E2F suppression and Sp1 overexpression are sufficient to induce the differentiation-specific marker, transglutaminase type 1, in a squamous cell carcinoma cell line

SP1‑mediated ADAMTS5 transcription promotes IL‑1β‑induced chondrocyte injury via Wnt/β‑catenin pathway in osteoarthritis

Osteoarthritis (OA) is a chronic disease that involves chondrocyte injury. ADAMTS5 has been confirmed to mediate chondrocyte injury and thus regulate OA progression, but its underlying molecular mechanisms remain unclear. In the present study, interleukin‑1β (IL‑1β)‑induced chondrocytes were used to mimic OA in vitro. Cell proliferation and apoptosis were assessed by MTT assay, EdU assay and flow cytometry, and protein levels of ADAMTS5, specificity protein 1 (SP1), matrix‑related markers and Wnt/β‑catenin pathway‑related markers were examined using western blotting. In addition, ELISA was performed to measure the concentrations of inflammation factors, and oxidative stress was evaluated by detecting SOD activity and MDA levels. The mRNA expression levels of ADAMTS5 and SP1 were determined by reverse transcription‑quantitative PCR, and the interaction between SP1 and ADAMTS5 was analyzed using a dual‑luciferase reporter assay and chromatin immunoprecipitation assay. IL‑1β suppressed proliferation, but promoted apoptosis, extracellular matrix degradation, inflammation and oxidative stress in chondrocytes. ADAMTS5 was upregulated in IL‑1β‑induced chondrocytes, and its knockdown alleviated IL‑1β‑induced chondrocyte injury. SP1 could bind to the ADAMTS5 promoter region to promote its transcription, and SP1 knockdown relieved IL‑1β‑induced chondrocyte injury by reducing ADAMTS5 expression. The SP1/ADAMTS5 axis activated the Wnt/β‑catenin pathway, and the Wnt/β‑catenin pathway agonist, SKL2001, reversed the protective effect of ADAMTS5 knockdown on chondrocyte injury induced by IL‑1β. To the best of our knowledge, the present study was the first to reveal the interaction between SP1 and ADAMTS5 in OA progression and indicated that the SP1/ADAMTS5 axis mediates OA progression by regulating the Wnt/β‑catenin pathway.

A Novel 10-Gene Signature Predicts Poor Prognosis in Low Grade Glioma

AIM

Low grade glioma (LGG) is a lethal brain cancer with relatively poor prognosis in young adults. Thus, this study was performed to develop novel molecular biomarkers to effectively predict the prognosis of LGG patients and finally guide treatment decisions.

METHODS

survival-related genes were determined by Kaplan-Meier survival analysis and multivariate Cox regression analysis using the expression and clinical data of 506 LGG patients from The Cancer Genome Atlas (TCGA) database and independently validated in a Chinese Glioma Genome Atlas (CGGA) dataset. A prognostic risk score was established based on a linear combination of 10 gene expression levels using the regression coefficients of the multivariate Cox regression models. GSEA was performed to analyze the altered signaling pathways between the high and low risk groups stratified by median risk score.

RESULTS

We identified a total of 1489 genes significantly correlated with patients' prognosis in LGG. The top 5 protective genes were DISP2, CKMT1B, AQP7, GPR162 and CHGB, the top 5 risk genes were SP1, EYA3, ZSCAN20, ITPRIPL1 and ZNF217 in LGG. The risk score was predictive of poor overall survival and relapse-free survival in LGG patients. Pathways of small cell lung cancer, pathways in cancer, chronic myeloid leukemia, colorectal cancer were the top 4 most enriched pathways in the high risk group. SP1, EYA3, ZSCAN20, ITPRIPL1, ZNF217 and GPR162 were significantly up-regulated, while DISP2, CKMT1B, AQP7 were down-regulated in 523 LGG tissues as compared to 1141 normal brain controls.

CONCLUSIONS

The 10-gene signature may become novel prognostic and diagnostic biomarkers to considerably improve the prognostic prediction in LGG.

Minimal essential region for krüppel-like factor 5 expression and the regulation by specificity protein 3-GC box binding

Krüppel-like factor 5 (KLF5) transcriptionally controls the proliferation-differentiation balance of epithelium and is overexpressed in carcinomas. Although genomic region modifying KLF5 expression is widespread in different types of cells, the region that commonly regulates basal expression of the genes across cell-types is uncertain. In this study we determined the minimal essential region for the expression and its regulatory transcription factors using oral carcinoma cells. A reporter assay defined a 186bp region downstream of the transcription start site and a cluster of six GC boxes (GC1-GC6) as the minimal essential region. Mutation in the GC1 or GC6 regions but not other GC boxes significantly decreased the reporter expression. The decrease by the GC1 mutation was reproduced in the 2kbp full-length promoter, but not by the GC6 mutation. Additionally, specificity proteins (Sp) that can be expressed in epithelial cells and bind GC box, Sp3 co-localized with KLF5 in oral epithelium and carcinomas and chromatin immunoprecipitation analyses showed Sp3 as the prime GC1-binding protein. Inhibition of Sp-GC box binding by mithramycin A and knockdown of Sp3 by the short interfering RNA decreased expression of the reporter gene and endogenous KLF5. These data demonstrate that a 186bp region is the minimal essential region and that Sp3-GC1 binding is essential to the basal expression of KLF5.

A novel E2F/sphingosine kinase 1 axis regulates anthracycline response in squamous cell carcinoma

PURPOSE

Head and neck squamous cell carcinomas (HNSCC) are frequently drug resistant and have a mortality rate of 45%. We have previously shown that E2F7 may contribute to drug resistance in SCC cells. However, the mechanism and pathways involved remain unknown.

EXPERIMENTAL DESIGN

We used transcriptomic profiling to identify candidate pathways that may contribute to E2F7-dependent resistance to anthracyclines. We then manipulated the activity/expression of the candidate pathway using overexpression, knockdown, and pharmacological inhibitors in in vitro and in vivo models of SCC to demonstrate causality. In addition, we examined the expression of E2F7 and a downstream effector in a tissue microarray (TMA) generated from HNSCC patient samples.

RESULTS

E2F7-deficient keratinocytes were selectively sensitive to doxorubicin and this was reversed by overexpressing E2F7. Transcriptomic profiling identified Sphingosine kinase 1 (Sphk1) as a potential mediator of E2F7-dependent drug resistance. Knockdown and overexpression studies revealed that Sphk1 was a downstream target of E2F7. TMA studies showed that E2F7 overexpression correlated with Sphk1 overexpression in human HNSCC. Moreover, inhibition of Sphk1 by shRNA or the Sphk1-specific inhibitor, SK1-I (BML-EI411), enhanced the sensitivity of SCC cells to doxorubicin in vitro and in vivo. Furthermore, E2F7-induced doxorubicin resistance was mediated via Sphk1-dependent activation of AKT in vitro and in vivo.

CONCLUSION

We identify a novel drugable pathway in which E2F7 directly increases the transcription and activity of the Sphk1/S1P axis resulting in activation of AKT and subsequent drug resistance. Collectively, this novel combinatorial therapy can potentially be trialed in humans using existing agents.

Differential regulation of MMPs by E2F1, Sp1 and NF-kappa B controls the small cell lung cancer invasive phenotype

Background

E2F1 transcription factor plays a vital role in the regulation of diverse cellular processes including cell proliferation, apoptosis, invasion and metastasis. E2F1 overexpression has been demonstrated in small cell lung cancer (SCLC), and extensive metastasis in early phase is the most important feature of SCLC. In this study, we investigated the involvement of E2F1 in the process of invasion and metastasis in SCLC by regulating the expression of matrix metalloproteinases (MMPs).

Methods

Immunohistochemistry was performed to evaluate the expression of E2F1 and MMPs in SCLC samples in a Chinese Han population. The impact of E2F1 on invasion and metastasis was observed by transwell and wound healing experiments with depletion of E2F1 by specific siRNA. The target genes regulated by E2F1 were identified by chromatin immunoprecipitation (ChIP)-to-sequence, and the expressions of target genes were detected by real time PCR and western blotting. The dual luciferase reporter system was performed to analyze the regulatory relationship between E2F1 and MMPs.

Results

E2F1 is an independent and adverse prognosis factor that is highly expressed in SCLC in a Chinese Han population. Knockdown of E2F1 by specific siRNA resulted in the downregulation of migration and invasion in SCLC. The expressions of MMP-9 and −16 in SCLC were higher than other MMPs, and their expressions were most significantly reduced after silencing E2F1. ChIP-to-sequence and promoter-based luciferase analysis demonstrated that E2F1 directly controlled MMP-16 expression via an E2F1 binding motif in the promoter. Although one E2F1 binding site was predicted in the MMP-9 promoter, luciferase analysis indicated that this binding site was not functionally required. Further study demonstrated that E2F1 transcriptionally controlled the expression of Sp1 and p65, which in turn enhanced the MMP-9 promoter activity in SCLC cells. The associations between E2F1, Sp1, p65, and MMP-9 were validated by immunohistochemistry staining in SCLC tumors.

Conclusions

E2F1 acts as a transcriptional activator for MMPs and directly enhances MMP transcription by binding to E2F1 binding sequences in the promoter, or indirectly activates MMPs through enhanced Sp1 and NF-kappa B as a consequence of E2F1 activation in SCLC.

Silver nanoparticles induce apoptosis through the toll-like receptor 2 pathway

OBJECTIVE

The objective of this study was to evaluate the effects of silver nanoparticles (AgNPs) on the Toll-like receptor 2 (TLR-2) pathway in cultured cells.

STUDY DESIGN

Human chondrocytes, periodontal ligament (PDL) cells, and SCC-9 cells (squamous cell carcinoma from the tongue) were cultured and subjected to cytotoxicity assays. To evaluate the effects of AgNPs on the TLR-2 pathway, TLR-2 small interfering (si) RNA or TLR-2 antibodies were applied to the chondrocytes, followed by the application of AgNPs.

RESULTS

AgNPs induced dose-dependent effects on the examined cell types in terms of both cytotoxicity and TLR-2 expression levels. AgNP-mediated apoptosis was reduced after treatment with TLR-2 siRNA in both PDL cells and chondrocytes. Furthermore, functional blocking of TLR-2 with anti-TLR2 antibodies inhibited AgNP-mediated cytotoxicity. AgNPs increased c-Jun phosphorylation, an effect that was reversed after treatment with TLR-2 siRNA.

CONCLUSIONS

The results indicate that AgNP-mediated apoptosis most likely occurs via the TLR-2 pathway.

Dysregulation of the repressive H3K27 trimethylation mark in head and neck squamous cell carcinoma contributes to dysregulated squamous differentiation

PURPOSE

Head and neck squamous cell carcinoma (HNSCC) is one of the most prevalent cancers diagnosed worldwide and is associated with a 5-year survival rate of 55%. EZH2, a component of the polycomb repressor complex 2, trimethylates H3K27 (H3K27me3), which has been shown to drive squamous differentiation in normal keratinocytes. This study determined whether inhibition of EZH2-mediated epigenetic silencing could induce differentiation or provide therapeutic benefit in HNSCC.

EXPERIMENTAL DESIGN

We determined the effects of inhibiting EZH2, by either RNA interference or pharmacologically, on HNSCC growth, viability, and differentiation in vitro. Xenografts of HNSCC cell lines were used to assess efficacy of 3-deazaneplanocin A (DZNep), an inhibitor of H3K27 trimethylation, in vivo.

RESULTS

EZH2 was highly expressed in HNSCC cell lines in vitro and tissue microarray analysis revealed high expression in (n = 59) in situ relative to normal oral epithelium (n = 12). Inhibition of EZH2 with siRNA could induce expression of differentiation genes in differentiation-refractory squamous cell carcinoma cell lines. Differentiation-refractory HNSCC cell lines displayed persistent H3K27me3 on the promoters of differentiation genes. DZNep caused cancer-cell-specific apoptosis in addition to a profound reduction in colony-forming efficiency and induction of some squamous differentiation genes. Furthermore, in vivo, DZNep attenuated tumor growth in two different xenograft models, caused intratumor inhibition of EZH2, and induction of differentiation genes in situ.

CONCLUSIONS

Collectively, these data suggest that aberrant differentiation in HNSCC may be attributed to epigenetic dysregulation and suggest that inhibition of PRC2-mediated gene repression may represent a potential therapeutic target.

Preclinical evaluation of dual PI3K-mTOR inhibitors and histone deacetylase inhibitors in head and neck squamous cell carcinoma

Background:

We examine the potential value of a series of clinically relevant PI3K-mTOR inhibitors alone, or in combination with histone deacetylase inhibitors, in a model of head and neck squamous cell carcinoma (HNSCC).

Methods:

Head and neck squamous cell carcinoma cell lines, human keratinocyte and HNSCC xenograft models were treated with histone deacetylase inhibitors (HDACIs) and new generation PI3K and dual PI3K-mTOR inhibitors either alone or in combination. Cell and tumour tissue viability and proliferation were then determined in vitro and in vivo.

Results:

Phosphatidylinositol-3-phosphate kinase, AKT and dual PI3K-mTOR inhibitors caused marked in vitro enhancement of cytotoxicity induced by HDACIs in HNSCC cancer cells. This effect correlates with AKT inhibition and is attenuated by expression of constitutively active AKT. Histone deacetylase inhibitor and phosphatidylinositol-3-phosphate kinase inhibitors (PI3KIs) inhibited tumour growth in xenograft models of HNSCC. Importantly, we observed intratumoural HDAC inhibition and PI3K inhibition as assessed by histone H3 acetylation status and phospho-AKT staining, respectively. However, we saw no evidence of improved efficacy with an HDACI/PI3KI combination.

Interpretation:

That PI3K and dual PI3K-mTOR inhibitors possess antitumour effect against HNSCC in vivo.

Apoptotic effect of Polygonum Cuspidatum in oral cancer cells through the regulation of specificity protein 1

OBJECTIVES

The aim of this study was to evaluate the growth inhibitory and apoptosis-inducing effects and mechanisms of Polygonum cuspidatum root in oral cancer cells.

MATERIALS AND METHODS

The testing materials were separated by normal-phase silica gel liquid chromatography. The effect of P. cuspidatum root on apoptotsis and its mechanism were performed using 3-(4,5-dimethylthiazol-20yl)-(3-carboxymethoxyphenyl)-2-(4-sulphophenyl)-2H-tetrazolium) (MTS) assay, western blot analysis, RT-PCR, promoter assay, and (4'-6-Diamidino-2-phenylindole) (DAPI) staining.

RESULTS

The methanol extract of P. cuspidatum (MEPC) inhibited the proliferation of oral cancer cells by inducing caspase-dependent apoptosis. Protein and mRNA expression levels and the transactivation of Specificity protein 1 (Sp1) were markedly decreased in KB cells treated with MEPC. Ethyl acetate fraction (EA) from MEPC was more potent than aqueous fraction (AQ) from MEPC to induce apoptosis. F2, F3, and F4 from EA differentially inhibited the growth of KB cells, and it depends on the amount of Emodin in F2, F3, and F4. Moreover, Emodin inhibited oral cancer cell growth and induced caspase-dependent apoptosis by decreasing Sp1. MEPC also decreased an apoptosis-related downstream target of Sp1 protein, survivin.

CONCLUSION

The results from this study strongly suggest that MEPC, its fraction, and Emodin may be potential bioactive materials to cause apoptosis mechanism via the down-regulation of Sp1 in oral cancer cells.

TALE homeodomain proteins regulate site-specific terminal differentiation, LCE genes and epidermal barrier

The epidermal barrier varies over the body surface to accommodate regional environmental stresses. Regional skin barrier variation is produced by site-dependent epidermal differentiation from common keratinocyte precursors and often manifests as site-specific skin disease or irritation. There is strong evidence for body-site-dependent dermal programming of epidermal differentiation in which the epidermis responds by altering expression of key barrier proteins, but the underlying mechanisms have not been defined. The LCE multigene cluster encodes barrier proteins that are differentially expressed over the body surface, and perturbation of LCE cluster expression is linked to the common regional skin disease psoriasis. LCE subclusters comprise genes expressed variably in either external barrier-forming epithelia (e.g. skin) or in internal epithelia with less stringent barriers (e.g. tongue). We demonstrate here that a complex of TALE homeobox transcription factors PBX1, PBX2 and Pknox (homologues of Drosophila Extradenticle and Homothorax) preferentially regulate external rather than internal LCE gene expression, competitively binding with SP1 and SP3. Perturbation of TALE protein expression in stratified squamous epithelia in mice produces external but not internal barrier abnormalities. We conclude that epidermal barrier genes, such as the LCE multigene cluster, are regulated by TALE homeodomain transcription factors to produce regional epidermal barriers.

Loss of E2F7 expression is an early event in squamous differentiation and causes derepression of the key differentiation activator Sp1

Squamous differentiation is controlled by key transcription factors such as Sp1 and E2F. We have previously shown that E2F1 can suppress transcription of the differentiation-specific gene, transglutaminase type 1 (TG1), by an indirect mechanism mediated by Sp1. Transient transfection of E2F1-E2F6 indicated that E2F-mediated reduction of Sp1 transcription was not responsible for E2F-mediated suppression of squamous differentiation. However, we found that E2F4 and E2F7, but not E2Fs 1, 2, 3, 5, or 6, could suppress the activation of the Sp1 promoter in differentiated keratinocytes (KCs). E2F4-mediated suppression could not be antagonized by E2Fs 1, 2, 3, 5, or 6 and was localized to a region of the human Sp1 promoter spanning -139 to + 35 bp. Chromatin immunoprecipitation analysis, as well as transient overexpression and short hairpin RNA knockdown experiments indicate that E2F7 binds to a unique binding site located between -139 and -119 bp of the Sp1 promoter, and knockdown of E2F7 in proliferating KCs leads to a derepression of Sp1 expression and the induction of TG1. In contrast, E2F4 knockdown in proliferating KCs did not alter Sp1 expression. These data indicate that loss of E2F7 during the initiation of differentiation leads to the derepression of Sp1 and subsequent transcription of differentiation-specific genes such as TG1.

E2F7 can regulate proliferation, differentiation, and apoptotic responses in human keratinocytes: implications for cutaneous squamous cell carcinoma formation

The E2F family of transcription factors plays a crucial role in the regulation of genes involved in cell proliferation, differentiation, and apoptosis. In keratinocytes, the inhibition of E2F is a key step in the control and initiation of squamous differentiation. Because the product of the recently identified E2F7a/E2F7b gene has been shown to repress E2F-regulated promoters, and to be abundant in skin, we examined its role in the epidermis. Our results indicate that E2F7b mRNA expression is selectively associated with proliferation-competent keratinocytes. Moreover, E2F7 was able to antagonize E2F1-induced proliferation and apoptosis. In contrast, although E2F7 was able to inhibit proliferation and initiate differentiation, it was unable to antagonize the differentiation suppression induced by E2F1. These data indicate that E2F7-mediated suppression of proliferation and apoptosis acts through E2F1-dependent pathways, whereas E2F7-induced differentiation acts through an E2F1-independent pathway. These data also suggest that proliferation, differentiation, and survival of primary human keratinocytes can be controlled by the relative ratio of E2F1 to E2F7. Because deregulated proliferation, differentiation, and apoptosis are hallmarks of cancer, we examined the expression levels of E2F1 and E2F7 in cutaneous squamous cell carcinomas (CSCC). We found that both genes were overexpressed in CSCCs compared with normal epidermis. Furthermore, inhibition of E2F7 in a SCC cell line sensitized the cells to UV-induced apoptosis and doxorubicin-induced apoptosis. Combined, these data suggest that the selected disruption of E2F1 and E2F7 in keratinocytes is likely to contribute to CSCC formation and may prove to be a viable therapeutic target.

Phosphorylation by c-Jun NH2-terminal kinase 1 regulates the stability of transcription factor Sp1 during mitosis

The transcription factor Sp1 is ubiquitously expressed in different cells and thereby regulates the expression of genes involved in many cellular processes. This study reveals that Sp1 was phosphorylated during the mitotic stage in three epithelial tumor cell lines and one glioma cell line. By using different kinase inhibitors, we found that during mitosis in HeLa cells, the c-Jun NH(2)-terminal kinase (JNK) 1 was activated that was then required for the phosphorylation of Sp1. In addition, blockade of the Sp1 phosphorylation via inhibition JNK1 activity in mitosis resulted in the ubiquitination and degradation of Sp1. JNK1 phosphorylated Sp1 at Thr278/739. The Sp1 mutated at Thr278/739 was unstable during mitosis, possessing less transcriptional activity for the 12(S)-lipoxygenase expression and exhibiting a decreased cell growth rate compared with wild-type Sp1 in HeLa cells. In N-methyl-N-nitrosourea-induced mammary tumors, JNK1 activation provided a potential relevance with the accumulation of Sp1. Together, our results indicate that JNK1 activation is necessary to phosphorylate Sp1 and to shield Sp1 from the ubiquitin-dependent degradation pathway during mitosis in tumor cell lines.

Role of Sp1 in Transcription of Human ATP2A2 Gene in Keratinocytes

The ATP2A2 gene encodes Ca2+-dependent ATPase, the dysfunction of which causes Darier disease. In this study, we analyzed the promoter structure of the human ATP2A2 gene using primary normal human keratinocytes (NHK). Reporter assays showed that deletion of -550/-529, -488/-472, -390/-362, or -42/-21 resulted in a significant decrease in human ATP2A2 promoter activity. Electrophoretic mobility shift assay (EMSA) showed that Sp1 is a transcription factor that binds to the -550/-529 and -488/-472 regions of the promoter. Chromatin immunoprecipitation (ChIP) assay demonstrated that Sp1, but not Sp3, binds to the promoter region of the ATP2A2 gene in NHK cells in vivo. Knockdown of Sp1 expression by small interfering RNA resulted in a marked reduction in ATP2A2 promoter activity and ATP2A2 mRNA levels in NHK, suggesting that Sp1 positively transactivates the ATP2A2 promoter in NHK. This is early evidence demonstrating that Sp1 plays an important and positive role in ATP2A2 gene expression in NHK in vivo and in vitro.

Indole-3-carbinol - induced growth inhibition can be converted to a cytotoxic response in the presence of TPA+Ca(2+) in squamous cell carcinoma cell lines

We examined the possibility that I3C, when combined with a differentiation stimulus (TPA+CaCl(2)), would sensitise SCC cells to a differentiation stimulus. We report that I3C induces a profound growth inhibition in SCC cells that is dissimilar to the growth inhibition required to initiate differentiation. Moreover, we report that I3C, when combined with TPA+CaCl(2) treatment, induces a loss of colony forming ability that was differentiation and senescence - independent but was due to delayed cytotoxicity. This study shows that I3C in combination with a PKC activator+Ca(2+) may be a useful therapeutic strategy for treating oral SCC.

Inactivation of glutathione peroxidase activity contributes to UV-induced squamous cell carcinoma formation

Cutaneous squamous cell carcinomas (CSCC) are a common malignancy of keratinocytes that arise in sites of the skin exposed to excessive UV radiation. In the present study, we show that human SCC cell lines, preneoplastic solar keratoses (SK), and CSCC are associated with perturbations in glutathione peroxidase (GPX) activity and peroxide levels. Specifically, we found that two of three SKs and four of five CSCCs, in vivo, were associated with decreased GPX activity and all SKs and CSCCs were associated with an elevated peroxide burden. Given the association of decreased GPX activity with CSCC, we examined the basis for the GPX deficiency in the CSCCs. Our data indicated that GPX was inactivated by a post-translational mechanism and that GPX could be inactivated by increases in intracellular peroxide levels. We next tested whether the decreased peroxidase activity coupled with an elevated peroxidative burden might contribute to CSCC formation in vivo. This was tested in Gpx1(-/-) and Gpx2(-/-) mice exposed to solar-simulated UV radiation. These studies showed that Gpx2 deficiency predisposed mice to UV-induced CSCC formation. These results suggest that inactivation of GPX2 in human skin may be an early event in UV-induced SCC formation.

PMA stimulates MUC5B gene expression through an Sp1-based mechanism in airway epithelial cells

We previously showed that the MUC5B gene expression was elevated by phorbol 12-myristate 13-acetate (PMA) through an epidermal growth factor receptor-independent Ras/MEKK1/JNK and P38 signaling-based transcriptional mechanism. In the current study, we elucidated the molecular basis of this transcriptional regulation using promoter-reporter gene expression and chromatin immunoprecipitation (ChIP) assays with primary human bronchial epithelial cells that are cultured at the air-liquid interface. We have observed that PMA-induced MUC5B promoter activity is blocked by the Sp1-binding inhibitor, mithramycin A, in a dose-dependent manner. Deletion analysis with the MUC5B promoter construct demonstrated that both basal and PMA-induced promoter-reporter activities reside within the -222/-78 bp region relative to the transcriptional start site. NoShift transcriptional factor assays demonstrated that PMA stimulated Sp1 binding, but not STAT1 and c-Myc binding. Immunoprecipitation studies also verified the enhanced phosphorylation of Sp1 after PMA treatment. Site-directed mutagenesis and transfection studies demonstrated the involvement of Sp1-1 (-122/-114) and the Sp1-2 (-197/-186) cis elements in the basal and PMA-induced MUC5B promoter activity. The ChIP assay with anti-RNA polymerase II reconfirmed the PMA-induced MUC5B promoter activity by showing enhanced RNA polymerase II-DNA complex containing putative MUC5B Sp1-1, Sp1-2, or Sp1-3 sites. However, the ChIP assay using anti-Sp1 antibody demonstrated that the PMA-stimulated binding is only at Sp1-2. These results suggested an Sp1-based transcriptional mechanism with Sp1-1 as the regulator of basal MUC5B promoter activity and Sp1-2 as the regulator of PMA-induced MUC5B gene expression in the human airway epithelial cells.

The modification of Sp3 isoforms by SUMOylation has differential effects on the SRC1A promoter

Previously, we had described a housekeeping like promoter that regulates expression of the SRC gene in many cell types. This promoter was found to be regulated by Sp1 and hnRNP-K. However, at that time we could find little evidence supporting a significant role for Sp3 in SRC activation. Interestingly, despite its first description some 12 years ago, a full length Sp3 clone has only recently been described. Previous mechanistic studies, including our own, employed a version of Sp3 that was significantly N-terminally truncated. In addition, several shorter Sp3 isoforms exist that result from internally initiated translation sites. To complicate matters further, all Sp3 isoforms can be modified by SUMO-1. Due to this newly emerging information few reports exist that systematically explore these various Sp3 isoforms (SUMOylated or not) and how they affect activity of specific mammalian promoters. We therefore undertook such a study to re-evaluate regulation of SRC by these various Sp3 isoforms. Using human and insect cells we found that the newly isolated full length version of Sp3 was only a weak to moderate activator of SRC. However, to our surprise, the more commonly used N-terminally truncated version of Sp3 was up to five times more active. We also found that mutations preventing SUMOylation of the shorter Sp3 isoforms were sufficient to convert them into potent transactivators of SRC. In contrast to other studies, however, we found that SUMOylation of full length Sp3 had little effect on its transcriptional properties. These results provide new insights into the complexity of Sp3 mediated transcription which appears to be highly dependent on the isoform bound, SUMOylation status and the promoter context.

Defining the regulatory elements in the proximal promoter of DeltaNp63 in keratinocytes: Potential roles for Sp1/Sp3, NF-Y, and p63

p63, a homolog of the tumor suppressor p53, plays an important role in the formation of stratified epithelium such as those in the epidermis of the skin. The p63 gene gives rise to multiple functionally distinct protein isoforms, including the DeltaNp63 class of isoforms, which lacks the N-terminal transactivation domain and is synthesized from an internal promoter. DeltaNp63 proteins are the predominant isoforms expressed in keratinocytes and are thought to be important for maintenance of the proliferative capacity of these cells. Here, we have examined the transcriptional control mechanisms that govern the expression DeltaNp63 in keratinocytes. We first performed DNase I hypersensitive site mapping and demonstrated that the promoter region of DeltaNp63 is in open chromatin state in keratinocytes. To identify the cis-elements that regulate DeltaNp63, we have performed transient transfection assays in keratinocytes with several DeltaNp63 promoter constructs. This identified a short evolutionarily conserved fragment that harbors most of the transcriptional activity of the DeltaNp63 promoter. Biochemical studies of this element have revealed critical roles for CCAAT-box-binding factor (CBF/NF-Y) and Sp1/Sp3 family of proteins. In addition, our data suggest that DeltaNp63 is recruited to and can activate its own promoter, possibly through protein-protein interactions, thus providing an auto-regulatory loop of self-regulation. These studies support the notion that unique and distinct pathways control the expression of individual p53 family members and their various isoforms.

Transcriptional regulation of the hypoxia inducible factor-2alpha (HIF-2alpha) gene during adipose differentiation in 3T3-L1 cells

Adipose differentiation is regulated by coordination of several signaling pathways and transcription factors. We recently showed that Hypoxia inducible factor-2alpha (HIF-2alpha) plays several supporting roles in adipose differentiation and adipocytes functions including regulation of glucose uptake followed by lipid synthesis. HIF-2alpha expression is increased during adipogenesis, indicating that its up-regulation is necessary for execution of adipogenesis and maintenance of mature adipocytes functions. Therefore, in this study, to understand the mechanism by which HIF-2alpha expression is induced during adipogenesis, we investigated the promoter activity of HIF-2alpha gene during adipogenesis in 3T3-L1 cells. A comparison of HIF-2alpha promoter activity between preadipocytes and adipocytes revealed that the sequence -478/-445 is the putative core element that contributes to differentiation-dependent up-regulation of HIF-2alpha promoter activity. Electrophoretic mobility shift assays showed the presence of the specific nuclear factor bound to the sequence -478/-445 in both preadipocytes and adipocytes. Computer analysis revealed that this element contains several Sp1/Sp3 binding sites. Indeed, the presence of Sp1/Sp3 consensus oligonucleotides diminished the formation of the complexes composed of the sequence -478/-445 and the nuclear factor. Furthermore, specific retarded bands were supershifted with anti-Sp1 or -Sp3 antibodies. Binding of Sp1 and Sp3 to this element was also confirmed by chromatin immunoprecipitation analysis. The element encompassing -478/-445 favors Sp3 in preadipocytes and Sp1 in adipocytes. Finally, the activity of -478/-445 was increased by Sp1 but decreased by Sp3. Consequently, these results suggest that Sp1 and Sp3 are involved in transcriptional regulation of HIF-2alpha expression during adipogenesis in 3T3-L1 cells.

Master or slave: the complex relationship of RBP2 and pRb

The retinoblastoma protein or its regulators are altered in most human cancers. Although commonly thought of as solely a repressor of E2F-dependent transcription and cell cycle progression, pRb has gained notoriety in recent years as a key actor in cellular differentiation programs. In the June issue of Molecular Cell, Benevolenskaya et al. report that a long-known but poorly understood pRb interactor, RBP2, acts as an inhibitor of differentiation contributing to pRb's role as a coordinator of differentiation and cell cycle exit. Loss of pRb may unleash RBP2, maintaining cells in a poorly differentiated progenitor state that is prerequisite to tumor formation.