The monoclonal antibody Alz50 recognizes both neurofibrillary pathology associated with Alzheimer's disease and subplate neurons in the developing human brain. To attempt to identify Alz50 antigens expressed during development, a human fetal brain cDNA library was immunoscreened. A positive clone was isolated and sequenced. The clone represents a novel gene named FAC1 (Fetal Alz-50-Reactive Clone 1). The FAC1 gene is located on human chromosome 17 and is conserved across species. In the human fetal brain, the FAC1 gene product is abundantly expressed and the protein is located both in the nucleus and the cytoplasm of cells throughout the developing cortex. Decreased levels of FAC1 protein are observed in adult brain by immunoblot analysis. By immunocytochemistry, the FAC1 protein is almost exclusively localized in the nucleus of neurons in the adult neocortex. Therefore, expression of the FAC1 gene is developmentally regulated and the cellular localization of the protein product is altered during development (Bowser, 1995).
Fetal Alz-50 clone 1 (FAC1) is a novel DNA binding protein with altered expression and subcellular localization during neuronal development and degeneration. FAC1 localizes to the cell body and neurites in undifferentiated neurons during development and in degenerating neurons during Alzheimer's disease progression. In the normal adult brain FAC1 is present predominantly in the nucleus of cortical neurons. When in the nucleus, FAC1 has been shown to repress transcription by binding a specific DNA sequence. The affinity of FAC1 for the identified DNA sequence is dramatically enhanced when FAC1 is phosphorylated. Phosphatase treatment of neuroblastoma nuclear extracts reduces FAC1 DNA binding affinity. Finally, inhibition of cellular serine/threonine phosphatases results in increased FAC1 DNA binding activity. These data suggest that FAC1 DNA binding activity is dependent upon and regulated by phosphorylation signals in the cell (Jordan-Sciutto. 1999a).
Fetal Alz-50 clone 1 (FAC1) is a novel, developmentally regulated gene that exhibits changes in protein expression and subcellular localization during neuronal development and neurodegeneration. To understand the functional implications of altered subcellular localization, a normal cellular function of FAC1 has been established. The FAC1 amino acid sequence contains regional homology to transcriptional regulators. Using the polymerase chain reaction-assisted binding site selection assay, a DNA sequence recognized by recombinant FAC1 has been identified. Mutation of any 2 adjacent base pairs in the identified binding site dramatically reduces the binding preference of FAC1, demonstrating that the binding is specific for the identified site. Nuclear extracts from neural and non-neural cell lines contain a DNA-binding activity with similar specificity and nucleotide requirements as the recombinant FAC1 protein. This DNA-binding activity can be attributed to FAC1 since it is dependent upon the presence of FAC1 and behaves identically on a nondenaturing polyacrylamide gel as transiently transfected FAC1. In NIH3T3 cells, luciferase reporter plasmids containing the identified binding site (CACAACAC) are repressed by cotransfected FAC1 whether the binding site is proximal or distal to the transcription initiation site. This study indicates that FAC1 is a DNA-binding protein that functions as a transcription factor when localized to the nucleus (Jordan-Sciutto, 1999b).
The bromodomain is a 110-amino-acid conserved structural region associated with proteins that regulate signal-dependent, nonbasal transcription. The bromodomain can regulate histone acetyl transferase activity and interacts specifically with acetylated lysine residues. A key role for bromodomain proteins in maintaining normal proliferation is indicated by the implication of several bromodomain proteins in cancer, with four of these identified at translocation breakpoints. EST databases were searched for novel bromodomain genes. The sequence from one EST was used to initiate generation of a full-length clone from a testis cDNA library. The completed sequence encodes a predicted protein of 2781 amino acids, which, in addition to the bromodomain, harbors further motifs characteristic of a transcriptional coactivator: two PHD fingers and an extensive glutamine-rich acidic domain. There are several other regions that are conserved with the Caenorhabditis elegans putative protein F26H11, which may be functionally homologous. The novel gene, called BPTF, is expressed in all tissues examined as a 10.5-kb transcript. The protein has extensive identity with the smaller FAC1 protein, suggesting that the two either are derived from the same locus or are synonymous. BPTF has been mapped to 17q23. Functional domains found within BPTF are consistent with a role for this protein in hormonally regulated, chromatin-mediated regulation of transcription (Jones, 2000).
Transcription factors mediate their regulatory effects through interaction with DNA and numerous nuclear proteins. The fetal Alz-50 clone 1 (FAC1) protein, a novel DNA-binding protein with the capacity to repress transcription, is likely to function through a similar mechanism. Using the two-hybrid yeast screen, it has been shown that FAC1 interacts with the myc-associated zinc finger protein (ZF87/MAZ). This association was confirmed in vitro with recombinant protein. The ZF87/MAZ interaction domain was mapped to the region containing a putative nuclear localization signal (NLS) and nuclear export sequence (NES) of FAC1, using deletion mutants of the FAC1 protein. However, FAC1 recognizes a conformational interface that includes the proline/alanine-rich domain of ZF87/MAZ and the first zinc finger. Cotransfection of NIH3T3 cells with ZF87/MAZ and a luciferase reporter containing the SV40 promoter and enhancer results in an increase in transcriptional activation, suggesting ZF87/MAZ is able to recognize its consensus binding site present in the SV40 promoter. Cotransfection with FAC1 reduces the level of ZF87/MAZ-induced activation of the SV40 promoter in a dose dependent manner. A mutant FAC1, lacking the ZF87/MAZ interaction domain, does not alter ZF87/MAZ activation of the SV40 promoter. These data demonstrate that interaction between FAC1 and ZF87/MAZ alters the transactivation capacity of ZF87/MAZ. By immunoblot analysis, FAC1 and ZF87/MAZ exhibit similar tissue distribution and co-localize to pathologic structures in Alzheimer's disease brain. Coexpression of FAC1 and ZF87/MAZ suggest that interaction of these two proteins will have biological implications for gene regulation in neurodegeneration (Jordan-Sciutto, 2000).
The class A, B and C synthetic multivulva (synMuv) genes act redundantly to negatively regulate the expression of vulval cell fates in Caenorhabditis elegans. The class B and C synMuv proteins include homologs of proteins that modulate chromatin and influence transcription in other organisms similar to members of the Myb-MuvB/dREAM, NuRD and Tip60/NuA4 complexes. To determine how these chromatin-remodeling activities negatively regulate the vulval cell-fate decision, a suppressor of the synMuv phenotype was isolated and it was found that the suppressor gene encodes the C. elegans homolog of Drosophila melanogaster ISWI. The C. elegans ISW-1 protein likely acts as part of a Nucleosome Remodeling Factor (NURF) complex with NURF-1, a nematode ortholog of NURF301, to promote the synMuv phenotype. isw-1 and nurf-1 mutations suppress both the synMuv phenotype and the multivulva phenotype caused by overactivation of the Ras pathway. These data suggest that a NURF-like complex promotes the expression of vulval cell fates by antagonizing the transcriptional and chromatin-remodeling activities of complexes similar to Myb-MuvB/dREAM, NuRD and Tip60/NuA4. Because the phenotypes caused by a null mutation in the tumor-suppressor and class B synMuv gene lin-35 Rb and a gain-of-function mutation in let-60 Ras are suppressed by reduction of isw-1 function, NURF complex proteins might be effective targets for cancer therapy (Andersen, 2006; full text of article).
Home page: The Interactive Fly © 1995, 1996 Thomas B. Brody, Ph.D.
The Interactive Fly resides on the
Society for Developmental Biology's Web server.