Major histocompatibility class II HLA-DR alpha gene expression in thyrocytes: counter regulation by the class II transactivator and the thyroid Y box protein

Expression and network analysis of YBX1 interactors for identification of new drug targets in lung adenocarcinoma

Y-Box Binding protein 1 (YBX-1) is known to be involved in various types of cancers. It's interactors also play major role in various cellular functions. Present work aimed to study the expression profile of the YBX-1 interactors during lung adenocarcinoma (LUAD). The differential expression analysis involved 57 genes from 95 lung adenocarcinoma samples, construction of gene network and topology analysis. A Total of 43 genes were found to be differentially expressed from which 17 genes were found to be down regulated and 26 genes were up-regulated. We observed that Polyadenylate-binding protein 1 (PABPC1), a protein involved in YBX1 translation, is highly correlated with YBX1. The interaction network analysis for a differentially expressed non-coding RNA Growth Arrest Specific 5 (GAS5) suggests that two proteins namely, Growth Arrest Specific 2 (GAS2) and Peripheral myelin protein 22 (PMP22) are potentially involved in LUAD progression. The network analysis and differential expression suggests that Collagen type 1 alpha 2 (COL1A2) can be potential biomarker and target for LUAD.

Regulation of major histocompatibility complex gene expression in thyroid epithelial cells by methimazole and phenylmethimazole

Increased expression of major histocompatibility complex (MHC) class-I genes and aberrant expression of MHC class-II genes in thyroid epithelial cells (TECs) are associated with autoimmune thyroid diseases. Previous studies have shown that methimazole (MMI) reduces MHC class-I expression and inhibits interferon-gamma (IFN-gamma or IFNG as listed in the MGI Database)-induced expression of the MHC class-II genes in TECs. The action of MMI on the MHC class-I genes is transcriptional, but its mechanism has not been investigated previously. In the present study, we show that in Fisher rat thyroid cell line 5 cells, the ability of MMI and its novel derivative phenylmethimazole (C10) to decrease MHC class-I promoter activity is similar to TSH/cAMP suppression of MHC class-I and TSH receptor genes, and involves a 39 bp silencer containing a cAMP response element (CRE)-like site. Furthermore, we show that C10 decreases MHC class-I gene expression to a greater extent than MMI and at 10- to 50-fold lower concentrations. C10 also reduces the IFN-gamma-induced increase in the expression of MHC class-I and MHC class-II genes more effectively than MMI. Finally, we show that in comparison to MMI, C10 is a better inhibitor of specific protein-DNA complexes that are formed with a CRE-like element on the MHC class-II promoter. These data support the conclusion that the immunosuppressive mechanism by which MMI and C10 inhibit MHC gene expression mimics 'normal' hormonal suppression by TSH/cAMP.

Influence of iodide excess and interferon-gamma on human primary thyroid cell proliferation, thyroglobulin secretion, and intracellular adhesion molecule-1 and human leukocyte antigen-DR expression

BACKGROUND

The effect of iodide on thyroid cell proliferation and function in vivo or in cultured thyroid cells has been previously reported and is still controversial. The aim of this study was to clarify these conflicting results by examining if prolonged high iodide exposition with or without interferon (IFN)-gamma has an effect on human primary thyroid cell proliferation, thyroglobulin (Tg) production, and intercellular adhesion molecule-1 (ICAM-1) and human leukocyte antigen (HLA)-DR expression.

METHODS

Primary human thyroid cells were used. Cells were cultured in Coon's modified Ham's F-12 medium supplemented with 5% fetal calf serum in monolayer conditions to induce proliferation and were aggregated for molecular expression and Tg production analysis. HLA-DR and ICAM-1 expression were measured by flow cytometry and Tg by immunometric assay.

RESULTS

Potassium iodide (KI) was more potent in arresting primary human thyroid cell proliferation as compared to sodium iodide and the effect was mediated by its action at G0/G1 and G2/M phases of the cell cycle. There were no signs of apoptosis or necrosis. An excess of KI alone did not change the expression of HLA-DR and Tg production, but gradually increased ICAM-1. Low-dose IFN-gamma and excess KI in combination transiently inhibited HLA-DR expression, while ICAM-1 was expressed at a higher level than with IFN-gamma alone. Tg production was moderately increased with low-dose IFN-gamma. However, a combination of high-dose KI with low-dose IFN-gamma significantly decreased Tg secretion, compared with IFN-gamma alone.

CONCLUSIONS

Augmented ICAM-1 in the presence of iodide excess and low-dose IFN-gamma could induce secretion of proinflammatory cytokines and lymphocytic infiltration in the thyroid gland. Decreased Tg production in the presence of KI excess and IFN-gamma could explain the development of hypothyroidism after adding iodide in a diet of subjects that already have lymphocytic infiltration and/or mild inflammation in the thyroid gland.

Major histocompatibility class II transactivator (CIITA) mediates repression of collagen (COL1A2) transcription by interferon gamma (IFN-gamma)

Interferon gamma (IFN-gamma) plays an important role during inflammation by repressing collagen and activating major histocompatibility class II (MHC-II) expression. Activation of MHC-II by IFN-gamma requires regulatory factor for X-box 5 (RFX5) complex as well as class II transactivator (CIITA). We have shown that the RFX family binds to the COL1A2 transcription start site, and the RFX5 complex represses COL1A2 gene expression during IFN-gamma response. In this report, we demonstrate that CIITA is a key mediator of COL1A2 repression by IFN-gamma. IFN-gamma up-regulates the expression of CIITA in a time-dependent manner in lung fibroblasts and promotes CIITA protein occupancy on COL1A2 transcription start site in vivo as judged by chromatin immunoprecipitation (ChIP) assays. There are coordinate decreases in the occupancy of RNA polymerase II on the collagen transcription start site with increasing CIITA occupancy during IFN-gamma treatment. In addition, we are able to specifically knockdown the IFN-gamma-stimulated expression of CIITA utilizing short hairpin interference RNA (shRNA) against CIITA. This leads to the alleviation of COL1A2 repression and MHC-II activation by IFN-gamma. RFX5 recruits CIITA to the collagen site as evidenced by DNA affinity chromatography. The presence of RFX5 complex proteins enhances the collagen repression by CIITA reaching levels occurring during IFN-gamma treatment. Co-expression of CIITA with deletion mutations and collagen promoter constructs demonstrates that CIITA represses collagen promoter mainly through its N-terminal region including the acidic domain and the proline/serine/threonine domain. Our data suggest that CIITA is a crucial member of a repressor complex responsible for mediating COL1A2 transcription repression by IFN-gamma.

Interferon-gamma interferes with transforming growth factor-beta signaling through direct interaction of YB-1 with Smad3

Transforming growth factor-beta (TGF-beta) and interferon-gamma (IFN-gamma) exert antagonistic effects on collagen synthesis in human dermal fibroblasts. We have recently shown that Y box-binding protein YB-1 mediates the inhibitory effects of IFN-gamma on alpha2(I) procollagen gene (COL1A2) transcription through the IFN-gamma response element located between -161 and -150. Here we report that YB-1 counter-represses TGF-beta-stimulated COL1A2 transcription by interfering with Smad3 bound to the upstream sequence around -265 and subsequently by interrupting the Smad3-p300 interaction. Western blot and immunofluorescence analyses using inhibitors for Janus kinases or casein kinase II suggested that the casein kinase II-dependent signaling pathway mediates IFN-gamma-induced nuclear translocation of YB-1. Down-regulation of endogenous YB-1 expression by double-stranded YB-1-specific RNA abrogated the transcriptional repression of COL1A2 by IFN-gamma in the absence and presence of TGF-beta. In transient transfection assays, overexpression of YB-1 in human dermal fibroblasts exhibited antagonistic actions against TGF-beta and Smad3. Physical interaction between Smad3 and YB-1 was demonstrated by immunoprecipitation-Western blot analyses, and electrophoretic mobility shift assays using the recombinant Smad3 and YB-1 proteins indicated that YB-1 forms a complex with Smad3 bound to the Smad-binding element. Glutathione S-transferase pull-down assays showed that YB-1 binds to the MH1 domain of Smad3, whereas the central and carboxyl-terminal regions of YB-1 were required for its interaction with Smad3. YB-1 also interferes with the Smad3-p300 interaction by its preferential binding to p300. Altogether, the results provide a novel insight into the mechanism by which IFN-gamma/YB-1 counteracts TGF-beta/Smad3. They also indicate that IFN-gamma/YB-1 inhibits COL1A2 transcription by dual actions: via the IFN-gamma response element and through a cross-talk with the TGF-beta/Smad signaling pathway.

The pleiotropic functions of the Y-box-binding protein, YB-1

The Y-box-binding protein (YB-1) represents the most evolutionary conserved nucleic-acid-binding protein currently known. YB-1 is a member of the cold-shock domain (CSD) protein superfamily. It performs a wide variety of cellular functions, including transcriptional regulation, translational regulation, DNA repair, drug resistance and stress responses to extracellular signals. As a result, YB-1 expression is closely associated with cell proliferation. In this review, we will begin by briefly describing the characteristics of YB-1 and will then summarize the pleiotropic functions brought about via DNA-RNA transaction and protein-protein interactions. In addition, we will discuss the diverse range of potential physiological and pathological functions of YB-1.

Methimazole protects from experimental autoimmune uveitis (EAU) by inhibiting antigen presenting cell function and reducing antigen priming

Methimazole (methyl-mercapto-imidazole, MMI), a compound used clinically in therapy of Graves' thyroiditis, was found to inhibit development of several autoimmune diseases in animal models. It was suggested on the basis of in vitro data that inhibition is through down-regulation of interferon-gamma (IFN-gamma)-induced expression of major histocompatibility complex class I and class II molecules. Here, we investigate the effect of MMI on experimental autoimmune uveoretinitis (EAU) and study its mechanism(s). Treatment of EAU with MMI administered in drinking water inhibited induction of the disease and associated antigen (Ag)-specific proliferation and cytokine production by draining lymph node cells (LNCs). The treatment was protective only if administered during the first but not during the second week after immunization, suggesting an effect on the induction phase of EAU. It is interesting that MMI inhibited disease in IFN-gamma knockout mice, indicating that the in vivo protective effect is IFN-gamma-independent. Flow cytometric analysis of draining LNCs extracted 5 days after immunization showed that MMI partly to completely reversed the increase in Mac-1(+)/class I(+)/class II(+) cells induced by immunization and reduced the proportion of B7-1 and CD40-positive cells, suggesting a deficit in the Ag-presenting cell (APC) population. APC from untreated mice largely restored antigen-specific proliferation of MMI-treated LNCs. We suggest that MMI inhibits EAU at least in part by preventing the recruitment and/or maturation of APC, resulting in reduced generation of Ag-specific T cells.

Graves' disease: a host defense mechanism gone awry

In this report we summarize evidence to support a model for the development of Graves' disease. The model suggests that Graves' disease is initiated by an insult to the thyrocyte in an individual with a normal immune system. The insult, infectious or otherwise, causes double strand DNA or RNA to enter the cytoplasm of the cell. This causes abnormal expression of major histocompatibility (MHC) class I as a dominant feature, but also aberrant expression of MHC class II, as well as changes in genes or gene products needed for the thyrocyte to become an antigen presenting cell (APC). These include increased expression of proteasome processing proteins (LMP2), transporters of antigen peptides (TAP), invariant chain (Ii), HLA-DM, and the co-stimulatory molecule, B7, as well as STAT and NF-kappaB activation. A critical factor in these changes is the loss of normal negative regulation of MHC class I, class II, and thyrotropin receptor (TSHR) gene expression, which is necessary to maintain self-tolerance during the normal changes in gene expression involved in hormonally-increased growth and function of the cell. Self-tolerance to the TSHR is maintained in normals because there is a population of CD8- cells which normally suppresses a population of CD4+ cells that can interact with the TSHR if thyrocytes become APCs. This is a host self-defense mechanism that we hypothesize leads to autoimmune disease in persons, for example, with a specific viral infection, a genetic predisposition, or even, possibly, a TSHR polymorphism. The model is suggested to be important to explain the development of other autoimmune diseases including systemic lupus or diabetes.

Class II transactivator suppresses transcription of thyroid-specific genes

Class II transactivator (CIITA) is the master regulator of MHC class II genes, and mediates their induction by interferon gamma (IFN gamma). To study the role of CIITA in modulating the expression of thyroid-specific genes, we cloned the full-length rat CIITA and use it to transfect a rat thyroid cell line. We found that only one type of CIITA, type IV, is induced in thyroid cells upon IFN gamma stimulation, and that CIITA is capable not only of inducing the expression of MHC genes in the thyroid, but also of differentially suppressing the expression of thyroid-specific genes. These findings suggest new avenues for the development of thyroid autoimmune diseases.

Physical and functional interaction between two pluripotent proteins, the Y-box DNA/RNA-binding factor, YB-1, and the multivalent zinc finger factor, CTCF

CTCF is a unique, highly conserved, and ubiquitously expressed 11 zinc finger (ZF) transcriptional factor with multiple DNA site specificities. It is able to bind to varying target sequences to perform different regulatory roles, including promoter activation or repression, creating hormone-responsive gene silencing elements, and functional block of enhancer-promoter interactions. Because different sets of ZFs are utilized to recognize different CTCF target DNA sites, each of the diverse DNA.CTCF complexes might engage different essential protein partners to define distinct functional readouts. To identify such proteins, we developed an affinity chromatography method based on matrix-immobilized purified recombinant CTCF. This approach resulted in isolation of several CTCF protein partners. One of these was identified as the multifunctional Y-box DNA/RNA-binding factor, YB-1, known to be involved in transcription, replication, and RNA processing. We examined CTCF/YB-1 interaction by reciprocal immunoprecipitation experiments with anti-CTCF and anti-YB-1 antibodies, and found that CTCF and YB-1 form complexes in vivo. We show that the bacterially expressed ZF domain of CTCF is fully sufficient to retain YB-1 in vitro. To assess possible functional significance of CTCF/YB-1 binding, we employed the very first identified by us, negatively regulated, target for CTCF (c-myc oncogene promoter) as a model in co-transfection assays with both CTCF and YB-1 expression vectors. Although expression of YB-1 alone had no effect, co-expression with CTCF resulted in a marked enhancement of CTCF-driven c-myc transcriptional repression. Thus our findings demonstrate, for the first time, the biological relevance of the CTCF/YB-1 interaction.

Role of peroxiredoxins in regulating intracellular hydrogen peroxide and hydrogen peroxide-induced apoptosis in thyroid cells

Peroxiredoxins (Prxs) play an important role in regulating cellular differentiation and proliferation in several types of mammalian cells. One mechanism for this action involves modulation of hydrogen peroxide (H(2)O(2))-mediated cellular responses. This report examines the expression of Prx I and Prx II in thyroid cells and their roles in eliminating H(2)O(2) produced in response to thyrotropin (TSH). Prx I and Prx II are constitutively expressed in FRTL-5 thyroid cells. Prx I expression, but not Prx II expression, is stimulated by exposure to TSH and H(2)O(2). In addition, methimazole induces a high level of Prx I mRNA and protein in these cells. Overexpression of Prx I and Prx II enhances the elimination of H(2)O(2) produced by TSH in FRTL-5 cells. Treatment with 500 micrometer H(2)O(2) causes apoptosis in FRTL-5 cells as evidenced by standard assays of apoptosis (i.e. terminal deoxynucleotidyl transferase deoxyuridine triphosphate-biotin nick end labeling, BAX expression, and poly(ADP-ribose) polymerase cleavage. Overexpression of Prx I and Prx II reduces the amount of H(2)O(2)-induced apoptosis measured by these assays. These results suggest that Prx I and Prx II are involved in the removal of H(2)O(2) in thyroid cells and can protect these cells from undergoing apoptosis. These proteins are likely to be involved in the normal physiological response to TSH-induced production of H(2)O(2) in thyroid cells.

Transcriptional regulation of the MHC II gene DRA in untransformed human thyrocytes

MHC class II molecules are heterodimeric, polymorphic transmembrane glycoproteins physiologically expressed on cells of the immune system and pathologically expressed on the affected target cells of autoimmunity. Their function is to present processed peptides to antigen-specific CD4(+) T cells. To understand the molecular mechanism of the regulation of class II genes in autoimmune target cell thyrocytes, we investigated the transcriptional regulation of DRA on untransformed, differentiated human thyroid cells following IFN-gamma stimulation, which is potentially relevant to the inappropriate class II expression found in Graves' disease. Data from this study show that IFN-gamma enhances a promoter Y box binding protein and induces an X box binding protein in untransformed thyrocytes, but not in SV-40-transfected thyrocytes. Initial characterization of the proteins has indicated that the Y box binding protein is approximately 132 kDa in size while the X box binding protein binds to the X2 region and is approximately 116 kDa. The X box binding protein may correspond to poly(ADP-ribose) polymerase, a recently described component of the X2 box binding protein, X2BP. In addition, the signal transducer and activator of transcription 1alpha protein (STAT1alpha) is also induced by IFN-gamma in these cells. These results further suggest that there are differences in class II gene regulation between differentiated cells and transformed cell lines.

Differential effects of acute and chronic exposure to interferon-gamma on cyclic adenosine 3',5'-monophosphate response element-regulated gene expression

TSH stimulates proliferation and maintains differentiated function in thyroid follicular cells. The mitogenic activity and the stimulatory effects of TSH on thyroid-specific gene expression are impaired by interferon-gamma (IFNgamma); however, the mechanisms for these effects have not been elucidated in detail. We examined the effects of IFNgamma on acute responses to TSH in rat thyroid cells. IFNgamma did not impair TSH-stimulated p70/p85 ribosomal protein S6 kinase (p70/p85s6k) activity or cAMP response element (CRE)-regulated gene expression, although it inhibited DNA synthesis and thyroglobulin expression, effects measured over a more prolonged time course than those on kinase activity and reporter gene expression. Unexpectedly, when cells were chronically exposed to IFNgamma, CRE-lacZ promoter activity was decreased, whereas other cAMP-mediated signals, such as p70/p85s6k activity and CRE-binding protein phosphorylation, were unaffected. Activating protein-1-regulated promoters were also impaired by IFNgamma treatment, but with kinetics that differed from those of CRE-regulated promoters. Neither acute nor chronic treatment with interleukin-1beta impaired cAMP signaling, indicating that the effects of IFNgamma are specific. These studies identify CRE- and activating protein-1-regulated promoters as targets of IFNgamma in thyroid cells and fibroblasts. IFNgamma-mediated inhibition of these promoters, in addition to those containing thyroid-specific transcription factor-1-binding sites, may contribute to the profound effects of IFNgamma on thyroid cells.

Physical and functional interaction between the Y-box binding protein YB-1 and human polyomavirus JC virus large T antigen

Y-box binding protein YB-1 is a member of a family of DNA and RNA binding proteins which have been shown to affect gene expression at both the transcriptional and translational levels. We have previously shown that YB-1 modulates transcription from the promoters of the ubiquitous human polyomavirus JC virus (JCV). Here we investigate the physical and functional interplay between YB-1 and the viral regulatory protein large T antigen (T-antigen), using JCV as a model system. Results of mobility band shift assays demonstrated that the efficiency of binding of YB-1 to a 23-bp single-stranded viral target sequence was significantly increased when T-antigen was included in the binding reaction mixture. Affinity chromatography and coimmunoprecipitation assays demonstrated that YB-1 and T-antigen physically interact with each other. Additionally, results of transcription studies demonstrated that these two proteins interact functionally on the JCV early and late gene promoters. Whereas ectopic expression of YB-1 and T-antigen results in synergistic transactivation of the viral late promoter, YB-1 alleviates T-antigen-mediated transcriptional suppression of the viral early promoter activity. Furthermore, we have localized, through the use of a series of deletion mutants, the sequences of these proteins which are important for their interaction. The T-antigen-interacting region of YB-1 is located in the cold shock domain of YB-1 and its immediate flanking sequences, and the YB-1-interacting domain of T-antigen maps to the carboxy-terminal half of T-antigen. Results of transient transfection assays with various YB-1 mutants and T-antigen expression constructs confirm the specificity of the functional interaction between YB-1 and T-antigen. Taken together, these data demonstrate that the cellular factor YB-1 and the viral regulatory protein T-antigen interact both physically and functionally and that this interaction modulates transcription from the JCV promoters.

Reciprocal interaction between two cellular proteins, Puralpha and YB-1, modulates transcriptional activity of JCVCY in glial cells

Cross communication between regulatory proteins is an important event in the control of eukaryotic gene transcription. Here we have examined the structural and functional interaction between two cellular regulatory proteins, YB-1 and Puralpha, on the 23-bp sequence element derived from the enhancer-promoter of the human polyomavirus JCV. YB-1 and Puralpha are single-stranded DNA binding proteins which recognize C/T- and GC/GA-rich sequences, respectively. Results from band shift studies demonstrated that while both proteins interact directly with their DNA target sequences within the 23-bp motif, each protein can regulate the association of the other one with the DNA. Affinity chromatography and coimmunoprecipitation provide evidence for a direct interaction between Puralpha and YB-1 in the absence of the DNA sequence. Ectopic expression of YB-1 and Puralpha in glial cells synergistically stimulated viral promoter activity via the 23-bp sequence element. Results from mutational studies revealed that residues between amino acids 75 and 203 of YB-1 and between amino acids 85 and 215 of Puralpha are important for the interaction between these two proteins. Functional studies with glial cells indicated that the region within Puralpha which mediates its association with YB-1 and binding to the 23-bp sequence is important for the observed activation of the JCV promoter by the Puralpha and YB-1 proteins. The results of this study suggest that the cooperative interaction between YB-1 and Puralpha mediates the synergistic activation of the human polyomavirus JCV genome by these cellular proteins. The importance of these findings for cellular and viral genes which are regulated by Puralpha and YB-1 is discussed.

Nicotinamide potentiates TSHR and MHC class II promoter activity in FRTL-5 cells

Here we show that nicotinamide modulates the promoter activity of rat thyrotropin (TSHR) and major histocompatibility complex (MHC) class II genes in rat FRTL-5 thyroid cells, and have identified a novel mechanism for its action. TSHR and MHC class II, are potentiated through reduced expression of a common repressor of these two genes, TSEP-1 (TSHR suppressor element binding protein-1)/YB-1. Thus we show that TSHR mRNA is increased and TSHR promoter activity was concentration-dependently activated from 0 to 40 mM nicotinamide. The promoter lengths of TSHR and MHC class II containing TSEP/YB-1 binding sites were enhanced by 40 mM nicotinamide, but not the ones deleted of these binding sites. TSEP-1/YB-1 binding to the recognition sites in both TSHR and MHC class II promoters was reduced in nicotinamide-treated FRTL-5 nuclear extracts. Nicotinamide reduced the expression of TSEP-1/YB-1 mRNA and TSEP-1/YB-1 protein in the nucleus.

Regulation of HLA-DR and costimulatory B7 molecules in human thyroid carcinoma cells: differential binding of transcription factors to the HLA-DRalpha promoter

The consequence of autoantigen presentation by thyroid cells is dependent on the magnitude of expression of both HLA class II antigens (mainly HLA-DR) and costimulatory molecules, such as B7 (CD80 and CD86). Autoimmune thyrocytes are induced to express HLA-DR by interferon-gamma (IFN-gamma). The costimulatory signal leading to autoantibody production or cytotoxic T-cell immune response could be provided by antigen presenting cells (APCs) attracted to the thyroid by the primary autoimmune stimulus. Malignant thyrocytes can express HLA-DR antigens either constitutively, as a result of a nonimmunologic stimulus, or on induction with IFN-gamma after triggering of an immune response. However, their ability to express B7 molecules, which may determine enhanced antitumoral immune response mainly in the absence of intrathyroidal macrophages, has not yet been studied. The regulation of HLA-DR gene expression in APCs, such as B cells, is mediated by a series of short DNA consensus sequences located in the promoter, termed the W, X, and Y boxes, which bind several known transcription factors. We have previously characterized the expression of HLA-DR in four human thyroid carcinoma cell lines and found differences between constitutive and high- or moderate-induced expression of the protein and mRNA. Evaluation of B7 expression on the surface of thyroid cancer cells and understanding the mechanisms of HLA-DR gene expression may help in designing efficient immune response to thyroid tumors. Using the electrophoretic mobility shift assay (EMSA), we have demonstrated differences between the four thyroid cell lines in the binding of transcription factors to each of the three boxes. The binding to the promoter in each of the cell lines resulted in a single band, probably representing a complex of proteins formed via protein-protein interactions. Using flow cytometry we have shown that the B7 molecule was absent in the four thyroid cell lines and could not be induced by IFN-gamma. The absence of surface B7 molecules from the malignant thyroid cells may lead to either suppression of antitumoral cytotoxic T cell response or demand the cooperation of infiltrating APCs to favor immune response. Differences previously found in HLA-DR expression in the four human malignant thyroid cell lines may be explained by the variation in the binding of transcription factors to the boxes in the HLA-DRalpha promoter. The binding patterns of nuclear proteins derived from the four thyroid cell lines or from the B lymphocyte cell line--Raji--to each of the boxes or to the whole promoter exhibit similarities, thus suggesting similar DNA-protein interactions.

Regulation of major histocompatibility class II gene expression in FRTL-5 thyrocytes: opposite effects of interferon and methimazole

Aberrant expression of major histocompatibility complex (MHC) class II antigens is associated with autoimmune thyroid disease; aberrant expression duplicating the autoimmune state can be induced by interferon-gamma (IFNgamma). We have studied IFNgamma-induced human leukocyte antigen (HLA)-DR alpha gene expression in rat FRTL-5 thyroid cells to identify the elements and factors important for aberrant expression. Using an HLA-DR alpha 5'-flanking region construct from -176 to +45 bp coupled to the chloramphenicol acetyltransferase reporter gene, we show that there is no basal class II gene expression in FRTL-5 thyroid cells, that IFNgamma can induce expression, and, as is the case for antigen-presenting cells from the immune system, that IFNgamma-induced expression requires several highly conserved elements on the 5'-flanking region, which, from 5' to 3', are the S, X1, X2, and Y boxes. Methimazole (MMI), a drug used to treat patients with Graves' disease and experimental thyroiditis in rats or mice, can suppress the IFNgamma-induced increase in HLA-DR alpha gene expression as a function of time and concentration; MMI simultaneously decreases IFNgamma-induced endogenous antigen presentation by the cell. Using gel shift assays and the HLA-DR alpha 5'-flanking region from -176 or -137 to +45 bp as radiolabeled probes, we observed the formation of a major protein-DNA complex with extracts from FRTL-5 cells untreated with IFNgamma, termed the basal or constitutive complex, and formation of an additional complex with a slightly faster mobility in extracts from cells treated with IFNgamma. MMI treatment of cells prevents IFNgamma from increasing the formation of this faster migrating complex. Formation of both complexes is specific, as evidenced in competition studies with unlabeled fragments between -137 and -38 bp from the start of transcription; nevertheless, they can be distinguished in such studies. Thus, high concentrations of double stranded oligonucleotides containing the sequence of the Y box, but not S, X1, or X2 box sequences, can prevent formation of the IFNgamma-increased faster migrating complex, but not the basal complex. Both complexes involve multiple proteins and can be distinguished by differences in their protein composition. Thus, using specific antisera, we show that two cAMP response element-binding proteins, activating transcription factor-1 and/or -2, are dominant proteins in the upper or basal complex. The upper or basal complex also includes c-Fos, Fra-2, Ets-2, and Oct-1. A dominant protein that distinguishes the IFNgamma-increased lower complex is CREB-binding protein (CBP), a coactivator of cAMP response element-binding proteins. We, therefore, show that aberrant expression of MHC class II in thyrocytes, induced by IFNgamma, is associated with the induction or increased formation of a novel protein-DNA complex and that its formation as well as aberrant class II expression are suppressed by MMI, a drug used to treat human and experimental autoimmune thyroid disease. Its component proteins differ from those in a major, basal, or constitutive protein-DNA complex formed with the class II 5'-flanking region in cells that are not treated with IFNgamma and that do not express the class II gene.