SummaryAlzheimer's disease (AD) is the leading cause of dementia in the elderly. Despite decades of study, effective treatments for AD are lacking. Mitochondrial dysfunction has been closely linked to the pathogenesis of AD, but the relationship between mitochondrial pathology and neuronal damage is poorly understood. Sirtuins (SIRT, silent mating type information regulation 2 homolog in yeast) are NAD‐dependent histone deacetylases involved in aging and longevity. The objective of this study was to investigate the relationship between SIRT3 and mitochondrial function and neuronal activity in AD. SIRT3 mRNA and protein levels were significantly decreased in AD cerebral cortex, and Ac‐p53 K320 was significantly increased in AD mitochondria. SIRT3 prevented p53‐induced mitochondrial dysfunction and neuronal damage in a deacetylase activity‐dependent manner. Notably, mitochondrially targeted p53 (mito‐p53) directly reduced mitochondria DNA‐encoded ND2 and ND4 gene expression resulting in increased reactive oxygen species (ROS) and reduced mitochondrial oxygen consumption. ND2 and ND4 gene expressions were significantly decreased in patients with AD. p53‐ChIP analysis verified the presence of p53‐binding elements in the human mitochondrial genome and increased p53 occupancy of mitochondrial DNA in AD. SIRT3 overexpression restored the expression of ND2 and ND4 and improved mitochondrial oxygen consumption by repressing mito‐p53 activity. Our results indicate that SIRT3 dysfunction leads to p53‐mediated mitochondrial and neuronal damage in AD. Therapeutic modulation of SIRT3 activity may ameliorate mitochondrial pathology and neurodegeneration in AD.

Aberrant transcriptional repression through chromatin remodeling and histone deacetylation has been postulated as the driving force for tumorigenesis. FBI-1 (formerly called Pokemon) is a member of the POK family of transcriptional repressors. Recently, FBI-1 was characterized as a critical oncogenic factor that specifically represses transcription of the tumor suppressor gene ARF, potentially leading indirectly to p53 inactivation. Our investigations on transcriptional repression of the p53 pathway revealed that FBI-1 represses transcription of ARF, Hdm2 (human analogue of mouse double minute oncogene), and p21CIP1 (hereafter indicated as p21) but not of p53. FBI-1 showed a more potent repressive effect on p21 than on p53. Our data suggested that FBI-1 is a master controller of the ARF-Hdm2-p53-p21 pathway, ultimately impinging on cell cycle arrest factor p21, by inhibiting upstream regulators at the transcriptional and protein levels. FBI-1 acted as a competitive transcriptional repressor of p53 and Sp1 and was shown to bind the proximal Sp1-3 GC-box and the distal p53-responsive elements of p21. Repression involved direct binding competition of FBI-1 with Sp1 and p53. FBI-1 also interacted with corepressors, such as mSin3A, NCoR, and SMRT, thereby deacetylating Ac-H3 and Ac-H4 histones at the promoter. FBI-1 caused cellular transformation, promoted cell cycle proliferation, and significantly increased the number of cells in S phase. FBI-1 is aberrantly overexpressed in many human solid tumors, particularly in adenocarcinomas and squamous carcinomas. The role of FBI-1 as a master controller of the p53 pathway therefore makes it an attractive therapeutic target.The BTB/POZ 2 domain, originally identified in Drosophila melanogaster bric-à-brac, tramtrack, and broad complex transcription regulators, and in pox virus zinc finger proteins (1, 2), is an evolutionarily conserved protein-protein interaction domain. About 1,000 distinct BTB/POZ entries exist in sequence data bases (3, 4). Among 194 human BTB/POZ domain regulatory proteins, about 40 proteins are POK proteins. POK proteins consist of an N-terminal POZ domain and a C-terminal Krüppel-type (C2H2) zinc finger domain. The C-terminal zinc fingers recognize and bind specific DNA sequences, and the POZ domain mediates homo-or heterodimerization and interacts with other proteins, such as corepressors, histone deacetylase, and other transcription factors, to regulate transcription (2-4).BTB/POZ domain regulatory proteins have various cellular regulatory functions. In particular, some of the POK proteins with a BTB/POZ domain and Krüppel-like zinc finger are major determinants in apoptosis (5), development (6, 7), transcription (8 -14), and oncogenesis (8,11,15,16). The oncogenic members of the POK family include promyelocytic leukemia zinc finger (PLZF) (11, 16), BCL-6 (B cell lymphoma-6) (17), and HIC-1 (hypermethylated in cancer) (18). Another interesting, newly identified POK transcription factor with proto-oncogenic activity is FBI-1 (mouse LRF), encoded by t...

FBI-1 (also called Pokemon/ZBTB7A) is a BTB/POZ-domainKrüppel-like zinc-finger transcription factor. Recently, FBI-1 was characterized as a proto-oncogenic protein, which represses tumor suppressor ARF gene transcription. The expression of FBI-1 is increased in many cancer tissues. We found that FBI-1 potently represses transcription of the Rb gene, a tumor suppressor gene important in cell cycle arrest. FBI-1 binds to four GC-rich promoter elements (FREs) located at bp ؊308 to ؊188 of the Rb promoter region. The Rb promoter also contains two Sp1 binding sites: GC-box 1 (bp ؊65 to ؊56) and GC-box 2 (bp ؊18 to ؊9), the latter of which is also bound by FBI-1. We found that FRE3 (bp ؊244 to ؊236) is also a Sp1 binding element. The importance of the tumor suppressor retinoblastoma (Rb) 3 protein in regulating key cellular events was first suggested by the identification of a tumor, retinoblastoma, in which the Rb locus was invariably deleted (1-3). Rb is implicated in the development of various cancers (4 and references therein). Rb suppresses tumorigenesis by inhibiting cell cycle progression at G 1 /S by preventing the transcription of several genes important in cell cycle control (5). Rb is phosphorylated in a cell cycle-dependent manner (6 and references therein). When Rb is hypophosphorylated, it forms complexes with E2F family proteins and inhibits transcription by recruiting proteins involved in transcriptional repression (7). Once phosphorylated, Rb can no longer form complexes with E2F proteins. E2F proteins, upon dimerization with their differentiation-regulated transcription factor partners, are capable of activating the expression of a number of genes that are likely to regulate or promote entry into S phase (6 and references therein). FBI-1 represses transcription of theInvestigations on how transcription of the Rb gene is regulated are important in elucidating the cellular regulatory mechanism of Rb gene expression (8 -12). For example, induction of Rb gene transcription by MyoD, via CREB, is a key event in muscle differentiation (9). Furthermore, transcriptional activation of the Rb gene by GABP and HCF-1 is also important in muscle differentiation (10, 11). In contrast, YY1 and MIZF repress transcription of Rb, and this repression is important for inhibiting myogenesis (10, 12). All these data suggest that multiple transcription factors act on the transcriptional regulation of Rb gene.We have been investigating the biological functions of FBI-1 (also called Pokemon/ZBTB7A), which contains a BTB/POZdomain at its N terminus and Krüppel-like zinc fingers at its C terminus (13,14). Recently, there have been several reports on the function of FBI-1. FBI-1 stimulates the Tat activity of human immunodeficiency virus, type 1 long terminal repeat and represses human ADH5/FDH gene expression by interacting with Sp1 zinc fingers (14, 15). The mouse counterpart of FBI-1, LRF, co-immunoprecipitates and co-localizes with Bcl-6, and is involved in chondrogenesis and adipogenesis (16 -18). The rat homolog of FBI-1...

We found that ZBTB2, a POK family transcription factor, is a potent repressor of the ARF-HDM2-p53-p21 pathway important in cell cycle regulation. ZBTB2 repressed transcription of the ARF, p53, and p21 genes, but activated the HDM2 gene. In particular, ZBTB2 repressed transcription of the p21 gene by acting on the two distal p53 binding elements and the proximal Sp1 binding GC-box 5/6 elements. ZBTB2 directly interacted with Sp1 via its POZ domain and zinc fingers, which was important in the repression of transcription activation by Sp1. ZBTB2 and Sp1 competed with each other in binding to the GC-box 5/6 elements and the two p53 binding elements. ZBTB2 directly interacted with p53 via its zinc fingers, inhibiting p53 binding and repressing transcription activation by p53. The POZ domain, required for transcription repression, interacted with corepressors such as BCoR, NCoR, and SMRT. The interactions deacetylated histones Ac-H3 and -H4 at the proximal promoter. Although ectopic ZBTB2 stimulated cell proliferation, knockdown of ZBTB2 expression decreased cell proliferation and DNA synthesis. Overall, our data suggest that ZBTB2 is a potential proto-oncogenic master control gene of the p53 pathway and, in particular, is a potent transcription repressor of the cell cycle arrest gene p21 by inhibiting p53 and Sp1.The POZ domain is an evolutionarily conserved proteinprotein interaction motif found in many cellular regulatory proteins (1, 2). POZ domain genes, first identified in Drosophila and poxvirus, have since been found in organisms ranging from yeast to humans (3, 4). As many as 184 known human proteins, 96 Drosophila proteins, and 137 Caenorhabditis elegans proteins are estimated to contain the POZ domain.POZ domain proteins are involved in many critical cellular processes such as apoptosis (5), development (6, 7), ion channel activity (4), oncogenesis (8 -10), and transcription (10 -16). In particular, some of the POZ domain Krüppel-like zinc finger (POK) 3 proteins are the major determinants of development, differentiation, and oncogenesis. PLZF-null mice display severe defects in limb development and germ stem cell maintenance (7, 17). T helper-inducing POZ/Krüppel-like factor (Th-POK/cKrox) has been recently reported as a master regulator of T-cell lineage commitment (18). BCL-6, PLZF, and HIC1 have been implicated in non-Hodgkin lymphoma, acute promyelocytic leukemia, and spontaneous malignant tumors, respectively (8,9,19). Recently, FBI-1 (also called Pokemon) has been shown to act as a proto-oncogene by repressing transcription of the ARF gene, causing down-regulation of p53 and promoting oncogenic cellular transformation (10).The most striking property of some POZ domain transcription factors is their ability to repress transcription via their POZ domains (10 -16, 20), although a few POZ domain transcription factors activate transcription (21,22). This characteristic probably underlies many biological processes controlled by these factors. The ability of the domain to interact with key regulatory protei...

FBI-1 (Pokemon/ZBTB7A