c-Myc Directly Regulates the Transcription of the NBS1 Gene Involved in DNA Double-strand Break Repair

Abstract

The c-myc proto-oncogene encodes a ubiquitous transcription factor involved in the control of cell growth and implicated in inducing tumorigenesis. Understanding the function of c-Myc and its role in cancer depends upon the identification of c-Myc target genes. Nijmegen breakage syndrome (NBS) is a chromosomal-instability syndrome associated with cancer predisposition, radiosensitivity, and chromosomal instability. The NBS gene product, NBS1 (p95 or nibrin), is a part of the hMre11 complex, a central player associated with double-strand break (DSB) repair. NBS1 contains domains characteristic for proteins involved in DNA repair, recombination, and replication. Here we show that c-Myc directly activates NBS1. c-Myc-mediated induction of NBS1 gene transcription occurs in different tissues, is independent of cell proliferation, and is mediated by a c-Myc binding site in the intron 1 region of NBS1 gene. Overexpression of NBS1 in Rat1a cells increased cell proliferation. These results indicate that NBS1 is a direct transcriptional target of c-Myc and links the function of c-Myc to the regulation of DNA DSB repair pathway operating during DNA replication.The c-myc proto-oncogene codes for a nuclear phosphoprotein ubiquitously expressed in somatic cells (1,2). Alterations of the c-myc locus, caused by chromosomal translocation, amplification, retroviral insertion, or retroviral transduction, deregulate c-Myc expression and contribute to tumorigenesis in different species (1,(3)(4)(5). The c-Myc protein contains a carboxyl-terminal basic, helix-loop-helix and leucine-zipper domain, which associates with another basic, helix-loop-helix and leucine-zipper protein (MAX) 1 as heterodimers, and an amino-terminal domain necessary for transcriptional transactivation (2, 6, 7). The heterodimeric complexes c-Myc⅐MAX are capable of binding DNA at a specific site (E-box) and activate transcription of downstream target genes by recruiting protein complexes that can regulate histone acetylation and modify chromatin structure (8 -10).The precise function of the c-Myc protein, and in particular the mechanism by which it promotes cell proliferation in normal and neoplastic cells, is not known. Using a variety of approaches, including genome-wide gene expression profiling, various c-Myc target genes have been identified and have been shown to be involved in heterogeneous functions, including cell cycle control, DNA synthesis, iron metabolism, protein synthesis, apoptosis, cell adhesion, and telomere maintenance (11). In Drosophila as well as in mammalian cells, c-Myc has been shown to promote cell growth (12, 13), although it has been recently reported that c-Myc may control organ and body size by regulating cell cycle entrance and cell number rather than cell size (14). A better understanding of the precise role of c-Myc depends upon the identification of the genes that are directly targeted by its transcriptional regulation.Nijmegen breakage syndrome (NBS) is an autosomal recessive hereditary disorder characterized by microcephaly,...

TEAD1 and c-Cbl are novel prostate basal cell markers that correlate with poor clinical outcome in prostate cancer

“…Although SNAP25 has not earlier been described in prostate, it has an established role in membrane trafficking and exocytosis for hormone secretion in other tissues, such as the pancreas (Sadoul et al, 1995). The basal cell profile was consistent with a proliferative phenotype, with expression of CXCL1, NBS1 and RPA, all of which encode proteins shown earlier to promote proliferation (Chiang et al, 2003;Li et al, 2004;Givalos et al, 2007). The expression of aV integrin has earlier been described in metastatic prostate cancer (McCabe et al, 2007) but not in benign prostate cells, where it may have a role in adhesion to the basement membrane.…”

Dysregulated TCL1 requires the germinal center and genome instability for mature B-cell transformation

“…Additionally, dysregulated MYC has been shown to impair double-stranded DNA break repair. 62,63 In some cell types, these changes are insufficient to induce transformation, indicating a need for complementing mutations. Studies of MYC transgenic mice using proviral insertional mutagenesis to tag interacting oncogenes identified several complementation groups for transformation.…”

Direct Activation of HSP90A Transcription by c-Myc Contributes to c-Myc-induced Transformation

“…RatHsp cell lines were generated by transfecting the HeBOCMVHSP90A plasmid into Rat1a cells, and the cells were selected under G418 (400 g/ml). The NIH3T3.Myc cell line, 293TMyci, and HeLaMyci cell lines were as described (45). The pSUPERHspi and pSUPERHspiR plasmids were generated by inserting the oligos of 5Ј-GATCCCTTCATCAGATGCATTGGACATTCAAGAGATGTCCAATGC-ATCTGATGAATTTTTGGAAA-3Ј and 5Ј-GATCCCCCAAAGAGATCT-TTCTGAGGGTTCAAGAGACCCTCAGAAAGATCTCTTTGTTTTTGG-AAA-3Ј into the pSUPER plasmids provided by Dr. R. Agami (46).…”

“…Chromatin Immunoprecipitation (ChIP) Assay-ChIP assay was performed following the procedure as described (45,50,51) with minor modifications. Briefly, CBMyc.Max, CB33 control, or EREB.TCMyc cells were cross-linked with 1% formaldehyde for 10 min and stopped by adding glycine to a final concentration of 0.125 M. Fixed cells were washed twice with TBS (20 mM Tris, pH 7.5, 150 mM NaCl) and harvested in 5 ml of SDS buffer (50 mM Tris, pH 8.0, 0.5% SDS, 100 mM NaCl, 5 mM EDTA, and protease inhibitors).…”

“…5C), indicating that c-Myc-mediated activation of HSP90A transcription required both the transactivation and heterodimerization domains with MAX, as expected for physiological c-Myc function. To determine whether c-Myc binds to the E-box in vivo, a ChIP assay using CB33Myc.Max cells was performed (45,50,51). Fig.…”