P300 Inhibition Improves Cell Apoptosis and Cognition Impairment Induced by Sevoflurane Through Regulating IL-17A Activation

BACKGROUND

Sevoflurane (Sev) is a rapidly acting, potent inhalation anesthetic with rapid uptake and elimination. But many studies have shown that Sev could result in cognition dysfunction in adolescent or aging patients. Now, therapeutic targeting with IL-17A antibody has shown a promising effect on Sev-induced cognition impairment. In the study we report that P300 inhibition could act as an alternative approach to decrease IL-17A activity.

METHODS

SHSY5Y cells were treated with Sev and cell apoptosis was evaluated by Annexin V-FITC/PI staining. The expression of P300 and IL-17A were assessed by Western blotting. Water maze tests were conducted in order to assess the cognitive function.

RESULTS

We found that P300 and IL-17A were activated in SHSY5Y cells treated with Sev. P300 inhibitor C646 could reduce the apoptosis induced by Sev through decreasing IL-17A avtivity. Furthermore, IL-17A expression was upregulated after neurons were transfected with P300 expression plasmid and IL-17A expression was downregulated after neurons were incubated with P300 inhibitor C646. P300 overexpression could upregulate the promoter activity of IL-17A. Finally, in a rat model treated with Sev, we also found C646 to significantly improve the cognition impairment through the IL-17A pathway.

CONCLUSIONS

These data show that P300 will potentially be a new drug target for the therapy of cognition impairment caused by Sev.

LINC00941 promotes oral squamous cell carcinoma progression via activating CAPRIN2 and canonical WNT/β-catenin signaling pathway

Dysregulation of long non-coding RNAs (lncRNAs) has been implicated in many cancer developments. Previous studies showed that lncRNA LINC00941 was aberrantly expressed in oral squamous cell carcinoma (OSCC). However, its role in OSCC development remains elusive. In this study, we demonstrated that in OSCC cells, EP300 activates LINC00941 transcription through up-regulating its promoter H3K27ac modification. Up-regulated LINC00941 in turn activates CAPRIN2 expression by looping to CAPRIN2 promoter. Functional assays suggest that both LINC00941 and CAPRIN2 play pivotal roles in promoting OSCC cell proliferation and colony formation. In vivo assay further confirmed the role of LINC00941 in promoting OSCC cell tumour formation. Lastly, we showed that the role of LINC00941 and CAPRIN2 in OSCC progression was mediated through activating the canonical WNT/β-catenin signaling pathway. Thus, LINC00941/CAPRIN2/ WNT/β-catenin signaling pathway provides new therapeutic targets for OSCC treatment.

EP300-ZNF384 fusion gene product up-regulates GATA3 gene expression and induces hematopoietic stem cell gene expression signature in B-cell precursor acute lymphoblastic leukemia cells

ZNF384-related fusion genes are associated with a distinct subgroup of B-cell precursor acute lymphoblastic leukemias in childhood, with a frequency of approximately 3-4%. We previously identified a novel EP300-ZNF384 fusion gene. Patients with the ZNF384-related fusion gene exhibit a hematopoietic stem cell (HSC) gene expression signature and characteristic immunophenotype with negative or low expression of CD10 and aberrant expression of myeloid antigens, such as CD33 and CD13. However, the molecular basis of this pathogenesis remains completely unknown. In the present study, we examined the biological effects of EP300-ZNF384 expression induced by retrovirus-mediated gene transduction in an REH B-cell precursor acute lymphoblastic leukemia cell line, and observed the acquisition of the HSC gene expression signature and an up-regulation of GATA3 gene expression, as assessed by microarray analysis. In contrast, the gene expression profile induced by wild-type ZNF384 in REH cells was significantly different from that by EP300-ZNF384 expression. Together with the results of reporter assays, which revealed the enhancement of GATA3-promoter activity by EP300-ZNF384 expression, these findings suggest that EP300-ZNF384 mediates GATA3 gene expression and may be involved in the acquisition of the HSC gene expression signature and characteristic immunophenotype in B-cell precursor acute lymphoblastic leukemia cells.

Transcriptional/epigenetic regulator CBP/p300 in tumorigenesis: structural and functional versatility in target recognition

In eukaryotic cells, gene transcription is regulated by sequence-specific DNA-binding transcription factors that recognize promoter and enhancer elements near the transcriptional start site. Some coactivators promote transcription by connecting transcription factors to the basal transcriptional machinery. The highly conserved coactivators CREB-binding protein (CBP) and its paralog, E1A-binding protein (p300), each have four separate transactivation domains (TADs) that interact with the TADs of a number of DNA-binding transcription activators as well as general transcription factors (GTFs), thus mediating recruitment of basal transcription machinery to the promoter. Most promoters comprise multiple activator-binding sites, and many activators contain tandem TADs, thus multivalent interactions may stabilize CBP/p300 at the promoter, and intrinsically disordered regions in CBP/p300 and many activators may confer adaptability to these multivalent complexes. CBP/p300 contains a catalytic histone acetyltransferase (HAT) domain, which remodels chromatin to 'relax' its superstructure and enables transcription of proximal genes. The HAT activity of CBP/p300 also acetylates some transcription factors (e.g., p53), hence modulating the function of key transcriptional regulators. Through these numerous interactions, CBP/p300 has been implicated in complex physiological and pathological processes, and, in response to different signals, can drive cells towards proliferation or apoptosis. Dysregulation of the transcriptional and epigenetic functions of CBP/p300 is associated with leukemia and other types of cancer, thus it has been recognized as a potential anti-cancer drug target. In this review, we focus on recent exciting findings in the structural mechanisms of CBP/p300 involving multivalent and dynamic interactions with binding partners, which may pave new avenues for anti-cancer drug development.

Transcriptional coactivators p300 and CBP stimulate estrogen receptor-beta signaling and regulate cellular events in prostate cancer

BACKGROUND

Steroid receptor coactivators p300 and CBP are highly expressed in advanced prostate cancer. They potentiate activation of androgen receptor by androgens and anti-androgens. In the present study, we have addressed the question whether these coactivators enhance activity of estrogen receptor-beta (ER-β), which is variably expressed in prostate cancers.

METHODS

Expression levels of the coactivators p300 and CBP were manipulated by plasmid or siRNA transfections and activity of ER-β was measured by luciferase assays. Viability was measured by MTT assays and cellular migration was determined by wound-healing and Boyden chamber assays.

RESULTS

High expression of ER-β was found in PC3 cells which were used for the experiments. p300 or CBP enhanced activation of ER-β by genistein. Antiestrogens did not acquire agonistic properties in the presence of increased concentrations of either coactivator. Inhibition of p300 or CBP decreased genistein stimulation of ER-β. Genistein reduced migration of PC3 prostate cancer cells and down-regulation of p300 potentiated this effect.

CONCLUSIONS

p300 and CBP are implicated in regulation of ER-β activity and cellular migration in prostate cancer. These findings are important for understanding of action of ER-β in carcinoma of the prostate.

PARP activation and the alteration of vasoactive factors and extracellular matrix protein in retina and kidney in diabetes

AIMS

The development of diabetic complications is associated with increased oxidative stress which may damage DNA leading to the activation of nuclear enzyme poly (ADP-ribose) polymerase (PARP). PARP overactivation may further exacerbate the oxidative state of the cell through its consumption of nicotinamide adenine dinucleotide. In diabetic retinopathy and nephropathy, early characteristic features include increased production of vasoactive factors such as endothelin 1 (ET-1) and increased synthesis of extracellular matrix (ECM) proteins such as fibronectin (FN) and its splice variant extra domain B containing (EDB(+)) FN. We investigated the role of PARP in the development of diabetic retinopathy and nephropathy.

METHODS

Two models of diabetic complications were used. PARP-1 knockout mice and their respective wild type controls were fed a 30% galactose diet for 2 months. The rats were given injections of PARP inhibitor 3-aminobenzamide (30 mg/kg/day).

RESULTS

Analysis of the retinal and kidney tissues showed hyperhexosemia-induced oxidative stress and increased expression of ET-1, FN and EDB(+) FN in association with increased transcriptional co-activator p300 along with p300-dependent transcription factors, myocyte enhancing factors 2A and 2C. Furthermore, we showed increased PARP expression in the kidneys and retina of the diabetic rats. PARP blockade in both animal models prevented these hyperhexosemia-induced effects.

CONCLUSIONS

These findings suggests that hyperhexosemia and diabetes causes upregulation of ET-1, FN and EDB(+) FN at the transcriptional level in the retina and kidney via a signaling pathway mediated by PARP and an epigenetic mechanism involving p300 and MEF2 transcription factors. Understanding these mechanisms is important in identifying novel treatment targets.

The P300 is sensitive to concealed face recognition

In two experiments, we investigated whether a P300 based Concealed Information Test (CIT) can be used to detect concealed face recognition. The results show that detection of concealed face recognition is highly successful when stimuli depict persons who are personally highly familiar, and instructions to conceal recognition are given. When pictures depict recognized, but personally less familiar faces, and no specific instructions to conceal recognition are given, detection is unsuccessful. These findings indicate that pictures of faces can be used in a P300 based CIT, and that mere recognition is not sufficient for successful detection of concealed information.

P300 plays a role in p16(INK4a) expression and cell cycle arrest

As a cyclin-dependent kinase inhibitor, p16(INK4a) plays a key role in cell cycle progression and cellular differentiation, and its expression is frequently altered in human cancers through epigenetically mediated transcriptional silencing. In this report, we demonstrate that p300 was able to induce cell cycle arrest, and this process was reversed by p16(INK4a) silencing by RNA interference in HeLa cells. We also show that p300 was involved in activation of p16(INK4a) expression in 293T cells. Specifically, p300 cooperated with Sp1 to stimulate both p16(INK4a) promoter activity and mRNA expression. Co-immunoprecipitation and mammalian two-hybrid assays revealed that p300 and Sp1 formed a complex through interaction between the Q domain of p300 and the N-terminal domain of Sp1. The chromatin immunoprecipitation assays verified that p300 was recruited to p16(INK4a) promoter, and the histone acetyltransferase domain of p300 participated in p16(INK4a) activation through inducing hyperacetylation of histone H4 at p16(INK4a) gene. These data suggest that p300 plays a critical role in transcriptional regulation of p16(INK4a) and in cell cycle arrest.

Transgenic mice expressing an inhibitory truncated form of p300 exhibit long-term memory deficits

The formation of many forms of long-term memory requires several molecular mechanisms including regulation of gene expression. The mechanisms directing transcription require not only activation of individual transcription factors but also recruitment of transcriptional coactivators. CBP and p300 are transcriptional coactivators that interact with a large number of transcription factors and regulate transcription through multiple mechanisms, including an intrinsic histone acetyltransferase (HAT) activity. HAT activity mediates acetylation of lysine residues on the amino-terminal tails of histone proteins, thereby increasing DNA accessibility for transcription factors to activate gene expression. CBP has been shown to play an important role in long-term memory formation. We have investigated whether p300 is also required for certain forms of memory. p300 shares a high degree of homology with CBP and has been shown to interact with transcription factors known to be critical for long-term memory formation. Here we demonstrate that conditional transgenic mice expressing an inhibitory truncated form of p300 (p300Delta1), which lacks the carboxy-terminal HAT and activation domains, have impaired long-term recognition memory and contextual fear memory. Thus, our study demonstrates that p300 is required for certain forms of memory and that the HAT and carboxy-terminal domains play a critical role.

Involvement of the constitutive complex formation of c-Ski/SnoN with Smads in the impaired negative feedback regulation of transforming growth factor beta signaling in scleroderma fibroblasts

OBJECTIVE

The principal effect of transforming growth factor beta1 (TGFbeta1) on mesenchymal cells is its stimulation of extracellular matrix synthesis. Previous reports indicated the significance of the autocrine TGFbeta loop in the pathogenesis of scleroderma. The aim of this study was to examine c-Ski and SnoN, principal molecules in the negative regulation of TGFbeta signaling, to further understand the autocrine TGFbeta loop in scleroderma.

METHODS

Levels of expression of c-Ski/SnoN on cultured normal and scleroderma fibroblasts were determined by Western blotting, Northern blotting, and immunohistochemical staining. To determine the protein-protein interaction between c-Ski/SnoN, Smads, and p300, immunoprecipitation was performed. A transient transfection assay was performed to measure promoter activity of the alpha2(I) collagen gene and the 3TP-Lux plasmid construct.

RESULTS

Scleroderma fibroblasts exhibited increased c-Ski/SnoN levels compared with normal fibroblasts, both in vivo and in vitro. Although c-Ski/SnoN constitutively formed a complex with Smads by immunoprecipitation, the inhibitory effect of c-Ski/SnoN on the promoter activity of human alpha2(I) collagen and 3TP-Lux was impaired in scleroderma fibroblasts. Immunoprecipitation analyses also revealed that overexpressed c-Ski/SnoN could not compete with p300 in these cells.

CONCLUSION

These results indicate that impaired competition with p300 is the possible cause of dysfunction of c-Ski/SnoN in scleroderma fibroblasts and that this might contribute to maintenance of the autocrine TGFbeta loop in this disease.

Opposite effects of CBP and p300 in glucocorticoid signaling in astrocytes

In the nervous system, glucocorticoid hormones play a major role during development, and they continue to affect functional and structural plasticity throughout life. Glucocorticoid actions are mediated by their cognate nuclear receptor, the glucocorticoid receptor (GR). The transcriptional activity of the GR is enhanced by the recruitment of one of the transcriptional coactivators of the p160 family (SRCs), which are a docking platform for secondary coactivators like CBP, or its close homologue p300. Here, we investigated the implication of CBP and p300 coactivators in glial cells of the central and peripheral nervous system, namely in primary cultures of astrocytes and in Schwann cells. We show that both coregulators behave differently in either cell type. CBP enhances GR transcriptional activation in astrocytes, and has no effect in Schwann cells, whereas p300 exerts an inhibitory effect in both glial cells. Studies with p300 deletion mutants show that the repressive capacity of p300 is related to its acetyltransferase activity. This work shows striking differences between CBP and p300 actions in astrocytes. Moreover, in astrocytes the opposite effects of CBP and p300 could lead to a balance in the transactivation potency of the GR, in order to fine tune the action of glucocorticoids.

The MN1-TEL myeloid leukemia-associated fusion protein has a dominant-negative effect on RAR-RXR-mediated transcription

The translocation t(12;22)(p13;q11) creates an MN1-TEL fusion gene leading to acute myeloid leukemia. MN1 is a transcription coactivator of the retinoic acid and vitamin D receptors, and TEL (ETV6) is a member of the E26-transformation-specific family of transcription factors. In MN1-TEL, the transactivating domains of MN1 are combined with the DNA-binding domain of TEL. We show that MN1-TEL inhibits retinoic acid receptor (RAR)-mediated transcription, counteracts coactivators such as p160 and p300, and acts as a dominant-negative mutant of MN1. Compared to MN1, the same transactivation domains in MN1-TEL are poorly stimulated by p160, p300 or histone deacetylase inhibitors, indicating that the block of RAR-mediated transcription by MN1-TEL is caused by dysfunctional transactivation domains rather than by recruitment of corepressors. The mechanism leading to myeloid leukemia in t(12;22) thus differs from the translocations that involve RAR itself.

Muscle cell survival mediated by the transcriptional coactivators p300 and PCAF displays different requirements for acetyltransferase activity

Normal skeletal muscle development requires the proper orchestration of genetic programs by myogenic regulatory factors (MRFs). The actions of the MRF protein MyoD are enhanced by the transcriptional coactivators p300 and the p300/CBP-associated factor (PCAF). We previously described C2 skeletal myoblasts lacking expression of insulin-like growth factor-II (IGF-II) that underwent progressive apoptotic death when incubated in differentiation-promoting medium. Viability of these cells was sustained by addition of IGF analogs or unrelated peptide growth factors. We now show that p300 or PCAF maintains myoblast viability as effectively as added growth factors through mechanisms requiring the acetyltransferase activity of PCAF but not of p300. The actions of p300 to promote cell survival were not secondary to increased expression of known MyoD targets, as evidenced by results of gene microarray experiments, but rather appeared to be mediated by induction of other genes, including fibroblast growth factor-1 (FGF-1). Conditioned culture medium from cells expressing p300 increased myoblast viability, and this was blocked by pharmacological inhibition of FGF receptors. Our results define a role for p300 in promoting cell survival, which is independent of its acetyltransferase activity and acts at least in part through FGF-1.

Absence of p300 induces cellular phenotypic changes characteristic of epithelial to mesenchyme transition

p300 is a transcriptional cofactor and prototype histone acetyltransferase involved in regulating multiple cellular processes. We generated p300 deficient (p300⁻) cells from the colon carcinoma cell line HCT116 by gene targeting. Comparison of epithelial and mesenchymal proteins in p300⁻ with parental HCT116 cells showed that a number of genes involved in cell and extracellular matrix interactions, typical of ‘epithelial to mesenchyme transition’ were differentially regulated at both the RNA and protein level. p300⁻ cells were found to have aggressive ‘cancer’ phenotypes, with loss of cell–cell adhesion, defects in cell–matrix adhesion and increased migration through collagen and matrigel. Although migration was shown to be metalloproteinase mediated, these cells actually showed a downregulation or no change in the level of key metalloproteinases, indicating that changes in cellular adhesion properties can be critical for cellular mobility.

GA-binding protein and p300 are essential components of a retinoic acid-induced enhanceosome in myeloid cells

Expression of CD18, the beta chain of the leukocyte integrins, is transcriptionally regulated by retinoic acid (RA) in myeloid cells. Full RA responsiveness of the CD18 gene requires its proximal promoter, which lacks a retinoic acid response element (RARE). Rather, RA responsiveness of the CD18 proximal promoter requires ets sites that are bound by GA-binding protein (GABP). The transcriptional coactivator, p300, further increases CD18 RA responsiveness. We demonstrate that GABPalpha, the ets DNA-binding subunit of GABP, physically interacts with p300 in myeloid cells. This interaction involves the GABPalpha pointed domain (PNT) and identifies p300 as the first known interaction partner of GABPalpha PNT. Expression of the PNT domain, alone, disrupts the GABPalpha-p300 interaction and decreases the RA responsiveness of the CD18 proximal promoter. Chromatin immunoprecipitation and chromosome conformation capture demonstrate that, in the presence of RA, GABPalpha and p300 at the proximal promoter recruit retinoic acid receptor/retinoid X receptor from a distal RARE to form an enhanceosome. A dominant negative p300 construct disrupts enhanceosome formation and reduces the RA responsiveness of CD18. Thus, proteins on the CD18 proximal promoter recruit the distal RARE in the presence of RA. This is the first description of an RA-induced enhanceosome and demonstrates that GABP and p300 are essential components of CD18 RA responsiveness in myeloid cells.

Conditional knockout mice reveal distinct functions for the global transcriptional coactivators CBP and p300 in T-cell development

The global transcriptional coactivators CREB-binding protein (CBP) and the closely related p300 interact with over 312 proteins, making them among the most heavily connected hubs in the known mammalian protein-protein interactome. It is largely uncertain, however, if these interactions are important in specific cell lineages of adult animals, as homozygous null mutations in either CBP or p300 result in early embryonic lethality in mice. Here we describe a Cre/LoxP conditional p300 null allele (p300flox) that allows for the temporal and tissue-specific inactivation of p300. We used mice carrying p300flox and a CBP conditional knockout allele (CBPflox) in conjunction with an Lck-Cre transgene to delete CBP and p300 starting at the CD4- CD8- double-negative thymocyte stage of T-cell development. Loss of either p300 or CBP led to a decrease in CD4+ CD8+ double-positive thymocytes, but an increase in the percentage of CD8+ single-positive thymocytes seen in CBP mutant mice was not observed in p300 mutants. T cells completely lacking both CBP and p300 did not develop normally and were nonexistent or very rare in the periphery, however. T cells lacking CBP or p300 had reduced tumor necrosis factor alpha gene expression in response to phorbol ester and ionophore, while signal-responsive gene expression in CBP- or p300-deficient macrophages was largely intact. Thus, CBP and p300 each supply a surprising degree of redundant coactivation capacity in T cells and macrophages, although each gene has also unique properties in thymocyte development.

Peroxisome proliferator-activated receptor gamma suppresses proximal alpha1(I) collagen promoter via inhibition of p300-facilitated NF-I binding to DNA in hepatic stellate cells

Depletion of peroxisome proliferator-activated receptor gamma (PPARgamma) represents one of the key molecular changes that underlie transdifferentiation (activation) of hepatic stellate cells in the genesis of liver fibrosis (Miyahara, T., Schrum, L., Rippe, R., Xiong, S., Yee, H. F., Jr., Motomura, K., Anania, F. A., Willson, T. M., and Tsukamoto, H. (2000) J. Biol. Chem. 275, 35715-35722; Hazra, S., Xiong, S., Wang, J., Rippe, R. A., Krishna, V., Chatterjee, K., and Tsukamoto, H. (2004) J. Biol. Chem. 279, 11392-11401). In support of this notion, ectopic expression of PPARgamma suppresses hepatic stellate cells activation markers, most notably expression of alpha1(I) procollagen. However, the mechanisms underlying this antifibrotic effect are largely unknown. The present study utilized deletion-reporter gene constructs of proximal 2.2-kb alpha1(I) procollagen promoter to demonstrate that a region proximal to -133 bp is where PPARgamma exerts its inhibitory effect. Within this region, two DNase footprints with Sp1 and reverse CCAAT box sites exist. NF-I, but not CCAAT DNA-binding factor/NF-Y, binds to the proximal CCAAT box in hepatic stellate cells. A mutation of this site almost completely abrogates the promoter activity. NF-I mildly but independently stimulates the promoter activity and synergistically promotes Sp1-induced activity. PPARgamma inhibits NF-I binding to the most proximal footprint (-97/-85 bp) and inhibits its transactivity. The former effect is mediated by the ability of PPARgamma to inhibit p300-facilitated NF-I binding to DNA as demonstrated by chromatin immunoprecipitation assay.

Modification of the Stat1 SH2 Domain Broadly Improves Interferon Efficacy in Proportion to p300/CREB-binding Protein Coactivator Recruitment

A normal level of interferon (IFN) responsiveness via the Stat1 transcription factor is critical to the host, since decreased Stat1 signaling causes immune compromise and increased signaling is associated with inflammatory and neoplastic disease. Here we report how this balance may be influenced by novel alterations in the efficiency of Stat1 signaling. To enable disulfide-dependent and spontaneous formation of active Stat1 homodimer (as was done previously for Stat3), we engineered Stat1-CC with double-cysteine substitutions in the Src homology 2 (SH2)-homodimerization domain (at Ala-656 and Asn-658). In this case, however, mutant and wild-type Stat1 exhibited no difference inspontaneousdimerization. Moreover, Stat1-CC still required ligand-dependent Tyr-701 phosphorylation for function and exhibited hyperresponsiveness to IFN-beta (that depends on Stat1/Stat2 heterodimerization) as well as IFN-gamma (that depends on Stat1/Stat1 homodimerization). Hyperresponsivenss of Stat1-CC was accompanied by increased capacities for Tyr-701 phosphorylation and DNA binding, but these features were also found in a similarly substituted serine mutant (Stat1-SS) that showed no hyperresponsiveness to IFN-gamma. This finding raised the possibility that SH2 domain mutations also influence downstream transcriptional efficiency. Indeed, each of these mutations also enhanced recruitment of the normally rate-limiting p300/CREB-binding Protein (CBP) coactivator to the transcriptional complex in proportion to the level of IFN-driven transactivation and gene expression. Additional modifications indicated that the mutant residues in the SH2 domain appeared to cooperate with Ser-727 in the C-terminal domain to regulate p300/CBP interaction with Stat1. The profile of IFN responsiveness translated into the same progressive increase in the level of viral clearance from Stat1- to Stat1-SS- to Stat1-CC-expressing cells. Thus, SH2 domain determinants may be modified to direct better Stat1 phosphorylation, DNA binding, and coactivator recruitment to fully improve IFN efficacy.

STAT1-Independent Down-Regulation of Interferon-Gamma-Induced Class II Transactivator and HLA-DR Expression by Transforming Growth Factor Beta-1 in Human Glomerular Endothelial Cells

BACKGROUND

The competition between STAT1 and Smad3 for a limiting amount of the nuclear protein p300, a transcriptional coactivator, was suggested to be a mechanism for the antagonism between interferon-gamma (IFN-gamma) and transforming growth factor-beta1 (TGF-beta1). We investigated the effect of TGF-beta1 on IFN-gamma-induced HLA-DR production in cultured human glomerular endothelial cells (HGECs), and the involvement of p300 in this process.

METHODS

Cell surface expression of HLA-DR and mRNA levels of HLA-DR and class II transactivator (CIITA), the master regulator of HLA-DR gene transcription, were measured by cellular ELISA and Northern blot, respectively. The levels of STAT1 and Smad3 protein were analyzed by Western blot. Nuclear binding activity of STAT1 was assessed by electrophoretic mobility shift assay.

RESULTS

IFN-gamma increased the cell surface expression of HLA-DR along with increases in the mRNA levels of CIITA and HLA-DR, while these stimulatory effects of IFN-gamma were down-regulated by TGF-beta1. IFN-gamma increased phosphorylation of STAT1 and this activation was not inhibited by TGF-beta1. IFN-gamma increased binding of p-STAT1 to p300, while TGF-beta1 increased binding of Smad3 to p300. TGF-beta1-induced Smad3 binding to p300 was inhibited by IFN-gamma, whereas IFN-gamma-induced p-STAT1 binding to p300 was not inhibited by TGF-beta1. IFN-gamma increased DNA binding activity of STAT1. Inhibition of interaction between STAT1 and p300 by addition of anti-p300 antibody to nuclear extract down-regulated DNA binding activity of STAT1. In contrast, TGF-beta1 did not inhibit IFN-gamma-induced STAT1 binding to DNA.

CONCLUSIONS

TGF-beta1 down-regulated IFN-gamma-induced CIITA and HLA-DR expression in HGECs. Though there was an antagonism between IFN-gamma and TGF-beta1, the competition for p300 between p-STAT1 and Smad3 was not the mechanism for it.