Building Career Paths for Ph.D., Basic and Translational Scientists in Clinical Departments in the United States: An Official American Thoracic Society Workshop Report

Rationale: To identify barriers and opportunities for Ph.D., basic and translational scientists to be fully integrated into clinical units. Objectives: In 2022, an ad hoc committee of the American Thoracic Society developed a project proposal and workshop to identify opportunities and barriers for scientists who do not practice medicine to develop successful careers and achieve tenure-track faculty positions in clinical departments and divisions within academic medical centers (AMCs) in the United States. Methods: This document focuses on results from a survey of adult and pediatric pulmonary, critical care, and sleep medicine division chiefs as well as a survey of workshop participants, including faculty in departmental and school leadership roles in both basic science and clinical units within U.S. AMCs. Results: We conclude that full integration of non-clinically practicing basic and translational scientists into the clinical units, in addition to their traditional placements in basic science units, best serves the tripartite mission of AMCs to provide care, perform research, and educate the next generation. Evidence suggests clinical units do employ Ph.D. scientists in large numbers, but these faculty are often hired into non-tenure track positions, which do not provide the salary support, start-up funds, research independence, or space often associated with hiring in basic science units within the same institution. These barriers to success of Ph.D. faculty in clinical units are largely financial. Conclusions: Our recommendation is for AMCs to consider and explore some of our proposed strategies to accomplish the goal of integrating basic and translational scientists into clinical units in a meaningful way.

Airway smooth muscle pathophysiology in asthma

The airway smooth muscle (ASM) cell plays a central role in the pathogenesis of asthma and constitutes an important target for treatment. These cells control muscle tone and thus regulate the opening of the airway lumen and air passage. Evidence indicates that ASM cells participate in the airway hyperresponsiveness as well as the inflammatory and remodeling processes observed in asthmatic subjects. Therapeutic approaches require a comprehensive understanding of the structure and function of the ASM in both the normal and disease states. This review updates current knowledge about ASM and its effects on airway narrowing, remodeling, and inflammation in asthma.

An Official American Thoracic Society Research Statement: Current Challenges Facing Research and Therapeutic Advances in Airway Remodeling

BACKGROUND

Airway remodeling (AR) is a prominent feature of asthma and other obstructive lung diseases that is minimally affected by current treatments. The goals of this Official American Thoracic Society (ATS) Research Statement are to discuss the scientific, technological, economic, and regulatory issues that deter progress of AR research and development of therapeutics targeting AR and to propose approaches and solutions to these specific problems. This Statement is not intended to provide clinical practice recommendations on any disease in which AR is observed and/or plays a role.

METHODS

An international multidisciplinary group from within academia, industry, and the National Institutes of Health, with expertise in multimodal approaches to the study of airway structure and function, pulmonary research and clinical practice in obstructive lung disease, and drug discovery platforms was invited to participate in one internet-based and one face-to-face meeting to address the above-stated goals. Although the majority of the analysis related to AR was in asthma, AR in other diseases was also discussed and considered in the recommendations. A literature search of PubMed was performed to support conclusions. The search was not a systematic review of the evidence.

RESULTS

Multiple conceptual, logistical, economic, and regulatory deterrents were identified that limit the performance of AR research and impede accelerated, intensive development of AR-focused therapeutics. Complementary solutions that leverage expertise of academia and industry were proposed to address them.

CONCLUSIONS

To date, numerous factors related to the intrinsic difficulty in performing AR research, and economic forces that are disincentives for the pursuit of AR treatments, have thwarted the ability to understand AR pathology and mechanisms and to address it clinically. This ATS Research Statement identifies potential solutions for each of these factors and emphasizes the importance of educating the global research community as to the extent of the problem as a critical first step in developing effective strategies for: (1) increasing the extent and impact of AR research and (2) developing, testing, and ultimately improving drugs targeting AR.

Cyclooxygenase-2 and microRNA-155 expression are elevated in asthmatic airway smooth muscle cells

Cyclooxygenase-2 (COX-2) expression and PGE2 secretion from human airway smooth muscle cells (hASMCs) may contribute to β2-adrenoceptor hyporesponsiveness, a clinical feature observed in some patients with asthma. hASMCs from patients with asthma exhibit elevated expression of cytokine-responsive genes, and in some instances this is attributable to an altered histone code and/or microRNA expression. We hypothesized that COX-2 expression and PGE2 secretion might be elevated in asthmatic hASMCs in response to proinflammatory signals in part due to altered histone acetylation and/or microRNA expression. hASMCs obtained from nonasthmatic and asthmatic human subjects were treated with cytomix (IL-1β, TNF-α, and IFN-γ). A greater elevation of COX-2 mRNA, COX-2 protein, and PGE2 secretion was observed in the asthmatic cells. We investigated histone H3/H4-acetylation, transcription factor binding, mRNA stability, p38 mitogen-activated protein kinase signaling, and microRNA (miR)-155 expression as potential mechanisms responsible for the differential elevation of COX-2 expression. We found that histone H3/H4-acetylation and transcription factor binding to the COX-2 promoter were similar in both groups, and histone H3/H4-acetylation did not increase after cytomix treatment. Cytomix treatment elevated NF-κB and RNA polymerase II binding to similar levels in both groups. COX-2 mRNA stability was increased in asthmatic cells. MiR-155 expression was higher in cytomix-treated asthmatic cells, and we show it enhances COX-2 expression and PGE2 secretion in asthmatic and nonasthmatic hASMCs. Thus, miR-155 expression positively correlates with COX-2 expression in the asthmatic hASMCs and may contribute to the elevated expression observed in these cells. These findings may explain, at least in part, β2-adrenoceptor hyporesponsiveness in patients with asthma.

Pleiotropic Effects of Bitter Taste Receptors on [Ca2+]i Mobilization, Hyperpolarization, and Relaxation of Human Airway Smooth Muscle Cells

Asthma is characterized by airway inflammation and airflow obstruction from human airway smooth muscle (HASM) constriction due to increased local bronchoconstrictive substances. We have recently found bitter taste receptors (TAS2Rs) on HASM, which increase [Ca2+]i and relax the muscle. We report here that some, but not all, TAS2R agonists decrease [Ca2+]i and relax HASM contracted by G-protein coupled receptors (GPCRs) that stimulate [Ca2+]i. This suggests both a second pathway by which TAS2Rs relax, and, a heterogeneity of the response phenotype. We utilized eight TAS2R agonists and five procontractile GPCR agonists in cultured HASM cells. We find that heterogeneity in the inhibitory response hinges on which procontractile GPCR is activated. For example, chloroquine inhibits [Ca2+]i increases from histamine, but failed to inhibit [Ca2+]i increases from endothelin-1. Conversely, aristolochic acid inhibited [Ca2+]i increases from endothelin-1 but not histamine. Other dichotomous responses were found when [Ca2+]i was stimulated by bradykinin, angiotensin, and acetylcholine. There was no association between [Ca2+]i inhibition and TAS2R subtype, nor whether [Ca2+]i was increased by Gq- or Gi-coupled GPCRs. Selected studies revealed a correlation between [Ca2+]i inhibition and HASM cell-membrane hyperpolarization. To demonstrate physiologic correlates, ferromagnetic beads were attached to HASM cells and cell stiffness measured by magnetic twisting cytometry. Consistent with the [Ca2+]i inhibition results, chloroquine abolished the cell stiffening response (contraction) evoked by histamine but not by endothelin-1, while aristolochic acid inhibited cell stiffening from endothelin-1, but not from histamine. In studies using intact human bronchi, these same differential responses were found. Those TAS2R agonists that decreased [Ca2+]i, promoted hyperpolarization, and decreased HASM stiffness, caused relaxation of human airways. Thus TAS2Rs relax HASM in two ways: a low-efficiency de novo [Ca2+]i stimulation, and, a high-efficiency inhibition of GPCR-stimulated [Ca2+]i. Furthermore, there is an interaction between TAS2Rs and some GPCRs that facilitates this [Ca2+]i inhibition limb.

Targeted transgenesis identifies Gαs as the bottleneck in β2-adrenergic receptor cell signaling and physiological function in airway smooth muscle

G protein-coupled receptors are the most pervasive signaling superfamily in the body and act as receptors to endogenous agonists and drugs. For β-agonist-mediated bronchodilation, the receptor-G protein-effector network consists of the β2-adrenergic receptor (β2AR), Gs, and adenylyl cyclase, expressed on airway smooth muscle (ASM). Using ASM-targeted transgenesis, we previously explored which of these three early signaling elements represents a limiting factor, or bottleneck, in transmission of the signal from agonist binding to ASM relaxation. Here we overexpressed Gαs in transgenic mice and found that agonist-promoted relaxation of airways was enhanced in direct proportion to the level of Gαs expression. Contraction of ASM from acetylcholine was not affected in Gαs transgenic mice, nor was relaxation by bitter taste receptors. Furthermore, agonist-promoted (but not basal) cAMP production in ASM cells from Gαs-transgenic mice was enhanced compared with ASM from nontransgenic littermates. Agonist-promoted inhibition of platelet-derived growth factor-stimulated ASM proliferation was also enhanced in Gαs mouse ASM. The enhanced maximal β-agonist response was of similar magnitude for relaxation, cAMP production, and growth inhibition. Taken together, it appears that a limiting factor in β-agonist responsiveness in ASM is the expression level of Gαs. Gene therapy or pharmacological means of increasing Gαs (or its coupling efficiency to β2AR) thus represent an interface for development of novel therapeutic agents for improvement of β-agonist therapy.

MicroRNA-146a and microRNA-146b expression and anti-inflammatory function in human airway smooth muscle

MicroRNA (miR)-146a and miR-146b are negative regulators of inflammatory gene expression in lung fibroblasts, epithelial cells, monocytes, and endothelial cells. The abundance of cyclooxygenase-2 (COX-2) and IL-1β is negatively regulated by the miR-146 family, suggesting miR-146a and/or miR-146b might modulate inflammatory mediator expression in airway smooth muscle thereby contributing to pathogenesis of asthma. To test this idea we compared miR-146a and miR-146b expression in human airway smooth muscle cells (hASMCs) from nonasthmatic and asthmatic subjects treated with cytomix (IL-1β, TNF-α, and IFNγ) and examined the miRNAs' effects on COX-2 and IL-1β expression. We found that cytomix treatment elevated miR-146a and miR-146b abundance. Induction with cytomix was greater than induction with individual cytokines, and asthmatic cells exhibited higher levels of miR-146a expression following cytomix treatment than nonasthmatic cells. Transfection of miR-146a or miR-146b mimics reduced COX-2 and IL-1β expression. A miR-146a inhibitor increased COX-2 and IL-1β expression, but a miR-146b inhibitor was ineffective. Repression of COX-2 and IL-1β expression by miR-146a correlated with reduced abundance of the RNA-binding protein human antigen R. These results demonstrate that miR-146a and miR-146b expression is inducible in hASMCs by proinflammatory cytokines and that miR-146a expression is greater in asthmatic cells. Both miR-146a and miR-146b can negatively regulate COX-2 and IL-1β expression at pharmacological levels, but loss-of-function studies showed that only miR-146a is an endogenous negative regulator in hASMCs. The results suggest miR-146 mimics may be an attractive candidate for further preclinical studies as an anti-inflammatory treatment of asthma.

Transforming growth factor-β-induced differentiation of airway smooth muscle cells is inhibited by fibroblast growth factor-2

In asthma, basic fibroblast growth factor (FGF-2) plays an important (patho)physiological role. This study examines the effects of FGF-2 on the transforming growth factor-β (TGF-β)-stimulated differentiation of airway smooth muscle (ASM) cells in vitro. The differentiation of human ASM cells after incubation with TGF-β (100 pM) and/or FGF-2 (300 pM) for 48 hours was assessed by increases in contractile protein expression, actin-cytoskeleton reorganization, enhancements in cell stiffness, and collagen remodeling. FGF-2 inhibited TGF-β-stimulated increases in transgelin (SM22) and calponin gene expression (n = 15, P < 0.01) in an extracellular signal-regulated kinase 1/2 (ERK1/2) signal transduction-dependent manner. The abundance of ordered α-smooth muscle actin (α-SMA) filaments formed in the presence of TGF-β were also reduced by FGF-2, as was the ratio of F-actin to G-actin (n = 8, P < 0.01). Furthermore, FGF-2 attenuated TGF-β-stimulated increases in ASM cell stiffness and the ASM-mediated contraction of lattices, composed of collagen fibrils (n = 5, P < 0.01). However, the TGF-β-stimulated production of IL-6 was not influenced by FGF-2 (n = 4, P > 0.05), suggesting that FGF-2 antagonism is selective for the regulation of ASM cell contractile protein expression, organization, and function. Another mitogen, thrombin (0.3 U ml(-1)), exerted no effect on TGF-β-regulated contractile protein expression (n = 8, P > 0.05), α-SMA organization, or the ratio of F-actin to G-actin (n = 4, P > 0.05), suggesting that the inhibitory effect of FGF-2 is dissociated from its mitogenic actions. The addition of FGF-2, 24 hours after TGF-β treatment, still reduced contractile protein expression, even when the TGF-β-receptor kinase inhibitor, SB431542 (10 μM), was added 1 hour before FGF-2. We conclude that the ASM cell differentiation promoted by TGF-β is antagonized by FGF-2. A better understanding of the mechanism of action for FGF-2 is necessary to develop a strategy for therapeutic exploitation in the treatment of asthma.

S100A12 and the Airway Smooth Muscle: Beyond Inflammation and Constriction

Airway inflammation, lung remodeling, and Airway Hyperresponsiveness (AHR) are major features of asthma and Chronic Obstructive Pulmonary Disease (COPD). The inflammatory response to allergens, air pollutants, and other insults is likely to play a key role in promoting structural changes in the lung including the overabundance of Airway Smooth Muscle (ASM) seen in asthmatics. These alterations or remodeling could, in turn, impact the immunmodulatory actions of the ASM, the ASM's contractile properties, and the development of AHR. New evidences suggest that airway inflammation and AHR are not tightly related to each other and that the structural component of the airway, mainly the ASM, is a chief driver of AHR. Members of the S100/calgranulins family have been implicated in the regulation of inflammation and cell apoptosis in various systems. S100A12 is highly expressed in neutrophils and is one of the most abundant proteins in the lungs of patients with asthma or COPD. Studies with genetic engineered mice with smooth muscle cell-targeted expression of human S100A12 revealed that S100A12 reduces airway smooth muscle amounts and dampens airway inflammation and airway hyperreactivity in a model of allergic lung inflammation. Thus, targeting airway smooth muscle for instance through delivery of pro-apoptotic S100A12 could represent an attractive means to promote ASM apoptosis and to reduce ASM abundance in asthmatics.

Transgenic expression of human S100A12 induces structural airway abnormalities and limited lung inflammation in a mouse model of allergic inflammation

BACKGROUND

The calcium-binding protein S100A12 is highly up-regulated in the serum and sputum of patients with allergic asthma and is suggested to be a biomarker and pathologic mediator of asthma.

OBJECTIVE

To test the role of S100A12 in mediating airway inflammation in a mouse model of allergic lung inflammation.

METHODS

Transgenic (TG) mice that express human S100A12 and wild-type (WT) littermates were sensitized and challenged with ovalbumin (OVA) and assessed for inflammation, lung structure, and function.

RESULTS

Following OVA sensitization and challenge, S100A12 TG mice showed reduced peribronchial and perivascular inflammation, mucus production, and eosinophilia as well as attenuated airway responsiveness to contractile agonist compared with WT sensitized and challenged animals. This is explained, at least in part, by remodelled airways in S100A12 TG mice with thinning of the airway smooth muscle. S100A12 exposure induced Fas expression and activation of caspase 3 in cultured airway smooth muscle cells, suggesting that airway smooth muscle abnormalities observed in S100A12 TG mice may be mediated through myocyte apoptosis.

CONCLUSION AND CLINICAL RELEVANCE

S100A12 is one of the most abundant proteins found in the airways of human asthmatics, and it was postulated that S100A12 could mediate the inflammatory process. Our study shows for the first time that TG expression of S100A12 in the lung of mice does not exacerbate lung inflammation in a model of OVA-induced allergic inflammation. We speculate that the high levels of S100/calgranulins found in bronchoalveolar lavage fluid of asthmatics and of OVA-treated TG S100A12 mice do not significantly mediate pulmonary inflammation.

Akt activation induces hypertrophy without contractile phenotypic maturation in airway smooth muscle

Airway smooth muscle (ASM) hypertrophy is a cardinal feature of severe asthma, but the underlying molecular mechanisms remain uncertain. Forced protein kinase B/Akt 1 activation is known to induce myocyte hypertrophy in other muscle types, and, since a number of mediators present in asthmatic airways can activate Akt signaling, we hypothesized that Akt activation could contribute to ASM hypertrophy in asthma. To test this hypothesis, we evaluated whether Akt activation occurs naturally within airway myocytes in situ, whether Akt1 activation is sufficient to cause hypertrophy of normal airway myocytes, and whether such hypertrophy is accompanied by excessive accumulation of contractile apparatus proteins (contractile phenotype maturation). Immunostains of human airway sections revealed concordant activation of Akt (reflected in Ser(473) phosphorylation) and of its downstream effector p70(S6Kinase) (reflected in Thr(389) phosphorylation) within airway muscle bundles, but there was no phosphorylation of the alternative Akt downstream target glycogen synthase kinase (GSK) 3β. Artificial overexpression of constitutively active Akt1 (by plasmid transduction or lentiviral infection) caused a progressive increase in size and protein content of cultured canine tracheal myocytes and increased p70(S6Kinase) phosphorylation but not GSK3β phosphorylation; however, constitutively active Akt1 did not cause disproportionate overaccumulation of smooth muscle (sm) α-actin and SM22. Furthermore, mRNAs encoding sm-α-actin and SM22 were reduced. These results indicate that forced Akt1 signaling causes hypertrophy of cultured airway myocytes without inducing further contractile phenotypic maturation, possibly because of opposing effects on contractile protein gene transcription and translation, and suggest that natural activation of Akt1 plays a similar role in asthmatic ASM.

Nuclear import of serum response factor in airway smooth muscle

We have previously shown that the transcription-promoting activity of serum response factor (SRF) is partially regulated by its extranuclear redistribution. In this study, we examined the cellular mechanisms that facilitate SRF nuclear entry in canine tracheal smooth muscle cells. We used in vitro pull-down assays to determine which karyopherin proteins bound SRF and found that SRF binds KPNA1 and KPNB1 through its nuclear localization sequence. Immunoprecipitation studies also demonstrated direct SRF-KPNA1 interaction in HEK293 cells. Import assays demonstrated that KPNA1 and KPNB1 together were sufficient to mediate rapid nuclear import of SRF-GFP. Our studies also suggest that SRF is able to gain nuclear entry through an auxiliary, nuclear localization sequence-independent mechanism.

Alternative promoter and GATA5 transcripts in mouse

GATA5 is a member of the GATA zinc finger transcription factor family involved in tissue-specific transcriptional regulation during cell differentiation and embryogenesis. Previous reports indicate that null mutation of the zebrafish GATA5 gene results in embryonic lethality, whereas deletion of exon 1 from the mouse GATA5 gene causes only derangement of female urogenital development. Here, we have identified an alternate promoter within intron 1 of the mouse GATA5 gene that transcribes a 2.5-kb mRNA that lacks exon 1 entirely but includes 82 bp from intron 1 and all of exons 2-6. The alternative promoter was active during transient transfection in cultured airway myocytes and bronchial epithelial cells, and it drove reporter gene expression in gastric epithelial cells in transgenic mice. The 2.5-kb alternative transcript encodes an NH(2)-terminally truncated "short GATA5" comprising aa 226-404 with a single zinc finger, which retains ability to transactivate the atrial natriuretic factor promoter (albeit less efficiently than full-length GATA5). Another new GATA5 transcript contains all of exons 1-5 and the 5' portion of exon 6 but lacks the terminal 1143 bp of the 3'-untranslated region from exon 6. These findings extend current understanding of the tissue distribution of GATA5 expression and suggests that GATA5 expression and function are more complex than previously appreciated.

Targeting the airway smooth muscle for asthma treatment

Asthma is a complex respiratory disease whose incidence has increased worldwide in the last decade. Currently there is no cure for asthma. Although bronchodilator and anti-inflammatory medications are effective medicines in some asthmatic patients, it is clear that an unmet therapeutic need persists for a subpopulation of individuals with severe asthma. This chronic lung disease is characterized by airflow limitation, lung inflammation, and remodeling that includes increased airway smooth muscle (ASM) mass. In addition to its contractile properties, the ASM also contributes to the inflammatory process by producing active mediators, which modify the extracellular matrix composition and interact with inflammatory cells. These undesirable functions make interventions aimed at reducing ASM abundance an attractive strategy for novel asthma therapies. The following three mechanisms could limit the accumulation of smooth muscle: decreased cell proliferation, augmented cell apoptosis, and reduced cell migration into the smooth muscle layer. Inhibitors of the mevalonate pathway or statins hold promise for asthma treatment, because they exhibit anti-inflammatory, antimigratory, and antiproliferative effects in preclinical and clinical studies, and they can target the smooth muscle. This review will discuss current knowledge of ASM biology and identify gaps in the field to stimulate future investigations of the cellular mechanisms that control ASM overabundance in asthma. Targeting ASM has the potential to be an innovative venue of treatment for patients with asthma.

Fibrillar collagen clamps lung mesenchymal cells in a nonproliferative and noncontractile phenotype

Pulmonary fibrosis is characterized by phenotypic changes to mesenchymal cells and an increase in the deposition of fibrillar collagen (fCollagen). This study investigated the effect of type I fCollagen on the phenotypic plasticity of human parenchymal fibroblasts (PFbs) in vitro. Cell numbers were 45% lower when cultured on fCollagen as compared with culture on its degradation product, monomeric collagen (mCollagen). DNA profiles indicated that fCollagen is antiproliferative, rather than proapoptotic. fCollagen suppressed basic fibroblast growth factor-stimulated increases in the levels of cyclin E and CDK2 mRNA. fCollagen also suppressed transforming growth factor-beta (100 pM)-stimulated increases in the mRNA and protein levels of alpha-smooth muscle actin (alpha-SMA), a marker of the myofibroblast phenotype. However, in cells exposed to fCollagen, the levels of matrix metalloproteinase (MMP)-1 and -14 mRNA, as well as active MMP-2 protein, were increased by between two- and fivefold. The MMP inhibitors, ilomastat (10 microM) and doxycycline (30 microM), attenuated the dissolution of collagen fibrils by fibroblasts maintained on fCollagen, with a corresponding decrease in cell number. Ilomastat also reduced alpha-SMA expression and the capacity of PFb to contract three-dimensional fCollagen gels. Thus, exposure of fibroblasts to the fibrillar form of type I collagen in vitro reduces cell proliferation, increases MMP production and activation, and attenuates differentiation of PFb into myofibroblasts. fCollagen appears to apply a phenotypic clamp on lung fibroblasts that may be partially released by autocrine MMP activity.

FIZZ1 plays a crucial role in early stage airway remodeling of OVA-induced asthma

The aim of this study was to elucidate the role of Found in Inflammatory Zone 1 (FIZZ1, also known as RELM-alpha or resistin-like molecule-alpha) in airway remodeling in asthma. We used a rat model of ovalbumin (OVA) sensitization and challenge to induce lung inflammation and remodeling. Expression of alpha -SMA in the lungs of OVA-treated rats was significantly elevated in the peribronchial regions compared with control saline-treated animals. Expression of FIZZ1 mRNA in alveolar epithelial type II cells (AECII) isolated from OVA-treated animals was higher than in control animals. Forced expression of recombinant FIZZ1 in rat-1 lung fibroblast cell line enhanced production of collagen type I and alpha -SMA compared with control transfected cells. These results suggest that FIZZ1 can induce fibroblasts to express markers of myofibroblast differentiation such as alpha -SMA and collagen type I, which are characteristic of early stages of airway remodeling seen in asthma.

Airway smooth muscle in asthma

Airway smooth muscle plays a multifaceted role in the pathogenesis of asthma. We review the current understanding of the contribution of airway myocytes to airway inflammation, airway wall remodeling, and airflow obstruction in this prevalent disease syndrome. Together, these roles make airway smooth muscle an attractive target for asthma therapy.

Regulation of Smad-mediated gene transcription by RGS3

Regulator of G protein signaling (RGS) proteins are united into a family by the presence of the homologous RGS domain that binds the alpha subunits of heterotrimeric G proteins and accelerates their GTPase activity. A member of this family, RGS3 regulates the signaling mediated by G(q) and G(i) proteins by binding the corresponding Galpha subunits. Here we show that RGS3 interacts with the novel partners Smad2, Smad3, and Smad4-the transcription factors that are activated through a transforming growth factor-beta (TGF-beta) receptor signaling. This interaction is mediated by the region of RGS3 outside of the RGS domain and by Smad's Mad homology 2 domain. Overexpression of RGS3 results in inhibition of Smad-mediated gene transcription. RGS3 does not affect TGF-beta-induced Smad phosphorylation, but it prevents heteromerization of Smad3 with Smad4, which is required for transcriptional activity of Smads. This translates to functional inhibition of TGF-beta-induced myofibroblast differentiation by RGS3. In conclusion, this study identifies a novel, noncanonical role of RGS3 in regulation of TGF-beta signaling through its interaction with Smads and interfering with Smad heteromerization.

Allele-specific targeting of microRNAs to HLA-G and risk of asthma

HLA-G is a nonclassic, class I HLA molecule that has important immunomodulatory properties. Previously, we identified HLA-G as an asthma-susceptibility gene and discovered that the risk of asthma in a child was determined by both the child's HLA-G genotype and the mother's affection status. Here we report a SNP in the 3' untranslated region of HLA-G that influences the targeting of three microRNAs (miRNAs) to this gene, and we suggest that allele-specific targeting of these miRNAs accounts, at least in part, for our earlier observations on HLA-G and the risk of asthma.

Allele-specific targeting of microRNAs to HLA-G and risk of asthma

HLA-G is a nonclassic, class I HLA molecule that has important immunomodulatory properties. Previously, we identified HLA-G as an asthma-susceptibility gene and discovered that the risk of asthma in a child was determined by both the child's HLA-G genotype and the mother's affection status. Here we report a SNP in the 3' untranslated region of HLA-G that influences the targeting of three microRNAs (miRNAs) to this gene, and we suggest that allele-specific targeting of these miRNAs accounts, at least in part, for our earlier observations on HLA-G and the risk of asthma.

Inhibition of transforming growth factor beta-enhanced serum response factor-dependent transcription by SMAD7

Transforming growth factor (TGF)-beta is present in large amounts in the airways of patients with asthma and with other diseases of the lung. We show here that TGFbeta treatment increased transcriptional activation of SM22alpha, a smooth muscle-specific promoter, in airway smooth muscle cells, and we demonstrate that this effect stems in part from TGFbeta-induced enhancement of serum response factor (SRF) DNA binding and transcription promoting activity. Overexpression of Smad7 inhibited TGFbeta-induced stimulation of SRF-dependent promoter function, and chromatin immunoprecipitation as well as co-immunoprecipitation assays established that endogenous or recombinant SRF interacts with Smad7 within the nucleus. The SRF binding domain of Smad7 mapped to the C-terminal half of the Smad7 molecule. TGFbeta treatment weakened Smad7 association with SRF, and conversely the Smad7-SRF interaction was increased by inhibition of the TGFbeta pathway through overexpression of a dominant negative mutant of TGFbeta receptor I or of Smad3 phosphorylation-deficient mutant. Our findings thus reveal that SRF-Smad7 interactions in part mediate TGFbeta regulation of gene transcription in airway smooth muscle. This offers potential targets for interventions in treating lung inflammation and asthma.

Cutting edge: polymorphisms in the ICOS promoter region are associated with allergic sensitization and Th2 cytokine production

The establishment of ICOS as an important regulator of Th2 development and effector function makes the ICOS locus an attractive candidate for Th2-mediated diseases, such as asthma and allergy. In evaluation of this candidate locus in humans, we identified 11 variants and determined that two in the putative promoter region are significantly associated with allergic sensitization and serum IgE levels. In addition, cultures of activated PBMCs from individuals homozygous for the associated polymorphisms produced increased levels of the Th2 cytokines, IL-4, IL-5, and IL-13, as well as TNF-alpha compared with controls. One of the polymorphisms, -1413G/A, demonstrated differential NF-kappaB binding in mobility shift analysis, suggesting that this polymorphism has functional consequences. Overall, these data demonstrate that ICOS is a susceptibility gene for allergic sensitization, perhaps through the promotion of Th2 differentiation.

Transforming growth factor-beta1 and disorders of the lung

The transforming growth factor (TGF) superfamily encompasses about 30 members in mammals. The effect of TGF-beta subfamily members is exerted and regulated via selective pathways of synthesis and signaling that involve activation of latent TGF-beta, specific and high-affinity binding to cell membrane serine/threonine kinase receptors, activation of intracellular cascades that include Smad molecules and mitogen-activated protein kinases, and regulated termination of the effect by diverse mechanisms including protein degradation and transcriptional activation. Several comprehensive reviews on TGF-beta biology in general and on the role of this cytokine in other diseases have been published recently. In recent years an unexpected role of TGF-beta on lung homeostasis has been revealed. Here, we discuss the contribution of TGF-beta to the pathogenesis of asthma and chronic obstructive pulmonary disease, two common illnesses of the lung, as well as of lymphangioleiomyomatosis, a rare disease in women. The information we collate and integrate places TGF-beta at a pivotal point within complex networks that control lung physiology as well as the physiopathology of these lung diseases.

On the terminology for describing the length-force relationship and its changes in airway smooth muscle

The observation that the length-force relationship in airway smooth muscle can be shifted along the length axis by accommodating the muscle at different lengths has stimulated great interest. In light of the recent understanding of the dynamic nature of length-force relationship, many of our concepts regarding smooth muscle mechanical properties, including the notion that the muscle possesses a unique optimal length that correlates to maximal force generation, are likely to be incorrect. To facilitate accurate and efficient communication among scientists interested in the function of airway smooth muscle, a revised and collectively accepted nomenclature describing the adaptive and dynamic nature of the length-force relationship will be invaluable. Setting aside the issue of underlying mechanism, the purpose of this article is to define terminology that will aid investigators in describing observed phenomena. In particular, we recommend that the term "optimal length" (or any other term implying a unique length that correlates with maximal force generation) for airway smooth muscle be avoided. Instead, the in situ length or an arbitrary but clearly defined reference length should be used. We propose the usage of "length adaptation" to describe the phenomenon whereby the length-force curve of a muscle shifts along the length axis due to accommodation of the muscle at different lengths. We also discuss frequently used terms that do not have commonly accepted definitions that should be used cautiously.

Phophatidylinositol-3 Kinase/Mammalian Target of Rapamycin/p70S6KRegulates Contractile Protein Accumulation in Airway Myocyte Differentiation

Increased airway smooth muscle in airway remodeling results from myocyte proliferation and hypertrophy. Skeletal and vascular smooth muscle hypertrophy is induced by phosphatidylinositide-3 kinase (PI(3) kinase) via mammalian target of rapamycin (mTOR) and p70S6 kinase (p70S6K). We tested the hypothesis that this pathway regulates contractile protein accumulation in cultured canine airway myocytes acquiring an elongated contractile phenotype in serum-free culture. In vitro assays revealed a sustained activation of PI(3) kinase and p70S6K during serum deprivation up to 12 d, with concomitant accumulation of SM22 and smooth muscle myosin heavy chain (smMHC) proteins. Immunocytochemistry revealed that activation of PI3K/mTOR/p70S6K occurred almost exclusively in myocytes that acquire the contractile phenotype. Inhibition of PI(3) kinase or mTOR with LY294002 or rapamycin blocked p70S6K activation, prevented formation of large elongated contractile phenotype myocytes, and blocked accumulation of SM22 and smMHC. Inhibition of MEK had no effect. Steady-state mRNA abundance for SM22 and smMHC was unaffected by blocking p70S6K activation. These studies provide primary evidence that PI(3) kinase and mTOR activate p70S6K in airway myocytes leading to the accumulation of contractile apparatus proteins, differentiation, and growth of large, elongated contractile phenotype airway smooth muscle cells.

Serum response factor function and dysfunction in smooth muscle

Tight control of smooth muscle cell (SM) proliferation, differentiation, and apoptosis requires a balance between signaling and transcriptional events. Recent developments in vascular research revealed that serum response factor (SRF) function is important for the regulation of each of these processes. The cloning and characterization of several SM specific genes and the discovery that SRF is central for their expression fueled studies aimed at understanding the role of molecular partners including co-activators and co-repressors. Perturbations of pathways involving SRF are associated with abnormalities in the myogenic program and aberrant phenotypic consequences. Surprisingly, studies on airway SM have remained an underrepresented area of investigation. Our laboratory described a novel regulatory mechanism of SRF function in airway myocytes by modulation of its subcellular localization. This review summarizes current knowledge on the structure and function of this essential transcription factor as well different modes of regulating SRF expression and activity that are becoming key players in directing SM function in health and disease.

The RhoA/Rho kinase pathway regulates nuclear localization of serum response factor

RhoA and its downstream target Rho kinase regulate serum response factor (SRF)-dependent skeletal and smooth muscle gene expression. We previously reported that long-term serum deprivation reduces transcription of smooth muscle contractile apparatus encoding genes, by redistributing SRF out of the nucleus. Because serum components stimulate RhoA activity, these observations suggest the hypothesis that the RhoA/Rho kinase pathway regulates SRF-dependent smooth muscle gene transcription in part by controlling SRF subcellular localization. Our present results support this hypothesis: cotransfection of cultured airway myocytes with a plasmid expressing constitutively active RhoAV14 selectively enhanced transcription from the SM22 and smooth muscle myosin heavy chain promoters and from a purely SRF-dependent promoter, but had no effect on transcription from the MSV-LTR promoter or from an AP2-dependent promoter. Conversely, inhibition of the RhoA/Rho kinase pathway by cotransfection with a plasmid expressing dominant negative RhoAN19, by cotransfection with a plasmid expressing Clostridial C3 toxin, or by incubation with the Rho kinase inhibitor, Y-27632, all selectively reduced SRF-dependent smooth muscle promoter activity. Furthermore, treatment with Y-27632 selectively reduced binding of SRF from nuclear extracts to its consensus DNA target, selectively reduced nuclear SRF protein content, and partially redistributed SRF from nucleus to cytoplasm, as revealed by quantitative immunocytochemistry. Treatment of cultured airway myocytes with latrunculin B, which reduces actin polymerization, also caused partial redistribution of SRF into the cytoplasm. Together, these results demonstrate for the first time that the RhoA/Rho kinase pathway controls smooth muscle gene transcription in differentiated smooth muscle cells, in part by regulating the subcellular localization of SRF. It is conceivable that the RhoA/Rho kinase pathway influences SRF localization through its effect on actin polymerization dynamics.

Calcium/calmodulin-dependent protein kinase activates serum response factor transcription activity by its dissociation from histone deacetylase, HDAC4. Implications in cardiac muscle gene regulation during hypertrophy

Serum response factor (SRF) plays a pivotal role in cardiac myocyte development, muscle gene transcription, and hypertrophy. Previously, elevation of intracellular levels of Ca2+ was shown to activate SRF function without involving the Ets family of tertiary complex factors through an unknown regulatory mechanism. Here, we tested the hypothesis that the chromatin remodeling enzymes of class II histone deacetylases (HDAC4) regulate SRF activity in a Ca2+-sensitive manner. Expression of HDAC4 profoundly repressed SRF-mediated transcription in both muscle and nonmuscle cells. Protein interaction studies demonstrated physical association of HDAC4 with SRF in living cells. The SRF/HDAC4 co-association was disrupted by treatment of cells with hypertrophic agonists such as angiotensin-II and a Ca2+ ionophore, ionomycin. Furthermore, activation of Ca2+/calmodulin-dependent protein kinase (CaMK)-IV prevented SRF/HDAC4 interaction and derepressed SRF-dependent transcription activity. The SRF.HDAC4 complex was localized to the cell nucleus, and the activated CaMK-IV disrupted HDAC4/SRF association, leading to export of HDAC4 from the nucleus and stimulation of SRF transcription activity. Thus, these results identify SRF as a functional interacting target of HDAC4 and define a novel tertiary complex factor-independent mechanism for SRF activation by Ca2+/CaMK-mediated signaling.

What evidence implicates airway smooth muscle in the cause of BHR?

Bronchial hyperresponsiveness (BHR), the occurrence of excessive bronchoconstriction in response to relatively small constrictor stimuli, is a cardinal feature of asthma. Here, we consider the role that airway smooth muscle might play in the generation of BHR. The weight of evidence suggests that smooth muscle isolated from asthmatic tissues exhibits normal sensitivity to constrictor agonists when studied during isometric contraction, but the increased muscle mass within asthmatic airways might generate more total force than the lesser amount of muscle found in normal bronchi. Another salient difference between asthmatic and normal individuals lies in the effect of deep inhalation (DI) on bronchoconstriction. DI often substantially reverses induced bronchoconstriction in normals, while it often has much less effect on spontaneous or induced bronchoconstriction in asthmatics. It has been proposed that abnormal dynamic aspects of airway smooth muscle contraction velocity of contraction or plasticity- elasticity balance might underlie the abnormal DI response in asthma. We suggest a speculative model in which abnormally long actin filaments might account for abnormally increased elasticity of contracted airway smooth muscle.

The RhoA/Rho kinase pathway regulates nuclear localization of serum response factor

RhoA and its downstream target Rho kinase regulate serum response factor (SRF)-dependent skeletal and smooth muscle gene expression. We previously reported that long-term serum deprivation reduces transcription of smooth muscle contractile apparatus encoding genes, by redistributing SRF out of the nucleus. Because serum components stimulate RhoA activity, these observations suggest the hypothesis that the RhoA/Rho kinase pathway regulates SRF-dependent smooth muscle gene transcription in part by controlling SRF subcellular localization. Our present results support this hypothesis: cotransfection of cultured airway myocytes with a plasmid expressing constitutively active RhoAV14 selectively enhanced transcription from the SM22 and smooth muscle myosin heavy chain promoters and from a purely SRF-dependent promoter, but had no effect on transcription from the MSV-LTR promoter or from an AP2-dependent promoter. Conversely, inhibition of the RhoA/Rho kinase pathway by cotransfection with a plasmid expressing dominant negative RhoAN19, by cotransfection with a plasmid expressing Clostridial C3 toxin, or by incubation with the Rho kinase inhibitor, Y-27632, all selectively reduced SRF-dependent smooth muscle promoter activity. Furthermore, treatment with Y-27632 selectively reduced binding of SRF from nuclear extracts to its consensus DNA target, selectively reduced nuclear SRF protein content, and partially redistributed SRF from nucleus to cytoplasm, as revealed by quantitative immunocytochemistry. Treatment of cultured airway myocytes with latrunculin B, which reduces actin polymerization, also caused partial redistribution of SRF into the cytoplasm. Together, these results demonstrate for the first time that the RhoA/Rho kinase pathway controls smooth muscle gene transcription in differentiated smooth muscle cells, in part by regulating the subcellular localization of SRF. It is conceivable that the RhoA/Rho kinase pathway influences SRF localization through its effect on actin polymerization dynamics.

Fas resistance of leukemic eosinophils is due to activation of NF-kappa B by Fas ligation

TNF family receptors can lead to the activation of NF-kappaB and this can be a prosurvival signal in some cells. Although activation of NF-kappaB by ligation of Fas (CD95/Apo-1), a member of the TNFR family, has been observed in a few studies, Fas-mediated NF-kappaB activation has not previously been shown to protect cells from apoptosis. We examined the Fas-induced NF-kappaB activation and its antiapoptotic effects in a leukemic eosinophil cell line, AML14.3D10, an AML14 subline resistant to Fas-mediated apoptosis. EMSA and supershift assays showed that agonist anti-Fas (CH11) induced nuclear translocation of NF-kappaB heterodimer p65(RelA)/p50 in these cells in both a time- and dose-dependent fashion. The influence of NF-kappaB on the induction of apoptosis was studied using pharmacological proteasome inhibitors and an inhibitor of IkappaBalpha phosphorylation to block IkappaBalpha dissociation and degradation. These inhibitors at least partially inhibited NF-kappaB activation and augmented CH11-induced cell death. Stable transfection and overexpression of IkappaBalpha in 3D10 cells inhibited CH11-induced NF-kappaB activation and completely abrogated Fas resistance. Increases in caspase-8 and caspase-3 cleavage induced by CH11 and in consequent apoptotic killing were observed in these cells. Furthermore, while Fas-stimulation of resistant control 3D10 cells led to increases in the antiapoptotic proteins cellular inhibitor of apoptosis protein-1 and X-linked inhibitor of apoptosis protein, Fas-induced apoptosis in IkappaBalpha-overexpressing cells led to the down-modulation of both of these proteins, as well as that of the Bcl-2 family protein, Bcl-x(L). These data suggest that the resistance of these leukemic eosinophils to Fas-mediated killing is due to induced NF-kappaB activation.

Structure and transcription of the human m3 muscarinic receptor gene

We have isolated and characterized the human m3 muscarinic receptor gene and its promoter. Using 5' rapid amplification of cDNA ends (RACE), internal polymerase chain reaction (PCR), and homology searching to identify EST clones, we determined that the cDNA encoding the m3 receptor comprises 4,559 bp in 8 exons, which are alternatively spliced to exclude exons 2, 4, 6, and/or 7; the receptor coding sequence occurs within exon 8. Analysis of P1 artificial chromosome (PAC) and bacterial artificial chromosome (BAC) clones and of PCR- amplified genomic DNA, and homology searching of human chromosome 1 sequence provided from the Sanger Centre (Hinxton, Cambridge, UK) revealed that the m3 muscarinic receptor gene spans at least 285 kb. A promoter fragment containing bp -1240 to +101 (relative to the most 5' transcription start site) exhibited considerable transcriptional activity during transient transfection in cultured subconfluent, serum-fed canine tracheal myocytes, and 5' deletion analysis of promoter function revealed the presence of positive transcriptional regulatory elements between bp -526 and -269. Sequence analysis disclosed three potential AP-2 binding sites in this region; five more AP-2 consensus binding motifs occur between bp -269 and +101. Cotransfection with a plasmid expressing human AP-2alpha substantially increased transcription from m3 receptor promoter constructs containing 526 or 269 bp of 5' flanking DNA. Furthermore, m3 receptor promoter activity was enhanced by long-term serum deprivation of canine tracheal myocytes, a treatment that is known to increase AP-2 transcription-promoting activity in these cells. Together, these data suggest that expression of the human m3 muscarinic receptor gene is regulated in part by AP-2 in airway smooth muscle.

Mutagenesis analysis of human SM22: characterization of actin binding

SM22 is a 201-amino acid actin-binding protein expressed at high levels in smooth muscle cells. It has structural homology to calponin, but how SM22 binds to actin remains unknown. We performed site-directed mutagenesis to generate a series of NH(2)-terminal histidine (His)-tagged mutants of human SM22 in Escherichia coli and used these to analyze the functional importance of potential actin binding domains. Purified full-length recombinant SM22 bound to actin in vitro, as demonstrated by cosedimentation assay. Binding did not vary with calcium concentration. The COOH-terminal domain of SM22 is required for actin affinity, because COOH terminally truncated mutants [SM22-(1-186) and SM22-(1-166)] exhibited markedly reduced cosedimentation with actin, and no actin binding of SM22-(1-151) could be detected. Internal deletion of a putative actin binding site (154-KKAQEHKR-161) partially prevented actin binding, as did point mutation to neutralize either or both pairs of positively charged residues at the ends of this region (KK154LL and/or KR160LL). Internal deletion of amino acids 170-180 or 170-186 also partially or almost completely inhibited actin cosedimentation, respectively. Of the three consensus protein kinase C or casein kinase II phosphorylation sites in SM22, only Ser-181 was readily phosphorylated by protein kinase C in vitro, and such phosphorylation greatly decreased actin binding. Substitution of Ser-181 to aspartic acid (to mimic serine phosphorylation) also reduced actin binding. Immunostains of transiently transfected airway myocytes revealed that full-length NH(2)-terminal FLAG-tagged SM22 colocalizes with actin filaments, whereas FLAG-SM22-(1-151) does not. These data confirm that SM22 binds to actin in vitro and in vivo and, for the first time, demonstrate that multiple regions within the COOH-terminal domain are required for full actin affinity.

Physiological control of smooth muscle-specific gene expression through regulated nuclear translocation of serum response factor

Prolonged serum deprivation induces a structurally and functionally contractile phenotype in about 1/6 of cultured airway myocytes, which exhibit morphological elongation and accumulate abundant contractile apparatus-associated proteins. We tested the hypothesis that transcriptional activation of genes encoding these proteins accounts for their accumulation during this phenotypic transition by measuring the transcriptional activities of the murine SM22 and human smooth muscle myosin heavy chain promoters during transient transfection in subconfluent, serum fed or 7 day serum-deprived cultured canine tracheal smooth muscle cells. Contrary to our expectation, SM22 and smooth muscle myosin heavy chain promoter activities (but not viral murine sarcoma virus-long terminal repeat promoter activity) were decreased in long term serum-deprived myocytes by at least 8-fold. Because serum response factor (SRF) is a required transcriptional activator of these and other smooth muscle-specific promoters, we evaluated the expression and function of SRF in subconfluent and long term serum-deprived cells. Whole cell SRF mRNA and protein were maintained at high levels in serum-deprived myocytes, but SRF transcription-promoting activity, nuclear SRF binding to consensus CArG sequences, and nuclear SRF protein were reduced. Furthermore, immunocytochemistry revealed extranuclear redistribution of SRF in serum-deprived myocytes; nuclear localization of SRF was restored after serum refeeding. These results uncover a novel mechanism for physiological control of smooth muscle-specific gene expression through extranuclear redistribution of SRF and consequent down-regulation of its transcription-promoting activity.

Fas cross-linking induces apoptosis in human airway smooth muscle cells

Hypertrophy and hyperplasia lead to excess accumulation of smooth muscle in the airways of human asthmatic subjects. However, little is known about mechanisms that might counterbalance these processes, thereby limiting the quantity of smooth muscle in airways. Ligation of Fas on the surface of vascular smooth muscle cells and nonmuscle airway cells can lead to apoptotic cell death. We therefore tested the hypotheses that 1) human airway smooth muscle (HASM) expresses Fas, 2) Fas cross-linking induces apoptosis in these cells, and 3) tumor necrosis factor (TNF)-alpha potentiates Fas-mediated airway myocyte killing. Immunohistochemistry using CH-11 anti-Fas monoclonal IgM antibody revealed Fas expression in normal human bronchial smooth muscle in vivo. Flow cytometry using DX2 anti-Fas monoclonal IgG antibody revealed that passage 4 cultured HASM cells express surface Fas. Surface Fas decreased partially during prolonged serum deprivation of cultured HASM cells and was upregulated by TNF-alpha stimulation. Fas cross-linking with CH-11 antibody induced apoptosis in cultured HASM cells, and this effect was reduced by long-term serum deprivation and synergistically potentiated by concomitant TNF-alpha exposure. TNF-alpha did not induce substantial apoptosis in the absence of Fas cross-linking. These data represent the first demonstration that Fas is expressed on HASM and suggest a mechanism by which Fas-mediated apoptosis could act to oppose excess smooth muscle accumulation during airway remodeling in asthma.

Divergent differentiation paths in airway smooth muscle culture: induction of functionally contractile myocytes

We tested the hypothesis that prolonged serum deprivation would allow a subset of cultured airway myocytes to reacquire the abundant contractile protein content, marked shortening capacity, and elongated morphology characteristic of contractile cells within intact tissue. Passage 1 or 2 canine tracheal smooth muscle (SM) cells were grown to confluence, then serum deprived for up to 19 days. During serum deprivation, two differentiation pathways emerged. One-sixth of the cells developed an elongated morphology and aligned into bundles. Elongated myocytes contained cables of contractile myofilaments, dense bodies, gap junctions, and membrane caveoli, ultrastructural features of contractile SM in tissue. These cells immunostained intensely for SM alpha-actin, SM myosin heavy chain (MHC), and SM22 (an SM-specific actin-binding protein), and Western analysis of culture lysates disclosed 1.8 (SM alpha-actin)-, 7.7 (SM MHC)-, and 5.8 (SM22)-fold protein increases during serum deprivation. Immunoreactive M3 muscarinic receptors were present in dense foci distributed throughout elongated, SM MHC-positive myocytes. ACh (10(-3) M) induced a marked shortening (59.7 +/- 14.4% of original length) in 62% of elongated myocytes made semiadherent by gentle proteolytic digestion, and membrane bleb formation (a consequence of contraction) occurred in all stimulated cells that remained adherent and so did not shorten. Cultured airway myocytes that did not elongate during serum deprivation instead became short and flattened, lost immunoreactivity for contractile proteins, lacked the M3 muscarinic-receptor expression pattern seen in elongated cells, and exhibited no contractile response to ACh. Thus we demonstrate that prolonged serum deprivation induces distinct differentiation pathways in confluent cultured tracheal myocytes and that one subpopulation acquires an unequivocally functional contractile phenotype in which structure and function resemble contractile myocytes from intact tissue.

Transcriptional regulation of smooth muscle contractile apparatus expression

The transcriptional regulatory mechanisms that control gene expression during differentiation and contractile protein accumulation are becoming well understood in skeletal and cardiac muscle lineages. Current understanding of smooth muscle-specific gene transcription is much more limited, though recent studies have begun to shed light on this topic. In this review, we summarize some of the themes emerging from these studies and identify transcriptional regulatory elements common to several smooth muscle genes. These include potential binding sites for serum response factor, Sp1, AP2, Mhox, and YY1, as well as a potential transforming growth factor-beta control element. We speculate that it may be possible to manipulate smooth muscle-specific gene expression in asthma or pulmonary arterial hypertension as an eventual therapy.

Sequence and structural analysis of feline interleukin-5 cDNA

OBJECTIVE

To clone and characterize the cDNA encoding feline interleukin-5 (IL-5) cDNA and the 170 basepairs (bp) of the 5' flanking region of the feline IL-5 gene.

SAMPLE POPULATION

Blood mononuclear cells from a healthy cat.

PROCEDURES

Cells were cultured, stimulated for 48 hours with concanavalin A, and harvested for RNA and DNA isolation. Recovered RNA was used in northern blot and reverse transcription-polymerase chain reaction analyses. Resulting cDNA was used for rapid amplification of 3' cDNA ends, dideoxy chain termination sequencing, and primer extension analysis.

RESULTS

Full length cDNA was 838 bp, including a 402-bp open reading frame that encoded a precursor protein of 134 amino acids including a putative peptide signal of 19 residues. Homologies of the nucleotide and derived protein sequences between feline and human IL-5 cDNA were 72 and 71%, respectively. There also was homology between the human and predicted feline cytokines at amino acid positions that are critical for IL-5 receptor binding and signal transduction. The 5' flanking region of the feline gene was homologous to corresponding regions of the human (88%) and murine (72%) genes, and included putative transcriptional regulatory elements.

CONCLUSIONS AND CLINICAL RELEVANCE

Identification of feline IL-5 cDNA is an important step toward a detailed, fully comprehensive characterization of the mechanisms that may be operative in the pathogenesis of eosinophilic disorders in cats. The striking homology between the human and feline IL-5 genes suggests that cats can be used as animal models for human diseases characterized by eosinophil infiltration of tissues.

Expression and cytogenetic localization of the human SM22 gene (TAGLN)

SM22 is a 22-kDa protein identified variously as SM22, transgelin, WS3-10, or mouse p27. Though its precise function is unknown, it is abundant in smooth muscle and so may contribute to the physiology of this widespread tissue. We found that cosmid 16b6 contains the entire 5.4-kb, five-exon human SM22 gene (HGMW-approved symbol, TAGLN), and we cytogenetically localized the gene to chromosome 11q23.2. Northern analysis of human adult tissues showed that SM22 mRNA is most prevalent in smooth muscle-containing tissues, but is also found at lower levels in heart. The human SM22 promoter contains nuclear factor-binding motifs known to regulate transcription in smooth muscle, and human SM22 promoter-luciferase reporter constructs exhibited high transcriptional activity in A7r5 or primary canine aortic smooth muscle cells, but show little activity in nonmuscle COS7 cells. In addition, human SM22 promoter activity increased by two- to threefold upon serum stimulation of nonmuscle cells.

Developmental shift of myosin heavy chain mRNA expression due to neural factor(s) and muscle activity

The adult ventricular isoform of chicken myosin heavy chain (MHC-V) is transiently expressed in all skeletal muscle primordia analyzed and is completely repressed around embryonic days 10-12, when functional innervation is established. By ribonuclease protection assay, we demonstrated that denervation of the adult anterior latissimus dorsi muscle resulted in reexpression of MHC-V mRNA. In contrast, treatment of primary cultures of fetal breast or leg muscles with embryonic brain extract or conditioned media from glial or neuroblastoma cell lines, but not from a myogenic cell line or primary muscle cell cultures, led to inhibition of MHC-V expression. This inhibitory activity was abolished by heating and increased with protein concentration. The acquisition of both brain inhibitory activity and the competence of myogenic cells to downregulate MHC-V mRNA expression were age dependent. Furthermore, either paralysis of muscle in ovo by curare or contraction arrest of cultured myotubes resulted in persistent expression of MHC-V mRNA. Thus a putative soluble factor(s) of nerve origin as well as muscle activity are involved in the developmental downregulation of MHC-V expression in muscle primordia.

Differential expression of ventricular-like myosin heavy chain mRNA in developing and regenerating avian skeletal muscles

Based on previous immunological data, cross-reactivity of myosin heavy chain (MHC) with the ventricular (V) isoform was observed in primordia of avian skeletal muscles and in regenerating adult anterior latissimus dorsi (ALD) muscle. To determine whether this primordial (P) MHC is identical to adult V-MHC gene product, we have cloned and characterized the 3' portion of MHC cDNA that is expressed in ALD muscle at 3 d of regeneration. Comparison of nucleotide sequences between adult V-MHC and P-MHC cDNAs revealed more than 98% homology in the 3'-untranslated (UT) portions of these genes. The expression pattern of P-MHC was analyzed in adult regenerating muscles using total RNA from two fast muscles, posterior latissimus dorsi (PLD) and pectoralis major (PM), as well as from slow ALD and mixed fast/slow gastrocnemius muscles at 0, 1, 3, 4, 6, 9, and 14 d after cold injury. Identical results were obtained by RNase protection assays using either a probe specifying the coding region of adult V-MHC or a P-MHC probe encoding the carboxy end plus the 3'-UT region. The expected protected fragments were detected early from day 2 up to day 6 in ALD muscle. Similar rate of appearance, reaching the highest level at day 3, was observed in PLD, PM, and gastrocnemius muscles. However, the amount and the kinetics of disappearance differed among the various muscles analyzed. In contrast, during development, steady-state levels and kinetics of V-MHC mRNA expression were found to be alike in axial and appendicular muscles. These data strongly suggest the identity of P-MHC as the ventricular isoform and support the concept that expression of P-MHC mRNA is a common feature of developing as well as of all regenerating adult skeletal muscles. Interestingly, no expression of cardiac specific myosin light chain (MLC) 2A was observed after cold injury, suggesting independent regulatory pathways for the two kinds of myosin subunits.

Structural and phylogenetic analysis of the chicken ventricular myosin heavy chain rod

We have isolated and characterized five overlapping clones that encompass 3.2 kb and encode a part of the short subfragment 2, the hinge, and the light meromyosin regions of the myosin heavy chain rod as well as 143 bp of the 3' untranslated portion of the mRNA. Northern blot analysis showed expression of this mRNA mainly in ventricular muscle of the adult chicken heart, with trace levels detected in the atrium. Transient expression was seen in skeletal muscle during development and in regenerating skeletal muscle following freeze injury. To our knowledge, this is the first report of an avian ventricular myosin heavy chain sequence. Phylogenetic analysis indicated that this isoform is a distant homolog of other ventricular and skeletal muscle myosin heavy chains and represents a distinct member of the multigene family of sarcomeric myosin heavy chains. The ventricular myosin heavy chain of the chicken is either paralogous to its counterpart in other vertebrates or has diverged at a significantly higher rate.

Porphobilinogen oxygenase. Purification and evidence of its hemoprotein structure

Porphobilinogen oxygenase oxidizes porphobilinogen to 2-hydroxy-5-oxo-porphobilinogen. This enzyme isolated from wheat germ has been purified to homogeneity, as judged by polyacrylamide gel electrophoresis under both nondenaturing and denaturing conditions. The molecular weight of the enzyme formed from two identical (or very similar) polypeptide chains is 70,000. It has a pI of 9.0 indicating its cationic nature. The pure enzyme contains 1 mol of high-spin heme and 2 mol of non-heme iron. It requires both of these as well as molecular O2 and a reducing agent for catalytic activity. Although the enzyme has many characteristics of a peroxidase, hydrogen peroxide cannot substitute for oxygen and dithionite for catalysis. The catalytic reaction is not affected by catalase, superoxide dismutase, or by hydroxyl radical scavengers. A comparison between porphobilinogen oxygenase and a commercial preparation of horseradish peroxidase was made. The latter also catalyzes aerobic porphobilinogen oxidation, with dithionite as electron donor. Here the oxidation of porphobilinogen is inhibited by superoxide dismutase and was not affected by catalase.