J Biol Chem. 2006 Mar 22; [Epub
ahead of print] Oncogene. 2005 Feb 24;24(9):1641-7. J Biol Chem. 2006 Feb 17;281(7):3889-98.
Epub 2005 Dec 14. Cardiovasc Res. 2006 Feb 1;69(2):520-6.
Epub 2005 Dec 1.
Bcl2 suppresses DNA repair by enhancing c-Myc transcriptional activity.
Jin Z, May WS, Gao F, Flagg T, Deng X.
Department of Medicine, University of
Bcl2 and c-Myc are two major oncogenic proteins that can functionally promote DNA damage, genetic instability and tumorigenesis. However, the mechanism(s) remains unclear. Nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is the most potent carcinogen contained in cigarette smoke that induces cellular DNA damage. Here we found that Bcl2 potently suppresses the repair of NNK-induced abasic sites of DNA lesions in association with increased c-Myc transcriptional activity. Bcl2's BH4 domain (aa 6-31) was found to bind directly to c-Myc's MBII domain (aa 106-143) and this interaction is required for Bcl2 to enhance c-Myc transcriptional activity and inhibit DNA repair. In addition to mitochondria, Bcl2 is also expressed in the nucleus where it co-localizes with c-Myc. Expression of nuclear-targeted Bcl2 enhances c-Myc transcriptional activity with suppression of DNA repair but fails to prolong cell survival. Depletion of c-Myc expression from cells overexpressing Bcl2 significantly accelerates the repair of NNK-induced DNA damage, indicating that c-Myc may be essential for Bcl2's effect on DNA repair. It is known that APE1 plays a crucial role in the repair of abasic sites of DNA lesions. Since overexpression of Bcl2 results in up-regulation of c-Myc and down-regulation of APE1, this suggests that APE1 may function as the downstream target of Bcl2/c-Myc in the DNA repair machinery. Thus, Bcl2, in addition to its survival function, may also suppress DNA repair in a novel mechanism involving c-Myc and APE1, which may lead to an accumulation of DNA damage in living cells, genetic instability and tumorigenesis.
PMID: 16554306 [PubMed - as supplied by publishe
Redox factor 1 (Ref-1) enhances specific DNA binding of p53 by promoting p53 tetramerization.
Hanson S, Kim E, Deppert W.
Heinrich-Pette-Institute for Experimental Virology and Immunology at the
Sequence-specific DNA binding is a major activity of the tumor suppressor p53 and a prerequisite for the transactivating potential of the protein. p53 interaction with target DNA is tightly regulated by various mechanisms, including binding of different components of the transcription machinery, post-translational modifications, and interactions with other factors that modulate p53 transactivation in a cell context- and promoter-specific manner. The bi-functional redox factor 1 (Ref-1/APE1) has been identified as one of the factors, which can stimulate p53 DNA binding by redox-dependent as well as redox-independent mechanisms. Whereas stimulation of p53 DNA binding by the redox activities of Ref-1 is understood quite well, little is known about mechanisms that underlie the redox-independent effects of Ref-1. We report in this study a previously unknown activity of Ref-1 as a factor promoting tetramerization of p53. We demonstrate that Ref-1 promotes association of dimers into tetramers, and de-stacking of higher oligomeric forms into the tetrameric form in vitro, thereby enhancing p53 binding to target DNA.
PMID: 15674341 [PubMed - indexed for MEDLINE]
Nucleotide sequence and DNA secondary structure, as well as replication protein A, modulate the single-stranded abasic endonuclease activity of APE1.
Fan J, Matsumoto Y, Wilson DM 3rd.
Laboratory of Molecular Gerontology, NIA, National Institutes of Health,
A major role of the multifunctional human Ape1 protein is to incise at apurinic/apyrimidinic (AP) sites in DNA via site-specific endonuclease activity. This nuclease function has been well characterized on double-stranded (ds) DNA substrates, where the complementary strand provides a template for subsequent base excision repair events. Recently, Ape1 was found to incise efficiently at AP sites positioned within the single-stranded (ss) regions of various biologically relevant DNA configurations. The studies within indicated that the ss endonuclease activity of Ape1 is poorly active on ss AP site-containing polyadenine or polythymine oligonucleotides, suggesting a requirement for some form of DNA secondary structure for efficient cleavage. Computational, footprinting, and biochemical analyses indicated that the nature of the secondary structure and the proximity of the AP site influence Ape1 incision efficiency significantly. Replication protein A (RPA), the major ssDNA-binding protein in mammalian cells, was found to bind ss AP-DNA with similar affinity as unmodified ssDNA and ds AP-DNA with lower affinity. Consistent with their known relative DNA binding affinities, RPA blocks/inhibits the ss, but not ds, AP endonuclease function of Ape1. Moreover, RPA inactivates Ape1 incision activity at an AP site within the ss region of a fork duplex, but not a transcription-like bubble intermediate. The data herein suggested a model whereby RPA selectively suppresses the nontemplated ss cleavage activity of Ape1 in vivo, particularly at sites of ongoing replication/recombination, by coating the ssDNA.
PMID: 16356936 [PubMed - in process]
Apurinic/apyrimidinic endonuclease1/redox factor-1 inhibits monocyte adhesion in endothelial cells.
Kim CS, Son SJ, Kim EK, Kim SN, Yoo DG, Kim HS, Ryoo SW, Lee SD, Irani K, Jeon BH.
Department of Physiology,
OBJECTIVE: Expression of adhesion molecules on endothelial cells and subsequent monocyte adhesion are initial events in the development of atherosclerosis. The purpose of this study was to investigate the role of apurinic/apyrmidinic endonuclease1/redox factor-1 (APE1/ref-1) in the interaction of monocytes with vascular endothelial cells. METHODS: Human umbilical vein endothelial cells (HUVECs) were transfected with an adenovirus encoding human APE1/ref-1. The effect of APE1/ref-1 overexpression on monocyte adhesion, vascular cell adhesion molecule-1 (VCAM-1) protein expression, and intracellular superoxide production in tumor necrosis factor (TNF)-alpha-activated HUVECs was examined. RESULTS: Adhesion of the monocytic cell line U937 to TNF-alpha-stimulated HUVECs in which APE1/ref-1 was overexpressed was suppressed. APE1/ref-1 overexpression also suppressed expression of VCAM-1 induced by TNF-alpha. APE1/ref-1-mediated suppression of VCAM-1 was blocked by pretreatment with the nitric oxide synthase (NOS) inhibitor l-nitroarginine methyl ester. Furthermore, APE1/ref-1 overexpression inhibited the TNF-alpha-induced increase in intracellular superoxide and p38 MAPK phosphorylation. CONCLUSIONS: These data provide evidence that APE1/ref-1 in endothelial cells mitigates TNF-alpha-induced monocyte adhesion and expression of vascular cell adhesion molecules, and this anti-adhesive property of APE1/ref-1 is primarily mediated by a NOS-dependent mechanism. Furthermore, APE1/ref-1 may inhibit VCAM-1 expression by inhibiting superoxide production and p38 MAPK activation.
J Biol Chem. 2006 Mar 22; [Epub ahead of print]
Oncogene. 2005 Feb 24;24(9):1641-7.
J Biol Chem. 2006 Feb 17;281(7):3889-98. Epub 2005 Dec 14.
Cardiovasc Res. 2006 Feb 1;69(2):520-6. Epub 2005 Dec 1.