Transcription of the lung-specific surfactant protein C gene is mediated by thyroid transcription factor 1

Tissue-specific translation of murine branched-chain alpha-ketoacid dehydrogenase kinase mRNA is dependent upon an upstream open reading frame in the 5'-untranslated region

The committed step in the pathway for leucine, isoleucine, and valine catabolism is catalyzed by branched-chain alpha-ketoacid dehydrogenase (BCKD). This multienzyme complex is itself regulated through reversible subunit phosphorylation by a specific kinase (BCKD-kinase). Although BCKD is present in the mitochondria of all mammalian cells, BCKD-kinase has a tissue-specific pattern of expression. Various experimental, nutritional, and hormonal conditions have been used to alter the expression of BCKD-kinase, yet little is known regarding the regulation of basal BCKD-kinase expression under normal conditions including the mechanism of its tissue specificity in any organism. Here we use tissue-derived cultured cells to explore the mechanisms used to control BCKD-kinase expression. Whereas the amount of BCKD-kinase protein is significantly higher in mitochondria from C2C12 myotubes than in BNL Cl.2 liver cells, gene transcription and stability of BCKD-kinase mRNA share similar properties in these two cell types. Our results show that the amount of protein synthesized is regulated at the level of translation of BCKD-kinase mRNA and that an upstream open reading frame in the 5'-untranslated region of this transcript controls its translation. The location and putative 19-residue peptide are conserved in the mouse, rat, chimpanzee, and human genes. Likewise, gene structure of mouse, chimpanzee, and human BCKD-kinase is conserved, whereas the rat gene has lost intron 9.

The utility and limitation of thyroid transcription factor-1 protein in primary and metastatic pulmonary neoplasms

Thyroid transcription factor-1 (TTF-1) is a tissue-specific transcription factor expressed in the thyroid and lung. The clinical utility and limitation of TTF-1 in primary or metastatic carcinomas of the lung have not been previously studied in detail. We examined TTF-1 expression in 510 primary lung and 107 metastatic neoplasms. TTF-1 was detectable in 4/99 (4%) squamous cell carcinomas, 169/176 (96%) solitary adenocarcinomas, 34/34 (100%) multifocal adenocarcinomas, 1/1 (100%) signet ring cell carcinoma, 16/20 (80%) mucinous adenocarcinomas, 23/23 (100%) nonmucinous bronchioloalveolar carcinomas, 19/36 (53%) small cell carcinomas, and 39/44 (89%) sclerosing hemangioma. TTF-1 was absent in all eight carcinoids, three atypical carcinoids, 23 pleomorphic carcinomas, 25 lymphoepithelioma-like carcinomas, the sarcomatous component of one pseudomesotheliomatous carcinoma, and one mesothelioma. In four combined small cell carcinomas and 12 adenosquamous carcinomas, TTF-1 expression was only demonstrated in the adenocarcinoma component. There were 78 TTF-1 non-immunoreactive metastatic cases from 22 livers, 20 colorectums, 10 breasts, six nasopharynx, four larynx, four ovaries, three salivary glands, three esophagus, two adrenal glands, two kidneys, one bile duct, and one endometrium. TTF-1 was also detected in all 10 cervical lymph nodes, seven brain, and 6/7 (86%) bony tissues of 24 patients with metastatic carcinomas of unknown primary site, but it was absent in 125 patients with metastatic carcinomas other than lung origin in cervical lymph nodes, brain, and bony tissues. These results indicate the clinical usefulness and limitation in certain primary and metastatic lung neoplasms.

NKX2.1 regulates transcription of the gene for human bone morphogenetic protein-4 in lung epithelial cells

Bone morphogenetic protein 4, BMP4, plays an important role in the development of various organs including the lungs. Little is known regarding the regulation of Bmp4 gene expression in any organ. In the lung, indirect evidence indicates that NKX2.1, a homeodomain transcriptional factor with a demonstrated role in lung morphogenesis, may be a potential upstream regulator of Bmp4 gene expression. In particular, Bmp4 mRNA is reduced or absent in Nkx2.1(-/-) lungs. The human Bmp4 gene has been reported to include two regions of promoter activity in an embryonal carcinoma cell line, Tera2EC. The hBmp4.1 promoter is located upstream of exon I, whereas the second promoter, hBmp4.2, is localized within intron 1 and upstream of exon II. In the current study, we used a co-transfection assay in lung epithelial cells to examine the response of the two hBmp4 promoters to transcriptional stimulation by NKX2.1. Two DNA sequences were identified on the hBmp4.1 promoter that bind NKX2.1 and serve as functional cis-active NKX2.1-responsive elements. Similarly, NKX2.1 stimulated transcription from the hBmp4.2 promoter through two consensus binding sites localized within 412 nucleotides from the site of transcriptional initiation. Thus, both hBmp4 promoters include specific cis-active elements that bind to and mediate transcriptional regulation by NKX2.1. These findings bear functional implications regarding the regulation of a key signaling molecule by a homeodomain transcriptional regulator of lung epithelial morphogenesis.

TAZ Interacts with TTF-1 and Regulates Expression of Surfactant Protein-C

Thyroid transcription factor-1 (TTF-1/Nkx-2.1) is required for formation of the lung and differentiation of peripheral respiratory epithelial cells. TTF-1 activates transcription of target genes, including the surfactant proteins critical for lung function. A recently identified protein TAZ (transcriptional co-activator with PDZ-binding motif) contains a WW domain and a COOH-terminal PDZ-binding motif that are proposed to mediate its interactions with various transcriptional proteins. To determine the role of TAZ in the regulation of gene expression in the lung, the sites of TAZ expression and the role of TAZ in the regulation of respiratory epithelial gene expression were assessed. TAZ mRNA was detected in immortalized mouse lung epithelial cells, primary isolates of mouse alveolar type II epithelial cells, and epithelial cells of fetal lung. Sites of TAZ mRNA and protein overlapped with those of TTF-1 and surfactant protein C (SP-C) in the respiratory epithelial cells of the mouse lung. In the presence of TTF-1, TAZ synergistically activated the expression of mouse SP-C-luciferase reporter constructs. Mammalian two-hybrid assays and pull-down experiments demonstrated that the TAZ directly interacted with TTF-1. Further, deletion analysis demonstrated that TAZ binds to the NH(2)-terminal domain of TTF-1. TAZ binds to TTF-1, increasing the transcriptional activity of TTF-1 on the SP-C promoter. Developmental and cell-selective regulation of TAZ provides a mechanism by which the activity of TTF-1 on target genes is modulated.

Nuclear factor I/thyroid transcription factor 1 interactions modulate surfactant protein C transcription

Surfactant protein C (SP-C; Sftpc) gene expression is restricted to pulmonary type II epithelial cells. The proximal SP-C promoter region contains critical binding sites for nuclear factor I (NFI) and thyroid transcription factor 1 (TTF-1; also called Nkx2.1). To test the hypothesis that NFI isoforms interact with TTF-1 to differentially regulate SP-C transcription, we performed transient transfection assays in JEG-3 cells, a choriocarcinoma cell line with negligible endogenous NFI or TTF-1 activity. Cotransfection of NFI family members with TTF-1 induced synergistic activation of the SP-C promoter that was further enhanced by p300. TTF-1 directly interacts with the conserved DNA binding and dimerization domain of all NFI family members in coimmunoprecipitation and mammalian two-hybrid experiments. To determine whether SP-C expression is regulated by NFI in vivo, a chimeric fusion protein containing the DNA binding and dimerization domain of NFI-A and the Drosophila engrailed transcriptional repression domain (NFIen) was conditionally expressed in mice under control of a doxycycline-inducible transgene. Induction of NFIen in a subset of type II cells inhibited SP-C gene expression without affecting expression of TTF-1 in doxycycline-treated double-transgenic mice. Taken together, these findings support the hypothesis that NFI family members interact with TTF-1 to regulate type II cell function.

FGF signaling is required for pulmonary homeostasis following hyperoxia

To assess the role of fibroblast growth factor (FGF) signaling in pulmonary function in the postnatal period, we generated transgenic mice in which a soluble FGF receptor (FGFR-HFc) was conditionally expressed in respiratory epithelial cells of the mouse lung, thereby inhibiting FGF activity. Although FGFR-HFc did not alter postnatal lung morphogenesis, male FGFR-HFc transgenic mice were more susceptible to hyperoxia and failed to recover when ambient oxygen concentrations were normalized. Inflammation, alveolar-capillary leak, and mortality were increased following exposure to 95% Fi(O(2)). Expression of surfactant protein (SP)-A and SP-B were significantly decreased in association with decreased immunostaining for thyroid transcription factor-1. FGF signaling is required for maintenance of surfactant homeostasis and lung function during hyperoxia in vivo, mediated, at least in part, by its role in the maintenance of SP-B expression.

Thyroid hormone affects distal airway formation during the late pseudoglandular period of mouse lung development

We recently showed that T3 treatment of cultured gestational day 11.5 early pseudoglandular period mouse lungs, accelerated terminal airway development at the expense of decreased branching morphogenesis. As the ability of T3 to influence epithelial cell differentiation increases with advancing development, we hypothesized that in the late pseudoglandular period, T3 would cause further premature changes in the morphology of the distal airways leading to abnormal saccular development. Gestational day 13.5 embryonic mouse lungs were cultured for 3 and 7 days without or with added T3. Increasing T3 dose and time in culture resulted in progressive development of thin walled, abnormal saccules, an increase in cuboidal and flattened epithelia and airway space with a concomitant decrease in mesenchymal cell volume. Consistent with increased cuboidal and flattened epithelial cell volume identified by morphometry, immunostaining suggested increased cell proliferation detected by localization of proliferating cell nuclear antigen (PCNA) in epithelial cells of T3 treated lungs. T3 decreased mesenchymal expression of Hoxb-5 protein and caused progressive localization of Nkx2.1 and SP-C proteins to distal cuboidal epithelia of early abnormal saccules, evidence that T3 prematurely and abnormally advanced mesenchymal and epithelial cell differentiation. Western blot showed a T3-dependent decrease in Hoxb-5 and a trend towards decreased Nkx2.1 and SP-C, after 3 and 7 days of culture, respectively. We conclude that exogenous T3 treatment during the late pseudoglandular period prematurely and abnormally accelerates terminal saccular development. This may lead to abnormal mesenchymal and epithelial cell fate.

Identification of uteroglobin-related protein 1 and macrophage scavenger receptor with collagenous structure as a lung-specific ligand-receptor pair

High in normal (HIN)-1 is a secreted protein highly expressed in normal breast epithelium and down-regulated in breast carcinomas. By searching GenBank expressed sequence tag databases, we identified HIN-2, a protein homologous to HIN-1. HIN-2 is identical with a recently identified protein called uteroglobin-related protein 1 (UGRP1). Northern blot analysis demonstrated that UGRP1 is specifically expressed by lung, but not by the other tissues examined. By in situ hybridization experiments, UGRP1 was shown to be expressed by lung Clara-like cells in the bronchial epithelium and to be up-regulated in cystic fibrosis. In a mammalian expression system, secreted recombinant UGRP1 was copurified with apolipoprotein A-I. Using a retroviral vector-mediated expression cloning approach, we identified macrophage scavenger receptor with collagenous structure (MARCO) as a receptor for UGRP1. Northern blot and in situ hybridization experiments indicated that MARCO is expressed by alveolar macrophages in the lung. UGRP1 also bound to bacteria and yeast. LPS, a previously identified MARCO ligand, competed with UGRP1 for binding to MARCO and bacteria. Our findings suggest that UGRP1-MARCO is a ligand-receptor pair that is probably involved in inflammation and pathogen clearance in the lung.

The paired domain-containing factor Pax8 and the homeodomain-containing factor TTF-1 directly interact and synergistically activate transcription

Pax genes encode for transcription factors essential for tissue development in many species. Pax8, the only member of the family expressed in the thyroid tissue, is involved in the morphogenesis of the gland and in the transcriptional regulation of thyroid-specific genes. TTF-1, a homeodomain-containing factor, is also expressed in the thyroid tissue and has been demonstrated to play a role in thyroid-specific gene expression. Despite the presence of Pax8 and TTF-1 also in a few other tissues, the simultaneous expression of the two transcription factors occurs only in the thyroid, supporting the idea that Pax8 and TTF-1 might cooperate to influence thyroid-specific gene expression. In this report, we describe a physical and functional interaction between these two factors. The fusion protein GST-Pax8 is able to bind TTF-1 present in thyroid or in non-thyroid cell extracts, and by using bacterial purified TTF-1 we demonstrate that the interaction is direct. By co-immunoprecipitation, we also show that the interaction between the two proteins occurs in vivo in thyroid cells. Moreover, Pax8 and TTF-1 when co-expressed in HeLa cells synergistically activate Tg gene transcription. The synergism requires the N-terminal activation domain of TTF-1, and deletions of Pax8 indicate that the C-terminal domain of the protein is involved. Our results demonstrate a functional cooperation and a physical interaction between transcription factors of the homeodomain-containing and of the paired domain-containing gene families in the regulation of tissue-specific gene expression.

Expression of thyroid transcription factor-1 in 16 human lung cancer cell lines

It has been suggested that thyroid transcription factor-1 (TTF-1) is frequently expressed in human lung cancer, especially in adenocarcinoma and small cell lung cancer, and the TTF-1 expression is closely related with the expression of surfactant protein. We hypothesized that TTF-1 is expressed in human lung cancer cell lines and its expression might be related to the expression of surfactant protein. To test this, expressions of TTF-1 and surfactant protein A (SP-A) were immunohistochemically evaluated in 16 human lung cancer cell lines. In addition, expressions of mRNAs for TTF-1 and SP-A were analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR) and sequencing. As a result, nuclear staining of TTF-1 was observed in two of six adenocarcinoma cell lines, none of seven small cell lung cancer cell lines, and none of three squamous lung cancer cell lines. Among the 16 cell lines, six cell lines (PC3, LC2/Ad, A549, RERF-LC-OK, HI1017, and PC9) expressed significant amounts of mRNA for TTF-1. In contrast, cytoplasmic staining of TTF-1 was observed in five of six adenocarcinoma cell lines, in six of seven small cell lung cancer cell lines, and in all three squamous cell lung cancer cell lines. One of the two adenocarcinoma cell lines those showed positive nuclear staining and cytoplasmic SP-A staining released a significant amount of SP-A in culture supernatant. Our present study demonstrates that the frequency of TTF-1 expression in the nucleus was very low in human lung cancer cell lines; however, their cytoplasmic positivities should be further investigated.

Synergistic transactivation of the differentiation-dependent lung gene Clara cell secretory protein (secretoglobin 1a1) by the basic region leucine zipper factor CCAAT/enhancer-binding protein alpha and the homeodomain factor Nkx2.1/thyroid transcription factor-1

The basic region-leucine zipper transcription factor CCAAT/enhancer-binding protein alpha (C/EBPalpha) and the homeodomain transcription factor Nkx2.1/thyroid transcription factor-1 are essential for normal lung morphogenesis. Nkx2.1 is expressed from the onset of lung development, whereas C/EBPalpha expression is turned on at later stages. The expression of C/EBPalpha correlates to the appearance of lung-specific proteins with differentiation-dependent expression patterns, such as the Clara cell secretory protein (secretoglobin 1a1 (Scgb1a1), CCSP). In this study, we demonstrate synergistic transactivation by C/EBPalpha and Nkx2.1 in the regulation of the CCSP gene. We show that the synergistic activity of C/EBPalpha and Nkx2.1 originates from cis-acting elements in the proximal promoter of CCSP and that the synergism is dependent on NH(2)-terminal transactivation domains of C/EBPalpha and Nkx2.1. Our results suggest that the cooperation of C/EBPalpha and Nkx2.1 is a major determinant for the high level, lung epithelial-specific expression of CCSP during the later stages of lung development and in the adult lung.

The WNT7b promoter is regulated by TTF-1, GATA6, and Foxa2 in lung epithelium

In this study, we find that WNT7b is the only member of the WNT family of autocrine/paracrine signaling molecules whose expression in the lung is restricted to the airway epithelium during embryonic development. To study the transcriptional mechanisms that underlie this restricted pattern of WNT7b expression, we isolated the proximal 1.0-kb mouse WNT7b promoter and mapped the transcriptional start sites. Transfection of the lung epithelial cell line MLE-15, which expresses WNT7b, shows that the 1.0-kb mouse WNT7b promoter is highly active in lung epithelial cells. This region of the WNT7b promoter contains several DNA binding sites for the important lung-restricted transcription factors TTF-1, GATA6, and Foxa2. Electrophoretic mobility shift assays showed that TTF-1, GATA6, and Foxa2 can bind to a specific subset of their consensus DNA binding sites within the WNT7b promoter. Using cotransfection assays, we demonstrate that TTF-1, GATA6, and Foxa2 can trans-activate the WNT7b promoter in NIH-3T3 cells. Truncation of GATA6 or Foxa2 binding sites reduced the ability of these transcriptional regulators to trans-activate the WNT7b promoter. Finally, the minimal 118-bp region of the mouse WNT7b promoter containing only TTF-1 binding sites was synergistically activated by TTF-1 and GATA6, and we show that TTF-1 and GATA6 physically interact in vivo. Together, these results suggest that WNT7b gene expression in the lung epithelium is regulated in a combinatorial fashion by TTF-1, GATA6, and Foxa2.

TTF-1 expression in pulmonary adenocarcinomas

Tissue-specific gene expression is mediated largely by transcription factors, and a master regulatory gene is thus a potential marker of cellular lineage. Using normal fetal through adult pulmonary tissues and 64 consecutive lung adenocarcinomas, we examined the expression of thyroid transcription factor (TTF-1), which plays a crucial role in normal lung function and morphogenesis. TTF-1 was expressed consistently throughout the life stages and uniformly in the terminal respiratory unit, which is comprised of peripheral airway cells and small-sized bronchioles. Furthermore, the expression was maintained in 72% of adenocarcinomas that exhibited high correlation with surfactant apoprotein (p <0.001) and morphologic resemblance to terminal respiratory unit cells (p <0.001). The staining pattern was also uniform in the adenocarcinomas despite histologic and microenvironmental diversity in individual tumors and their metastatic foci. This consistency and uniformity, therefore, suggested that TTF-1 expression could be used as a lineage marker of terminal respiratory unit. We also identified interesting distinctions between TTF-1-positive and -negative adenocarcinomas based on their clinicopathologic features and expression of various cancer-associated genes. TTF-1-positive adenocarcinomas had statistically significant prevalence of female (p <0.01), nonsmoker (p <0.05), negative p53 staining (p <0.01), less frequent RB loss (p <0.05), and preserved expression of p27 (p <0.01). The results supported the TTF-1 lineage marker and suggested that molecular pathogenesis may in part be characterized by cellular lineage.

Thyroid transcription factor-1 is highly sensitive and specific in differentiating metastatic pulmonary from extrapulmonary adenocarcinoma in effusion fluid cytology specimens

BACKGROUND

Thyroid transcription factor-1 (TTF-1) is a homeodomain-containing transcription factor selectively expressed in thyroid, lung and diencephalon. It has been shown to label pulmonary adenocarcinoma, thyroid tumors, and small cell carcinoma (pulmonary and extrapulmonary) with relatively high sensitivity and specificity. The usefulness of this immunostain in cytology specimens has not been thoroughly discussed in the literature.

METHODS

The authors evaluated 36 effusion cytology cases (17 pleural effusion, 18 ascitic fluid, and 1 pericardial effusion) diagnosed as metastatic adenocarcinoma and with cell blocks prepared from the file of Pamela Youde Nethersole Eastern Hospital, Hong Kong, during a three-year period from 1998 to early 2001. The clinical, radiologic, cytologic, and histologic (if any) findings were reviewed. A provisional diagnosis of the primary site was deduced for each of the 36 cases by clinical, radiologic, and/or histologic correlation. Immunohistochemical study was performed on the cell block sections of the effusion cytology specimens using mouse monoclonal antibody against TTF-1, after microwave heat-antigen retrieval. The results were correlated with the primary origin of the metastatic adenocarcinoma.

RESULTS

Among the 17 cases of metastatic pulmonary adenocarcinoma, 15 cases showed nuclear staining for TTF-1 in most of the tumor cells (sensitivity, 88.2%). None of the 19 cases of metastatic extrapulmonary adenocarcinoma expressed TTF-1 (specificity, 100%).

CONCLUSIONS

The current study validates TTF-1 as a highly sensitive and specific immunomarker for distinguishing between metastatic pulmonary and extrapulmonary adenocarcinoma in effusion cytology specimens, which are known to be associated with intrinsic artifact due to less than ideal cellular preservation.

Increased expression of thyroid transcription factor-1 (TTF-1) in respiratory epithelial cells inhibits alveolarization and causes pulmonary inflammation

Thyroid transcription factor-1 (TTF-1), a member of the Nkx2 family of homeodomain-containing transcription factors, is expressed in the epithelium of the lung. TTF-1 is a critical regulator of transcription for the surfactant proteins (SP) A, B, and C and is essential for lung morphogenesis. Sites and levels of TTF-1 expression vary during lung morphogenesis and following injury. In order to determine the role of TTF-1 in lung formation, transgenic mice were generated in which TTF-1 was expressed in respiratory epithelial cells of wild-type and Ttf1 null mutant (-/-) mice, using the lung-specific SP-C promoter. The SP-C-Ttf1 transgene did not rescue the severe pulmonary hypoplasia characteristic of the Ttf1 (-/-) mice. Increased expression of TTF-1, however, caused dose-dependent alterations in postnatal lung morphology of wild-type mice. Modest overexpression of TTF-1 caused type II cell hyperplasia and increased the cellular content of SP-B. In contrast, higher expression levels of TTF-1 disrupted alveolar septation, causing emphysema. In mice with the highest transgene expression, TTF-1 caused severe inflammation, pulmonary fibrosis, respiratory failure, and death, associated with eosinophil infiltration and increased expression of eotaxin and IL-6. Increased expression of TTF-1 altered alveolarization and caused chronic pulmonary inflammation, demonstrating that precise regulation of TTF-1 is critical for homeostasis in the postnatal lung.

GATA-6 and thyroid transcription factor-1 directly interact and regulate surfactant protein-C gene expression

GATA-6, a member of the GATA family of zinc finger domain containing transcription factors, is expressed in endodermally derived tissues including the lung, where GATA-6 influences the transcription of target genes, TTF-1, and surfactant proteins. Whereas GATA-6 did not directly alter expression of sp-C constructs in HeLa cells, GATA-6 synergistically activated sp-C gene transcription when co-expressed with TTF-1, supporting the concept that GATA-6 and TTF-1 might directly interact to influence target gene expression. GST-GATA-6 directly co-precipitated with TTF-1 after in vitro translation and directly interacted with the TTF-1-binding element in the sp-C promoter. Binding of TTF-1 to GATA-6 required the homeodomain of TTF-1, but optimal interactions with GATA-6 required the homeodomain and either carboxyl- or amino-terminal domains of TTF-1. Interactions between TTF-1 and GATA-6 required the amino-terminal and zinc finger domains of GATA-6. Although GATA-4 also interacted with TTF-1 in two-hybrid assays, GATA-4 was not as active as GATA-6 in the activation of the sp-C promoter with TTF-1. Deletion and substitution mutations between GATA-4 and GATA-6 demonstrated that the carboxyl-terminal zinc finger domain of GATA-6 contributed to its synergistic activation of the sp-C promoter with TTF-1. GATA-6 influenced the activity of the sp-C promoter, binding and acting synergistically with TTF-1.

The pulmonary surfactant system matures upon pipping in the freshwater turtle Chelydra serpentina

Pulmonary surfactant (PS), a mixture of phospholipids (PL), neutral lipids and surfactant proteins (SP), lowers surface tension within the lung, which increases lung compliance and improves the removal of fluid at birth. Here, we have examined the expression of thyroid transcription factor-1 (TTF-1) and the surfactant protein SP-B, and also the composition of pulmonary surfactant lipids in the developing lung of the turtle Chelydra serpentina. Lavage and lung tissue were collected from late embryonic, pipped and hatchling turtles. TTF-1, a regulator of gene expression of surfactant proteins and cell differentiation in mammals, was detected using immunohistochemistry in epithelia of the gas-exchange area and conducting airways during late development. Expression declined in hatchlings. SP-B was detected in subsets of cells within the respiratory epithelium at all stages sampled. The same cell types also stained for TTF-1. Turtle surfactant lipids matured toward the end of incubation. Maximal secretion of both total phospholipids and disaturated phospholipid (DSP) occurred at the time of pipping, coincident with the onset of breathing. The DSP/PL ratio increased after pipping, whereas cholesterol levels (Chol) increased prior to pipping. This resulted in a decrease in the Chol/PL and Chol/DSP ratios after pipping. Thus, TTF-1 and SP-B appear to be highly conserved within the vertebrates. Maturation of surfactant phospholipid content occurred with the commencement of pulmonary ventilation.

Pseudomonas aeruginosa and tumor necrosis factor-alpha attenuate Clara cell secretory protein promoter function

The Clara cell secretory protein (CCSP, also CC-10/uterglobin) is a 16-kD homodimeric protein abundantly expressed in the airways of mammals. Although the molecular function is unknown, gene-targeting studies indicate CCSP as a regulator of lung inflammation following acute respiratory infection or injury. CCSP is decreased in the lungs of mice following acute Pseudomonas aeruginosa (P.a.) infection. In the present study, the role of decreased promoter function in the regulation of CCSP by P.a. was assessed using an in vitro co-culture system and in vivo studies of transgenic mice. CCSP promoter activity in lung epithelial cells was markedly decreased by P.a. or tumor necrosis factor-alpha (TNF-alpha) in a dose-dependent manner. Regulation of CCSP promoter function by either P.a. or TNF-alpha was localized to the proximal 166 bp flanking region of the CCSP promoter activity. Decreased regulation of the CCSP promoter by P.a. or TNF-alpha was specific to CCSP, as human surfactant protein D (SP-D) promoter activity was unaffected or increased by P.a. or TNF-alpha, respectively. A neutralizing antibody against human TNF-alpha was able to reverse both the TNF-alpha- mediated as well as P.a.-mediated decrease in CCSP promoter function in lung epithelial cells. TNF-alpha secretion by lung epithelial cells coincided with the decrease in CCSP promoter function following P.a. administration. Using a transgenic mouse model, P.a. administration to the lung markedly attenuated CCSP promoter-conferred gene expression in vivo. The attenuation of CCSP promoter activity in lung epithelial cells by P.a. involves, in part, autocrine/paracrine secretion of TNF-alpha, which in turn regulates CCSP transcription through cis-active elements in the proximal promoter region.

Role of CBP/p300 and SRC-1 in transcriptional regulation of the pulmonary surfactant protein-A (SP-A) gene by thyroid transcription factor-1 (TTF-1)

Surfactant protein-A (SP-A) gene expression is developmentally regulated in fetal lung type II cells and is enhanced by cAMP. cAMP stimulation of SP-A gene expression is mediated by protein kinase A (PKA) phosphorylation of thyroid transcription factor 1 (TTF-1), expressed selectively in developing lung epithelium. In this study, we analyzed roles of CREB-binding protein (CBP) and steroid receptor coactivator-1 (SRC-1) in TTF-1 regulation of SP-A expression. Upon differentiation of human fetal lung in culture, nuclear localization of CBP, SRC-1, and TTF-1 increased in ductular epithelium in association with type II cell differentiation and induction of SP-A expression. In transient transfections, CBP and SRC-1 acted synergistically with TTF-1 to increase SP-A promoter activity. Overexpression of PKA catalytic subunit enhanced hSP-A promoter activation by SRC-1 plus TTF-1. Adenoviral E1A overexpression reduced TTF-1 +/- SRC-1 induction of SP-A promoter activity, suggesting a role of endogenous CBP/p300. TTF-1 interacted with SRC-1 and CBP in vitro. SRC-1 immunodepletion from type II cell nuclear extracts reduced binding to the TTF-1 binding element upstream of SP-A gene. In cultured type II cells, cAMP increased TTF-1 acetylation. This suggests that cAMP-mediated TTF-1 phosphorylation facilitates interaction with CBP and SRC-1, resulting in its hyperacetylation, further enhancing TTF-1 DNA-binding and transcriptional activity.

Primary signet-ring cell carcinoma of lung: immunohistochemical study and comparison with non-pulmonary signet-ring cell carcinomas

Signet-ring cell carcinoma (SRCC) of lung is a rare variant of pulmonary adenocarcinoma. In view of this rarity, the question of whether an SRCC is primary pulmonary or metastatic arises frequently because the majority of SRCCs seen in lung are metastatic tumors having arisen in stomach, colon, or breast. On routine histologic examination it is difficult to distinguish between pulmonary SRCC from SRCC metastasizing from other organs. Thyroid transcription factor-1 (TTF-1) is a homeodomain-containing transcription factor that is almost exclusively expressed in thyroid and pulmonary epithelial cells. TTF-1 expression has been demonstrated in various neoplasms of lung; however, the expression of TTF-1 in SRCCs has not been investigated so far. In the present study, using an immunoperoxidase staining procedure on paraffin sections, we investigated the expression of TTF-1, cytokeratin 7, cytokeratin 20, and villin (a specific marker expressed in tumors of the digestive tract, renal proximal tubules, and hepatic bile ducts) in 32 SRCCs from various organs (17 lung, 5 breast, 5 stomach, and 5 colon). Fourteen (82.4%) of 17 pulmonary SRCCs exhibited TTF-1 positivity, whereas none of the SRCCs of other organs were positive for TTF-1. A cytokeratin profile (CK7+/CK20-) was identified in 94.1% of pulmonary SRCC, and although it differed from the profile exhibited in colonic SRCCs (CK7-/CK20+), a similar profile was seen in breast SRCCs and some SRCCs arising in the stomach. Villin was identified in 29.4% of pulmonary SRCCs and 20% (one case) arising in the breast. Although the pattern of villin immunostaining exhibited by nondigestive tract SRCCs (cytoplasmic) differed from those of digestive tract SRCCs (membranous), distinguishing between the two groups based on their pattern of immunostaining alone would be difficult. The results of this study indicate that TTF-1 is expressed in a high percentage of pulmonary SRCCs and is very specific and that TTF-1 would be extremely valuable in distinguishing pulmonary SRCCs from those arising in other organs.

Malignant pleural effusions due to small-cell lung carcinoma: a cytologic and immunocytochemical study

Patients with small-cell lung carcinoma (SCLC) rarely present with pleural effusions. Based on morphology alone, recognition of SCLC in effusion cytology may be challenging because of the resemblance of neoplastic cells to lymphocytes. Immunocytochemistry may be helpful in its diagnosis. The objective of this study was to review the morphology and evaluate the use of immunocytochemistry in diagnosing SCLC in pleural fluids. Patients with SCLC who presented with pleural effusions were identified during a 6-yr period. The cytology and medical records were reviewed. Formalin-fixed, paraffin-embedded cell blocks of fluid specimens were immunostained with neuroendocrine markers (chromogranin A and synatophysin), cytokeratin 20 (CK20), and thyroid transcription factor-1 (TTF-1). The latter is a nuclear transcription protein that is expressed in normal respiratory epithelium and also in more than 90% of SCLCs. Of the 256 patients diagnosed with SCLC during the study period, 8 (2.7%) patients (3 females and 4 males, age range from 56-85 yr) also developed pleural effusions. One patient had 2 fluid specimens during the course of their disease, giving a total of 9 specimens. Four specimens had a positive cytologic diagnosis of SCLC, and 2 were initially diagnosed as suspicious for SCLC. The remaining 3 specimens were negative for SCLS. The specimens with a positive or suspicious diagnosis showed single and aggregates of small to medium-sized single cells with a high nuclear:cytoplasmic (N:C) ratio, round to angulated nuclei, and salt-and-pepper chromatin. Nuclear molding was also noted. Five out of 6 (83%) specimens with a positive or suspicious diagnosis of SCLC were positive for both chromogranin A and TTF-1. Synaptophysin was positive in 3 of 6 (50%) positive or suspicious cases. None of the cases were positive for CK20. All cases with a negative cytologic diagnosis were negative for chromogranin A, synatophysin, CK20, and TTF-1. In conclusion, patients with SCLC rarely present with pleural effusions. The cytology of SCLC is characteristic. The use of immunocytochemistry, particularly with antibodies to chromogranin A, TTF-1, and CK 20, aids in the differential diagnosis.

claudin-18, a novel downstream target gene for the T/EBP/NKX2.1 homeodomain transcription factor, encodes lung- and stomach-specific isoforms through alternative splicing

T/EBP/NKX2.1, a member of the NKX family of homeodomain-containing transcription factors, regulates the expression of a number of genes in lung and thyroid. Here we describe the isolation and characterization of a novel target gene, termed claudin-18, that is down-regulated in the lungs of T/ebp/Nkx2.1-null mouse embryos. The gene product exhibits an amino acid sequence similar to those of the claudin multigene family of proteins that constitute tight junction strands in epithelial cells. The gene was localized by fluorescence in situ hybridization to mouse chromosome 9 at region 9E3-F1 and to human chromosome 3 at region 3q21-23. The claudin-18 gene has two promoters, each with its own unique exon 1 that is spliced to common exons 2 through 5. Alternative usage of these promoters leads to production of lung and stomach-specific transcripts. The downstream lung-specific promoter contains two T/EBP/NKX2.1 binding sites responsible for trans activation of the gene by T/EBP/NKX2.1 in lung cells. Only claudin-18 was down-regulated in T/ebp/Nkx2.1-null embryo lungs among 11 claudin transcripts examined. Furthermore, the claudin-18 transcript has an alternative 12-bp insertion derived from the 5' end of intron 4, which produces a C-terminally truncated isoform in lung and stomach. Immunohistochemistry demonstrated complete membrane localization of claudin-18 with small focal dots in the lung and stomach epithelial cells. Immunogold electron microscopy analysis revealed that claudin-18 is concentrated at the cell-cell borders of epithelial cells. These unique features suggest a potentially important role for claudin-18 in the structure and function of tight junctions in lung and stomach.

Use of thyroid transcription factor 1, PE-10, and cytokeratins 7 and 20 in discriminating between primary lung carcinomas and metastatic lesions in fine-needle aspiration biopsy specimens

BACKGROUND

The distinction of a primary lung carcinoma from a metastatic lesion is important, because the treatment and prognosis differ for patients with these malignancies. Such a distinction can be difficult because of overlapping cytologic features. It has been shown that antibodies to thyroid transcription factor 1 (TTF-1) and PE-10 are fairly specific markers for primary lung tumors in histologic specimens. TTF-1 regulates the expression of surfactant protein production, and PE-10 is a monoclonal antibody against components of human surfactant proteins. The combination of cytokeratin 7 (CK7) and cytokeratin 20 (CK20) immunoprofiling has been helpful in the identification of the primary site of origin of lung tumors.

METHODS

In the current study, the authors evaluated the utility of TTF-1 and PE-10 immunostaining and also compared the staining with expression of CK7 and CK20 in the discrimination between primary lung tumors and metastatic lesions in 55 specimens from fine-needle aspiration (FNA) biopsies of the lung. Formalin fixed, paraffin embedded cell blocks from 35 primary lung tumors (16 adenocarcinomas, 8 squamous cell carcinomas, 6 large cell undifferentiated carcinomas, and 5 small cell carcinomas) and 20 metastatic carcinomas (6 breast lesions, 6 colon lesions, 3 urinary bladder lesions, 2 kidney lesions, 1 biliary tract lesion, 1 endometrial lesion, and 1 thyroid lesion) were immunostained with monoclonal antibodies to TTF-1, PE-10, CK7, and CK 20. Positive immunostaining for CK7, CK20, and PE-10 was based on cytoplasmic staining, whereas TTF-1 positive staining was based on nuclear staining of the neoplastic cells.

RESULTS

Positive immunostaining with TTF-1 and PE-10 was noted in six primary lung tumors (17%). One metastatic lesion (5%) and two metastatic lesions (10%) were positive for TTF-1 and PE-10, respectively. The CK7 positive/CK20 negative immunophenotype was noted in 30 primary lung tumors (86%) and in 11 metastatic lesions (55%). The CK7 negative/CK20 negative immunophenotype was seen in four metastatic lesions and in the remaining five primary lung tumors. The CK7 negative/CK20 positive and CK7 positive/CK20 positive immunophenotypes were seen in two and three metastatic lesions, respectively, but in none of the primary lung tumors. When a CK7 positive/CK20 negative adenocarcinoma also demonstrated either TTF-1 positive or PE-10 positive staining, it was likely that the adenocarcinoma was of pulmonary origin (P < 0.035; Fisher exact test). The specificity of such a combination for discriminating between primary and metastatic adenocarcinomas was 94%.

CONCLUSIONS

The results suggest that TTF-1, PE-10, or CK7/CK20 alone did not distinguish reliably between primary pulmonary tumors carcinomas and metastatic neoplasms of the lung in FNA biopsy specimens because of low sensitivity and specificity. The use of a panel of antibodies that includes CK7/CK20, TTF-1, and PE-10 may be helpful in discriminating between primary and metastatic adenocarcinomas of the lung. An adenocarcinoma is likely a primary lung tumor when it is of the CK7 positive/CK20 negative phenotype and demonstrates either TTF-1 positive or PE-10 positive staining.

The DNA glycosylase T:G mismatch-specific thymine DNA glycosylase represses thyroid transcription factor-1-activated transcription

The transcription factor thyroid transcription factor-1 (TTF-1) is a homeodomain-containing protein that belongs to the NK2 family of genes involved in organogenesis. TTF-1 is required for normal development of the forebrain, lung, and thyroid. In a search for factors that regulate TTF-1 transcriptional activity, we isolated three genes (T:G mismatch-specific thymine DNA glycosylase (TDG), homeodomain-interacting protein kinase 2 (HIPK2), and Ajuba), whose products can interact with TTF-1 in yeast and in mammalian cells. TDG is an enzyme involved in base excision repair. In the present paper, we show that TDG acts as a strong repressor of TTF-1 transcriptional activity in a dose-dependent manner, while HIPK2 and Ajuba display no effect on TTF-1 activity, at least under the tested conditions. TDG-mediated inhibition occurs specifically on TTF-1-responsive promoters in thyroid and non thyroid cells. TDG associates with TTF-1 in mammalian cells through the TTF-1 carboxyl-terminal activation domain and is independent of the homeodomain. These findings reveal a previously unsuspected role for the repair enzyme TDG as a transcriptional repressor and open new routes toward the understanding of the regulation of TTF-1 transcriptional activity.

Mucinous and nonmucinous bronchioloalveolar adenocarcinomas have distinct staining patterns with thyroid transcription factor and cytokeratin 20 antibodies

We studied 14 mucinous and 26 nonmucinous bronchioloalveolar adenocarcinomas (BACs) with thyroid transcription factor (TTF), cytokeratin (CK) 7, CK20, and villin to characterize their staining patterns with these antibodies and identify staining differences between the neoplasms. We also stained 11 mucinous colon adenocarcinomas with the same antibodies to compare their reaction patterns with mucinous BACs. All pulmonary neoplasms were confirmed pulmonary primary BACs. Three (21%) of 14 mucinous neoplasms had weak TTF reactivity in fewer than 25% of neoplastic cell nuclei, and the other 11 (79%) were nonreactive. In contrast, 24 (92%) of 26 nonmucinonus BACs were strongly TTF reactive. Eleven mucinous BACs (79%) had CK20 reactivity in more than 25% of neoplastic cells, whereas only 1 nonmucinous BAC (4%) had reactivity in fewer than 50% of the cells. One mucinous BAC (7%) had villin reactivity in approximately 10% of the neoplastic cells. All mucinous colon adenocarcinomas were diffusely reactive with CK20 and villin. Mucinous and nonmucinous BACs have disparate staining patterns with TTF and CK20. Mucinous BACs are usually TTF nonreactive and CK20 reactive, but nonreactive with villin, which distinguishes them from mucinous colon adenocarcinomas.

Characterization of a New Subfamily of Winged-helix/Forkhead (Fox) Genes That Are Expressed in the Lung and Act as Transcriptional Repressors

Epithelial gene expression in the lung is thought to be regulated by the coordinate activity of several different families of transcription factors including the Fox family of winged-helix/forkhead DNA-binding proteins. In this report, we have identified and characterized two members of this Fox gene family, Foxp1 and Foxp2, and show that they comprise a new subfamily of Fox genes expressed in the lung. Foxp1 and Foxp2 are expressed at high levels in the lung as early as E12.5 of mouse development with Foxp2 expression restricted to the airway epithelium. In addition, Foxp1 and Foxp2 are expressed at lower levels in neural, intestinal, and cardiovascular tissues during development. Upon differentiation of the airway epithelium along the proximal-distal axis, Foxp2 expression becomes restricted to the distal alveolar epithelium whereas Foxp1 expression is observed in the distal epithelium and mesenchyme. Foxp1 and Foxp2 can regulate epithelial lung gene transcription as was demonstrated by their ability to dramatically repress the mouse CC10 promoter and, to a lesser extent, the human surfactant protein C promoter. In addition, GAL4 fusion proteins encoding subdomains of Foxp1 and Foxp2 demonstrate that an independent and homologous transcriptional repression domain lies within the N-terminal end of the proteins. Together, these studies suggest that Foxp1 and Foxp2 are important regulators of lung epithelial gene transcription.

Thyroid transcription factor-1 distinguishes metastatic pulmonary from well-differentiated neuroendocrine tumors of other sites

Metastatic neuroendocrine neoplasms can have similar histologic appearances, and without an obvious primary, it may be difficult to determine the site of origin of the metastasis. Thyroid transcription factor-1 (TTF-1) is a nuclear protein expressed during the development of thyroid, lung, and forebrain. The clinical utility of TTF-1 to distinguishing between metastatic pulmonary and nonpulmonary well-differentiated neuroendocrine tumors (WDNET) has not been previously studied. One hundred fifty-eight primary and metastatic WDNET were evaluated for TTF-1 expression. The tumors included 20 pulmonary WDNET, including 17 typical and 3 atypical carcinoid tumors, 10 metastatic pulmonary WDNET, 26 intestinal WDNET, 24 metastatic intestinal WDNET, 3 thymic mediastinal WDNET, 30 thyroid tumors (10 medullary carcinomas, 5 follicular carcinomas, 5 follicular adenomas, 5 papillary carcinomas, and 5 anaplastic carcinomas), 10 parathyroid adenomas, 20 pituitary adenomas, 10 pancreatic WDNET, and 5 pheochromocytomas. TTF-1 expression was found in 19 of 20 (95%) pulmonary WDNET, 8 of 10 (80%) metastatic pulmonary WDNET, and in 0 of 50 (0%) intestinal WDNET. All thyroid tumors were diffusely positive for TTF-1, except for three anaplastic carcinomas. All parathyroid and pituitary adenomas, pancreatic and thymic WDNET, and pheochromocytomas were uniformly negative for TTF-1. These results indicate that TTF-1 is clinically useful in distinguishing metastatic pulmonary from metastatic WDNET of extrapulmonary origin.

A unique combination of transcription factors controls differentiation of thyroid cells

The thyroid follicular cell type is devoted to the synthesis of thyroid hormones. Several genes, whose protein products are essential for efficient hormone biosynthesis, are uniquely expressed in this cell type. A set of transcriptional regulators, unique to the thyroid follicular cell type, has been identified as responsible for thyroid specific gene expression; it comprises three transcription factors, named TTF-1, TTF-2, and Pax8, each of which is expressed also in cell types different from the thyroid follicular cells. However, the combination of these factors is unique to the thyroid hormone producing cells, strongly suggesting that they play an important role in differentiation of these cells. An overview of the molecular and biological features of these transcription factors is presented here. Data demonstrating that all three play also an important role in early thyroid development, at stages preceding expression of the differentiated phenotype, are also reviewed. The wide temporal expression, from the beginning of thyroid organogenesis to the adult state, is suggestive of a recycling of the thyroid-specific transcription factors, that is, the control of different sets of target genes at diverse developmental stages. The identification of molecular mechanisms leading to specific gene expression in thyroid cells renders this cell type an interesting model in which to address several aspects of cell differentiation and organogenesis.

The transcription factor GATA6 is essential for branching morphogenesis and epithelial cell differentiation during fetal pulmonary development

Recent loss-of-function studies in mice show that the transcription factor GATA6 is important for visceral endoderm differentiation. It is also expressed in early bronchial epithelium and the observation that this tissue does not receive any contribution from Gata6 double mutant embryonic stem (ES) cells in chimeric mice suggests that GATA6 may play a crucial role in lung development. The aim of this study was to determine the role of GATA6 in fetal pulmonary development. We show that Gata6 mRNA is expressed predominantly in the developing pulmonary endoderm and epithelium, but at E15.5 also in the pulmonary mesenchyme. Blocking or depleting GATA6 function results in diminished branching morphogenesis both in vitro and in vivo. TTF1 expression is unaltered in chimeric lungs whereas SPC and CC10 expression are attenuated in abnormally branched areas of chimeric lungs. Chimeras generated in a ROSA26 background show that endodermal cells in these abnormally branched areas are derived from Gata6 mutant ES cells, implicating that the defect is intrinsic to the endoderm. Taken together, these data demonstrate that GATA6 is not essential for endoderm specification, but is required for normal branching morphogenesis and late epithelial cell differentiation.

BR22, a novel protein, interacts with thyroid transcription factor-1 and activates the human surfactant protein B promoter

Surfactant protein (SP)-B expression is restricted to type II pneumocytes and Clara cells in the lung. Previously, a promoter region of human SP-B gene from -64 to -118 has been identified as critical for the tissue-specific expression of this gene. Two cis-elements for thyroid transcription factor (TTF)-1 and hepatocyte nuclear factor (HNF)-3alpha binding were found within this area. Using an oligonucleotide fragment, we incorporated this region sequence into the promoter of a HIS3 reporter gene in yeast. With this modified yeast a human lung complementary DNA (cDNA) library was screened for DNA-binding proteins, other than TTF-1 and HNF-3alpha, that interacted with this promoter segment. A cDNA clone encoding a novel polypeptide, BR22, was identified that activated the reporter gene expression in yeast. This gene is expressed in many tissues and encodes a protein with bipartite nuclear localization signals. Studies using in vivo yeast two-hybrid analysis, in vitro protein-protein interactions, and coimmunoprecipitation analyses demonstrated that BR22 formed a protein complex with TTF-1. In vivo cotransfection studies further indicated that BR22 could act with TTF-1 to synergistically activate the SP-B promoter in mammalian cells. Our data suggest that BR22 is a TTF-1-associated protein. Through a protein-protein interaction with TTF-1, BR22 can form a complex and activate the human SP-B promoter in vivo.

KGF regulates pulmonary epithelial proliferation and surfactant protein gene expression in adult rat lung

Keratinocyte growth factor (KGF, FGF-7) is a potent mitogen for epithelial cells. We instilled recombinant human KGF to determine the effects of KGF on alveolar epithelial cells. Left lungs of adult rats were instilled intrabronchially with KGF (5 mg/kg) or normal saline. KGF instillation resulted in epithelial cell hyperplasia, and the alveolar bromodeoxyuridine (BrdU) labeling index peaked at 35% on day 2 after instillation. The mRNA levels for the surfactant proteins (SPs) SP-A, SP-B, and SP-D were increased in whole lung tissue on days 1 and 2 after KGF treatment and then returned to control levels on days 3-7. SP-C mRNA levels were increased on days 2-5 after KGF instillation. However, all surfactant protein mRNAs were reduced in type II cells isolated from rats instilled with KGF 2 or 3 days before isolation. These observations were confirmed by in situ hybridization. Instillation of KGF also increased the amount of SP-A and SP-D in lavage fluid. Transcripts for CC10, the 10-kDa Clara cell protein, were decreased. KGF increases the mRNA for the surfactant proteins per lung because of type II cell hyperplasia, but the mRNA per cell is slightly diminished as measured in isolated cells or estimated by in situ hybridization.

Pulmonary sclerosing hemangioma consistently expresses thyroid transcription factor-1 (TTF-1): a new clue to its histogenesis

The histogenesis of pulmonary sclerosing hemangioma has remained controversial despite extensive studies by many investigators. The availability of an antibody to thyroid transcription factor-1 (TTF-1), which is expressed in type II pneumocytes and Clara cells, has prompted us to readdress this issue. Sixteen cases were immunostained with a panel of antibodies including TTF-1. The patients were predominantly women with an age range of 30 to 73 years (mean, 52 yrs). All tumors were solitary. The single male patient showed regional lymph node metastases, an unusual occurrence reported only once in the literature. All cases exhibited the classic histologic features, with variegated patterns. TTF-1 expression was observed in both the surface lining cells and the pale polygonal cells. The surface lining cells were epithelial membrane antigen (EMA)+ cytokeratin+ surfactant apoprotein A+, whereas the polygonal cells were EMA+ cytokeratin- surfactant apoprotein A-. The neuroendocrine markers synaptophysin and chromogranin were both negative. The metastatic deposits in the lymph nodes comprised only polygonal cells and exhibited an EMA+ cytokeratin- surfactant apoprotein A- TTF- 1+ immunophenotype. These results suggest that pulmonary sclerosing hemangioma is an epithelial neoplasm derived from primitive respiratory epithelium or incompletely differentiated type II pneumocyte or Clara cell.

Proximal promoter of the surfactant protein D gene: regulatory roles of AP-1, forkhead box, and GT box binding proteins

Surfactant protein D (SP-D) plays roles in pulmonary host defense and surfactant homeostasis and is increased following lung injury. Because AP-1 proteins regulate cellular responses to diverse environmental stimuli, we hypothesized that the conserved AP-1 motif (at -109) and flanking sequences in the human SP-D promoter contribute to the regulation of SP-D expression. The AP-1 sequence specifically bound to fra-1, junD, and junB in H441 lung adenocarcinoma nuclear extracts. Mutagenesis of the AP-1 motif in a chloramphenicol acetyltransferase reporter construct containing 285 base pairs of upstream sequence nearly abolished promoter activity, and co-transfection of junD significantly increased wild type but not mutant promoter activity. The sequence immediately downstream of the AP-1 element contained a binding site for HNF-3 (FOXA), and simultaneous mutation of this site (fox-d) and an upstream FoxA binding site (-277, fox-u) caused a 4-fold reduction in chloramphenicol acetyltransferase activity. Immediately upstream of the AP-1-binding site, we identified a GT box-containing positive regulatory element. Despite finding regions of limited homology to the thyroid transcription factor 1-binding site, SP-D promoter activity did not require thyroid transcription factor 1. Thus, transcriptional regulation of SP-D gene expression involves complex interactions with ubiquitous and lineage-dependent factors consistent with more generalized roles in innate immunity.

Role of transcription factors in fetal lung development and surfactant protein gene expression

Branching morphogenesis of the lung and differentiation of specialized cell populations is dependent upon reciprocal interactions between epithelial cells derived from endoderm of embryonic foregut and surrounding mesenchymal cells. These interactions are mediated by elaboration and concerted actions of a variety of growth and differentiation factors binding to specific receptors. Such factors include members of the fibroblast growth factor family, sonic hedgehog, members of the transforming growth factor-beta family, epidermal growth factor, and members of the platelet-derived growth factor family. Hormones that increase cyclic AMP formation, glucocorticoids, and retinoids also play important roles in branching morphogenesis, alveolar development, and cellular differentiation. Expression of the genes encoding these morphogens and their receptors is controlled by a variety of transcription factors that also are highly regulated. Several of these transcription factors serve dual roles as regulators of genes involved in early lung development and in specialized functions of differentiated cells. Targeted null mutations of genes encoding many of these morphogens and transcription factors have provided important insight into their function during lung development. In this chapter, the cellular and molecular mechanisms that control lung development are considered, as well as those that regulate expression of the genes encoding the surfactant proteins.

Value of thyroid transcription factor-1 immunostaining in distinguishing small cell lung carcinomas from other small cell carcinomas

The distinction between small cell lung carcinoma (SCLC) and small cell carcinomas of other sites is difficult by routine histology. Thyroid transcription factor-1 (TTF-1) is a homeodomain-containing transcription factor that is selectively expressed in thyroid and pulmonary epithelial cells. TTF-1 expression has also been demonstrated in adenocarcinomas of the thyroid and lung, and SCLC. However, the value of TTF-1 immunostaining in discriminating between SCLC and nonpulmonary small cell carcinomas has not been investigated. In the present study using an immunoperoxidase staining procedure on paraffin sections, we investigated the expression of TTF-1 and cytokeratin 20 (CK20), a marker that has previously been demonstrated in small cell carcinomas of the skin (Merkel cell carcinomas), in 82 small cell carcinomas from a wide variety of sites (28 lung, 18 skin, 12 gastrointestinal tract, 8 sinonasal, 5 bladder, 3 prostate, 3 uterine cervix, 2 thyroid, 2 salivary gland, and 1 pancreas). Twenty-seven (96%) of the 28 SCLCs were positive for TTF-1. Among the nonpulmonary small cell carcinomas, two tumors of the gastrointestinal tract, one of the bladder, and one of the uterine cervix exhibited TTF-1 positivity. Sixteen (89%) of the 18 Merkel cell carcinomas and one SCLC were CK20-positive. All other small cell carcinomas were negative for this marker. These results indicate that although TTF-1 is not a specific marker for SCLC, it may assist in distinguishing SCLC from some nonpulmonary small cell carcinomas, particularly Merkel cell carcinoma, especially when it is used in conjunction with CK20.

Expression of thyroid transcription factor-1 in congenital cystic adenomatoid malformation of the lung

Congenital cystic adenomatoid malformation (CCAM) is an abnormality of branching morphogenesis of the lung. CCAM types 1, 2, and 3 exhibit a cellular composition that is different from that of CCAM type 4 when evaluated with bronchiolar and alveolar cell markers. Thyroid transcription factor 1 (TTF-1) regulates early lung development. To evaluate the potential role of TTF-1 in the development of CCAM, TTF-1 expression in CCAM was compared to that of fetal lungs at varying gestational ages. Twenty-three CCAM cases (17 type 1, two type 2, two type 3, and two type 4) and 11 fetal lungs (3 pseudoglandular, 4 canalicular, and 4 terminal sac stages) were analyzed using a rabbit polyclonal antiserum to rat TTF-1. Nuclear staining for TTF-1 was observed in ciliated and nonciliated cells of the bronchial and bronchiolar epithelia and in cells lining the distal air spaces by 12 weeks gestational age. By mid-gestation, proximal bronchial cells were TTF-1 negative, except for the basal cells, while TTF-1 staining was maintained in distal bronchiolar and alveolar cells. TTF-1 expression decreased in both bronchial, bronchiolar, and alveolar epithelia with advancing gestational age and cytodifferentiation. At term, TTF-1 expression persisted in a few bronchial and bronchiolar basal cells and in all alveolar type II cells, whereas type I cells were negative. In CCAM, TTF-1 was detected in the nuclei of epithelial cells lining the cysts. TTF-1 was expressed in a majority of the bronchiolar-like epithelial cells of the cysts in CCAM types 1, 2, and 3, where almost 100% of the cells were TTF-1 positive. In contrast, TTF-1 expression in the alveolar-like epithelium of CCAM type 4 cysts was restricted to type II cells and only 30%-60% of the lining cells were TTF-1 positive. These results support the hypothesis that CCAM types 1, 2, and 3 reflect abnormalities in lung morphogenesis and differentiation that are distinct from those for CCAM type 4. The role played by TTF-1 in the development of CCAM, if any, is not clear.

Patterning of the "distal esophagus" in esophageal atresia with tracheo-esophageal fistula: is thyroid transcription factor 1 a player?

BACKGROUND

We have recently proposed that the "distal esophagus" in esophageal atresia with tracheo-esophageal fistula (EA/TEF) is actually embryologically derived from the middle branch of a trifurcation of the embryonic lung bud, which subsequently grows caudally in the foregut to connect with the developing stomach. We hypothesized that differential mRNA expression of the lung-specific patterning transcription factor, thyroid transcription factor 1 (TTF-1), in the developing fistula tract in TEF relative to the bronchi (the other branches of the lung bud trifurcation) might explain the unique nonbranching pattern of growth of the fistula tract.

MATERIALS AND METHODS

EA/TEF was induced in Sprague-Dawley rat embryos via intraperitoneal injection of 2.2 mg/kg adriamycin into pregnant dams on Days 6-9 of gestation. The foregut from embryos developing EA/TEF and from control embryos (no adriamycin) were isolated on Gestational Days 13.5, 15.5, and 17.5 (term = 21 days). Some were processed for whole-mount in situ hybridization for TTF-1, while others were embedded and sectioned for histologic analysis via in situ hybridization for TTF-1.

RESULTS

The expression of the respiratory-specific transcription factor TTF-1 is conserved in the epithelium of the developing fistula tract in TEF. The pattern of expression of TTF-1 in the fistula tract mirrors the expression in the large airways of the developing lungs, despite the fact that the fistula tract does not form secondary branches to give rise to a lung.

CONCLUSIONS

The fistula tract in TEF is a respiratory-derived structure that expresses the lung-specific transcription factor TTF-1 throughout its development in the foregut. Contrary to the patterning role that it normally plays in the developing lung, TTF-1 does not induce branching morphogenesis in the fistula tract. Thus, the nonbranching pattern of growth of the fistula tract may be attributable to local mesenchymal-epithelial interactions that override TTF-1 patterning activity.

Activation of surfactant protein-B transcription: signaling through the SP-A receptor utilizing the PI3 kinase pathway

This study describes receptor-activated signaling initiated by surfactant protein-A (SP-A), and the means by which it activates transcription of surfactant protein-B. Pulmonary surfactant is a mixture of lipids and associated proteins produced by type II pneumocytes. Interaction of SP-A with its cognate receptor (SPAR) on type II cells is involved in regulating surfactant secretion. This interaction also increases transcription of surfactant proteins and several other genes. To study SP-A cytokine activity, we used as a model surfactant-protein (SP-B) transcription, the activators of which have been characterized. HNF-3 and TTF-1 transcription factors are known to stimulate SP-B transcription. SP-A caused increased phosphorylation and nuclear localization of both. Corresponding increases in protein binding to the SP-B promoter were demonstrated by gel shift analysis. SP-A increased protein binding to HNF-3 and TTF-1 consensus recognition elements. Footprinting analysis indicated that SP-A-induced protein binding to SP-B promoter was greater in amount, but not different in location, from that seen in control cells, which normally transcribe SP-B. SP-A caused transient increases in PI3 kinase localization at the plasma membrane, and SP-A signaling to elicit increased SP-B transcription was blocked by LY294002, an inhibitor of PI3 kinase. Therefore, SP-A signals through PI3 kinase to increase SP-B transcription in type II pneumocytes by enhancing TTF-1 and HNF-3 activation of the SP-B promoter. SP-A activation of this signaling pathway, which affects many cellular functions and has not previously been implicated in type II cell transcriptional activity, has profound import for understanding type II cell biology.

Deletion of NKX2.1 gene encoding thyroid transcription factor-1 in two siblings with hypothyroidism and respiratory failure

Thyroid transcription factor-1 encoded by the NKX2.1 gene is a candidate regulator of thyroid and lung morphogenesis and function in humans. We report 2 female siblings with congenital thyroid dysfunction and recurrent acute respiratory distress carrying a heterozygous deletion of chromosome 14q12-13.3, resulting in haploinsufficiency for the NKX2.1 gene. This observation further supports a physiologic role for thyroid transcription factor-1 in early human thyroid and pulmonary function.

Transforming growth factor-beta(1) regulation of surfactant protein B gene expression is mediated by protein kinase-dependent intracellular translocation of thyroid transcription factor-1 and hepatocyte nuclear factor 3

The transforming growth factor-beta (TGF beta) polypeptides control a variety of cellular processes including organogenesis and cellular proliferation and differentiation. In the developing lung, TGF beta(1) treatment inhibits airway branching and expression of the genes for surfactant proteins (SP). Many effects of TGF beta are mediated at the level of gene transcription but there is limited information regarding signaling pathways and target transcription factors. In this study with human pulmonary adenocarcinoma H441 cells, we investigated TGF beta(1) effects on SP-B, a protein which is essential for normal function of pulmonary surfactant. TGF beta(1) (10 ng/ml) reduced SP-B mRNA content in a time-dependent fashion, and transient transfection studies localized responsiveness to the region of the SP-B promoter (-112/-72 bp) containing binding sites for thyroid transcription factor-1 (TTF-1) and hepatocyte nuclear factor 3 (HNF3), transcription factors that are important enhancers of SP gene expression. Using electrophoretic mobility shift assay and immunofluorescence, we demonstrated rapid accumulation of these transcription factors in the cytoplasm and subsequent loss from the nucleus on TGF beta(1) treatment of both adenocarcinoma cells and cultured human fetal lung. TGF beta(1) treatment caused intracellular translocation of protein kinase C and effects of TGF beta(1) were mostly abrogated in the presence of the protein kinase inhibitor calphostin C. We conclude that TGF beta(1), acting via protein phosphorylation, blocks nuclear translocation of TTF-1 and HNF3 which results in down-regulation of the SP-B gene and presumably other pulmonary genes which are transactivated by these factors.

Down-regulation of thyroid transcription factor-1 gene expression in fetal lung hypoplasia is restored by glucocorticoids

The thyroid transcription factor (TTF)-1 has an essential role in lung morphogenesis and development. It is involved in the transcription of surfactant proteins (SP), which are critical in respiratory function. Neonates with congenital diaphragmatic hernia die of respiratory failure caused by pulmonary hypoplasia with associated biochemical immaturity. To gain new insights into the causes of this disorder and the effect of prenatal hormonal treatment on reducing mortality in these infants, we evaluated the expression of TTF-1 as marker of lung morphogenesis and SP-B as marker of lung maturity. Using a rat model of lung immaturity, we show that TTF-1 and SP-B messenger RNA (mRNA) levels are drastically reduced in congenital lung hypoplasia. Interestingly, prenatal dexamethasone (Dex) treatment increased both TTF-1 and SP-B mRNAs over control levels when administered to rats with lung hypoplasia, but it had no effect on TTF-1 or a moderate effect on SP-B mRNA when administered to control rats. TRH alone also increases TTF-1 and SP-B mRNA levels but to a lesser extent than Dex. When administered together with Dex, TRH counteracts the induction observed with the glucocorticoid. The decrease in TTF-1 mRNA levels in lung hypoplasia is paralleled by a down-regulation of TTF-1 protein levels, as well as by a decrease in the TTF-1/DNA complex when the TTF-1-binding site of the SP-B promoter was used as a probe. Both parameters were reestablished after glucocorticoid treatment. Moreover, the regulation of TTF-1 gene expression described in this report is accompanied by the same regulation in its promoter activity, as demonstrated in transfection experiments performed in H-441 human lung-derived adenocarcinoma cells. In conclusion, our data demonstrate, for the first time, that lung hypoplasia and the associated respiratory dysfunction caused by SP-B deficiency are caused, in part, by down-regulation of TTF-1 gene expression. The observations that prenatal glucocorticoid treatment induces the expression of TTF-1 supports routine in utero glucocorticoid treatment of patients expected to have lung hypoplasia.

Human SP-C gene sequences that confer lung epithelium-specific expression in transgenic mice

We used transgenic mice to identify cis-active regions of the human pulmonary surfactant protein C (SP-C) gene that impart tissue- and cell-specific expression in vivo in the lung. Approximately 3.7 kb of genomic SP-C DNA upstream of the transcription start site was sufficient to direct chloramphenicol acetyltransferase (CAT) reporter gene expression specifically in bronchiolar and alveolar epithelial cells of the lung. To further define cis-active regulatory elements that mediate cell-specific expression, we tested deletions of the parental 3.7-kb human SP-C sequence in transgenic mice. Tissue CAT assays of mice generated with truncations or overlapping internal deletions of the 3.7-kb construct functionally map alveolar cell-specific regulatory elements to within -215 bp of the SP-C promoter. Analysis of SP-C promoter deletions demonstrate that sequences between -3.7 kb and -1.9 kb contain enhancer sequences that stimulate SP-C transgene expression. In situ hybridization studies demonstrate that deletion of the -1,910- to -215-bp region abolishes the ectopic bronchiolar expression seen with the original 3.7-kb SP-C promoter construct. Comparison of sequences from -215 to +1 bp identified consensus binding sites for the homeodomain transcription factor thyroid transcription factor-1 (TTF-1). Cotransfection assays of the human 3.7-kb SP-C or -1,910- to -215-bp SP-C deletion construct with a TTF-1 expression plasmid demonstrates that TTF-1 transactivates the human SP-C gene. These results suggest that the TTF-1 cis-active sites are important in directing cell-specific expression of the SP-C gene in vivo.

Thyroid transcription factor-1 in normal, hyperplastic, and neoplastic follicular thyroid cells examined by immunohistochemistry and nonradioactive in situ hybridization

Thyroid transcription factor-1 (TTF-1) has been known to regulate the transcriptional activity of thyroid-specific genes. We examined the expression of TTF-1 in non-neoplastic and neoplastic thyroid tissues. By immunohistochemistry, the nuclei of normal and hyperplastic follicular cells strongly reacted with the antibody against TTF-1. Immunohistochemistry also revealed a distinctive nuclear positivity of TTF-1 in all 33 differentiated follicular cell tumors, including 15 follicular adenomas, 5 follicular carcinomas, and 13 papillary carcinomas. No immunoreactions were observed in three of four undifferentiated carcinomas, whereas an isolated and weak nuclear positivity was obtained in one. In normal and hyperplastic tissues, the distribution of TTF-1 was fairly related to that of thyroid-specific proteins thyroglobulin and thyroperoxidase. However, discrepancies in the distribution were observed in tumor tissues. By in situ hybridization, the riboprobe hybridized distinctively with the cytoplasm of neoplastic cells as well as normal follicular cells. Papillary carcinoma cells expressed TTF-1 mRNA in all but two cases, and its expression was also demonstrated in one of four undifferentiated carcinomas. Reverse transcription-polymerase chain reaction confirmed the presence of TTF-1 mRNA in two human undifferentiated carcinoma cell lines, TTA-1 and TTA-2. In conclusion, the investigation of TTF-1 provides useful information on the functional activities and/or differentiation of thyroid tumors and may lead to an increase in our understanding of the biologic nature of thyroid tumors.

Two functionally distinct forms of NKX2.1 protein are expressed in the pulmonary epithelium

The homeodomain transcriptional factor NKX2.1 is critical for normal morphogenesis of the lung, thyroid, and the brain. In the lung, NKX2. 1 binds to and activates the expression of pulmonary differentiation-specific genes SP-A, SP-B, and SP-C. The Nkx2.1 gene is comprised of three exons separated by two introns. In both thyroid and lung, the predominant Nkx2.1 transcript includes exons II and III and is translated into a 371 amino acid protein. A minor transcript also exists which includes all three exons. This transcript encodes a 401 amino acid isoform of NKX2.1. The 30 amino acid extension is highly conserved amongst various mammalian species. In the current study, we demonstrate that the two NKX2.1 isoforms are functionally distinct and their corresponding transcripts are expressed differentially during mouse embryonic lung development. The results demonstrate that the longer isoform of NKX2.1 exhibits reduced activity in transactivating an SP-C target promoter when compared to the truncated major NKX2.1 protein. Site directed mutagenesis of the 30 amino acid peptide extension suggests that this fragment alters the activity of 5E likely by steric interference.

The molecular basis of lung morphogenesis

To form a diffusible interface large enough to conduct respiratory gas exchange with the circulation, the lung endoderm undergoes extensive branching morphogenesis and alveolization, coupled with angiogenesis and vasculogenesis. It is becoming clear that many of the key factors determining the process of branching morphogenesis, particularly of the respiratory organs, are highly conserved through evolution. Synthesis of information from null mutations in Drosophila and mouse indicates that members of the sonic hedgehog/patched/smoothened/Gli/FGF/FGFR/sprouty pathway are functionally conserved and extremely important in determining respiratory organogenesis through mesenchymal-epithelial inductive signaling, which induces epithelial proliferation, chemotaxis and organ-specific gene expression. Transcriptional factors including Nkx2.1, HNF family forkhead homologues, GATA family zinc finger factors, pou and hox, helix-loop-helix (HLH) factors, Id factors, glucocorticoid and retinoic acid receptors mediate and integrate the developmental genetic instruction of lung morphogenesis and cell lineage determination. Signaling by the IGF, EGF and TGF-beta/BMP pathways, extracellular matrix components and integrin signaling pathways also directs lung morphogenesis as well as proximo-distal lung epithelial cell lineage differentiation. Soluble factors secreted by lung mesenchyme comprise a 'compleat' inducer of lung morphogenesis. In general, peptide growth factors signaling through cognate receptors with tyrosine kinase intracellular signaling domains such as FGFR, EGFR, IGFR, PDGFR and c-met stimulate lung morphogenesis. On the other hand, cognate receptors with serine/threonine kinase intracellular signaling domains, such as the TGF-beta receptor family are inhibitory, although BMP4 and BMPR also play key inductive roles. Pulmonary neuroendocrine cells differentiate earliest in gestation from among multipotential lung epithelial cells. MASH1 null mutant mice do not develop PNE cells. Proximal and distal airway epithelial phenotypes differentiate under distinct transcriptional control mechanisms. It is becoming clear that angiogenesis and vasculogenesis of the pulmonary circulation and capillary network are closely linked with and may be necessary for lung epithelial morphogenesis. Like epithelial morphogenesis, pulmonary vascularization is subject to a fine balance between positive and negative factors. Angiogenic and vasculogenic factors include VEGF, which signals through cognate receptors flk and flt, while novel anti-angiogenic factors include EMAP II.

A novel DNA element mediates transcription of Nkx2.1 by Sp1 and Sp3 in pulmonary epithelial cells

NKX2.1 is a member of the NK2 family of homeodomain-containing transcription factors whose targeted disruption in mouse results in the absence of thyroid tissue and a severely abnormal lung phenotype. Little is known regarding the mechanisms that control tissue and temporal specificity of Nkx2.1 gene expression. The Nkx2.1 gene has been cloned from a number of species and it is composed of three exons and two introns. Two distinct DNA domains located 5' of exon I and within intron I have been found to exhibit promoter activity in lung and thyroid cells. In the current study we used deletional analysis of the 5' flanking region of exon I and identified a 300 bp TATA-less region that exhibits significant promoter activity in H441 cells. The DNA sequence of this region contains multiple palindromes, composed of G/C-rich elements. DNase I footprinting demonstrates that this promoter region interacts with nuclear factors present in H441 cells. In particular electrophoretic mobility shift assay using antibodies against the Sp family members show that both Sp1 and Sp3 as well as an as yet unknown H441-specific factor interact with the palindromic structure within this promoter region. Co-transfection studies show that this promoter region responds to Sp1 and Sp3 and mutations therein result in a significantly diminished response to these transcriptional factors. Therefore, we have identified a novel DNA structure on the Nkx2.1 gene which participates in transcription of this gene in pulmonary epithelial cells by Sp1 and Sp3 transcription factors.

GATA-6 activates transcription of surfactant protein A

Surfactant protein A (SP-A) is a member of the collectin family of innate host defense molecules expressed primarily in respiratory epithelial cells of the lung. SP-A concentrations are influenced by both cell-specific and ubiquitous nuclear proteins that regulate SP-A gene transcription in a cell-selective and temporally regulated manner. In this work, a consensus GATA-binding site (GBS) was identified at positions -69 to -64 of the mouse SP-A gene. The transcriptional activity of wild-type SP-A reporter constructs in HeLa cells was increased 5-10-fold when cotransfected with a GATA-6 expression plasmid. Deletion of the GBS completely blocked transactivation by GATA-6. Transfection of a construct expressing GATA-6-engrailed fusion protein inhibited basal expression of the SP-A/chloramphenicol acetyltransferase construct in MLE-15 cells. Nuclear extract proteins from MLE-15 cells bound to the GBS in the mouse SP-A gene, and a supershifted band was detected with a GATA-6-specific antibody. Transactivation of the wild-type SP-A constructs by GATA-6 increased transcriptional activity 7-10-fold, whereas thyroid transcription factor-1 (TTF-1) increased the activity of these constructs 12-18-fold. The effects of cotransactivating with both GATA-6 and TTF-1 expression constructs were additive. However, mutation of the TTF-1-binding sites alone or in combination decreased GATA-6 transactivation. Likewise, mutation of the GBS blocked TTF-1 activation of the SP-A promoter. In situ hybridization demonstrated GATA-6 mRNA in the peripheral epithelial cells of fetal mouse lung, consistent with the sites of SP-A expression. GATA-6 is expressed in respiratory epithelial cells and binds to a cis-acting element in the SP-A gene promoter, activating the transcriptional activity of the gene.

Critical residues of the homeodomain involved in contacting DNA bases also specify the nuclear accumulation of thyroid transcription factor-1

The N-terminal end of thyroid transcription factor-1 (TTF-1) homeodomain is composed of a stretch of five basic amino-acids that is conserved in both POU- and NK2-class homeodomains and constitutes a functional nuclear localization signal. By analyzing the cellular distribution of fusion proteins, composed of a jellyfish green fluorescent variant and different parts of TTF-1, we show here that the presence of this basic sequence is not sufficient by itself to confer complete nuclear accumulation. By mutagenesis, we identified a second region located in the center of the DNA recognition helix of the homeodomain that is also able to specify a predominantly nuclear localization of the chimeric proteins, independently of the presence of the basic NLS. The destruction, by mutagenesis, of both the basic stretch and the motif in the DNA recognition helix led to the total loss of nuclear accumulation, indicating that complete nuclear accumulation of TTF-1 results from the concerted action of these two proteic signals. Both of the regions of the homeodomain that are involved in nuclear targeting also encompass critical amino-acids responsible for DNA binding site recognition, as evidenced by the loss of DNA binding activity in vitro upon mutagenesis. Specifically, residues in the central part of the DNA recognition helix are involved in contacting bases in the major groove of DNA and are the most conserved in homeodomain proteins, suggesting that this part of the homeodomain could play a general role in the nuclear localization of members of this family of proteins.

Transcriptional regulation of the murine surfactant protein-A gene by B-Myb

Surfactant protein A (SP-A) is selectively synthesized in subsets of cells lining the respiratory epithelium, where its expression is regulated by various transcription factors including thyroid transcription factor-1 (TTF-1). Cell-specific transcription of the mouse SP-A promoter is mediated by binding of TTF-1 at four distinct cis-active sites located in the 5'-flanking region of the gene. Mutation of TTF-1-binding sites (TBE) 1, 3, and 4 in combination markedly decreased transcriptional activity of SP-A promoter-chloramphenicol acetyltransferase constructs containing SP-A gene sequences from -256 to +45. In contrast, the same mutations enhanced transcriptional activity in constructs containing additional 5' SP-A sequences from -399 to +45 suggesting that cis-acting elements within the region -399 to -256 influence effects of TTF-1 on SP-A promoter activity. A consensus Myb-binding site was identified within the region, located at positions -380 to -371 in the mouse gene. Mutation of the Myb-binding site decreased activity of SP-A promoter constructs in MLE-15 cells. MLE-15 cells, a cell line expressing SP-A mRNA, also expressed B-Myb. B-Myb bound to the MBS in the SP-A gene as assessed by electrophoretic mobility shift assay. While co-transfection of HeLa cells with a B-Myb expression plasmid activated the transfected SP-A promoter about 3-fold, co-transfection of B-myb with cyclin A and cdk-2, to enhance phosphorylation of B-Myb, increased transcriptional activity of SP-A constructs approximately 20-fold. Taken together, the data support activation of SP-A gene promoter activity by B-Myb which acts at a cis-acting element in the SP-A gene.