The alpha and beta subunits of the GA-binding protein form a stable heterodimer in solution. Revised model of heterotetrameric complex assembly

Shaping DNA damage responses: Therapeutic potential of targeting telomeric proteins and DNA repair factors in cancer

Shelterin proteins regulate genomic stability by preventing inappropriate DNA damage responses (DDRs) at telomeres. Unprotected telomeres lead to persistent DDR causing cell cycle inhibition, growth arrest, and apoptosis. Cancer cells rely on DDR to protect themselves from DNA lesions and exogenous DNA-damaging agents such as chemotherapy and radiotherapy. Therefore, targeting DDR machinery is a promising strategy to increase the sensitivity of cancer cells to existing cancer therapies. However, the success of these DDR inhibitors depends on other mutations, and over time, patients develop resistance to these therapies. This suggests the need for alternative approaches. One promising strategy is co-inhibiting shelterin proteins with DDR molecules, which would offset cellular fitness in DNA repair in a mutation-independent manner. This review highlights the associations and dependencies of the shelterin complex with the DDR proteins and discusses potential co-inhibition strategies that might improve the therapeutic potential of current inhibitors.

Association of single nucleotide polymorphisms in the nuclear respiratory factor-2 beta subunit-encoding GABPB1 gene with the occupational environment

GABPB1, known as nuclear respiratory factor 2 (Nrf2), activates the mitochondrial genes that are responsible for antioxidant action and detoxification. Two single nucleotide polymorphisms (SNPs) of GABPB1, such as rs7181866 and rs8031031, were reported to be associated with the prevention of the increasing cancer risk caused by environmental deterioration. Between March 1 and May 1, 2018, human peripheral blood mononuclear cells (PBMCs) from a cohort of 300 volunteers working in adverse occupational environments were genotyped for the two SNPs in the present study. The SNP rs7181866 was found to be significantly greater in the male group than in the female group. Frequencies of SNP rs7181866 and bi-allele SNPs (rs7181866 + rs8031031) were significantly different between the <35-year-old group and the ≥35-year-old group. Further, multinomial logistic regression analysis of the occupational environments revealed the highest predictive frequency of SNPs for four environmental factors, of which chemical factors accounted for 15.33% rs7181866, physical factors accounted for 34.79% rs7181866 + rs8031031, physical + chemical factors accounted for 39.5% rs8031031, and unknown factors accounted for 26.5% rs7181866 + rs8031031. In conclusion, the G allele of rs7181866 was found to be significantly more susceptible than the rs8031031 allele under adverse occupational environmental factors, and physical factors such as noise, which appear to play vital roles in causing SNP mutations.

Cancer-specific loss of TERT activation sensitizes glioblastoma to DNA damage

Glioblastoma is a highly lethal form of brain cancer with no current treatment options that substantially improve patient outcomes. A key therapeutic challenge is the identification of methods that reduce tumor burden while leaving normal cells unaffected. We show that TERT-promoter mutations, common in glioblastoma, lead to TERT reactivation through increased binding of GABPB1L-isoform–containing transcription factor complexes. In turn, we find that cancer-cell–specific inhibition of TERT through GABPB1L reduction results in near-term anti-growth effects and an impaired DNA damage response that profoundly increase the sensitivity of glioblastoma tumors to frontline chemotherapy. Our results thus provide rationale for GABPB1L inhibition combined with temozolomide chemotherapy treatment as a promising therapeutic strategy for glioblastoma.

Most glioblastomas (GBMs) achieve cellular immortality by acquiring a mutation in the telomerase reverse transcriptase (TERT) promoter. TERT promoter mutations create a binding site for a GA binding protein (GABP) transcription factor complex, whose assembly at the promoter is associated with TERT reactivation and telomere maintenance. Here, we demonstrate increased binding of a specific GABPB1L-isoform–containing complex to the mutant TERT promoter. Furthermore, we find that TERT promoter mutant GBM cells, unlike wild-type cells, exhibit a critical near-term dependence on GABPB1L for proliferation, notably also posttumor establishment in vivo. Up-regulation of the protein paralogue GABPB2, which is normally expressed at very low levels, can rescue this dependence. More importantly, when combined with frontline temozolomide (TMZ) chemotherapy, inducible GABPB1L knockdown and the associated TERT reduction led to an impaired DNA damage response that resulted in profoundly reduced growth of intracranial GBM tumors. Together, these findings provide insights into the mechanism of cancer-specific TERT regulation, uncover rapid effects of GABPB1L-mediated TERT suppression in GBM maintenance, and establish GABPB1L inhibition in combination with chemotherapy as a therapeutic strategy for TERT promoter mutant GBM.

Synergistic activation of mutant TERT promoter by Sp1 and GABPA in BRAFV600E-driven human cancers

The activating TERT promoter mutations and BRAF^V600E mutation are well-established oncogenic alterations in human cancers. Coexistence of BRAF^V600E and TERT promoter mutations is frequently found in multiple cancer types, and is strongly associated with poor patient prognosis. Although the BRAF^V600E-elicited activation of ERK has been demonstrated to contribute to TERT reactivation by maintaining an active chromatin state, it still remains to be addressed how activated ERK is selectively recruited to mutant TERT promoter. Here, we report that transcription factor GABPA mediates the regulation of BRAF^V600E/MAPK signaling on TERT reactivation by selectively recruiting activated ERK to mutant TERT promoter, where activated ERK can phosphorylate Sp1, thereby resulting in HDAC1 dissociation and an active chromatin state. Meanwhile, phosphorylated Sp1 further enhances the binding of GABPA to mutant TERT promoter. Taken together, our data indicate that GABPA and Sp1 synergistically activate mutant TERT promoter, contributing to tumorigenesis and cancer progression, particularly in the BRAF^V600E-driven human cancers. Thus, our findings identify a direct mechanism that bridges two frequent oncogenic alterations together in TERT reactivation.

12-h clock regulation of genetic information flow by XBP1s

Our group recently characterized a cell-autonomous mammalian 12-h clock independent from the circadian clock, but its function and mechanism of regulation remain poorly understood. Here, we show that in mouse liver, transcriptional regulation significantly contributes to the establishment of 12-h rhythms of mRNA expression in a manner dependent on Spliced Form of X-box Binding Protein 1 (XBP1s). Mechanistically, the motif stringency of XBP1s promoter binding sites dictates XBP1s’s ability to drive 12-h rhythms of nascent mRNA transcription at dawn and dusk, which are enriched for basal transcription regulation, mRNA processing and export, ribosome biogenesis, translation initiation, and protein processing/sorting in the Endoplasmic Reticulum (ER)-Golgi in a temporal order consistent with the progressive molecular processing sequence described by the central dogma information flow (CEDIF). We further identified GA-binding proteins (GABPs) as putative novel transcriptional regulators driving 12-h rhythms of gene expression with more diverse phases. These 12-h rhythms of gene expression are cell autonomous and evolutionarily conserved in marine animals possessing a circatidal clock. Our results demonstrate an evolutionarily conserved, intricate network of transcriptional control of the mammalian 12-h clock that mediates diverse biological pathways. We speculate that the 12-h clock is coopted to accommodate elevated gene expression and processing in mammals at the two rush hours, with the particular genes processed at each rush hour regulated by the circadian and/or tissue-specific pathways.

Distinct from the well-known 24-hour circadian clock, this study shows that the mammalian 12-hour clock upregulates genetic information flow capacity during the two "rush hours" (dawn and dusk) in a manner dependent on the transcription factor XBP1s.

Disruption of the β1L Isoform of GABP Reverses Glioblastoma Replicative Immortality in a TERT Promoter Mutation-Dependent Manner

TERT promoter mutations reactivate telomerase, allowing for indefinite telomere maintenance and enabling cellular immortalization. These mutations specifically recruit the multimeric ETS factor GABP, which can form two functionally independent transcription factor species: a dimer or a tetramer. We show that genetic disruption of GABPβ1L (β1L), a tetramer-forming isoform of GABP that is dispensable for normal development, results in TERT silencing in a TERT promoter mutation-dependent manner. Reducing TERT expression by disrupting β1L culminates in telomere loss and cell death exclusively in TERT promoter mutant cells. Orthotopic xenografting of β1L-reduced, TERT promoter mutant glioblastoma cells rendered lower tumor burden and longer overall survival in mice. These results highlight the critical role of GABPβ1L in enabling immortality in TERT promoter mutant glioblastoma.

A Hepatic GAbp-AMPK Axis Links Inflammatory Signaling to Systemic Vascular Damage

Increased pro-inflammatory signaling is a hallmark of metabolic dysfunction in obesity and diabetes. Although both inflammatory and energy substrate handling processes represent critical layers of metabolic control, their molecular integration sites remain largely unknown. Here, we identify the heterodimerization interface between the α and β subunits of transcription factor GA-binding protein (GAbp) as a negative target of tumor necrosis factor alpha (TNF-α) signaling. TNF-α prevented GAbpα and β complex formation via reactive oxygen species (ROS), leading to the non-energy-dependent transcriptional inactivation of AMP-activated kinase (AMPK) β1, which was identified as a direct hepatic GAbp target. Impairment of AMPKβ1, in turn, elevated downstream cellular cholesterol biosynthesis, and hepatocyte-specific ablation of GAbpα induced systemic hypercholesterolemia and early macro-vascular lesion formation in mice. As GAbpα and AMPKβ1 levels were also found to correlate in obese human patients, the ROS-GAbp-AMPK pathway may represent a key component of a hepato-vascular axis in diabetic long-term complications.

Long-Range Chromatin Interactions Drive Mutant TERT Promoter Activation

Cancer-specific TERT promoter mutations (-146C>T and -124C>T) have been linked to reactivation of the epigenetically silenced telomerase reverse transcriptase gene (TERT). Understanding how these single-nucleotide alterations drive TERT reactivation is a fundamental unanswered question and is key for making successful therapeutics. We show that unlike wild-type promoters, recruitment of the transcription factor GABPA specifically to mutant TERT promoters mediates long-range chromatin interaction and enrichment of active histone marks, and hence drives TERT transcription. CRISPR-mediated reversal of mutant TERT promoters, or deletion of its long-range interacting chromatin, abrogates GABPA binding and long-range interactions, leading to depletion of active histone marks, loss of POL2 recruitment, and suppression of TERT transcription. In contrast, de novo introduction of a TERT promoter mutation enables GABPA binding and upregulation of TERT via long-range interactions, acquisition of active histone marks, and subsequent POL2 recruitment. This study provides a unifying mechanistic insight into activation of mutant TERT promoters across various human cancers.

SIGNIFICANCE

This study identifies a key mechanism by which cancer-specific mutant TERT promoters cause reactivation of TERT Because the mechanism uncovered here is not utilized by promoters that drive TERT in normal cells, this mechanism could be exploited to make inhibitors which have the potential to block telomerase function and hence the progression of up to 90% of human cancers. Cancer Discov; 6(11); 1276-91. ©2016 AACR.See related commentary by Min and Shay, p. 1212This article is highlighted in the In This Issue feature, p. 1197.

Mechanism of allele specific assembly and disruption of master regulator transcription factor complexes of NF-KBp50, NF-KBp65 and HIF1a on a non-coding FAS SNP

A challenging question in genetics is to understand the molecular function of non-coding variants of the genome. By using differential EMSA, ChIP and functional genome analysis, we have found that changes in transcription factors (TF) apparent binding affinity and dissociation rates are responsible for allele specific assembly or disruption of master TFs: we observed that NF-KBp50, NF-KBp65 and HIF1a bind with an affinity of up to 10 fold better to the C-allele than to the T-allele of rs7901656 both in vivo and in vitro. Furthermore, we showed that NF-KBp50, p65 and HIF1a form higher order heteromultimeric complexes overlapping rs7901656, implying synergism of action among TFs governing cellular response to infection and hypoxia. With rs7901656 on the FAS gene as a paradigm, we show how allele specific transcription factor complex assembly and disruption by a causal variant contributes to disease and phenotypic diversity. This finding provides the highly needed mechanistic insight into how the molecular etiology of regulatory SNPs can be understood in functional terms.

An interaction proteomics survey of transcription factor binding at recurrent TERT promoter mutations

Aberrant telomerase reactivation in differentiated cells represents a major event in oncogenic transformation. Recurrent somatic mutations in the human telomerase reverse transcriptase (TERT) promoter region, predominantly localized to two nucleotide positions, are highly prevalent in many cancer types. Both mutations create novel consensus E26 transformation-specific (ETS) motifs and are associated with increased TERT expression. Here, we perform an unbiased proteome-wide survey of transcription factor binding at TERT promoter mutations in melanoma. We observe ELF1 binding at both mutations in vitro and we show that increased recruitment of GABP is enabled by the spatial architecture of native and novel ETS motifs in the TERT promoter region. We characterize the dynamics of competitive binding between ELF1 and GABP and provide evidence for ELF1 exclusion by transcriptionally active GABP. This study thus provides an important description of proteome-wide, mutation-specific binding at the recurrent, oncogenic TERT promoter mutations.

Zinc finger independent genome-wide binding of Sp2 potentiates recruitment of histone-fold protein Nf-y distinguishing it from Sp1 and Sp3

Transcription factors are grouped into families based on sequence similarity within functional domains, particularly DNA-binding domains. The Specificity proteins Sp1, Sp2 and Sp3 are paradigmatic of closely related transcription factors. They share amino-terminal glutamine-rich regions and a conserved carboxy-terminal zinc finger domain that can bind to GC rich motifs in vitro. All three Sp proteins are ubiquitously expressed; yet they carry out unique functions in vivo raising the question of how specificity is achieved. Crucially, it is unknown whether they bind to distinct genomic sites and, if so, how binding site selection is accomplished. In this study, we have examined the genomic binding patterns of Sp1, Sp2 and Sp3 in mouse embryonic fibroblasts by ChIP-seq. Sp1 and Sp3 essentially occupy the same promoters and localize to GC boxes. The genomic binding pattern of Sp2 is different; Sp2 primarily localizes at CCAAT motifs. Consistently, re-expression of Sp2 and Sp3 mutants in corresponding knockout MEFs revealed strikingly different modes of genomic binding site selection. Most significantly, while the zinc fingers dictate genomic binding of Sp3, they are completely dispensable for binding of Sp2. Instead, the glutamine-rich amino-terminal region is sufficient for recruitment of Sp2 to its target promoters in vivo. We have identified the trimeric histone-fold CCAAT box binding transcription factor Nf-y as the major partner for Sp2-chromatin interaction. Nf-y is critical for recruitment of Sp2 to co-occupied regulatory elements. Equally, Sp2 potentiates binding of Nf-y to shared sites indicating the existence of an extensive Sp2-Nf-y interaction network. Our results unveil strikingly different recruitment mechanisms of Sp1/Sp2/Sp3 transcription factor members uncovering an unexpected layer of complexity in their binding to chromatin in vivo.

A major question in eukaryotic gene regulation is how transcription factors with similar structural features elicit specific biological responses. We used the three transcription factors Sp1, Sp2 and Sp3 as a paradigm for investigating this question. All three proteins are ubiquitously expressed, and they share glutamine-rich domains as well as a conserved bona fide zinc finger DNA binding domain. Yet, each of the three proteins carries out unique functions in vivo, and each is absolutely essential for mouse development. By genome-wide binding analysis, we found that Sp1 and Sp3 on the one hand, and Sp2 on the other hand engage completely different protein domains for their genomic binding site selection. Most strikingly, the zinc finger domain of Sp2 is dispensable for recruitment to its target sites in vivo. Moreover, we provide strong evidence that the histone-fold protein Nf-y is necessary for recruitment of Sp2. Conversely, Sp2 potentiates Nf-y binding showing that binding of Sp2 and Nf-y to shared sites is mutually dependent. Our findings uncover an unexpected mechanistic diversity in promoter recognition by seemingly similar transcription factors. This work has broader implications for our understanding of how members of other multi-protein transcription factor families could achieve specificity.

Targeting tetramer-forming GABPβ isoforms impairs self-renewal of hematopoietic and leukemic stem cells

Hematopoietic stem cells (HSCs) and leukemic stem cells (LSCs) are both capable of self-renewal, with HSCs sustaining multiple blood lineage differentiation and LSCs indefinitely propagating leukemia. The GABP complex, consisting of DNA binding GABPα subunit and transactivation GABPβ subunit, critically regulates HSC multipotency and self-renewal via controlling an essential gene regulatory module. Two GABPβ isoforms, GABPβ1L and GABPβ2, contribute to assembly of GABPα(2)β(2) tetramer. We demonstrate that GABPβ1L/β2 deficiency specifically impairs HSC quiescence and survival, with little impact on cell cycle or apoptosis in differentiated blood cells. The HSC-specific effect is mechanistically ascribed to perturbed integrity of the GABP-controlled gene regulatory module in HSCs. Targeting GABPβ1L/β2 also impairs LSC self-renewal in p210(BCR-ABL)-induced chronic myelogenous leukemia (CML) and exhibits synergistic effects with tyrosine kinase inhibitor imatinib therapy in inhibiting CML propagation. These findings identify the tetramer-forming GABPβ isoforms as specific HSC regulators and potential therapeutic targets in treating LSC-based hematological malignancy.

Highly cooperative recruitment of Ets-1 and release of autoinhibition by Pax5

Pax5 (paired box binding factor 5) is a critical regulator of transcription and lineage commitment in B lymphocytes. In B cells, mb-1 (Ig-alpha/immunoglobulin-associated alpha) promoter transcription is activated by Pax5 through its recruitment of E74-like transforming sequence (Ets) family proteins to a composite site, the P5-EBS (Pax5-Ets binding site). Previously, X-ray crystallographic analysis revealed a network of contacts between the DNA-binding domains of Pax5 and Ets-1 while bound to the P5-EBS. Here, we report that Pax5 assembles these ternary complexes via highly cooperative interactions that overcome the autoinhibition of Ets-1. Using recombinant proteins, we calculated K(d(app)) values for the binding of Pax5, Ets-1, and GA-binding proteins, separately or together, to the P5-EBS. By itself, Pax5 binds the P5-EBS with high affinity (K(d) approximately equal 2 nM). Ets-1(331-440) bound the P5-EBS by itself with low affinity (K(d)=136 nM). However, autoinhibited Ets-1(280-440) alone does not bind detectably to the suboptimal sequences of the P5-EBS. Recruitment of Ets-1(331-440) or Ets-1(280-440) resulted in highly efficient ternary complex assembly with Pax5. Pax5 counteracts autoinhibition and increases binding of Ets-1 of the mb-1 promoter by >1000-fold. Mutation of Pax5 Gln22 to alanine (Q22A) enhances promoter binding by Pax5; however, Q22A greatly reduces recruitment of Ets-1(331-440) and Ets-1(280-440) by Pax5 (8.9- or >300-fold, respectively). Thus, Gln22 of Pax5 is essential for overcoming Ets-1 autoinhibition. Pax5 wild type and Q22A each recruited GA-binding protein alpha/beta1 to the mb-1 promoter with similar affinities, but recruitment was less efficient than that of Ets-1 (reduced by approximately 8-fold). Our results suggest a mechanism that allows Pax5 to overcome autoinhibition of Ets-1 DNA binding. In summary, these data illustrate requirements for partnerships between Ets proteins and Pax5.

Nuclear control of respiratory chain expression by nuclear respiratory factors and PGC-1-related coactivator

Expression of the respiratory apparatus depends on both nuclear and mitochondrial genes. Although these genes are sequestered in distinct cellular organelles, their transcription relies on nucleus-encoded factors. Certain of these factors are directed to the mitochondria, where they sponsor the bi-directional transcription of mitochondrial DNA. Others act on nuclear genes that encode the majority of the respiratory subunits and many other gene products required for the assembly and function of the respiratory chain. The nuclear respiratory factors, NRF-1 and NRF-2, contribute to the expression of respiratory subunits and mitochondrial transcription factors and thus have been implicated in nucleo-mitochondrial interactions. In addition, coactivators of the PGC-1 family serve as mediators between the environment and the transcriptional machinery governing mitochondrial biogenesis. One family member, peroxisome proliferator-activated receptor gamma coactivator PGC-1-related coactivator (PRC), is an immediate early gene product that is rapidly induced by mitogenic signals in the absence of de novo protein synthesis. Like other PGC-1 family members, PRC binds NRF-1 and activates NRF-1 target genes. In addition, PRC complexes with NRF-2 and HCF-1 (host cell factor-1) in the activation of NRF-2-dependent promoters. HCF-1 functions in cell-cycle progression and has been identified as an NRF-2 coactivator. The association of these factors with PRC is suggestive of a role for the complex in cell growth. Finally, shRNA-mediated knock down of PRC expression results in a complex phenotype that includes the inhibition of respiratory growth on galactose and the loss of respiratory complexes. Thus, PRC may help integrate the expression of the respiratory apparatus with the cell proliferative program.

Transcriptional paradigms in mammalian mitochondrial biogenesis and function

Mitochondria contain their own genetic system and undergo a unique mode of cytoplasmic inheritance. Each organelle has multiple copies of a covalently closed circular DNA genome (mtDNA). The entire protein coding capacity of mtDNA is devoted to the synthesis of 13 essential subunits of the inner membrane complexes of the respiratory apparatus. Thus the majority of respiratory proteins and all of the other gene products necessary for the myriad mitochondrial functions are derived from nuclear genes. Transcription of mtDNA requires a small number of nucleus-encoded proteins including a single RNA polymerase (POLRMT), auxiliary factors necessary for promoter recognition (TFB1M, TFB2M) and activation (Tfam), and a termination factor (mTERF). This relatively simple system can account for the bidirectional transcription of mtDNA from divergent promoters and key termination events controlling the rRNA/mRNA ratio. Nucleomitochondrial interactions depend on the interplay between transcription factors (NRF-1, NRF-2, PPARalpha, ERRalpha, Sp1, and others) and members of the PGC-1 family of regulated coactivators (PGC-1alpha, PGC-1beta, and PRC). The transcription factors target genes that specify the respiratory chain, the mitochondrial transcription, translation and replication machinery, and protein import and assembly apparatus among others. These factors are in turn activated directly or indirectly by PGC-1 family coactivators whose differential expression is controlled by an array of environmental signals including temperature, energy deprivation, and availability of nutrients and growth factors. These transcriptional paradigms provide a basic framework for understanding the integration of mitochondrial biogenesis and function with signaling events that dictate cell- and tissue-specific energetic properties.

Identification and structural characterization of a CBP/p300-binding domain from the ETS family transcription factor GABP alpha

Using NMR spectroscopy, we identified and characterized a previously unrecognized structured domain near the N-terminus (residues 35-121) of the ETS family transcription factor GABP alpha. The monomeric domain folds as a five-stranded beta-sheet crossed by a distorted helix. Although globally resembling ubiquitin, the GABP alpha fragment differs in its secondary structure topology and thus appears to represent a new protein fold that we term the OST (On-SighT) domain. The surface of the GABP alpha OST domain contains two predominant clusters of negatively-charged residues suggestive of electrostatically driven interactions with positively-charged partner proteins. Following a best-candidate approach to identify such a partner, we demonstrated through NMR-monitored titrations and glutathione S-transferase pulldown assays that the OST domain binds to the CH1 and CH3 domains of the co-activator histone acetyltransferase CBP/p300. This provides a direct structural link between GABP and a central component of the transcriptional machinery.

GA-binding protein regulates KIS gene expression, cell migration, and cell cycle progression

The cyclin-dependent kinase inhibitor p27(Kip1) arrests cell cycle progression through G1/S phases and is regulated by phosphorylation of serine/threonine residues. Recently, we identified the serine/threonine kinase, KIS, which phosphorylates p27(Kip1) on serine 10 leading to nuclear export of p27(Kip1) and protein degradation. However, the molecular mechanisms of transcriptional activation of the human KIS gene and its biological activity are not known. We mapped the transcription initiation site approximately 116 bp 5' to the translation start site, and sequences extending to -141 were sufficient for maximal promoter activity. Mutation in either of two Ets-binding sites in this region resulted in an approximately 75-80% decrease in promoter activity. These sites form at least 3 specific complexes, which contained GA-binding protein (GABP). Knocking down GABPalpha by siRNA in vascular smooth muscle cells (VSMCs) diminished KIS gene expression and reduced cell migration. Correspondingly, in serum stimulated GABPalpha-deficient mouse embryonic fibroblasts (MEFs), KIS gene expression was also significantly reduced, which was associated with an increase in p27(Kip1) protein levels and a decreased percentage of cells in S-phase. Consistent with these findings, following vascular injury in vivo, GABPalpha-heterozygous mice demonstrated reduced KIS gene expression within arterial lesions and these lesions were significantly smaller compared to GABP+/+ mice. In summary, serum-responsive GABP binding to Ets-binding sites activates the KIS promoter, leading to KIS gene expression, cell migration, and cell cycle progression.

NRF-2 transcription factor is required for human TOMM20 gene expression

TOMM20 is a subunit of the outer mitochondrial membrane translocase that plays a major role as a receptor of precursor proteins with N-terminal cleavable presequences targeted to the mitochondria. Nuclear respiratory factors 1 and 2 (NRF-1 and NRF-2) play an important role in governing nucleo-mitochondrial interactions implicated in mitochondrial biogenesis. It was recently reported that NRF-2 is critical for maintaining normal transcriptional levels of the TOMM20 gene, but the promoter of this gene is uncharacterized. We report the presence of a NRF-2 and two NRF-1 binding motifs in the 5'-flanking region of the human TOMM20 gene and provide insight into their roles for promoter activity by using chromatin immunoprecipitation experiments and reporter assays in HeLa S3 and A204 cells. We show that only NRF-2 and the proximal NRF-1 motifs are involved in the expression of the gene. The NRF-2 binding site is required to activate transcription. The proximal NRF-1 site cooperates with NRF-2 in regulating the expression of the gene. The distal NRF-1 binding site is not functional.

Regulation of the interleukin-7 receptor alpha promoter by the Ets transcription factors PU.1 and GA-binding protein in developing B cells

Signaling through the IL-7 receptor (IL-7R) is required for development and maintenance of the immune system. The receptor for IL-7 is heterodimeric, consisting of a common gamma chain (gammac, encoded by Il2rg) and an alpha subunit (IL-7Ralpha, encoded by Il7r). The Il7r gene is expressed specifically in the immune system in a developmental stage-specific manner. It is not known how the Il7r gene is transcriptionally regulated during B cell development. The goal of this study is to elucidate the function of the Il7r promoter region in developing B cells. Using a combination of 5' rapid amplification of cDNA ends analysis, transient transfection assays, and DNase I hypersensitivity mapping, we identified the location of the Il7r promoter. Using a combination of electrophoretic mobility shift analysis, chromatin immunoprecipitation experiments, and RNA interference experiments, we found that the Ets transcription factors PU.1 and GA-binding protein (GABP) activate the Il7r promoter by interacting with a highly conserved Ets binding site. In committed B lineage cells, GABP can promote Il7r transcription in the absence of PU.1. However, the results of retroviral gene transfer experiments suggest that PU.1 is uniquely required to initiate transcription of the Il7r locus at the earliest stages of progenitor B cell generation. In summary, these results suggest that Il7r transcription is regulated by both PU.1 and GABP in developing B cells.

GA-binding protein and p300 are essential components of a retinoic acid-induced enhanceosome in myeloid cells

Expression of CD18, the beta chain of the leukocyte integrins, is transcriptionally regulated by retinoic acid (RA) in myeloid cells. Full RA responsiveness of the CD18 gene requires its proximal promoter, which lacks a retinoic acid response element (RARE). Rather, RA responsiveness of the CD18 proximal promoter requires ets sites that are bound by GA-binding protein (GABP). The transcriptional coactivator, p300, further increases CD18 RA responsiveness. We demonstrate that GABPalpha, the ets DNA-binding subunit of GABP, physically interacts with p300 in myeloid cells. This interaction involves the GABPalpha pointed domain (PNT) and identifies p300 as the first known interaction partner of GABPalpha PNT. Expression of the PNT domain, alone, disrupts the GABPalpha-p300 interaction and decreases the RA responsiveness of the CD18 proximal promoter. Chromatin immunoprecipitation and chromosome conformation capture demonstrate that, in the presence of RA, GABPalpha and p300 at the proximal promoter recruit retinoic acid receptor/retinoid X receptor from a distal RARE to form an enhanceosome. A dominant negative p300 construct disrupts enhanceosome formation and reduces the RA responsiveness of CD18. Thus, proteins on the CD18 proximal promoter recruit the distal RARE in the presence of RA. This is the first description of an RA-induced enhanceosome and demonstrates that GABP and p300 are essential components of CD18 RA responsiveness in myeloid cells.

Nuclear control of respiratory gene expression in mammalian cells

The mitochondrial respiratory apparatus is the product of both nuclear and mitochondrial genes. The protein coding capacity of mtDNA is restricted to the expression of 13 respiratory subunits and thus nuclear genes play a predominant role in the biosynthesis of the respiratory chain and in the expression of the mitochondrial genome. Transcriptional regulators that act on both nuclear and mitochondrial genes have been implicated in the bi-genomic expression of the respiratory chain. Mitochondrial transcription is directed by a small number of nucleus-encoded factors (Tfam, TFB1M, TFB2M, mTERF). The expression of these factors is coordinated with that of nuclear respiratory proteins through the action of transcriptional activators and coactivators. In particular, environmental signals induce the expression of PGC-1 family coactivators (PGC-1alpha, PGC-1beta, and PRC), which in turn target specific transcription factors (NRF-1, NRF-2, and ERR alpha) in the expression of respiratory genes. This system provides a mechanism for linking respiratory chain expression to environmental conditions and for integrating it with other functions related to cellular energetics.

Identification of functional elements in the murine Gabp alpha/ATP synthase coupling factor 6 bi-directional promoter

The GA-repeat binding protein (GABP) is a ubiquitous transcription factor involved in transcriptional regulation of genes encoding proteins involved in a variety of cellular processes including adipocyte differentiation, mitochondrial respiration, and neuromuscular signaling. GABP is composed of two subunits; the GABP alpha subunit is a member of the Ets-family of transcription factors, and the unrelated ankyrin repeat containing GABP beta subunit. We previously identified a bidirectional promoter directing the expression of Gabpa (GAA) gene in one direction and ATP Synthase Coupling Factor 6 (Atp5j) (CF6) gene in the other [Chinenov, Y., Coombs, C. and Martin, M. E., 2000a. "Isolation of a bi-directional promoter directing the expression of the mouse GABP alpha and ATP Synthase Coupling Factor 6 genes. Gene 261:311-320.]. In this study we characterize sequence elements and regulatory factors contributing to the promoter activities of the GAA/CF6 bidirectional promoter. The core of the GAA/CF6 bidirectional promoter is retained within a 400 bp sequence and contains four GABP binding sites, a Sp1/3 binding site and an YY1 binding site. Site-directed mutagenesis demonstrated that while no single factor binding site was essential for promoter activity in either direction, the GA1 site located proximal to the previously mapped transcription start sites functioned cooperatively with the other GABP binding sites and with the Sp1/3 and YY1 sites to provide transcriptional activation of the GAA and CF6 promoters. The other GABP sites and the Sp1/3 and YY1 binding sites were functionally redundant for basal promoter activities in both directions. Electrophoretic mobility shift assays identified multiple DNA-protein complexes containing GABP alpha, GABP beta, Sp1, Sp3 or YY1 proteins, including one ternary complex containing GABP alpha, GABP beta and Sp1 proteins. Binding of GABP to the GAA/CF6 bi-directional promoter provides the potential for autoregulation of GABP alpha expression and confirms the importance of GABP in the coordinate expression of respiratory chain components.

A Binding Free Energy Hot Spot in the Ankyrin Repeat Protein GABPβ Mediated Protein–Protein Interaction

The frequently observed ankyrin repeat motif represents a structural scaffold evolved for mediating protein-protein interactions. As such, these repeats modulate a diverse range of cellular functions. We thermodynamically characterized the heterodimeric GA-binding protein (GABP) alphabeta complex and focused specifically on the interaction mediated by the ankyrin repeat domain of the GABPbeta. Our isothermal titration calorimetric analysis of the interaction between the GABP subunits determined an association constant (K(A)) of 6.0 x 10(8) M(-1) and that the association is favorably driven by a significant change in enthalpy (DeltaH) and a minor change in entropy (-TDeltaS). A total of 16 GABPbeta interface residues were chosen for alanine scanning mutagenesis. The calorimetrically measured differences in the free energy of binding were compared to computationally calculated values resulting in a correlation coefficient r = 0.71. We identified three spatially contiguous hydrophobic and aromatic residues that form a binding free energy hot spot (DeltaDeltaG > 2.0 kcal/mol). One residue provides structural support to the hot spot residues. Three non-hot spot residues are intermediate contributors (DeltaDeltaG approximately 1.0 kcal/mol) and create a canopy-like structure over the hot spot residues to possibly occlude solvent and orientate the subunits. The remaining interface residues are located peripherally and have weak contributions. Finally, our mutational analysis revealed a significant entropy-enthalpy compensation for this interaction.

Identification of a crucial site for synoviolin expression

Synoviolin is an E3 ubiquitin ligase localized in the endoplasmic reticulum (ER) and serving as ER-associated degradation system. Analysis of transgenic mice suggested that synoviolin gene dosage is implicated in the pathogenesis of arthropathy. Complete deficiency of synoviolin is fatal embryonically. Thus, alternation of Synoviolin could cause breakdown of ER homeostasis and consequently lead to disturbance of cellular homeostasis. Hence, the expression level of Synoviolin appears to be important for its biological role in cellular homeostasis under physiological and pathological conditions. To examine the control of protein level, we performed promoter analysis to determine transcriptional regulation. Here we characterize the role of synoviolin transcription in cellular homeostasis. The Ets binding site (EBS), termed EBS-1, from position -76 to -69 of the proximal promoter, is responsible for synoviolin expression in vivo and in vitro. Interestingly, transfer of EBS-1 decoy into NIH 3T3 cells conferred not only the repression of synoviolin gene expression but also a decrease in cell number. Fluorescence-activated cell sorter analysis using annexin V staining confirmed the induction of apoptosis by EBS-1 decoy and demonstrated recovery of apoptosis by overexpression of Synoviolin. Our results suggest that transcriptional regulation of synoviolin via EBS-1 plays an important role in cellular homeostasis. Our study provides novel insight into the transcriptional regulation for cellular homeostasis.

GABP, HCF-1 and YY1 are involved in Rb gene expression during myogenesis

Muscle cell differentiation, or myogenesis, is a well-characterized process and involves the expression of specific sets of genes in an orderly manner. A prerequisite for myogenesis is the exit from the cell cycle, which is associated with the up-regulation of the tumor suppressor Rb. In this study, we set to investigate the regulatory mechanism of the Rb promoter that allows adequate up-regulation in differentiating myoblasts. We report that Rb expression is regulated by the transcription factors GABP, HCF-1 and YY1. Before induction of differentiation, Rb is expressed at a low level and GABP and YY1 are both present on the promoter. YY1, which exerts an inhibitory effect on Rb expression, is removed from the promoter as cells advance through myogenesis and translocates from the nucleus to the cytoplasm. On the other hand, upon induction of differentiation, the GABP cofactor HCF-1 is recruited to and coactivates the promoter with GABP. RNAi-mediated knock-down of HCF-1 results in inhibition of Rb up-regulation as well as myotube formation. These results indicate that the Rb promoter is subject to regulation by positive and negative factors and that this intricate activation mechanism is critical to allow the accurate Rb gene up-regulation observed during myogenesis.

Identification and expression analysis of alternative transcripts of the mouse GA-binding protein (Gabp) subunits α and β1

The erythroblast transformation specific (ETS) transcription factor GA-binding protein (Gabp) is widely expressed and acts on a diverse range of target genes, including nuclear-encoded mitochondrial proteins and neuromuscular-specific genes. The GABPalpha subunit contains an ETS DNA binding domain and the beta subunit contains a nuclear localization signal (NLS) and transactivation domain. Here, we show coincident expression of Gabpalpha and beta1 throughout mouse embryogenesis, consistent with the gene products functioning in a complex. We have also identified 2 alternatively spliced, tissue-specific exons 1 (5' untranslated regions) of mouse Gabpalpha and 4 alternative 3' polyadenylation signals that, in combination, result in 12 transcripts for Gabpalpha. These alternative transcripts are suggested to have altered stability, subcellular localization and/or translation efficiency. Further, we identified nine differentially expressed splice variants of mouse Gabpbeta1 that encode beta protein forms lacking functional domains, suggesting a dominant negative function. Together, alternative transcripts of Gabpalpha and beta1 provide a mechanism for tissue-specific regulation of Gabp activity.

Diversity in structure and function of the Ets family PNT domains

The PNT (or Pointed) domain, present within a subset of the Ets family of transcription factors, is structurally related to the larger group of SAM domains through a common tertiary arrangement of four alpha-helices. Previous studies have shown that, in contrast to the PNT domain from Tel, this domain from Ets-1 contains an additional N-terminal helix integral to its folded structure. To further investigate the structural plasticity of the PNT domain, we have used NMR spectroscopy to characterize this domain from two additional Ets proteins, Erg and GABPalpha. These studies both define the conserved and variable features of the PNT domain, and demonstrate that the additional N-terminal helix is also present in GABPalpha, but not Erg. In contrast to Tel and Yan, which self-associate to form insoluble polymers, we also show that the isolated PNT domains from Ets-1, Ets-2, Erg, Fli-1, GABPalpha, and Pnt-P2 are monomeric in solution. Furthermore, these soluble PNT domains do not associate in any pair-wise combination. Thus these latter Ets family PNT domains likely mediate interactions with additional components of the cellular signaling or transcriptional machinery.

Erralpha and Gabpa/b specify PGC-1alpha-dependent oxidative phosphorylation gene expression that is altered in diabetic muscle

Recent studies have shown that genes involved in oxidative phosphorylation (OXPHOS) exhibit reduced expression in skeletal muscle of diabetic and prediabetic humans. Moreover, these changes may be mediated by the transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha). By combining PGC-1alpha-induced genome-wide transcriptional profiles with a computational strategy to detect cis-regulatory motifs, we identified estrogen-related receptor alpha (Erralpha) and GA repeat-binding protein alpha as key transcription factors regulating the OXPHOS pathway. Interestingly, the genes encoding these two transcription factors are themselves PGC-1alpha-inducible and contain variants of both motifs near their promoters. Cellular assays confirmed that Erralpha and GA-binding protein a partner with PGC-1alpha in muscle to form a double-positive-feedback loop that drives the expression of many OXPHOS genes. By using a synthetic inhibitor of Erralpha, we demonstrated its key role in PGC-1alpha-mediated effects on gene regulation and cellular respiration. These results illustrate the dissection of gene regulatory networks in a complex mammalian system, elucidate the mechanism of PGC-1alpha action in the OXPHOS pathway, and suggest that Erralpha agonists may ameliorate insulin-resistance in individuals with type 2 diabetes mellitus.

Phosphorylation-elicited quaternary changes of GA binding protein in transcriptional activation

Enrichment of nicotinic acetylcholine receptors (nAChR) on the tip of the subjunctional folds of the postsynaptic membrane is a central event in the development of the vertebrate neuromuscular junction. This is attained, in part, through a selective transcription in the subsynaptic nuclei, and it has recently been shown that the GA binding protein (GABP) plays an important role in this compartmentalized expression. The neural factor heregulin (HRG) activates nAChR transcription in cultured cells by stimulating a signaling cascade of protein kinases. Hence, it is speculated that GABP becomes activated by phosphorylation, but the mechanism has remained elusive. To fully understand the consequences of GABP phosphorylation, we examined the effect of heregulin-elicited GABP phosphorylation on cellular localization, DNA binding, transcription, and mobility. We demonstrate that HRG-elicited phosphorylation dramatically changes the transcriptional activity and mobility of GABP. While phosphorylation of GABPbeta seems to be dispensable for these changes, phosphorylation of GABPalpha is crucial. Using fluorescence resonance energy transfer, we furthermore showed that phosphorylation of threonine 280 in GABPalpha triggers reorganizations of the quaternary structure of GABP. Taken together, these results support a model in which phosphorylation-elicited structural changes of GABP enable engagement in certain interactions leading to transcriptional activation.

Requirements for selective recruitment of Ets proteins and activation of mb-1/Ig-alpha gene transcription by Pax-5 (BSAP)

Pax-5, a member of the paired domain family of transcription factors, is a key regulator of B lymphocyte-specific transcription and differentiation. A major target of Pax-5-mediated activation is the mb-1 gene, which encodes the essential transmembrane signaling protein Ig-alpha. Pax-5 recruits three members of the Ets family of transcription factors: Ets-1, Fli-1 and GABPalpha (with GABPbeta1), to assemble ternary complexes on the mb-1 promoter in vitro. Using the Pax-5:Ets-1:DNA crystal structure as a guide, we defined amino acid requirements for transcriptional activation of endogenous mb-1 genes using a novel cell-based assay. Mutations in the beta-hairpin/beta-turn of the DNA-binding domain of Pax-5 demonstrated its importance for DNA sequence recognition and activation of mb-1 transcription. Mutations of amino acids contacting Ets-1 in the crystal structure reduced or blocked mb-1 promoter activation. One of these mutations, Q22A, resulted in greatly reduced mb-1 gene transcript levels, concurrent with the loss of its ability to recruit Fli-1 to bind the promoter in vitro. In contrast, the mutation had no effect on recruitment of the related Ets protein GABPalpha (with GABPbeta1). These data further define requirements for Pax-5 function in vivo and reveal the complexity of interactions required for cooperative partnerships between transcription factors.

Ets transcription factors ER81 and Elk1 regulate the transcription of the human presenilin 1 gene promoter

We have previously defined a crucial DNA element controlling 90% of the expression of the presenilin 1 gene at (-35 to +6). This region contains an Ets transcription factor binding motif, and a 2-base pair alteration within the core sequence (GGAA to TTAA) of the Ets consensus also reduced transcription by over 90%. We have shown that Ets1/2 transcription factors bind specifically to the -10 Ets element and activate PS1 transcription. The identification of other transcription factors recognizing specifically this promoter area should provide insights into the regulation of PS1. We have used the -10 Ets element as a bait in yeast one hybrid screening of a human brain cDNA library. This assay selected three factors from the Ets family: Ets2, ER81 and Elk1. We show that in vitro translated ER81 indeed binds specifically to the -10 region of the PS1 promoter and that ER81 activates by two- to threefold the basal transcription of a presenilin-1 promoter-chloramphenicol acetyltransferase reporter synthetic gene (-119, +178)PS1CAT in transient infection assays in neuroblastoma cells (SK-N-SH). GABPalpha, a member of the Ets family closely related to Ets2 and also containing a pointed domain, only increased PS1 transcription by about twofold. Cotransfection of GABPbeta together with GABPalpha did not increase PS1 transcription. However, GABPbeta alone activated PS1 transcription by two- to threefold. In contrast, the more distantly related Ets factor Elk1 repressed PS1 transcription very effectively.

Differential gene expression in the distal tip endoderm of the embryonic mouse lung

During the early development of the mouse lung a number of genes encoding signaling molecules are differentially expressed in the epithelium and mesenchyme of the distal buds. Evidence suggests they play a role in regulating the stereotypic processes of bud outgrowth and branching as well as proximal-distal patterning of both cell layers. To better understand the mechanisms underlying branching morphogenesis, a subtractive hybridization and differential screen was carried out for genes preferentially expressed in the epithelium at the tips of embryonic day 11.5 lung buds, versus more proximal regions. Twenty genes were identified, assigned to different categories based on sequence analysis, and their distal expression confirmed by whole-mount in situ hybridization.

Hsc70-interacting HPD loop of the J domain of polyomavirus T antigens fluctuates in ps to ns and micros to ms

The backbone dynamics of the J domain from polyomavirus T antigens have been investigated using 15N NMR relaxation and molecular dynamics simulation. Model-free relaxation analysis revealed picosecond to nanosecond motions in the N terminus, the I-II loop, the C-terminal end of helix II through the HPD loop to the beginning of helix III, and the C-terminal end of helix III to the C terminus. The backbone dynamics of the HPD loop and termini are dominated by motions with moderately large amplitudes and correlation times of the order of a nanosecond or longer. Conformational exchange on the microsecond to millisecond timescale was identified in the HPD loop, the N and C termini, and the I-II loop. A 9.7ns MD trajectory manifested concerted swings of the HPD loop. Transitions between major and minor conformations of the HPD loop featured distinct patterns of change in backbone dihedral angles and hydrogen bonds. Fraying of the C-terminal end of helix II and the N-terminal end of helix III correlated with displacements of the HPD loop. Correlation of crankshaft motions of Gly46 and Gly47 with the collective motions of the HPD loop suggested an important role of the two glycine residues in the mobility of the loop. Fluctuations of the HPD loop correlated with relative reorientation of side-chains of Lys35 and Asp44 that interact with Hsc70.

Nuclear activators and coactivators in mammalian mitochondrial biogenesis

The biogenesis of mitochondria requires the expression of a large number of genes, most of which reside in the nuclear genome. The protein-coding capacity of mtDNA is limited to 13 respiratory subunits necessitating that nuclear regulatory factors play an important role in governing nucleo-mitochondrial interactions. Two classes of nuclear transcriptional regulators implicated in mitochondrial biogenesis have emerged in recent years. The first includes DNA-binding transcription factors, typified by nuclear respiratory factor (NRF)-1, NRF-2 and others, that act on known nuclear genes that specify mitochondrial functions. A second, more recently defined class, includes nuclear coactivators typified by PGC-1 and related family members (PRC and PGC-1 beta). These molecules do not bind DNA but rather work through their interactions with DNA-bound transcription factors to regulate gene expression. An important feature of these coactivators is that their expression is responsive to physiological signals mediating thermogenesis, cell proliferation and gluconeogenesis. Thus, they have the ability to integrate the action of multiple transcription factors in orchestrating programs of gene expression essential to cellular energetics. The interplay of these nuclear factors appears to be a major determinant in regulating the biogenesis of mitochondria.

Mitochondrial contributions to cancer cell physiology: potential for drug development

Mitochondria make an integral contribution to the regulation of several aspects of cell biology such as energy production, molecular metabolism, redox status, calcium signalling and programmed cell death. In accordance with an endosymbiotic origin, mitochondria rely upon the nucleus for synthesis and function. In addition, these organelles can respond to intra- and extracellular cues independently, and there exists a highly coordinated "cross talk" between mitochondrial and nuclear signals that can greatly influence cell behaviour. This review focuses upon the putative roles of altered mitochondrial physiology in the process of cellular transformation. Discussed are: mitochondria as targets of drug-induced cytotoxicity or cancer promotion, as regulators of apoptosis, as sources of cell signalling through reactive oxygen species, and mitochondrial control of specific nuclear responses.

Kinetic studies of Fos.Jun.DNA complex formation: DNA binding prior to dimerization

The bZIP proteins Fos and Jun bind DNA rapidly and with high affinity, forming a heteromeric complex that mediates activated transcription. Here we use stopped-flow fluorescence resonance energy transfer (FRET) to study the kinetic pathway by which Fos.Jun. DNA complexes assemble. Though dimerization of Fos and Jun occurs rapidly in the absence of DNA, the rate of dimerization is enhanced in the presence of DNA. Global analysis of the kinetic data shows that the favored DNA binding pathway is one is which the two protein monomers bind DNA sequentially and assemble their dimerization interface while bound to DNA.

Isolation of a bi-directional promoter directing expression of the mouse GABPalpha and ATP synthase coupling factor 6 genes

The GA-binding protein (GABP) is a ubiquitous heteromeric transcription factor implicated in the regulation of several genes involved in mitochondrial energy metabolism including subunits of cytochrome c oxidase, ATP synthase, and mitochondrial transcription factor 1 (mtTF1). GABPalpha subunit binds the PEA3/Ets binding sites (EBS), while GABPbeta contains a transcription activation domain and mediates alphabeta dimer and alpha(2)beta(2) tetramer formation essential for activation of transcription. Here we report the cloning of 2449 bp of the mouse (m) GABPalpha promoter region including 201 bp of the 5' end of the published mGABPalpha cDNA sequence. Surprisingly, sequences homologous to the 5'UTR of mouse, rat and human mitochondrial ATP synthase coupling factor 6 (ATPsynCF6) cDNAs were found165-240 bp upstream of the mGABPalpha cDNA. A search of the non-redundant nucleotide database revealed a human genomic sequence derived from chromosome 21 (21q22) bearing significant homology to the mGABPalpha/ATPsynCF6 promoter region and encompassed the entire hGABPalpha and hATPsynCF6 genes. Primer extension analysis revealed multiple transcription start sites for both mGABPalpha and mATPsynCF6 mRNAs that mapped near the published cDNA 5' ends. Sequence analysis identified several binding sites upstream of the GABPalpha cDNA sequence including sites for GABP (-86, -104, -169, -257, and -994), YY1 (-57), Sp1 (-242 and -226), and NRF1 (-5). No 'TATA' motif was identified near either the GABPalpha or ATPsynCF6 transcription start sites. The human and mouse promoters retain significant sequence identity including binding sites for several tissue-specific transcription factors. Transient transfection assays using Luciferase reporter constructs containing the intergenic region and flanking sequences confirmed that this region of DNA promotes transcription in both directions.

Sequence and functional properties of Ets genes in the model organism Drosophila

Detailed molecular and genetic studies, coupled with the recent sequencing of the fly genome, have identified eight Ets-related genes in the model organism Drosophila. All show homology to genes in vertebrate species. Functional analyses of some of the Drosophila ets genes have revealed their essential roles in developmental processes such as metamorphosis, oogenesis, neurogenesis, myogenesis, and eye development. Such studies have yielded important insights into our understanding of the genetic control of hormonally-regulated gene expression, programmed cell death, and signal transduction during cell fate determination and differentiation. The developmental roles of E74 (ELF1), pointed (Ets 1), yan (TEL), and D-elg (GABPalpha) will be reviewed in this article. The context of their participation in signal transduction and gene regulation will also be discussed. The information should be of significant value to the study of related processes in higher organisms due to the growing evidence for the cross species conservation of developmental mechanisms.