Detection of Polymorphisms in the Human Urokinase-type Plasminogen Activator Gene

Expressed polymorphisms in the genes encoding components of the fibrinolytic cascade could have implications for the predisposition to thrombolytic disorders and/or for tumor metastasis. The occurrence of published two amino acid sequences at position 194 of the human urokinase-type plasminogen activator prompted us to search by SSCP for frequent polymorphisms in several exons of the gene. Surprisingly, only one sequence was detected in codon 194 (>200 alleles). Two polymorphisms were observed in this study: the most frequent one, a C to T change near the beginning of exon 8, is probably silent; a less frequent polymorphism results in the replacement of a Leu residue by a Pro, in the kringle domain.

The anterior insula bidirectionally modulates cost-benefit decision-making on a rodent gambling task

Deficits in cost‐benefit decision‐making, as assessed in the Iowa Gambling Task (IGT), are commonly observed in neuropsychiatric disorders such as addiction. There is considerable variation in the maximization of rewards on such tasks, both in the general population and in rodent models, suggesting individual differences in decision‐making may represent a key endophenotype for vulnerability to neuropsychiatric disorders. Increasing evidence suggests that the insular cortex, which is involved in interoception and emotional processes in humans, may be a key neural locus in the control of decision‐making processes. However, the extent to which the insula contributes to individual differences in cost‐benefit decision‐making remains unknown. Using male Sprague Dawley rats, we first assessed individual differences in the performance over the course of a single session on a rodent analogue of the IGT (rGT). Rats were matched for their ability to maximize reward and received bilateral excitotoxic or sham lesions of the anterior insula cortex (AIC). Animals were subsequently challenged on a second rGT session with altered contingencies. Finally, animals were also assessed for instrumental conditioning and reversal learning. AIC lesions produced bidirectional alterations on rGT performance; rats that had performed optimally prior to surgery subsequently showed impairments, and animals that had performed poorly showed improvements in comparison with sham‐operated controls. These bidirectional effects were not attributable to alterations in behavioural flexibility or in motivation. These data suggest that the recruitment of the AIC during decision‐making may be state‐dependent and help guide response selection towards subjectively favourable options.

From impulses to maladaptive actions: the insula is a neurobiological gate for the development of compulsive behavior

Impulsivity is an endophenotype of vulnerability for compulsive behaviors. However, the neural mechanisms whereby impulsivity facilitates the development of compulsive disorders, such as addiction or obsessive compulsive disorder, remain unknown. We first investigated, in rats, anatomical and functional correlates of impulsivity in the anterior insular (AI) cortex by measuring both the thickness of, and cellular plasticity markers in, the AI with magnetic resonance imaging and in situ hybridization of the immediate early gene zif268, respectively. We then investigated the influence of bilateral AI cortex lesions on the high impulsivity trait, as measured in the five-choice serial reaction time task (5-CSRTT), and the associated propensity to develop compulsivity as measured by high drinking levels in a schedule-induced polydipsia procedure (SIP). We demonstrate that the AI cortex causally contributes to individual vulnerability to impulsive-compulsive behavior in rats. Motor impulsivity, as measured by premature responses in the 5-CSRTT, was shown to correlate with the thinness of the anterior region of the insular cortex, in which highly impulsive (HI) rats expressed lower zif268 mRNA levels. Lesions of AI reduced impulsive behavior in HI rats, which were also highly susceptible to develop compulsive behavior as measured in a SIP procedure. AI lesions also attenuated both the development and the expression of SIP. This study thus identifies the AI as a novel neural substrate of maladaptive impulse control mechanisms that may facilitate the development of compulsive disorders.

Cocaine-induced sensitization is associated with altered dynamics of transcriptional responses of the dopamine transporter, tyrosine hydroxylase, and dopamine D2 receptors in C57Bl/6J mice

RATIONALE

Behavioural sensitization is a long lasting phenomenon that has been proposed to be involved in drug addiction. Although the expression of cocaine-induced sensitization has been associated with the activity of the mesencephalic dopaminergic neurons, little is known about the transcriptional adaptations of these neurons to a new challenge with cocaine long after cessation of repeated exposure to the drug.

OBJECTIVES

We studied the time course of the mRNA levels of three main regulatory elements of dopaminergic transmission after a challenge with cocaine (15 mg/kg) that followed 21 days of withdrawal from a cocaine pretreatment (20 mg/kg, ip, every 2 days for 21 days) in C57Bl/6J mice.

MATERIALS AND METHODS

Mice were placed 45 min in activity chambers and were killed 45 min, 2 h or 24 h after the challenge injection. Dopamine transporter (DAT), D2 auto-receptor (D2) and tyrosine hydroxylase (TH) mRNA levels were assessed by in situ hybridization in the ventral tegmental area and the substantia nigra compacta.

RESULTS

As compared to vehicle challenge, cocaine challenge in vehicle pretreated mice induced a rapid increase (+208%) in DAT mRNA (45 min) followed by a delayed decrease (-70%) (24 h), while TH and D2 mRNA were both increased (+45%) 24 h after the challenge. In cocaine pretreated mice, cocaine-induced short-term increase and long-term decrease in DAT mRNA levels were amplified (+328%) and reduced (-40%), respectively.

CONCLUSIONS

Repeated exposure to cocaine alters the transcriptional response of DA neurons to a new cocaine challenge long after cessation of repeated exposure to the drug. They point to the DAT mRNA as a major responsive element to a new presentation of cocaine.

Tissue plasminogen activator in psoriasis

Elevated levels of the serine proteinase plasminogen activator are observed in psoriatic lesions. In contrast to normal epidermis, lesional psoriatic epidermis contains primarily tissue type plasminogen activator (tPA) activity and much lower levels of urokinase type plasminogen activator (uPA) activity. Tissue plasminogen activator is also detectable immunocytochemically in lesional psoriatic but not normal epidermis. Similarly, mRNA for tPA is observed in lesional epidermis only. These results suggest that lesional psoriatic epidermis synthesizes enhanced levels of tPA compared to normal. Additional data support the hypothesis that enhanced tPA may be another marker common to psoriatic epidermis, epidermis during wound repair, and keratinocytes in culture. The significance of elevated tPA in psoriatic lesions is presently unclear, but its possible relationship to epidermal proliferation and cutaneous inflammation is under study.

Functional activity of eukaryotic signal sequences in Escherichia coli: the ovalbumin family of serine protease inhibitors

It is widely assumed that the functional activity of signal sequences has been conserved throughout evolution, at least between Gram-negative bacteria and eukaryotes. The ovalbumin family of serine protease inhibitors (serpins) provides a unique tool to test this assumption, since individual members can be secreted (ovalbumin), cytosolic (leukocyte elastase inhibitor, LEI), or targeted to both compartments (plasminogen activator inhibitor 2, PAI-2). The facultative secretion of PAI-2 is mediated by a signal sequence proposed to be inefficient by design. We show here that the same internal domain that promotes an inefficient translocation of murine PAI-2 in mammalian cells is a weak signal sequence in Escherichia coli. In contrast, the ovalbumin signal sequence is much more efficient, whereas the corresponding sequence elements from LEI, maspin and PI-10 are entirely devoid of signal sequence activity in E.coli. Mutations that improve the activity of the PAI-2 signal sequence and that convert the N-terminal regions of maspin and PI-10 into efficient signal sequences have been characterized. Taken together, these results indicate that several structural features contribute to the weak activity of the PAI-2 signal sequence and provide new insights into the plasticity of the "hydrophobic core" of signal sequences. High-level expression of two chimeric proteins containing the PAI-2 signal sequence is toxic, and the reduced viability is accompanied by a rapid decrease in the membrane proton motive force, in ATP levels and in translation. In unc- cells, which lack the F0F1 ATP-synthase, the chimeric proteins retain their toxicity and their expression only affected the proton motive force. Thus, the properties of these toxic signal sequences offer a new tool to dissect the interactions of signal sequences with the protein export machinery.

Haemolytic onset of Wilson disease in a patient with homozygous truncation of ATP7B at Arg1319

We describe a 19-year-old woman with haemolytic anaemia and thrombocytopenia as the initial manifestation of Wilson disease (WD). There are two reasons for reporting such an improbable case. First, it emphasizes the importance of recognizing atypical clinical presentations of potentially lethal recessive traits for which therapy is available. Second, it shows that, even in a monogenic disorder like WD, the phenotype cannot be extrapolated from the mutated genotype in a simple fashion; this patient had a relatively late-onset form of WD despite homozygosity for a genetic lesion leading to an apparent complete loss of function of the WD copper transporter.

Human myoblast fusion requires expression of functional inward rectifier Kir2.1 channels

Myoblast fusion is essential to skeletal muscle development and repair. We have demonstrated previously that human myoblasts hyperpolarize, before fusion, through the sequential expression of two K+ channels: an ether-à-go-go and an inward rectifier. This hyperpolarization is a prerequisite for fusion, as it sets the resting membrane potential in a range at which Ca2+ can enter myoblasts and thereby trigger fusion via a window current through alpha1H T channels.

Expression of the endogenous type II secretion pathway in Escherichia coli leads to chitinase secretion

Escherichia coli K-12, the most widely used laboratory bacterium, does not secrete proteins into the extracellular medium under standard growth conditions, despite possessing chromosomal genes encoding a putative type II secretion machinery (secreton). We show that in wild-type E.coli K-12, divergent transcription of the two operons in the main chromosomal gsp locus, encoding the majority of the secreton components, is silenced by the nucleoid-structuring protein H-NS. In mutants lacking H-NS, the secreton genes cloned on a moderate-copy-number plasmid are expressed and promote efficient secretion of the endogenous, co-regulated endochitinase ChiA. This is the first time that secretion of an endogenous extracellular protein has been demonstrated in E.coli K-12.

Both transmembrane domains of SecG contribute to signal sequence recognition by the Escherichia coli protein export machinery

A chimeric protein containing the uncleaved signal sequence of plasminogen activators inhibitor-2 (PAI2) fused to alkaline phosphatase (AP) interferes with Escherichia coli protein export and arrests growth. Suppressors of this toxicity include secG mutations that define the Thr-41-Leu-42-Phe-43 (TLF) domain of SecG. These mutations slow down the export of PAI2-AP. Another construct encoding a truncated PAI2 signal sequence (hB-AP) is also toxic. Most suppressors exert their effect on both chimeric proteins. We describe here five secG suppressors that only suppress the toxicity of hB-AP and selectively slow down its export. These mutations do not alter the TLF domain: three encode truncated SecG, whereas two introduce Arg residues in the transmembrane domains of SecG. The shortest truncated protein only contains 13 residues of SecG, suggesting that the mutation is equivalent to a null allele. Indeed, a secG disruption selectively suppresses the toxicity of hB-AP. However, the missense mutations are not null alleles. They allow SecG binding to SecYE, although with reduced affinity. Furthermore, these mutated SecG are functional, as they facilitate the export of endogenous proteins. Thus, SecG participates in signal sequence recognition, and both transmembrane domains of SecG contribute to ensure normal signal sequence recognition by the translocase.

Urokinase redistribution from the secreted to the cell-bound fraction in granulosa cells of rat preovulatory follicles

Plasminogen activators (PAs) have been shown to be synthesized in ovarian follicles of several mammalian species, where they contribute to the ovulation process. The type of PA secreted by granulosa cells is species-specific. In fact, whereas in the rat, gonadotropins stimulate tissue-type PA (tPA) production, the same hormonal stimulation induces urokinase PA (uPA) secretion in mouse cells. To investigate in more detail the hormonal regulation of this system, we used the rat ovary as a model in which we analyzed the production of PAs by theca-interstitial (TI) and granulosa cells obtained from preovulatory follicles after gonadotropin stimulation. In untreated rats, uPA was the predominant enzyme in both TI and granulosa cells. After hormonal stimulation, an increase in uPA and tPA activity was observed in both cell types. Surprisingly, only tPA mRNA increased in a time-dependent manner in both cell types, while uPA mRNA increased only in TI cells and actually decreased in granulosa cells. These divergent results between uPA enzyme activity and mRNA levels in granulosa cells were explained by studying the localization of the enzyme. Analysis of granulosa cell lysates showed that after hormonal stimulation, 60-70% of the uPA behaved as a cell-associated protein, suggesting that uPA, already present in the follicle, accumulates on the granulosa cell surface through binding to specific uPA receptors. The redistribution of uPA in granulosa cells and the differing regulation of the two PAs by gonadotropins in the rat ovary suggest that the two enzymes might have different functions during the ovulation process. Moreover, the ability of antibodies anti-tPA and anti-uPA to significantly inhibit ovulation only when coinjected with hCG confirmed that the PA contribution to ovulation occurs at the initial steps.

Membrane topology of CadA homologous P-type ATPase of Helicobacter pylori as determined by expression of phoA fusions in Escherichia coli and the positive inside rule

The only experimental data available on the membrane topology of transition metal ATPases are from in vitro studies on two distinct P-type ATPases (CadA and CopA) of a gastric bacterium, Helicobacter pylori, both postulated to contain eight transmembrane domains (H1 to H8). In this study, H. pylori CadA ATPase was subjected to analysis of membrane topology in vivo by expression of ATPase-alkaline phosphatase (AP) hybrid proteins in Escherichia coli using a novel vector, pBADphoA. This vector contains an inducible arabinose promoter and unique restriction sites for fusion of DNA fragments to phoA. The phoA gene lacking sequences encoding its N-terminal signal peptide was linked to the C-terminal regions of the postulated five cytoplasmic and four periplasmic segments of the H. pylori pump. The results obtained by heterologous expression of ATPase-AP hybrid proteins showed consistence with a model of eight transmembrane domains. They also demonstrated that the H. pylori ATPase sequences are well assembled in the cytoplasmic membrane of E. coli, a neutralophilic bacterium. Cloning and amino acid sequence analysis of the homologous ATPase of Helicobacter felis further verified the topological model for the H. pylori pump analyzed here, although the degree of amino acid sequence identity varied between the corresponding transmembrane segments, from 25% for H1 up to 100% for H6. It was found that the topology of ATPase follows the 'positive inside rule'. With respect to the bioenergetic capacities of H. pylori, we discuss here the membrane potential as a possible factor directing insertion of ATPases in the cytoplasmic membrane of gastric bacteria.

Urokinase receptor (uPAR, CD87) is a platelet receptor important for kinetics and TNF-induced endothelial adhesion in mice

BACKGROUND

Urokinase plasminogen activator receptor (uPAR, CD87) is a widely distributed 55-kD, glycoprotein I-anchored surface receptor. On binding of its ligand uPA, it is known to increase leukocyte adhesion and traffic. Using genetically deficient mice, we explored the role of uPAR in platelet kinetics and TNF-induced platelet consumption.

METHODS AND RESULTS

Anti-uPAR antibody stained platelets from normal (+/+) but not from uPAR-/- mice, as seen by fluorescence-activated cell sorter analysis. 51Cr-labeled platelets from uPAR-/- donors survived longer than those from +/+ donors when injected into a +/+ recipient. Intratracheal TNF injection induced thrombocytopenia and a platelet pulmonary localization, pronounced in +/+ but absent in uPAR-/- mice. Aprotinin, a plasmin inhibitor, decreased TNF-induced thrombocytopenia. TNF injection markedly reduced the survival and increased the pulmonary localization of 51Cr-labeled platelets from +/+ but not from uPAR-/- donors, indicating that it is the platelet uPAR that is critical for their response to TNF. As seen by electron microscopy, TNF injection increased the number of platelets and polymorphonuclear neutrophils (PMNs) in the alveolar capillaries of +/+ mice, whereas in uPAR-/- mice, platelet trapping was insignificant and PMN trapping was slightly reduced. Platelets within alveolar capillaries of TNF-injected mice were activated, as judged from their shape, and this was evident in +/+ but not in uPAR-/- mice.

CONCLUSIONS

These results demonstrate for the first time the critical role of platelet uPAR for kinetics as well as for activation and endothelium adhesion associated with inflammation.

Single stress induces long-lasting elevations in vasopressin mRNA levels in CRF hypophysiotrophic neurones, but repeated stress is required to modify AVP immunoreactivity

Repeated stress is known to induce an increased vasopressin (AVP) expression in paraventricular corticotrophin-releasing factor (CRF) neurones which is supposed to enhance the ACTH-releasing capacity of these cells. To test the hypothesis that a single stress is sufficient to produce these changes, we used quantitative in-situ hybridization analysis to measure steady state CRF and AVP mRNA. Moreover the colocalized AVP and CRF immunoreactive sites were assessed in the dense core vesicle compartment of CRF axon terminals in the external zone of the median eminence with quantitative immunoelectron microscopy. Acute immobilization produced a significant increase in the average AVP and CRF mRNA levels (145% and 65%, respectively, above control values) in the medial parvocellular subdivisions of the paraventricular nucleus (PVN), and these changes persisted for over 4 days after stress. In contrast to these changes in AVP mRNA levels, there were no concomitant changes in AVP immunostaining in CRF terminals and axons during the 4-day period. However, when immobilization stress was repeated daily, the number of CRF terminals containing AVP increased progressively. Moreover, the ratio of AVP and CRF immunoreactivity in the dense core vesicle compartment was increased. Taken together, these results provide evidence that single stress experience can cause long-lasting changes in AVP and CRF mRNA steady state expression that is not apparently accompanied by changes in peptide levels. They also suggest that repeated stress is required for developing progressive shifts in the neurohormone storage pattern of these neurones.

Transcriptional activation of ydeA, which encodes a member of the major facilitator superfamily, interferes with arabinose accumulation and induction of the Escherichia coli arabinose PBAD promoter

Induction of genes expressed from the arabinose PBAD promoter is very rapid and maximal at low arabinose concentrations. We describe here two mutations that interfere with the expression of genes cloned under arabinose control. Both mutations map to the ydeA promoter and stimulate ydeA transcription; overexpression of YdeA from a multicopy plasmid confers the same phenotype. One mutation is a large deletion that creates a more efficient -35 region (ATCACA changed to TTCACA), whereas the other affects the initiation site (TTTT changed to TGTT). The ydeA gene is expressed at extremely low levels in exponentially growing wild-type cells and is not induced by arabinose. Disruption of ydeA has no detectable effect on cell growth. Thus, ydeA appears to be nonessential under usual laboratory growth conditions. The ydeA gene encodes a membrane protein with 12 putative transmembrane segments. YdeA belongs to the largest family of bacterial secondary active transporters, the major facilitator superfamily, which includes antibiotic resistance exporters, Lac permease, and the nonessential AraJ protein. Intracellular accumulation of arabinose is strongly decreased in mutant strains overexpressing YdeA, suggesting that YdeA facilitates arabinose export. Consistent with this interpretation, very high arabinose concentrations can compensate for the negative effect of ydeA transcriptional activation. Our studies (i) indicate that YdeA, when transcriptionally activated, contributes to the control of the arabinose regulon and (ii) demonstrate a new way to modulate the kinetics of induction of cloned genes.

Adenovirus-mediated delivery of a uPA/uPAR antagonist suppresses angiogenesis-dependent tumor growth and dissemination in mice

AdmATF is a recombinant adenovirus encoding a secreted version of the amino-terminal fragment (ATF) of murine urokinase (uPA). This defective adenovirus was used in three murine models to assess the antitumoral effects associated with local or systemic delivery of ATF, a broad cell invasion inhibitor that antagonizes uPA binding to its cell surface receptor (uPAR). A single intratumoral injection of AdmATF into pre-established MDA-MB-231 human breast xenografts grown in athymic mice, or into pre-established C57/BL6 syngeneic Lewis lung carcinoma resulted in a specific arrest of tumor growth. Neovascularization within and at the vicinity of the injection site was also suppressed, suggesting that AdmATF inhibited primary tumor growth by targeting angiogenesis. AdmATF also interfered with tumor cell establishment at distant sites: (1) lung dissemination of Lewis lung carcinoma cells was significantly reduced following intratumoral injection at the primary site; and (2) systemic administration of AdmATF inhibited subsequent liver metastasis in a LS174T human colon carcinoma xenograft model. These data outline the potential of using a recombinant adenovirus directing the secretion of an antagonist of cell-associated uPA for cancer gene therapy.

Binding of human urokinase-type plasminogen activator to its receptor: residues involved in species specificity and binding

Urokinase-type plasminogen activator (UPA), particularly when bound to its receptor (UPAR), is thought to play a major role in local proteolytic processes, thus facilitating cell migration as may occur during angiogenesis, neointima and atherosclerotic plaque formation, and tumor cell invasion. To facilitate understanding of the need and function of the UPA/UPAR interaction in cell migration and vascular remodeling, we changed several amino acid residues in UPA so as to interfere with its interaction with its receptor. The receptor-binding domain of UPA has been localized to a region in the growth factor domain between residues 20 and 32. Since the binding of UPA to UPAR appears to be species specific, we used the differences in amino acid sequences in the growth factor domain of UPA between various species to construct a human UPA variant that does not bind to the human UPAR. We substituted Asn22 for its mouse equivalent Tyr by site-directed mutagenesis. This mutant UPA had similar plasminogen activator characteristics as wild-type UPA, including its specific activity and interaction with plasminogen activator inhibitor-1. However, no UPA/UPAR complexes could be observed in cross-linking experiments using DFP-treated 125I-labeled mutant UPA and lysates of various cells, including U937 histiocytic lymphoma cells, phorbol myristate acetate-treated human ECs, and mouse LB6 cells transfected with human UPAR cDNA. In direct binding experiments, DFP-treated 125I-labeled mutant UPA could not bind to phorbol myristate acetate-treated ECs, whereas wild-type UPA did bind. Furthermore, a 25-fold excess of wild-type UPA completely prevented the binding of DFP-treated 125I-labeled wild-type UPA to the human receptor on transfected LB6 cells, whereas an equal amount of mutant UPA had only a very small effect. In ligand blotting assays, very weak binding of mutant UPA to human UPAR could be observed. Changing Asn22 into the other amino acid residues alanine or glutamine had no effect on binding to UPAR on human ECs. The functional integrity of the growth factor domain in the non-receptor binding Asn22Tyr mutant is suggested by the fact that binding of this mutant to a murine UPAR can be restored after additional mutations in the growth factor domain, Asn27,His29,Trp30 to Arg27,Arg29,Arg30. We conclude that Asn22 and Asn27,His29,Trp30 in human UPA are key determinants in the species-specific binding of the enzyme to its receptor and that changing Asn22 into Tyr results in a UPA mutant with strongly reduced binding to UPAR.

Soluble form of complement C3b/C4b receptor (CR1) results from a proteolytic cleavage in the C-terminal region of CR1 transmembrane domain

The complement C3b/C4b receptor (CR1) is an integral protein, anchored in the plasma membrane through a hydrophobic domain of 25 amino acids, but is also found in the plasma in soluble form (sCR1). A recombinant, soluble form of CR1 has been demonstrated to reduce complement-dependent tissue injury in animal models of ischaemia/reperfusion. In view of the important pathophysiological relevance of sCR1, we have investigated the mechanisms governing CR1 release by using various mutated and chimaeric receptors transiently expressed in COS cells. Pulse-chase experiments revealed that (1) sCR1 is produced by a proteolytic process, (2) the cleavage site lies within the C-terminus of CR1 transmembrane domain, (3) the proteolytic process involves a fully glycosylated CR1 form and (4) this process takes place in late secretory vesicles or at the plasma membrane.

Regulation of Escherichia coli cell envelope proteins involved in protein folding and degradation by the Cpx two-component system

We show that the two-component signal transduction system of Escherichia coli, CpxA-CpxR, controls the expression of genes encoding cell envelope proteins involved in protein folding and degradation. These findings are based on three lines of evidence. First, activation of the Cpx pathway induces 5- to 10-fold the synthesis of DsbA, required for disulfide bond formation, and DegP, a major periplasmic protease. Second, using electrophoretic mobility shift and DNase I protection assays, we have shown that phosphorylated CpxR binds to elements upstream of the transcription start sites of dsbA, degP, and ppiA (rotA), the latter coding for a peptidyl-prolyl cis/trans isomerase. Third, we have demonstrated increased in vivo transcription of all three genes, dsbA, degP, and ppiA, when the Cpx pathway is activated. We have identified a putative CpxR consensus binding site that is found upstream of a number of other E. coli genes. These findings suggest a potentially extensive Cpx regulon including genes transcribed by sigma70 and sigma(E), which encode factors involved in protein folding as well as other cellular functions.

In vivo antisense oligodeoxynucleotide mapping reveals masked regulatory elements in an mRNA dormant in mouse oocytes

In mouse oocytes, tissue-type plasminogen activator (tPA) mRNA is under translational control. The newly transcribed mRNA undergoes deadenylation and translational silencing in growing oocytes, while readenylation and translation occur during meiotic maturation. To localize regulatory elements controlling tPA mRNA expression, we identified regions of the endogenous transcript protected from hybridization with injected antisense oligodeoxynucleotides. Most of the targeted sequences in either the 5' untranslated region (5'UTR), coding region, or 3'UTR were accessible to hybridization, as revealed by inhibition of tPA synthesis and by RNase protection. Two protected regions were identified in the 3'UTR of tPA mRNA in primary oocytes: the adenylation control element (ACE) and the AAUAAA polyadenylation signal. These sequences were previously shown to be involved in the translational control of injected reporter transcripts. During the first hour of meiotic maturation, part of the ACE and the AAUAAA hexanucleotide became accessible to hybridization, suggesting a partial unmasking of the 3'UTR of this mRNA before it becomes translationally competent. Our results demonstrate that in vivo antisense oligodeoxynucleotide mapping can reveal the dynamics of regulatory features of a native mRNA in the context of the intact cell. They suggest that specific regions in the 3'UTR of tPA mRNA function as cis-acting masking determinants involved in the silencing of tPA mRNA in primary oocytes.

The use of RNA probes for the analysis of gene expression

The monomeric bacteriophage RNA polymerases allow the synthesis of virtually any RNA molecule in unlimited quantity. In this protocol, we describe the preparation of plasmid and PCR-derived templates. A basic transcription protocol is provided with several optional modifications. The use of RNA probes in Northern blot hybridization and in RNase protection assays is described. The relative advantages and pitfalls of these two methods to quantitatively detect mRNA targets are discussed.

Detection of polymorphisms in the human urokinase-type plasminogen activator gene

Expressed polymorphisms in the genes encoding components of the fibrinolytic cascade could have implications for the predisposition to thrombolytic disorders and/or for tumor metastasis. The occurrence of published two amino acid sequences at position 194 of the human urokinase-type plasminogen activator prompted us to search by SSCP for frequent polymorphisms in several exons of the gene. Surprisingly, only one sequence was detected in codon 194 (> 200 alleles). Two polymorphisms were observed in this study: the most frequent one, a C to T change near the beginning of exon 8, is probably silent; a less frequent polymorphism results in the replacement of a Leu residue by a Pro, in the kringle domain.

prl mutations in the Escherichia coli secG gene

SecG, an integral membrane component of the Escherichia coli preprotein translocase, contributes to the efficiency of the export process by undergoing cycles of topology inversion in the membrane, coupled with the insertion-deinsertion cycles of SecA. We have previously identified sec alleles of secG that cause a generalized secretion defect. In this study, by screening mutagenized secG libraries for suppressors of a malE signal sequence mutation, we isolated prl alleles of secG. By analogy with secY/prlA, secA/prlD, and secE/prlG, secG could therefore be called secG/prlH. The prlH mutations affect 13 codons distributed along the secG sequence, and none map to the codons affected by sec mutations. prlH suppressors suppress a variety of signal sequence mutations and they allow export of alkaline phosphatase lacking its entire signal sequence. Although secG was not identified in previous selections for prl mutants, several prlH alleles are as strong as the strongest known prlG alleles of secE. Some prlH alleles can also promote the export of alkaline phosphatase fused to predicted cytoplasmic domains of UhpT, an integral membrane protein. These results support the notion that SecG contributes to signal sequence recognition, and suggest that it may also contribute to the topology of integral membrane proteins.

Plasminogen activator inhibitor-1 in acute hyperoxic mouse lung injury

Hyperoxia-induced lung disease is associated with prominent intraalveolar fibrin deposition. Fibrin turnover is tightly regulated by the concerted action of proteases and antiproteases, and inhibition of plasmin-mediated proteolysis could account for fibrin accumulation in lung alveoli. We show here that lungs of mice exposed to hyperoxia overproduce plasminogen activator inhibitor-1 (PAI-1), and that PAI-1 upregulation impairs fibrinolytic activity in the alveolar compartment. To explore whether increased PAI-1 production is a causal or only a correlative event for impaired intraalveolar fibrinolysis and the development of hyaline membrane disease, we studied mice genetically deficient in PAI-1. We found that these mice fail to develop intraalveolar fibrin deposits in response to hyperoxia and that they are more resistant to the lethal effects of hyperoxic stress. These observations provide clear and novel evidence for the pathogenic contribution of PAI-1 in the development of hyaline membrane disease. They identify PAI-1 as a major deleterious mediator of hyperoxic lung injury.

An in vivo pathway for disulfide bond isomerization in Escherichia coli

Biochemical studies have shown that the periplasmic protein disulfide oxidoreductase DsbC can isomerize aberrant disulfide bonds. Here we present the first evidence for an in vivo role of DsbC in disulfide bond isomerization. Furthermore, our data suggest that the enzymes DsbA and DsbC play distinct roles in the cell in disulfide bond formation and isomerization, respectively. We have shown that mutants in dsbC display a defect in disulfide bond formation specific for proteins with multiple disulfide bonds. The defect can be complemented by the addition of reduced dithiothreitol to the medium, suggesting that absence of DsbC results in accumulation of misoxidized proteins. Mutations in the dipZ and trxA genes have similar phenotypes. We propose that DipZ, a cytoplasmic membrane protein with a thioredoxin-like domain, and thioredoxin, the product of the trxA gene, are components of a pathway for maintaining DsbC active as a protein disulfide bond isomerase.

A two-step recognition of signal sequences determines the translocation efficiency of proteins

The cytosolic and secreted, N-glycosylated, forms of plasminogen activator inhibitor-2 (PAI-2) are generated by facultative translocation. To study the molecular events that result in the bi-topological distribution of proteins, we determined in vitro the capacities of several signal sequences to bind the signal recognition particle (SRP) during targeting, and to promote vectorial transport of murine PAI-2 (mPAI-2). Interestingly, the six signal sequences we compared (mPAI-2 and three mutated derivatives thereof, ovalbumin and preprolactin) were found to have the differential activities in the two events. For example, the mPAI-2 signal sequence first binds SRP with moderate efficiency and secondly promotes the vectorial transport of only a fraction of the SRP-bound nascent chains. Our results provide evidence that the translocation efficiency of proteins can be controlled by the recognition of their signal sequences at two steps: during SRP-mediated targeting and during formation of a committed translocation complex. This second recognition may occur at several time points during the insertion/translocation step. In conclusion, signal sequences have a more complex structure than previously anticipated, allowing for multiple and independent interactions with the translocation machinery.

A new genetic selection identifies essential residues in SecG, a component of the Escherichia coli protein export machinery

The signal sequence of the murine serine protease inhibitor PAI-2 promotes alkaline phosphatase export to the E. coli periplasm. However, high level expression of this chimeric protein interferes with cell growth. Since most suppressors of this toxic phenotype map to secA and secY, growth arrest results from a defective interaction of the chimeric protein with the export machinery. We have characterized suppressors which map in secG, a newly defined gene of the export machinery. All single amino acid substitutions map to three adjacent codons. These secG mutants have a weak Sec phenotype, as determined by their effect on export mediated by wild-type and mutant signal sequences. Whilst a secG disruption allele also confers a weak Sec phenotype, it does not suppress the toxicity of the chimeric protein. This difference results from a selective effect of the secG suppressors on the kinetics of export mediated by the PAI-2 signal sequence. Using a malE signal sequence mutant, which has a Mal-phenotype in secG mutant strains, we have isolated extragenic Mal+ suppressors. Most suppressors map to secY, and several are allele-specific. Finally, SecG overexpression accelerates the kinetics of protein export, suggesting that there are two types of functional translocation complexes: with or without SecG.

Tight regulation, modulation, and high-level expression by vectors containing the arabinose PBAD promoter

We have constructed a series of plasmid vectors (pBAD vectors) containing the PBAD promoter of the araBAD (arabinose) operon and the gene encoding the positive and negative regulator of this promoter, araC. Using the phoA gene and phoA fusions to monitor expression in these vectors, we show that the ratio of induction/repression can be 1,200-fold, compared with 50-fold for PTAC-based vectors. phoA expression can be modulated over a wide range of inducer (arabinose) concentrations and reduced to extremely low levels by the presence of glucose, which represses expression. Also, the kinetics of induction and repression are very rapid and significantly affected by the ara allele in the host strain. Thus, the use of this system which can be efficiently and rapidly turned on and off allows the study of important aspects of bacterial physiology in a very simple manner and without changes of temperature. We have exploited the tight regulation of the PBAD promoter to study the phenotypes of null mutations of essential genes and explored the use of pBAD vectors as an expression system.

The A985G mutation in the medium-chain acyl-CoA dehydrogenase gene: high prevalence in the Swiss population resident in Geneva

We have determined the frequency of the A985G mutation in the medium-chain acyl-CoA dehydrogenase (MCAD) gene in a cohort of 1142 healthy babies born in two Geneva hospitals. Among babies with at least one Swiss parent, heterozygotes were detected at a frequency of 1/52, with a 95% confidence range from 1/82 to 1/38. The high frequency of the carrier state for this mutation suggests that MCAD-deficient babies are born with a frequency of 1/10,000 in the Swiss population. This number is in sharp contrast with the low number of symptomatic MCAD-deficient patients diagnosed in this country. Thus, the fraction of homozygotes who remain asymptomatic is likely to be very high in the Swiss population, and possibly higher than in other countries of northern Europe.

Urokinase and type I plasminogen activator inhibitor production by normal human hepatocytes: modulation by inflammatory agents

We examined the effects of inflammatory cytokines (interleukin-1 beta, tumor necrosis factor-alpha and transforming growth factor-beta) on the plasminogen activator system (urokinase, tissue-type plasminogen activator, type 1 plasminogen activator inhibitor) in primary cultures of human hepatocytes. We show that interleukin-1 beta and tumor necrosis factor-alpha increase urokinase-type plasminogen activator production, reinforcing the concept that increased urokinase production is associated with inflammatory processes. By contrast, the same agents (i.e., interleukin-1 beta and tumor necrosis factor-alpha) do not stimulate plasminogen activator inhibitor type 1 production. This latter observation rules out hepatocytes as a major cellular source of plasmatic plasminogen activator inhibitor type 1 during acute-phase-related responses. Among the inflammatory agents used, transforming growth factor-beta was found to be the most effective modulator of both urokinase-type plasminogen activator and plasminogen activator inhibitor type 1, inducing severalfold increases of activity of urokinase-type plasminogen activator, antigen and the corresponding mRNA and increasing plasminogen activator inhibitor type 1 antigen and mRNA levels. Urokinase-type plasminogen activator and plasminogen activator inhibitor type 1 modulation by transforming growth factor-beta may play a critical role in hepatic pathophysiology.

Mutations that allow disulfide bond formation in the cytoplasm of Escherichia coli

Disulfide bonds are rarely found in cytoplasmic proteins. Mutations were selected for in Escherichia coli that allow disulfide bond formation in the cytoplasm. In the presence of these mutations, export-defective versions of alkaline phosphatase and mouse urokinase were able to fold into their enzymatically active conformations in the cytoplasm because their disulfide bonds were formed. The mutations were mapped to the gene for thioredoxin reductase and diminish or eliminate the activity of this enzyme. Thioredoxin itself was found to be unnecessary for this disulfide bond formation. Thioredoxin reductase, but not thioredoxin, is thus implicated in keeping cysteines reduced in cytoplasmic proteins.

Murine clusterin: molecular cloning and mRNA localization of a gene associated with epithelial differentiation processes during embryogenesis

Clusterin is a broadly distributed glycoprotein constitutively expressed by various tissues and cell types, that has been shown to be involved in cell-cell adhesion and expressed during cellular differentiation in vitro. To assess the suggested participation of clusterin in these processes in vivo, we have cloned the cDNA encoding murine clusterin and studied the cellular distribution of clusterin mRNA during murine embryogenesis. Sequence analysis of the cDNA encoding murine clusterin revealed 92 and 75% sequence identity with the rat and human cDNAs, respectively, and conservation of the predicted structural features which include alpha-helical regions and heparin-binding domains. From 12.5 d of development onwards, the clusterin gene is widely expressed in developing epithelia, and selectively localized within the differentiating cell layers of tissues such as the developing skin, tooth, and duodenum where proliferating and differentiating compartments are readily distinguished. In addition, transient and localized clusterin gene expression was detected in certain morphogenetically active epithelia. In the lung, abundant gene transcripts were detected in cuboidal epithelial cells of the terminal lung buds during branching morphogenesis, and in the kidney, clusterin gene expression in the epithelial cells of comma and S-shaped bodies coincided with the process of polarization. Our results demonstrate the in vivo expression of the clusterin gene by differentiating epithelial cells during murine embryogenesis, and provide novel evidence suggesting that clusterin may be involved in the differentiation and morphogenesis of certain epithelia.

Intracellular Ca2+ and the regulation of early response gene expression in HL-60 myeloid leukemia cells

To gain direct insight into the action of the second messenger Ca2+ on transcriptional regulation, we have developed an intact cell model in which the intracellular free Ca2+ concentration ([Ca2+]i) can be measured, set, and varied at any level within the physiological range and in which the expression of early response genes is assayed in parallel. Using promyelocytic HL-60 cells, we have observed an exquisite sensitivity to Ca2+ of c-fos, c-jun, and zif268 mRNA accumulation, since early and maximal inductions were observed at 200-300 nM [Ca2+]i. At early times (10-20 min), the [Ca2+]i dose dependence of c-fos transcription and mRNA accumulation displayed a bell shape since c-fos expression was barely modified at high (700-1,250 nM) [Ca2+]i. The threshold [Ca2+]i concentration for prolonged (60 min) c-fos mRNA accumulation was greater than 200 nM. This indicates that the quantitative effects of Ca2+ on a given gene can vary markedly as a function of both the [Ca2+]i concentration and the duration of stimulation. Strikingly, a [Ca2+]i perturbation of only 1 min was sufficient for full induction of c-fos and zif268 transcripts. This demonstrates that a transient perturbation of [Ca2+]i has long term effects on gene expression. The half-life of c-fos mRNA (16 min) was unaltered by Ca2+. Nuclear run-on analysis of the distribution of RNA polymerase II along the c-fos locus indicated that Ca2+ promotes a small increase in transcriptional initiation and a pronounced relief of a block to transcriptional elongation beyond intron 1. The extreme sensitivity to [Ca2+]i, in terms of both the length of time and the dose of [Ca2+]i required for maximal gene induction, demonstrates that Ca2+ is a major physiological regulator of early response gene expression. In addition, the results indicate that a c-fos intragenic element is the main target of Ca(2+)-regulated transcriptional activation.

Extracellular proteolysis in the adult murine brain

Plasminogen activators are important mediators of extracellular metabolism. In the nervous system, plasminogen activators are thought to be involved in the remodeling events required for cell migration during development and regeneration. We have now explored the expression of the plasminogen activator/plasmin system in the adult murine central nervous system. Tissue-type plasminogen activator is synthesized by neurons of most brain regions, while prominent tissue-type plasminogen activator-catalyzed proteolysis is restricted to discrete areas, in particular within the hippocampus and hypothalamus. Our observations indicate that tissue-type plasminogen activator-catalyzed proteolysis in neural tissues is not limited to ontogeny, but may also contribute to adult central nervous system physiology, for instance by influencing neuronal plasticity and synaptic reorganization. The identification of an extracellular proteolytic system active in the adult central nervous system may also help gain insights into the pathogeny of neurodegenerative disorders associated with extracellular protein deposition.

Involvement of the plasminogen activator/plasmin proteolytic cascade in fertilization

At the time of fertilization both murine gametes express plasminogen-dependent proteolytic activity: unfertilized eggs secrete tissue-type plasminogen activator and ejaculated spermatozoa have urokinase-type plasminogen activator bound to their surface. We now report that plasminogen is present in the fertilization environment and that both spermatozoa and eggs are able to specifically bind plasminogen. Furthermore, in vitro fertilization of mouse eggs is inhibited by antibodies which inhibit the catalytic activity of plasmin. Finally, with two different in vitro fertilization protocols, the addition of plasminogen to the fertilization medium increases the yield of fertilized eggs. These results provide evidence for a role of the plasminogen activator/plasmin proteolytic cascade in mammalian fertilization.

Protease-nexin I as an androgen-dependent secretory product of the murine seminal vesicle

A search for inhibitors of urokinase-type plasminogen activator (uPA) in the male and female murine genital tracts revealed high levels of a uPA ligand in the seminal vesicle. This ligand is functionally, biochemically and immunologically indistinguishable from protease-nexin I (PN-I), a serpin ligand of thrombin and uPA previously detected only in mesenchymal cells and astrocytes. A survey of murine tissues indicates that PN-I mRNA is most abundant in seminal vesicles, where it represents 0.2-0.4% of the mRNAs. PN-I is synthesized in the epithelium of the seminal vesicle, as determined by in situ hybridization, and is secreted in the lumen of the gland. PN-I levels are much lower in immature animals, and strongly decreased upon castration. Testosterone treatment of castrated males rapidly restores PN-I mRNA levels, indicating that PN-I gene expression is under androgen control.

A pathway for disulfide bond formation in vivo

Protein disulfide bond formation in Escherichia coli requires the periplasmic protein DsbA. We describe here mutations in the gene for a second protein, DsbB, which is also necessary for disulfide bond formation. Evidence suggests that DsbB may act by reoxidizing DsbA, thereby regenerating its ability to donate its disulfide bond to target proteins. We propose that DsbB, an integral membrane protein, may be involved in transducing redox potential across the cytoplasmic membrane.

Expression of a tumor necrosis factor alpha transgene in murine pancreatic beta cells results in severe and permanent insulitis without evolution towards diabetes

Mice bearing a tumor necrosis factor (TNF) alpha transgene controlled by an insulin promoter developed an increasingly severe lymphocytic insulitis, apparently resulting from the induction of endothelial changes with features similar to those observed in other places of intense lymphocytic traffic. This was accompanied by dissociation of the endocrine tissue (without marked decrease in its total mass), islet fibrosis, and the development of intraislet ductules containing, by places, beta cells in their walls, suggesting a regenerative capacity. Islet disorganization and fibrosis did not result from lymphocytic infiltration, since they were also observed in SCID mice bearing the transgene. Diabetes never developed, even though a number of potentially inducing conditions were used, including the prolonged perfusion of interferon gamma and the permanent expression of a nontolerogenic viral protein on beta cells (obtained by using mice bearing two transgenes). It is concluded that (a) a slow process of TNF release in pancreatic islets induces insulitis, and may be instrumental in the insulitis resulting from local cell-mediated immune reactions, but (b) that insulitis per se is not diabetogenic, lymphocyte stimulation by cells other than beta cells being necessary to trigger extensive beta cell damage. This provides an explanation for the discrepancy between the occurrence of insulitis and that of clinical disease in autoimmune diabetes.