[Show abstract][Hide abstract] ABSTRACT: Cyclic AMP Response Element Binding protein (CREB)-binding protein (CBP) is an acetyltransferase important for modifying histones
and chromatin-associated proteins and thus affecting transcription and other DNA metabolic processes. We found that the Drosophila CBP (dCBP) is associated with the NAD+-dependent deacetylase, SIR2, which was originally identified as a silencing information regulator in yeast that models silenced
and repeated sequence chromatin such as centric heterochromatin, telomeres, and the repeated rDNA sequences. As in yeast,
Drosophila sir2 (dsir2) affects the formation and/or function of centric heterochromatin. The fact that we found dCBP in immunecomplexes with dSIR2
in vivo and found that dCBP can interact with dSIR2 directly in vitro suggested that dCBP might affect the packaging of silencing
heterochromatin as well. A careful study of the dCBP mutations provides evidence that dCBP does not affect the formation and/or
function of centric heterochromatin and thus may affect other dSIR2 functions.
Preview · Article · May 2009 · The Journal of heredity
[Show abstract][Hide abstract] ABSTRACT: The CBP/p300 family of proteins comprises related acetyltransferases that coactivate signal-responsive transcription. Recent
evidence suggests that p300/CBP may also interact directly with complexes that mediate different aspects of DNA metabolism
such as replication and repair. In this report, we show that loss of dCBP in Drosophila cells and eye discs results in a defect in the cell cycle arrest induced by stalled DNA replication. We show that dCBP and
the checkpoint kinase Mei-41 can be found together in a complex and, furthermore, that dCBP has a genetic interaction with mei-41 in the response to stalled DNA replication. These observations suggest a broader role for the p300/CBP acetyltransferases
in the modulation of chromatin structure and function during DNA metabolic events as well as for transcription.
Preview · Article · Feb 2007 · Molecular and Cellular Biology
[Show abstract][Hide abstract] ABSTRACT: In Drosophila embryos, the Torso receptor tyrosine kinase (RTK) activates the small G protein Ras (D-Ras1) and the protein kinase Raf (D-Raf) to activate ERK to direct differentiation of terminal structures . However, genetic studies have demonstrated that Torso, and by extension other RTKs, can activate Raf and ERK independently of Ras . In mammalian cells, the small G protein Rap1 has been proposed to couple RTKs to ERKs. However, the ability of Rap1 to activate ERKs remains controversial, in part because direct genetic evidence supporting this hypothesis is lacking. Here, we present biochemical and genetic evidence that D-Rap1, the Drosophila homolog of Rap1, can activate D-Raf and ERK. We show that D-Rap1 binds D-Raf and activates ERKs in a GTP- and D-Raf-dependent manner. Targeted disruption of D-Rap1 expression decreased both Torso-dependent ERK activation and the ERK-dependent expression of the zygotic genes tailless and huckebein to levels similar to those achieved in D-Ras1 null embryos. Furthermore, combined deficiencies of D-Ras1 and D-Rap1 completely abolished expression of these genes, mimicking the phenotype observed in embryos lacking D-Raf. These studies provide the first direct genetic evidence of Rap1-mediated activation of the MAP kinase cascade in eukaryotic organisms.
[Show abstract][Hide abstract] ABSTRACT: Glutathione SH-transferase (GST) is a 25-kDa protein and a member of a large family that plays a critical role in the cellular homeostasis of all organisms. In this report, we describe a novel GST-containing protein identified and cloned from Drosophila. This 1045 amino acid protein possesses a zinc finger domain with a tandem array of four FLYWCH zinc finger motifs at its N-terminus and a C-terminal domain that shares a 46% homology with GST. The gene maps to chromosome 3 at position 84C6. Further characterization of this protein shows that it localizes to the cytoplasm of fly cells and is expressed through all stages of fly embryonic development. It binds to glutathione-S agarose beads in vitro. These results indicate that this new protein belongs to the GST family, thus named a Drosophila GST-containing FLYWCH zinc finger protein (dGFZF).
[Show abstract][Hide abstract] ABSTRACT: A striking example of multiple signaling pathways eliciting their effects through the regulation of a single transcription factor is seen in the coregulation of embryonic segmental patterning and limb development in Drosophila by the hedgehog (hh) and protein kinase A (PKA) signal transduction pathways. The Hh signaling cascade activates a series of genes through the transcription factor Cubitus interruptus (Ci). The PKA signaling pathway suppresses the expression of hh-responsive genes in cells that do not receive a Hh signal by phosphorylating the 155-kDa form of Ci and targeting it for proteolysis to a 75-kDa repressor form (Ci[rep]). Paradoxically, PKA can further activate Ci-mediated transcription in cells that do receive a Hh signal. Thus both the activation and repression of hh-responsive transcription is modulated by the PKA signaling pathway. Further studies will certainly bring us closer to an understanding of the intricacies involved in the regulation of development by signal transduction cascades.
[Show abstract][Hide abstract] ABSTRACT: Control of chromosome structure is important in the regulation of gene expression, recombination, DNA repair, and chromosome stability. In a two-hybrid screen for proteins that interact with the Drosophila CREB-binding protein (dCBP), a known histone acetyltransferase and transcriptional coactivator, we identified the Drosophila homolog of a yeast chromatin regulator, Sir2. In yeast, Sir2 silences genes via an intrinsic NAD(+)-dependent histone deacetylase activity. In addition, Sir2 promotes longevity in yeast and in Caenorhabditis elegans. In this report, we characterize the Drosophila Sir2 (dSir2) gene and its product and describe the generation of dSir2 amorphic alleles. We found that dSir2 expression is developmentally regulated and that dSir2 has an intrinsic NAD(+)-dependent histone deacetylase activity. The dSir2 mutants are viable, fertile, and recessive suppressors of position-effect variegation (PEV), indicating that, as in yeast, dSir2 is not an essential function for viability and is a regulator of heterochromatin formation and/or function. However, mutations in dSir2 do not shorten life span as predicted from studies in yeast and worms.
[Show abstract][Hide abstract] ABSTRACT: CBP is a critical coactivator of transcription, but little is understood about the importance of its intrinsic acetyltransferase
(AT) activity in gene activation in vivo. We show that the intrinsic AT function of CBP in Drosophila melanogaster (dCBP) is necessary to maintain a dCBP overexpression phenotype in the eye, for the in vivo activation of a specific target
gene, wingless, and for the global acetylation of histone H4. These findings indicate that a point mutation which alters the intrinsic AT
activity of CBP (only one of many CBP functions) has profound effects on CBP-induced gene activation in a physiologically
intact transcription system. Furthermore, the effects of CBP AT activity are not limited to a few specific promoters, but
rather CBT AT activity may play a role in regulating global histone acetylation throughout the developing organism.
[Show abstract][Hide abstract] ABSTRACT: The development of Drosophila requires the function of the CREB-binding protein, dCBP. In flies, dCBP serves as a coactivator for the transcription factors Cubitus interruptus, Dorsal, and Mad, and as a cosuppressor of Drosophila T cell factor. Current models propose that CBP, through its intrinsic and associated histone acetyltransferase activities, affects transient chromatin changes that allow the preinitiation complex to access the promoter. In this report, we provide evidence that dCBP may regulate the formation of chromatin states through interactions with the modulo (mod) gene product, a protein that is thought to be involved in chromatin packaging. We demonstrate that dCBP and Modulo bind in vitro and in vivo, that mutations in mod enhance the embryonic phenotype of a dCBP mutation, and that dCBP mutations enhance the melanotic tumor phenotype characteristic of mod homozygous mutants. These results imply that, in addition to its histone acetyltransferase activity, dCBP may affect higher-order chromatin structure.
Full-text · Article · Apr 2002 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: CREB-binding protein (CBP) is a coactivator for multiple transcription factors that transduce a variety of signaling pathways. Current models propose that CBP enhances gene expression by bridging the signal-responsive transcription factors with components of the basal transcriptional machinery and by augmenting the access of transcription factors to DNA through the acetylation of histones. To define the pathways and proteins that require CBP function in a living organism, we have begun a genetic analysis of CBP in flies. We have overproduced Drosophila melanogaster CBP (dCBP) in a variety of cell types and obtained distinct adult phenotypes. We used an uninflated-wing phenotype, caused by the overexpression of dCBP in specific central nervous system cells, to screen for suppressors of dCBP overactivity. Two genes with mutant versions that act as dominant suppressors of the wing phenotype were identified: the PKA-C1/DCO gene, encoding the catalytic subunit of cyclic AMP protein kinase, and ash1, a member of the trithorax group (trxG) of chromatin modifiers. Using immunocolocalization, we showed that the ASH1 protein is specifically expressed in the majority of the dCBP-overexpressing cells, suggesting that these proteins have the potential to interact biochemically. This model was confirmed by the findings that the proteins interact strongly in vitro and colocalize at specific sites on polytene chromosomes. The trxG proteins are thought to maintain gene expression during development by creating domains of open chromatin structure. Our results thus implicate a second class of chromatin-associated proteins in mediating dCBP function and imply that dCBP might be involved in the regulation of higher-order chromatin structure.
Full-text · Article · Jan 2001 · Molecular and Cellular Biology
[Show abstract][Hide abstract] ABSTRACT: CREB-binding protein (CBP) serves as a transcriptional coactivator in multiple signal transduction pathways. The Drosophilahomologue of CBP, dCBP, interacts with the transcription factors Cubitus interruptus (CI), MAD, and Dorsal (DL) and functions
as a coactivator in several signaling pathways during Drosophiladevelopment, including the hedgehog (hh),decapentaplegic (dpp), and Tollpathways. Although dCBP is required for the expression of thehh target genes, wingless (wg) andpatched (ptc) in vivo, and potentiatesci-mediated transcriptional activation in vitro, it is not known that ci absolutely requires dCBP for its activity. We used a yeast genetic screen to identify several ci point mutations that disrupt CI-dCBP interactions. These mutant proteins are unable to transactivate a reporter gene regulated
by cibinding sites and have a lower dCBP-stimulated activity than wild-type CI. When expressed exogenously in embryos, the CI point
mutants cannot activate endogenous wg expression. Furthermore, a CI mutant protein that lacks the entire dCBP interaction domain functions as a negative competitor
for wild-type CI activity, and the expression of dCBP antisense RNAs can suppress CI transactivation in Kc cells. Taken together,
our data suggest that dCBP function is necessary forci-mediated transactivation of wg duringDrosophila embryogenesis.
[Show abstract][Hide abstract] ABSTRACT: Postsynaptic dCBP (Drosophila homolog of the CREB binding protein) is required for presynaptic functional development. Viable, hypomorphic dCBP mutations have a approximately 50% reduction in presynaptic transmitter release without altering the Ca2+ cooperativity of release or synaptic ultrastructure (total bouton number is increased by 25%-30%). Exogenous expression of dCBP in muscle rescues impaired presynaptic release in the dCBP mutant background, while presynaptic dCBP expression does not. In addition, overexpression experiments indicate that elevated dCBP can also inhibit presynaptic functional development in a manner distinct from the effects of dCBP loss of function. Pre- or postsynaptic overexpression of dCBP (in wild type) reduces presynaptic release. However, we do not observe an increase in bouton number, and presynaptic overexpression impairs short-term facilitation. These data suggest that dCBP participates in a postsynaptic regulatory system that controls functional synaptic development.
[Show abstract][Hide abstract] ABSTRACT: Postsynaptic dCBP (Drosophila homolog of the CREB binding protein) is required for presynaptic functional development. Viable, hypomorphic dCBP mutations have a ∼50% reduction in presynaptic transmitter release without altering the Ca2+ cooperativity of release or synaptic ultrastructure (total bouton number is increased by 25%–30%). Exogenous expression of dCBP in muscle rescues impaired presynaptic release in the dCBP mutant background, while presynaptic dCBP expression does not. In addition, overexpression experiments indicate that elevated dCBP can also inhibit presynaptic functional development in a manner distinct from the effects of dCBP loss of function. Pre- or postsynaptic overexpression of dCBP (in wild type) reduces presynaptic release. However, we do not observe an increase in bouton number, and presynaptic overexpression impairs short-term facilitation. These data suggest that dCBP participates in a postsynaptic regulatory system that controls functional synaptic development.
[Show abstract][Hide abstract] ABSTRACT: Hedgehog (HH) is an important morphogen involved in pattern formation during Drosophila embryogenesis and disc development. cubitus interruptus (ci) encodes a transcription factor responsible for transducing the hh signal in the nucleus and activating hh target gene expression. Previous studies have shown that CI exists in two forms: a 75 kDa proteolytic repressor form and a 155 kDa activator form. The ratio of these forms, which is regulated positively by hh signaling and negatively by PKA activity, determines the on/off status of hh target gene expression. In this paper, we demonstrate that the exogenous expression of CI that is mutant for four consensus PKA sites [CI(m1-4)], causes ectopic expression of wingless (wg) in vivo and a phenotype consistent with wg overexpression. Expression of CI(m1-4), but not CI(wt), can rescue the hh mutant phenotype and restore wg expression in hh mutant embryos. When PKA activity is suppressed by expressing a dominant negative PKA mutant, the exogenous expression of CI(wt) results in overexpression of wg and lethality in embryogenesis, defects that are similar to those caused by the exogenous expression of CI(m1-4). In addition, we demonstrate that, in cell culture, the mutation of any one of the three serine-containing PKA sites abolishes the proteolytic processing of CI. We also show that PKA directly phosphorylates the four consensus phosphorylation sites in vitro. Taken together, our results suggest that positive hh and negative PKA regulation of wg gene expression converge on the regulation of CI phosphorylation.
[Show abstract][Hide abstract] ABSTRACT: Cubitus interruptus (Ci) is a transcriptional factor that is positively regulated by the hedgehog (hh) signaling pathway. Recent work has shown that a 75-kDa proteolytic product of the full-length CI protein translocates to the nucleus and represses the transcription of CI target genes. In cells that receive the hh signal, the proteolysis of CI is inhibited and the full-length protein can activate the hh target genes. Because protein kinase A (PKA) inhibits the expression of the hh target genes in developing embryos and discs and the loss of PKA activity results in elevated levels of full-length CI protein, PKA might be involved directly in the regulation of CI proteolysis. Here we demonstrate that the PKA pathway antagonizes the hh pathway by phosphorylating CI. We show that the PKA-mediated phosphorylation of CI promotes its proteolysis from the full-length active form to the 75-kDa repressor form. The PKA catalytic subunit increases the proteolytic processing of CI and the PKA inhibitor, PKI, blocks the processing. In addition, cells do not process the CI protein to the 75-kDa repressor when all of the PKA sites in CI are mutated. Mutant CI proteins that cannot be phosphorylated by PKA have increased transcriptional activity compared with wild-type CI. In addition, exogenous PKA can increase further the transcriptional activity of the CI mutant, suggesting that PKA has a second positive, indirect effect on CI activity. In summary, we show that the modulation of the hh signaling pathway by PKA occurs directly at the level of CI phosphorylation.
Preview · Article · Apr 1998 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: We have previously described the cloning of a cyclic AMP response-element (CRE)-binding protein, dCREB-A, in Drosophila melanogaster that is similar to the mammalian CRE-binding protein CREB. dCREB-A is a member of the bZIP family of transcription factors, shows specific binding to the (CRE), and can activate transcription in cell culture. In this report, we describe the gene structure for dCREB-A, protein expression patterns throughout development and the necessary role for this gene in embryogenesis. The 4.5-kb transcript is encoded in six exons that are distributed over 21 kb of DNA. There are seven start sites and no TATA consensus sequences upstream. The dCREB-A protein is expressed in the nuclei of the embryonic salivary gland, proventriculus and stomadeum. Late in embryogenesis, tracheal cell nuclei and specific nuclei within the segments show staining with anti-dCREB-A antibodies. In adult female ovaries, dCREB-A is expressed in the stage 9 through stage 11 follicle cell nuclei. Null mutations of the dCREB-A gene give rise to animals that no longer express dCREB-A protein and die late in embryogenesis before or at hatching. The absolute requirement of dCREB-A for embryogenesis demonstrates a nonredundant function for a CRE-binding protein that will be useful in studying the role of specific signal transduction cascades in development.
[Show abstract][Hide abstract] ABSTRACT: The transcription factor CBP, originally identified as a coactivator for CREB, enhances transcription mediated by many other transcription factors. Mutations in the human CBP gene are associated with Rubinstein-Taybi syndrome, a haploinsufficiency disorder characterized by abnormal pattern formation, but the mechanism by which decreased CBP levels affect pattern formation is unclear. The hedgehog (hh) signalling pathway is an important determinant of pattern formation. cubitus interruptus (ci), a component in hh signalling, encodes a transcription factor homologous to the Gli family of proteins and is required for induction of the hh-dependent expression of patched (ptc), decapentaplegic (dpp) and wingless (wg). Haploinsufficiency for the ci-related transcription factor Gli3 causes phenotypic changes in mice (known as 'extra-toes) and humans (Greig's cephalopolysyndactyly syndrome) that have similarities to Rubinstein-Taybi syndrome. Here we show that Drosophila CBP (dCBP) functions as a coactivator of Ci, suggesting that the dCBP-Ci interaction may shed light on the contribution of CBP to pattern formation in mammals.
[Show abstract][Hide abstract] ABSTRACT: We report on the characterization of the first loss-of-function mutation in a Drosophila CREB gene, dCREB-A. In the epidermis, dCREB-A is required for patterning cuticular structures on both dorsal and ventral surfaces since dCREB-A mutant larvae have only lateral structures around the entire circumference of each segment. Based on results from epistasis tests with known dorsal/ventral patterning genes, we propose that dCREB-A encodes a transcription factor that functions near the end of both the DPP- and SPI-signaling cascades to translate the corresponding extracellular signals into changes in gene expression. The lateralizing phenotype of dCREB-A mutants reveals a much broader function for CREB proteins than previously thought.
[Show abstract][Hide abstract] ABSTRACT: Each of the homeotic genes of the HOM or HOX complexes is expressed in a limited domain along the anterior-posterior axis. Each homeotic protein directs the formation of characteristic structures, such as wings or ribs. In flies, when a heat shock-inducible homeotic gene is used to produce a homeotic protein in all cells of the embryo, only some cells respond by altering their fates. We have identified genes that limit where the homeotic gene Sex combs reduced (Scr) can affect cell fates in the Drosophila embryo. In the abdominal cuticle Scr is prevented from inducing prothoracic structures by the three bithorax complex (BX-C) homeotic genes. However, two of the BX-C homeotic genes, Ultrabithorax (Ubx) and abdominal-A (abd-A), have no effect on the ability of Scr to direct the formation of salivary glands. Instead, salivary gland induction by Scr is limited in the trunk by the homeotic gene teashirt (tsh) and in the last abdominal segment by the third BX-C gene, Abdominal-B (AbdB). Therefore, spatial restrictions on homeotic gene activity differ between tissues and result both from the regulation of homeotic gene transcription and from restraints on where homeotic proteins can function.
[Show abstract][Hide abstract] ABSTRACT: CREB is a DNA-binding protein that stimulates gene transcription upon activation of the cAMP signaling pathway. The mammalian CREB protein consists of an amino-terminal transcriptional activation domain and a carboxy-terminal DNA-binding domain comprised of a basic region and a leucine zipper. Recent studies have shown that the mammalian CREB is one of many transcription factors that can bind to the cAMP regulated enhancer (CRE) sequence. Consequently, a complete understanding of regulation through the CRE sequence requires the elucidation of how the various CRE-binding proteins interact with each other. To accomplish this goal, we have begun to characterize the family of CRE-binding proteins in a system that is amenable to genetic manipulations, Drosophila melanogaster. We have previously cloned a protein designated dCREB-A from a Drosophila embryonic cDNA library. Here, we describe an additional member of the Drosophila CREB gene family, isolated by screening a lambda gt11 library of adult Drosophila head cDNAs with a multimerized CRE sequence. This protein, dCREB-B, contains 285 amino acids and is remarkably similar within the basic/zipper region to the corresponding portion of mammalian CREB. In contrast, the dCREB-B and mammalian CREB zipper domains differ considerably from the dCREB-A zipper in both length and composition. However, the putative DNA binding domains for all three proteins are highly conserved. The activator region of dCREB-B is completely different from that of both mammalian CREB and dCREB-A. Northern blot analysis shows that multiple transcripts of the dCREB-B gene are expressed in embryonic and adult tissues and that these transcripts arise from both strands of the DNA.(ABSTRACT TRUNCATED AT 250 WORDS)
No preview · Article · Oct 1993 · DNA and Cell Biology