Redox effector factor-1 regulates the activity of thyroid transcription factor 1 by controlling the redox state of the N transcriptional activation domain

Targeting APE1: Advancements in the Diagnosis and Treatment of Tumors

With the emergence of the precision medicine era, targeting specific proteins has emerged as a pivotal breakthrough in tumor diagnosis and treatment. Apurinic/apyrimidinic Endonuclease 1 (APE1) is a multifunctional protein that plays a crucial role in DNA repair and cellular redox regulation. This article comprehensively explores the fundamental mechanisms of APE1 as a multifunctional enzyme in biology, with particular emphasis on its potential significance in disease diagnosis and strategies for tumor treatment. Firstly, this article meticulously analyzes the intricate biological functions of APE1 at a molecular level, establishing a solid theoretical foundation for subsequent research endeavors. In terms of diagnostic applications, the presence of APE1 can be detected in patient serum samples, biopsy tissues, and through cellular in situ testing. The precise detection methods enable changes in APE1 levels to serve as reliable biomarkers for predicting tumor occurrence, progression, and patient prognosis. Moreover, this article focuses on elucidating the potential role of APE1 in tumor treatment by exploring various inhibitors, including nucleic acid-based inhibitors and small molecule drug inhibitors categories, and revealing their unique advantages in disrupting DNA repair function and modulating oxidative-reduction activity. Finally, the article provides an outlook on future research directions for APE1 while acknowledging major technical difficulties and clinical challenges that need to be overcome despite its immense potential as a target for tumor therapy.

α-synucleinopathy exerts sex-dimorphic effects on the multipurpose DNA repair/redox protein APE1 in mice and humans

Lewy body disorders are characterized by oxidative damage to DNA and inclusions rich in aggregated forms of α-synuclein. Among other roles, apurinic/apyrimidinic endonuclease 1 (APE1) repairs oxidative DNA damage, and APE1 polymorphisms have been linked to cases of Lewy body disorders. However, the link between APE1 and α-synuclein is unexplored. We report that knockdown or inhibition of APE1 amplified inclusion formation in primary hippocampal cultures challenged with preformed α-synuclein fibrils. Fibril infusions into the mouse olfactory bulb/anterior olfactory nucleus (OB/AON) elicited a modest decrease in APE1 expression in the brains of male mice but an increase in females. Similarly, men with Lewy body disorders displayed lower APE1 expression in the OB and amygdala compared to women. Preformed fibril infusions of the mouse OB/AON induced more robust base excision repair of DNA lesions in females than males. No fibril-mediated loss of APE1 expression was observed in male mice when the antioxidant N-acetylcysteine was added to their diet. These findings reveal a potential sex-biased link between α-synucleinopathy and APE1 in mice and humans. Further studies are warranted to determine how this multifunctional protein modifies α-synuclein inclusions and, conversely, how α-synucleinopathy and biological sex interact to modify APE1.

Deciphering an isolated lung phenotype of NKX2-1 frameshift pathogenic variant

BACKGROUND

to perform a functional analysis of a new NK2 homeobox 1 (NKX2-1) variant (c.85_86del denominated NKX2-1^DEL) identified in a family presenting with isolated respiratory disease, in comparison to another frameshift variant (c.254dup denominated NKX2-1^DUP) identified in a subject with classical brain-lung-thyroid syndrome.

METHODS

pathogenic variants were introduced into the pcDNA3-1(+)-wt-TTF1 plasmid. The proteins obtained were analyzed by western blot assay. Subcellular localization was assessed by confocal microscopy in A549 and Nthy cells. Transactivation of SFTPA, SFTPB, SFTPC, and ABCA3 promoters was assessed in A549 cells. Thyroglobulin promoter activity was measured with the paired box gene 8 (PAX8) cofactor in Nthy cells.

RESULTS

The two sequence variants were predicted to produce aberrant proteins identical from the 86th amino acid, with deletion of their functional homeodomain, including the nuclear localization signal. However, 3D conformation prediction of the conformation prediction of the mutant protein assumed the presence of a nuclear localization signal, a bipartite sequence, confirmed by confocal microscopy showing both mutant proteins localized in the nucleus and cytoplasm. Transcriptional activity with SFTPA, SFTPB, SFTPC, ABCA3 and thyroglobulin promoters was significantly decreased with both variants. However, with NKX2-1^DEL, thyroglobulin transcriptional activity was maintained with the addition of PAX8.

CONCLUSION

These results provide novel insights into understanding the molecular mechanism of phenotypes associated with NKX2-1 pathogenic variants.

Thyroid Transcription Factor-1: Structure, Expression, Function and Its Relationship with Disease

Thyroid transcription factor-1 (TTF-1/NKx2.1) is a member of the NKx2 tissue-specific transcription factor family, which is expressed in thyroid follicle, parathyroid gland, alveolar epithelium, and diencephalon which originated from ectoderm, and participates in the differentiation, development, and functional maintenance of the above organs. Recent studies have shown that the abnormal expression of TTF-1 is closely related to the occurrence of a variety of human diseases and can be used as a potential new target for the diagnosis and treatment of related diseases. In this article, in order to strengthen the systematic understanding of TTF-1 and promote the progress of related research, we reviewed the structure, expression regulation, biological functions of TTF-1, and its role in the occurrence and development of human-related clinical diseases. Meanwhile, we prospect the future research direction of TTF-1, which might ultimately contribute to the understanding of the pathogenesis of related clinical diseases and the development of new prevention and treatment strategies.

The multifunctional APE1 DNA repair-redox signaling protein as a drug target in human disease

Apurinic/apyrimidinic (AP) endonuclease-reduction/oxidation factor 1 (APE1/Ref-1, also called APE1) is a multifunctional enzyme with crucial roles in DNA repair and reduction/oxidation (redox) signaling. APE1 was originally described as an endonuclease in the Base Excision Repair (BER) pathway. Further study revealed it to be a redox signaling hub regulating critical transcription factors (TFs). Although a significant amount of focus has been on the role of APE1 in cancer, recent findings support APE1 as a target in other indications, including ocular diseases [diabetic retinopathy (DR), diabetic macular edema (DME), and age-related macular degeneration (AMD)], inflammatory bowel disease (IBD) and others, where APE1 regulation of crucial TFs impacts important pathways in these diseases. The central responsibilities of APE1 in DNA repair and redox signaling make it an attractive therapeutic target for cancer and other diseases.

Cardiac Cell Senescence and Redox Signaling

Aging is characterized by a progressive loss of the ability of the organism to cope with stressors and to repair tissue damage. As a result, chronic diseases, including cardiovascular disease, increase their prevalence with aging, underlining the existence of common mechanisms that lead to frailty and age-related diseases. In this frame, the progressive decline of the homeostatic and reparative function of primitive cells has been hypothesized to play a major role in the evolution of cardiac pathology to heart failure. Although initially it was believed that reactive oxygen species (ROS) were produced in an unregulated manner as a byproduct of cellular metabolism, causing macromolecular damage and aging, accumulating evidence indicate the major role played by redox signaling in physiology. Aim of this review is to critically revise evidence linking ROS to cell senescence and aging and to provide evidence of the primary role played by redox signaling, with a particular emphasis on the multifunctional protein APE1/Ref in stem cell biology. Finally, we will discuss evidence supporting the role of redox signaling in cardiovascular cells.

TTF-1/NKX2-1 binds to DDB1 and confers replication stress resistance to lung adenocarcinomas

TTF-1, also known as NKX2-1, is a transcription factor that has indispensable roles in both lung development and physiology. We and others have reported that TTF-1 frequently exhibits high expression with increased copy number in lung adenocarcinomas, and also has a role as a lineage-survival oncogene through transcriptional activation of crucial target genes including ROR1 and LMO3. In the present study, we employed a global proteomic search for proteins that interact with TTF-1 in order to provide a more comprehensive picture of this still enigmatic lineage-survival oncogene. Our results unexpectedly revealed a function independent of its transcriptional activity, as TTF-1 was found to interact with DDB1 and block its binding to CHK1, which in turn attenuated ubiquitylation and subsequent degradation of CHK1. Furthermore, TTF-1 overexpression conferred resistance to cellular conditions under DNA replication stress (RS) and prevented an increase in consequential DNA double-strand breaks, as reflected by attenuated induction of pCHK2 and γH2AX. Our findings suggest that the novel non-transcriptional function of TTF-1 identified in this study may contribute to lung adenocarcinoma development by conferring tolerance to DNA RS, which is known to be inherently elicited by activation of various oncogenes.

Peroxiredoxin 1 interacts with and blocks the redox factor APE1 from activating interleukin-8 expression

APE1 is an essential DNA repair protein that also possesses the ability to regulate transcription. It has a unique cysteine residue C65, which maintains the reduce state of several transcriptional activators such as NF-κB. How APE1 is being recruited to execute the various biological functions remains unknown. Herein, we show that APE1 interacts with a novel partner PRDX1, a peroxidase that can also prevent oxidative damage to proteins by serving as a chaperone. PRDX1 knockdown did not interfere with APE1 expression level or its DNA repair activities. However, PRDX1 knockdown greatly facilitates APE1 detection within the nucleus by indirect immunofluorescence analysis, even though APE1 level was unchanged. The loss of APE1 interaction with PRDX1 promotes APE1 redox function to activate binding of the transcription factor NF-κB onto the promoter of a target gene, the proinflammatory chemokine IL-8 involved in cancer invasion and metastasis, resulting in its upregulation. Depletion of APE1 blocked the upregulation of IL-8 in the PRDX1 knockdown cells. Our findings suggest that the interaction of PRDX1 with APE1 represents a novel anti-inflammatory function of PRDX1, whereby the association safeguards APE1 from reducing transcription factors and activating superfluous gene expression, which otherwise could trigger cancer invasion and metastasis.

Hypothalamus-Pituitary-Thyroid Axis

The hypothalamus-pituitary-thyroid (HPT) axis determines the set point of thyroid hormone (TH) production. Hypothalamic thyrotropin-releasing hormone (TRH) stimulates the synthesis and secretion of pituitary thyrotropin (thyroid-stimulating hormone, TSH), which acts at the thyroid to stimulate all steps of TH biosynthesis and secretion. The THs thyroxine (T4) and triiodothyronine (T3) control the secretion of TRH and TSH by negative feedback to maintain physiological levels of the main hormones of the HPT axis. Reduction of circulating TH levels due to primary thyroid failure results in increased TRH and TSH production, whereas the opposite occurs when circulating THs are in excess. Other neural, humoral, and local factors modulate the HPT axis and, in specific situations, determine alterations in the physiological function of the axis. The roles of THs are vital to nervous system development, linear growth, energetic metabolism, and thermogenesis. THs also regulate the hepatic metabolism of nutrients, fluid balance and the cardiovascular system. In cells, TH actions are mediated mainly by nuclear TH receptors (210), which modify gene expression. T3 is the preferred ligand of THR, whereas T4, the serum concentration of which is 100-fold higher than that of T3, undergoes extra-thyroidal conversion to T3. This conversion is catalyzed by 5'-deiodinases (D1 and D2), which are TH-activating enzymes. T4 can also be inactivated by conversion to reverse T3, which has very low affinity for THR, by 5-deiodinase (D3). The regulation of deiodinases, particularly D2, and TH transporters at the cell membrane control T3 availability, which is fundamental for TH action. © 2016 American Physiological Society. Compr Physiol 6:1387-1428, 2016.

Thioredoxin-1 redox signaling regulates cell survival in response to hyperoxia

The most common form of newborn chronic lung disease, bronchopulmonary dysplasia (BPD), is thought to be caused by oxidative disruption of lung morphogenesis, which results in decreased pulmonary vasculature and alveolar simplification. Although cellular redox status is known to regulate cellular proliferation and differentiation, redox-sensitive pathways associated with these processes in developing pulmonary epithelium are unknown. Redox-sensitive pathways are commonly regulated by cysteine thiol modifications. Therefore two thiol oxidoreductase systems, thioredoxin and glutathione, were chosen to elucidate the roles of these pathways on cell death. Studies herein indicate that thiol oxidation contributes to cell death through impaired activity of glutathione-dependent and thioredoxin (Trx) systems and altered signaling through redox-sensitive pathways. Free thiol content decreased by 71% with hyperoxic (95% oxygen) exposure. Increased cell death was observed during oxygen exposure when either the Trx or the glutathione-dependent system was pharmacologically inhibited with aurothioglucose (ATG) or buthionine sulfoximine, respectively. However, inhibition of the Trx system yielded the smallest decrease in free thiol content (1.44% with ATG treatment vs 21.33% with BSO treatment). Although Trx1 protein levels were unchanged, Trx1 function was impaired during hyperoxic treatment as indicated by progressive cysteine oxidation. Overexpression of Trx1 in H1299 cells utilizing an inducible construct increased cell survival during hyperoxia, whereas siRNA knockdown of Trx1 during oxygen treatment reduced cell viability. Overall, this indicated that a comparatively small pool of proteins relies on Trx redox functions to mediate cell survival in hyperoxia, and the protective functions of Trx1 are progressively lost by its oxidative inhibition. To further elucidate the role of Trx1, potential Trx1 redox protein-protein interactions mediating cytoprotection and cell survival pathways were determined by utilizing a substrate trap (mass action trapping) proteomics approach. With this method, known Trx1 targets were detected, including peroxiredoxin-1as well as novel targets, including two HSP90 isoforms (HSP90AA1 and HSP90AB1). Reactive cysteines within the structure of HSP90 are known to modulate its ATPase-dependent chaperone activity through disulfide formation and S-nitrosylation. Whereas HSP90 expression is unchanged at the protein level during hyperoxic exposure, siRNA knockdown significantly increased hyperoxic cell death by 2.5-fold, indicating cellular dependence on HSP90 chaperone functions in response to hyperoxic exposure. These data support the hypothesis that hyperoxic impairment of Trx1 has a negative impact on HSP90-oxidative responses critical to cell survival, with potential implications for pathways implicated in lung development and the pathogenesis of BPD.

Protein-disulfide isomerase regulates the thyroid hormone receptor-mediated gene expression via redox factor-1 through thiol reduction-oxidation

Protein-disulfide isomerase (PDI) is a dithiol/disulfide oxidoreductase that regulates the redox state of proteins. We previously found that overexpression of PDI in rat pituitary tumor (GH3) cells suppresses 3,3',5-triiodothyronine (T(3))-stimulated growth hormone (GH) expression, suggesting the contribution of PDI to the T(3)-mediated gene expression via thyroid hormone receptor (TR). In the present study, we have clarified the mechanism of regulation by which TR function is regulated by PDI. Overexpression of wild-type but not redox-inactive mutant PDI suppressed the T(3)-induced GH expression, suggesting that the redox activity of PDI contributes to the suppression of GH. We considered that PDI regulates the redox state of the TR and focused on redox factor-1 (Ref-1) as a mediator of the redox regulation of TR by PDI. Interaction between Ref-1 and TRβ1 was detected. Overexpression of wild-type but not C64S Ref-1 facilitated the GH expression, suggesting that redox activity of Cys-64 in Ref-1 is involved in the TR-mediated gene expression. Moreover, PDI interacted with Ref-1 and changed the redox state of Ref-1, suggesting that PDI controls the redox state of Ref-1. Our studies suggested that Ref-1 contributes to TR-mediated gene expression and that the redox state of Ref-1 is regulated by PDI. Redox regulation of PDI via Ref-1 is a new aspect of PDI function.

Understanding different functions of mammalian AP endonuclease (APE1) as a promising tool for cancer treatment

The apurinic endonuclease 1/redox factor-1 (APE1) has a crucial function in DNA repair and in redox signaling in mammals, and recent studies identify it as an excellent target for sensitizing tumor cells to chemotherapy. APE1 is an essential enzyme in the base excision repair pathway of DNA lesions caused by oxidation and alkylation. As importantly, APE1 also functions as a redox agent maintaining transcription factors involved in cancer promotion and progression in an active reduced state. Very recently, a new unsuspected function of APE1 in RNA metabolism was discovered, opening new perspectives for this multifunctional protein. These observations underline the necessity to understand the molecular mechanisms responsible for fine-tuning its different biological functions. This survey intends to give an overview of the multifunctional roles of APE1 and their regulation in the context of considering this protein a promising tool for anticancer therapy.

Transcriptional regulation of SP-B gene expression by nitric oxide in H441 lung epithelial cells

Surfactant protein B (SP-B) is essential for the surface tension-lowering function of pulmonary surfactant. Surfactant dysfunction and reduced SP-B levels are associated with elevated nitric oxide (NO) in inflammatory lung diseases, such as acute respiratory distress syndrome. We previously found that NO donors decreased SP-B expression in H441 and MLE-12 lung epithelial cells by reducing SP-B promoter activity. In this study, we determined the roles of DNA elements and interacting transcription factors necessary for NO inhibition of SP-B promoter activity in H441 cells. We found that the NO donor diethylenetriamine-nitric oxide adduct (DETA-NO) decreased SP-B promoter thyroid transcription factor 1 (TTF-1), hepatocyte nuclear factor 3 (HNF-3), and Sp1 binding activities but increased activator protein 1 (AP-1) binding activity. DETA-NO decreased TTF-1, but not Sp1, levels, suggesting that reduced TTF-1 expression contributes to reduced TTF-1 binding activity. Lack of effect on Sp1 levels suggested that DETA-NO inhibits Sp1 binding activity per se. Overexpression of Sp1, but not TTF-1, blocked DETA-NO inhibition of SP-B promoter activity. DETA-NO inhibited SP-B promoter induction by exogenous TTF-1 without altering TTF-1 levels. DETA-NO decreased TTF-1 mRNA levels and gene transcription rate, indicating that DETA-NO inhibits TTF-1 expression at the transcriptional level. We conclude that NO inhibits SP-B promoter by decreasing TTF-1, Sp1, and HNF-3 binding activities and increasing AP-1 binding activity. NO inhibits TTF-1 levels and activity to decrease SP-B expression. NO inhibition of SP-B expression could be a mechanism by which surfactant dysfunction occurs in inflammatory lung diseases.

Nuclear redox signaling

Reactive oxygen species have been described to modulate proteins within the cell, a process called redox regulation. However, the importance of compartment-specific redox regulation has been neglected for a long time. In the early 1980s and 1990s, many in vitro studies introduced the possibility that nuclear redox signaling exists. However, the functional relevance for that has been greatly disregarded. Recently, it has become evident that nuclear redox signaling is indeed one important signaling mechanism regulating a variety of cellular functions. Transcription factors, and even kinases and phosphatases, have been described to be redox regulated in the nucleus. This review describes several of these proteins in closer detail and explains their functions resulting from nuclear localization and redox regulation. Moreover, the redox state of the nucleus and several important nuclear redox regulators [Thioredoxin-1 (Trx-1), Glutaredoxins (Grxs), Peroxiredoxins (Prxs), and APEX nuclease (multifunctional DNA-repair enzyme) 1 (APEX1)] are introduced more precisely, and their necessity for regulation of transcription factors is emphasized.

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

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

Transcriptional control of lung morphogenesis

The vertebrate lung consists of multiple cell types that are derived primarily from endodermal and mesodermal compartments of the early embryo. The process of pulmonary organogenesis requires the generation of precise signaling centers that are linked to transcriptional programs that, in turn, regulate cell numbers, differentiation, and behavior, as branching morphogenesis and alveolarization proceed. This review summarizes knowledge regarding the expression and proposed roles of transcription factors influencing lung formation and function with particular focus on knowledge derived from the study of the mouse. A group of transcription factors active in the endodermally derived cells of the developing lung tubules, including thyroid transcription factor-1 (TTF-1), beta-catenin, Forkhead orthologs (FOX), GATA, SOX, and ETS family members are required for normal lung morphogenesis and function. In contrast, a group of distinct proteins, including FOXF1, POD1, GLI, and HOX family members, play important roles in the developing lung mesenchyme, from which pulmonary vessels and bronchial smooth muscle develop. Lung formation is dependent on reciprocal signaling among cells of both endodermal and mesenchymal compartments that instruct transcriptional processes mediating lung formation and adaptation to breathing after birth.

Proteasome dysfunction inhibits surfactant protein gene expression in lung epithelial cells: mechanism of inhibition of SP-B gene expression

Surfactant proteins maintain lung function through their actions to reduce alveolar surface tension and control of innate immune responses in the lung. The ubiquitin proteasome pathway is responsible for the degradation of majority of intracellular proteins in eukaryotic cells, and proteasome dysfunction has been linked to the development of neurodegenerative, cardiac, and other diseases. Proteasome function is impaired in interstitial lung diseases associated with surfactant protein C (SP-C) mutation mapping to the BRICHOS domain located in the proSP-C protein. In this study we determined the effects of proteasome inhibition on surfactant protein expression in H441 and MLE-12 lung epithelial cells to understand the relationship between proteasome dysfunction and surfactant protein gene expression. Proteasome inhibitors lactacystin and MG132 reduced the levels of SP-A, SP-B, and SP-C mRNAs in a concentration-dependent manner in H441 and MLE-12 cells. In H441 cells, lactacystin and MG132 inhibition of SP-B mRNA was associated with similar decreases in SP-B protein, and the inhibition was due to inhibition of gene transcription. Proteasome inhibitors decreased thyroid transcription factor-1 (TTF-1)/Nkx2.1 DNA binding activity, and the reduced TTF-1 DNA binding activity was due to reduced expression levels of TTF-1 protein. These data indicated that the ubiquitin proteasome pathway is essential for the maintenance of surfactant protein gene expression and that disruption of this pathway inhibits surfactant protein gene expression via reduced expression of TTF-1 protein.

Ischemia-reperfusion and cardioprotection: a delicate balance between reactive oxygen species generation and redox homeostasis

Ischemia-reperfusion injury of the myocardium has long been a subject of intense research. Cardiac preconditioning, an associated phenomenon, has also been critically investigated over the past two decades. Although the biochemistry of ischemia-reperfusion and its association with oxidative metabolism has long been established, recent studies have further revealed a more intricate role of a number of reactive oxygen-nitrogen species in those processes. Emerging evidence suggests that an elaborate network of enzymes (and other biomolecules) dedicated to the generation, utilization, and diminution of reactive oxygen-nitrogen species maintains the redox homeostasis in the myocardium, and any perturbation of its status has distinctive effects. It thus appears that while excessive generation of reactive species leads to cellular injury, their regulated generation may cause transient and reversible modifications of cellular proteins leading the transmission of intracellular signals with specific effects. Taken together, generation of reactive oxygen-nitrogen species in the myocardium plays a nodal role in mediating both ischemic injury and cardioprotection.

Ape1 regulates hematopoietic differentiation of embryonic stem cells through its redox functional domain

Ape1 is a molecule with dual functions in DNA repair and redox regulation of transcription factors. In Ape1-deficient mice, embryos do not survive beyond embryonic day 9, indicating that this molecule is required for normal embryo development. Currently, direct evidence of the role of Ape1 in regulating hematopoiesis is lacking. We used the embryonic stem (ES) cell differentiation system and an siRNA approach to knockdown Ape1 gene expression to test the role of Ape1 in hematopoiesis. Hemangioblast development from ES cells was reduced 2- to 3-fold when Ape1 gene expression was knocked down by Ape1-specific siRNA, as was primitive and definitive hematopoiesis. Impaired hematopoiesis was not associated with increased apoptosis in siRNA-treated cells. To begin to explore the mechanism whereby Ape1 regulates hematopoiesis, we found that inhibition of the redox activity of Ape1 with E3330, a specific Ape1 redox inhibitor, but not Ape1 DNA repair activity, which was blocked using the small molecule methoxyamine, affected cytokine-mediated hemangioblast development in vitro. In summary, these data indicate Ape1 is required in normal embryonic hematopoiesis and that the redox function, but not the repair endonuclease activity, of Ape1 is critical in normal embryonic hematopoietic development.

PARP-2 Interacts with TTF-1 and Regulates Expression of Surfactant Protein-B

Thyroid transcription factor 1 (TTF-1/Nkx-2.1) plays a critical role in lung morphogenesis and regulates the expression of lung-specific genes, including the surfactant proteins required for pulmonary function after birth. The activity of TTF-1 is influenced by its interactions with other transcription factors and coactivators, including CBP/p300 and SRC-1. In this study, we have identified poly(ADP-ribose) polymerases (PARP-2 and PARP-1) as TTF-1 interacting proteins that influence its transcriptional activity. Endogenous PARP-2 was coimmunoprecipitated from transformed mouse lung epithelial cell (MLE15) extracts with TTF-1 and was identified by mass spectrometry. PARP-1 and Ku70/Ku80 were also coimmunoprecipitated from the cell extracts with TTF-1. The E domain of PARP-2 interacted via the C-terminal domain of TTF-1. Both PARP-1 and PARP-2 enhanced the activity of the promoter of surfactant protein-B (Sftpb gene) but not other surfactant proteins in vitro. PARP-2 was selectively expressed in epithelial cells of the conducting and peripheral lung tubules of the fetal mouse lung from embryonic day 12.5 and was detected in bronchial epithelial cells in the adult lung at cellular sites consistent with that of surfactant protein B. PARP-2 and PARP-1 interact with TTF-1 and regulate the expression of surfactant protein B, a protein required for lung function.

Ceramide decreases surfactant protein B gene expression via downregulation of TTF-1 DNA binding activity

Ceramide, a sphingolipid, is an important signaling molecule in the inflammatory response. Mediators of acute lung injury such as TNF-alpha, platelet-activating factor, and Fas/Apo ligand stimulate sphingomyelin hydrolysis to increase intracellular ceramide levels. Surfactant protein B (SP-B), a hydrophobic protein of pulmonary surfactant, is essential for surfactant function and lung stability. In this study we investigated the effects of ceramide on SP-B gene expression in H441 lung epithelial cells. Ceramide decreased SP-B mRNA levels in control and dexamethasone-treated cells after 24-h incubation and inhibition of SP-B mRNA was associated with inhibition of immunoreactive SP-B. In transient transfections assays, ceramide inhibited SP-B promoter activity, indicating that the inhibitory effects are exerted at the transcriptional level. Deletion mapping experiments showed that the ceramide-responsive region is located within the -233/-80-bp region of human SP-B promoter. Electrophoretic mobility shift and reporter assays showed that ceramide reduced the DNA binding activity and transactivation capability of thyroid transcription factor 1 (TTF-1/Nkx2.1), a key factor for SP-B promoter activity. Collectively these data showed that ceramide inhibits SP-B gene expression by reducing the DNA biding activity of TTF-1/Nkx2.1 transcription factor. Protein kinase C inhibitor bisindolylmaleimide and the protein tyrosine kinase inhibitor genistein partially reversed ceramide inhibition, indicating that protein kinases play important roles in the ceramide inhibition of SP-B gene expression. Chemical inhibitors of de novo ceramide synthesis and sphingomyelin hydrolysis had no effect on TNF-alpha inhibition of SP-B promoter activity and mRNA levels, suggesting that ceramide does not play a role in the inhibition.

Transgenic extracellular superoxide dismutase protects postnatal alveolar epithelial proliferation and development during hyperoxia

Transgenic (TG) human (h) extracellular superoxide dismutase (EC-SOD) targeted to type II cells protects postnatal newborn mouse lung development against hyperoxia by unknown mechanisms. Because alveolar development depends on timely proliferation of type II epithelium and differentiation to type I epithelium, we measured proliferation in bronchiolar and alveolar (surfactant protein C-positive) epithelium in air and 95% O2-exposed wild-type (WT) and TG hEC-SOD newborn mice at postnatal days 3, 5, and 7 (P3-P7), traversing the transition from saccular to alveolar stages. We found that TG hEC-SOD ameliorated the 95% O2-impaired bromodeoxyuridine uptake in alveolar and bronchiolar epithelium at P3, but not at P5 and P7, when overall epithelial proliferation rates were lower in air-exposed WT mice. Mouse EC-, CuZn-, and Mn-SOD expression were unaffected by hyperoxia or genotype. TG mice had less DNA damage than 95% O2-exposed WT mice at P3, measured by TdT-mediated dUTP nick end labeling (P < 0.05). Hyperoxia induced cell-cycle inhibitory protein p21cip/waf mRNA at P3, WT > TG, P = 0.06. 95% O2 impaired apical expression of type I cell alpha protein (T1alpha) in WT but not in TG mice at P3 and increased T1alpha in WT and TG mice at P7. Reducing the 95% O2-induced impairment of epithelial proliferation at a critical window of lung development was associated with protection against DNA damage and preservation of apical T1alpha expression at P3.

Activation of APE1/Ref-1 is dependent on reactive oxygen species generated after purinergic receptor stimulation by ATP

Apurinic apyrimidinic endonuclease redox effector factor-1 (APE1/Ref-1) is involved both in the base excision repair (BER) of DNA lesions and in the eukaryotic transcriptional regulation. APE1/Ref-1 is regulated at both the transcriptional and post-translational levels, through control of subcellular localization and post-translational modification. In response to stress conditions, several cell types release ATP, which exerts stimulatory effects on eukaryotic cells via the purinergic receptors (P2) family. By using western blot and immunofluorescence analysis on a human tumour thyroid cell line (ARO), we demonstrate that purinergic stimulation by extracellular ATP induces quick cytoplasm to nucleus translocation of the protein at early times and its neosynthesis at later times. Continuous purinergic triggering by extracellular ATP released by ARO cells is responsible for the control of APE1/Ref-1 intracellular level. Interference with intracellular pathways activated by P2 triggering demonstrates that Ca²⁺ mobilization and intracellular reactive oxygen species (ROS) production are responsible for APE1/Ref-1 translocation. The APE1/Ref-1 activities on activator protein-1 (AP-1) DNA binding and DNA repair perfectly match its nuclear enrichment upon ATP stimulation. The biological relevance of our data is reinforced by the observation that APE1/Ref-1 stimulation by ATP protects ARO cells by H₂O₂-induced cell death. Our data provide new insights into the complex mechanisms regulating APE1/Ref-1 functions.

The intracellular localization of APE1/Ref-1: more than a passive phenomenon?

Human apurinic/apyrimidinic endonuclease 1/redox effector factor-1 (APE1/Ref-1) is a perfect paradigm of the functional complexity of a biological macromolecule. First, it plays a crucial role, by both redox-dependent and -independent mechanisms, as a transcriptional coactivator for different transcription factors, either ubiquitous (i.e., AP-1, Egr-1, NF-kappaB, p53, HIF) or tissue-specific (i.e., PEBP-2, Pax-5 and -8, TTF-1), in controlling different cellular processes such as apoptosis, proliferation, and differentiation. Second, it acts, as an apurinic/apyrimidinic endonuclease, during the second step of the DNA base excision repair pathway, which is responsible for the repair of cellular alkylation and oxidative DNA damages. Third, it controls the intracellular reactive oxygen species production by negatively regulating the activity of the Ras-related GTPase Rac1. Despite these known functions of APE1/Ref-1, information is still scanty about the molecular mechanisms responsible for the coordinated control of its several activities. Some evidence suggests that the expression and subcellular localization of APE1/Ref-1 are finely tuned. APE1/Ref-1 is a ubiquitous protein, but its expression pattern differs according to the different cell types. APE1/Ref-1 subcellular localization is mainly nuclear, but cytoplasmic staining has also been reported, the latter being associated with mitochondria and/or presence within the endoplasmic reticulum. It is not by chance that both expression and subcellular localization are altered in several metabolic and proliferative disorders, such as in tumors and aging. Moreover, a fundamental role played by different posttranslational modifications in modulating APE1/Ref-1 functional activity is becoming evident. In the present review, we tried to put together a growing body of information concerning APE1/Ref-1's different functions, shedding new light on present and future directions to understand fully this unique molecule.

Pleiomorphic adenoma gene-like-2, a zinc finger protein, transactivates the surfactant protein-C promoter

Expression of surfactant protein (SP)-C occurs principally in type II pneumocytes located in the distal lung alveolae. SP-C expression is thought to be primarily regulated by thyroid transcription factor (TTF)-1 and its associated proteins interacting with a previously defined promoter region between -197 and -158 in mice. We screened a human lung cDNA library using a modified yeast one-hybrid system and identified pleiomorphic adenoma gene-like (PLAGL)-2, a ubiquitously expressed zinc finger protein, as a transfactor of the SP-C promoter. The PLAGL2 DNA-binding site was located in the SP-C promoter proximal region close to the TTF-1 sites. This site was demonstrated to be functional by use of electrophoresis mobility shift assay, mutagenesis analysis, and transfection studies. PLAGL2 bound to DNA via its N-terminus zinc fingers and activated the SP-C promoter in a TTF-1-independent manner. Both human and mouse SP-C promoters, but not the SP-B promoter, could be activated by PLAGL2 in transfected human embryonic kidney-293 (HEK293) cells as well as in murine type II (MLE12) cells. The expression of PLAGL2 in isolated human embryonic lung type II cells and its transactivation activity on the SP-C promoter suggest that PLAGL2 may modulate SP-C expression during lung development.

FGF signaling is required for pulmonary homeostasis following hyperoxia

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

Identification of different isoforms of eEF1A in the nuclear fraction of human T-lymphoblastic cancer cell line specifically binding to aptameric cytotoxic GT oligomers

GT oligomers, showing a dose-dependent cytotoxic effect on a variety of human cancer cell lines, but not on normal human lymphocytes, recognize and form complexes with nuclear proteins. By working with human T-lymphoblastic CCRF-CEM cells and by using MS and SouthWestern blotting, we identified eukaryotic elongation factor 1 alpha (eEF1A) as the main nuclear protein that specifically recognizes these oligonucleotides. Western blotting and supershift assays confirmed the nature of this protein and its involvement in forming a cytotoxicity-related complex (CRC). On the contrary, normal human lymphocytes did not show nuclear proteins able to produce CRC in a SouthWestern blot. Comparative bidimensional PAGE and Western-blotting analysis for eEF1A revealed the presence of a specific cluster of spots, focusing at more basic pH, in nuclear extracts of cancer cells but absent in those of normal lymphocytes. Moreover, a bidimensional PAGE SouthWestern blot demonstrated that cytotoxic GT oligomers selectively recognized the more basic eEF1A isoform expressed only in cancer cells. These results suggest the involvement of eEF1A, associated with the nuclear-enriched fraction, in the growth and maintenance of tumour cells, possibly modulated by post-translational processing of the polypeptide chain.

Enhanced binding of Sp1/Sp3 transcription factors mediates the hyperoxia-induced increased expression of the lung type I cell gene T1alpha

The transcription factor Sp1 plays an important regulatory role in transactivation of the lung type I cell differentiation gene T1alpha. Like other lung cells, type I cells may encounter changes in oxygen concentration during the lifetime of the organism. We found that exposure of mice to hyperoxia rapidly increases expression of T1alpha and other type I cell genes, and that returning the mice to normoxia quickly decreases expression. Likewise hyperoxia increases both endogenous T1alpha expression in lung epithelial cell lines and transcription of luciferase (Luc) from T1alpha promoter deletion constructs. Using wild-type promoter fragments and gel shift assays, we determined that Sp1/Sp3 and a key Sp cis-element in the proximal promoter mediate the hyperoxic response. Mutations of this element and inhibition of Sp-DNA binding by mithramycin block the hyperoxic response. Western analyses of cell homogenates show that the overall abundance of Sp1 and Sp3 proteins is not altered by hyperoxia. However, the abundance of nuclear Sp1 increases after short hyperoxic exposures, suggesting that signaling pathways activated by hyperoxia lead to Sp protein translocation, perhaps as a result of increased Sp phosphorylation.

Measuring the immeasurable

Many bacterial pathogens turn on virulence genes at host body temperature. In the September 6, 2002, issue of Cell, Johansson et al. show that the Listeria monocytogenes thermosensor is an RNA structure in the 5' untranslated region of the mRNA for the virulence-activating transcription factor PrfA. The stem-loop structure blocks translation initiation at 30 degrees C but melts away at 37 degrees C.

APE/Ref-1 is increased in nuclear fractions of human thyroid hyperfunctioning nodules

Apurinic/apyrimidinic endonuclease APE/Ref-1 is a multifunctional protein provided with DNA repair, transcription-factor regulation and anti-apoptotic activities. We have previously reported that, in thyroid cells, TSH regulates both the synthesis and nuclear translocation of APE/Ref-1. We have also shown that nuclear levels of this protein are reduced both in thyroid carcinoma tissues and cell lines. In the present study, APE/Ref-1 expression and cellular localization were analysed by Western blot in hyperfunctioning thyroid nodules from patients with toxic adenoma and/or toxic multinodular goiter. The total content of APE/Ref-1 protein was increased in the majority of the hyperfunctioning tissues with respect to normal adjacent tissue. There was also an increase in the nuclear levels of APE/Ref-1, suggesting enhanced cytoplasm-to-nucleus translocation of the protein in addition to its increased rate of synthesis. These results demonstrate that the phenomenon of nuclear translocation of APE/Ref-1 hypothesized on the basis of cell culture experiments does actually occur in vivo. Together with previous observations in thyroid carcinomas and tumoral cell lines, our findings suggest a two-stage model of APE/Ref-1 behaviour during malignant thyrocyte transformation: an early stage characterized by simple hyperplasia and upregulation of APE/Ref-1 in the nuclear compartment of the cell and a later stage in which nuclear levels of the protein drop to below-normal levels as the cell becomes progressively undifferentiated.

A novel transactivating factor that regulates interferon-gamma-dependent gene expression

We have previously identified a novel interferon (IFN)-stimulated cis-acting enhancer element, gamma-IFN-activated transcriptional element (GATE). GATE differs from the known IFN-stimulated elements in its primary sequence. Preliminary analysis has indicated that the GATE-dependent transcriptional response requires the binding of novel transacting factors. A cDNA expression library derived from an IFN-gamma-stimulated murine macrophage cell line was screened with a (32)P-labeled GATE probe to identify the potential GATE-binding factors. A cDNA coding for a novel transcription-activating factor was identified. Based on its discovery, we named it as GATE-binding factor-1 (GBF-1). GBF-1 homologs are present in mouse, human, monkey, and Drosophila. It activates transcription from reporter genes carrying GATE. It possesses a strong transactivating activity but has a weak DNA binding property. GBF-1 is expressed in most tissues with relatively higher steady-state levels in heart, liver, kidney, and brain. Its expression is induced by IFN-gamma treatment. GBF-1 is present in both cytosolic and nuclear compartments. These studies thus identify a novel transactivating factor in IFN signaling pathways.