Imprinted Rasgrf1 expression in neonatal mice affects olfactory learning and memory

Rasgrf1 is genomically imprinted; only the paternally inherited allele is expressed in the neonatal mouse brain until weaning, at which time expression becomes biallelic. Whereas Rasgrf1 has been implicated in learning and memory via knockout studies in adult mice, the effect of its normal imprinted expression on these phenotypes has not yet been examined. Neonatal mice with experimentally manipulated patterns of imprinted Rasgrf1 expression were assessed on an associative olfactory task. Neonates lacking the normally expressed wild-type paternal allele exhibited significant impairment in olfactory associative memory. Adult animals in which neonatal imprinting had been manipulated were also behaviorally assessed; while neonatal imprinting significantly affects body weight even into adulthood, no learning and memory phenotype attributable to imprinting was observed in adults. Additional analyses of neonates showed imprinted Rasgrf1 transcript selective to olfactory bulb even in mice that were null for Rasgrf1 in the rest of the brain and showed that Rasgrf1 affects Ras and Rac activation in the brain. Taken together, these results indicate that Rasgrf1 expression from the wild-type paternal allele contributes to learning and memory in neonatal mice.

Mouse embryonic stem cells that express a NUP98-HOXD13 fusion protein are impaired in their ability to differentiate and can be complemented by BCR-ABL

NUP98-HOXD13 (NHD13) fusions have been identified in patients with myelodysplastic syndrome, acute myelogenous leukemia and chronic myeloid leukemia blast crisis. We generated 'knock-in' mouse embryonic stem (ES) cells that express a NHD13 fusion gene from the endogenous murine NUP98 promoter, and used an in vitro differentiation system to differentiate the ES cells to hematopoietic colonies. Replating assays demonstrated that the partially differentiated NHD13 ES cells were immortal, and two of these cultures were transferred to liquid culture. These cell lines are partially differentiated immature hematopoietic cells, as determined by morphology, immunophenotype and gene expression profile. Despite these characteristics, they were unable to differentiate when exposed to high concentrations of erythropoietin (Epo), granulocyte colony-stimulating factor or macrophage colony-stimulating factor. The cell lines are incompletely transformed, as evidenced by their dependence on interleukin 3 (IL-3), and their failure to initiate tumors when injected into immunodeficient mice. We attempted genetic complementation of the NHD13 gene using IL-3 independence and tumorigenicity in immunodeficient mice as markers of transformation, and found that BCR-ABL successfully transformed the cell lines. These findings support the hypothesis that expression of a NHD13 fusion gene impairs hematopoietic differentiation, and that these cell lines present a model system to study the nature of this impaired differentiation.

Regulation of imprinted DNA methylation

DNA methylation is an essential enzymatic modification in mammals. This common epigenetic mark occurs predominantly at the fifth carbon of cytosines within the palindromic dinucleotide 5'-CpG-3'. The majority of methylated CpGs are located within repetitive elements including centromeric repeats, satellite sequences and gene repeats encoding ribosomal RNAs. CpG islands, frequently located at the 5' end of genes, are typically unmethylated. DNA methylation also occurs at imprinted genes which exhibit parent-of-origin-specific patterns of methylation and expression. Imprinted methylation at differentially methylated domains (DMDs) is one of the regulatory mechanisms controlling the allele-specific expression of imprinted genes. Proper control of DNA methylation is needed for normal development and loss of methylation control can contribute to initiation and progression of tumorigenesis (reviewed in Plass and Soloway, 2002). Because patterns of imprinted DNA methylation are highly reproducible, imprinted loci make useful models for studying regulation of DNA methylation and may provide insights into how this regulation goes awry in cancer. Here, we review what is currently known about the mechanisms regulating imprinted DNA methylation. We will focus on cis-acting DNA sequences, trans-acting protein factors and the possible involvement of RNAs in control of imprinted DNA methylation.

Regulation of hepatic fibrosis and extracellular matrix genes by the th response: new insight into the role of tissue inhibitors of matrix metalloproteinases

Hepatic fibrosis is the hallmark of Schistosoma mansoni infection and often results in portal hypertension and bleeding from esophageal varices. The fibrotic process is highly dependent on type 2 cytokines, yet their role in the regulation of extracellular matrix remodeling genes remains largely unknown. Here, we examined the expression of matrix metalloproteases (MMP) -2, -3, -9, -12, and -13 and their inhibitors, tissue inhibitor of metalloproteases (TIMP) -1, -2, and -3, in the livers of infected mice and correlated their expression profiles with fibrosis and type 2 cytokine production. Expression of MMP-2, -3, -9, -12, and -13 and of TIMP-1 and -2 mRNA rapidly increased at the onset of egg laying in infected mice, while TIMP-3 was unchanged. Because TIMP are presumed to be important regulators of the extracellular matrix, and their expression correlated with the development of fibrosis, we studied their role in fibrogenesis by infecting TIMP-1- and TIMP-2-deficient mice. Strikingly, our data revealed no role for TIMP-1 or -2 in the fibrotic pathology induced by S. mansoni eggs. Because of these findings, we infected IL-10/IFN-gamma-deficient mice that develop an exaggerated fibrotic response to determine whether changes in type 2 cytokine dominance influence the pattern of MMP and TIMP expression. Fibrosis and type 2 cytokine production correlated with increased MMP-2/MMP-9 vs TIMP-1/TIMP-2 expression. These data, in addition to our knockout studies, demonstrate that TIMP-1/TIMP-2 play no essential role in fibrogenesis in schistosomiasis. Indeed, our findings suggest that inhibiting profibrotic cytokines or specific MMP may be a more effective strategy to ameliorate fibrotic pathology.

Cellular activation of MMP-2 (gelatinase A) by MT2-MMP occurs via a TIMP-2-independent pathway

The role of membrane-type (MT) 2-matrix metalloproteinase (MMP) in the cellular activation of MMP-2 and the tissue inhibitor of matrix metalloproteinase (TIMP) requirements for this process have not been clearly established. To address these issues a TIMP-2-free cell line derived from a Timp2-/- mouse was transfected for stable cell surface expression of hMT2-MMP. Untransfected cells did not activate endogenous or exogenous TIMP-2-free MMP-2 unless both TIMP-2 and concanavalin A (ConA) were added. Transfected cells expressing hMT2-MMP efficiently activated both endogenous and exogenous MMP-2 (within 4 h) via the 68-kDa intermediate in the absence of TIMP-2 and ConA. In contrast, activation of MMP-2 by Timp2-/- cells expressing recombinant hMT1-MMP occurred more slowly (12 h) and required the addition of 0.3-27 nm TIMP-2. Addition of TIMP-2 or TIMP-4 did not enhance MMP-2 activation by MT2-MMP at any concentration tested; furthermore, activation was inhibited by both TIMPs at concentrations >9 nm, consistent with the similar association rate constants (k(on)) calculated for the binding of TIMP-4 and TIMP-2 to MT2-MMP (3.56 x 10(5) m(-1) s(-1) and 6.52 x 10(5) m(-1) s(-1), respectively). MT2-MMP-mediated activation involved cell surface association of the MMP-2 in a hemopexin carboxyl-terminal domain (C domain)-dependent manner: Exogenous MMP-2 hemopexin C domain blocked activation, and cells expressing hMT2-MMP did not bind or activate a truncated form of MMP-2 lacking the hemopexin C domain. These studies demonstrate the existence of an alternative TIMP-2-independent pathway for MMP-2 activation involving MT2-MMP, which may be important in mediating MMP-2 activation in specific tissues or pathologies where MT2-MMP is expressed.

Inactivation of the murine pyruvate dehydrogenase (Pdha1) gene and its effect on early embryonic development

A deficiency of pyruvate dehydrogenase complex (PDC) in humans results in lactic acidosis and neurological dysfunction that frequently results in death during infancy. Using gene targeting technology, a silent mutation was introduced into the murine X-linked Pdha1 gene that encodes the alpha subunit of the pyruvate dehydrogenase or E1 component of the complex. Two loxP sequences were introduced into intronic sequences flanking exon 8 to generate the Pdha1(flox8) allele. In vitro studies in embryonic stem cells demonstrated that deletion of exon 8 ablated PDC activity. Homozygous Pdha1(flox8) females were bred with male mice carrying a wild-type Pdha1 allele and a transgene that ubiquitously expresses the Cre recombinase to produce progeny with a deletion in exon 8, Pdha1(Deltaex8). The majority of progeny were found to be mosaic with the presence of both the flox and deleted alleles, and there were no apparent phenotypic effects associated with the null allele. The mosaic mice were interbred to increase the degree of mosaicism for the Pdha1(Deltaex8) allele in the subsequent generation, resulting in a significantly smaller litter size (54% reduction). Embryos carrying predominantly the Pdha1(Deltaex8) allele were found to be globally delayed in development by 9.5 days postcoitus, with resorption occurring over the following several days. These findings demonstrate an essential role for oxidative metabolism of glucose during the early postimplantation period of prenatal development.

MMP inhibitors augment fibroblast adhesion through stabilization of focal adhesion contacts and up-regulation of cadherin function

Increased pericellular proteolysis due to an imbalance between MMPs (matrix metalloproteinases) and TIMPs (tissue inhibitors of metalloproteinases) promotes early stages of tumorigenesis. We have reported that TIMP-1 down-regulation confers tumorigenicity on immortal Swiss 3T3 fibroblasts. In pursuit of the mechanism involved in this transformation, we asked whether MMP inhibitors modulate contact inhibition and cell adhesion, because the dysregulation of these events is essential for cellular transformation. Using both genetic and biochemical means, we demonstrate that MMP inhibitors regulate fibroblast cell adhesion. TIMP-1 down-regulated cells formed dense, multilayered colonies, suggesting a loss of contact inhibition. Recombinant TIMP-1 and synthetic MMP inhibitors (MMPi) restored normal cell contact and density of these cells in a dose-dependent manner. Consequently, the effect of MMPi on both cell-extracellular matrix (ECM) and cell-cell adhesion were investigated. Upon MMPi treatment, p125(FAK) was redistributed, together with vinculin, to points of cell-ECM contact. Furthermore, phosphorylation of p125(FAK) was restored to levels similar to that of wild type. In parallel, MMPi treatment increased cadherin levels and stabilized cadherin-mediated cell-cell contacts. Moreover, enhanced cadherin function was evident as increased calcium-dependent cell-cell aggregation and co-localization of cadherin and beta-catenin at the cell membrane. We also obtained independent evidence of altered cadherin function using timp-1(-/-) mouse embryonic fibroblasts. Our data provide provocative evidence that increased pericellular proteolysis impacts cell adhesion systems to offset normal contact inhibition, with subsequent effects on cell transformation and tumorigenesis.

Tissue inhibitor of metalloproteinases-4 inhibits but does not support the activation of gelatinase A via efficient inhibition of membrane type 1-matrix metalloproteinase

The tissue inhibitors of metalloproteinases 1-4 (TIMPs) have discrete regulatory roles in the activation of matrix metalloproteinase (MMP)-2 (gelatinase A), an important basement membrane-degrading MMP pivotal to tumor metastasis and angiogenesis. TIMP-2 binds to both the hemopexin C domain of progelatinase A and the active site of membrane type-1 (MT1) MMP. This trimeric complex presents the cell surface-bound gelatinase A zymogen to a free MT1-MMP molecule for activation. To investigate the role of TIMP-4 in the activation process, we developed a new procedure for the expression and purification of recombinant human TIMP-4 from baby hamster kidney cells. The recombinant TIMP-4 was a potent inhibitor of gelatinase A (apparent K(i) [Ki(app.)] < or = 9 pM; k(on) (association rate constant), 4.57 +/- 0.13 x 10(6) M(-1)s(-1)) and was less dependent upon hemopexin C domain interactions than TIMP-2 in its mode of binding and inhibition. Unlike TIMP-1, TIMP-4 strongly inhibited MT1-MMP (Ki(app.) < or = 100 pM; k(on), 3.49 +/- 0.34 x 10(6) M(-1)s(-1)) and blocked the concanavalin A-induced cellular activation of progelatinase A. In concanavalin A-stimulated homozygous Timp2 -/- fibroblasts or unstimulated MT1-MMP-transfected Timp2 -/- cells, which cannot activate progelatinase A, activation was restored by the addition of 0.3-5 nM TIMP-2 but not by TIMP-4, unequivocally showing the TIMP-2 dependency of MT1-MMP-induced activation of gelatinase A and the fact that TIMP-4 cannot support activation. The dominance of TIMP-2 in the activation process was further supported by the preferential binding of TIMP-2 compared with TIMP-4 to the hemopexin C domain of progelatinase A in inhibitor mixtures and by the ability of TIMP-2 to displace TIMP-4 from the hemopexin C domain. Hence, TIMP-4 regulates gelatinase A activity by efficient inhibition of MT1-MMP-mediated activation and by inhibiting the activated enzyme and, thus, is a tumor resistance factor in the peritumor stroma.

Differential roles of TIMP-4 and TIMP-2 in pro-MMP-2 activation by MT1-MMP

The tissue inhibitors of metalloproteinases (TIMPs) are specific inhibitors of MMP enzymatic activity. However, TIMP-2 can promote the activation of pro-MMP-2 by MT1-MMP. This process is mediated by the formation of a complex between MT1-MMP, TIMP-2, and pro-MMP-2. Binding of TIMP-2 to active MT1-MMP also inhibits the autocatalytic turnover of MT1-MMP on the cell surface. Thus, under certain conditions, TIMP-2 is a positive regulator of MMP activity. TIMP-4, a close homologue of TIMP-2 also binds to pro-MMP-2 and can potentially participate in pro-MMP-2 activation. We coexpressed MT1-MMP with TIMP-4 and investigated its ability to support pro-MMP-2 activation. TIMP-4, unlike TIMP-2, does not promote pro-MMP-2 activation by MT1-MMP. However, TIMP-4 binds to MT1-MMP inhibiting its autocatalytic processing. When coexpressed with TIMP-2, TIMP-4 competitively reduced pro-MMP-2 activation by MT1-MMP. A balance between TIMP-2 and TIMP-4 may be a critical factor in determining the degradative potential of cells in normal and pathological conditions.

TIMP-1 promotes VEGF-induced neovascularization in the retina

Proteolysis of vascular basement membranes and surrounding extracellular matrix is a critical early step in neovascularization. It requires alteration of the balance between matrix metalloproteinases (MMPs) and proteins that bind to and inactivate MMPs, tissue inhibitors of metalloproteinases (TIMPs). TIMP-1 has been demonstrated to inhibit neovascularization in chick chorioallantoic membranes. However, TIMP-1 has also been shown to either promote or inhibit cell proliferation and migration in different settings. To determine whether genetic alteration of the MMP/TIMP-1 ratio would alter retinal neovascularization, we crossed mice that express vascular endothelial growth factor (VEGF) in photoreceptors with TIMP-1-deficient mice or mice that overexpress TIMP-1. Compared to VEGF transgene-positive/TIMP-1-sufficient mice, VEGF transgene-positive/TIMP-1-deficient mice showed smaller neovascular lesions. There was also no difference between the two groups of mice in the appearance of the neovascularization by light or electron microscopy. Compound VEGF/TIMP-1 transgenic mice had increased expression of both VEGF and TIMP-1 in the retina, and had more neovascularization than mice that had increased expression of VEGF alone. These gain- and loss-of-function data suggest that alteration of the TIMP-1/MMP ratio modulates retinal neovascularization in a complex manner and not simply by altering the proteolytic activity and thereby invasiveness of endothelial cells.

Tissue inhibitor of metalloproteinase (TIMP)-2 acts synergistically with synthetic matrix metalloproteinase (MMP) inhibitors but not with TIMP-4 to enhance the (Membrane type 1)-MMP-dependent activation of pro-MMP-2

The membrane-type 1 matrix metalloproteinase (MT1-MMP) has been shown to be a key enzyme in tumor angiogenesis and metastasis. MT1-MMP hydrolyzes a variety of extracellular matrix components and is a physiological activator of pro-MMP-2, another MMP involved in malignancy. Pro-MMP-2 activation by MT1-MMP involves the formation of an MT1-MMP.tissue inhibitors of metalloproteinases 2 (TIMP-2). pro-MMP-2 complex on the cell surface that promotes the hydrolysis of pro-MMP-2 by a neighboring TIMP-2-free MT1-MMP. The MT1-MMP. TIMP-2 complex also serves to reduce the intermolecular autocatalytic turnover of MT1-MMP, resulting in accumulation of active MT1-MMP (57 kDa) on the cell surface. Evidence shown here in Timp2-null cells demonstrates that pro-MMP-2 activation by MT1-MMP requires TIMP-2. In contrast, a C-terminally deleted TIMP-2 (Delta-TIMP-2), unable to form ternary complex, had no effect. However, Delta-TIMP-2 and certain synthetic MMP inhibitors, which inhibit MT1-MMP autocatalysis, can act synergistically with TIMP-2 in the promotion of pro-MMP-2 activation by MT1-MMP. In contrast, TIMP-4, an efficient MT1-MMP inhibitor, had no synergistic effect. These studies suggest that under certain conditions the pericellular activity of MT1-MMP in the presence of TIMP-2 can be modulated by synthetic and natural (TIMP-4) MMP inhibitors.

Interstitial fibrosis in mice with overload proteinuria: deficiency of TIMP-1 is not protective

BACKGROUND

Progressive renal interstitial fibrosis is characterized by up-regulated expression of the gene that encodes the tissue inhibitor of metalloproteinases-1 (TIMP-1), a regulator of extracellular matrix remodeling, suggesting that impaired matrix turnover contributes to the fibrogenic process. The present study was designed to develop a murine model of renal interstitial fibrosis, and to determine the functional significance of up-regulated Timp-1 expression by comparing the severity of this renal disease in wild-type mice and mice genetically deficient in Timp-1.

METHODS

Initial pilot studies developed and characterized a murine model of bovine serum albumin (BSA)-induced protein-overload proteinuria with respect to the degree of proteinuria, severity of interstitial fibrosis, and renal mRNA levels for genes encoding matrix proteins, transforming growth factor-beta1 (TGF-beta1), and TIMP-1, -2, -3, and -4. In the final study, the severity of interstitial fibrosis was compared in wild-type and Timp-1-deficient mice after six weeks of proteinuria.

RESULTS

Mice injected with large daily intraperitoneal doses of BSA developed proteinuria, interstitial inflammation, and progressive interstitial fibrosis. A time course study based on measurements after one, two, and six weeks of BSA injections showed increased renal mRNA levels for the matrix genes procollagens alpha1(I), alpha1(III), and alpha2(IV) and TGF-beta1 and Timp-1. Timp-2 and Timp-3 genes were constitutively expressed at high levels in the normal kidneys and showed little change in the proteinuric kidneys. Timp-4 transcripts were not detected in any of the kidneys. After six weeks of BSA overload-proteinuria, the groups (N = 8 per group) of wild-type and Timp-1-deficient mice developed significant interstitial fibrosis compared with the control saline-injected groups. The severity of the interstitial fibrosis was similar in both proteinuric groups based on an assessment of the final kidney weight, total kidney collagen content, and the number of interstitial fields with increased fibronectin staining.

CONCLUSIONS

Results of the present study indicate that TIMP-1 deficiency does not alter the degree of interstitial fibrosis in the murine overload proteinuria model. Potential explanations include Timp-1 genetic redundancy, as suggested by the observation that, despite significant intrarenal induction of the Timp-1 gene expression, net renal metalloproteinase-9 (MMP-9) activity was not significantly altered. TIMP-1 is a multifunctional protein that may play a metalloproteinase-independent role in response to renal injury.

Novel implications in the development of endometriosis: biphasic effect of macrophage activation on peritoneal tissue expression of tissue inhibitor of metalloproteinase-1

PROBLEM

Elevated levels of activated macrophages are associated with endometriosis, but their role in the etiology of the disease is uncertain. The current study was undertaken to examine whether activated macrophages could modulate peritoneal tissue expression of the tissue inhibitor of metalloproteinase-1 (TIMP-1), which may play a role in the development of endometriosis.

METHOD OF STUDY

Female mice were treated with the macrophage activator lipopolysaccharide (LPS), and peritoneum TIMP-1 mRNA was examined by Northern blot analysis.

RESULTS

LPS induced a dose-dependent increase (P < 0.05) in TIMP-1 mRNA expression at levels of 1 microgram (70.0% +/- 5.8% greater than the control), 10 micrograms (83.0% +/- 12.0% greater than the control), and 25 micrograms (100.0% +/- 10.0% greater than the control). In contrast, the administration of 50 micrograms of LPS resulted in a decrease in TIMP-1 mRNA expression below baseline levels (18.0% +/- 6.0% less than the control values).

CONCLUSIONS

Activated macrophages and/or their products modulate peritoneum TIMP-1 expression. These data suggest that, in addition to their phagocytotic role in the peritoneal cavity, these immune cells also may play a novel role in influencing the ability of the peritoneum to regulate tissue/cell invasion and in the development of endometriosis through TIMP-1 expression.

Pattern of messenger ribonucleic acid expression of tissue inhibitors of metalloproteinases (TIMPs) during testicular maturation in male mice lacking a functional TIMP-1 gene

It has been proposed that proteolytic remodeling of the testicular extracellular matrix (ECM) plays a fundamental role in testicular development, morphogenesis, and spermatogenesis. Tissue inhibitor of metalloproteinase (TIMP)-1 regulates ECM turnover and has been reported to stimulate Leydig cell steroidogenesis. To assess the developmental changes in TIMP mRNA expression and the potential steroidogenic role of TIMP-1 in testicular physiology, an experiment was conducted that used male mice incapable of expressing the TIMP-1 gene product. TIMP-1-deficient and wild-type male mice (n = 6 to 15 per age group per genotype) were killed at 18, 21, 24, 27, 33, 41, and 49 days of age. Body weight, testis weight, serum total testosterone, and TIMP-1, -2, -3, and -4 transcript expression were determined. Northern analysis revealed the detection of TIMP-1 mRNA in wild-type males only. TIMP-1 mRNA levels (per 20 microg total RNA) were highest in 18- to 27-day-old male mice and decreased approximately 13-fold by Day 41. The pattern of TIMP-2 expression was similar between genotypes, with testicular levels of the 1. 0-kilobase transcript increasing between Days 18 and 27 of age. The pattern of TIMP-3 transcript expression (per 20 microg total RNA) was similar between genotypes and decreased between Days 18 and 41 of age. When TIMP-3 mRNA levels were expressed on a per testis basis, TIMP-3 was seen to have increased throughout testicular development. TIMP-4 mRNA expression was undetectable by Northern analysis in all mice. No significant difference was detected in body weight or testis weight between genotypes, with the exceptions that 21-day-old TIMP-1 mutants had higher (p < 0.05) testis weights and lower (p < 0. 05) serum total testosterone levels than age-matched wild-type males. It is concluded that each TIMP displays its own unique pattern of expression during the prepubertal period, suggesting that the various TIMPs may have specific roles in testicular development. The modest effect of TIMP-1 ablation on testosterone is interpreted to mean that TIMP-1 may function as a coregulator of basal testicular steroidogenesis; but overall, TIMP-1 appears to have little effect on testosterone production in mice lacking the TIMP-1 gene.

Targeted mutagenesis of Timp-1 reveals that lung tumor invasion is influenced by Timp-1 genotype of the tumor but not by that of the host

Timp-1 has been implicated as a suppressor of tumor metastasis. To study the relative importance of Timp-1 expression by tumor vs host during tumor invasion, three pairs of co-isogenic, tumorigenic cells containing wild-type or mutant Timp-1 alleles were generated. These were used in experimental metastasis assays in wild-type or Timp-1-deficient mice. Timp-1 expression in tumorigenic cells could either increase or decrease tumor invasion of lungs in a tumor cell-specific manner. This suggests that depending on the tumor, Timp-1 can either suppress or potentiate metastasis. Mice deficient for Timp-1 were indistinguishable from wild-type mice in metastasis assays with all tumorigenic cells tested. Although Timp-1 is a secreted protein, and lung produces other Timps, the influence of Timp-1 on lung invasion by the tumorigenic cells tested is cell-autonomous, depending only on Timp-1 genotype of tumor and not that of host.

Nicotine and cotinine stimulate secretion of basic fibroblast growth factor and affect expression of matrix metalloproteinases in cultured human smooth muscle cells

PURPOSE

We have recently shown that nicotine and its metabolite cotinine are mitogenic for smooth muscle cells in vitro. In the present study, we examined the effect of nicotine and cotinine on the production of growth factors and the expression of matrix metallo-proteinases in smooth muscle cells.

METHODS

Smooth muscle cells were harvested from human arteries and grown in culture. Subconfluent cultures were incubated for 24 hours in M199 containing 0.1% fetal bovine serum with or without nicotine or cotinine at concentrations ranging from 10(-9) mol/L to 10(-6) mol/L. The supernatants and cell lysates were assayed by enzyme-linked immunosorbent assay for basic fibroblast growth factor (bFGF), tumor necrosis factor alpha (TNF-alpha), platelet-derived growth factor AB (PDGF-AB), and transforming growth factor beta (TGF-beta). Matrix metalloproteinase expression was determined in subconfluent cultures incubated in albumin with or without nicotine or cotinine at 10(-8) mol/L and 10(-7) mol/L for 6, 12, 18, 24 and 36 hours. Northern blot analyses were performed with human cDNA probes for collagenase-1, stromelysin-1, gelatinase A, gelatinase B, and triose phosphate isomerase. Blots were quantified by phosphor-imaging techniques.

RESULTS

Both nicotine and cotinine stimulated the production and secretion of bFGF in a dose-dependent manner. PDGF, TNF-alpha, and TGF-beta secretions were not significantly affected by nicotine or cotinine. Collagenase was up-regulated by nicotine at 18 and 24 hours (4.5-fold to 5.8-fold) and by cotinine at 18 hours (from 5.0-fold to 29-fold). Stromelysin-1 was up-regulated by nicotine and cotinine at 12 and 18 hours (1.5-fold to 7.0-fold). Gelatinase A generally peaked at 12 hours and was up-regulated by both agents (2.0-fold to 6.5-fold).

CONCLUSION

Nicotine and cotinine enhanced the production of bFGF, a major mitogen for smooth muscle cells, and up-regulated the expression of several matrix metalloproteinases that are critical in cell migration. These data demonstrate mechanisms by which smoking may contribute to the development of intimal hyperplasia, atherosclerosis, and aneurysms.

Pertussis toxin prevents the induction of peripheral T cell anergy and enhances the T cell response to an encephalitogenic peptide of myelin basic protein

In a murine model of T cell-mediated autoimmune disease, experimental autoimmune encephalitis (EAE), 80% of all encephalitogenic T cell clones in H-2u mice use the V beta 8.2 TCR element. To induce EAE in susceptible strains of mice either heat-killed Bordetella pertussis organisms or Bordetella pertussis toxin (PT) must be injected in addition to Ag in CFA. We investigated the mechanisms by which PT facilitates the induction of EAE. Our data show, that PT interferes with the induction of Ag-induced peripheral T cell anergy. Furthermore it has a specific adjuvanticity for the autoantigen pAc1-11 in vivo and acts as a selective mitogen in vitro. We also tested the hypothesis that PT is a bacterial superantigen that specifically expands the V beta 8.2+ subset of T cells, thereby expanding the encephalitogenic T cell clones that are contained in this subset, so that the number of autoreactive T cells is brought over a critical threshold, necessary to induce autoimmune disease. Our data show that PT is not a superantigen. Staphylococcal enterotoxin B, a V beta 8.2-specific superantigen, does not enhance the immune response to the encephalitogenic peptide.

Pertussis toxin prevents the induction of peripheral T cell anergy and enhances the T cell response to an encephalitogenic peptide of myelin basic protein

In a murine model of T cell-mediated autoimmune disease, experimental autoimmune encephalitis (EAE), 80% of all encephalitogenic T cell clones in H-2u mice use the V beta 8.2 TCR element. To induce EAE in susceptible strains of mice either heat-killed Bordetella pertussis organisms or Bordetella pertussis toxin (PT) must be injected in addition to Ag in CFA. We investigated the mechanisms by which PT facilitates the induction of EAE. Our data show, that PT interferes with the induction of Ag-induced peripheral T cell anergy. Furthermore it has a specific adjuvanticity for the autoantigen pAc1-11 in vivo and acts as a selective mitogen in vitro. We also tested the hypothesis that PT is a bacterial superantigen that specifically expands the V beta 8.2+ subset of T cells, thereby expanding the encephalitogenic T cell clones that are contained in this subset, so that the number of autoreactive T cells is brought over a critical threshold, necessary to induce autoimmune disease. Our data show that PT is not a superantigen. Staphylococcal enterotoxin B, a V beta 8.2-specific superantigen, does not enhance the immune response to the encephalitogenic peptide.

The adenovirus type 5 i-leader open reading frame functions in cis to reduce the half-life of L1 mRNAs

The 440-nucleotide adenovirus type 5 i-leader sequence, encoding a 13.6-kilodalton protein, is located between the second and third components of the tripartite leader sequence. It appears primarily on the L1 family of mRNAs. To study its function, we constructed two point mutations within the i leader. pm382 lacks the wild-type i-leader splice acceptor and failed to splice the leader onto L1 mRNAs. pm383 lacks the ATG used for translation of the i-leader protein; it synthesized i-leader-containing mRNAs, but failed to produce detectable levels of the polypeptide. Both mutants exhibited modestly reduced yields in some but not all cell lines tested and accumulated slightly elevated levels of L1 mRNA and L1 52- and 55-kilodalton proteins in infected cells. Mutant phenotypes were consistently more pronounced in pm382- than in pm383-infected cells. In wild-type virus-infected cells, L1 mRNAs lacking the i leader displayed a half-life of about 26 h, whereas L1 mRNAs containing the leader were much less stable, with a half-life of less than 4 h. In pm383-infected cells (ATG mutant), L1 mRNAs containing the i leader exhibited a half-life of 26 h. The abnormally long half-life of pm383-encoded L1 mRNAs containing a mutant i leader was not reduced by coinfection with wild-type virus, suggesting that synthesis of the i-leader protein leads to destabilization of the i-leader-containing L1 mRNA undergoing translation.

Adenovirus L1 52- and 55-kilodalton proteins are required for assembly of virions

A variant of adenovirus type 5 that contained a mutation within the L1 52- and 55-kilodalton (52/55K) protein-coding region was isolated. The mutant, termed ts369, produced L1 52/55K proteins with a two-amino-acid substitution and was temperature sensitive. Temperature-shift experiments indicated that the ts369 defect was late in the viral growth cycle. DNA replication and synthesis of late proteins occurred normally in ts369-infected cells at the nonpermissive temperature, but mature virions were not produced. Rather, capsidlike particles associated with the left-terminal region of the viral chromosome accumulated. These incomplete particles could not be chased into mature virions when the infected cells were shifted to the permissive temperature. However, previously synthesized proteins could be assembled into virions in the presence of a protein synthesis inhibitor upon shiftdown from the nonpermissive temperature, suggesting that the inactivation of the L1 52/55K proteins was reversible. These results indicate that the adenovirus L1 52/55K proteins play a role in the assembly of infectious virus particles.