratin 8 proteins in different grades of cancer using tissue microarray point out at the inverse expression profiles of these genes (i.e. low levels of SMAR1 correlating with high expression of Cytokeratin 8) in higher grades of breast cancer. Therefore, the results presented here highlight the mechanism of Cytokeratin 8 gene regulation by interplay of tumor suppressor proteins SMAR1 and p53.

Aberrant NF-kappaB activity promotes tumorigenesis. However, NF-kappaB also inhibits tumor growth where tumor suppressor pathways remain unaltered. Thus, its role in tumorigenesis depends upon the function of other cellular factors. Tumor suppressor SMAR1 down-modulated in high grade breast cancers is regulated by p53 and is reported to interact and stabilize p53. Because both SMAR1 and NF-kappaB are involved in tumorigenesis, we investigated the effect of SMAR1 upon NF-kappaB activity. We show that SMAR1 induction by doxorubicin or overexpression produces functional NF-kappaB complexes that are competent for binding to NF-kappaB consensus sequence. However, SMAR1 induced p65-p50 complex is phosphorylation- and transactivation-deficient. Induction of functional NF-kappaB complexes stems from down-regulation of IkappaBalpha transcription through direct binding of SMAR1 to the matrix attachment region site present in IkappaBalpha promoter and recruitment of corepressor complex. Real time PCR array for NF-kappaB target genes revealed that SMAR1 down-regulates a subset of NF-kappaB target genes that are involved in tumorigenesis. We also show that SMAR1 inhibits tumor necrosis factor alpha-induced induction of NF-kappaB suggesting that activation of NF-kappaB by SMAR1 is independent and different from classical pathway. Thus, for the first time we report that a tumor suppressor protein SMAR1 can modulate NF-kappaB transactivation and inhibit tumorigenesis by regulating NF-kappaB target genes.

BACKGROUND: Imaging tools such as scanning electron microscope (SEM) and atomic force microscope (AFM) can be used to produce high-resolution topographic images of biomedical specimens and hence are well suited for imaging alterations in cell morphology. We have studied the correlation of SMAR1 expression with cell surface smoothness in cell lines as well as in different grades of human breast cancer and mouse tumor sections. METHODS: We validated knockdown and overexpression of SMAR1 using RT-PCR as well as Western blotting in human embryonic kidney (HEK) 293, human breast cancer (MCF-7) and mouse melanoma (B16F1) cell lines. The samples were then processed for cell surface roughness studies using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The same samples were used for microarray analysis as well. Tumors sections from control and SMAR1 treated mice as well as tissues sections from different grades of human breast cancer on poly L-lysine coated slides were used for AFM and SEM studies. RESULTS: Tumor sections from mice injected with melanoma cells showed pronounced surface roughness. In contrast, tumor sections obtained from nude mice that were first injected with melanoma cells followed by repeated injections of SMAR1-P44 peptide, exhibited relatively smoother surface profile. Interestingly, human breast cancer tissue sections that showed reduced SMAR1 expression exhibited increased surface roughness compared to the adjacent normal breast tissue. Our AFM data establishes that treatment of cells with SMAR1-P44 results into increase in cytoskeletal volume that is supported by comparative gene expression data showing an increase in the expression of specific cytoskeletal proteins compared to the control cells. Altogether, these findings indicate that tumor suppressor function of SMAR1 might be exhibited through smoothening of cell surface by regulating expression of cell surface proteins. CONCLUSION: tumor suppressor protein SMAR1 might be used as a phenotypic differentiation marker between cancerous and non-cancerous cells.

Here, we report Prostaglandin A2 (PGA2) induced binding of HSP70 to a novel site on phi1 SMAR1 5 UTR which stabilizes the wild type transcript and leads to subsequent increase in SMAR1 protein levels. SMAR1 mediated cell cycle arrest is perturbed in PGA2-treated cells when HSP70 is knocked-down. Contrarily HSP70, unlike SMAR1, is overexpressed in breast cancers. We demonstrate that this is because of the inability of HSP70 to bind to the phi17 SMAR1 UTR variant which is the predominant form in breast cancers.