Molecular cloning and characterization of P113, a mouse SNF2/SWI2-related transcription factor

The role of SMARCAL1 in replication fork stability and telomere maintenance

SMARCAL1 (SWI/SNF Related, Matrix Associated, Actin Dependent Regulator Of Chromatin, Subfamily A-Like 1), also known as HARP, is an ATP-dependent annealing helicase that stabilizes replication forks during DNA damage. Mutations in this gene are the cause of Schimke immune-osseous dysplasia (SIOD), an autosomal recessive disorder characterized by T-cell immunodeficiency and growth dysfunctions. In this review, we summarize the main roles of SMARCAL1 in DNA repair, telomere maintenance and replication fork stability in response to DNA replication stress.

HIV-1 Vpr degrades the HLTF DNA translocase in T cells and macrophages

Viruses often interfere with the DNA damage response to better replicate in their hosts. The human immunodeficiency virus 1 (HIV-1) viral protein R (Vpr) protein has been reported to modulate the activity of the DNA repair structure-specific endonuclease subunit (SLX4) complex and to promote cell cycle arrest. Vpr also interferes with the base-excision repair pathway by antagonizing the uracil DNA glycosylase (Ung2) enzyme. Using an unbiased quantitative proteomic screen, we report that Vpr down-regulates helicase-like transcription factor (HLTF), a DNA translocase involved in the repair of damaged replication forks. Vpr subverts the DDB1-cullin4-associated-factor 1 (DCAF1) adaptor of the Cul4A ubiquitin ligase to trigger proteasomal degradation of HLTF. This event takes place rapidly after Vpr delivery to cells, before and independently of Vpr-mediated G2 arrest. HLTF is degraded in lymphocytic cells and macrophages infected with Vpr-expressing HIV-1. Our results reveal a previously unidentified strategy for HIV-1 to antagonize DNA repair in host cells.

The helicase-like transcription factor (HLTF) in cancer: loss of function or oncomorphic conversion of a tumor suppressor?

The Helicase-like Transcription Factor (HLTF) belongs to the SWI/SNF family of proteins involved in chromatin remodeling. In addition to its role in gene transcription, HLTF has been implicated in DNA repair, which suggests that this protein acts as a tumor suppressor. Accumulating evidence indicates that HLTF expression is altered in various cancers via two mechanisms: gene silencing through promoter hypermethylation or alternative mRNA splicing, which leads to the expression of truncated proteins that lack DNA repair domains. In either case, the alteration of HLTF expression in cancer has a poor prognosis. In this review, we gathered published clinical and molecular data on HLTF. Our purposes are (a) to address whether HLTF alterations could be considered as cancer drivers or passengers and (b) to determine whether its different functions (transcription or DNA repair) could be diverted in clonal selection during cancer progression.

Helicase-like transcription factor (Hltf) regulates G2/M transition, Wt1/Gata4/Hif-1a cardiac transcription networks, and collagen biogenesis

HLTF/Hltf regulates transcription, remodels chromatin, and coordinates DNA damage repair. Hltf is expressed in mouse brain and heart during embryonic and postnatal development. Silencing Hltf is semilethal. Seventy-four percent of congenic C57BL/6J Hltf knockout mice died, 75% within 12-24 hours of birth. Previous studies in neonatal (6-8 hour postpartum) brain revealed silencing Hltf disrupted cell cycle progression, and attenuated DNA damage repair. An RNA-Seq snapshot of neonatal heart transcriptome showed 1,536 of 20,000 total transcripts were altered (p < 0.05) - 10 up- and 1,526 downregulated. Pathway enrichment analysis with MetaCore™ showed Hltf’s regulation of the G2/M transition (p=9.726E^-15) of the cell cycle in heart is nearly identical to its role in brain. In addition, Brca1 and 12 members of the Brca1 associated genome surveillance complex are also downregulated. Activation of caspase 3 coincides with transcriptional repression of Bcl-2. Hltf loss caused downregulation of Wt1/Gata4/Hif-1a signaling cascades as well as Myh7b/miR499 transcription. Hltf-specific binding to promoters and/or regulatory regions of these genes was authenticated by ChIP-PCR. Hif-1a targets for prolyl (P4ha1, P4ha2) and lysyl (Plod2) collagen hydroxylation, PPIase enzymes (Ppid, Ppif, Ppil3) for collagen trimerization, and lysyl oxidase (Loxl2) for collagen-elastin crosslinking were downregulated. However, transcription of genes for collagens, fibronectin, Mmps and their inhibitors (Timps) was unaffected. The collective downregulation of genes whose protein products control collagen biogenesis caused disorganization of the interstitial and perivascular myocardial collagen fibrillar network as viewed with picrosirius red-staining, and authenticated with spectral imaging. Wavy collagen bundles in control hearts contrasted with collagen fibers that were thin, short and disorganized in Hltf null hearts. Collagen bundles in Hltf null hearts were tangled and fragmented. Thus, silencing Hltf during heart organogenesis compromised DNA double-strand break repair, and caused aberrant collagen biogenesis altering the structural network that transmits cardiomyocyte force into muscle contraction.

Role of helicase-like transcription factor (hltf) in the G2/m transition and apoptosis in brain

HLTF participates in transcription, chromatin remodeling, DNA damage repair, and tumor suppression. Aside from being expressed in mouse brain during embryonic and postnatal development, little is known about Hltf's functional importance. Splice variant quantification of wild-type neonatal (6-8 hour postpartum) brain gave a ratio of 5:1 for Hltf isoform 1 (exons 1-25) to isoform 2 (exons 1-21 with exon 21 extended via a partial intron retention event). Western analysis showed a close correlation between mRNA and protein expression. Complete loss of Hltf caused encephalomalacia with increased apoptosis, and reduced viability. Sixty-four percent of Hltf null mice died, 48% within 12-24 hours of birth. An RNA-Seq snapshot of the neonatal brain transcriptome showed 341 of 20,000 transcripts were altered (p < 0.05) - 95 up regulated and 246 down regulated. MetaCore^TM enrichment pathway analysis revealed Hltf regulates cell cycle, cell adhesion, and TGF-beta receptor signaling. Hltf's most important role is in the G2/M transition of the cell cycle (p  =  4.672e-7) with an emphasis on transcript availability of major components in chromosome cohesion and condensation. Hltf null brains have reduced transcript levels for Rad21/Scc1, histone H3.3, Cap-E/Smc2, Cap-G/G2, and Aurora B kinase. The loss of Hltf in its yeast Rad5-like role in DNA damage repair is accompanied by down regulation of Cflar, a critical inhibitor of TNFRSF6-mediated apoptosis, and increased (p<0.0001) active caspase-3, an indicator of intrinsic triggering of apoptosis in null brains. Hltf also regulates Smad7/Bambi/Tgf-beta/Bmp5/Wnt10b signaling in brain. ChIP confirmed Hltf binding to consensus sequences in predicted (promoter Scgb3a1 gene) and previously unidentified (P-element on chromosome 7) targets. This study is the first to provide a comprehensive view of Hltf targets in brain. Moreover, it reveals how silencing Hltf disrupts cell cycle progression, and attenuates DNA damage repair.

Biology and significance of the JAK/STAT signalling pathways

Since its discovery two decades ago, the activation of the Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway by numerous cytokines and growth factors has resulted in it becoming one of the most well-studied intracellular signalling networks. The field has progressed from the identification of the individual components to high-resolution crystal structures of both JAK and STAT, and an understanding of the complexities of the molecular activation and deactivation cycle which results in a diverse, yet highly specific and regulated pattern of transcriptional responses. While there is still more to learn, we now appreciate how disruption and deregulation of this pathway can result in clinical disease and look forward to adoption of the next generation of JAK inhibitors in routine clinical treatment.

Role of yeast Rad5 and its human orthologs, HLTF and SHPRH in DNA damage tolerance

In the yeast Saccharomyces cerevisiae, the Rad6-Rad18 DNA damage tolerance pathway constitutes a major defense system against replication fork blocking DNA lesions. The Rad6-Rad18 ubiquitin-conjugating/ligase complex governs error-free and error-prone translesion synthesis by specialized DNA polymerases, as well as an error-free Rad5-dependent postreplicative repair pathway. For facilitating replication through DNA lesions, translesion synthesis polymerases copy directly from the damaged template, while the Rad5-dependent damage tolerance pathway obtains information from the newly synthesized strand of the undamaged sister duplex. Although genetic data demonstrate the importance of the Rad5-dependent pathway in tolerating DNA damages, there has been little understanding of its mechanism. Also, the conservation of the yeast Rad5-dependent pathway in higher order eukaryotic cells remained uncertain for a long time. Here we summarize findings published in recent years regarding the role of Rad5 in promoting error-free replication of damaged DNA, and we also discuss results obtained with its human orthologs, HLTF and SHPRH.

Progesterone regulation of RUSH/SMARCA3/HLTF includes DNA looping

RUSH/SMARCA3 (SWI/SNF-related matrix-associated actin-dependent regulator of chromatin subfamily A, member 3) is capable of sequence-selective DNA binding and ATP-dependent DNA unwinding. In rabbit uterine epithelial cells, RUSH-1alpha (113 kDa) is the progesterone-dependent splice variant and RUSH-1beta (95 kDa) is the oestrogen-dependent splice variant. Rabbit RUSH/SMARCA3 mRNA is primarily regulated at the proximal promoter (-162/+90) via a PRE (progesterone-response element) half-site/overlapping Y-box domain (-38/-26) and two Sp (specificity protein) 3 sites centred at -128 and -58. We investigated hormone regulation by exploring binding of transcription factors to a putative RUSH/SMARCA3 site (-616/-611) and the distal Sp3 (-131/-126) site. In response to progesterone, RUSH-1alpha binds the RUSH site and the Sp3 site becomes a functional binding site for Egr-1 (early growth-response gene product 1)/Sp (specificity protein)1/3/MAZ (Myc-associated zinc-finger protein)/MZF1 (myeloid zinc finger 1)/c-Rel. TransSignal TF-TF Interaction Arrays, supershift assays and ChIP (chromatin immunoprecipitation) analyses confirmed strong physical interactions between RUSH and Egr-1/c-Rel. Higher-order long-range interactions between RUSH and the Egr-1/c-Rel derivative of the anisotropic flexibility of the intervening DNA sequence were shown with 3C (chromosome conformation capture) assays. Transient transfection assays with mutant constructs showed the co-operative interaction between RUSH and Egr-1 mediates repression by c-Rel. Thus DNA-bound RUSH/SMARCA3 communicates with its own proximal promoter by looping the intervening DNA. Moreover, progesterone-dependent DNA looping is an adjunct to progesterone induction of the RUSH/SMARCA3 gene because the availability of RUSH isoforms and relevant binding partners is progesterone-regulated.

Human HLTF functions as a ubiquitin ligase for proliferating cell nuclear antigen polyubiquitination

Human helicase-like transcription factor (HLTF) is frequently inactivated in colorectal and gastric cancers. Here, we show that HLTF is a functional homologue of yeast Rad5 that promotes error-free replication through DNA lesions. HLTF and Rad5 share the same unique structural features, including a RING domain embedded within a SWI/SNF helicase domain and an HIRAN domain. We find that inactivation of HLTF renders human cells sensitive to UV and other DNA-damaging agents and that HLTF complements the UV sensitivity of a rad5Delta yeast strain. Also, similar to Rad5, HLTF physically interacts with the Rad6-Rad18 and Mms2-Ubc13 ubiquitin-conjugating enzyme complexes and promotes the Lys-63-linked polyubiquitination of proliferating cell nuclear antigen at its Lys-164 residue. A requirement of HLTF for error-free postreplication repair of damaged DNA is in keeping with its cancer-suppression role.

Early expression of the Helicase-Like Transcription Factor (HLTF/SMARCA3) in an experimental model of estrogen-induced renal carcinogenesis

BACKGROUND

The Helicase-Like Transcription Factor (HLTF/SMARCA3) belongs to the family of SWI/SNF proteins that use the energy of ATP hydrolysis to remodel chromatin in a variety of cellular processes. Several SWI/SNF genes are disrupted in cancer, suggesting a role of tumor suppressor. Similarly, the HLTF gene was recently found to be inactivated by hypermethylation in a number of advanced colon and gastric tumors. However, other evidences indicated a 20-fold HLTF overexpression in cell lines derived from various neoplasms (ovary, breast, cervix, kidney...).

RESULTS

In the present study, we investigated HLTF expression by immunohistochemistry in a model of kidney tumors induced by continuous administration of diethylstilbestrol to male Syrian golden hamsters. A strong labeling was already detected in small tumor buds, making HLTF an early cancer marker in this model. Although every cell stained for HLTF at this early stage, the number of HLTF-positive cells decreased to 10% with cancer progression, and these positive cells were dispersed in the tumor mass. HLTF expression was conserved in the HKT-1097 cell line established from kidney tumors, but again only 10% of positive cells were found in xenografts produced by HKT-1097 cells in nude mice.

CONCLUSION

In conclusion, our data suggest that HLTF gene activation is linked to initial steps of carcinogenesis in this model and should be investigated in early stages of other neoplasms.

The NEF4 complex regulates Rad4 levels and utilizes Snf2/Swi2-related ATPase activity for nucleotide excision repair

Nucleotide excision repair factor 4 (NEF4) is required for repair of nontranscribed DNA in Saccharomyces cerevisiae. Rad7 and the Snf2/Swi2-related ATPase Rad16 are NEF4 subunits. We report previously unrecognized similarity between Rad7 and F-box proteins. Rad16 contains a RING domain embedded within its ATPase domain, and the presence of these motifs in NEF4 suggested that NEF4 functions as both an ATPase and an E3 ubiquitin ligase. Mutational analysis provides strong support for this model. The Rad16 ATPase is important for NEF4 function in vivo, and genetic analysis uncovered new interactions between NEF4 and Rad23, a repair factor that links repair to proteasome function. Elc1 is the yeast homologue of a mammalian E3 subunit, and it is a novel component of NEF4. Moreover, the E2s Ubc9 and Ubc13 were linked to the NEF4 repair pathway by genetic criteria. Mutations in NEF4 or Ubc13 result in elevated levels of the DNA damage recognition protein Rad4 and an increase in ubiquitylated species of Rad23. As Rad23 also controls Rad4 levels, these results suggest a complex system for globally regulating repair activity in vivo by controlling turnover of Rad4.

An Sp1-NF-Y/progesterone receptor DNA binding-dependent mechanism regulates progesterone-induced transcriptional activation of the rabbit RUSH/SMARCA3 gene

Steroids regulate alternative splicing of rabbit RUSH/SMARCA3, an SWI/SNF-related transcription factor. Transactivation was evaluated in 2057 bp of genomic sequence. Truncation analysis identified a minimal 252-bp region with strong basal promoter activity in transient transfection assays. The size of the 5'-untranslated region (233 bp) and the transcription start site were determined by primer extension analysis. The transcription start site mapped to a consensus initiator (Inr) element in a TATA-less region with a downstream promoter element (+29). These elements were authenticated by mutation/deletion analysis. The Inr/downstream promoter element combination is conserved in the putative core promoter (-35/+35) of the human ortholog, suggesting that transcription initiation is similarly conserved. Two Sp1 sites that are also conserved in the putative promoter of human SMARCA3 and a RUSH binding site (-616/-611) that is unique to the rabbit promoter repress basal transcription. These sites were variously authenticated by gel shift and chromatin immunoprecipitation assays. Analysis of the proximal promoter showed the -162/+90 region was required for progesterone responsiveness in transient transfection assays. Subsequent mutation/deletion analysis revealed a progesterone receptor half-site mediated induction by progesterone. An overlapping Y-box (in the reverse ATTGG orientation) repressed basal transcription and progesterone-induced transcriptional activation in the presence of the Sp1 sites. The specificity of progesterone receptor and transcription factor NF-Y binding were authenticated by gel shift assays. Chromatin immunoprecipitation assays confirmed the Y-box effects were mediated in a DNA binding-dependent fashion. This represents a unique regulatory scenario in which ligand-dependent transactivation by the progesterone receptor is subject to Sp1/NF-Y repression.

Identification of the RUSH consensus-binding site by cyclic amplification and selection of targets: demonstration that RUSH mediates the ability of prolactin to augment progesterone-dependent gene expression

RUSH-1alpha(beta) transcription factors were cloned by recognition site screening with an 85-bp region (-170/-85) of the rabbit uteroglobin gene. Deletion analysis showed this region was essential to prolactin (PRL) action, but conclusions were limited by the complexity of the large deletion. Cyclic amplification and selection of targets (CASTing) was used to identify the RUSH-binding site (-126/-121). Endometrial nuclear proteins were incubated with a pool of degenerate oligonucleotides and immunoprecipitated with RUSH-1alpha(beta) antibodies. Bound DNA was amplified by PCR. The consensus motif (MCWTDK) was identified after five rounds of CASTing, authenticated by CASTing with RUSH-1alpha-specific antibodies and recombinant protein, and refined with EMSA. Dissociation rate constants (K(d) = 0.1-1.0 nM; r = 0.99) revealed high-affinity binding. Chromatin immunoprecipitation confirmed in vivo binding of RUSH to the transcriptionally active uteroglobin promoter. CASTing also revealed RUSH-GATA transcription factor interactions. Endometrial GATA-4 expression is progesterone dependent (Northern analysis) and preferentially localized in the epithelium (in situ hybridization). Although physically affiliated with RUSH, uterine forms of GATA-4 were not required for RUSH-DNA binding. Site-directed mutagenesis and transient transfection assays showed the RUSH motif mediates the ability of PRL to augment progesterone-dependent uteroglobin transcription. RUSH is central to the mechanism whereby PRL augments progesterone-dependent gene transcription.

DNA-dependent adenosine triphosphatase (helicaselike transcription factor) activates beta-globin transcription in K562 cells

Correct developmental regulation of beta-like globin gene expression is achieved by preferential transcription of a gene at a given developmental stage, silencing of other beta-like gene promoters, and competition among these promoters for interaction with the locus control region (LCR). Several evolutionarily conserved DNA elements in the promoters of the beta-like genes and LCR have been studied in detail, and the role of their binding factors has been investigated. However, the beta-globin promoter includes additional evolutionarily conserved sequences of unknown function. The present study examined the properties of a 21-base pair (bp) promoter-conserved sequence (PCS) located at positions -115 to -136 bp relative to the transcription start site of the beta-globin gene. A helicaselike transcription factor (HLTF) belonging to the SWI2/SNF2 family of proteins binds to the PCS and a partly homologous sequence in the enhancer region of the LCR hypersensitive site 2 (HS2). Elevation of the level of HLTF in K562 erythroleukemic cells increases beta-promoter activity in transient transfection experiments, and mutations in the PCS that remove HLTF-binding regions abolish this effect, suggesting that HLTF is an activator of beta-globin transcription. Overexpression of HLTF in K562 cells does not affect the endogenous levels of gamma- and epsilon-globin message, but it markedly activates beta-globin transcription. In conclusion, this study reports a transcription factor belonging to the SWI2/SNF2 family, which preferentially activates chromosomal beta-globin gene transcription and which has not previously been implicated in globin gene regulation.

Recombinant adeno-associated virus vector-transduced vascular endothelial cells express the thrombomodulin transgene under the regulation of enhanced plasminogen activator inhibitor-1 promoter

We were able to facilitate plasminogen activator inhibitor 1 (PAI-1) promoter activity approximately by 14-fold using an enhancer element. This enhanced PAI-1 promoter has a strong basal activity, comparable to CAG promoter activity, and has a response similar to the PAI-1 promoter with respect to TGFbeta 1 and TNFalpha stimulation. The characteristics of the enhanced PAI-1 promoter are thought to be suited to timely and tissue-specific expression of anticoagulant molecules in the vascular cells. Thus, we developed recombinant adeno-associated virus (rAAV) vectors using the enhanced PAI-1 promoter and were successful in transducing vascular endothelial cells to express the thrombomodulin transgene under the regulation of the enhanced PAI-1 promoter in vitro. Thromobomodulin transgene expression driven by the enhanced PAI-1 promoter in rAAV vector-transduced cultured endothelial cells was between 600- and 1000-fold higher than constitutive thrombomodulin gene expression in cultured human umbilical vein endothelial cells and was up-regulated by TGFbeta1 and TNFalpha stimulation which may down-regulate endogenous thrombomodulin gene expression in endothelial cells. The brain vascular endothelial cells of Mongolian gerbils could also be transduced by the same rAAV vector in vivo. Transduction of endothelial cells by rAAV vectors to express enhanced PAI-1 promoter-driven transgenes may be a useful gene therapy approach for vascular diseases.

Uteroglobin gene transcription: what's the RUSH?

Prolactin enhances progesterone-dependent transcription of the rabbit uteroglobin gene. RUSH transcription factors are implicated in the signal transduction pathway. The RUSH acronym identifies key features of these nuclear phosphoproteins, that is, RING-finger motif, binds the uteroglobin promoter, structurally related to the SWI/SNF family of transcription factors, and helicase-like. Cloned by recognition site screening, RUSH proteins bind to an 85-bp region (-170/-85) of the uteroglobin promoter that was subsequently identified as a novel prolactin-responsive region by promoter deletion analysis. Gel shift and linker-scanning assays further reduced the RUSH target site to -160/-110. A hexameric core of MCWTDK was identified as the RUSH-specific DNA-binding site (-126/-121) by CASTing. This site overlaps authentic HNF3 beta and OCT-1 binding sites. A unique Type IV P-type ATPase that is embedded in the inner nuclear membrane binds the RING domain of RUSH. The conformationally flexible loop portion of this RING-finger binding protein (RFBP) extends into the nucleoplasm to contact euchromatin. The physical association of RFBP with transcriptionally active chromatin supports the speculation that RFBP targets RUSH transcription factors to the active uteroglobin promoter.

Stability of a human SWI-SNF remodeled nucleosomal array

SWI-SNF alters DNA-histone interactions within a nucleosome in an ATP-dependent manner. These alterations cause changes in the topology of a closed circular nucleosomal array that persist after removal of ATP from the reaction. We demonstrate here that a remodeled closed circular array will revert toward its original topology when ATP is removed, indicating that the remodeled array has a higher energy than that of the starting state. However, reversion occurs with a half-life measured in hours, implying a high energy barrier between the remodeled and standard states. The addition of competitor DNA accelerates reversion of the remodeled array by more than 10-fold, and we interpret this result to mean that binding of human SWI-SNF (hSWI-SNF), even in the absence of ATP hydrolysis, stabilizes the remodeled state. In addition, we also show that SWI-SNF is able to remodel a closed circular array in the absence of topoisomerase I, demonstrating that hSWI-SNF can induce topological changes even when conditions are highly energetically unfavorable. We conclude that the remodeled state is less stable than the standard state but that the remodeled state is kinetically trapped by the high activation energy barrier separating it from the unremodeled conformation.

Expression of RUSH transcription factors in developing and adult rabbit gonads

The RUSH transcription factors 1alpha and 1beta bind to the Rabbit Uteroglobin promoter and are members of the SWI/SNF complex that facilitates transcription by remodeling chromatin (Helicase). To characterize gonadal expression of RUSH, a cRNA probe that recognizes both isoforms was used for in situ hybridization studies. We found RUSH mRNA to be abundant in Sertoli cells from embryonic, neonatal, prepubertal, and pubertal rabbit testes. In adults, RUSH mRNA was detected in tubules with preleptotene spermatocytes and mature spermatids lining the lumen. However, RUSH was undetectable in tubules that contained leptotene spermatocytes and that lacked mature spermatids. In females, RUSH was expressed in presumptive granulosa cells of embryonic and neonatal ovaries before follicle organization. Abundant RUSH mRNA was detected in granulosa and theca cells surrounding preantral follicles of prepubertal and adult ovaries. Expression of RUSH remained high in granulosa cells of antral follicles in mature ovaries but was negligible in late-stage atretic follicles and in corpora lutea. Western blot analysis confirmed the RUSH-1alpha isoform predominated in both testicular and ovarian tissues. The expression pattern of RUSH indicates transcriptional activity in Sertoli cells and during multiple stages of differentiating granulosa cells, especially those of primordial follicles, which heretofore were considered to be dormant.

Functional interactions between Sp1 or Sp3 and the helicase-like transcription factor mediate basal expression from the human plasminogen activator inhibitor-1 gene

Basal expression of the human plasminogen activator inhibitor-1 (PAI-1) is mediated by a promoter element named B box that binds the helicase-like transcription factor (HLTF), homologous to SNF/SWI proteins. Electrophoretic mobility shift assays performed on a set of B box point mutants demonstrated two HLTF sites flanking and partially overlapping with a GT box binding Sp1 and Sp3. Mutations affecting either the Sp1/Sp3 or the two HLTF sites inhibited by 6- and 2.5-fold, respectively, transient expression in HeLa cells of a reporter gene fused to the PAI-1 promoter. In Sp1/Sp3-devoid insect cells, co-expression of PAI-1-lacZ with Sp1 or Sp3 led to a 14-26-fold induction while HLTF had no effect. Simultaneous presence of Sp1 or Sp3 and the short HLTF form (initiating at Met-123) provided an additional 2-3-fold synergistic activation suppressed by mutations that prevented HLTF binding. Moreover, a DNA-independent interaction between HLTFMet123 and Sp1/Sp3 was demonstrated by co-immunoprecipitation from HeLa cell extracts and glutathione S-transferase pull-down experiments. The interaction domains were mapped to the carboxyl-terminal region of each protein; deletion of the last 85 amino acids of HLTFMet123 abolished the synergy with Sp1. This is the first demonstration of a functional interaction between proteins of the Sp1 and SNF/SWI families.

Identification of a novel SNF2/SWI2 protein family member, SRCAP, which interacts with CREB-binding protein

The ability of cAMP response-element binding protein (CREB)-binding protein (CBP) to function as a co-activator for a number of transcription factors appears to be mediated by its ability to act as a histone acetyltransferase and through its interaction with a number of other proteins (general transcription factors, histone acetyltransferases, and other co-activators). Here we report that CBP also interacts with a novel ATPase termed Snf2-Related CBP Activator Protein (SRCAP). Consistent with this activity, SRCAP contains the conserved ATPase domain found within members of the Snf2 family. Transfection experiments demonstrate that SRCAP is able to activate transcription when expressed as a Gal-SRCAP chimera and that SRCAP also enhances the ability of CBP to activate transcription. The adenoviral protein E1A was found to disrupt interaction between SRCAP and CBP possibly representing a mechanism for E1A-mediated transcriptional repression.

After chromatin is SWItched-on can it be RUSHed?

Repressive chromatin must be remodeled to allow for transcriptional activation of genes in eukaryotic cells. Factors that alter chromatin structure to permit access of transcriptional activators, RNA polymerase II and the polymerase-associated general transcription factors to nucleosomal promoter sequences are as highly conserved as the basic mechanism of transcription. One group of promoter restructuring factors that perturbs chromatin in an ATP-dependent manner includes NURF, CHRAC, ACF, the SWI/SNF complex, and SWI/SNF-related proteins. Each member of this group contains a subunit homologous to the DNA-dependent ATPase; however, their individual mechanisms of action are unique. The small amount of SWI/SNF complex (100-200 copies/cell), its affiliation with a select number of inducible genes, and its interaction with the glucocorticoid and estrogen receptors, suggests the SWI/SNF complex might be preferentially targeted to active promoters. The SWI/SNF-related family of RUSH proteins which includes RUSH-1alpha and beta, hHLTF, HIP116, Zbu1, P113, and the transcription factor RUSH-1alpha isolog has been implicated as a highly conserved DNA binding site-specific ATPase.