Regulation of the human involucrin gene promoter by co-activator proteins

Identifying novel interactions of the colon-cancer related APC protein with Wnt-pathway nuclear transcription factors

BACKGROUND

Colon cancer is often driven by mutations of the adenomatous polyposis coli (APC) gene, an essential tumor suppressor gene of the Wnt β-catenin signaling pathway. APC and its cytoplasmic interactions have been well studied. However, various groups have also observed its presence in the nucleus. Identifying novel interactions of APC in the Wnt pathway will provide an opportunity to understand APC's nuclear role better and ultimately identify potential cancer treatment targets.

METHODS

We used the all-vs-all sequencing (AVA-Seq) method to interrogate the interactome of protein fragments spanning most of the 60 Wnt β-catenin pathway proteins. Using protein fragments identified the interacting regions between the proteins with more resolution than a full-length protein approach. Pull-down assays were used to validate a subset of these interactions.

RESULTS

74 known and 703 novel Wnt β-catenin pathway protein-protein interactions were recovered in this study. There were 8 known and 31 novel APC protein-protein interactions. Novel interactions of APC and nuclear transcription factors TCF7, JUN, FOSL1, and SOX17 were particularly interesting and confirmed in validation assays.

CONCLUSION

Based on our findings of novel interactions between APC and transcription factors and previous evidence of APC localizing to the nucleus, we suggest APC may compete and repress CTNNB1. This would occur through APC binding to the transcription factors (JUN, FOSL1, TCF7) to regulate the Wnt signaling pathway including through enhanced marking of CTNNB1 for degradation in the nucleus by APC binding with SOX17. Additional novel Wnt β-catenin pathway protein-protein interactions from this study could lead researchers to novel drug designs for cancer.

Interleukin-4 Downregulation of Involucrin Expression in Human Epidermal Keratinocytes Involves Stat6 Sequestration of the Coactivator CREB-Binding Protein

Skin barrier defects play an important role in atopic dermatitis (AD). Involucrin, an important barrier protein suppressed in human AD, is downregulated by interleukin-4 (IL-4). However, the molecular mechanism for IL-4 downregulation of involucrin has not been delineated, and especially how Stat6, a transcriptional activator, represses involucrin expression is unknown. Since Stats usually recruit p300/CBP in the general transcription machinery of their target genes and involucrin expression also involves p300/CBP, we hypothesize that Stat6 activated by IL-4 may sequestrate p300/CBP from the involucrin transcription complex, thus suppressing involucrin expression in keratinocytes. Using IL-4 transgenic mice, an AD mouse model, we find that involucrin expression is similarly downregulated as in human AD. In HaCat cells, the Jak inhibitor and dominant negative studies indicate that the Jaks-Stat6 pathway is involved in IL-4 downregulation of involucrin. Next, we transfected HaCat cells with an involucrin promoter-luciferase construct and then treated them with IL-4. IL-4 greatly suppresses the promoter activity, which is totally abolished by cotransfecting the CREB-binding protein (CBP) expression vector, indicating that IL-4 cannot downregulate involucrin in the presence of excess CBP. Finally, chromatin immunoprecipitation assay demonstrates that IL-4 decreases CBP binding to the involucrin transcription complex. For the first time, we defined a molecular mechanism for IL-4 downregulation of involucrin in keratinocytes, which may play an important role in the pathogenesis of AD.

Construction and detection of the tissue-specific pINV-HPV16 E6/7 vector

A tissue-specific promoter can control downstream gene expression in tissues or organs. The human involucrin (hINV) promoter (pINV) that contains 2474 bp of hINV upstream sequence is able to regulate tissue-specific gene expression. This tissue specificity may be important for the prevention and treatment of human papilloma virus infections. pINV was cloned by polymerase chain reaction and the human papillomavirus (HPV)16 E6/7 gene was obtained from the cancer tissue samples of patients with cervical carcinoma at the Yangzhou Maternal and China Health-Care Center of Jinagsu Province (Yangzhou, China). First, specific primers were designed according to the genomic DNA sequence of the HPV16-type standard strain that has been reported and the E6/7 gene was acquired by PCR. The carcinogenic fraction of the E6/7 gene was removed and the remaining section was cloned into T vectors, sequenced correctly and then cloned into the eukaryotic expression vector pCEP4, which was lacking the CMV promoter. The positive recombinants were identified using blue-white screening and endonuclease digestion, subsequent to sequencing and analysis, and the tissue-specific recombinant pINV-HPV16E6/7 plasmids was detected.

Combinatorial recruitment of CREB, C/EBPβ and c-Jun determines activation of promoters upon keratinocyte differentiation

Background

Transcription factors CREB, C/EBPβ and Jun regulate genes involved in keratinocyte proliferation and differentiation. We questioned if specific combinations of CREB, C/EBPβ and c-Jun bound to promoters correlate with RNA polymerase II binding, mRNA transcript levels and methylation of promoters in proliferating and differentiating keratinocytes.

Results

Induction of mRNA and RNA polymerase II by differentiation is highest when promoters are bound by C/EBP β alone, C/EBPβ together with c-Jun, or by CREB, C/EBPβ and c-Jun, although in this case CREB binds with low affinity. In contrast, RNA polymerase II binding and mRNA levels change the least upon differentiation when promoters are bound by CREB either alone or in combination with C/EBPβ or c-Jun. Notably, promoters bound by CREB have relatively high levels of RNA polymerase II binding irrespective of differentiation. Inhibition of C/EBPβ or c-Jun preferentially represses mRNA when gene promoters are bound by corresponding transcription factors and not CREB. Methylated promoters have relatively low CREB binding and, accordingly, those which are bound by C/EBPβ are induced by differentiation irrespective of CREB. Composite “Half and Half” consensus motifs and co localizing consensus DNA binding motifs are overrepresented in promoters bound by the combination of corresponding transcription factors.

Conclusion

Correlational and functional data describes combinatorial mechanisms regulating the activation of promoters. Colocalization of C/EBPβ and c-Jun on promoters without strong CREB binding determines high probability of activation upon keratinocyte differentiation.

Effect of artemisinin combined with glucocorticoid on the expressions of glucocorticoid receptor α mRNA, glucocorticoid receptor β mRNA and P300/CBP protein in lupus nephritis mice

OBJECTIVE

To investigate the therapeutic effects and mechanisms of using artemisinin (Art) combined with glucocorticoid (GC) to treat lupus nephritis (LN) mice.

METHODS

Forty hybrid female mice were randomly and equally divided into four groups with the method of random number table: control group, model group, prednisone group administrated with 6.45 mg/(kg·d) prednisone suspension, and Art+prednisone group administrated with 150 mg/(kg·d) Art suspension and 3.225 mg/(kg·d) prednisone suspension. A mice model of LN was established by injection with living lymph cell suspension. The changes of urine protein/24h, the expressions of GC receptor α (GRα) mRNA, GC receptor β (GRβ) mRNA in peripheral blood mononuclear cells (PBMCs), and transcriptional coactivator P300/CBP protein in renal tissue were measured.

RESULTS

Compared with the model group, the treatment groups had significant decrease in urine protein/24 h, and renal pathological lesion (P<0.01). In the same groups, the expression of transcriptional coactivator P300/CBP protein in renal tissue and GRα mRNA were significantly increased, and GRβ mRNA expression was significantly decreased (P<0.01). And the Art+prednisone group has a better therapeutic effect than the prednisone group (P<0.01).

CONCLUSIONS

Art has therapeutic sensitization effects on GC in the LN mice. The underlying mechanism could be correlated with the effect of Art on the increase of the expressions of GRα mRNA and transcriptional coactivator P300 300/CBP protein in renal tissue and on the decrease of the expression of GRβ mRNA in PBMC.

Arsenite suppression of involucrin transcription through AP1 promoter sites in cultured human keratinocytes

While preserving keratinocyte proliferative ability, arsenite suppresses cellular differentiation markers by preventing utilization of AP1 transcriptional response elements. In present experiments, arsenite had a dramatic effect in electrophoretic mobility supershift analysis of proteins binding to an involucrin promoter AP1 response element. Without arsenite treatment, binding of JunB and Fra1 was readily detected in nuclear extracts from preconfluent cultures and was not detected a week after confluence, while c-Fos was detected only after confluence. By contrast, band shift of nuclear extracts from arsenite treated cultures showed only JunB and Fra1 binding in postconfluent as well as preconfluent cultures. Immunoblotting of cell extracts showed that arsenite treatment prevented the loss of Fra1 and the increase in c-Fos proteins that occurred after confluence in untreated cultures. Chromatin immunoprecipitation assays demonstrated substantial reduction of c-Fos and acetylated histone H3 at the proximal and distal AP1 response elements in the involucrin promoter and of coactivator p300 at the proximal element. Alteration of AP1 transcription factors was also examined in response to treatment with four metal containing compounds (chromate, vanadate, hemin, divalent cadmium) that also suppress involucrin transcription. These agents all influenced transcription at AP1 elements in a transcriptional reporter assay, but exhibited less effect than arsenite on binding activity assessed by mobility shift and chromatin immunoprecipitation and displayed variable effects on AP1 protein levels. These findings help trace a mechanism by which transcriptional effects of arsenite become manifest and help rationalize the unique action of arsenite, compared to the other agents, to preserve proliferative ability.

Extracellular signals regulate rapid coactivator recruitment at AP-1 sites by altered phosphorylation of both CREB binding protein and c-jun

Retinoic acid (RA) inhibits matrix metalloproteinase 9 (MMP-9) expression due to AP-1 inhibition resulting from retinoic acid receptors (RARs) competing for limiting amounts of coactivator proteins. However, given the rapid kinetics of MMP-9 transcription, it seems unlikely that these interactions can be explained passively. Our previous studies indicated that coactivator and transcription factor phosphorylation may allow for rapid regulation of MMP-9 expression. In the present study we tested this hypothesis directly. CREB binding protein (CBP) and p300/CBP-associated factor (PCAF) were displaced from transcription factor binding sites on the MMP-9 promoter within minutes of RA treatment. The RAR interaction domains of CBP and PCAF were not required for this displacement. RA and epidermal growth factor had opposing effects on phosphorylation of CBP by extracellular signal-regulated kinase 1 that correlated with altered CBP occupancy of AP-1 sites and differential MMP-9 promoter activation. We identified a novel phosphorylation site in the CBP carboxyl terminus that mediated association with AP-1 sites in the MMP-9 promoter. Inhibition of c-jun phosphorylation displaced PCAF from AP-1 sites and reduced promoter activity. Phosphorylation deficient c-jun was less able to recruit PCAF to AP-1 sites. We also demonstrated novel interactions between coactivators and AP-1 proteins. We propose that extracellular signal-mediated coactivator exchange at AP-1 sites is mediated via protein kinase pathways.

Phosphorylation of the human retinoid X receptor alpha at serine 260 impairs coactivator(s) recruitment and induces hormone resistance to multiple ligands

The retinoid X receptor alpha (RXRalpha) is a member of the nuclear receptor superfamily that regulates transcription of target genes through heterodimerization with several partners, including peroxisome proliferator-activated receptor, retinoic acid receptor, thyroid receptor, and vitamin D receptor (VDR). We have shown previously that signaling through VDR.RXRalpha heterodimers was attenuated in ras-transformed keratinocytes due to phosphorylation of serine 260 of the RXRalpha via the activated Ras-Raf-MAPK cascade in these cells. In this study we demonstrate that phosphorylation at serine 260, a site located in the omega loop-AF-2 interacting domain of RXRalpha, inhibits signaling through several heterodimeric partners of the RXRalpha. The inhibition of signaling results in reduced transactivational response to ligand presentation and the reduced physiological response of growth inhibition not only of 1,25-dihydroxyvitamin D3 but also of retinoic acid receptor alpha ligands and LG1069 (an RXRalpha ligand). This partial resistance to ligands could be reversed by inhibition of MAPK activity or by overexpression of a non-phosphorylable RXRalpha mutant at serine 260 (RXRalpha Ser-260-->Ala). Importantly, phosphorylation of RXRalpha at serine 260 impaired the recruitment of DRIP205 and other coactivators to the VDR.RXRalpha complex. Chromatin immunoprecipitation and pulldown assays further demonstrated that coactivator recruitment to the VDR.RXR complex could be restored by treatment with a MAPK inhibitor. Our data suggest that phosphorylation at serine 260 plays a critical role in inducing hormone resistance of RXRalpha-mediated signaling likely through structural changes in the H1-H3 omega loop-AF2 coactivator(s) interacting domain.

Synergistic activation of human involucrin gene expression by Fra-1 and p300--evidence for the presence of a multiprotein complex

Involucrin is expressed in the differentiated suprabasal epidermal layers, and an AP1 transcription factor-binding site present in the involucrin promoter distal regulatory region is required for this regulation. This site binds Fra-1, but cofactor interaction at this site has not been adequately characterized. We show that Fra-1 and p300 histone acetyltransferase are present at the AP1 site, as detected by chromatin immunoprecipitation. This interaction is functional, as treating p300 expressing keratinocytes with calcium or 12-O-tetradeconylphorbol-13-acetate, results in a synergistic increase in hINV expression, and this enhanced activation can be reproduced by coexpression of Fra-1 and p300. p300 also co-precipitates with Fra-1, but protein fractionation studies suggest that this interaction requires an additional protein. Fra-1 also interacts with other proteins that interact at the AP1-5 site, including JunD, JunB, Sp1, and P/CAF. Contrary to results in some other systems, Fra-1 functions as a positive transcriptional regulator in human keratinocytes. These studies suggest that a large multiprotein complex, which includes Fra-1, p300, P/CAF, junD, junB, and Sp1 acts at the AP1-5 site to produce a synergistic increase in hINV gene expression.

The p38α/β Mitogen-activated Protein Kinases Mediate Recruitment of CREB-binding Protein to Preserve Fast Myosin Heavy Chain IId/x Gene Activity in Myotubes

In skeletal muscle, the transformation of fast into slow fiber type is accompanied by shifts in fiber type-specific gene expression that includes down-regulation of the adult fast fiber myosin heavy chain IId/x (MyHCIId/x) gene. Here, we report that the mitogen-activated protein kinases (MAPKs) p38alpha/beta regulate MyHCIId/x gene expression. Electrical stimulation of rabbit skeletal muscle cells with a slow fiber type activity pattern and treatment of C2C12 myotubes with Ca(2+)-ionophore inhibited p38alpha/beta MAPKs and reduced fast fiber type MyHC protein expression and promoter activity. Pharmacological inhibition of p38alpha/beta also down-regulated MyHCII gene expression. In controls, binding of the myocyte enhancer factor-2 (MEF-2) isoforms C and D as a heterodimer to a proximal consensus site within the MyHCIId/x promoter and recruitment of a transcriptional coactivator, the CREB-binding protein CBP, were observed. Overexpression of wild type MEF-2C but not of a MEF-2C mutant that cannot be phosphorylated by p38 induced promoter activity. Mutation of the MEF-2-binding site decreased the inducing effect of overexpressed CBP. Inhibition of p38alpha/beta MAPKs abolished CBP binding, whereas enforced induction of p38 by activated MAPK kinase 6 (MKK6EE) enhanced binding of CBP and increased promoter activity. Furthermore, knockdown of endogenous CBP by RNA interference eliminated promoter activation by MEF-2C or MKK6EE. In electrical stimulated and Ca(2+)-ionophore-treated myotubes, CBP was absent in complex formation at that site. Taken together, the data indicate that p38alpha/beta MAPKs-mediated coactivator recruitment at a proximal MEF-2 site is important for MyHCIId/x gene regulation in skeletal muscle.

Two major 5'-untranslated regions for type XVII collagen mRNA

BACKGROUND

Type XVII collagen is an important structural component of keratinocyte hemidesmosomes and its functional loss in genetic or autoimmune disease results in blistering of the skin. In neoplastic tissue aberrant expression is seen dependent on the stage of the tumor. While the sequence of the type XVII collagen encoding gene -COL17A1 - is now completely elucidated, the sequence of the 5'-untranslated region (UTR) of the mRNA is still unknown. Since UTRs can modulate translation efficiency, the determination of the UTR sequence is indispensable for understanding the regulation of translation of type XVII collagen mRNA.

OBJECTIVE

To resolve the sequence of the 5'UTR of type XVII collagen mRNA and to analyse the promoter region for transcription motifs.

METHODS

5' Rapid amplification of cDNA ends (RACE) followed by sequence analysis and ribonuclease protection assays (RPA) were performed.

RESULTS

RACE and sequence analysis revealed the presence of six different 5'UTRs for the type XVII collagen mRNA. The start points of these six transcripts differ but no alternative exons are used. The longest 5'UTR starts 220 nucleotides before the open reading frame, whereas the shortest UTR is only 89 nucleotides in length. RPA confirmed the RACE results and furthermore demonstrated that the 5'UTRs with lengths of 102 and 220 nucleotides are the two major transcripts. Transcription motif analysis of the 5' region of the COL17A gene demonstrated several binding sites for transcription factors including the Sp1 and activating protein-1 (AP-1) families.

CONCLUSION

Type XVII collagen mRNA is alternatively transcribed, which may result in complex regulation of type XVII collagen.

Regulation of ERK1 gene expression by coactivator proteins

RARs (retinoic acid receptors) mediate the effect of their ligand RA (retinoic acid) on gene expression. We previously showed that RA inhibited cellular proliferation in part by decreasing expression of the mitogen activated protein kinase ERK1 (extracellular signal regulated kinase 1). However, the mechanism by which RA regulates ERK1 expression is largely uncharacterized. The present study characterizes coactivator-mediated regulation of RA target gene expression by analysing ERK1 promoter activation. CBP (CREB-binding protein) and PCAF (p300/CBP associated factor) are transcriptional coactivators that interact with nuclear hormone receptors such as RARs. CBP and PCAF differentially regulated ERK1 expression in stable clones. CBP clones expressed higher ERK1 protein levels, proliferated faster in culture and were resistant to RA-mediated growth inhibition. PCAF clones expressed lower levels of ERK1 protein and cells grew more slowly than controls. CBP and PCAF regulation of the ERK1 promoter was dependent on two Sp1 (specificity protein 1) sites located between -86 and -115 bp. Immunoprecipitation and yeast two-hybrid analysis revealed that PCAF interacted with Sp1 via CBP. A putative p53 binding site at -360 bp functioned as a major repressor of ERK1 promoter activity even in the absence of exogenous p53 expression. CBP and PCAF occupancy of the proximal ERK1 promoter was dramatically decreased by RA treatment. PCAF mediated inhibition of ERK1 expression was due to decreased stability of the kinase mRNA. We conclude that CBP and PCAF coactivators mediate ERK1 gene expression at both the transcriptional and post-transcriptional level.