Transcriptomic analysis by RNA-seq reveals AP-1 pathway as key regulator that green tea may rely on to inhibit lung tumorigenesis.

Green tea is a promising chemopreventive agent for lung cancer. Multiple signaling events have been reported, however, the relative importance of these mechanisms in mediating the chemopreventive function of green tea is unclear. In the present study, to examine the involvement of AP-1 in green tea polyphenols induced tumor inhibition, human NSCLC cell line H1299 and mouse SPON 10 cells were identified as AP-1 dependent, as these two lines exhibit high constitutive AP-1 activity, and when TAM67 expression was induced with doxycycline, cell growth was inhibited and correlated with suppressed AP-1 activity. RNA-seq was used to determine the global transcriptional effects of AP-1 inhibition and also uncover the possible involvement of AP-1 in tea polyphenols induced chemoprevention. TAM67 mediated changes in gene expression were identified, and within down-regulated genes, AP-1 was identified as a key transcription regulator. RNA-seq analysis revealed that Polyphenon E-treated cells shared 293 commonly down-regulated genes within TAM67 expressing H1299 cells, and by analysis of limited Chip-seq data, over 10% of the down-regulated genes contain a direct AP-1 binding site, indicating that Polyphenon E elicits chemopreventive activity by regulating AP-1 target genes. Conditional TAM67 expressing transgenic mice and NSCLC cell lines were used to further confirm that the chemopreventive activity of green tea is AP-1 dependent. Polyphenon E lost its chempreventive function both in vitro and in vivo when AP-1 was inhibited, indicating that AP-1 inhibition is a major pathway through which green tea exhibits chemopreventive effects.

Neutrophils are required for 3-methylcholanthrene-initiated, butylated hydroxytoluene-promoted lung carcinogenesis.

Multiple studies have shown a link between chronic inflammation and lung tumorigenesis. Inbred mouse strains vary in their susceptibility to methylcholanthrene (MCA)-initiated butylated hydroxytoluene (BHT)-promoted lung carcinogenesis. In the present study we investigated whether neutrophils play a role in strain dependent differences in susceptibility to lung tumor promotion. We observed a significant elevation in homeostatic levels of neutrophils in the lungs of tumor-susceptible BALB/cByJ (BALB) mice compared to tumor-resistant C57BL/6J (B6) mice. Additionally, BHT treatment further elevated neutrophil numbers as well as neutrophil chemoattractant keratinocyte-derived cytokine (KC)/chemokine (C-X-C motif) ligand 1 (Cxcl1) levels in BALB lung airways. Lung CD11c+ cells were a major source of KC expression and depletion of neutrophils in BALB mice resulted in a 71% decrease in tumor multiplicity. However, tumor multiplicity did not depend on the presence of T cells, despite the accumulation of T cells following BHT treatment. These data demonstrate that neutrophils are essential to promote tumor growth in the MCA/BHT two-step lung carcinogenesis model.

Surfactant-associated protein B is critical to survival in nickel-induced injury in mice.

The etiology of acute lung injury is complex and associated with numerous, chemically diverse precipitating factors. During acute lung injury in mice, one key event is epithelial cell injury that leads to reduced surfactant biosynthesis. We have previously reported that transgenic mice that express transforming growth factor alpha (TGFA) in the lung were protected during nickel-induced lung injury. Here, we find that the mechanism by which TGFA imparts protection includes maintenance of surfactant-associated protein B (SFTPB) transcript levels and epidermal growth factor receptor-dependent signaling in distal pulmonary epithelial cells. This protection is complex and not accompanied by a diminution in inflammatory mediator transcripts or additional stimulation of antioxidant transcripts. In mouse lung epithelial (MLE-15) cells, microarray analysis demonstrated that nickel increased transcripts of genes enriched in MTF1, E2F-1, and AP-2 transcription factor-binding sites and decreased transcripts of genes enriched in AP-1-binding sites. Nickel also increased Jun transcript and DNA-binding activity, but decreased SFTPB transcript. Expression of SFTPB under the control of a doxycycline-sensitive promoter increased survival during nickel-induced injury as compared with control mice. Together, these findings support the idea that maintenance of SFTPB expression is critical to survival during acute lung injury.

Effect of dietary green tea extract and aerosolized difluoromethylornithine during lung tumor progression in A/J strain mice.

Chemoprevention strategies to prevent the development of lung cancer in at-risk individuals are a key component in disease management. In addition to being highly effective, an ideal chemopreventive agent will require low toxicity as patients are likely to require treatment for several years before their risk of cancer is lowered to background levels. In principle, a combination of safe agents that work through distinct mechanisms will improve efficacy while simultaneously maintaining a favorable safety profile. Here, we describe the use of the decaffeinated green tea extract Polyphenon E (Poly E) (1% in diet) and aerosolized difluoromethylornithine (DFMO) (20 mg/kg/day, 5 days/week) in a mouse lung cancer chemoprevention study using a progression protocol. Female A/J mice were injected with benzo[a]pyrene (B[a]P) at 8 weeks of age and precancerous lesions allowed to form over a period of 21 weeks before chemoprevention treatment for an additional 25 weeks. Poly E treatment did not significantly inhibit average tumor multiplicity but reduced per animal tumor load. Analysis of tumor pathology revealed a specific inhibition of carcinomas, with the largest carcinomas significantly decreased in Poly E-treated animals. Aerosolized DFMO did not have a significant effect on lung tumor progression. Magnetic resonance imaging of B[a]P-induced lung tumors confirmed the presence of a subset of large, rapidly growing tumors in untreated mice. Our results suggest a potential role for green tea extracts in preventing the progression of large, aggressive lung adenocarcinomas.

Over expression of FGF7 enhances cell proliferation but fails to cause pathology in corneal epithelium of Kerapr-rtTA/FGF7 bitransgenic mice.

PURPOSE: Available evidence suggests that fibroblast growth factor 7 (FGF7, also known as keratinocyte growth factor, KGF) serves as a paracrine growth factor modulating corneal epithelial cell proliferation. In the present study, we used a binary inducible transgenic mouse model to examine the role of FGF7 on corneal epithelium proliferation. METHODS: A keratocyte specific 3.2 kb murine keratocan promoter (Kerapr) was used to prepare Kerapr-rtTA transgenic (Kr) mice that constitutively overexpress reverse tetracycline transcription activator (rtTA) by cornea stromal keratocytes. The Kr mice were crossed with tet-O-FGF7 mice to produce Kr/tet-O-FGF7 bitransgenic mice. Expression of human FGF7 (hFGF7) was induced by the administration of doxycycline via intraperitoneal injection and/or feeding mice doxycycline in drinking water and chow. Overexpression of hFGF7 was confirmed by RT-PCR and western blot. BrdU incorporation was used to determine cell proliferation. RESULTS: The rtTA mRNA and protein were constitutively expressed by the cornea with or without doxycycline induction, whereas hFGF7 was detected only in Kr/tet-O-FGF7 bitransgenic mice upon induction by doxycycline. Examination of induction kinetics in adult Kr/tet-O-FGF7 bitransgenic mice after a single intraperitoneal injection of doxycycline revealed that hFGF7 mRNA expression was detected 12 h after doxycycline administration, peaked at 36 h, was sustained up to 48 h, and declined thereafter. The elevated level of hFGF7 expression coincided with hyperproliferation of corneal epithelial cells. In bitransgenic mice, the number of BrdU labeled cells increased after 36 and 48 h of transgene induction compared to controls of noninduced bitransgenic or doxycycline treated single transgenic mice. The BrdU labeling index was 33+/-9.2 positive cells per corneal section for Kr/tet-O-FGF7 bitransgenic mice and 25+/-9.3 for tet-O-FGF7 single transgenic mice at 36 h post-doxycycline treatment. However, the excess FGF7 driven by doxycycline induction did not produce severe perturbation of corneal epithelium homeostasis. CONCLUSIONS: Our results demonstrate that the doxycycline inducible system is effective in regulating transgene expression in corneal stroma of Kr/tet-O-FGF7 bitransgenic mice. However, the development of pathology resulting from the overexpression of transgenes may depend on whether the amount of transgene product present is sufficient to alter the homeostasis of the targeted tissues.

Increased staining for phospho-Akt, p65/RELA and cIAP-2 in pre-neoplastic human bronchial biopsies.

BACKGROUND: The development of non-small cell lung carcinoma proceeds through a series of well-defined pathological steps before the appearance of invasive lung carcinoma. The molecular changes that correspond with pathology changes are not well defined and identification of the molecular events may provide clues on the progression of intraepithelial neoplasia in the lung, as well as suggest potential targets for chemoprevention. The acquisition of anti-apoptotic signals is critical for the survival of cancer cells but the pathways involved are incompletely characterized in developing intra-epithelial neoplasia (IEN). METHODS: We used immunohistochemistry to determine the presence, relative levels, and localization of proteins that mediate anti-apoptotic pathways in developing human bronchial neoplasia. RESULTS: Bronchial epithelial protein levels of the phosphorylated (active) form of AKT kinase and the caspase inhibitor cIAP-2 were increased in more advanced grades of bronchial IEN lesions than in normal bronchial epithelium. Additionally, the percentage of biopsies with nuclear localization of p65/RELA in epithelial cells increased with advancing pathology grade, suggesting that NF-kappaB transcriptional activity was induced more frequently in advanced IEN lesions. CONCLUSION: Our results indicate that anti-apoptotic pathways are elevated in bronchial IEN lesions prior to the onset of invasive carcinoma and that targeting these pathways therapeutically may offer promise in prevention of non-small cell lung carcinoma.

Mouse models of chemically-induced lung carcinogenesis.

Primary pulmonary malignancies remain the major source of cancer-related deaths in the Western World. While surgical resection is an efficacious therapy for those with early stage disease, the majority of patients present with advanced malignancies and systemic treatments, such as cytotoxic chemotherapy, have only limited efficacy in lung cancer. Furthermore, chemoprevention for current or former smokers has demonstrated only limited success using available agents. The mouse model of primary lung carcinogenesis represents a very valuable tool for the study of tumor initiation, promotion, and therapy. Here we discuss several models of chemically-induced murine lung cancer with a specific emphasis on translational and clinically-relevant lines of investigation. We emphasize the pros and cons of currently available models in order to facilitate further investigations into the development and treatment of primary pulmonary malignancies.

GM-CSF modulates pulmonary resistance to influenza A infection.

Alveolar type II epithelial or other pulmonary cells secrete GM-CSF that regulates surfactant catabolism and mucosal host defense through its capacity to modulate the maturation and activation of alveolar macrophages. GM-CSF enhances expression of scavenger receptors MARCO and SR-A. The alveolar macrophage SP-R210 receptor binds the surfactant collectin SP-A mediating clearance of respiratory pathogens. The current study determined the effects of epithelial-derived GM-CSF in host resistance to influenza A pneumonia. The results demonstrate that GM-CSF enhanced resistance to infection with 1.9×10(4) ffc of the mouse-adapted influenza A/Puerto Rico/8/34 (PR8) H1N1 strain, as indicated by significant differences in mortality and mean survival of GM-CSF-deficient (GM(-/-)) mice compared to GM(-/-) mice in which GM-CSF is expressed at increased levels. Protective effects of GM-CSF were observed both in mice with constitutive and inducible GM-CSF expression under the control of the pulmonary-specific SFTPC or SCGB1A1 promoters, respectively. Mice that continuously secrete high levels of GM-CSF developed desquamative interstitial pneumonia that impaired long-term recovery from influenza. Conditional expression of optimal GM-CSF levels at the time of infection, however, resulted in alveolar macrophage proliferation and focal lymphocytic inflammation of distal airways. GM-CSF enhanced alveolar macrophage activity as indicated by increased expression of SP-R210 and CD11c. Infection of mice lacking the GM-CSF-regulated SR-A and MARCO receptors revealed that MARCO decreases resistance to influenza in association with increased levels of SP-R210 in MARCO(-/-) alveolar macrophages. In conclusion, GM-CSF enhances early host resistance to influenza. Targeting of MARCO may reinforce GM-CSF-mediated host defense against pathogenic influenza.

A dominant-negative c-jun mutant inhibits lung carcinogenesis in mice.

Lung cancer is the leading cause of cancer mortality in the United States and worldwide. The identification of key regulatory and molecular mechanisms involved in lung tumorigenesis is therefore critical to increase our understanding of this disease and could ultimately lead to targeted therapies to improve prevention and treatment. Induction of members of the activator protein-1 (AP-1) transcription factor family has been described in human non-small cell lung carcinoma. Activation of AP-1 can either stimulate or repress transcription of multiple gene targets, ultimately leading to increased cell proliferation and inhibition of apoptosis. In the present study, we show induction of AP-1 in carcinogen-induced mouse lung tumors compared with surrounding normal lung tissue. We then used a transgenic mouse model directing conditional expression of the dominant-negative c-jun mutant TAM67 in lung epithelial cells to determine the effect of AP-1 inhibition on mouse lung tumorigenesis. Consistent with low AP-1 activity in normal lung tissue, TAM67 expression had no observed effects in adult mouse lung. TAM67 decreased tumor number and overall lung tumor burden in chemically induced mouse lung tumor models. The most significant inhibitory effect was observed on carcinoma burden compared with lower-grade lesions. Our results support the concept that AP-1 is a key regulator of mouse lung tumorigenesis, and identify AP-1-dependent transcription as a potential target to prevent lung tumor progression.

Sustained CTL activation by murine pulmonary epithelial cells promotes the development of COPD-like disease.

Chronic obstructive pulmonary disease (COPD) is a lethal progressive lung disease culminating in permanent airway obstruction and alveolar enlargement. Previous studies suggest CTL involvement in COPD progression; however, their precise role remains unknown. Here, we investigated whether the CTL activation receptor NK cell group 2D (NKG2D) contributes to the development of COPD. Using primary murine lung epithelium isolated from mice chronically exposed to cigarette smoke and cultured epithelial cells exposed to cigarette smoke extract in vitro, we demonstrated induced expression of the NKG2D ligand retinoic acid early transcript 1 (RAET1) as well as NKG2D-mediated cytotoxicity. Furthermore, a genetic model of inducible RAET1 expression on mouse pulmonary epithelial cells yielded a severe emphysematous phenotype characterized by epithelial apoptosis and increased CTL activation, which was reversed by blocking NKG2D activation. We also assessed whether NKG2D ligand expression corresponded with pulmonary disease in human patients by staining airway and peripheral lung tissues from never smokers, smokers with normal lung function, and current and former smokers with COPD. NKG2D ligand expression was independent of NKG2D receptor expression in COPD patients, demonstrating that ligand expression is the limiting factor in CTL activation. These results demonstrate that aberrant, persistent NKG2D ligand expression in the pulmonary epithelium contributes to the development of COPD pathologies.

Nonredundant functions of alphabeta and gammadelta T cells in acrolein-induced pulmonary pathology.

Acrolein exposure represents a significant human health hazard. Repeated acrolein exposure causes the accumulation of monocytes/macrophages and lymphocytes, mucous cell metaplasia, and epithelial injury. Currently, the mechanisms that control these events are unclear, and the relative contribution of T-cell subsets to pulmonary pathologies following repeated exposures to irritants is unknown. To examine whether lymphocyte subpopulations regulate inflammation and epithelial cell pathology, we utilized a mouse model of pulmonary pathology induced by repeated acrolein exposures. The role of lymphocyte subsets was examined by utilizing transgenic mice genetically deficient in either alphabeta T cells or gammadelta T cells, and changes in cellular, molecular, and pathologic outcomes associated with repeated inhalation exposure to 2.0 and 0.5 ppm acrolein were measured. To examine the potential functions of lymphocyte subsets, we purified these cells from the lungs of mice repeatedly exposed to 2.0 ppm acrolein, isolated and amplified messenger RNA, and performed microarray analysis. Our data demonstrate that alphabeta T cells are required for macrophage accumulation, whereas gammadelta T cells are critical regulators of epithelial cell homeostasis, as identified by epithelial cell injury and apoptosis, following repeated acrolein exposure. This is supported by microarray analyses that indicated the T-cell subsets are unique in their gene expression profiles following acrolein exposures. Microarray analyses identified several genes that may contribute to phenotypes mediated by T-cell subpopulations including those involved in cytokine receptor signaling, chemotaxis, growth factor production, lymphocyte activation, and apoptosis. These data provide strong evidence that T-cell subpopulations in the lung are major determinants of pulmonary pathology and highlight the advantages of dissecting their effector functions in response to toxicant exposures.

Duration-dependent cytoprotective versus inflammatory effects of lung epithelial fibroblast growth factor-7 expression.

Fibroblast growth factor-7 (FGF7) is a lung epithelial cell mitogen that is cytoprotective during injury. Transgenic mice that conditionally expressed FGF7 were used to dissect the mechanisms of FGF7 protection during lung injury. FGF7 improved survival when induced 3 days prior to acute lung injury. In contrast, FGF7 caused pulmonary inflammation and lung injury after 7 days or longer. Gene expression analysis of mouse lung mRNA identified mRNAs that contribute to the protective effects of FGF7. FGF7 improved survival during acute lung injury in adult mouse lung after short-term expression, but paradoxically induced inflammation and injury after persistent expression.

CD8+ T cells contribute to macrophage accumulation and airspace enlargement following repeated irritant exposure.

BACKGROUND: Persistent macrophage accumulation and alveolar enlargement are hallmark features of chronic obstructive pulmonary disease (COPD). A role for CD8(+) lymphocytes in the development of COPD is suggested based on observations that this T cell subset is increased in the airways and parenchyma of smokers that develop COPD with airflow limitation. In this study, we utilize a mouse model of COPD to examine the contributions of CD8(+) T cells in the persistent macrophage accumulation and airspace enlargement resulting from chronic irritant exposure. METHODS: We analyzed pulmonary inflammation and alveolar destruction in wild-type and Cd8-deficient mice chronically exposed to acrolein, a potent respiratory tract irritant. We further examined cytokine mRNA expression levels by RNase protection assay, matrix metalloproteinase (MMP) activity by gelatin zymography, and epithelial cell apoptosis by active caspase3 immunohistochemistry in wild-type and Cd8-deficient mice exposed chronically to acrolein. RESULTS: These studies demonstrate that CD8(+) T cells are important mediators of macrophage accumulation in the lung and the progressive airspace enlargement in response to chronic acrolein exposures. The expression of several inflammatory cytokines (IP-10, IFN-gamma, IL-12, RANTES, and MCP-1), MMP2 and MMP9 gelatinase activity, and caspase3 immunoreactivity in pulmonary epithelial cells were attenuated in the Cd8-deficient mice compared to wild-type. CONCLUSIONS: These results indicate that CD8(+) T cells actively contribute to macrophage accumulation and the development of irritant-induced airspace enlargement.

Interleukin-1beta causes pulmonary inflammation, emphysema, and airway remodeling in the adult murine lung.

The production of the inflammatory cytokine interleukin (IL)-1 is increased in lungs of patients with chronic obstructive pulmonary disease (COPD) or asthma. To characterize the in vivo actions of IL-1 in the lung, transgenic mice were generated in which human IL-1beta was expressed in the lung epithelium with a doxycycline-inducible system controlled by the rat Clara cell secretory protein (CCSP) promoter. Induction of IL-1beta expression in the lungs of adult mice caused pulmonary inflammation characterized by neutrophil and macrophage infiltrates. IL-1beta caused distal airspace enlargement, consistent with emphysema. IL-1beta caused disruption of elastin fibers in alveolar septa and fibrosis in airway walls and in the pleura. IL-1beta increased the thickness of conducting airways, enhanced mucin production, and caused lymphocytic aggregates in the airways. Decreased immunostaining for the winged helix transcription factor FOXA2 was associated with goblet cell hyperplasia in IL-1beta-expressing mice. The production of the neutrophil attractant CXC chemokines KC (CXCL1) and MIP-2 (CXCL2), and of matrix metalloproteases MMP-9 and MMP-12, was increased by IL-1beta. Chronic production of IL-1beta in respiratory epithelial cells of adult mice causes lung inflammation, enlargement of distal airspaces, mucus metaplasia, and airway fibrosis in the adult mouse.

Gene expression changes during the development of acute lung injury: role of transforming growth factor beta.

RATIONALE: Acute lung injury can occur from multiple causes, resulting in high mortality. The pathophysiology of nickel-induced acute lung injury in mice is remarkably complex, and the molecular mechanisms are uncertain. OBJECTIVES: To integrate molecular pathways and investigate the role of transforming growth factor beta (TGF-beta) in acute lung injury in mice. METHODS: cDNA microarray analyses were used to identify lung gene expression changes after nickel exposure. MAPPFinder analysis of the microarray data was used to determine significantly altered molecular pathways. TGF-beta1 protein in bronchoalveolar lavage fluid, as well as the effect of inhibition of TGF-beta, was assessed in nickel-exposed mice. The effect of TGF-beta on surfactant-associated protein B (Sftpb) promoter activity was measured in mouse lung epithelial cells. MEASUREMENTS AND MAIN RESULTS: Genes that decreased the most after nickel exposure play important roles in lung fluid absorption or surfactant and phospholipid synthesis, and genes that increased the most were involved in TGF-beta signaling. MAPPFinder analysis further established TGF-beta signaling to be significantly altered. TGF-beta-inducible genes involved in the regulation of extracellular matrix function and fibrinolysis were significantly increased after nickel exposure, and TGF-beta1 protein was also increased in the lavage fluid. Pharmacologic inhibition of TGF-beta attenuated nickel-induced protein in bronchoalveolar lavage. In addition, treatment with TGF-beta1 dose-dependently repressed Sftpb promoter activity in vitro, and a novel TGF-beta-responsive region in the Sftpb promoter was identified. CONCLUSIONS: These data suggest that TGF-beta acts as a central mediator of acute lung injury through the alteration of several different molecular pathways.

Conditional gene expression in the respiratory epithelium of the mouse.

Transgenic mouse models mediating conditional temporal and spatial regulation of gene expression to the respiratory epithelium were developed utilizing the reverse tetracycline transactivator (rtTA) expressed under the control of SP-C and CCSP promoters. Luciferase activity was detected in the lungs of fetal and adult double transgenic mice but was not detected in other tissues or in single transgenic mice. In adult mice, maximal luciferase activity was detected 16 h after the administration of doxycycline in the drinking water, or 2 h after the injection of doxycycline. Activation of the transgene was observed after the administration of doxycycline in food pellets. After prolonged exposure to doxycycline, luciferase activity decreased slowly following removal of doxycycline, suggesting the importance of tissue pools which maintained expression of the transgene. In SP-C-rtTA mice, exposure of the pregnant dam to doxycycline induced luciferase activity in fetal lung tissue as early as E10.5. Luciferase activity was maintained in the lung tissue of pups during the period of lactation when the mother received doxycycline in the drinking water. In the CCSP-rtTA mice, luciferase was not detected in the absence of doxycycline. In the SP-C-rtTA mice, luciferase activity was detected in the absence of doxycycline but was enhanced approximately 10-fold by administration of drugs. The SP-C-rtTA and CCSP-rtTA activator mice control the expression of transgenes in the developing and mature respiratory epithelium, and will be useful for the study of gene function in the lung.

Conditional expression of transforming growth factor-alpha in adult mouse lung causes pulmonary fibrosis.

To determine whether overexpression of transforming growth factor (TGF)-alpha in the adult lung causes remodeling independently of developmental influences, we generated conditional transgenic mice expressing TGF-alpha in the epithelium under control of the doxycycline (Dox)-regulatable Clara cell secretory protein promoter. Two transgenic lines were generated, and following 4 days of Dox-induction TGF-alpha levels in whole lung homogenate were increased 13- to 18-fold above nontransgenic levels. After TGF-alpha induction, transgenic mice developed progressive pulmonary fibrosis and body weight loss, with mice losing 15% of their weight after 6 wk of TGF-alpha induction. Fibrosis was detected within 4 days of TGF-alpha induction and developed initially in the perivascular, peribronchial, and pleural regions but later extended into the interstitium. Fibrotic regions were composed of increased collagen and cellular proliferation and were adjacent to airway and alveolar epithelial sites of TGF-alpha expression. Fibrosis progressed in the absence of inflammatory cell infiltrates as determined by histology, without changes in bronchiolar alveolar lavage total or differential cell counts and without changes in proinflammatory cytokines TNF-alpha or IL-6. Active TGF-beta in whole lung homogenate was not altered 1 and 4 days after TGF-alpha induction, and immunostaining was not increased in the peribronchial/perivascular areas at all time points. Chronic epithelial expression of TGF-alpha in adult mice caused progressive pulmonary fibrosis associated with increased collagen and extracellular matrix deposition and increased cellular proliferation. Induction of pulmonary fibrosis by TGF-alpha was independent of inflammation or early activation of TGF-beta.

SP-B deficiency causes respiratory failure in adult mice.

Targeted deletion of the surfactant protein (SP)-B locus in mice causes lethal neonatal respiratory distress. To assess the importance of SP-B for postnatal lung function, compound transgenic mice were generated in which the mouse SP-B cDNA was conditionally expressed under control of exogenous doxycycline in SP-B-/- mice. Doxycycline-regulated expression of SP-B fully corrected lung function in compound SP-B-/- mice and protected mice from respiratory failure at birth. Withdrawal of doxycycline from adult compound SP-B-/- mice resulted in decreased alveolar content of SP-B, causing respiratory failure when SP-B concentration was reduced to <25% of normal levels. Decreased SP-B was associated with low alveolar content of phosphatidylglycerol, accumulation of misprocessed SP-C proprotein in the air spaces, increased protein content in bronchoalveolar lavage fluid, and altered surfactant activity in vitro. Consistent with surfactant dysfunction, hysteresis, maximal tidal volumes, and end expiratory volumes were decreased. Reduction of alveolar SP-B content causes surfactant dysfunction and respiratory failure, indicating that SP-B is required for postnatal lung function.