Transcription factor USF2 is developmentally regulated in fetal lung and acts together with USF1 to induce SP-A gene expression

USF2 and TFEB compete in regulating lysosomal and autophagy genes

Autophagy, a highly conserved self-digestion process crucial for cellular homeostasis, is triggered by various environmental signals, including nutrient scarcity. The regulation of lysosomal and autophagy-related processes is pivotal to maintaining cellular homeostasis and basal metabolism. The consequences of disrupting or diminishing lysosomal and autophagy systems have been investigated; however, information on the implications of hyperactivating lysosomal and autophagy genes on homeostasis is limited. Here, we present a mechanism of transcriptional repression involving upstream stimulatory factor 2 (USF2), which inhibits lysosomal and autophagy genes under nutrient-rich conditions. We find that USF2, together with HDAC1, binds to the CLEAR motif within lysosomal genes, thereby diminishing histone H3K27 acetylation, restricting chromatin accessibility, and downregulating lysosomal gene expression. Under starvation, USF2 competes with transcription factor EB (TFEB), a master transcriptional activator of lysosomal and autophagy genes, to bind to target gene promoters in a phosphorylation-dependent manner. The GSK3β-mediated phosphorylation of the USF2 S155 site governs USF2 DNA-binding activity, which is involved in lysosomal gene repression. These findings have potential applications in the treatment of protein aggregation-associated diseases, including α1-antitrypsin deficiency. Notably, USF2 repression is a promising therapeutic strategy for lysosomal and autophagy-related diseases.

Early human fetal lung atlas reveals the temporal dynamics of epithelial cell plasticity

Studying human fetal lungs can inform how developmental defects and disease states alter the function of the lungs. Here, we sequenced >150,000 single cells from 19 healthy human pseudoglandular fetal lung tissues ranging between gestational weeks 10-19. We capture dynamic developmental trajectories from progenitor cells that express abundant levels of the cystic fibrosis conductance transmembrane regulator (CFTR). These cells give rise to multiple specialized epithelial cell types. Combined with spatial transcriptomics, we show temporal regulation of key signalling pathways that may drive the temporal and spatial emergence of specialized epithelial cells including ciliated and pulmonary neuroendocrine cells. Finally, we show that human pluripotent stem cell-derived fetal lung models contain CFTR-expressing progenitor cells that capture similar lineage developmental trajectories as identified in the native tissue. Overall, this study provides a comprehensive single-cell atlas of the developing human lung, outlining the temporal and spatial complexities of cell lineage development and benchmarks fetal lung cultures from human pluripotent stem cell differentiations to similar developmental window.

Differential Regulation of Human Surfactant Protein A Genes, SFTPA1 and SFTPA2, and Their Corresponding Variants

The human SFTPA1 and SFTPA2 genes encode the surfactant protein A1 (SP-A1) and SP-A2, respectively, and they have been identified with significant genetic and epigenetic variability including sequence, deletion/insertions, and splice variants. The surfactant proteins, SP-A1 and SP-A2, and their corresponding variants play important roles in several processes of innate immunity as well in surfactant-related functions as reviewed elsewhere [1]. The levels of SP-A have been shown to differ among individuals both under baseline conditions and in response to various agents or disease states. Moreover, a number of agents have been shown to differentially regulate SFTPA1 and SFTPA2 transcripts. The focus in this review is on the differential regulation of SFTPA1 and SFTPA2 with primary focus on the role of 5′ and 3′ untranslated regions (UTRs) and flanking sequences on this differential regulation as well molecules that may mediate the differential regulation.

Taiji: System-level identification of key transcription factors reveals transcriptional waves in mouse embryonic development

Transcriptional regulation is pivotal to the specification of distinct cell types during embryonic development. However, it still lacks a systematic way to identify key transcription factors (TFs) orchestrating the temporal and tissue specificity of gene expression. Here, we integrated epigenomic and transcriptomic data to reveal key regulators from two cells to postnatal day 0 in mouse embryogenesis. We predicted three-dimensional chromatin interactions in 12 tissues across eight developmental stages, which facilitates linking TFs to their target genes for constructing transcriptional regulatory networks. To identify driver TFs, we developed a new algorithm, dubbed Taiji, to assess the global influence of each TF and systematically uncovered TFs critical for lineage-specific and stage-dependent tissue specification. We have also identified TF combinations that function in spatiotemporal order to form transcriptional waves regulating developmental progress. Furthermore, lacking stage-specific TF combinations suggests a distributed timing strategy to orchestrate the coordination between tissues during embryonic development.

A Multiomics Approach to Identify Genes Associated with Childhood Asthma Risk and Morbidity

Childhood asthma is a complex disease. In this study, we aim to identify genes associated with childhood asthma through a multiomics "vertical" approach that integrates multiple analytical steps using linear and logistic regression models. In a case-control study of childhood asthma in Puerto Ricans (n = 1,127), we used adjusted linear or logistic regression models to evaluate associations between several analytical steps of omics data, including genome-wide (GW) genotype data, GW methylation, GW expression profiling, cytokine levels, asthma-intermediate phenotypes, and asthma status. At each point, only the top genes/single-nucleotide polymorphisms/probes/cytokines were carried forward for subsequent analysis. In step 1, asthma modified the gene expression-protein level association for 1,645 genes; pathway analysis showed an enrichment of these genes in the cytokine signaling system (n = 269 genes). In steps 2-3, expression levels of 40 genes were associated with intermediate phenotypes (asthma onset age, forced expiratory volume in 1 second, exacerbations, eosinophil counts, and skin test reactivity); of those, methylation of seven genes was also associated with asthma. Of these seven candidate genes, IL5RA was also significant in analytical steps 4-8. We then measured plasma IL-5 receptor α levels, which were associated with asthma age of onset and moderate-severe exacerbations. In addition, in silico database analysis showed that several of our identified IL5RA single-nucleotide polymorphisms are associated with transcription factors related to asthma and atopy. This approach integrates several analytical steps and is able to identify biologically relevant asthma-related genes, such as IL5RA. It differs from other methods that rely on complex statistical models with various assumptions.

Fetal-to-maternal signaling in the timing of birth

Preterm birth remains the major cause of neonatal morbidity and mortality throughout the world. This is due, in part, to our incomplete understanding of the mechanisms that underlie the maintenance of pregnancy and the initiation of parturition at term. In this article, we review our current knowledge of the complex, interrelated and concerted mechanisms whereby progesterone maintains myometrial quiescence throughout most of pregnancy, as well as those that mediate the upregulation of the inflammatory response and decline in progesterone receptor function leading to parturition. Herein, we review findings that demonstrate a role of the fetus in the timing of birth. Specifically, we focus on our own studies indicating that maturation of the fetal lung and enhanced secretion of the surfactant components, surfactant protein A (SP-A) and the potent inflammatory glycerophospholipid, platelet-activating factor (PAF), initiate a signaling cascade culminating in parturition. Our studies suggest an essential role of steroid receptor coactivators, SRC-1 and SRC-2, which activate expression of genes encoding SP-A and LPCAT1. LPCAT1 is a key enzyme in the synthesis of PAF, as well as DPPC, a highly surface-active glycerophospholipid component of surfactant. Thus, we describe a novel pathway through which the fetus contributes to the initiation of labor by signaling the mother when its lungs have achieved sufficient maturity for survival in an aerobic environment.

Genome-wide profiling of long non-coding RNA expression patterns in the EGFR-TKI resistance of lung adenocarcinoma by microarray

Mutations in the epidermal growth factor receptor (EGFR) make lung adenocarcinoma cells sensitive to EGFR tyrosine kinase inhibitors (TKIs). Long-term cancer therapy may cause the occurrence of acquired resistance to EGFR TKIs. Long non-coding RNAs (lncRNAs) play important roles in tumor formation, tumor metastasis and the development of EGFR-TKI resistance in lung cancer. To gain insight into the molecular mechanisms of EGFR-TKI resistance, we generated an EGFR-TKI-resistant HCC827-8-1 cell line and analyzed expression patterns by lncRNA microarray and compared it with its parental HCC827 cell line. A total of 1,476 lncRNA transcripts and 1,026 mRNA transcripts were dysregulated in the HCC827‑8-1 cells. The expression levels of 7 chosen lncRNAs were validated by real-time quantitative PCR. As indicated by functional analysis, several groups of lncRNAs may be involved in the bio-pathways associated with EGFR-TKI resistance through their cis- and/or trans‑regulation of protein-coding genes. Thus, lncRNAs may be used as novel candidate biomarkers and potential targets in EGFR-TKI therapy in the future.

Genetic complexity of the human surfactant-associated proteins SP-A1 and SP-A2

Pulmonary surfactant protein A (SP-A) plays a key role in innate lung host defense, in surfactant-related functions, and in parturition. In the course of evolution, the genetic complexity of SP-A has increased, particularly in the regulatory regions (i.e. promoter, untranslated regions). Although most species have a single SP-A gene, two genes encode SP-A in humans and primates (SFTPA1 and SFTPA2). This may account for the multiple functions attributed to human SP-A, as well as the regulatory complexity of its expression by a relatively diverse set of protein and non-protein cellular factors. The interplay between enhancer cis-acting DNA sequences and trans-acting proteins that recognize these DNA elements is essential for gene regulation, primarily at the transcription initiation level. Furthermore, regulation at the mRNA level is essential to ensure proper physiological levels of SP-A under different conditions. To date, numerous studies have shown significant complexity of the regulation of SP-A expression at different levels, including transcription, splicing, mRNA decay, and translation. A number of trans-acting factors have also been described to play a role in the control of SP-A expression. The aim of this report is to describe the genetic complexity of the SFTPA1 and SFTPA2 genes, as well as to review regulatory mechanisms that control SP-A expression in humans and other animal species.

Upstream stimulatory factor 2 and hypoxia-inducible factor 2α (HIF2α) cooperatively activate HIF2 target genes during hypoxia

While the functions of hypoxia-inducible factor 1α (HIF1α)/aryl hydrocarbon receptor nuclear translocator (ARNT) and HIF2α/ARNT (HIF2) proteins in activating hypoxia-inducible genes are well established, the role of other transcription factors in the hypoxic transcriptional response is less clear. We report here for the first time that the basic helix-loop-helix-leucine-zip transcription factor upstream stimulatory factor 2 (USF2) is required for the hypoxic transcriptional response, specifically, for hypoxic activation of HIF2 target genes. We show that inhibiting USF2 activity greatly reduces hypoxic induction of HIF2 target genes in cell lines that have USF2 activity, while inducing USF2 activity in cells lacking USF2 activity restores hypoxic induction of HIF2 target genes. Mechanistically, USF2 activates HIF2 target genes by binding to HIF2 target gene promoters, interacting with HIF2α protein, and recruiting coactivators CBP and p300 to form enhanceosome complexes that contain HIF2α, USF2, CBP, p300, and RNA polymerase II on HIF2 target gene promoters. Functionally, the effect of USF2 knockdown on proliferation, motility, and clonogenic survival of HIF2-dependent tumor cells in vitro is phenocopied by HIF2α knockdown, indicating that USF2 works with HIF2 to activate HIF2 target genes and to drive HIF2-depedent tumorigenesis.

Epigenetic regulation of surfactant protein A gene (SP-A) expression in fetal lung reveals a critical role for Suv39h methyltransferases during development and hypoxia

SP-A gene expression is developmentally regulated in fetal lung. Cyclic AMP (cAMP) induction of SP-A expression in human fetal lung type II cells is O(2) dependent and is mediated by increased binding of TTF-1/Nkx2.1 and NF-κB to a critical response element (TBE). This is associated with increased acetylation and decreased methylation of H3K9 at the TBE. Using chromatin immunoprecipitation analysis of fetal lung between 15.5 and 19.0 days of gestation, we observed that the developmental induction of SP-A was associated with increased recruitment of TTF-1, NF-κB, PCAF, and CBP, as well as enhanced acetylation and decreased methylation of histone H3K9 at the TBE. Importantly, expression and TBE binding of the H3K9 methyltransferases, Suv39h1 and Suv39h2, was inversely correlated with the developmental upregulation of SP-A. In human fetal lung epithelial cells, Suv39H1 and Suv39H2 mRNA levels declined with cAMP induction of SP-A. Moreover, hypoxia, which inhibits cAMP stimulation of SP-A, markedly increased Suv39h1 and Suv39h2 binding to the TBE. Finally, short hairpin RNA knockdown of Suv39H1 or Suv39H2 in fetal lung epithelial cells repressed H3K9 methylation and greatly enhanced SP-A expression. Collectively, our findings suggest that Suv39H1 and Suv39H2 are key hypoxia-induced methyltransferases; their decline in fetal lung during late gestation is critical for epigenetic changes resulting in the developmental induction of SP-A.

cAMP enhances estrogen-related receptor alpha (ERRalpha) transcriptional activity at the SP-A promoter by increasing its interaction with protein kinase A and steroid receptor coactivator 2 (SRC-2)

Estrogen-related receptor (ERRalpha) plays a critical role in basal and cAMP-induced expression of the human surfactant protein-A (SP-A) gene in lung type II cells through direct binding to an ERR response element (ERRE, 5'-TGACCTTA-3') within its 5'-flanking region. Furthermore, protein kinase A (PKA) up-regulates ERRalpha activation of the hSP-A promoter. In the present study, using cultured human fetal lung type II cells, we observed that cAMP enhanced ERRalpha phosphorylation and nuclear expression levels. cAMP/PKA stimulation of ERRalpha activation of the SP-A promoter was blocked by the PKA inhibitor, H89, whereas the MAPK P38 inhibitor, SB203580, and the MAPK kinase inhibitor, PD98059, had negligible to modest effects. This suggests that cAMP acts selectively through PKA to increase ERRalpha transcriptional activity. Of several coactivators tested, steroid receptor coactivator 2 (SRC-2) had the most pronounced effect to increase ERRalpha transcriptional activity at the SP-A promoter; this was enhanced by cotransfection with PKA catalytic subunit (PKAcat). Interestingly, SRC-2, ERRalpha, and PKAcat in type II cell nuclear extracts interacted at the ERRE; this was enhanced by cAMP and inhibited by H89. cAMP increased in vivo binding of PKAcat and SRC-2 to the ERRE genomic region in lung type II cells. In mutagenesis studies, three serines (S87, S114, and S277) were found to be critical for PKA and SRC-2 induction of ERRalpha transcriptional activity. Collectively, these findings indicate that cAMP/PKA signaling enhances ERRalpha phosphorylation and nuclear localization, recruitment to the SP-A promoter, and interaction with PKAcat and SRC-2, resulting in the up-regulation of SP-A gene transcription.

TTF-1 response element is critical for temporal and spatial regulation and necessary for hormonal regulation of human surfactant protein-A2 promoter activity

Expression of the human surfactant protein-A2 (hSP-A2) gene is lung specific, occurs in type II and Clara cells, and is developmentally and hormonally regulated in fetal lung. Using transfected human fetal type II cells, we previously observed that approximately 300 bp of 5'-flanking DNA mediated cAMP and interleukin-1 (IL-1) stimulation and dexamethasone (Dex) inhibition of hSP-A2 promoter activity. This region contains response elements for estrogen-related receptor alpha element (ERRE, -241 bp), thyroid transcription factor (TTF)-1/Nkx2.1 (TTF-binding protein, -171 bp), upstream stimulatory factor 1/2 (E-box, -80 bp), and stimulatory protein (Sp) 1 (G/T-box, -62 bp), which are essential for basal and cAMP induction of hSP-A2 expression. To define genomic regions necessary for developmental, hormonal, and tissue-specific regulation of hSP-A2 expression in vivo, we analyzed transgenic mice carrying hGH reporter genes comprised of 313 bp of hSP-A2 gene 5'-flanking DNA +/- mutation in the TBE or 175 bp of 5'-flanking DNA, containing TBE, E-box and G/T-box, but lacking ERRE. Transgenes containing 313 or 175 bp of hSP-A2 5'-flanking DNA were expressed in a lung cell-specific manner and developmentally regulated in concert with the endogenous mouse SP-A gene. In cultured lung explants from hSP-A(-313):hGH transgenic fetal mice, cAMP and IL-1 induced and Dex inhibited transgene expression. However, the 175-bp hSP-A2 genomic region was insufficient to mediate hormonal regulation of hSP-A2 promoter activity. The finding that expression of the hSP-A(-313TBEmut):hGH transgene was essentially undetectable in fetal lung and was not hormonally regulated in transgenic fetal lung explants underscores the critical importance of the TBE in lung cell-specific, developmental, and hormonal regulation of hSP-A2 gene expression.

Permissive effects of oxygen on cyclic AMP and interleukin-1 stimulation of surfactant protein A gene expression are mediated by epigenetic mechanisms

Surfactant protein A (SP-A) is important for immune defense within the alveolus. Cyclic AMP (cAMP) stimulation of SP-A expression in lung type II cells is O(2) dependent and mediated by increased phosphorylation and binding of thyroid transcription factor 1 (TTF-1) to an upstream response element (TTF-1-binding element [TBE]). Interleukin-1 (IL-1) stimulation of SP-A expression is mediated by NF-kappaB (p65/p50) activation and increased binding to the TBE. In this study, we found that O(2) also was permissive for IL-1 induction of SP-A expression and for cAMP and IL-1 stimulation of type II cell nuclear protein binding to the TBE. Using chromatin immunoprecipitation, we observed that when type II cells were cultured in 20% O(2), cAMP and IL-1 stimulated the recruitment of TTF-1, p65, CBP, and steroid receptor coactivator 1 to the TBE region of the SP-A promoter and increased local acetylation of histone H3; these effects were prevented by hypoxia. Hypoxia markedly reduced global levels of CBP and acetylated histone H3 and increased the expression of histone deacetylases. Furthermore, hypoxia caused a global increase in histone H3 dimethylated on Lys9 and increased the association of dimethyl histone H3 with the SP-A promoter. These results, together with findings that the histone deacetylase inhibitor trichostatin A and the methyltransferase inhibitor 5'-deoxy(5'-methylthio)adenosine markedly enhanced SP-A expression in lung type II cells, suggest that increased O(2) availability to type II cells late in gestation causes epigenetic changes that permit access of TTF-1 and NF-kappaB to the SP-A promoter. The binding of these transcription factors facilitates the recruitment of coactivators, resulting in the further opening of the chromatin structure and activation of SP-A transcription.

Human prolyl-4-hydroxylase alpha(I) transcription is mediated by upstream stimulatory factors

Prolyl-4-hydroxylase alpha(I) (P4Halpha(I)) is the rate-limiting subunit for P4H enzyme activity, which is essential for procollagen hydroxylation and secretion. In the current study, we have characterized the human P4Halpha(I) promoter for transcription factors and DNA elements regulating P4Halpha(I) expression. Using a progressive deletion cloning approach, we have constructed pGL3-P4Halpha(I) recombinant plasmids. We have identified a positive regulatory region at the positions of bp -184 to -97 responsible for approximately 80% of the P4Halpha(I) promoter efficiency. Three E-boxes were located within this region, and the E-box at position bp -135 explains most of the regulatory capacity. Upstream stimulatory factors (USF1/USF2) were shown to bind on the E-box using chromatin immunoprecipitation assay. Suppression of USF1 and/or USF2 using specific short interference RNA resulted in a significant reduction in P4Halpha(I) promoter activity, and overexpressed USF1 or USF2 increased P4Halpha(I) promoter activity significantly. Although transforming growth factor beta1 increased the USF1/USF2-E-box binding and P4Halpha(I) promoter activity, this up-regulatory effect can be largely prevented by USF1/USF2-specific short interference RNA. On the other hand, cigarette smoking extracts, which have been shown to suppress P4Halpha(I) expression, inhibited the binding between the USF1/USF2 and E-box, resulting in a reduced P4Halpha(I) promoter activity. Furthermore, the E-box on the P4Halpha(I) promoter appeared to indiscriminately bind with either USF1 or USF2, with a similar outcome on the promoter efficiency. In conclusion, our study shows that USF1/USF2 plays a critical role in basal P4Halpha(I) expression, and both positive (transforming growth factor beta1) and negative (cigarette smoking extract) regulators appear to influence the USF-E-box interaction and affect P4Halpha(I) expression.

In vivo and in vitro analysis of factor binding sites in Jaagsiekte sheep retrovirus long terminal repeat enhancer sequences: roles of HNF-3, NF-I, and C/EBP for activity in lung epithelial cells

Jaagsiekte sheep retrovirus (JSRV) is the causative agent of ovine pulmonary adenocarcinoma, a contagious lung cancer of sheep that arises from type II pneumocytes and Clara cells of the lung epithelium. Studies of the tropism of this virus have been hindered by the lack of an efficient system for viral replication in tissue culture. To map regulatory regions important for transcriptional activation, an in vivo footprinting method that couples dimethyl sulfate treatment and ligation-mediated PCR was performed in murine type II pneumocyte-derived MLE-15 cells infected with a chimeric Moloney murine leukemia virus driven by the JSRV enhancers (DeltaMo+JS Mo-MuLV). In vivo footprints were found in the JSRV enhancers in two regions previously shown to be important for JSRV long terminal repeat (LTR) activity: a binding site for the lung-specific transcription factor HNF-3beta and an E-box element in the distal enhancer adjacent to an NF-kappaB-like binding site. In addition, in vivo footprints were detected in two downstream motifs likely to bind C/EBP and NF-I. Mutational analysis of a JSRV LTR reporter construct (pJS21luc) revealed that the C/EBP binding site is critical for LTR activity, while the putative NF-I binding element is less important; elimination of these sites resulted in 70% and 40% drops in LTR activity, respectively. Electrophoretic mobility shift assays using nuclear extracts from MLE-15 murine Clara cell-derived mtCC1-2 cells with probes corresponding to the NF-I or C/EBP sites revealed several complexes. Antiserum directed against NF-IA, C/EBPalpha, or C/EBPbeta supershifted the corresponding protein-DNA complexes, indicating that these isoforms, which are also important for the expression of several cellular lung-specific genes, may be important for JSRV expression in lung epithelial cells.

Down-regulation of the polymeric immunoglobulin receptor in non-small cell lung carcinoma: correlation with dysregulated expression of the transcription factors USF and AP2

The polymeric immunoglobulin receptor (PIGR) mediates transport of IgA and IgM antibodies across mucosal and glandular epithelia. Several studies have utilized immunohistochemistry to demonstrate that PIGR expression varies in different types of lung carcinoma, and is down-regulated during tumor progression. We have previously shown in cultured tumor cell-lines that basal transcription of the PIGR gene is regulated by the transcription factors USF1, USF2 and AP2. To examine the mechanism by which PIGR expression is down-regulated in lung carcinoma, RNA was microdissected from formalin-fixed, paraffin-embedded lung carcinomas (14 adenocarcinomas and 8 squamous cell carcinomas). Levels of PIGR, USF1, USF2 and AP2-alpha mRNA were quantified by real-time reverse transcriptase-polymerase chain reaction and normalized to mRNA for the housekeeping gene GAPDH. PIGR mRNA levels were decreased in adenocarcinomas and squamous cell carcinomas relative to adjacent non-tumor tissue, and were inversely correlated with stage of differentiation. USF1 and USF2 mRNA levels were reduced in adenocarcinomas relative to non-tumor tissue, while AP2-alpha levels were elevated. Multivariate regression analysis demonstrated that reduced USF2 mRNA and increased AP2-alpha mRNA levels were predictive of down-regulated PIGR mRNA expression in the majority of adenocarcinomas and in moderately differentiated squamous cell carcinomas.

O2 enhancement of human trophoblast differentiation and hCYP19 (aromatase) gene expression are mediated by proteasomal degradation of USF1 and USF2

When cultured in 20% O(2), human cytotrophoblasts fuse to form the syncytiotrophoblast with marked induction of hCYP19 (aromatase) gene expression. When cultured in 2% O(2), cytotrophoblast fusion and induced hCYP19 expression are prevented. These effects of hypoxia are mediated by increased expression of mammalian achaete/scute homologue-2 (Mash-2), which increases levels of upstream stimulatory factors 1 and 2 (USF1/2) and their binding as heterodimers to E-boxes surrounding the hCYP19 promoter. In studies to define mechanisms for O(2) regulation of syncytiotrophoblast differentiation, we found that hypoxia and overexpression of Mash-2 markedly increased cyclin B1 levels in cultured trophoblasts and the proportion of cells at the G(2)/M transition. Unlike USF proteins, USF1/2 mRNA levels are unaffected by O(2) tension. To determine whether increased O(2) might enhance proteasomal degradation of USF1/2, human trophoblasts were cultured in 2% or 20% O(2) with or without proteasome inhibitors. In cells cultured in 20% O(2), proteasome inhibitors increased USF1/2 protein levels and blocked spontaneous induction of hCYP19 expression, cell fusion, and differentiation. Like hypoxia, inhibitory effects of proteasome inhibitors on hCYP19 expression were mediated by increased binding of USF1/2 to the E-boxes. In human trophoblast cells cultured in 20% O(2), increased polyubiquitylation of USF1/2 proteins was observed. Thus, early in gestation when the placenta is relatively hypoxic, increased USF1/2 may block trophoblast differentiation and hCYP19 gene expression. In the second trimester, increased O(2) tension promotes proteasomal degradation of USF1/2, resulting in syncytiotrophoblast differentiation and induction of hCYP19 expression.

Roles for USF-2 in lung cancer proliferation and bronchial carcinogenesis

The upstream stimulatory factors USF-1 and USF-2 dimerize to regulate transcription through E-box motifs in target genes. Although widely expressed, they can mediate tissue-specific transcription and we previously reported that USF-2 can enhance transcription of arginine vasopressin, a neuropeptide growth factor in small cell lung cancer. Here we determine the expression and role of USF-2 in lung cancer subtypes and examine USF-2 distribution in the bronchial epithelium. For a panel of 12 cell lines and 10 frozen human tumour samples, immunoblotting demonstrated that USF-2 expression was more frequent and abundant in small cell lung cancer than in non-small cell lung cancer. An immunohistochemical study of 108 formalin-fixed and paraffin-embedded human samples was undertaken to localize USF-2 expression and included 44 small cell and 32 non-small cell lung cancers, and 32 samples with bronchial dysplasia. USF-2 was restricted to ciliated cells in normal bronchial epithelium, but was more strongly expressed in dysplastic epithelium (72%) and certain lung cancer types, including small cell lung cancer (71%), squamous cell carcinoma (69%) and a large cell neuroendocrine carcinoma, but was less common in adenocarcinoma (11%). In a small series, expression was assessed adjacent to positively staining tumours; in phenotypically normal bronchial tissues, USF-2 was more highly expressed at 1 cm than at 5 cm from the tumour. Transient USF-2 overexpression in non-small cell lung cancer cell lines significantly stimulated in vitro cell proliferation; this response was most apparent for NCI-H460 (p < 0.005), reducing the mean cell doubling time from 19 to 16 h. Dominant-negative USF-2 mutants had no significant effect on cell growth. Taken together, these data suggest that USF-2 represents a relatively early molecular marker for the development of bronchial dysplasia and non-adenocarcinoma lung cancer. USF may also play a role in bronchial carcinogenesis, perhaps through promoting cell proliferation, although the genes through which this is regulated remain to be determined.