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

PRDM3/16 Regulate Chromatin Accessibility Required for NKX2-1 Mediated Alveolar Epithelial Differentiation and Function

Differential chromatin accessibility accompanies and mediates transcriptional control of diverse cell fates and their differentiation during embryogenesis. While the critical role of NKX2-1 and its transcriptional targets in lung morphogenesis and pulmonary epithelial cell differentiation is increasingly known, mechanisms by which chromatin accessibility alters the epigenetic landscape and how NKX2-1 interacts with other co-activators required for alveolar epithelial cell differentiation and function are not well understood. Here, we demonstrate that the paired domain zinc finger transcriptional regulators PRDM3 and PRDM16 regulate chromatin accessibility to mediate cell differentiation decisions during lung morphogenesis. Combined deletion of Prdm3 and Prdm16 in early lung endoderm caused perinatal lethality due to respiratory failure from loss of AT2 cell function. Prdm3/16 deletion led to the accumulation of partially differentiated AT1 cells and loss of AT2 cells. Combination of single cell RNA-seq, bulk ATAC-seq, and CUT&RUN demonstrated that PRDM3 and PRDM16 enhanced chromatin accessibility at NKX2-1 transcriptional targets in peripheral epithelial cells, all three factors binding together at a multitude of cell-type specific cis-active DNA elements. Network analysis demonstrated that PRDM3/16 regulated genes critical for perinatal AT2 cell differentiation, surfactant homeostasis, and innate host defense. Lineage specific deletion of PRDM3/16 in AT2 cells led to lineage infidelity, with PRDM3/16 null cells acquiring partial AT1 fate. Together, these data demonstrate that NKX2-1-dependent regulation of alveolar epithelial cell differentiation is mediated by epigenomic modulation via PRDM3/16.

NK2 homeobox gene cluster: Functions and roles in human diseases

NK2 genes (NKX2 gene cluster in humans) encode for homeodomain-containing transcription factors that are conserved along the phylogeny. According to the most detailed classifications, vertebrate NKX2 genes are classified into two distinct families, NK2.1 and NK2.2. The former is constituted by NKX2-1 and NKX2-4 genes, which are homologous to the Drosophila scro gene; the latter includes NKX2-2 and NKX2-8 genes, which are homologous to the Drosophila vnd gene. Conservation of these genes is not only related to molecular structure and expression, but also to biological functions. In Drosophila and vertebrates, NK2 genes share roles in the development of ventral regions of the central nervous system. In vertebrates, NKX2 genes have a relevant role in the development of several other organs such as the thyroid, lung, and pancreas. Loss-of-function mutations in NKX2-1 and NKX2-2 are the monogenic cause of the brain-lung-thyroid syndrome and neonatal diabetes, respectively. Alterations in NKX2-4 and NKX2-8 genes may play a role in multifactorial diseases, autism spectrum disorder, and neural tube defects, respectively. NKX2-1, NKX2-2, and NKX2-8 are expressed in various cancer types as either oncogenes or tumor suppressor genes. Several data indicate that evaluation of their expression in tumors has diagnostic and/or prognostic value.

FoxA1 and FoxA2 control growth and cellular identity in NKX2-1-positive lung adenocarcinoma

Changes in cellular identity (also known as histologic transformation or lineage plasticity) can drive malignant progression and resistance to therapy in many cancers, including lung adenocarcinoma (LUAD). The lineage-specifying transcription factors FoxA1 and FoxA2 (FoxA1/2) control identity in NKX2-1/TTF1-negative LUAD. However, their role in NKX2-1-positive LUAD has not been systematically investigated. We find that Foxa1/2 knockout severely impairs tumorigenesis in KRAS-driven genetically engineered mouse models and human cell lines. Loss of FoxA1/2 leads to the collapse of a dual-identity state, marked by co-expression of pulmonary and gastrointestinal transcriptional programs, which has been implicated in LUAD progression. Mechanistically, FoxA1/2 loss leads to aberrant NKX2-1 activity and genomic localization, which in turn actively inhibits tumorigenesis and drives alternative cellular identity programs that are associated with non-proliferative states. This work demonstrates that FoxA1/2 expression is a lineage-specific vulnerability in NKX2-1-positive LUAD and identifies mechanisms of response and resistance to targeting FoxA1/2 in this disease.

FOXO1 Couples KGF and PI-3K/AKT Signaling to NKX2.1-Regulated Differentiation of Alveolar Epithelial Cells

NKX2.1 is a master regulator of lung morphogenesis and cell specification; however, interactions of NKX2.1 with various transcription factors to regulate cell-specific gene expression and cell fate in the distal lung remain incompletely understood. FOXO1 is a key regulator of stem/progenitor cell maintenance/differentiation in several tissues but its role in the regulation of lung alveolar epithelial progenitor homeostasis has not been evaluated. We identified a novel role for FOXO1 in alveolar epithelial cell (AEC) differentiation that results in the removal of NKX2.1 from surfactant gene promoters and the subsequent loss of surfactant expression in alveolar epithelial type I-like (AT1-like) cells. We found that the FOXO1 forkhead domain potentiates a loss of surfactant gene expression through an interaction with the NKX2.1 homeodomain, disrupting NKX2.1 binding to the SFTPC promoter. In addition, blocking PI-3K/AKT signaling reduces phosphorylated FOXO-1 (p-FOXO1), allowing accumulated nuclear FOXO1 to interact with NKX2.1 in differentiating AEC. Inhibiting AEC differentiation in vitro with keratinocyte growth factor (KGF) maintained an AT2 cell phenotype through increased PI3K/AKT-mediated FOXO1 phosphorylation, resulting in higher levels of surfactant expression. Together these results indicate that FOXO1 plays a central role in AEC differentiation by directly binding NKX2.1 and suggests an essential role for FOXO1 in mediating AEC homeostasis.

Interstitial lung disease in infancy

There is a wide differential diagnosis of early onset respiratory distress especially in term babies, and interstitial lung disease (chILD) is a rare but important consideration in this context. chILD manifesting immediately after birth is usually related to mutations in surfactant protein genes, or conditions related to the Congenital Acinar Dysplasia -Alveolar capillary dysplasia - Congenital Alveolar Dysplasia (CAD-ACD) spectrum. There is currently no specific treatment for these conditions, and management is supportive. Prognosis is very poor in most of these babies if onset is early, with relentless respiratory deterioration unless transplanted. Ideally, the diagnosis is made on genetic analysis, but this may be time-consuming and complex in CAD-ACD spectrum, so lung biopsy may be needed to avoid prolonged and futile treatment being instituted. Milder forms with prolonged survival have been reported. Early onset, less severe chILD is usually related to neuroendocrine cell hyperplasia of infancy (NEHI), pulmonary interstitial glycogenosis (PIG) and less severe disorders of surfactant proteins. PIG and NEHI are not specific entities, but are pulmonary dysmaturity syndromes, and there may be a number of underlying genetic and other cause. If the child is stable and thriving, many will not be subject to lung biopsy, and slow improvement and weaning of supplemental oxygen can be anticipated. Where possible, a precise genetic diagnosis should be made in early onset cHILD allow for genetic counselling. chILD survivors and their families have complex respiratory and other needs, and co-ordinated, multi-disciplinary support in the community is essential.

High-resolution computed tomography findings of thyroid transcription factor 1 deficiency (NKX2-1 mutations)

BACKGROUND

The expression of the NKX2-1 gene and its encoded protein, thyroid transcription factor 1 (TTF-1), plays a role in pulmonary surfactant homeostasis and lung development. NKX2-1 mutations have been associated with neonatal respiratory distress, hypotonia, choreoathetosis and congenital hypothyroidism. These clinical findings have been coined brain-lung-thyroid syndrome, although not all three organs are always involved. While many of these children develop interstitial lung disease, no systematic review of chest high-resolution CT (HRCT) findings has been reported.

OBJECTIVE

To summarize the clinical presentations, pathology and HRCT imaging findings of children with NKX2-1 mutations.

MATERIALS AND METHODS

We identified six children with NKX2-1 mutations, deletions or duplications confirmed via genetic testing at our institution. Three pediatric radiologists reviewed the children's HRCT imaging findings and ranked the dominant findings in order of prevalence via consensus. We then correlated the imaging findings with histopathology and clinical course.

RESULTS

All children in the study were heterozygous for NKX2-1 mutations, deletions or duplications. Ground-glass opacities were the most common imaging feature, present in all but one child. Consolidation was also a prevalent finding in 4/6 of the children. Architectural distortion was less common.

CONCLUSION

HRCT findings of TTF-1 deficiency are heterogeneous and evolve over time. There is significant overlap between the HRCT findings of TTF-1 deficiency, other surfactant dysfunction mutations, and pulmonary interstitial glycogenosis. TTF-1 deficiency should be considered in term infants presenting with interstitial lung disease, especially if hypotonia or hypothyroidism is present.

Maternal smoking and high BMI disrupt thyroid gland development

BACKGROUND

Maternal lifestyle factors, including smoking and increased body weight, increase risks of adult diseases such as metabolic syndrome and infertility. The fetal thyroid gland is essential for the control of fetal metabolic rate, cardiac output, and brain development. Altered fetal thyroid function may contribute to increased disease onset later in life. Here, we investigated the impact of maternal smoking and high maternal weight on human fetal thyroid function during the second trimester.

METHODS

Thyroid glands and plasma were collected from fetuses electively terminated in the second trimester (normally progressing pregnancies). Plasma total triiodothyronine (T3) and total thyroxine (T4) were measured by solid-phase extraction-liquid chromatography-tandem mass spectrometry. Fetal plasma thyroid-stimulating hormone (TSH) levels were measured using a multiplex assay for human pituitary hormones. Histology and immunolocalization of thyroid developmental markers were examined in thyroid sections. Transcript levels of developmental, functional, apoptotic, and detoxification markers were measured by real-time PCR. Statistical analyses were performed using multivariate linear regression models with fetal age, sex, and maternal smoking or maternal body mass index (BMI) as covariates.

RESULTS

Maternal smoking was associated with significant changes in fetal plasma T4 and TSH levels during the second trimester. Smoke-exposed thyroids had reduced thyroid GATA6 and NKX2-1 transcript levels and altered developmental trajectories for ESR2 and AHR transcript levels. Maternal BMI > 25 was associated with increased fetal thyroid weight, increased plasma TSH levels, and abnormal thyroid histology in female fetuses. Normal developmental changes in AHR and ESR1 transcript expression were also abolished in fetal thyroids from mothers with BMI > 25.

CONCLUSIONS

For the first time, we show that maternal smoking and high maternal BMI are associated with disturbed fetal thyroid gland development and endocrine function in a sex-specific manner during the second trimester. These findings suggest that predisposition to post-natal disease is mediated, in part, by altered fetal thyroid gland development.

Expression of TTF-1 in breast cancer independently of ER expression: A case report and pathogenic implications

Thyroid Transcription Factor 1 (TTF-1) is often used for the immunohistochemical evaluation of lung cancers, as a significant proportion of these cancers are positive while other adenocarcinomas are usually negative. Breast cancers are known to express TTF-1 only in a small minority of cases but this may be problematic when this staining is used for its differential diagnosis from lung cancer. We present a case of ER-positive breast cancer in 30% of tumor cells that was also TTF-1 positive in some areas of the primary tumor but lost ER expression completely in the metastatic recurrence site while retaining TTF-1 positivity. Additionally, a PTEN mutation was present on genomic evaluation of the primary tumor. Diagnostic, pathogenic and therapeutic implications of these findings are discussed.

GATA6-positive lung adenocarcinomas are associated with invasive mucinous adenocarcinoma morphology, hepatocyte nuclear factor 4α expression, and KRAS mutations

AIMS

GATA6 is known to play a role in lung development. However, its role in the carcinogenesis of lung cancer is not well studied. The aim of this study was to analyse GATA6 expression in lung adenocarcinomas (LAs) by immunohistochemistry (IHC) in order to define its association with clinicopathological characteristics.

METHODS AND RESULTS

IHC analysis of GATA6 was performed with tissue microarray slides containing 348 LAs. The association between GATA6 expression and clinicopathological parameters was evaluated. GATA6 expression in epithelial tumours other than lung cancer was also evaluated. GATA6 expression was found in 47 LAs (13.5%). This occurred more frequently in younger patients (P = 0.005), and was associated with the absence of lymph node metastasis (P =0.024), well-differentiated to moderately differentiated tumours (P < 0.001), the absence of lymphatic invasion (P = 0.020), and the absence of vascular invasion (P = 0.011). GATA6 expression was associated with mucin production (P < 0.001), the invasive mucinous adenocarcinoma subtype (P < 0.001), KRAS mutations (P = 0.026), expression of MUC2 (P < 0.001), CDX2 (P = 0.049), and MUC5AC (P < 0.001), and absence of expression of TTF-1 (P = 0.002). GATA6 expression was also associated with hepatocyte nuclear factor 4α (HNF4α) expression (P < 0.001). GATA6 expression tended to indicate better prognoses, whereas patients with HNF4α expression had significantly worse prognoses (P = 0.033). Of 270 tumours other than lung cancer, 110 expressed GATA6.

CONCLUSIONS

These findings suggest that GATA6 might interact with HNF4α and contribute to the development of mucinous-type LAs.

TAZ/WWTR1 Mediates the Pulmonary Effects of NKX2-1 Mutations in Brain-Lung-Thyroid Syndrome

CONTEXT

Identification of a frameshift heterozygous mutation in the transcription factor NKX2-1 in a patient with brain-lung-thyroid syndrome (BLTS) and life-threatening lung emphysema.

OBJECTIVE

To study the genetic defect that causes this complex phenotype and dissect the molecular mechanism underlying this syndrome through functional analysis.

METHODS

Mutational study by DNA sequencing, generation of expression vectors, site-directed mutagenesis, protein-DNA-binding assays, luciferase reporter gene assays, confocal microscopy, coimmunoprecipitation, and bioinformatics analysis.

RESULTS

We identified a mutation [p.(Val75Glyfs*334)] in the amino-terminal domain of the NKX2-1 gene, which was functionally compared with a previously identified mutation [p.(Ala276Argfs*75)] in the carboxy-terminal domain in other patients with BLTS but without signs of respiratory distress. Both mutations showed similar protein expression profiles, subcellular localization, and deleterious effects on thyroid-, brain-, and lung-specific promoter activity. Coexpression of the coactivator TAZ/WWTR1 (transcriptional coactivator with PDZ-binding motif/WW domain-containing transcription regulator protein 1) restored the transactivation properties of p.(Ala276Argfs*75) but not p.(Val75Glyfs*334) NKX2-1 on a lung-specific promoter, although both NKX2-1 mutants could interact equally with TAZ/WWTR1. The retention of residual transcriptional activity in the carboxy-terminal mutant, which was absent in the amino-terminal mutant, allowed the functional rescue by TAZ/WWTR1.

CONCLUSIONS

Our results support a mechanistic model involving TAZ/WWTR1 in the development of human congenital emphysema, suggesting that this protein could be a transcriptional modifier of the lung phenotype in BLTS.

Retinoic Acid affects Lung Adenocarcinoma growth by inducing differentiation via GATA6 activation and EGFR and Wnt inhibition

A fundamental task in cancer research aims at the identification of new pharmacological therapies that can affect tumor growth. Differentiation therapy might exploit this function not only for hematological diseases, such as acute promyelocytic leukemia (APML) but also for epithelial tumors, including lung cancer. Here we show that Retinoic Acid (RA) arrests in vitro and in vivo the growth of Tyrosine Kinase Inhibitors (TKI) resistant Non Small Cell Lung Cancer (NSCLC). In particular, we found that RA induces G0/G1 cell cycle arrest in TKI resistant NSCLC cells and activates terminal differentiation programs by modulating the expression of GATA6, a key transcription factor involved in the physiological differentiation of the distal lung. In addition, our results demonstrate that RA inhibits EGFR and Wnt signaling activation, two pathways involved in NSCLC progression. Furthermore, we uncovered a novel mechanism in NSCLC that shows how RA exerts its function; we found that RA-mediated GATA6 activation is necessary for EGFR and Wnt inhibition, thus leading to 1) increased differentiation and 2) loss of proliferation. All together, these findings prove that differentiation therapy might be feasible in TKI resistant NSCLCs, and shed light on new targets to define new pharmacological therapies.

Cell-specific expression of aquaporin-5 (Aqp5) in alveolar epithelium is directed by GATA6/Sp1 via histone acetylation

Epigenetic regulation of differentiation-related genes is poorly understood. We previously reported that transcription factors GATA6 and Sp1 interact with and activate the rat proximal 358-bp promoter/enhancer (p358P/E) of lung alveolar epithelial type I (AT1) cell-specific gene aquaporin-5 (Aqp5). In this study, we found that histone deacetylase (HDAC) inhibitor suberoylanilide hydroxamic acid (SAHA) increased AQP5 expression and Sp1-mediated transcription of p358P/E. HDAC3 overexpression inhibited Sp1-mediated Aqp5 activation, while HDAC3 knockdown augmented AQP5 protein expression. Knockdown of GATA6 or transcriptional co-activator/histone acetyltransferase p300 decreased AQP5 expression, while p300 overexpression enhanced p358P/E activation by GATA6 and Sp1. GATA6 overexpression, SAHA treatment or HDAC3 knockdown increased histone H3 (H3) but not histone H4 (H4) acetylation within the homologous p358P/E region of mouse Aqp5. HDAC3 binds to Sp1 and HDAC3 knockdown increased interaction of GATA6/Sp1, GATA6/p300 and Sp1/p300. These results indicate that GATA6 and HDAC3 control Aqp5 transcription via modulation of H3 acetylation/deacetylation, respectively, through competition for binding to Sp1, and suggest that p300 modulates acetylation and/or interacts with GATA6/Sp1 to regulate Aqp5 transcription. Cooperative interactions among transcription factors and histone modifications regulate Aqp5 expression during alveolar epithelial cell transdifferentiation, suggesting that HDAC inhibitors may enhance repair by promoting acquisition of AT1 cell phenotype.

Thyroid transcription factor 1 expression is associated with outcome of patients with non-squamous non-small cell lung cancer treated with pemetrexed-based chemotherapy

Pemetrexed is an antifolate cytostatic agent targeting several folate-dependent enzymatic pathways, widely used in the treatment of locally advanced or metastatic stage non-small cell lung cancer. Aside from the non-squamous histology, there is still no available molecular biomarker predicting treatment efficacy of pemetrexed-based chemotherapy. The aim of our retrospective study was to evaluate the association of thyroid transcription factor 1 expression with outcome of a large cohort of patients with non-squamous non-small cell lung cancer treated with pemetrexed. We retrospectively analysed clinical data of 463 patients with advanced-stage non-small cell lung cancer (IIIB or IV) treated with pemetrexed-based chemotherapy. Thyroid transcription factor 1 expression was assessed using indirect immunohistochemical detection in formalin-fixed paraffin-embedded tumour tissue at the time of diagnosis. Thyroid transcription factor 1 expression was detected in the tumour tissue from 76.0% of patients, and tumours from 24.0% of patients were thyroid transcription factor 1 negative. The median progression-free survival and overall survival for patients with thyroid transcription factor 1 positive tumours were 4.8 and 11.8 months compared to 2.8 and 8.3 months for those with thyroid transcription factor 1 negative tumours (p = 0.001 and p < 0.001). The multivariable Cox proportional hazards model revealed that thyroid transcription factor 1 expression was significantly associated with progression-free survival (hazard ratio = 1.57, p < 0.001) and also with overall survival (hazard ratio = 1.73, p < 0.001). In conclusion, the results of the conducted retrospective study suggest that the thyroid transcription factor 1 expression was independently associated with progression-free survival and overall survival in patients with advanced-stage non-squamous non-small cell lung cancer treated with pemetrexed-based chemotherapy.

HOPX: The Unusual Homeodomain-Containing Protein

The homeodomain-only protein homeobox (HOPX) is the smallest known member of the homeodomain-containing protein family, atypically unable to bind DNA. HOPX is widely expressed in diverse tissues, where it is critically involved in the regulation of proliferation and differentiation. In human skin, HOPX controls epidermal formation through the regulation of late differentiation markers, and HOPX expression correlates with the level of differentiation in cutaneous pathologies. In mouse skin, Hopx was additionally identified as a lineage tracing marker of quiescent hair follicle stem cells. This review discusses current knowledge of HOPX structure and function in normal and pathological conditions.

Functional characterization of two novel mutations in TTF-1/NKX2.1 homeodomain in patients with benign hereditary chorea

The thyroid transcription factor 1 (TTF-1) is encoded, on chromosome 14q13, by the gene termed TITF-1/NKX2.1. Mutations in this gene have been associated with chorea, hypothyroidism, and lung disease, all included in the "brain-thyroid-lung syndrome." We here describe two cases of novel missense mutations [NM_003317.3:c.516G>T and c.623G>C resulting in p.(Gln172His) and p.(Trp208Ser), respectively] in TITF-1/NKX2-1 in non-consanguineous patients. We provide a functional study of the role of the two mutations on the TTF-1 ability to bind DNA and to trans-activate both thyroid and lung specific gene promoters. Our results confirm the difficulty to correlate the TTF-1 activity with the clinical phenotype of affected patients and highlight the need to increase the limited knowledge we have on the activity of TTF-1 in neuronal cells.

Co-expression of TTF-1 and neuroendocrine markers in the human fetal lung and pulmonary neuroendocrine tumors

The expression pattern of thyroid transcription factor 1 (TTF-1) and neuroendocrine markers, neuron cell adhesion molecule (NCAM; CD56), chromogranin A (CgA) and synaptophysin (Syp), of different lung cell lineages was histologically analyzed in 15 normal human fetal lungs and 12 neuroendocrine tumors (NETs) using immunohistochemical methods. During pseudoglandular phase strong nuclear TTF-1 staining was detected in the columnar nonciliated epithelial cells, while NCAM, CgA and Syp had a moderate expression in the proximal airways and mild expression in the distal airways. Neuroendocrine cells (NECs) in proximal lung airway were co-localizing TTF-1 and other neuroendocrine markers while neuroendocrine bodies (NEBs) exhibit only staining with NCAM and Syp. In the canalicular phase TTF-1 nuclear staining was expressed only in several epithelial cells in proximal airways, while budding airways epithelium showed strong TTF-1 expression. Expression of NCAM, CgA and Syp in this phase equals the one in pseudoglandular phase. NEBs cells were co-localizing TTF-1 and NCAM in proximal airways and few NECs in distal airway were co-localizing TTF-1 and Syp. TTF-1 staining in the saccular phase was limited to subsets of epithelial cells in the proximal airways with stronger positivity in the distal airways. NCAM expression is moderate only in proximal airways, while Syp and CgA show mild expression in proximal and distal airways. NECs were co-localizing TTF-1 and NCAM in proximal lung airway. With regard to NECs, all small cell lung cancer (SCLC) cells had strong TTF-1, NCAM, Syp and CgA positivity and TTF-1 co-localized with other neuroendocrine markers. All pulmonary typical carcinoids were TTF-1 negative, while pulmonary atypical carcinoids were focal positive for TTF-1 and some neoplastic cells co-localized TTF-1 with neuroendocrine markers. Our results indicate that TTF-1 expression in NECs suggests a possible role in their normal development and differentiation. Our results also indicate that possible cell of origin for poorly differentiated SCLC and some atypical carcinoid could be a progenitor cell in neuroendocrine lineage while in typical carcinoids possible cell of origin is localized in terminally differentiated NECs.

Lineage factors and differentiation states in lung cancer progression

Lung cancer encompasses a heterogeneous group of malignancies. Here we discuss how the remarkable diversity of major lung cancer subtypes is manifested in their transforming cell of origin, oncogenic dependencies, phenotypic plasticity, metastatic competence and response to therapy. More specifically, we review the increasing evidence that links this biological heterogeneity to the deregulation of cell lineage-specific pathways and the transcription factors that ultimately control them. As determinants of pulmonary epithelial differentiation, these poorly characterized transcriptional networks may underlie the etiology and biological progression of distinct lung cancers, while providing insight into innovative therapeutic strategies.

The disruption of a novel limb cis-regulatory element of SHH is associated with autosomal dominant preaxial polydactyly-hypertrichosis

The expression gradient of the morphogen Sonic Hedgehog (SHH) is crucial in establishing the number and the identity of the digits during anteroposterior patterning of the limb. Its anterior ectopic expression is responsible for preaxial polydactyly (PPD). Most of these malformations are due to the gain-of-function of the Zone of Polarizing Activity Regulatory Sequence, the only limb-specific enhancer of SHH known to date. We report a family affected with a novel condition associating PPD and hypertrichosis of the upper back, following an autosomal dominant mode of inheritance. This phenotype is consistent with deregulation of SHH expression during limb and follicle development. In affected members, we identified a 2 kb deletion located ~240 kb upstream from the SHH promoter. The deleted sequence is capable of repressing the transcriptional activity of the SHH promoter in vitro, consistent with a silencer activity. We hypothesize that the deletion of this silencer could be responsible for SHH deregulation during development, leading to a PPD-hypertrichosis phenotype.

Amino-terminal extension of 146 residues of L-type GATA-6 is required for transcriptional activation but not for self-association

Transcription factor GATA-6 plays essential roles in developmental processes and tissue specific functions through regulation of gene expression. GATA-6 mRNA utilizes two Met-codons in frame as translational initiation codons. Deletion of the nucleotide sequence encoding the PEST sequence (Glu(31)-Cys(46)) between the two initiation codons unusually reduced the protein molecular size on SDS-polyacrylamide gel-electrophoresis, and re-introduction of this sequence reversed this change. The long-type (L-type) GATA-6 containing this PEST sequence self-associated similarly to the short-type (S-type) GATA-6, as determined on co-immunoprecipitation of Myc-tagged GATA-6 with HA-tagged GATA-6. The L-type and S-type GATA-6 also interacted mutually. The L-type GATA-6 without the PEST sequence also self-associated and interacted with the S-type GATA-6. The transcriptional activation potential of L-type GATA-6 is higher than that of S-type GATA-6. When the PEST sequence (Glu(31)-Cys(46)) was inserted into the L-type GATA-6 without Arg(13)-Gly(101), the resultant recombinant protein showed significantly higher transcriptional activity, while the construct with an unrelated sequence exhibited lower activity. These results suggest that the Glu(31)-Cys(46) segment plays an important role in the transcriptional activation, although it does not participate in the self-association.

Respiratory insufficiency in a newborn with congenital hypothyroidism due to a new mutation of TTF-1/NKX2.1 gene

NK2 homeobox-1 (NKX2.1) gene encoding the thyroid transcription factor-1 (TTF-1) plays a critical role in lung, thyroid, and central nervous system morphogenesis and function; mutations cause a rare form of progressive respiratory failure associated with alterations of surfactant synthesis, composition, and homeostasis. Molecular mechanisms are heterogeneous and poorly explored. A 28 days old male, soon after birth, presented respiratory failure requiring oxygen treatment at FiO2 27%, prolonged for 2 weeks. Routine neonatal screenings detected a high thyroid stimulating hormone concentration. On day 27 congenital hypothyroidism was confirmed and substitutive treatment was begun. Since the persistence of respiratory symptoms sweat test, CFTR mutation, lymphocyte subpopulations, and sputum cultures were tested, resulting negative. Brain and cardiac defects were also ruled out. Bronchoscopy and BAL analysis were normal. Computed tomography showed bilateral multiple ground glass attenuation, consolidative areas and diffuse bronchial wall thickening. Based on the severity of symptoms, the exclusion of other causes of respiratory disease and the CT findings of interstitial lung disease, we investigated genes affecting the surfactant homeostasis. Sequencing analysis of the three exons of the TTF1 revealed a heterozygous mutation c.334G > T that results in the replacement of glycine in position 112 with a stop codon, generating a nonsense protein that lacks the correct transactivation domain in the C-terminal region. Genetic analysis of the family showed that the father, who was asymptomatic, carried the mutation. Screening for TTF-1 deletions or mutations should always be considered in children with congenital hypothyroidism and an unexplained neonatal respiratory distress or neurodevelopmental deficits.

The fetal sheep lung does not respond to cortisol infusion during the late canalicular phase of development

The prepartum surge in plasma cortisol concentrations in humans and sheep promotes fetal lung and surfactant system maturation in the support of air breathing after birth. This physiological process has been used to enhance lung maturation in the preterm fetus using maternal administration of betamethasone in the clinical setting in fetuses as young as 24 weeks gestation (term = 40 weeks). Here, we have investigated the impact of fetal intravenous cortisol infusion during the canalicular phase of lung development (from 109- to 116-days gestation, term = 150 ± 3 days) on the expression of genes regulating glucocorticoid (GC) activity, lung liquid reabsorption, and surfactant maturation in the very preterm sheep fetus and compared this to their expression near term. Cortisol infusion had no impact on mRNA expression of the corticosteroid receptors (GC receptor and mineralocorticoid receptor) or HSD11B-2, however, there was increased expression of HSD11B-1 in the fetal lung. Despite this, cortisol infusion had no effect on the expression of genes involved in lung sodium (epithelial sodium channel -α, -β, or -γ subunits and sodium–potassium ATPase-β1 subunit) or water (aquaporin 1, 3, and 5) reabsorption when compared to the level of expression during exposure to the normal prepartum cortisol surge. Furthermore, in comparison to late gestation, cortisol infusion does not increase mRNA expression of surfactant proteins (SFTP-A, -B, and -C) or the number of SFTP-B-positive cells present in the alveolar epithelium, the cells that produce pulmonary surfactant. These data suggest that there may be an age before which the lung is unable to respond biochemically to an increase in fetal plasma cortisol concentrations.

E-cadherin controls bronchiolar progenitor cells and onset of preneoplastic lesions in mice

Although progenitor cells of the conducting airway have been spatially localized and some insights have been gained regarding their molecular phenotype, relatively little is known about the mechanisms regulating their maintenance, activation, and differentiation. This study investigates the potential roles of E-cadherin in mouse Clara cells, as these cells were shown to represent the progenitor/stem cells of the conducting airways and have been implicated as the cell of origin of human non-small cell lung cancer. Postnatal inactivation of E-cadherin affected Clara cell differentiation and compromised airway regeneration under injury conditions. In steady-state adult lung, overexpression of the dominant negative E-cadherin led to an expansion of the bronchiolar stem cells and decreased differentiation concomitant with canonical Wnt signaling activation. Expansion of the bronchiolar stem cell pool was associated with an incessant proliferation of neuroepithelial body.associated Clara cells that ultimately gave rise to bronchiolar hyperplasia. Despite progressive hyperplasia, only a minority of the mice developed pulmonary solid tumors, suggesting that the loss of E-cadherin function leads to tumor formation when additional mutations are sustained. The present study reveals that E-cadherin plays a critical role in the regulation of proliferation and homeostasis of the epithelial cells lining the conducting airways.

Control of alveolar differentiation by the lineage transcription factors GATA6 and HOPX inhibits lung adenocarcinoma metastasis

Molecular programs that mediate normal cell differentiation are required for oncogenesis and tumor cell survival in certain cancers. How cell-lineage-restricted genes specifically influence metastasis is poorly defined. In lung cancers, we uncovered a transcriptional program that is preferentially associated with distal airway epithelial differentiation and lung adenocarcinoma (ADC) progression. This program is regulated in part by the lineage transcription factors GATA6 and HOPX. These factors can cooperatively limit the metastatic competence of ADC cells, by modulating overlapping alveolar differentiation and invasogenic target genes. Thus, GATA6 and HOPX are critical nodes in a lineage-selective pathway that directly links effectors of airway epithelial specification to the inhibition of metastasis in the lung ADC subtype.

NKX2-1/TTF-1: an enigmatic oncogene that functions as a double-edged sword for cancer cell survival and progression

Emerging evidence indicates that NKX2-1, a homeobox-containing transcription factor also known as TTF-1, plays a role as a "lineage-survival" oncogene in lung adenocarcinomas. In T cell acute lymphoblastic leukemia, gene rearrangements lead to aberrant expression of NKX2-1/TTF-1. Despite accumulating evidence supporting its oncogenic role, it has become apparent that NKX2-1/TTF-1 expression also has biological and clinical functions in the opposite direction that act against tumor progression. Herein, we review recent findings showing these enigmatic double-edged characteristics, with special attention given to the roles of NKX2-1/TTF-1 in lung development and carcinogenesis.

MicroRNA-365 regulates NKX2-1, a key mediator of lung cancer

MicroRNAs constitute a class of small noncoding RNAs that play roles in tumorigenesis. We found that NKX2-1 protein levels were generally high in the lung cancer tissues whereas miRNA-365 expression levels were downregulated. Ectopic miR-365 expression decreased NKX2-1 expression in lung cancer cell lines. Transfection of a miR-365 mimic led to reduced proliferation of lung cancer cells; conversely, a miR-365 inhibitor slightly increased cell proliferation. The NKX2-1 overexpression significantly increased the cell proliferation by overcoming the suppressive effect of miR-365. Our data suggest that miR-365 is an important regulator of NKX2-1 and can be a target for lung cancer therapies.

Novel NKX2.1 mutation associated with hypothyroidism and lethal respiratory failure in a full-term neonate

We report a case of lethal neonatal hypoxic respiratory failure and hypothyroidism in an infant with a novel missense mutation in NKX2.1.

MYC-induced epigenetic activation of GATA4 in lung adenocarcinoma

Human lung cancer is a disease with high incidence and accounts for most cancer-related deaths in both men and women. Metastasis is a common event in non-small cell lung carcinoma (NSCLC), diminishing the survival chance of the patients with this type of tumor. It has been shown that MYC is involved in the development of metastasis from NSCLC, but the mechanism underlying this switch remained to be identified. Here, we focus on GATA4 as a MYC target in the development of metastasis with origin in lung adenocarcinoma, the most common type of NSCLC. Epigenetic alterations at the GATA4 promoter level were observed after MYC expression in lung adenocarcinoma in vivo and in vitro. Such alterations include site-specific demethylation that accompanies the displacement of the MYC-associated zinc finger protein (MAZ) from the GATA4 promoter, which leads to GATA4 expression. Histone modification analysis of the GATA4 promoter revealed a switch from repressive histone marks to active histone marks after MYC binding, which corresponds to active GATA4 expression. Our results thus identify a novel epigenetic mechanism by which MYC activates GATA4 leading to metastasis in lung adenocarcinoma, suggesting novel potential targets for the development of antimetastatic therapy.

Nkx2-1: a novel tumor biomarker of lung cancer

Nkx2-1 (Nkx homeobox-1 gene), also known as TTF-1 (thyroid transcription factor-1), is a tissue-specific transcription factor of the thyroid, lung, and ventral forebrain. While it has been shown to play a critical role in lung development and lung cancer differentiation and morphogenesis, molecular mechanisms mediating Nkx2-1 cell- and tissue-specific expression in normal and cancerous lungs have yet to be fully elucidated. The recent identification of prognostic biomarkers in lung cancer, particularly in lung adenocarcinoma (ADC), and the different reactivity of patients to chemotherapeutic drugs have opened new avenues for evaluating patient survival and the development of novel effective therapeutic strategies. The function of Nkx2-1 as a proto-oncogene was recently characterized and the gene is implicated as a contributory factor in lung cancer development. In this review, we summarize the role of this transcription factor in the development, diagnosis, and prognosis of lung cancer in the hope of providing insights into the utility of Nkx2-1 as a novel biomarker of lung cancer.

Transcriptional programs controlling perinatal lung maturation

The timing of lung maturation is controlled precisely by complex genetic and cellular programs. Lung immaturity following preterm birth frequently results in Respiratory Distress Syndrome (RDS) and Broncho-Pulmonary Dysplasia (BPD), which are leading causes of mortality and morbidity in preterm infants. Mechanisms synchronizing gestational length and lung maturation remain to be elucidated. In this study, we designed a genome-wide mRNA expression time-course study from E15.5 to Postnatal Day 0 (PN0) using lung RNAs from C57BL/6J (B6) and A/J mice that differ in gestational length by ∼30 hr (B6<A/J). Comprehensive bioinformatics and functional genomics analyses were used to identify key regulators, bioprocesses and transcriptional networks controlling lung maturation. We identified both temporal and strain dependent gene expression patterns during lung maturation. For time dependent changes, cell adhesion, vasculature development, and lipid metabolism/transport were major bioprocesses induced during the saccular stage of lung development at E16.5–E17.5. CEBPA, PPARG, VEGFA, CAV1 and CDH1 were found to be key signaling and transcriptional regulators of these processes. Innate defense/immune responses were induced at later gestational ages (E18.5–20.5), STAT1, AP1, and EGFR being important regulators of these responses. Expression of RNAs associated with the cell cycle and chromatin assembly was repressed during prenatal lung maturation and was regulated by FOXM1, PLK1, chromobox, and high mobility group families of transcription factors. Strain dependent lung mRNA expression differences peaked at E18.5. At this time, mRNAs regulating surfactant and innate immunity were more abundantly expressed in lungs of B6 (short gestation) than in A/J (long gestation) mice, while expression of genes involved in chromatin assembly and histone modification were expressed at lower levels in B6 than in A/J mice. The present study systemically mapped key regulators, bioprocesses, and transcriptional networks controlling lung maturation, providing the basis for new therapeutic strategies to enhance lung function in preterm infants.

NKL homeobox genes in leukemia

NK-like (NKL) homeobox genes code for transcription factors, which can act as key regulators in fundamental cellular processes. NKL genes have been implicated in divergent types of cancer. In this review, we summarize the involvement of NKL genes in cancer and leukemia in particular. NKL genes can act as tumor-suppressor genes and as oncogenes, depending on tissue type. Aberrant expression of NKL genes is especially common in T-cell acute lymphoblastic leukemia (T-ALL). In T-ALL, 8 NKL genes have been reported to be highly expressed in specific T-ALL subgroups, and in ~30% of cases, high expression is caused by chromosomal rearrangement of 1 of 5 NKL genes. Most of these NKL genes are normally not expressed in T-cell development. We hypothesize that the NKL genes might share a similar downstream effect that promotes leukemogenesis, possibly due to mimicking a NKL gene that has a physiological role in early hematopoietic development, such as HHEX. All eight NKL genes posses a conserved Eh1 repressor motif, which has an important role in regulating downstream targets in hematopoiesis and possibly in leukemogenesis as well. Identification of a potential common leukemogenic NKL downstream pathway will provide a promising subject for future studies.

A novel nonsense mutation in the TITF-1 gene in a Japanese family with benign hereditary chorea

A Japanese family with a novel nonsense mutation in the TITF-1 gene (p.Y98X) is described. The proband showed severe generalized chorea, delayed motor development, subnormal intelligence, congenital hypothyroidism, bronchial asthma, and a history of pulmonary infection, all of which are characteristic features of Brain-Thyroid-Lung syndrome. On the other hand, her brother and mother showed a mild benign hereditary chorea (BHC) phenotype with congenital hypothyroidism. Intrafamilial phenotypic variation is common in BHC/Brain-Thyroid-Lung syndrome and suggests the existence of other genetic or environmental factors regulating TITF-1 function. Although choreic movement in BHC/Brain-Thyroid-Lung syndrome is recognized as non-progressive, the proband showed re-exacerbation of choreic movement at puberty. The dopamine agonist, ropinirole hydrochloride, reduced her choreic movements, suggesting that levodopa and/or dopamine agonists may compensate for underdeveloped dopaminergic pathways in this disorder.

Expression of Transcription Factor GATA-6 in Alveolar Epithelial Cells Is Linked to Neonatal Lung Disease

BACKGROUND

Premature birth and respiratory distress syndrome (RDS) are risk factors for disturbed lung development and bronchopulmonary dysplasia (BPD). The molecular mechanisms related to prematurity and BPD remain largely unknown. Epithelial expression of the transcription factor GATA-6 has been implicated in normal and abnormal murine lung development.

OBJECTIVES

The possible involvement of GATA-6 in the normal development and in RDS and BPD was investigated in the human and baboon lung.

METHODS

Immunohistochemistry was used to study the expression of GATA-6 and thyroid transcription factor 1 in lung specimens from different age groups of human and baboon fetuses and newborns with lung disease. Furthermore, the regulatory role of TGF-β₁ in GATA-6 expression was investigated in human pulmonary epithelial cell lines using RT-PCR.

RESULTS

GATA-6 expression increased in the developing human airway epithelium along with advancing gestation, but diminished to negligible at birth. In RDS, GATA-6 expression was enhanced at 5-7 days after birth, and decreased thereafter. In BPD, the expression of GATA-6 in alveolar epithelial cells was low. These results were confirmed and extended using an established baboon model of prematurity. The in vitro experiments revealed that TGF-β₁ induces GATA-6 and thyroid transcription factor 1 expression in lung epithelial cells.

CONCLUSIONS

Our results suggest that the expression of GATA-6 at the early stages of the preterm lung may be related to impaired postnatal alveolar development.

Temporal changes in expression of FoxA1 and Wnt7A in isolated adult human alveolar epithelial cells enhanced by heparin

Pre- and postnatal developmental studies of the lung have provided compelling evidence demonstrating multiple factors that orchestrate alveolar epithelial cell differentiation. The extent to which reactivation of certain developmental pathways in the adult might influence the course of differentiation of alveolar type 2 cells (AT2) into AT1 cells is not known. In this study, we examined selected members of the forkhead (Fox) family of transcription factors and the Wnt (wingless) family of signaling proteins for expression during human alveolar cell differentiation in vitro and determined their potential responses to sulfated components of extracellular matrix (ECM), like those shed from cell surfaces or found in basement membrane and modeled by heparin. Isolated adult human AT2 cells cultured over a 9-day period were used to define the temporal profile of expression of targeted factors during spontaneous differentiation to AT1-like cells. FoxA1 protein was upregulated at early to intermediate time points, where it was strongly elevated by heparin. Gene expression of wnt7A increased dramatically beginning on day 3 and was enhanced even further on days 7 and 9 by heparin, whereas protein expression appeared at days 7 and 9. These temporal changes of expression suggest that sulfated ECMs may act to enhance the increase in FoxA1 at the critical juncture when AT2 cells commence the differentiation process to AT1 cells, in addition to enhancing the increase in wnt7A when the AT1 cell phenotype stabilizes. Collectively, these factors may act to modulate differentiation in the adult human pulmonary alveolus.

The mouse Muc5b mucin gene is transcriptionally regulated by thyroid transcription factor-1 (TTF-1) and GATA-6 transcription factors

MUC5B is one of the major mucin genes expressed in the respiratory tract. Previous studies in our laboratory have demonstrated that MUC5B is expressed in human lung adenocarcinomas and during lung morphogenesis. Moreover, in human lung adenocarcinoma tissues, a converse correlation between MUC5B and thyroid transcription factor-1 (TTF-1) expression, a lung-specific transcription factor, has been established. However, the molecular mechanisms that govern the regulation of MUC5B expression in the lung are largely unknown. In order to better understand the biological role of MUC5B in lung pathophysiology, we report the characterization of the promoter region of the mouse Muc5b mucin gene. The promoter is flanked by a TATA box (TACATAA) identical to that in the human gene. Human and murine promoters share 67.5% similarity over the first 170 nucleotides. By RT-PCR, co-transfection studies and gel-shift assays, we show that Muc5b promoter activity is completely inhibited by TTF-1, whereas factors of the GATA family (GATA-4/GATA-5/GATA-6) are activators. Together, these results demonstrate, for the first time, that Muc5b is a target gene of transcription factors (TTF-1, GATA-6) involved in lung differentiation programs during development and carcinogenesis, and identify TTF-1 as a strong repressor of Muc5b. The characterization of the structural and functional features of the Muc5b mucin gene will provide us with a strong base to develop studies in murine models aimed at the identification of its biological role in lung pathophysiology.

A systems approach to mapping transcriptional networks controlling surfactant homeostasis

Background

Pulmonary surfactant is required for lung function at birth and throughout life. Lung lipid and surfactant homeostasis requires regulation among multi-tiered processes, coordinating the synthesis of surfactant proteins and lipids, their assembly, trafficking, and storage in type II cells of the lung. The mechanisms regulating these interrelated processes are largely unknown.

Results

We integrated mRNA microarray data with array independent knowledge using Gene Ontology (GO) similarity analysis, promoter motif searching, protein interaction and literature mining to elucidate genetic networks regulating lipid related biological processes in lung. A Transcription factor (TF) - target gene (TG) similarity matrix was generated by integrating data from different analytic methods. A scoring function was built to rank the likely TF-TG pairs. Using this strategy, we identified and verified critical components of a transcriptional network directing lipogenesis, lipid trafficking and surfactant homeostasis in the mouse lung.

Conclusions

Within the transcriptional network, SREBP, CEBPA, FOXA2, ETSF, GATA6 and IRF1 were identified as regulatory hubs displaying high connectivity. SREBP, FOXA2 and CEBPA together form a common core regulatory module that controls surfactant lipid homeostasis. The core module cooperates with other factors to regulate lipid metabolism and transport, cell growth and development, cell death and cell mediated immune response. Coordinated interactions of the TFs influence surfactant homeostasis and regulate lung function at birth.

The SP-C promoter facilitates alveolar type II epithelial cell-specific plasmid nuclear import and gene expression

Although nonviral gene therapy has great potential for use in the lung, the relative lack of cell-specific targeting has limited its applications. We have developed a new approach for cell-specific targeting based on selective nuclear import of plasmids in non-dividing cells. Using a microinjection and in situ hybridization approach, we tested several potential DNA sequences for the ability to mediate plasmid nuclear import in alveolar type II epithelial (ATII) cells. Of these, only a sequence within the human surfactant protein C (SP-C) promoter was able to mediate nuclear localization of plasmid DNA specifically in ATII cells but not in other cell types. We have mapped the minimal import sequence to the proximal 318 nucleotides of the promoter, and demonstrate that binding sites for NFI, TTF-1, and GATA-6 and the proteins themselves are required for import activity. Using intratracheal delivery of DNA followed by electroporation, we demonstrate that the SP-C promoter sequence will enhance gene expression specifically in ATII cells in mouse lung. This represents a novel activity for the SP-C promoter and thus ATII cell-specific nuclear import of DNA may prove to be a safe and effective method for targeted and enhanced gene expression in ATII cells.

Transcription factor GATA-6 is expressed in quiescent myofibroblasts in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) (histopathology of usual interstitial pneumonia [UIP]) is a progressive disease with poor prognosis. Characteristic features of IPF/UIP include fibroblastic foci, which are patchy lesions of focal, disarranged myofibroblasts. GATA-6 is a transcription factor linked with cell differentiation. Its role in the development of IPF has not previously been investigated. We hypothesized that GATA-6 participates in the differentiation of fibroblasts into myofibroblasts in IPF/UIP lungs. The expression patterns of GATA-6, the mesenchymal marker alpha-smooth muscle actin (alpha-SMA), and markers for proliferation (Ki67) and apoptosis (caspase-3) were analyzed in human IPF/UIP tissue samples. The effects of GATA-6 overexpression and silencing were studied in cell cultures. The results show that the alpha-SMA-positive fibroblastic foci in IPF/UIP lungs are positive for GATA-6, but negative for Ki67 and caspase-3. Cultured human IPF/UIP fibroblasts expressed GATA-6 mRNA, whereas cells from the normal adult lung did not. In cultured A549 lung epithelial cells, the induction of GATA-6 by transforming growth factor-beta1 resulted in simultaneous expression of alpha-SMA and decrease of E-cadherin. The inhibition of GATA-6 expression in fibroblasts showed that GATA-6 mediates the alpha-SMA-inducing signal of transforming growth factor-beta1. In conclusion, the hallmark of IPF/UIP histopathology, the fibroblast focus, consists of differentiated, quiescent cells that prominently express GATA-6.

MYC is a metastasis gene for non-small-cell lung cancer

Background

Metastasis is a process by which cancer cells learn to form satellite tumors in distant organs and represents the principle cause of death of patients with solid tumors. NSCLC is the most lethal human cancer due to its high rate of metastasis.

Methodology/Principal Findings

Lack of a suitable animal model has so far hampered analysis of metastatic progression. We have examined c-MYC for its ability to induce metastasis in a C-RAF-driven mouse model for non-small-cell lung cancer. c-MYC alone induced frank tumor growth only after long latency at which time secondary mutations in K-Ras or LKB1 were detected reminiscent of human NSCLC. Combination with C-RAF led to immediate acceleration of tumor growth, conversion to papillary epithelial cells and angiogenic switch induction. Moreover, addition of c-MYC was sufficient to induce macrometastasis in liver and lymph nodes with short latency associated with lineage switch events. Thus we have generated the first conditional model for metastasis of NSCLC and identified a gene, c-MYC that is able to orchestrate all steps of this process.

Conclusions/Significance

Potential markers for detection of metastasis were identified and validated for diagnosis of human biopsies. These markers may represent targets for future therapeutic intervention as they include genes such as Gata4 that are exclusively expressed during lung development.

Five new TTF1/NKX2.1 mutations in brain-lung-thyroid syndrome: rescue by PAX8 synergism in one case

Thyroid transcription factor 1 (NKX2-1/TITF1) mutations cause brain-lung-thyroid syndrome, characterized by congenital hypothyroidism (CH), infant respiratory distress syndrome (IRDS) and benign hereditary chorea (BHC). The objectives of the present study were (i) detection of NKX2-1 mutations in patients with CH associated with pneumopathy and/or BHC, (ii) functional analysis of new mutations in vitro and (iii) description of the phenotypic spectrum of brain-lung-thyroid syndrome. We identified three new heterozygous missense mutations (L176V, P202L, Q210P), a splice site mutation (376-2A-->G), and one deletion of NKX2-1 at 14q13. Functional analysis of the three missense mutations revealed loss of transactivation capacity on the human thyroglobulin enhancer/promoter. Interestingly, we showed that deficient transcriptional activity of NKX2-1-P202L was completely rescued by cotransfected PAX8-WT, whereas the synergistic effect was abolished by L176V and Q210P. The clinical spectrum of 6 own and 40 published patients with NKX2-1 mutations ranged from the complete triad of brain-lung-thyroid syndrome (50%), brain and thyroid disease (30%), to isolated BHC (13%). Thyroid morphology was normal (55%) and compensated hypothyroidism occurred in 61%. Lung disease occurred in 54% of patients (IRDS at term 76%; recurrent pulmonary infections 24%). On follow-up, 20% developed severe chronic interstitial lung disease, and 16% died. In conclusion, we describe five new NKX2.1 mutations with, for the first time, complete rescue by PAX8 of the deficient transactivating capacity in one case. Additionally, our review shows that the majority of affected patients display neurological and/or thyroidal problems and that, although less frequent, lung disease is responsible for a considerable mortality.

Retinoic acid receptors and GATA transcription factors activate the transcription of the human lecithin:retinol acyltransferase gene

Lecithin:retinol acyltransferase (LRAT) catalyzes the esterification of retinol (vitamin A). Retinyl esters and LRAT protein levels are reduced in many types of cancer cells. We present data that both the LRAT and retinoic acid receptor beta(2) (RARbeta(2)) mRNA levels in the human prostate cancer cell line PC-3 are lower than those in cultured normal human prostate epithelial cells (PrEC). The activity of the human LRAT promoter (2.0 kb) driving a luciferase reporter gene in PC-3 cells is less than 40% of that in PrEC cells. Retinoic acid (RA) treatment increased this LRAT promoter-luciferase activity in PrEC cells, but not in PC-3 cells. Deletion of various regions of the human LRAT promoter demonstrated that a 172-bp proximal promoter region is essential for LRAT transcription and confers RA responsiveness in PrEC cells. This 172-bp region, contained within the 186 bp pLRAT/luciferase construct, has five putative GATA binding sites. Cotransfection of RARbeta(2) or RARgamma and the transcription factor GATA-4 increased LRAT (pLRAT186) promoter activity in both PrEC and PC-3 cells. In addition, we found that both retinoic acid and retinol induced transcripts for the STRA6 gene, which encodes a membrane receptor involved in retinol (vitamin A) uptake, in PrEC cells but not in PC-3 cells. In summary, our data show that the transcriptional regulation of the human LRAT gene is aberrant in human prostate cancer cells and that GATA transcription factors are involved in the transcriptional activation of LRAT in PrEC cells.

Thyroid transcription factor-1 (TTF-1/Nkx2.1/TITF1) gene regulation in the lung

TTF-1 [thyroid transcription factor-1; also known as Nkx2.1, T/EBP (thyroid-specific-enhancer-binding protein) or TITF1] is a homeodomain-containing transcription factor essential for the morphogenesis and differentiation of the thyroid, lung and ventral forebrain. TTF-1 controls the expression of select genes in the thyroid, lung and the central nervous system. In the lung, TTF-1 controls the expression of surfactant proteins that are essential for lung stability and lung host defence. Human TTF-1 is encoded by a single gene located on chromosome 14 and is organized into two/three exons and one/two introns. Multiple transcription start sites and alternative splicing produce mRNAs with heterogeneity at the 5' end. The 3' end of the TTF-1 mRNA is characterized by a rather long untranslated region. The amino acid sequences of TTF-1 from human, rat, mouse and other species are very similar, indicating a high degree of sequence conservation. TTF-1 promoter activity is maintained by the combinatorial or co-operative actions of HNF-3 [hepatocyte nuclear factor-3; also known as FOXA (forkhead box A)], Sp (specificity protein) 1, Sp3, GATA-6 and HOXB3 (homeobox B3) transcription factors. There is limited information on the regulation of TTF-1 gene expression by hormones, cytokines and other biological agents. Glucocorticoids, cAMP and TGF-beta (transforming growth factor-beta) have stimulatory effects on TTF-1 expression, whereas TNF-alpha (tumour necrosis factor-alpha) and ceramide have inhibitory effects on TTF-1 DNA-binding activity in lung cells. Haplo-insufficiency of TTF-1 in humans causes hypothyroidism, respiratory dysfunction and recurring pulmonary infections, underlining the importance of optimal TTF-1 levels for the maintenance of thyroid and lung function. Recent studies have implicated TTF-1 as a lineage-specific proto-oncogene for lung cancer.

TAZ is a coactivator for Pax8 and TTF-1, two transcription factors involved in thyroid differentiation

Pax8 and TTF-1 are transcription factors involved in the morphogenesis of the thyroid gland and in the transcriptional regulation of thyroid-specific genes. Both proteins are expressed in few tissues but their simultaneous presence occurs only in the thyroid where they interact physically and functionally allowing the regulation of genes that are markers of the thyroid differentiated phenotype. TAZ is a transcriptional coactivator that regulates the activity of several transcription factors therefore playing a central role in tissue-specific transcription. The recently demonstrated physical and functional interaction between TAZ and TTF-1 in the lung raised the question of whether TAZ could be an important regulatory molecule also in the thyroid. In this study, we demonstrate the presence of TAZ in thyroid cells and the existence of an important cooperation between TAZ and the transcription factors Pax8 and TTF-1 in the modulation of thyroid gene expression. In addition, we reveal that the three proteins are co-expressed in the nucleus of differentiated thyroid cells and that TAZ interacts with both Pax8 and TTF-1, in vitro and in vivo. More importantly, we show that this interaction leads to a significant enhancement of the transcriptional activity of Pax8 and TTF-1 on the thyroglobulin promoter thus suggesting a role of TAZ in the control of genes involved in thyroid development and differentiation.

GATA-6 mediates transcriptional activation of aquaporin-5 through interactions with Sp1

We investigated mechanisms underlying GATA-6-mediated transcriptional activation of the alveolar epithelial type I cell-enriched gene aquaporin-5 (AQP5). GATA-6 expression increases in alveolar epithelial cells in primary culture, concurrent with upregulation of AQP5 and transition to a type I cell-like phenotype. Cotransfections in MLE-15 and NIH 3T3 cells demonstrated trans-activation by GATA-6 of a rat 1,716-bp-AQP5-luciferase (-1716-AQP5-Luc) reporter. Electrophoretic mobility shift assay and chromatin immunoprecipitation identified an interaction between GATA-6 and putative binding sites in the AQP5 promoter. However, mutation of these sites did not reduce GATA-6-mediated activation, implicating mechanisms in addition to direct binding of GATA-6 to DNA. A 5'-deletion construct, -358-AQP5-Luc, that does not encompass GATA motifs was still activated by GATA-6 by as much as 50% relative to -1716-AQP5-Luc. Internal deletion of the -358/-173 GC-rich domain, which includes several putative Sp1 consensus sites, reduced trans-activation by approximately 60%, suggesting importance of this region for GATA-mediated activity. -358-AQP5-Luc was similarly activated by both GATA-6 and a GATA DNA-binding defective mutant, whereas cotransfections in Schneider S2 cells demonstrated dose-dependent trans-activation of -358-AQP5-Luc by Sp1. Activation of -358-AQP5-Luc by GATA-6 was dramatically reduced by Sp1 small-interfering RNA, and -358-AQP5-Luc was activated synergistically by GATA-6 and Sp1 in NIH 3T3 cells. Furthermore, association between endogenous GATA-6 and Sp1 was demonstrated by coimmunoprecipitation. These results suggest that transcriptional activation of AQP5 by GATA-6 is mediated at least in part through cooperative interactions with Sp1 occurring at the proximal promoter.

NKX2.1 specifies cortical interneuron fate by activating Lhx6

In the ventral telencephalon, the medial ganglionic eminence (MGE) is a major source of cortical interneurons. Expression of the transcription factor NKX2.1 in the MGE is required for the specification of two major subgroups of cortical interneurons - those that express parvalbumin (PV) or somatostatin (SST) - but direct targets of NKX2.1 remain to be established. We find that electroporation of Nkx2.1 cDNA into the ventral telencephalon of slice cultures from Nkx2.1-/- mouse embryos, followed by transplantation into neonatal cortex to permit postnatal analysis of their fate, rescues the loss of PV- and SST-expressing cells. The LIM-homeobox gene Lhx6 is induced by this rescue experiment, and gain- and loss-of-function studies suggest that Lhx6 is necessary and sufficient to rescue these and other interneuron phenotypes in cells transplanted from Nkx2.1-/- slices. Finally, NKX2.1 protein binds a highly conserved sequence in the Lhx6 promoter, and this sequence appears to mediate the direct activation of Lhx6 by NKX2.1. The slice transfection and transplantation methods employed here are beginning to uncover embryonic mechanisms for specifying neuronal fates that only become definable postnatally.

Human heart LIM protein activates atrial-natriuretic-factor gene expression by interacting with the cardiac-restricted transcription factor Nkx2.5

hhLIM [human heart LIM (Lin-11/IsI-1/Mec-3) protein] is a muscle-specific LIM-only protein that consists of two LIM motifs. hhLIM functions as a positive regulator for cardiac hypertrophy. Here we report that hhLIM serves as a cofactor regulating the expression of the ANF (atrial natriuretic factor) gene in H9c2 rat cardiomyoblast cells. We found that hhLIM promoted the expression of the ANF gene in H9c2 cells, but not in A293 human embryonic kidney cells. Furthermore, we showed that hhLIM interacted with Nkx2.5 (a cardiac-restricted transcription factor) in vivo and in vitro using its N-terminal LIM domain and enhanced the binding ability of Nkx2.5 to the NKE (Nkx2.5-binding element) boxes in the ANF promoter. These results suggest that hhLIM promotes the specific expression of the ANF gene by co-operating with Nkx2.5.

Foxp2 inhibits Nkx2.1-mediated transcription of SP-C via interactions with the Nkx2.1 homeodomain

The transcription factor (TF) Foxp2 has been shown to partially repress surfactant protein C (SP-C) transcription, presumably through interaction of an independent repressor domain with a conserved Foxp2 consensus site in the SP-C promoter. We explored the role of interactions between Foxp2 and the homeodomain TF Nkx2.1 that may contribute to the marked reduction in SP-C expression accompanying phenotypic transition of alveolar epithelial type II (AT2) to type I (AT1) cells. Foxp2 dose-dependently inhibited Nkx2.1-mediated activation of SP-C in MLE-15 cells. While electrophoretic mobility shift assays and chromatin immunoprecipitations revealed an interaction between Foxp2 and the conserved consensus motif in the SP-C promoter, Nkx2.1-mediated activation of the 318-bp proximal SP-C promoter (which lacks a Foxp2 consensus) was attenuated by increasing amounts of Foxp2. Co-immunoprecipitation and mammalian two-hybrid assays confirmed a physical interaction between Nkx2.1 and Foxp2 mediated through the Nkx2.1 homeodomain. Formation of an Nkx2.1 complex with an SP-C oligonucleotide was inhibited dose-dependently by recombinant Foxp2. These findings demonstrate that direct interaction between Foxp2 and Nkx2.1 inhibits Nkx2.1 DNA-binding and transcriptional activity and suggest a mechanism for down-regulation of SP-C (and probably other AT2 cell genes) during transition of AT2 cells to an AT1 cell phenotype.

Repression via the GATA box is essential for tissue-specific erythropoietin gene expression

In response to anemia, erythropoietin (Epo) gene transcription is markedly induced in the kidney and liver. To elucidate how Epo gene expression is regulated in vivo, we established transgenic mouse lines expressing green fluorescent protein (GFP) under the control of a 180-kb mouse Epo gene locus. GFP expression was induced by anemia or hypoxia specifically in peritubular interstitial cells of the kidney and hepatocytes surrounding the central vein. Surprisingly, renal Epo-producing cells had a neuronlike morphology and expressed neuronal marker genes. Furthermore, the regulatory mechanisms of Epo gene expression were explored using transgenes containing mutations in the GATA motif of the promoter region. A single nucleotide mutation in this motif resulted in constitutive ectopic expression of transgenic GFP in renal distal tubules, collecting ducts, and certain populations of epithelial cells in other tissues. Since both GATA-2 and GATA-3 bind to the GATA box in distal tubular cells, both factors are likely to repress constitutively ectopic Epo gene expression in these cells. Thus, GATA-based repression is essential for the inducible and cell type-specific expression of the Epo gene.

Cooperative interaction between hepatocyte nuclear factor 4 alpha and GATA transcription factors regulates ATP-binding cassette sterol transporters ABCG5 and ABCG8

Cholesterol homeostasis is maintained by coordinate regulation of cholesterol synthesis and its conversion to bile acids in the liver. The excretion of cholesterol from liver and intestine is regulated by ATP-binding cassette half-transporters ABCG5 and ABCG8. The genes for these two proteins are closely linked and divergently transcribed from a common intergenic promoter region. Here, we identified a binding site for hepatocyte nuclear factor 4alpha (HNF4alpha) in the ABCG5/ABCG8 intergenic promoter, through which HNF4alpha strongly activated the expression of a reporter gene in both directions. The HNF4alpha-responsive element is flanked by two conserved GATA boxes that were also required for stimulation by HNF4alpha. GATA4 and GATA6 bind to the GATA boxes, coexpression of GATA4 and HNF4alpha leads to a striking synergistic activation of both the ABCG5 and the ABCG8 promoters, and binding sites for HNF4alpha and GATA were essential for maximal synergism. We also show that HNF4alpha, GATA4, and GATA6 colocalize in the nuclei of HepG2 cells and that a physical interaction between HNF4alpha and GATA4 is critical for the synergistic response. This is the first demonstration that HNF4alpha acts synergistically with GATA factors to activate gene expression in a bidirectional fashion.

GATA and Nkx factors synergistically regulate tissue-specific gene expression and development in vivo

In vitro studies have suggested that members of the GATA and Nkx transcription factor families physically interact, and synergistically activate pulmonary epithelial- and cardiac-gene promoters. However, the relevance of this synergy has not been demonstrated in vivo. We show that Gata6-Titf1 (Gata6-Nkx2.1) double heterozygous (G6-Nkx DH) embryos and mice have severe defects in pulmonary epithelial differentiation and distal airway development, as well as reduced phospholipid production. The defects in G6-Nkx DH embryos and mice are similar to those observed in human neonates with respiratory distress syndromes, including bronchopulmonary dysplasia, and differential gene expression analysis reveals essential developmental pathways requiring synergistic regulation by both Gata6 and Titf1 (Nkx2.1). These studies indicate that Gata6 and Nkx2.1 act in a synergistic manner to direct pulmonary epithelial differentiation and development in vivo, providing direct evidence that interactions between these two transcription factor families are crucial for the development of the tissues in which they are co-expressed.