A novel 9-amino-acid transactivation domain in the C-terminal part of Sox18

Evaluation of the determinants for improved pluripotency induction and maintenance by engineered SOX17

An engineered SOX17 variant with point mutations within its DNA binding domain termed SOX17FNV is a more potent pluripotency inducer than SOX2, yet the underlying mechanism remains unclear. Although wild-type SOX17 was incapable of inducing pluripotency, SOX17FNV outperformed SOX2 in mouse and human pluripotency reprogramming. In embryonic stem cells, SOX17FNV could replace SOX2 to maintain pluripotency despite considerable sequence differences and upregulated genes expressed in cleavage-stage embryos. Mechanistically, SOX17FNV co-bound OCT4 more cooperatively than SOX2 in the context of the canonical SoxOct DNA element. SOX2, SOX17, and SOX17FNV were all able to bind nucleosome core particles in vitro, which is a prerequisite for pioneer transcription factors. Experiments using purified proteins and in cellular contexts showed that SOX17 variants phase-separated more efficiently than SOX2, suggesting an enhanced ability to self-organise. Systematic deletion analyses showed that the N-terminus of SOX17FNV was dispensable for its reprogramming activity. However, the C-terminus encodes essential domains indicating multivalent interactions that drive transactivation and reprogramming. We defined a minimal SOX17FNV (miniSOX) that can support reprogramming with high activity, reducing the payload of reprogramming cassettes. This study uncovers the mechanisms behind SOX17FNV-induced pluripotency and establishes engineered SOX factors as powerful cell engineering tools.

The NFkB activation domain is 14-amino-acid-long variant of the 9aaTAD

The nine-amino-acid transactivation domains (9aaTAD) was identified in numerous transcription factors including Gal4, p53, E2A, MLL, c-Myc, N-Myc, and also in SP, KLF, and SOX families. Most of the 9aaTAD domains interact with the KIX domain of transcription mediators MED15 and CBP to activate transcription. The NFkB activation domain occupied the same position on the KIX domain as the 9aaTADs of MLL, E2A, and p53. Binding of the KIX domain is established by the two-point interaction involving 9aaTAD positions p3-4 and p6-7. The NFkB primary binding region (positions p3-4) is almost identical with MLL and E2A, but secondary NFkB binding region differs by the position and engages the distal NFkB region p10-11. Thus, the NFkB activation domain is five amino acids longer than the other 9aaTADs. The NFkB activation domain includes an additional region, which we called the Omichinski Insert extending activation domain length to 14 amino acids. By deletion, we demonstrated that Omichinski Insert is an entirely non-essential part of NFkB activation domain. In summary, we recognized the NFkB activation domain as prolonged 9aaTAD conserved in evolution from humans to amphibians.

NF-κB-dependent repression of Sox18 transcription factor requires the epigenetic regulators histone deacetylases 1 and 2 in acute lung injury

In acute lung injury (ALI), the NF-κB-mediated downregulation of Sox18 gene expression leads to the disruption of the pulmonary endothelial barrier. Previous studies have suggested that the action of NF-κB as a transcriptional repressor also requires the action of class I histone deacetylases (HDACs). Thus, the purpose of this study was to investigate and further delineate the mechanism of Sox18 repression during lipopolysaccharide (LPS) induced ALI. Using selective inhibitors and specific siRNA-driven depletion of HDACs 1-3 in human lung microvascular endothelial cells (HLMVEC) we were able to demonstrate a critical role for HDACs 1 and 2 in the LPS-mediated repression of Sox18 gene expression and the loss of endothelial monolayer integrity. Moreover, our data demonstrate that HDAC1 associates with a transcription-repressive complex within the NF-κB-binding site of Sox18 promoter. Further, we were able to show that the selective inhibitor of HDAC1, tacedinaline, significantly reduced the endothelial permeability and injury associated with LPS challenge in the mouse lung. Taken together, our data demonstrate, for the first time, that transcription repressors HDACs 1 and 2 are involved in pathological mechanism of ALI and can be considered as therapeutic targets.

Cryptic inhibitory regions nearby activation domains

Previously, the Nine amino acid TransActivation Domain (9aaTAD) was identified in the Gal4 region 862-870 (DDVYNYLFD). Here, we identified 9aaTADs in the distal Gal4 orthologs by our prediction algorithm and found their conservation in the family. The 9aaTAD function as strong activators was demonstrated. We identified adjacent Gal4 region 871-811 (DEDTPPNPKKE) as a natural 9aaTAD inhibitory domain located at the extreme Gal4 terminus. Moreover, we identified conserved Gal4 region 172-185 (FDWSEEDDMSDGLP), which was capable to reverse the 9aaTAD inhibition. In conclusion, our results uncover the existence of the cryptic inhibitory domains, which need to be carefully implemented in all functional studies with transcription factors to avoid incorrect conclusions.

Case report: A de novo Non-sense SOX9 mutation (p.Q417*) located in transactivation domain is Responsible for Campomelic Dysplasia

BACKGROUND

Campomelic dysplasia (CD) is an autosomal dominant skeletal dysplasia syndrome characterized by shortness and bowing of lower extremities, and often accompanied by XY sex reversal. Heterozygous pathogenic variants of SOX9 or rearrangement involving the long arm of chromosome 17 are the causes of disease. However, evidence for pathogenesis of SOX9 haploinsufficiency is insufficient.

METHODS

We enrolled a Chinese family where the fetus was diagnosed with CD. The affected fetus was selected for whole-exome sequencing to identify the pathogenic mutations in this family.

RESULTS

After data filtering, a novel non-sense SOX9 variant (NM_000346.3; c.1249C > T; p.Q417*) was identified as the pathogenic lesion in the fetus. Further co-segregation analysis using Sanger sequencing confirmed that this novel SOX9 mutation (c.1249C > T; p.Q417*) was a de novo mutation in the affected fetus. This terminated codon mutation identified by bioinformatics was located at an evolutionarily conserved site of SOX9. The bioinformatics-based analysis predicted this variant was pathogenic and affected SOX9 transactivation activity.

CONCLUSION

CD is a rare condition, which connected with SOX9 tightly. We identified a novel heterozygous SOX9 variant (p.Q417*) in a Chinese CD family. Our study supports the putative reduced transactivation of SOX9 variants in the pathogenicity of CD.

Characterization of the transactivation and nuclear localization functions of Pichia pastoris zinc finger transcription factor Mxr1p

The zinc finger transcription factor Mxr1p regulates the transcription of genes involved in methanol, acetate, and amino acid metabolism of the industrial yeast Pichia pastoris (a.k.a. Komagataella phaffii) by binding to Mxr1p response elements in their promoters. Here, we demonstrate that Mxr1p is a key regulator of ethanol metabolism as well. Using transcriptomic analysis, we identified target genes of Mxr1p that mediate ethanol metabolism, including ALD6-1 encoding an aldehyde dehydrogenase. ALD6-1 is essential for ethanol metabolism, and the ALD6-1 promoter harbors three Mxr1p response elements to which Mxr1p binds in vitro and activates transcription in vivo. We show that a nine-amino acid transactivation domain located between amino acids 365 and 373 of Mxr1p is essential for the transactivation of ALD6-1 to facilitate ethanol metabolism. Mxr1N250, containing the N-terminal 250 amino acids of Mxr1p, localized to the nucleus of cells metabolizing ethanol dependent on basic amino acid residues present between amino acids 75 and 85. While the N-terminal 400 amino acids of Mxr1p are sufficient for the activation of target genes essential for ethanol metabolism, the region between amino acids 401 and 1155 was also required for the regulation of genes essential for methanol metabolism. Finally, we identified several novel genes whose expression is differentially regulated by Mxr1p during methanol metabolism by DNA microarray. This study demonstrates that Mxr1p is a key regulator of ethanol metabolism and provides new insights into the mechanism by which Mxr1p functions as a global regulator of multiple metabolic pathways of P. pastoris.

Universal two-point interaction of mediator KIX with 9aaTAD activation domains

The nine-amino-acid activation domain (9aaTAD) is defined by a short amino acid pattern including two hydrophobic regions (positions p3-4 and p6-7). The KIX domain of mediator transcription CBP interacts with the 9aaTAD domains of transcription factors MLL, E2A, NF-kB, and p53. In this study, we analyzed the 9aaTADs-KIX interactions by nuclear magnetic resonance. The positions of three KIX helixes α1-α2-α3 are influenced by sterically-associated hydrophobic I611, L628, and I660 residues that are exposed to solvent. The positions of two rigid KIX helixes α1 and α2 generate conditions for structural folding in the flexible KIX-L12-G2 regions localized between them. The three KIX I611, L628, and I660 residues interact with two 9aaTAD hydrophobic residues in positions p3 and p4 and together build a hydrophobic core of five residues (5R). Numerous residues in 9aaTAD position p3 and p4 could provide this interaction. Following binding of the 9aaTAD to KIX, the hydrophobic I611, L628, and I660 residues are no longer exposed to solvent and their position changes inside the hydrophobic core together with position of KIX α1-α2-α3 helixes. The new positions of the KIX helixes α1 and α2 allow the KIX-L12-G2 enhanced formation. The second hydrophobic region of the 9aaTAD (positions p6 and p7) provides strong binding with the KIX-L12-G2 region. Similarly, multiple residues in 9aaTAD position p6 and p7 could provide this interaction. In conclusion, both 9aaTAD regions p3, p4 and p6, p7 provide co-operative and highly universal binding to mediator KIX. The hydrophobic core 5R formation allows new positions of the rigid KIX α-helixes and enables the enhanced formation of the KIX-L12-G2 region. This contributes to free energy and is the key for the KIX-9aaTAD binding. Therefore, the 9aaTAD-KIX interactions do not operate under the rigid key-and-lock mechanism what explains the 9aaTAD natural variability.

Genome wide identification, phylogeny, and synteny analysis of sox gene family in common carp (Cyprinus carpio)

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27 SOX (high-mobility group HMG-box) genes were identified in the C. carp genome.

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SOX genes ranging from 3496 (SOX6) to 924bp (SOX17b) which coded with putative protein series from 307 to 509 amino acids.

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Gene ontology revealed SOX proteins maximum involvement is in metabolic process 49.796 %.

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Chromosomal location and synteny analysis display all SOX gene are located on different chromosomes.

Common carp (Cyprinus carpio) is a commercial fish species valuable for nutritious components and plays a vital role in human healthy nutrition. The SOX (SRY-related genes systematically characterized by a high-mobility group HMG-box) encoded important gene regulatory proteins, a family of transcription factors found in a broad range of animal taxa and extensively known for its contribution in multiple developmental processes including contribution in sex determination across phyla. In our current study, we initially accomplished a genome-wide analysis to report the SOX gene family in common carp fish based on available genomic sequences of zebrafish retrieved from gene repository databases, we focused on the global identification of the Sox gene family in Common carp among wide range of vertebrates and teleosts based on bioinformatics tools and techniques and explore the evolutionary relationships. In our results, a total of 27 SOX (high-mobility group HMG-box) domain genes were identified in the C. carp genome. The full length sequences of SOX genes ranging from 3496 (SOX6) to 924bp (SOX17b) which coded with putative proteins series from 307 to 509 amino acids and all gene having exon number expect SOX9 and SOX13. All the SOX proteins contained at least one conserved DNA-binding HMG-box domain and two (SOX7 and SOX18) were found C terminal. The Gene ontology revealed SOX proteins maximum involvement is in metabolic process 49.796 %, average in biological regulation 45.188 %, biosynthetic process (19.992 %), regulation of cellular process 39.68, 45.508 % organic substance metabolic process, multicellular organismal process 23.23 %,developmental process 21.74 %, system development 16.59 %, gene expression 16.05 % and 14.337 % of RNA metabolic process. Chromosomal location and syntanic analysis show all SOX gene are located on different chromosomes and apparently does not fallow the unique pattern. The maximum linkage of chromosome is (2) on Unplaced Scaffold region. Finally, our results provide important genomic suggestion for upcoming studies of biochemical, physiological, and phylogenetic understanding on SOX genes among teleost.

The evolution of the 9aaTAD domain in Sp2 proteins: inactivation with valines and intron reservoirs

The universal nine-amino-acid transactivation domains (9aaTADs) have been identified in numerous transcription activators. Here, we identified the conserved 9aaTAD motif in all nine members of the specificity protein (SP) family. Previously, the Sp1 transcription factor has been defined as a glutamine-rich activator. We showed by amino acid substitutions that the glutamine residues are completely dispensable for 9aaTAD function and are not conserved in the SP family. We described the origin and evolutionary history of 9aaTADs. The 9aaTADs of the ancestral Sp2 gene became inactivated in early chordates. We next discovered that an accumulation of valines in 9aaTADs inactivated their transactivation function and enabled their strict conservation during evolution. Subsequently, in chordates, Sp2 has duplicated and created new paralogs, Sp1, Sp3, and Sp4 (the SP1-4 clade). During chordate evolution, the dormancy of the Sp2 activation domain lasted over 100 million years. The dormant but still intact ancestral Sp2 activation domains allowed diversification of the SP1-4 clade into activators and repressors. By valine substitution in the 9aaTADs, Sp1 and Sp3 regained their original activator function found in ancestral lower metazoan sea sponges. Therefore, the vertebrate SP1-4 clade could include both repressors and activators. Furthermore, we identified secondary 9aaTADs in Sp2 introns present from fish to primates, including humans. In the gibbon genome, introns containing 9aaTADs were used as exons, which turned the Sp2 gene into an activator. Similarly, we identified introns containing 9aaTADs used conditionally as exons in the (SP family-unrelated) transcription factor SREBP1, suggesting that the intron-9aaTAD reservoir is a general phenomenon.

The SOXE transcription factors-SOX8, SOX9 and SOX10-share a bi-partite transactivation mechanism

SOX8, SOX9 and SOX10 compose the SOXE transcription factor group. They govern cell fate and differentiation in many lineages, and mutations impairing their activity cause severe diseases, including campomelic dysplasia (SOX9), sex determination disorders (SOX8 and SOX9) and Waardenburg-Shah syndrome (SOX10). However, incomplete knowledge of their modes of action limits disease understanding. We here uncover that the proteins share a bipartite transactivation mechanism, whereby a transactivation domain in the middle of the proteins (TAM) synergizes with a C-terminal one (TAC). TAM comprises amphipathic α-helices predicted to form a protein-binding pocket and overlapping with minimal transactivation motifs (9-aa-TAD) described in many transcription factors. One 9-aa-TAD sequence includes an evolutionarily conserved and functionally required EΦ[D/E]QYΦ motif. SOXF proteins (SOX7, SOX17 and SOX18) contain an identical motif, suggesting evolution from a common ancestor already harboring this motif, whereas TAC and other transactivating SOX proteins feature only remotely related motifs. Missense variants in this SOXE/SOXF-specific motif are rare in control individuals, but have been detected in cancers, supporting its importance in development and physiology. By deepening understanding of mechanisms underlying the central transactivation function of SOXE proteins, these findings should help further decipher molecular networks essential for development and health and dysregulated in diseases.

Nuclear hormone receptors: Ancient 9aaTAD and evolutionally gained NCoA activation pathways

In higher metazoans, the nuclear hormone receptors activate transcription trough their specific adaptors, nuclear hormone receptor adaptors NCoA, which are absent in lower metazoans. The Nine amino acid TransActivation Domain, 9aaTAD, was reported for a large number of the transcription activators that recruit general mediators of transcription. In this study, we demonstrated that the 9aaTAD from NHR-49 receptor of nematode C.elegans activates transcription as a small peptide. We showed that the ancient 9aaTAD domains are conserved in the nuclear hormone receptors including human HNF4, RARa, VDR and PPARg. Also their small 9aaTAD peptides effectively activated transcription in absence of the NCoA adaptors. We also showed that adjacent H11 domains in ancient and modern hormone receptors have an inhibitory effect on their 9aaTAD function.

The 9aaTAD Is Exclusive Activation Domain in Gal4

The Gal4 protein is a well-known prototypic acidic activator that has multiple activation domains. We have previously identified a new activation domain called the nine amino acid transactivation domain (9aaTAD) in Gal4 protein. The family of the 9aaTAD activators currently comprises over 40 members including p53, MLL, E2A and other members of the Gal4 family; Oaf1, Pip2, Pdr1 and Pdr3. In this study, we revised function of all reported Gal4 activation domains. Surprisingly, we found that beside of the activation domain 9aaTAD none of the previously reported activation domains had considerable transactivation potential and were not involved in the activation of transcription. Our results demonstrated that the 9aaTAD domain is the only decisive activation domain in the Gal4 protein. We found that the artificial peptides included in the original Gal4 constructs were results of an unintended consequence of cloning that were responsible for the artificial transcriptional activity. Importantly, the activation domain 9aaTAD, which is the exclusive activation domain in Gal4, is also the central part of a conserved sequence recognized by the inhibitory protein Gal80. We propose a revision of the Gal4 regulation, in which the activation domain 9aaTAD is directly linked to both activation function and Gal80 mediated inhibition.

The 9aaTAD Transactivation Domains: From Gal4 to p53

The family of the Nine amino acid Transactivation Domain, 9aaTAD family, comprises currently over 40 members. The 9aaTAD domains are universally recognized by the transcriptional machinery from yeast to man. We had identified the 9aaTAD domains in the p53, Msn2, Pdr1 and B42 activators by our prediction algorithm. In this study, their competence to activate transcription as small peptides was proven. Not surprisingly, we elicited immense 9aaTAD divergence in hundreds of identified orthologs and numerous examples of the 9aaTAD species' convergence. We found unforeseen similarity of the mammalian p53 with yeast Gal4 9aaTAD domains. Furthermore, we identified artificial 9aaTAD domains generated accidentally by others. From an evolutionary perspective, the observed easiness to generate 9aaTAD transactivation domains indicates the natural advantage for spontaneous generation of transcription factors from DNA binding precursors.

Shared structural features of the 9aaTAD family in complex with CBP

Analysis of E2A, MLL, FOXO3 and p53 structural data defines fundamental requirements and sheds light on the ambiguous 9aaTAD domain.

Interaction studies of the human and Arabidopsis thaliana Med25-ACID proteins with the herpes simplex virus VP16- and plant-specific Dreb2a transcription factors

Mediator is an evolutionary conserved multi-protein complex present in all eukaryotes. It functions as a transcriptional co-regulator by conveying signals from activators and repressors to the RNA polymerase II transcription machinery. The Arabidopsis thaliana Med25 (aMed25) ACtivation Interaction Domain (ACID) interacts with the Dreb2a activator which is involved in plant stress response pathways, while Human Med25-ACID (hMed25) interacts with the herpes simplex virus VP16 activator. Despite low sequence similarity, hMed25-ACID also interacts with the plant-specific Dreb2a transcriptional activator protein. We have used GST pull-down-, surface plasmon resonance-, isothermal titration calorimetry and NMR chemical shift experiments to characterize interactions between Dreb2a and VP16, with the hMed25 and aMed25-ACIDs. We found that VP16 interacts with aMed25-ACID with similar affinity as with hMed25-ACID and that the binding surface on aMed25-ACID overlaps with the binding site for Dreb2a. We also show that the Dreb2a interaction region in hMed25-ACID overlaps with the earlier reported VP16 binding site. In addition, we show that hMed25-ACID/Dreb2a and aMed25-ACID/Dreb2a display similar binding affinities but different binding energetics. Our results therefore indicate that interaction between transcriptional regulators and their target proteins in Mediator are less dependent on the primary sequences in the interaction domains but that these domains fold into similar structures upon interaction.

Transcription factor Nrf1 is topologically repartitioned across membranes to enable target gene transactivation through its acidic glucose-responsive domains

The membrane-bound Nrf1 transcription factor regulates critical homeostatic and developmental genes. The conserved N-terminal homology box 1 (NHB1) sequence in Nrf1 targets the cap‘n’collar (CNC) basic basic-region leucine zipper (bZIP) factor to the endoplasmic reticulum (ER), but it is unknown how its activity is controlled topologically within membranes. Herein, we report a hitherto unknown mechanism by which the transactivation activity of Nrf1 is controlled through its membrane-topology. Thus after Nrf1 is anchored within ER membranes, its acidic transactivation domains (TADs), including the Asn/Ser/Thr-rich (NST) glycodomain situated between acidic domain 1 (AD1) and AD2, are transiently translocated into the lumen of the ER, where NST is glycosylated in the presence of glucose to yield an inactive 120-kDa Nrf1 glycoprotein. Subsequently, portions of the TADs partially repartition across membranes into the cyto/nucleoplasmic compartments, whereupon an active 95-kDa form of Nrf1 accumulates, a process that is more obvious in glucose-deprived cells and may involve deglycosylation. The repartitioning of Nrf1 out of membranes is monitored within this protein by its acidic-hydrophobic amphipathic glucose-responsive domains, particularly the Neh5L subdomain within AD1. Therefore, the membrane-topological organization of Nrf1 dictates its post-translational modifications (i.e. glycosylation, the putative deglycosylation and selective proteolysis), which together control its ability to transactivate target genes.

TNFα-induced down-regulation of Sox18 in endothelial cells is dependent on NF-κB

The transcription factor Sox18 plays a role in angiogenesis, including lymphangiogenesis, where it is upregulated by growth factors and directs the expression of genes encoding, e.g., guidance molecules and a matrix metalloproteinase. Conversely, we found that in human umbilical vein endothelial cells (HUVEC) Sox18 is repressed by the pro-inflammatory mediator TNFα (as well as IL-1 and LPS). Since a common feature of these mediators is the activation of the NF-κB signaling pathway, we investigated whether Sox18 downregulation is dependent on this transcription factor. Transduction of HUVEC with an adenoviral vector directing the expression of the NF-κB inhibitor IκBα prevented the downregulation of Sox18. Transient transfections of Sox18 promoter reporter genes revealed that the downregulation takes place on the level of transcription, and that the p65/RelA subunit of NF-κB was operative. Furthermore, the responsible promoter region of Sox18 is located within -1.0kb from the transcriptional start site. The repression of Sox18 and its target genes may lead to altered formation of vessels in inflamed settings.

The transcription factor SOX18 regulates the expression of matrix metalloproteinase 7 and guidance molecules in human endothelial cells

Background

Mutations in the transcription factor SOX18 are responsible for specific cardiovascular defects in humans and mice. In order to gain insight into the molecular basis of its action, we identified target genes of SOX18 and analyzed one, MMP7, in detail.

Methodology/Principal Findings

SOX18 was expressed in HUVEC using a recombinant adenoviral vector and the altered gene expression profile was analyzed using microarrays. Expression of several regulated candidate SOX18 target genes was verified by real-time PCR. Knock-down of SOX18 using RNA interference was then used to confirm the effect of the transcription factor on selected genes that included the guidance molecules ephrin B2 and semaphorin 3G. One gene, MMP7, was chosen for further analysis, including detailed promoter studies using reporter gene assays, electrophoretic mobility shift analysis and chromatin-immunoprecipitation, revealing that it responds directly to SOX18. Immunohistochemical analysis demonstrated the co-expression of SOX18 and MMP7 in blood vessels of human skin.

Conclusions/Significance

The identification of MMP7 as a direct SOX18 target gene as well as other potential candidates including guidance molecules provides a molecular basis for the proposed function of this transcription factor in the regulation of vessel formation.

Interactions between SOX factors and Wnt/beta-catenin signaling in development and disease

The SOX family of transcription factors have emerged as modulators of canonical Wnt/beta-catenin signaling in diverse development and disease contexts. There are over 20 SOX proteins encoded in the vertebrate genome and recent evidence suggests that many of these can physically interact with beta-catenin and modulate the transcription of Wnt-target genes. The precise mechanisms by which SOX proteins regulate beta-catenin/TCF activity are still being resolved and there is evidence to support a number of models including: protein-protein interactions, the binding of SOX factors to Wnt-target gene promoters, the recruitment of co-repressors or co-activators, modulation of protein stability, and nuclear translocation. In some contexts, Wnt signaling also regulates SOX expression resulting in feedback regulatory loops that fine-tune cellular responses to beta-catenin/TCF activity. In this review, we summarize the examples of Sox-Wnt interactions and examine the underlying mechanisms of this potentially widespread and underappreciated mode of Wnt-regulation.

Cell signaling, internalization, and nuclear localization of the angiotensin converting enzyme in smooth muscle and endothelial cells

The angiotensin converting enzyme (ACE) catalyzes the extracellular formation of angiotensin II, and degradation of bradykinin, thus regulating blood pressure and renal handling of electrolytes. We have previously shown that exogenously added ACE elicited transcriptional regulation independent of its enzymatic activity. Because transcriptional regulation generates from protein-DNA interactions within the cell nucleus we have investigated the initial cellular response to exogenous ACE and the putative internalization of the enzyme in smooth muscle cells (SMC) and endothelial cells (EC). The following phenomena were observed when ACE was added to cells in culture: 1) it bound to SMC and EC with high affinity (K(d) = 361.5 +/- 60.5 pM) and with a low binding occupancy (B(max) = 335.0 +/- 14.0 molecules/cell); 2) it triggered cellular signaling resulting in late activation of focal adhesion kinase and SHP2; 3) it modulated platelet-derived growth factor receptor-beta signaling; 4) it was endocytosed by SMC and EC; and 5) it transited through the early endosome, partially occupied the late endosome and the lysosome, and was localized to the nuclei. The incorporation of ACE or a fragment of it into the nuclei reached saturation at 120 min, and was preceded by a lag time of 40 min. Internalized ACE was partially cleaved into small fragments. These results revealed that extracellular ACE modulated cell signaling properties, and that SMC and EC have a pathway for delivery of extracellular ACE to the nucleus, most likely involving cell surface receptor(s) and requiring transit through late endosome/lysosome compartments.

Metal-responsive transcription factor 1 (MTF-1) activity is regulated by a nonconventional nuclear localization signal and a metal-responsive transactivation domain

Metal-responsive transcription factor 1 (MTF-1) mediates both basal and heavy metal-induced transcription of metallothionein genes and also regulates other genes involved in the cell stress response and in metal homeostasis. In resting cells, MTF-1 localizes to both the cytoplasm and the nucleus but quantitatively accumulates in the nucleus upon metal load and under other stress conditions. Here we show that within the DNA-binding domain, a region spanning zinc fingers 1 to 3 (amino acids [aa] 137 to 228 in human MTF-1) harbors a nonconventional nuclear localization signal. This protein segment confers constitutive nuclear localization to a cytoplasmic marker protein. The deletion of the three zinc fingers impairs nuclear localization. The export of MTF-1 to the cytoplasm is controlled by a classical nuclear export signal (NES) embedded in the acidic activation domain. We show that this activation domain confers metal inducibility in distinct cell types when fused to a heterologous DNA-binding domain. Furthermore, the cause of a previously described stronger inducibility of human versus mouse MTF-1 could be narrowed down to a 3-aa difference in the NES; "humanizing" mouse MTF-1 at these three positions enhanced its metal inducibility to the level of human MTF-1.

Vascular defects in a mouse model of hypotrichosis-lymphedema-telangiectasia syndrome indicate a role for SOX18 in blood vessel maturation

Mutations in the transcription factor gene SOX18 cause vascular, lymphatic and hair follicle defects in humans with dominant and recessive forms of hypotrichosis-lymphedema-telangiectasia (HLT) syndrome. Here, we clarify the role of SOX18 in the vascular dysfunction in HLT by ultrastructural, immunofluorescence, molecular and functional analysis of vascular anomalies in embryos of the naturally occurring Sox18-mutant mouse strain ragged-opossum (Ra(Op)). Early genesis and patterning of vasculature was unimpaired in Ra(Op) embryos, but surface capillaries became enlarged from 12.5 dpc and embryos developed massive surface hemorrhage by 14.5 dpc. Large focal breaches in the endothelial barrier were observed, in addition to endothelial hyperplasia associated with impaired pericyte recruitment to the microvasculature. Expression of the genes encoding the endothelial factors MMP7, IL7R and N-cadherin was reduced in Ra(Op) embryos, suggesting that these are downstream targets of SOX18. Together, our results indicate that vascular anomalies in HLT arise from defects in regulation of genes required for the acquisition of structural integrity during microvascular maturation.