The transcription factor TTF-1 is expressed at the onset of thyroid and lung morphogenesis and in restricted regions of the foetal brain

Potential role of nuclear factor kappaB and reactive oxygen species in cAMP and cytokine regulation of surfactant protein-A gene expression in lung type II cells

The human surfactant protein-A2 (hSP-A2) gene is developmentally regulated, expressed in type II pneumonocytes, and induced by cAMP. cAMP induction of hSP-A2 expression is O2 dependent and mediated by increased phosphorylation, DNA binding, and transcriptional activation of thyroid transcription factor-1 (TTF-1). The TTF-1-binding element (TBE) at -175 bp contains a reverse-oriented nuclear factor-kappaB (NF-kappaB) binding site. IL-1 increased SP-A expression in lung type II cells and had additive stimulatory effects with cAMP. Nuclear extracts from cAMP- or IL-1-treated type II cells manifested increased binding to NF-kappaB consensus and TBE probes; cAMP and IL-1 had additive effects. Competitive and antibody supershift EMSA revealed that NF-kappaB and TTF-1 interact with TBE. IL-1 treatment of type II cells caused rapid (1 h) increases in nuclear levels of NF-kappaB (p50 and p65) and in binding to NF-kappaB and TBE probes; nuclear levels of TTF-1 were unaffected. Bt2cAMP increased binding to NF-kappaB and TBE probes more slowly; no changes in nuclear levels of p50, p65, or TTF-1 were evident, suggesting that IL-1 and cAMP act by different mechanisms. A role for endogenous NF-kappaB in cAMP and IL-1 regulation of SP-A was suggested by findings that dominant-negative forms of inhibitor of kappaB reduced binding of type II cell nuclear proteins to TBE and inhibited SP-A expression. In cotransfection assays, NF-kappaB and TTF-1 cooperatively interacted at TBE to stimulate SP-A promoter activity; this was further enhanced by IL-1. In coimmunoprecipitation assays using type II cell nuclear extracts, TTF-1 was found to interact with p65 in vivo. Finally, antioxidant inhibitors of NF-kappaB reduced type II cell nuclear protein binding to TBE and blocked stimulatory effects of cAMP on SP-A expression. This provides intriguing evidence that permissive effects of O2/reactive oxygen species on cAMP regulation of SP-A expression may be mediated by cooperative interactions of TTF-1 and NF-kappaB at the TBE.

Thyroid transcription factor-1: a review

Thyroid transcription factor-1 (TTF-1) is a 38-kd homeodomain containing DNA-binding protein originally identified in follicular cells of the thyroid and subsequently in pneumocytes. This review focuses on the utility of antisera in TTF-1 immunohistochemical staining in the diagnosis of neoplastic conditions. Based on published studies to date, anti-TTF-1 is a very useful reagent in distinguishing pulmonary adenocarcinoma from other primary carcinomas, identifying differentiated thyroid neoplasms, distinguishing mesothelioma from pulmonary adenocarcinoma, and distinguishing small cell carcinoma of the lung from Merkel cell carcinoma. It may also be useful in distinguishing neuroendocrine (NE) tumors of the lung from well-differentiated NE tumors from other sites, such as the intestine.

Expression of thyroid transcription factor-1, cytokeratin 7, and cytokeratin 20 in bronchioloalveolar carcinomas: an immunohistochemical evaluation of 67 cases

Distinguishing primary pulmonary adenocarcinoma from metastatic adenocarcinoma involving the lung is a common challenging task. The distinction between mucinous bronchioloalveolar carcinoma (BAC) and metastatic mucinous carcinoma of other sites, in particular, is difficult by routine histology. Immunohistochemical expression of thyroid transcription factor-1 (TTF-1), as well as cytokeratin 7 (CK 7) and cytokeratin 20 (CK 20), has proven diagnostic utility in discerning primary from metastatic neoplasms in the lung. Rigorous studies assessing the expression of these markers in BACs, particularly in regard to nonmucinous and mucinous subtypes, have not been performed. In this study, we evaluated the immunohistochemical expression of TTF-1, CK 7, and CK 20 in 67 BACs (48 nonmucinous, 12 mucinous, and 7 of mixed histology). Overall, 42 (63%) of the 67 BACs were positive for TTF-1. When stratified according to subtype, all 12 mucinous BACs were observed to be TTF-1 negative. This trend toward absence of TTF-1 expression in mucinous areas was also maintained among tumors with mixed histology. Sixty-three (94%) of 67 BACs were CK 7 positive, with no differences in expression observed upon subtype stratification. Three cases were noted to be positive for CK 20; all exhibited mucinous morphology. These results indicate that in contrast to the immunophenotypic profile exhibited by most pulmonary neoplasms, mucinous BACs are TTF-1 negative and may express CK 20. This suggests that in the context of differentiating mucinous BACs from extrapulmonary mucinous tumors metastatic to the lung, evaluation of TTF-1 and CK 20 expression may have limited diagnostic utility.

Cancer-specific mRNAs in thyroid carcinomas: detection, use, and their implication in thyroid carcinogenesis

Molecular-based diagnosis ofthyroid carcinomas can be more easily establishedby utilizing specific mRNAs that are expressed in a restricted manner in cancer tissues. Accordingly, several cancer-specific mRNAs in thyroid carcinomas have been identified by means of sequence specific-differential display (SS-DD), serial analysis of gene expression (SAGE) and other new techniques. By using these cancer-specific mRNAs, some new methods of preoperative diagnosis of thyroid carcinomas have been developed. In one such method, Aspiration Biopsy-Reverse Transcription-Polymerase Chain Reaction (ABRP), RNA is extracted from leftover cells within the needle used for fine needle aspiration biopsies (FNABs), thereby allowing cytological and molecular-based diagnoses to be performed simultaneously. ABRP provides both RNA information and a cytological diagnosis without further invasion to the patient. By ABRP detection of cancer-specific mRNAs, papillary, anaplastic and medullary carcinomas and a part of malignant lymphomas can be accurately diagnosed preoperatively. It remains to be clarified why cancer-specific mRNAs, especially those that are overexpressed in fetal tissues, can clearly distinguish benign tissues from carcinomas, while genomic alternations, such as mutations in the RAS or P53 gene cannot. Further, the widely accepted hypothesis of multi-step carcinogenesis cannot explain some of the clinical and experimental findings of thyroid carcinomas. Considering these facts, we propose a novel hypothesis of thyroid carcinogenesis, the "germ-cell carcinogenesis" hypothesis, in which cancer cells derive from the remnants of fetal thyroid germ cells (thyroblasts) instead of normal thyroid follicular cells.

The synergistic activity of thyroid transcription factor 1 and Pax 8 relies on the promoter/enhancer interplay

The transcription factors, thyroid transcription factor 1 (TTF-1) and Pax 8, play a pivotal role in the transcriptional regulation of the thyroid differentiation marker genes and in the differentiation of the thyroid follicular cells. They have a very restricted tissue distribution, and the thyrocyte is the only cell type with the simultaneous expression of these factors. Here we show that TTF-1 and Pax 8 cooperatively activate their target genes and that their synergistic activity requires the cross-talk between enhancer and gene promoter. We have characterized the cis and trans requirements of the TTF1/Pax 8 synergistic activity on the thyroperoxidase gene. We show that their synergy is also important for thyroglobulin gene transcription.

An autosomal recessive syndrome of choanal atresia, hypothelia/athelia and thyroid gland anomalies overlapping bamforth syndrome, ANOTHER syndrome and methimazole embryopathy

Two sibs from an inbred Arab family are described with an autosomal syndrome of choanal atresia, hypothelia/athelia and thyroid gland anomalies overlapping Bamforth syndrome, ANOTHER syndrome and methimazole embryopathy. In one case the syndrome described was lethal. Cases with similar features are reviewed and genetic mutations discussed.

Transcriptional stimulation of the surfactant protein B gene by STAT3 in respiratory epithelial cells

The function of the lung is dependent upon differentiation and proliferation of respiratory epithelial cells and the synthesis/secretion of surfactant lipids and proteins into air space. During the respiratory inflammatory response, cytokines produced by macrophages and epithelial cells in the respiratory system have significant influence on surfactant protein homeostasis. We report here that among family members of Janus family tyrosine kinase (JAK) and signal transducers and activators of transcription (STAT), only JAK 1 and STAT3 stimulated the -500 to +41 promoter activity of the surfactant protein B (SP-B) gene in respiratory epithelial cells. JAK1 and STAT3 were co-localized in alveolar type II epithelial cells where SP-B is synthesized and secreted. Interleukin 6 and interleukin 11, known to activate STAT3 synergistically, stimulated the SP-B promoter activity with retinoic acid, which is at least partially mediated through interactions between STAT3 and retinoid nuclear receptor enhanceosome proteins in pulmonary epithelial cells.

Expression and localization of the homeodomain-containing protein HEX in human thyroid tumors

Homeobox genes are involved in neoplastic transformation of both epithelial and hemopoietic tissues. The divergent homeobox gene HEX is expressed in the anterior visceral endoderm during early mouse development and in some adult tissues of endodermal origin, including liver and thyroid. Whereas a role in leukemyogenesis has been proposed already, few data are available on the involvement of HEX in human epithelial tumors. Herein, we analyzed HEX expression and subcellular localization in a series of 55 human thyroid tumors and in several tumoral cell lines. HEX mRNA was detected by RT-PCR either in normal tissues or in thyroid adenomas and differentiated (papillary and follicular) carcinomas. HEX mRNA was also expressed in most undifferentiated carcinomas. Subcellular localization of HEX protein was investigated by immunohistochemistry. In normal tissues and adenomas, HEX protein was present both in nucleus and cytoplasm. In contrast, both differentiated and undifferentiated carcinomas, as well as the tumoral cell lines investigated, showed HEX protein only in the cytoplasm. These findings suggest that regulation of HEX entry in the nucleus of thyrocytes may represent a critical step during human thyroid tumorigenesis.

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.

Dorsalization of the neural tube by Xenopus tiarin, a novel patterning factor secreted by the flanking nonneural head ectoderm

We have isolated a novel secreted dorsalizing factor of the neural tube, Xenopus Tiarin, which belongs to the olfactomedin-related family. Tiarin expression starts at the late gastrula stage in the nonneural ectoderm adjacent to the anterior neural plate. Overexpression of Tiarin in the embryo causes expansion of dorsal neural markers and suppression of ventral markers. In the eye-forming field, Tiarin overexpression induces the retinal markers and represses optic stalk markers. Tiarin directly dorsalizes neural tissues in the absence of mesodermal tissues and antagonizes the ventralizing activity of Sonic hedghog (Shh). Unlike BMP4, another dorsalizing factor, Tiarin does not display antineuralizing activity on the ectoderm or mesoderm-ventralizing activity. These findings show that Tiarin is a novel patterning signal candidate acting in the specification of the dorsal neural tube.

Expression of thyroid transcription factor-1 in the spectrum of neuroendocrine cell lung proliferations with special interest in carcinoids

The World Health Organization's classification of lung tumors separately categorizes neuroendocrine (NE) lung tumors, small cell lung carcinoma (SCLC), and large cell neuroendocrine carcinoma (LCNEC) as high-grade NE malignancies and carcinoids (typical, [TC] and atypical [AC]) as low- and intermediate-grade malignancies. Although these NE tumors are considered with NE hyperplasia (NEH) and tumorlets as part of a spectrum of NE proliferations, their derivation from a common progenitor cell has not received full agreement. With the aim of refining their differential diagnosis and extending our understanding of their histogenesis, we studied the expression of thyroid transcription factor-1 (TTF-1), a transcription factor that regulates lung morphogenesis and differentiation, along the spectrum of NE lung tumors. Two hundred and twenty- seven NE proliferations and tumors were immunostained with TTF-1 antibody. Positive immunostaining for TTF-1 was detected in 47 of 55 (85.5%) pure SCLCs, in 31 of 64 (49%) pure LCNECs, but in none of 15 NEHs, 23 tumorlets, or 50 carcinoid tumors (27 TCs and 23 ACs). In 19 of 20 (95%) combined SCLCs and LCNECs, TTF-1 expression was identical in both NE and non-NE components. These results show that TTF-1 is not expressed in normal and hyperplastic NE cells or in carcinoids, but is expressed in high-grade NE proliferations and in lung adenocarcinomas. This challenges the concept of a spectrum of NE proliferations and tumors and lends credence to the alternative hypothesis of a common derivation for SCLC and non-SCLC including LCNEC, with carcinoids deriving from a different stem cell.

Dorsoventral patterning in oesophageal atresia with tracheo-oesophageal fistula: Evidence from a new mouse model

BACKGROUND/PURPOSE

The well-established Adriamycin rat model of oesophageal atresia (OA) and tracheo-oesophageal fistula (TOF) complements recently described mouse genetic models in which loss of function mutations in foregut patterning genes, such as Nkx2.1 (Ttf 1), lead to OA/TOF. The authors aimed to integrate the 2 systems by adapting the Adriamycin model to the mouse to study molecular aspects of tracheo-oesophageal development.

METHODS

Pregnant CBA/Ca mice were injected intraperitoneally with 4 mg/kg of Adriamycin on embryonic days 7.5 and 8.5. Embryos and fetuses of various gestational ages were subjected to morphologic or histologic examination. Sections were stained with H & E or processed for immunohistochemistry using an antibody specific for Nkx2.1.

RESULTS

Tracheo-oesophageal malformations were observed in 47% of Adriamycin-treated embryos. Early foregut development was similar in Adriamycin-exposed and control embryos but, by E11.5, many treated embryos had an undivided oesophago-trachea, which gave rise to the lung buds and a fistula to the stomach. The fistula originated from the dorsal aspect of the undivided tube and was negative for Nkx2.1, or showed only transient Nkx2.1 expression, compared to the strongly positive bronchi ventrally.

CONCLUSIONS

The Adriamycin model of OA is adaptable to the mouse. In the absence of tracheo-oesophageal separation, the dorsal fistula retains its nonrespiratory commitment suggesting that dorsoventral patterning of foregut development is undisturbed by Adriamycin exposure.

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.

Overexpression of surfactant protein-C mature peptide causes neonatal lethality in transgenic mice

Surfactant replacement preparations containing either surfactant protein (SP)-B or SP-C significantly improve lung function in surfactant-deficient infants, suggesting that these peptides may be functionally redundant. SP-B is absent and SP-C is greatly diminished in the airspaces of SP-B (-/-) mice, which die of respiratory distress syndrome (RDS) shortly after birth. The goal of this study was to determine if elevated expression of SP-C mature peptide could reverse the neonatal lethality in SP-B (-/-) mice. SP-C peptide (residues 24-57 of mouse SP-C proprotein) with a hemagglutinin epitope (SP-C(24-57)HA) was expressed in type II cells of transgenic mice, with the goal of crossing these animals into the SP-B (-/-) background. Unexpectedly, expression of the SP-C(24-57)HA transgene resulted in delayed/arrested lung development and lethal, neonatal RDS of all transgenic progeny in two independent transgenic lines. In transgenic mice, SP-C(24-57)HA was localized predominantly to the endoplasmic reticulum and Golgi; in contrast, SP-B and SP-C were very difficult to detect in the endoplasmic reticulum of wild-type mice. These results suggest that elevated expression of SP-C(24-57)HA in type II cells resulted in aggregation of SP-C in the early secretory pathway, leading to cytotoxicity and, ultimately, altered lung development.

Low-density cDNA array-coupled to PCR differential display identifies new estrogen-responsive genes during the postnatal differentiation of the rat hypothalamus

To identify estrogen (E)-responsive genes that may play important roles in the sexual differentiation and maturation of the neuroendocrine hypothalamus, we used mRNA differential display PCR to analyze hypothalamic RNA derived from estrogen-sterilized rats (ESRs). Neonatal rats were s.c.-injected with 100 microg of 17 beta-estradiol-benzoate (EB) for 5 days. Approximately 300 out of more than 2000 RNAs examined displayed a differential expression pattern between hypothalami of the ESR females compared to their 60-day-old controls. EB-dependent expression of these genes was further analyzed by low-density cDNA array using cDNA probe sets reverse-transcribed from the same groups; 98 genes were confirmed to be differentially expressed. We selected 41 clones that showed higher density differences between the two probe sets than mean density difference in control cyclophilin cDNA blots in the cDNA array. After being cloned into pGEM-T vectors, their sequences were analyzed. Homology searches identified four genes as a protein kinase C (PKC)-binding protein, NELL2 (clone 6-1), a thyroid nuclear factor, TTF-1 (9-1), Munc18-1 (17-6), and leuserpin-2 (18-5). The other 22 genes were similar to reported genes or cDNAs such as mouse kinesin-associated protein 3 (KAP3, 8b), mouse IgE binding lectin (15-1), normalized rat brain cDNA (5-1), rat cDNA (8-1) and rat embryonic cDNA (17-1). Fifteen clones such as clone 7-3 showed no match in the GenBank Database. Further characterization of eight clones (17-1, 7-3, 8-1, 5-1, NELL2, KAP3 homolog, IgE binding lectin homolog, and TTF-1) showed that their expression in the adult female rat hypothalamus is sensitive to neonatal treatment with EB. They showed brain-specific expression and moreover, showed an increase in their mRNA level before the initiation of puberty. Some of them showed gender differences in their different postnatal expression pattern. We speculate that further study will demonstrate that many of the E-regulated genes identified in the present study play important roles in the regulation of the sexual differentiation and E-dependent maturation of the hypothalamus.

Nestin is a neuroepithelial target gene of thyroid transcription factor-1, a homeoprotein required for forebrain organogenesis

Thyroid transcription factor-1 (TTF-1, also known as NKX2.1 and T/EBP), a transcription factor belonging to the NKX-2 family of homeodomain-containing genes, plays an essential role in the organogenesis of the thyroid gland, lung, and ventral forebrain. Nestin is an intermediate filament protein strongly expressed in multipotential neuroepithelial stem cells and rapidly down-regulated during postnatal life. Here we show that stable fibroblastic clones expressing TTF-1 acquire a phenotype reminiscent of neuroepithelial cells in culture and up-regulate the endogenous nestin gene. TTF-1 transactivates in HeLa and NIH3T3 cells a reporter gene driven by a central nervous system-specific enhancer element from the second intron of the rat nestin gene, where it recognizes a DNA-binding site (NestBS) whose sequence resembles a nuclear hormone/cAMP-responsive element very different from canonical TTF-1 binding sites. Nuclear extracts from the head of mouse embryos form a retarded complex with NestBS of the same mobility of the extracts obtained from TTF1-expressing clones, which is either abolished or supershifted in the presence of two different antibodies recognizing the TTF-1 protein. Thus, the neuroepithelial marker nestin is a direct central nervous system-specific target gene of TTF-1, leading to the hypothesis that it might be the effector through which TTF-1 plays its role in the organogenesis of the forebrain.

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.

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.

The avian telencephalic subpallium originates inhibitory neurons that invade tangentially the pallium (dorsal ventricular ridge and cortical areas)

Recent data on the development of the mammalian neocortex support that the majority of its inhibitory GABAergic interneurons originate within the subpallium (ganglionic eminences). Support for such tangential migration into the pallium has come from experiments using fluorescent tracers or lineage analysis with retrovirus, and the phenotypes of mutant mice with different abnormalities in the developing subpallium. In the present study, we describe tangential migration of subpallial-derived neurons in the developing chick telencephalon. Using quail-chick grafts, we precisely identified the neuroepithelial origin, time-course, and pathways of migration, as well as the identity and relative distribution of the diverse tangentially migrated neurons. The analysis of selective grafts of the pallidal and striatal primordia allowed us to determine the relative contribution of each primordium to the population of migrating neurons. Moreover, we found that, like in mammals, the vast majority of the GABAergic and calbindin-immunoreactive neurons within the pallium (dorsal ventricular ridge and cortical areas) have an extracortical, subpallial origin. Our results suggest that the telencephalon of birds and mammals share developmental mechanisms for the origin and migration of their cortical interneurons, which probably first evolved at an earlier stage in the radiation of vertebrates than was thought before.

A model of pulmonary adenocarcinoma in transgenic mice expressing the simian virus 40 T antigen driven by the rat Calbindin-D9K (CaBP9K) promoter

Lung cancer is the most frequent cause of cancer deaths. Its origin and development remain poorly understood, partly because of the lack of pertinent animal models. This study produced transgenic mice expressing the simian virus (SV) 40 T antigen (Tag) driven by a 1011 base-pair DNA fragment of the rat Calbindin-D9K (CaBP9K) promoter. All transgenic animals developed multifocal pulmonary tumours with pathological and ultrastructural features consistent with adenocarcinomas. Using immunohistochemistry, northern blot or western blot, tumours were found to express the transcription factor TTF-1, as well as specific markers of the peripheral airway Clara cells (CC10) and alveolar type II cells (surfactant proteins A, B, C, and D). This model, with its similarities to human adenocarcinoma, should be useful not only for addressing the mechanisms underlying the development and progression of lung cancer, but also for testing new therapeutic approaches.

Sclerosing hemangioma of lung: A close cytologic mimicker of pulmonary adenocarcinoma

We report the fine-needle aspiration biopsy findings of sclerosing hemangioma of lung occurring in a 40-yr-old Chinese woman. Cytologically, there were hyalinized stromal tissue fragments admixed with clusters of nondescript mononuclear tumor cells. Scattered foamy macrophages and red blood cells were also noted in the background. Focal papillary and acinar configurations were seen. However, some of the epithelial cells show nuclear pleomorphism with nuclear hyperchromasia, prominent nucleoli, and occasional intranuclear inclusions. Mitotic activity was virtually absent. The cytologic atypia present may result in misdiagnosis of well-differentiated pulmonary adenocarcinoma, especially bronchioloalveolar carcinoma. Recognition of the subtle cytologic differences, together with cell block examination, immunocytochemistry, and proper clinicoradiologic correlation, is crucial for an accurate preoperative diagnosis.

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.

Immunohistochemical analyses of thyroid-specific enhancer-binding protein in the fetal and adult rat hypothalami and pituitary glands

Thyroid-specific enhancer-binding protein (T/EBP), also known as NKX2.1 or TTF-1, regulates the expression of thyroid- and lung-specific genes. The t/ebp/Nkx2.1-null mutant mouse was stillborn but lacked the thyroid gland, pituitary gland, ventral region of the forebrain and normal lungs. These data demonstrated that T/EBP/NKX2.1 plays an important role not only in tissue-specific gene expressions in adults but also in genesis of these organs during development. Although the expression of t/ebp/Nkx2.1 in the brain has been reported, its function in the brain remains unknown. The present study was designed to determine the localization of T/EBP/NKX2.1 in the hypothalamus and pituitary gland of fetal and adult rats by immunohistochemistry as the first step toward understanding the function of T/EBP/NKX2.1 in the rat brain. In the fetal rat hypothalamus, T/EBP/NKX2.1 was localized widely in the ventral hypothalamic areas. In the adult rat brain, T/EBP/NKX2.1 was localized in the ventromedial hypothalamic nucleus, medial tuberal nucleus, arcuate nucleus and mammillary body. No T/EBP/NKX2.1 immunoreactivity was observed in the anterior or intermediate lobe of the pituitary gland in either fetal or adult rats. On the other hand, immunoreactive T/EBP/NKX2.1 was found in the posterior lobe of the pituitary gland. This paper presents results of detailed analyses of the distributions of T/EBP/NKX2.1 protein in the fetal and adult rat hypothalami and pituitary glands, and these results should provide important information for understanding the function of T/EBP/NKX2.1 in the brain.

Cytokeratin 7 and 20 and thyroid transcription factor 1 can help distinguish pulmonary from gastrointestinal carcinoid and pancreatic endocrine tumors

Expression of cytokeratin (CK) 7 and 20 is commonly used to help distinguish adenocarcinomas from different sites. Thyroid transcription factor 1 (TTF-1) is a 38-kd protein, located primarily in the nucleus of type 2 pneumocytes and clara cells. TTF-1 has been shown to be present in a variety of lung and thyroid tumors and in pulmonary small-cell carcinomas. Carcinoid tumors from the lung and the gastrointestinal (GI) tract are histologically similar and thus are difficult to differentiate from each other based on histologic criteria. Pancreatic endocrine tumors (PET) have a similar histologic appearance to these other tumors. The purpose of this study was to determine the efficacy of differentiating these 3 groups of tumors by their expression of CK7, CK20, and TTF-1. Routinely processed paraffin-embedded tissue sections from 62 carcinoid tumors (lung, 16; gastrointestinal [GI] tract, 46) and 12 PETs were immunohistochemically stained for CK7, CK20, and TTF-1. The degree of expression in each tumor was graded as 1+ (1% to 10% of cells positive), 2+ (11% to 25%), 3+ (26% to 50%), and 4+ (>50%). The data were compared between tumor types and between carcinoid tumors from the various locations in the GI tract (stomach, 8; small intestine, 19; large intestine, 17; appendix, 2). CK7 was expressed in 10 (63%) of 16 pulmonary carcinoid tumors and only 5 (11%) of 46 GI carcinoid tumors (P <.001). Pancreatic endocrine tumors showed CK7 positivity in 6 (50%) of 12 cases, which was similar to the findings in lung carcinoids and significantly higher than in GI carcinoids (P <.01). CK20 was expressed in 0 (0%) of 16 pulmonary carcinoid tumors, in contrast to 24% and 33% of GI carcinoid tumors (P <.05) and PETs (P <.05), respectively. TTF-1 expression was highly specific for pulmonary carcinoid tumors. This peptide was present in 11 (69%) of 16 pulmonary carcinoid tumors and in only 1 (2%) of 46 and 0 (0%) of 12 GI carcinoid tumors (P <.001) and PETs (P <.001), respectively. A CK7(+)/CK20(-)/TTF-1(+) immunopanel result was moderately sensitive (sensitivity, 50%), and highly specific (specificity, 100%), for a diagnosis of pulmonary carcinoid tumor. CK7, CK20, and TTF-1 did not differ significantly between carcinoid tumors located in different sites of the GI tract. However, a trend was observed toward a lower prevalence of CK20 positivity in gastric tumors (P =.06) than in GI carcinoid tumors from the small intestine, colon, or appendix. Expression of CK7 and CK20, and particularly TTF-1, may be useful in distinguishing pulmonary from GI carcinoid tumors and PETs, especially when evaluated as a panel of markers. TTF-1 is highly specific for pulmonary carcinoid tumors.

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.

Thyroid transcription factor 1 and cytokeratins 1, 5, 10, 14 (34betaE12) expression in basaloid and large-cell neuroendocrine carcinomas of the lung

Basaloid carcinoma (BC) and large-cell neuroendocrine carcinoma (LCNEC) are 2 recently recognized variants of large-cell lung carcinomas that may overlap in their morphology, and are discriminated by expression of neuroendocrine markers in LCNEC. Because thyroid transcription factor 1 (TTF-1) is expressed in lung adenocarcinomas but not in squamous cell carcinomas (SCC), and 34betaE12 recognizes a set of high-molecular-weight cytokeratins characteristic of basal stem cells, we hypothesized that these 2 markers could help in distinguishing BC from LCNEC. Immunostaining for TTF-1 was detected in 40.9% of pure LCNEC but in no BC or basaloid variant of SCC. In contrast, immunoreactivity for 34betaE12 was shown in all BC and basaloid variant of SCC but in only 1 LCNEC. Bouin fixation was less efficient than formalin in the immunodetection of both markers for its well-known deleterious effect on antigen preservation. Specificity of TTF-1 for LCNEC (100%) and that of 34betaE12 for BC (98.3%) exceeded that of NE markers for distinction of these 2 entities. These data show that TTF-1 and 34betaE12, in association with specific neuroendocrine markers, represent a useful panel of antibodies in differentiating carcinomas presenting with a solid pattern, palisading, or pseudorosettes, the expression of TTF-1 excluding the diagnosis of BC, and staining with 34betaE12 excluding pure LCNEC.

Absence of thyroid transcription factor-1 expression in human parathyroid and pituitary glands

Thyroid transcription factor-1 (TTF-1), a tissue-specific nuclear transcription factor involved in the embryogenesis and differentiation of human thyroid, lung and brain, has been recently identified in other rat tissues, including parafollicular C cells and parathyroid chief cells. Based on this distribution, a possible role for this factor in calcium homeostasis has been suggested. This study investigated the presence of TTF-1 transcripts and protein in human tissues expressing the calcium sensing receptor (CaSR). Using a RT-PCR technique, complemented by Southern blot analysis, TTF-1 expression was detected in human C cells (two medullary thyroid carcinomas), but not in normal and adenomatous (four adenomas and three hyperplasia) parathyroid, and normal and adenomatous (six adenomas) pituitary tissues. CaSR was expressed in all samples. The absence of expression was confirmed by Western blot. In contrast to previous studies in the rat, this study demonstrates the absence of TTF-1 transcripts in the human adult parathyroid and pituitary glands, although a role for this factor during the ontogeny of these organs cannot be excluded.

Down-regulation of regulatory proteins for differentiation and proliferation in murine fetal hypoplastic lungs: altered mesenchymal-epithelial interactions

We compared proliferation (growth) and differentiation (development) related proteins in normal and hypoplastic fetal murine lungs. The hypoplastic lungs were created in CD-1 fetal mice by nitrofen exposure (25 mg per pregnant mouse given intragastrically on gestational day 8 [Gd8]), as published earlier. The lungs were harvested at Gd14, 16, 19 and from neonates. Immunoblot analyses were carried out for transcription factors (oncogenic proteins, nuclear receptor, and transmembrane receptor proteins) in severely hypoplastic murine fetal lungs with coexistent diaphragmatic hernia, and results were compared with those derived from normal lungs of equivalent age. These proteins have proposed roles in the regulation of proliferation and differentiation processes of fetal lungs. We have shown that the product of the oncogene c-myc was reduced in hypoplastic lungs at all stages of gestation, whereas c-Fos protein levels were variable. These proteins are known to regulate transcription of various developmental proteins, such as those responsible for proliferation and differentiation. Further, the nuclear transcription factors thyroid transcription factor-1 (TITF-1) and glucocorticoid receptor (GR) were reduced, and thyroid hormone receptor (TR) and retinoic acid receptors (RARs) were inhibited in severely hypoplastic lungs compared to normal lungs of equivalent gestational stage, except in neonatal lungs, where signals for RARs were seen. TITF-1 is known to localize in bronchial epithelial cells in developing lungs. It is restricted to type II pneumocytes with gestational development in the normal lungs and regulates surfactant proteins. Earlier, we have reported that surfactant proteins are reduced in hypoplastic lungs. In the current study, reduced GR and TITF-1 proteins may play a role in reducing surfactant proteins in the hypoplastic lungs. The significant inhibition in TR and RARalpha in the severely hypoplastic lungs reflects on affected epithelial cell maturation and alveolar formation, respectively. Altered RARbeta levels correlate with affected lung growth and branching morphogenesis of nitrofen-exposed lungs. A transmembrane receptor protein EGFR was reduced in hypoplastic lungs, suggesting the involvement of altered mesenchymal-epithelial signal transduction pathways. We conclude (1) Our data suggest altered levels of various nuclear transcription factors in the murine fetal hypoplastic lungs; (2) Reduced levels TITF-1 protein in hypoplastic lungs may have caused the functional immaturity of distal lung, immature airways and thus may affect overall differentiation of lungs. These results correlated with low levels of surfactant proteins in these lungs; (3) TR and RAR inhibition indicate their roles through reduced or retarded proliferation and differentiation processes in the severely hypoplastic lungs; (4) GR down-regulation in developing fetal murine hypoplastic lungs indicate delayed development, and GR up-regulation in affected neonates may be induced by stress/stretch caused at birth due to air-breathing; (5) Down- regulation of EGFR indicate altered mesenchymal-epithelial interactions and possible influence on lung proliferation and differentiation.

C-cell and thyroid epithelial tumours and altered follicular development in transgenic mice expressing the long isoform of MEN 2A RET

Gain-of-function mutations in the gene encoding the receptor tyrosine kinase RET have been identified as the aetiological factor for multiple endocrine neoplasia type 2A (MEN2A). MEN2A is a dominantly-inherited cancer predisposition syndrome characterized by medullary thyroid carcinoma, a tumour of the calcitonin-producing thyroid C-cells. There are three isoforms of RET: RET9, RET43 and RET51, and although in vitro evidence suggests they vary in cellular transformation activities, little is known about their function in tumorigenesis in vivo. To address this, we used RET51 cDNA to construct mice in which the most frequent MEN2A mutation, Cys-634-Arg, was expressed under the control of the human calcitonin promoter (CT-2A mice). These mice developed C-cell tumours resembling human MTC and follicular tumours resembling human papillary thyroid carcinoma (PTC) depending on the founder line examined. One founder line developed compound MTC/PTC at low frequency (8%) and pancreatic cystadenocarcinoma. CT-2A mice also displayed a developmental defect in thyroid follicular structure, in which much of the thyroid was occupied by large irregular cystic follicles thought to be derived from the ultimobranchial body, a developmental precursor of the thyroid gland. The CT-2A mice will provide a suitable model to further study the effects of the MEN 2A RET mutation in vivo.

Branching and differentiation defects in pulmonary epithelium with elevated Gata6 expression

The transcription factor GATA6 is expressed in the fetal pulmonary epithelium of the developing mouse lung and loss of function studies strongly suggested that it is required for proper branching morphogenesis and epithelial differentiation. We have further investigated the role of GATA6 in this process by utilizing a pulmonary epithelium specific promoter to maintain high levels of GATA6 protein during fetal lung development. Transgenic mice expressing Gata6 cDNA under the control of the human Surfactant Protein-C (SP-C) promoter were generated and their lungs were analyzed during fetal stages. Transgenic lungs exhibit branching defects as early as embryonic day (E) 14.5 and molecular analysis just before birth (E18.5) shows a lack of distal epithelium differentiation whereas proximal epithelium is unaffected. Electron microscopic analysis and glycogen staining confirm the lack of differentiation to mature Type II cells. Thus, elevated levels of GATA6 protein affect early lung development and in analogy to other GATA factors in other tissues, GATA6 also plays a crucial role in the terminal differentiation in this case of the distal pulmonary epithelium.

Protein-protein interaction of retinoic acid receptor alpha and thyroid transcription factor-1 in respiratory epithelial cells

Surfactant protein B (SP-B) is a 79-amino acid peptide critical to postnatal respiratory adaptation and is developmentally regulated. Previous studies demonstrated that retinoic acid receptors (RARs) and thyroid transcription factor 1 (TTF-1) stimulated SP-B gene expression in respiratory epithelial cells. Clustered retinoic acid-responsive element and TTF-1 binding sites were identified in the enhancer region of the SP-B gene and were required for retinoic acid stimulation of the human SP-B (hSP-B) promoter. In addition, RAR and TTF-1 were colocalized in mouse bronchiolar and alveolar type II epithelial cells, the cellular site of SP-B synthesis. In the present studies, RAR and TTF-1 were colocalized in the nucleus of H441 cells. RAR and TTF-1 synergistically stimulated the hSP-B promoter in H441 cells. Direct protein-protein interactions between RAR and TTF-1 were demonstrated by the glutathione S-transferase pull-down assay and the mammalian cell two hybrid assay. Truncation/deletion studies showed that the RAR-TTF-1 interaction was mediated through the RAR DNA binding domain (DBD) and the TTF-1 homeodomain. RAR DBD greatly enhanced TTF-1 homeodomain DNA binding activity to a hSP-B enhancer oligonucleotide, in which retinoic acid-responsive element and TTF-1 DNA binding sites overlap. Chromatin immunoprecipitation assay demonstrated that retinoic acid treatment of H441 cells greatly stimulated both RAR and TTF-1 DNA binding to the hSP-B enhancer region in H441 cells. These findings support a model in which RAR/retinoid X receptor, TTF-1, and coactivators (p160 members and CBP) form an enhanceosome in the enhancer region of the hSP-B gene.

Thyrocyte integration, and thyroid folliculogenesis and tissue regeneration: perspective for thyroid tissue engineering

The thyroid gland is composed of many ball-like structures called thyroid follicles, which are supported by the interfollicular extracellular matrix (ECM) and a capillary network. The component thyrocytes are highly integrated in their specific structural and functional polarization. In conventional monolayer and floating culture systems, thyrocytes cannot organize themselves into follicles with normal polarity. In contrast, in 3-D collagen gel culture, thyrocytes easily form stable follicles with physiological polarity. Integration of thyrocyte growth and differentiation results ultimately in thyroid folliculogenesis. This culture method and subacute thyroiditis are two promising models for addressing mechanisms of folliculogenesis, because thyroid-follicle formation actively occurs both in the culture system and at the regenerative phase of the disorder. The understanding of the mechanistic basis of folliculogenesis is prerequisite for generation of artificial thyroid tissue, which would enable a more physiological strategy to the treatment of hypothyroidism caused by various diseases and surgical processes than conventional hormone replacement therapy. We review here thyrocyte integration, and thyroid folliculogenesis and tissue regeneration. We also briefly discuss a perspective for thyroid tissue regeneration and engineering.

Expression of thyroid transcription factor-1 (TTF-1) gene in the ventral forebrain and endostyle of the agnathan vertebrate, Lampetra japonica

The Thyroid transcription factor-1 (TTF-1) gene belongs to the Nkx-2.1 subfamily and encodes a transcription factor containing an NK-2-type homeodomain. In our study, we isolated and characterized cDNA clones for the TTF-1/Nkx-2.1 orthologue (LjTTF-1) from the agnathan vertebrate Lampetra japonica. Spatial and temporal expression patterns assessed by in situ hybridization revealed the expression of LjTTF-1 in the anterior nerve cord and anteroventral region of the pharynx. The neural expression was subsequently restricted to the ventral diencephalon. The pharyngeal expression, on the other hand, extended posteriorly to the fourth pharyngeal-pouch level and was finally localized in the endostyle anlage. In the differentiated endostyle of ammocoete larvae, the expression of LjTTF-1 was chiefly detected in type 2a, 2b, and 2c cells, which develop adjacent to glandular cells. These expression patterns of LjTTF-1 support the idea that this gene family plays an important role in the development of the rostral brain and endostyle equivalent organs. Furthermore, histological comparisons between TTF-1/Nkx-2.1 expression in the endostyles of ammocoetes and ascidians suggested the possibility that the organogenetic architecture of the endostyle is conserved among chordates.

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.

Transcription factors in mouse lung development and function

Development of the mouse lung initiates on day 9.5 postcoitum from the laryngotracheal groove and involves mesenchymal-epithelial interactions, in particular, those between the splanchnic mesoderm and epithelial cells (derived from foregut endoderm) that induce cellular proliferation, migration, and differentiation, resulting in branching morphogenesis. This developmental process mediates formation of the pulmonary bronchiole tree and integrates a terminal alveolar region with an extensive endothelial capillary bed, which facilitates efficient gas exchange with the circulatory system. The major function of the mesenchymal-epithelial signaling is to potentiate the activity or expression of cell type-specific transcription factors in the developing lung, which, in turn, cooperatively bind to distinct promoter regions and activate target gene expression. In this review, we focus on the role of transcription factors in lung morphogenesis and the maintenance of differentiated gene expression. These lung transcription factors include forkhead box A2 [also known as hepatocyte nuclear factor (HNF)-3beta], HNF-3/forkhead homolog (HFH)-8 [also known as FoxF1 or forkhead-related activator-1], HNF-3/forkhead homolog-4 (also known as FoxJ1), thyroid transcription factor-1 (Nkx2.1), and homeodomain box A5 transcription factors, the zinc finger Gli (mouse homologs of the Drosophila cubitus interruptus) and GATA transcription factors, and the basic helix-loop-helix Pod1 transcription factor. We summarize the phenotypes of transgenic and knockout mouse models, which define important functions of these transcription factors in cellular differentiation and lung branching morphogenesis.

A bipotential precursor population for pancreas and liver within the embryonic endoderm

The pancreas emerges independently from dorsal and ventral domains of embryonic gut endoderm. Gene inactivation experiments in mice have identified factors required for dorsal pancreas development, but factors that initiate the ventral pancreas have remained elusive. In this study, we investigated the hypothesis that the emergence of the ventral pancreas is related to the emergence of the liver. We find that the liver and ventral pancreas are specified at the same time and in the same general domain of cells. Using embryo tissue explantation experiments, we find that the default fate of the ventral foregut endoderm is to activate the pancreas gene program. FGF signalling from the cardiac mesoderm diverts this endoderm to express genes for liver instead of those for pancreas. No evidence was found to indicate that the cell type choice for pancreas or liver involves a selection for growth or viability. Cardiac mesoderm or FGF induces the local expression of sonic hedgehog, which in turn is inhibitory to pancreas but not to liver. The bipotential precursor cell population for pancreas and liver in embryonic development and its fate selection by FGF has features that appear to be recapitulated in the adult pancreas and are reflected in the evolution of these organs.

Regulation of the Clara cell secretory protein/uteroglobin promoter in lung

Clara cell secretory protein/uteroglobin (CCSP/UG) is specifically expressed in the conducting airway epithelium of the lung in a differentiation-dependent manner. The proximal promoter region of the rodent CCSP/UG gene directs Clara cell specificity. Previously, it was shown that the forkhead transcription factors HNF-3 alpha and beta and the homeodomain factor TTF-1 are important transcription factors acting through this region, suggesting that they contribute to cell specificity of the CCSP/UG gene. Members of the C/EBP family of transcription factors can also interact with elements of the proximal rat and mouse CCSP/UG promoters. The onset of C/EBP alpha expression in Clara cells correlates with the strong increase of CCSP/UG expression. Thus, C/EBP alpha may play a crucial role for differentiation-dependent CCSP/UG expression. Transfection studies demonstrate that C/EBP alpha and TTF-1 can synergistically activate the murine CCSP/UG promoter. Altogether, these results suggest that C/EBP alpha, TTF-1, and HNF-3 determine the Clara cell-specific, differentiation-dependent expression of the CCSP/UG gene in murine lung. The relative importance of these three transcription factors, however, differs in rabbits and humans.

Immunoreactivity for thyroid transcription factor-1 in stage I non-small cell carcinomas of the lung

Thyroid transcription factor-1 (TTF-1) is a nuclear protein regulating the transcriptional activity of lung-specific genes in the normal and neoplastic bronchioloalveolar cells. It has been implicated in the normal growth and development of the lung, and the disruption of the TTF-1 locus leads to neonatal death with pulmonary hypoplasia. We evaluated retrospectively the prevalence and clinical significance of TTF-1 immunoreactivity in 222 patients with stage I non-small cell lung carcinoma (NSCLC) with a follow-up time of at least 5 years, and we investigated its relationship with other markers of tumor growth, namely cell proliferation and angiogenesis. TTF-1 immunoreactivity was documented by using the commercially available monoclonal antibody 8G7G3/1 in 72% of 97 adenocarcinomas, 5% of 119 squamous cell carcinomas, and in the glandular component of two adenosquamous carcinomas. Four large cell carcinomas were completely unreactive. In adenocarcinomas, but not squamous cell carcinomas, TTF-1 immunoreactivity correlated significantly with microvessel density (p = 0.04) and inversely with the tumor proliferation fraction assessed by Ki-67 immunostaining (p = 0.03). Also, TTF-1-immunoreactive adenocarcinomas showed a trend for a size less than 3 cm (p = 0.08). TTF-1 expression was not related to specific growth patterns, tumor grade, or tumor cell typing. TTF-1 immunoreactivity did not significantly affect patient survival, although patients with more than 75% immunoreactive neoplastic cells showed a trend for longer overall and disease-free survival. Our findings suggest that TTF-1 could be involved in the development of small pulmonary adenocarcinomas, but it has not prognostic implications in patients with stage I NSCLC.

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.

Combined analysis of MIB-1 and thyroid transcription factor-1 predicts survival in non-small cell lung carcinomas

The prognostic value of combined immunohistochemical analysis for the thyroid transcription factor-1 (TTF-1) and the proliferation marker MIB-1 was assessed in a consecutive series of non-small cell lung carcinomas (NSCLC). Tumor immunoreactivity for TTF-1 and MIB-1 was classified in three groups (-,+,++) and in two groups (-,+), respectively. Comparison across groups for TTF-1 reactivity showed significantly different survival curves (P=0.04). In particular, the best prognosis was associated with a TTF-1 negative pattern, whereas the TTF-1 '++' cases showed the worst prognosis. A trend towards better prognosis was observed for MIB-1 negative cases (P=0.09). Multivariate analysis confirmed independent prognostic significance of TTF-1 (P=0.002), MIB-1 (P=0.01) and pStage (P=0.04). Accordingly, analysing TTF-1 and MIB-1 together, a better prediction of survival was obtained (P=0.02), with the poorest prognosis for the 'TTF-1++/MIB-1+' cases.

The human, but not rat, dio2 gene is stimulated by thyroid transcription factor-1 (TTF-1)

Types 1 and 2 iodothyronine deiodinases (D1 and D2) catalyze the production of T(3) from T(4). D2 mRNA is abundant in the human thyroid but very low in adult rat thyroid, whereas D1 activity is high in both. To understand the molecular regulation of these genes in thyroid cells, the effect of thyroid transcription factor 1 (TTF-1) and the paired domain-containing protein 8 (Pax-8) on the transcriptional activity of the deiodinase promoters were studied. Both the approximately 6.5-kb hdio2 sequence and its most 3' 633 bp were activated 10-fold by transiently expressed TTF-1 in COS-7 cells, but the hdio1 was unaffected. Surprisingly, the response of the rdio2 gene to TTF-1 was only 3-fold despite the 73% identity with the proximal 633-bp region of hdio2 including complete conservation of a functional cAMP response element at -90. Neither human nor rat dio2 nor human dio1 was induced by Pax-8. The binding affinity of four putative TTF-1 binding sites in hdio2 were compared by a semiquantitative gel retardation assay using in vitro expressed TTF-1 homeodomain protein. Only two sites, D and C1 (both of which are absent in rdio2), had significant affinity. Functional analyses showed that both sites are required for the full response to TTF-1. These results can explain the differential expression of dio2 in thyroid and potentially other tissues in humans and rats.

TTF-1, a homeodomain gene required for diencephalic morphogenesis, is postnatally expressed in the neuroendocrine brain in a developmentally regulated and cell-specific fashion

TTF-1 is a member of the Nkx family of homeodomain genes required for morphogenesis of the hypothalamus. Whether TTF-1, or other Nkx genes, contributes to regulating differentiated hypothalamic functions is not known. We now report that postnatal hypothalamic TTF-1 expression is developmentally regulated and associated with the neuroendocrine process of female sexual development. Lesions of the hypothalamus that cause sexual precocity transiently activate neuronal TTF-1 expression near the lesion site. In intact animals, hypothalamic TTF-1 mRNA content also increases transiently, preceding the initiation of puberty. Postnatal expression of the TTF-1 gene was limited to subsets of hypothalamic neurons, including LHRH neurons, which control sexual maturation, and preproenkephalinergic neurons of the lateroventromedial nucleus of the basal hypothalamus, which restrain sexual maturation and facilitate reproductive behavior. TTF-1 mRNA was also detected in astrocytes of the median eminence and ependymal/subependymal cells of the third ventricle, where it colocalized with erbB-2, a receptor involved in facilitating sexual development. TTF-1 binds to and transactivates the erbB-2 and LHRH promoters, but represses transcription of the preproenkephalin gene. The singular increase in hypothalamic TTF-1 gene expression that precedes the initiation of puberty, its highly specific pattern of cellular expression, and its transcriptional actions on genes directly involved in neuroendocrine reproductive regulation suggest that TTF-1 may represent one of the controlling factors that set in motion early events underlying the central activation of mammalian puberty.

Multiple roles for Gata5 in zebrafish endoderm formation

Previous studies have indicated that gata5, a zinc-finger transcription factor gene, is required for the development of the zebrafish gut tube. Here, we show that gata5 mutants also display defects in the development of other endodermal organs such as the liver, pancreas, thyroid and thymus. gata5 is expressed in the endodermal progenitors from late blastula stages, suggesting that it functions early during endoderm development. We indeed find that during gastrulation stages, gata5 mutants form fewer endodermal cells than their wild-type siblings. In addition, the endodermal cells that form in gata5 mutants appear to express lower than wild-type levels of endodermal genes such as sox17 and axial/foxA2. Conversely, overexpression of gata5 leads to expanded endodermal gene expression. These data indicate that Gata5 is involved both in the generation of endodermal cells at late blastula stages and in the maintenance of endodermal sox17 expression during gastrulation. We have also analyzed the relationship of Gata5 to other factors involved in endoderm formation. Using complementary mutant and overexpression analyses, we show that Gata5 regulates endoderm formation in cooperation with the Mix-type transcription factor Bon, that Gata5 and Bon function downstream of Nodal signaling, and that cas function is usually required for the activity of Gata5 in endoderm formation. Finally, we show that fau/gata5, bon and cas exhibit dominant genetic interactions providing additional support that they function in the same pathway. Together, these data demonstrate that Gata5 plays multiple roles in endoderm development in zebrafish, and position Gata5 relative to other regulators of endoderm formation.

The evolution of the vertebrates--genes and development

In the past year, studies on protochordates have provided evidence that many features that we take to be indicative of the vertebrates were evident early in chordate evolution. Furthermore, many of the important developmental regulatory genes have also been identified in these invertebrates. Finally, we are also gaining a better insight into how the vertebrate genome itself evolved.

Temporal/spatial expression of nuclear receptor coactivators in the mouse lung

Our laboratory has previously demonstrated that retinoic acid nuclear receptor, thyroid transcription factor-1 (TTF-1), and nuclear receptor coactivators such as cAMP response element binding protein (CREB) binding protein (CBP)/p300 and steroid receptor coactivator-1 (SRC-1) form an enhanceosome on the 5'-enhancer region of the human surfactant protein B gene. Immunohistochemistry was used to identify cells that coexpressed CBP/p300, SRC-1, retinoid X receptor, and TTF-1 in the developing and mature lung. CBP/p300 and SRC-1 were expressed in the adult mouse lung, CBP and p300 being present in both alveolar type I and type II epithelial cells and SRC-1 and TTF-1 being restricted to type II epithelial cells. CBP/p300, SRC-1, and TTF-1 were readily detected in the nuclei of developing respiratory epithelial tubules in fetal mice from embryonic days 10 to 18. CBP/p300 and SRC-1 were also detected in developing mesenchymal cells. These coactivators were coexpressed with TTF-1 and SP-B in human pulmonary adenocarcinoma cells (H441 cells) in vitro. Interaction assays with a two-hybrid reporter analysis demonstrated direct interactions among TTF-1, SRC-1, and CBP/p300 in H441 cells. These findings support a role for retinoic acid receptor and nuclear receptor coactivators in the regulation of SP-B gene expression in the respiratory epithelium.

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.