SREBP-1, a membrane-bound transcription factor released by sterol-regulated proteolysis

Sterol regulatory element-binding protein 1 (SREBP-1), a member of the basic-helix-loop-helix-leucine zipper (bHLH-ZIP) family of transcription factors, is synthesized as a 125 kd precursor that is attached to the nuclear envelope and endoplasmic reticulum. In sterol-depleted cells, the membrane-bound precursor is cleaved to generate a soluble NH2-terminal fragment (apparent molecular mass, 68 kd) that translocates to the nucleus. This fragment, which includes the bHLH-ZIP domain, activates transcription of the genes for the LDL receptor and HMG CoA synthase. Sterols inhibit the cleavage of SREBP-1, and the 68 kd nuclear form is rapidly catabolized, thereby reducing transcription. ALLN, an inhibitor of neutral cysteine proteases, blocks the breakdown of the 68 kd form and superinduces sterol-regulated genes. Sterol-regulated proteolysis of a membrane-bound transcription factor provides a novel mechanism by which transcription can be regulated by membrane lipids.

SREBP-1, a basic-helix-loop-helix-leucine zipper protein that controls transcription of the low density lipoprotein receptor gene

Sterol regulatory element 1 (SRE-1), a decamer (5'-ATC-ACCCCAC-3') flanking the low density lipoprotein (LDL) receptor gene, activates transcription in sterol-depleted cells and is silenced by sterols. We report the cDNA cloning of human SREBP-1, a protein that binds SRE-1, activates transcription, and thereby mediates the final regulatory step in LDL metabolism. SREBP-1 contains a basic-helix-loop-helix-leucine zipper (bHLH-ZIP) motif, but it differs from other bHLH-ZIP proteins in its larger size (1147 amino acids) and target sequence. Instead of an inverted repeat (CANNTG), the target for all known bHLH-ZIP proteins, SRE-1 contains a direct repeat of CAC. Overexpression of SREBP-1 activates transcription of reporter genes containing SRE-1 in the absence (15-fold) and presence (90-fold) of sterols, abolishing sterol regulation. We suggest that SREBP-1 is regulated by an unknown factor that is overwhelmed when SREBP-1 is overexpressed. Understanding the regulation of SREBP-1 may be crucial for understanding the control of plasma cholesterol in humans.

Neurogenin promotes neurogenesis and inhibits glial differentiation by independent mechanisms

The mechanisms by which neural stem cells give rise to neurons, astrocytes, or oligodendrocytes are beginning to be elucidated. However, it is not known how the specification of one cell lineage results in the suppression of alternative fates. We find that in addition to inducing neurogenesis, the bHLH transcription factor neurogenin (Ngn1) inhibits the differentiation of neural stem cells into astrocytes. While Ngn1 promotes neurogenesis by functioning as a transcriptional activator, Ngn1 inhibits astrocyte differentiation by sequestering the CBP-Smad1 transcription complex away from astrocyte differentiation genes, and by inhibiting the activation of STAT transcription factors that are necessary for gliogenesis. Thus, two distinct mechanisms are involved in the activation and suppression of gene expression during cell-fate specification by neurogenin.

SREBP-2, a second basic-helix-loop-helix-leucine zipper protein that stimulates transcription by binding to a sterol regulatory element

We report the cDNA cloning of SREBP-2, the second member of a family of basic-helix-loop-helix-leucine zipper (bHLH-Zip) transcription factors that recognize sterol regulatory element 1 (SRE-1). SRE-1, a conditional enhancer in the promoters for the low density lipoprotein receptor and 3-hydroxy-3-methylglutaryl-coenzyme A synthase genes, increases transcription in the absence of sterols and is inactivated when sterols accumulate. Human SREBP-2 contains 1141 amino acids and is 47% identical to human SREBP-1a, the first recognized member of this family. The resemblance includes an acidic NH2 terminus, a highly conserved bHLH-Zip motif (71% identical), and an unusually long extension of 740 amino acids on the COOH-terminal side of the bHLH-Zip region. SREBP-2 possesses one feature lacking in SREBP-1a--namely, a glutamine-rich region (27% glutamine over 121 residues). In vitro SREBP-2 bound SRE-1 with the same specificity as SREBP-1a. In vivo it mimicked SREBP-1a in activating transcription of reporter genes containing SRE-1. As with SREBP-1a, activation by SREBP-2 occurred in the absence and presence of sterols, abolishing regulation. Cotransfection of low amounts of pSREBP-1a and pSREBP-2 into human embryonic kidney 293 cells stimulated transcription of promoters containing SRE-1 in an additive fashion. At high levels transcription reached a maximum, and the effects were no longer additive. The reason for the existence of two SREBPs and the mechanism by which they are regulated by sterols remain to be determined.

Co-existence of substance P and calcitonin gene-related peptide-like immunoreactivities in sensory nerves in relation to cardiovascular and bronchoconstrictor effects of capsaicin

Immunohistochemical studies showed that substance P (SP) and calcitonin gene-related peptide (CGRP) immunoreactivity co-exist in capsaicin-sensitive primary sensory neurons. Varicose SP- and CGRP-immunoreactive nerve fibres with a similar distribution pattern were seen in the lower airways and heart. The functional analysis revealed that CGRP caused cardiac stimulation and had, together with SP and neurokinin A, potent hypotensive effects. Vascular permeability was increased by SP and neurokinin A, and the bronchial smooth muscle was particularly sensitive to neurokinin A. Thus, multiple peptides stored in an possible released from the same nerve endings by capsaicin may exert differential effects in various target tissues.

Sterol-regulated release of SREBP-2 from cell membranes requires two sequential cleavages, one within a transmembrane segment

Sterol regulatory element binding proteins (SREBPs) are transcription factors attached to the endoplasmic reticulum. The NH2-segment, which activates transcription, is connected to membranes by a hairpin anchor formed by two transmembrane sequences and a short lumenal loop. Using H-Ras-SREBP-2 fusion proteins, we show that the NH2-segment is released from membranes by two sequential cleavages. The first, regulated by sterols, occurs in the lumenal loop. The second, not regulated by sterols, occurs within the first transmembrane domain. The liberated NH2-segment enters the nucleus and activates genes controlling cholesterol synthesis and uptake. Certain mutant Chinese hamster ovary cells are auxotrophic for cholesterol because they fail to carry out the second cleavage; the NH2-segment remains membrane-bound and transcription is not activated.

Sterol resistance in CHO cells traced to point mutation in SREBP cleavage-activating protein

Through expression cloning we have isolated a cDNA-encoding SREBP cleavage-activating protein (SCAP), which regulates cholesterol metabolism by stimulating cleavage of transcription factors SREBP-1 and -2, thereby releasing them from membranes. The cDNA was isolated from Chinese hamster ovary cells with a dominant mutation that renders them resistant to sterol-mediated suppression of cholesterol synthesis and uptake. Sterol resistance was traced to a G-->A transition at codon 443 of SCAP, changing aspartic acid to asparagine. The D443N mutation enhances the cleavage-stimulating ability of SCAP and renders it resistant to inhibition by sterols. SCAP has multiple membrane-spanning regions, five of which resemble the sterol-sensing domain of HMG CoA reductase, an endoplasmic reticulum enzyme whose degradation is accelerated by sterols. SCAP appears to be a central regulator of cholesterol metabolism in animal cells.

Synergistic cooperation of TFE3 and smad proteins in TGF-beta-induced transcription of the plasminogen activator inhibitor-1 gene

Members of the TGF-beta superfamily influence a broad range of biological activities including stimulation of wound healing and inhibition of cell growth. TGF-beta signals through type I and II receptor serine/ threonine kinases and induces transcription of many genes including plasminogen activator inhibitor-1 (PAI-1). To identify proteins that participate in TGF-beta-induced gene expression, we developed a novel retrovirus-mediated expression cloning strategy; and using this approach, we established that transcription factor microE3 (TFE3) is involved in TGF-beta-induced activation of the PAI-1 promoter. We showed that TFE3 binds to an E-box sequence in PE2, a 56-bp promoter fragment of the PAI-1 promoter, and that mutation of this sequence abolishes both TFE3 binding as well as TGF-beta-dependent activation. TFE3 and Smad3 synergistically activate the PE2 promoter and phosphorylated Smad3 and Smad4 bind to a sequence adjacent to the TFE3-binding site in this promoter. Binding of both TFE3 and the Smad proteins to their cognate sequences is indispensable for TGF-beta-inducible activation of the PE2 promoter. Hence, TFE3 is an important transcription factor in at least one TGF-beta-activated signal transduction pathway.

Structure of the human gene encoding sterol regulatory element binding protein-1 (SREBF1) and localization of SREBF1 and SREBF2 to chromosomes 17p11.2 and 22q13

Sterol regulatory element binding protein-1 (SREBP1) and SREBP2 are structurally related proteins that control cholesterol homeostasis by stimulating transcription of sterol-regulated genes, including those encoding the low-density lipoprotein (LDL) receptor and 3-hydroxy-3-methylglutaryl CoA synthase. SREBP1 and SREBP2 are 47% identical, and they share a novel structure comprising a transcriptionally active NH2-terminal basic helix-loop-helix-leucine zipper (bHLH-Zip) domain followed by a membrane attachment domain. Cleavage by a sterol-regulated protease frees the bHLH-Zip domain from the membrane and allows it to enter the nucleus. SREBP1 exists in several forms, possibly as a result of alternative splicing at both the 5' and the 3' ends of the mRNA. The genes for SREBP1 (SREBF1) and SREBP2 (SREBF2) have not been studied. In this paper we describe the cloning and characterization of the human SREBF1 gene. The gene is 26 kb in length and has 22 exons and 20 introns. The 5' and 3' sequences that differ between the two SREBP1 cDNAs are encoded by discrete exons, confirming the hypothesis that they result from alternative splicing. The chromosomal locations of human SREBF1 and SREBF2 were determined by analysis of human-rodent somatic cell hybrids and fluorescence in situ hybridization. The SREBF1 gene mapped to the proximal short arm of chromosome 17 (17p11.2), and the SREBF2 gene was localized to the long arm of chromosome 22 (22q13).

Vascular permeability changes and smooth muscle contraction in relation to capsaicin-sensitive substance P afferents in the guinea-pig

The occurrence of neurogenic inflammation as indicated by Evans blue extravasation was studied in various organs of the guinea-pig. Electrical stimulation of the trigeminal nerve caused Evans blue extravasation due to increased vascular permeability in the nasal mucosa and gingiva. Vagal stimulation induced extravasation in the epiglottis, larynx, trachea, bronchial tree and esophagus. Splanchnic stimulation induced Evans blue extravasation in the gall bladder, bile ducts and superior mesenteric artery. Stimulation of the inferior mesenteric ganglion caused a marked extravasation in the upper and middle part of both ureters, while pelvic activation induced a reaction in the lower ureter, urinary bladder, urethra and vagina. I.v. substance P (SP) (3 nmol X kg11) or capsaicin (1 mumol X kg-1) both induced extravasation in many tissues including those in which nerve stimulation produced a response. The extravasation responses to SP, capsaicin or nerve stimulation all had similar border-line zones, such as esophagus to stomach, bile ducts to duodenum, rectum to anal mucosa, pulmonary artery to heart and vagina to uterus. Quantitative determinations showed especially large permeability effects in the trachea, umbilical ligament and ureter. The permeability effect of capsaicin and nerve stimulation was abolished in capsaicin-pretreated animals, while the response to SP was still present. Capsaicin pretreatment caused an almost total loss of SP in several visceral organs including the respiratory and urinary tracts. The SP content in these tissues was correlated (r = 0.97) to the Evans blue extravasation following nerve stimulation or i.v. capsaicin. SP and capsaicin caused contractions in vitro of the esophagus, ureter, urinary bladder, trachea and gall bladder. The capsaicin-induced contraction of the trachea was resistant to tetrodotoxin pretreatment. The non-cholinergic, non-adrenergic contraction of the urinary bladder upon field stimulation was still present in capsaicin-pretreated animals. In conclusion, neurogenic inflammation occurs in several organs with a highly region-specific distribution, which is accompanied by the presence of capsaicin-sensitive SP neurons. Both parasympathetic and sympathetic pathways contain capsaicin-sensitive afferent fibres which mediate an increase in vascular permeability most likely by releasing SP. In addition, both capsaicin and SP cause smooth muscle contraction in several visceral organs.

Regulated cleavage of sterol regulatory element binding proteins requires sequences on both sides of the endoplasmic reticulum membrane

Sterol regulatory element binding proteins (SREBP-1 and SREBP-2) are attached to the endoplasmic reticulum (ER) and nuclear envelope by a hairpin domain consisting of two transmembrane regions connected by a short lumenal loop of approximately 30 hydrophilic amino acids. In sterol-depleted cells, a protease cleaves the protein in the region of the first transmembrane domain, releasing an NH2-terminal fragment of approximately 500 amino acids that activates transcription of genes encoding the low density lipoprotein receptor and enzymes of cholesterol synthesis. In sterol-overloaded cells, proteolysis does not occur, and transcription is repressed. Through mutational analysis in transfected cells, we identify two segments of SREBPs that are required for proteolysis, one on either side of the ER membrane. An arginine in the lumenal loop is essential. A tetrapeptide sequence (DRSR) on the cytosolic face adjacent to the first transmembrane domain is also required for maximal cleavage. Both of these elements are conserved in the human and hamster versions of SREBP-1 and SREBP-2. Sterol-mediated suppression of cleavage of SREBP-1 was found to be dependent on the extreme COOH-terminal region (residue 1034 to the COOH terminus), which exists in two forms as a result of alternative splicing. The form encoded by the "a" class exons (exons 18a and 19a) undergoes sterol-regulated cleavage. The form encoded by the "c" class exons (18c and 19c) is cleaved less efficiently and is not suppressed by sterols. These studies were made possible through use of a vector that achieves low level expression of epitope-tagged SREBPs under control of the relatively weak thymidine kinase promoter from herpes simplex virus. In contrast to SREBPs overproduced by high level expression vectors, the SREBPs produced at low levels were subject to the same regulated cleavage pattern as the endogenous SREBPs. These results indicate that sterol-regulated proteolysis of SREBPs is a complex process, requiring sequences on both sides of the ER membrane.

Critical role of Smads and AP-1 complex in transforming growth factor-beta -dependent apoptosis

Transforming growth factor-beta1 (TGF-beta1) induces not only cell growth inhibition but also apoptosis in hepatocytes, myeloid cells, and epithelial cells. Although Smad proteins are identified as key signal transducers in TGF-beta1-dependent growth inhibition, their roles in the induction of apoptosis are unclear. We show here that both Smad proteins and AP-1 complex are involved in TGF-beta1 signaling for apoptosis. Overexpression of a dominant-negative Smad3 mutant or Smad7, both of which impair Smad-mediated signal transduction, inhibits TGF-beta1-dependent apoptosis. Only the JunD. FosB form of the AP-1 complex is markedly activated during TGF-beta1-dependent apoptosis. FosB substantially enhances Smad3. Smad4-dependent transcription, and dominant-negative FosB blocks TGF-beta1-dependent apoptosis but not growth inhibition. Expression of JunD.FosB enhances induction of apoptosis by TGF-beta1. Moreover, JunD.FosB binds to the 12-O-tetradecanoyl-13-acetate-responsive gene promoter element and recruits Smad3.Smad4 to form a multicomponent complex. These results suggest that Smad proteins and AP-1 complex synergize to mediate TGF-beta1-dependent apoptosis.

Act1, an NF-kappa B-activating protein

Use of an NF-kappaB-dependent selectable marker facilitated the isolation of a cell line containing a cDNA encoding Act1, an NF-kappaB activator. Act1 associates with and activates IkappaB kinase (IKK), leading to the liberation of NF-kappaB from its complex with IkappaB. Many signaling pathways that liberate NF-kappaB also activate activating transcription factor (ATF) and activator protein 1 (AP-1) through Jun kinase (JNK). Act1 also activates JNK, suggesting that it might be part of a multifunctional complex involved in the activation of both NF-kappaB and JNK. Act1 fails to activate NF-kappaB in an IL-1-unresponsive mutant cell line in which all known signaling components are present, suggesting that it interacts with an unknown component in IL-1 signaling.

Specificity in transforming growth factor beta-induced transcription of the plasminogen activator inhibitor-1 gene: interactions of promoter DNA, transcription factor muE3, and Smad proteins

Transforming growth factor beta (TGF-beta) regulates a broad range of biological processes, including cell growth, development, differentiation, and immunity. TGF-beta signals through its cell surface receptor serine kinases that phosphorylate Smad2 or Smad3 proteins. Because Smad3 and its partner Smad4 bind to only 4-bp Smad binding elements (SBEs) in DNA, a central question is how specificity of TGF-beta-induced transcription is achieved. We show that Smad3 selectively binds to two of the three SBEs in PE2.1, a TGF-beta-inducible fragment of the plasminogen activator inhibitor-1 promoter, to mediate TGF-beta-induced transcription; moreover, a precise 3-bp spacer between one SBE and the E-box, a binding site for transcription factor muE3 (TFE3), is essential for TGF-beta-induced transcription. Whereas an isolated Smad3 MH1 domain binds to TFE3, TGF-beta receptor-mediated phosphorylation of full-length Smad3 enhances its binding to TFE3. Together, these studies elucidate an important mechanism for specificity in TGF-beta-induced transcription of the plasminogen activator inhibitor-1 gene.

Hairpin orientation of sterol regulatory element-binding protein-2 in cell membranes as determined by protease protection

Sterol regulatory element-binding proteins (SREBP-1 and SREBP-2) are proteins of approximately 1150 amino acids each that are attached to membranes of the endoplasmic reticulum (ER). In sterol-depleted cells, a protease releases an NH2-terminal fragment of approximately 500 amino acids that contains a basic helix-loop-helix leucine zipper motif. This fragment enters the nucleus and stimulates transcription of genes encoding the low density lipoprotein receptor and enzymes of cholesterol biosynthesis. Prior evidence indicates that the SREBPs are attached to membranes by virtue of an 80-residue segment located approximately 80 amino acids to the COOH-terminal side of the leucine zipper. This segment contains two long hydrophobic sequences separated by a short hydrophilic sequence of approximately 30 amino acids. We have proposed a hairpin model in which the two hydrophobic sequences span the membrane, separated by the short hydrophilic sequence which projects into the lumen of the ER (the "lumenal loop"). The model predicts that the NH2- and COOH-terminal segments face the cytosol. To test this model, we constructed a cDNA encoding human SREBP-2 with epitope tags at the NH2 terminus and in the lumenal loop. The COOH-terminal region was visualized with a newly developed monoclonal antibody against this region. Sealed membrane vesicles were isolated from cells expressing the epitope-tagged version of SREBP-2. Trypsin treatment of these vesicles destroyed the NH2- and COOH-terminal segments and reduced the lumenal epitope to a size consistent with protection of the lumenal sequence plus the two membrane-spanning segments. The lumenal epitope tag contained two potential sites for N-linked glycosylation. The size of the trypsin-protected fragment was reduced by treatment with N-Glycanase and endoglycosidase H, indicating that this segment was located in the lumen of the ER where it was glycosylated. These data provide strong support for the hairpin model.

Comparison of cardiovascular and bronchoconstrictor effects of substance P, substance K and other tachykinins

The effects of substance P (SP), substance K (SK), physalaemin, eledoisin, kassinin, neuromedin K and bombesin on blood pressure, heart rate, respiratory insufflation pressure and plasma extravasation were studied in the guinea-pig. All tachykinins except neuromedin K caused a fall in blood pressure with rather similar potency. The hypotensive response after physalaemin was comparatively more long-lasting. SK and eledoisin (2.5 nmol X kg-1 i.v.) caused an initial bradycardia which then changed into tachycardia. The other tachykinins induced a slowly developing tachycardia. Neuromedin K (up to 40 nmol X kg-1) did not influence heart rate. SK, kassinin and eledoisin were more potent than SP and physalaemin in increasing respiratory insufflation pressure. The effect of SK had a particularly long duration. Neuromedin K only induced a weak increase in insufflation pressure at a very high dose. All tachykinins except neuromedin K induced an increase in vascular permeability to plasma proteins in many visceral organs, as indicated by Evans blue extravasation. The trachea and ureter were the most sensitive organs with regard to this effect. Physalaemin and eledoisin were generally more potent in increasing vascular permeability in various organs than SP and SK. The maximal permeability-increasing effect of SK was smaller than that of SP, although the potency was similar. Bombesin increased insufflation pressure with no clearcut effects on vascular permeability. It is concluded that in the same species, i.e. guinea-pig, several tachykinins have rather similar hypotensive action, while the vascular permeability increase to plasma proteins is especially pronounced after physalaemin and eledoisin. SK, kassinin and eledoisin have prominent bronchoconstrictor effects.(ABSTRACT TRUNCATED AT 250 WORDS)

China's floating population and the potential for HIV transmission: a social-behavioural perspective

Historical, geo-economic and behavioural perspectives are used in an exploratory analysis of China's migrant or 'floating' population as a factor in the spread of HIV on the mainland. Participants in the interview format survey (N = 506) included in-transit individuals in Beijing, and peddlers, restaurant workers, and employment seekers in Shanghai. When viewed in light of various social dynamics, the convenience survey data suggest that elements within this migrant population, as well as their rurally located partners and spouses, may be at increased risk of acquiring the virus. Given the sheer size and broad movement of this population, it is contended that it may well be a 'tipping point' factor in AIDS prevention and control in China.

Hepatitis E virus infection among domestic animals in eastern China

Hepatitis E virus (HEV) is a zoonotic pathogen of which several species of animal were reported as reservoirs. Antibodies to HEV and HEV RNA have been detected in some Chinese population and swine groups but few other domestic animals. In this study, to investigate the HEV prevalence, we tested sera from 788 pigs, 100 cows, 50 goats, 49 horses, 101 pet dogs, 105 chickens, 47 duck and 45 pigeons in eastern China for anti-HEV immunoglobulin G (IgG). We also tested 50% of the swine sera, all of sera from the other domestic animals and 13 Shanghai human sera which were positive for anti-HEV immunoglobulin M (IgM) for HEV RNA using reverse transcriptase-polymerase chain reaction. Our results indicated that 82.5% (222/269) of the sows, 53.9% (104/193) of the 4- to 6-month-old swine, 63.4% (168/265) of the 1- to 3-month-old swine, 55.7% (34/61) of the slaughterhouse swine, 24% (12/50) of the goats, 16.3% (8/49) of the horses, 17.8% (21/101) of the pet dogs, 6% (6/100) of the cows, 12.8% (6/47) of the ducks, 4.4% (2/45) of the pigeons and 1.9% (2/105) of the chickens exhibited positive for anti-HEV IgG. Inhibition assay confirmed the infection with HEV or HEV-like viruses in these domestic animals except pigeons and chickens. From the sera, we isolated 18 swine HEV strains, one horse HEV strain and two human HEV strains. Sequence analysis showed that the horse HEV isolate and one swine isolate belonged to genotype 3. The other isolates belonged to genotype 4. The two human isolates were phylogenetically closely related to eight of the swine isolates. In short, the presence of anti-HEV antibody had been confirmed in several species of domestic animals in eastern China and HEV RNA has been identified in swine, human and horse. This suggested that the authorities should pay more attention to the prevalence of HEV in eastern China.

3D maps localize caudate nucleus atrophy in 400 Alzheimer's disease, mild cognitive impairment, and healthy elderly subjects

MRI research examining structural brain atrophy in Alzheimer's disease (AD) generally focuses on medial temporal and cortical structures, but amyloid and tau deposits also accumulate in the caudate. Here we mapped the 3D profile of caudate atrophy using a surface mapping approach in subjects with AD and mild cognitive impairment (MCI) to identify potential clinical and pathological correlates. 3D surface models of the caudate were automatically extracted from 400 baseline MRI scans (100 AD, 200 MCI, 100 healthy elderly). Compared to controls, caudate volumes were lower in MCI (2.64% left, 4.43% right) and AD (4.74% left, 8.47% right). Caudate atrophy was associated with age, sum-of-boxes and global Clinical Dementia Ratings, Delayed Logical Memory scores, MMSE decline 1 year later, and body mass index. Reduced right (but not left) volume was associated with MCI-to-AD conversion and CSF tau levels. Normal caudate asymmetry (with the right 3.9% larger than left) was lost in AD, suggesting preferential right caudate atrophy. Automated caudate maps may complement other MRI-derived measures of disease burden in AD.

Tumor suppressor menin: the essential role of nuclear localization signal domains in coordinating gene expression

Menin is encoded by the tumor suppressor gene MEN1 that is mutated in patients with an inherited tumor syndrome, multiple endocrine neoplasia type 1 (MEN1). Although menin is a nuclear protein and directly binds to DNA through its nuclear localization signals (NLSs), the precise role for each of the NLSs in nuclear translocation and gene expression remains to be elucidated. Here, we show that point mutations in three individual NLSs, NLS1, NLS2, and a novel accessory NLS, NLSa, do not block nuclear translocation, but compromise the ability of menin to repress expression of the endogenous insulin-like growth factor binding protein-2 (IGFBP-2) gene. This repression is not released by an inhibitor of histone deacetylases. Although subtle mutations in menin NLSs do not affect menin association with chromatin, they abolish menin binding to the IGFBP-2 promoter in vivo. Furthermore, each of the NLSs is also crucial for menin-mediated induction of caspase 8 expression. Together, these results suggest that menin may act as a scaffold protein in coordinating activation and repression of gene transcription and that its NLSs play a more important role in controlling gene transcription than merely targeting menin into the nucleus.

Capsaicin-induced substance P release and sensory control of vascular permeability in the guinea-pig ureter

Substance P-immunoreactivity (SP-IR) in the guinea-pig ureter was found to be totally depleted after systemic capsaicin pretreatment. Removal of the inferior mesenteric ganglion (IMG) led to a total depletion of SP-IR from the rostral third of the ureter and to a partial depletion from the caudal third. Electrical stimulation of the IMG caused Evans blue extravasation mainly in the rostral third of both ureters, whereas stimulation of the right pelvic nerve caused Evans blue extravasation in the caudal third of the ureters on both sides. The responses to nerve stimulation were absent in capsaicin-pretreated animals. Furthermore, capsaicin caused release of SP-IR from ureter slices in vitro, this release was not inhibited by tetrodotoxin. Potassium (60 and 120 mM) also released SP-IR. It is concluded that SP-IR in the ureter is contained in capsaicin-sensitive sensory neurons reaching the ureter via both parasympathetic (caudal part) and sympathetic nerves (rostral part). Activation of these neurons by capsaicin leads to a peripheral release of SP-IR which most likely increases vascular permeability.

Cell cycle controlling the silencing and functioning of mammalian activators

Naïve CD4(+) helper T (T(H)) cells respond to stimulation by terminally differentiating into two mature classes, T(H)1 cells, which express interferon gamma (IFN-gamma), and T(H)2 cells, which express interleukin 4 (IL-4). The transcriptional activators T-bet and Gata-3 mediate commitment to the T(H)1 and T(H)2 fates, respectively, including chromatin remodeling of signature genes. The cytokine IL-12 fosters growth of committed T(H)1 cells, while IL-4 fosters growth of committed T(H)2 cells. IL-12 and IL-4 also play critical roles in commitment by promoting transcriptional silencing of Gata-3 and T-bet, respectively. We now show that both T-bet and Gata-3 are induced in a cell cycle-independent manner in bipotent progenitor cells. In contrast, both lineage-restricted gene induction by the activator proteins and heritable silencing of the transcription of each activator, the hallmarks of terminal differentiation, are cell cycle dependent. We found that cells that cannot cycle remain uncommitted and bipotent in response to the most polarizing signals for maturation. These results provide mechanistic insight into a mammalian model of terminal differentiation by illustrating that cell cycle-coupled epigenetic effects, as originally described in yeast, may represent an evolutionarily conserved strategy for organizing signaling and cell fate.

Synergism between transcription factors TFE3 and Smad3 in transforming growth factor-beta-induced transcription of the Smad7 gene

Activation of transforming growth factor-beta (TGF-beta) receptors triggers phosphorylation of Smad2 and Smad3. After binding to Smad4, the complex enters the nucleus and interacts with other transcription factors to activate gene transcription. Unlike other Smads, Smad7 inhibits phosphorylation of Smad2 and Smad3, and its transcription is induced by TGF-beta, suggesting a negative feedback loop. Here, we show that TFE3 and Smad3 synergistically mediate TGF-beta-induced transcription from the Smad7 promoter by binding to an E-box and two adjacent Smad binding elements (SBEs), respectively. A precise 3-base pair spacer between one SBE and the E-box is essential. Previously, we showed that a similar arrangement between a SBE and an E-box of an element is essential for TGF-beta-dependent transcription of the plasminogen activator inhibitor-1 gene (PAI-1) and that TGF-beta-induced phosphorylation of Smad3 triggers its association with TFE3. Thus, TFE3-Smad3 response elements may represent a common target for TGF-beta-induced gene expression.