Tandem Sp1/Sp3 sites together with an Ets-1 site cooperate to mediate α11 integrin chain expression in mesenchymal cells

Decoding key cell sub-populations and molecular alterations in glioblastoma at recurrence by single-cell analysis

Glioblastoma (GBM) is the most frequent malignant brain tumor, the relapse of which is unavoidable following standard treatment. However, the effective treatment for recurrent GBM is lacking, necessitating the understanding of key mechanisms driving tumor recurrence and the identification of new targets for intervention. Here, we integrated single-cell RNA-sequencing data spanning 36 patient-matched primary and recurrent GBM (pGBM and rGBM) specimens, with 6 longitudinal GBM spatial transcriptomics to explore molecular alterations at recurrence, with each cell type characterized in parallel. Genes involved in extracellular matrix (ECM) organization are preferentially enriched in rGBM cells, and MAFK is highlighted as a potential regulator. Notably, we uncover a unique subpopulation of GBM cells that is much less detected in pGBM and highly expresses ECM and mesenchyme related genes, suggesting it may contribute to the molecular transition of rGBM. Further regulatory network analysis reveals that transcription factors, such as NFATC4 and activator protein 1 members, may function as hub regulators. All non-tumor cells alter their specific sets of genes as well and certain subgroups of myeloid cells appear to be physically associated with the mesenchyme-like GBM subpopulation. Altogether, our study provides new insights into the molecular understanding of GBM relapse and candidate targets for rGBM treatment.

The small-molecule protein ligand interface stabiliser E7820 induces differential cell line specific responses of integrin α2 expression

BACKGROUND

The mechanism of small-molecule stabilised protein-protein interactions is of growing interest in the pharmacological discovery process. A plethora of different substances including the aromatic sulphonamide E7820 have been identified to act by such a mechanism. The process of E7820 induced CAPERα degradation and the resultant transcriptional down regulation of integrin α2 expression has previously been described for a variety of different cell lines and been made responsible for E7820's antiangiogenic activity. Currently the application of E7820 in the treatment of various malignancies including pancreas carcinoma and breast cancer is being investigated in pre-clinical and clinical trials. It has been shown, that integrin α2 deficiency has beneficial effects on bone homeostasis in mice. To transfer E7820 treatment to bone-related pathologies, as non-healing fractures, osteoporosis and bone cancer might therefore be beneficial. However, at present no data is available on the effect of E7820 on osseous cells or skeletal malignancies.

METHODS

Pre-osteoblastic (MC3T3 and Saos-2) cells and endothelial (eEnd2 cells and HUVECs) cells, each of human and murine origin respectively, were investigated. Vitality assay with different concentrations of E7820 were performed. All consecutive experiments were done at a final concentration of 50 ng/ml E7820. The expression and production of integrin α2 and CAPERα were investigated by quantitative real-time PCR and western blotting. Expression of CAPERα splice forms was differentiated by semi-quantitiative reverse transcriptase PCR.

RESULTS

Here we present the first data showing that E7820 can increase integrin α2 expression in the pre-osteoblast MC3T3 cell line whilst also reproducing canonical E7820 activity in HUVECs. We show that the aberrant activity of E7820 in MC3T3 cells is likely due to differential activity of CAPERα at the integrin α2 promoter, rather than due to differential CAPERα degradation or differential expression of CAPERα spliceforms.

CONCLUSION

The results presented here indicate that E7820 may not be suitable to treat certain malignancies of musculoskeletal origin, due to the increase in integrin α2 expression it may induce. Further investigation of the differential functioning of CAPERα and the integrin α2 promoter in cells of various origin would however be necessary to more clearly differentiate between cell lines that will positively respond to E7820 from those that will not.

Generation of a novel mouse strain with fibroblast-specific expression of Cre recombinase

Cell-specific expression of genes offers the possibility to use their promoters to drive expression of Cre-recombinase, thereby allowing for detailed expression analysis using reporter gene systems, cell lineage tracing, conditional gene deletion, and cell ablation. In this context, current data suggest that the integrin α11 subunit has the potential to serve as a fibroblast biomarker in tissue regeneration and pathology, in particular in wound healing and in tissue- and tumor fibrosis. The mesenchyme-restricted expression pattern of integrin α11 thus prompted us to generate a novel ITGA11-driver Cre mouse strain using a ϕC31 integrase-mediated knock-in approach. In this transgenic mouse, the Cre recombinase is driven by regulatory promoter elements within the 3 kb segment of the human ITGA11 gene. β-Galactosidase staining of embryonic tissues obtained from a transgenic ITGA11-Cre mouse line crossed with Rosa 26R reporter mice (ITGA11-Cre;R26R) revealed ITGA11-driven Cre expression and activity in mesenchymal cells in a variety of mesenchymal tissues in a pattern reminiscent of endogenous α11 protein expression in mouse embryos. Interestingly, X-gal staining of mouse embryonic fibroblasts (MEFs) isolated from the ITGA11-Cre;R26R mice indicated heterogeneity in the MEF population. ITGA11-driven Cre activity was shown in approximately 60% of the MEFs, suggesting that the expression of integrin α11 could be exploited for isolation of different fibroblast populations. ITGA11-driven Cre expression was found to be low in adult mouse tissues but was induced in granulation tissue of excisional wounds and in fibrotic hearts following aortic banding. We predict that the ITGA11-Cre transgenic mouse strain described in this report will be a useful tool in matrix research for the deletion of genes in subsets of fibroblasts in the developing mouse and for determining the function of subsets of pro-fibrotic fibroblasts in tissue fibrosis and in different subsets of cancer-associated fibroblasts in the tumor microenvironment.

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A mouse strain with Cre-recombinase driven by the human integrin α11 promoter has been generated.

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Cre-recombinase expression in this strain has been characterized using the Rosa26R reporter mouse.

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ITGA11-Cre is restricted to fibroblast subsets in mouse embryos, skin wounds and fibrotic hearts.

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This Cre-driver strain will be a useful tool to study role fibroblasts in fibrosis and tumors.

Most of the tight positional conservation of transcription factor binding sites near the transcription start site reflects their co-localization within regulatory modules

Background

Transcription factors (TFs) form complexes that bind regulatory modules (RMs) within DNA, to control specific sets of genes. Some transcription factor binding sites (TFBSs) near the transcription start site (TSS) display tight positional preferences relative to the TSS. Furthermore, near the TSS, RMs can co-localize TFBSs with each other and the TSS. The proportion of TFBS positional preferences due to TFBS co-localization within RMs is unknown, however. ChIP experiments confirm co-localization of some TFBSs genome-wide, including near the TSS, but they typically examine only a few TFs at a time, using non-physiological conditions that can vary from lab to lab. In contrast, sequence analysis can examine many TFs uniformly and methodically, broadly surveying the co-localization of TFBSs with tight positional preferences relative to the TSS.

Results

Our statistics found 43 significant sets of human motifs in the JASPAR TF Database with positional preferences relative to the TSS, with 38 preferences tight (±5 bp). Each set of motifs corresponded to a gene group of 135 to 3304 genes, with 42/43 (98%) gene groups independently validated by DAVID, a gene ontology database, with FDR < 0.05. Motifs corresponding to two TFBSs in a RM should co-occur more than by chance alone, enriching the intersection of the gene groups corresponding to the two TFs. Thus, a gene-group intersection systematically enriched beyond chance alone provides evidence that the two TFs participate in an RM. Of the 903 = 43*42/2 intersections of the 43 significant gene groups, we found 768/903 (85%) pairs of gene groups with significantly enriched intersections, with 564/768 (73%) intersections independently validated by DAVID with FDR < 0.05. A user-friendly web site at http://go.usa.gov/3kjsH permits biologists to explore the interaction network of our TFBSs to identify candidate subunit RMs.

Conclusions

Gene duplication and convergent evolution within a genome provide obvious biological mechanisms for replicating an RM near the TSS that binds a particular TF subunit. Of all intersections of our 43 significant gene groups, 85% were significantly enriched, with 73% of the significant enrichments independently validated by gene ontology. The co-localization of TFBSs within RMs therefore likely explains much of the tight TFBS positional preferences near the TSS.

Electronic supplementary material

The online version of this article (doi:10.1186/s12859-016-1354-5) contains supplementary material, which is available to authorized users.

Glycated Collagen Induces α11 Integrin Expression Through TGF-β2 and Smad3

The adhesion of cardiac fibroblasts to the glycated collagen interstitium in diabetics is associated with de novo expression of the α11 integrin, myofibroblast formation and cardiac fibrosis. We examined how methylglyoxal-glycated collagen regulates α11 integrin expression. In cardiac fibroblasts plated on glycated collagen but not glycated fibronectin, there was markedly increased α11 integrin and α-smooth muscle actin expression. Compared with native collagen, binding of purified α11β1 integrin to glycated collagen was reduced by >fourfold, which was consistent with reduced fibroblast attachment to glycated collagen. Glycated collagen strongly enhanced the expression of TGF-β2 but not TGF-β1 or TGF-β3. The increased expression of TGF-β2 was inhibited by triple helical collagen peptides that mimic the α11β1 integrin binding site on type I collagen. In cardiac fibroblasts transfected with α11 integrin luciferase promoter constructs, glycated collagen activated the α11 integrin promoter. Analysis of α11 integrin promoter truncation mutants showed a novel Smad2/3 binding site located between -809 and -1300 nt that was required for promoter activation. We conclude that glycated collagen in the cardiac interstitium triggers an autocrine TGF-β2 signaling pathway that stimulates α11 integrin expression through Smad2/3 binding elements in the α11 integrin promoter, which is important for myofibroblast formation and fibrosis.

FGF2 Overrides TGFβ1-Driven Integrin ITGA11 Expression in Human Dermal Fibroblasts

Deposition of collagen-based extracellular matrix by fibroblasts during wound healing leads to scar formation--a typical outcome of the healing process in soft tissue wounds. The process can, however, be skewed in favor of tissue regeneration by manipulation of wound environment. Low oxygen conditions and supplementation with FGF2 provide extracellular cues that drive wound fibroblasts towards a pro-regenerative phenotype. Under these conditions, fibroblasts dramatically alter expression of many genes among which the most significantly deregulated are extracellular matrix and adhesion molecules. Here we investigate the mechanism of a collagen I binding integrin α11 (ITGA11) deregulation in response to low oxygen-mediated FGF2 effects in dermal fibroblasts. Using RT-PCR, qRT-PCR, Western blotting, and immunocytochemistry, we describe significant down-regulation of ITGA11. Decrease in ITGA11 is associated with its loss from focal adhesions. We show that loss of ITGA11 requires FGF2 induced ERK1/2 activity and in the presence of FGF2, ITGA11 expression cannot be rescued by TGFβ1, a potent activator of ITGA11. Our results indicate that FGF2 may be redirecting fibroblasts towards an anti-fibrotic phenotype by overriding TGFβ1 mediated ITGA11 expression.

Berberine represses DAXX gene transcription and induces cancer cell apoptosis

Death-domain-associated protein (DAXX) is a multifunctional protein that regulates a wide range of cellular signaling pathways for both cell survival and apoptosis. Regulation of DAXX gene expression remains largely obscure. We recently reported that berberine (BBR), a natural product derived from a plant used in Chinese herbal medicine, downregulates DAXX expression at the transcriptional level. Here, we further investigate the mechanisms underlying the transcriptional suppression of DAXX by BBR. By analyzing and mapping the putative DAXX gene promoter, we identified the core promoter region (from -161 to -1), which contains consensus sequences for the transcriptional factors Sp1 and Ets1. We confirmed that Sp1 and Ets1 bound to the core promoter region of DAXX and stimulated DAXX transcriptional activity. In contrast, BBR bound to the DAXX core promoter region and suppressed its transcriptional activity. Following studies demonstrated a possible mechanism that BBR inhibited the DAXX promoter activity through blocking or disrupting the association of Sp1 or Ets1 and their consensus sequences in the promoter. Downregulation of DAXX by BBR resulted in inhibition of MDM2 and subsequently, activation of p53, leading to cancer cell death. Our results reveal a novel possible mechanism: by competitively binding to the Sp1 and Ets1 consensus sequences, BBR inhibits the transcription of DAXX, thus inducing cancer cell apoptosis through a p53-dependent pathway.

Identification of an inhibitor of the EWS-FLI1 oncogenic transcription factor by high-throughput screening

BACKGROUND

Chromosomal translocations generating oncogenic transcription factors are the hallmark of a variety of tumors, including many sarcomas. Ewing sarcoma family of tumors (ESFTs) are characterized by the t(11;22)(q24;q12) translocation that generates the Ewing sarcoma breakpoint region 1 and Friend leukemia virus integration 1 (EWS-FLI1) fusion transcription factor responsible for the highly malignant phenotype of this tumor. Although continued expression of EWS-FLI1 is believed to be critical for ESFT cell survival, a clinically effective small-molecule inhibitor remains elusive likely because EWS-FLI1 is a transcription factor and therefore widely felt to be "undruggable."

METHODS

We developed a high-throughput screen to evaluate more than 50 000 compounds for inhibition of EWS-FLI1 activity in TC32 ESFT cells. We used a TC32 cell-based luciferase reporter screen using the EWS-FLI1 downstream target NR0B1 promoter and a gene signature secondary screen to sort and prioritize the compounds. We characterized the lead compound, mithramycin, based on its ability to inhibit EWS-FLI1 activity in vitro using microarray expression profiling, quantitative reverse transcription-polymerase chain reaction, and immunoblot analysis, and in vivo using immunohistochemistry. We studied the impact of this inhibition on cell viability in vitro and on tumor growth in ESFT xenograft models in vivo (n = 15-20 mice per group). All statistical tests were two-sided.

RESULTS

Mithramycin inhibited expression of EWS-FLI1 downstream targets at the mRNA and protein levels and decreased the growth of ESFT cells at half maximal inhibitory concentrations between 10 (95% confidence interval [CI] = 8 to 13 nM) and 15 nM (95% CI = 13 to 19 nM). Mithramycin suppressed the growth of two different ESFT xenograft tumors and prolonged the survival of ESFT xenograft-bearing mice by causing a decrease in mean tumor volume. For example, in the TC32 xenograft model, on day 15 of treatment, the mean tumor volume for the mithramycin-treated mice was approximately 3% of the tumor volume observed in the control mice (mithramycin vs control: 69 vs 2388 mm(3), difference = 2319 mm(3), 95% CI = 1766 to 2872 mm(3), P < .001).

CONCLUSION

Mithramycin inhibits EWS-FLI1 activity and demonstrates ESFT antitumor activity both in vitro and in vivo.

The fibroblast integrin alpha11beta1 is induced in a mechanosensitive manner involving activin A and regulates myofibroblast differentiation

Fibrotic tissue is characterized by an overabundance of myofibroblasts. Thus, understanding the factors that induce myofibroblast differentiation is paramount to preventing fibrotic healing. Previous studies have shown that mechanical stress derived from the integrin-mediated interaction between extracellular matrix and the cytoskeleton promotes myofibroblast differentiation. Integrin alpha11beta1 is a collagen receptor on fibroblasts. To determine whether alpha11beta1 can act as a mechanosensor to promote the myofibroblast phenotype, mouse embryonic fibroblasts and human corneal fibroblasts were utilized. We found that alpha11 mRNA and protein levels were up-regulated in mouse embryonic fibroblasts grown in attached three-dimensional collagen gels and conversely down-regulated in cells grown in floating gels. alpha11 up-regulation could be prevented by manually detaching the collagen gels or by cytochalasin D treatment. Furthermore, SB-431542, an inhibitor of signaling via ALK4, ALK5, and ALK7, prevented the up-regulation of alpha11 and the concomitant phosphorylation of Smad3 under attached conditions. In attached gels, TGF-beta1 was secreted in its inactive form but surprisingly not further activated, thus not influencing alpha11 regulation. However, inhibition of activin A attenuated the up-regulation of alpha11. To determine the role of alpha11 in myofibroblast differentiation, human corneal fibroblasts were transfected with small interfering RNA to alpha11, which decreased alpha-smooth muscle actin expression and myofibroblast differentiation. Our data suggest that alpha11beta1 is regulated by cell/matrix stress involving activin A and Smad3 and that alpha11beta1 regulates myofibroblast differentiation.

Scalp fibroblasts have a shared expression profile in monogenic craniosynostosis

Background

Craniosynostosis can be caused by both genetic and environmental factors, the relative contributions of which vary between patients. Genetic testing identifies a pathogenic mutation or chromosomal abnormality in ∼21% of cases, but it is likely that further causative mutations remain to be discovered.

Objective

To identify a shared signature of genetically determined craniosynostosis by comparing the expression patterns in three monogenic syndromes with a control group of patients with non-syndromic sagittal synostosis.

Methods

Fibroblasts from 10 individuals each with Apert syndrome (FGFR2 substitution S252W), Muenke syndrome (FGFR3 substitution P250R), Saethre–Chotzen syndrome (various mutations in TWIST1) and non-syndromic sagittal synostosis (no mutation detected) were cultured. The relative expression of ∼47 000 transcripts was quantified on Affymetrix arrays.

Results

435, 45 and 46 transcripts were identified in the Apert, Muenke and Saethre–Chotzen groups, respectively, that differed significantly from the controls. Forty-six of these transcripts were shared between two or more syndromes and, in all but one instance, showed the same direction of altered expression level compared with controls. Pathway analysis showed over-representation of the shared transcripts in core modules involving cell-to-cell communication and signal transduction. Individual samples from the Apert syndrome cases could be reliably distinguished from non-syndromic samples based on the gene expression profile, but this was not possible for samples from patients with Muenke and Saethre–Chotzen syndromes.

Conclusions

Common modules of altered gene expression shared by genetically distinct forms of craniosynostosis were identified. Although the expression profiles cannot currently be used to classify individual patients, this may be overcome by using more sensitive assays and sampling additional tissues.

A Role for α11β1 Integrin in the Human Periodontal Ligament

We previously demonstrated a role for α11β1 integrin in periodontal ligament (PDL)-driven tooth eruption in the mouse. To explore a possible role for α11β1 in the human periodontium, we have characterized the expression and function of α11 in human PDL tissue, in human PDL fibroblasts (hPDLF), and in human gingival fibroblasts (hGF). α11 expression was detected in PDL tissue, in hPDLF, and in hGF cells. Platelet-derived growth factor-BB and insulin-like growth factor II stimulated contraction of collagen lattices by both types of fibroblasts. α2 integrin blocking antibodies and the use of α11 siRNA demonstrated a role for both α2β1 and α11β1 in collagen lattice remodeling. Analysis of the proximal ITGA11 promoter from persons with chronic periodontal disease failed to reveal any polymorphism. Analysis of our data shows that α11β1 is a major collagen receptor on cultured human PDL cells and implies that it is also functionally important in the PDL in vivo.

Essential contribution of Ets-1 to constitutive Pim-3 expression in human pancreatic cancer cells

We previously demonstrated that the proto-oncogene Pim-3 with serine/threonine kinase activity was aberrantly expressed in cancer cells but not in the normal cells of the pancreas. In order to elucidate the molecular mechanism underlying aberrant Pim-3 expression in pancreatic cancer cells, we constructed luciferase expression vectors linked to 5'-flanking deletion mutants of the human Pim-3 gene and transfected human pancreatic cancer cells with the resultant vectors. The region up to -264 bp was essential for constitutive Pim-3 gene expression, and the mutation in the Ets-1 binding site (between -216 and -211 bp) reduced luciferase activities. Moreover, Ets-1 mRNA and protein were constitutively expressed together with Pim-3 in human pancreatic cancer cell lines. Chromatin immunoprecipitation assay demonstrated constitutive binding of Ets-1 to the 5'-flanking region of human Pim-3 gene between -249 and -183 bp. Pim-3 promoter activity and its protein expression were induced by transfection with wild type-Ets-1 and were reduced by transfection with dominant negative-Ets-1 or Ets-1 small-interfering RNA (siRNA). Furthermore, dominant negative-Ets-1 and Ets-1 siRNA reduced the amount of Bad phosphorylated at its Ser(112) and induced apoptosis, when they were transfected into human pancreatic cancer cells. Finally, Pim-3 cDNA transfection reversed Ets-1 siRNA-induced increase in apoptosis and decrease in Bad phosphorylation at its Ser(112). These observations would indicate that the transcription factor Ets-1 can induce aberrant Pim-3 expression and subsequently prevent apoptosis in human pancreatic cancer cells.

Transforming growth factor beta1 induces alphavbeta3 integrin expression in human lung fibroblasts via a beta3 integrin-, c-Src-, and p38 MAPK-dependent pathway

In response to transforming growth factor beta1 (TGFbeta) stimulation, fibroblasts modify their integrin repertoire and adhesive capabilities to certain extracellular matrix proteins. Although TGFbeta has been shown to increase the expression of specific alphav integrins, the mechanisms underlying this are unknown. In this study we demonstrate that TGFbeta1 increased both beta3 integrin subunit mRNA and protein levels as well as surface expression of alphavbeta3 in human lung fibroblasts. TGFbeta1-induced alphavbeta3 expression was strongly adhesion-dependent and associated with increased focal adhesion kinase and c-Src kinase phosphorylation. Inhibition of beta3 integrin activation by the Arg-Gly-Asp tripeptide motif-specific disintegrin echistatin or alphavbeta3 blocking antibody prevented the increase in beta3 but not beta5 integrin expression. In addition, echistatin inhibited TGFbeta1-induced p38 MAPK but not Smad3 activation. Furthermore, inhibition of the Src family kinases, but not focal adhesion kinase, completely abrogated TGFbeta1-induced expression of alphavbeta3 and p38 MAPK phosphorylation but not beta5 integrin expression and Smad3 activation. The TGFbeta1-induced alphavbeta3 expression was blocked by pharmacologic and genetic inhibition of p38 MAPK- but not Smad2/3-, Sp1-, ERK-, phosphatidylinositol 3-kinase, and NF-kappaB-dependent pathways. Our results demonstrate that TGFbeta1 induces alphavbeta3 integrin expression via a beta3 integrin-, c-Src-, and p38 MAPK-dependent pathway. These data identify a novel mechanism for TGFbeta1 signaling in human lung fibroblasts by which they may contribute to normal and pathological wound healing.

Poly-N-acetyl glucosamine nanofibers regulate endothelial cell movement and angiogenesis: dependency on integrin activation of Ets1

Poly-N-acetyl glucosamine (pGlcNAc) nanofiber-derived materials effectively achieve hemostasis during surgical procedures. Treatment of cutaneous wounds with pGlcNAc in a diabetic mouse animal model causes marked increases in cell proliferation and angiogenesis. We sought to understand the effect of the pGlcNAc fibers on primary endothelial cells (EC) in culture and found that pGlcNAc induces EC motility. Cell motility induced by pGlcNAc fibers is blocked by antibodies directed against alphaVbeta3 and alpha5beta1 integrins, both known to play important roles in the regulation of EC motility, in vitroand in vivo. pGlcNAc treatment activates mitogen-activated protein kinase and increases Ets1, vascular endothelial growth factor (VEGF) and interleukin 1 (IL-1) expression. pGlcNAc activity is not secondary to its induction of VEGF; inhibition of the VEGF receptor does not inhibit the pGlcNAc-induced expression of Ets1 nor does pGlcNAc cause the activation of VEGF receptor. Both dominant negative and RNA interference inhibition of Ets1 blocks pGlcNAc-induced EC motility. Antibody blockade of integrin results in the inhibition of pGlcNAc-induced Ets1 expression. These findings support the hypothesis that pGlcNAc fibers induce integrin activation which results in the regulation of EC motility and thus in angiogenesis via a pathway dependent on the Ets1 transcription factor and demonstrate that Ets1 is a downstream mediator of integrin activation.

Physiology and pathology of collagen receptors

Just before the transition from pre-genomic to the post-genomic era, the two latest members of the mammalian integrin family were identified. These integrins, which were named alpha10beta1 and alpha11beta1, are both collagen receptors and are related. Rather than being twins, they can be regarded as close cousins. They both belong to the subfamily of integrins that contain an I-domain in the alpha subunit. This domain is also the part that endows these integrins with the capacity to bind the GFOGER sequence in collagens. In the current review, we summarize and update the current knowledge about the in vitro and in vivo functions of these integrins.

Transcriptional regulation of the cyclin-dependent kinase inhibitor 1A (p21) gene by NFI in proliferating human cells

The cyclin-dependent kinase inhibitor 1A (CDKN1A), also known as p21 (WAF1/CIP1) modulates cell cycle, apoptosis, senescence and differentiation via specific protein-protein interactions with the cyclins, cyclin-dependent kinase (Cdk), and many others. Expression of the p21 gene is mainly regulated at the transcriptional level. By conducting both ligation-mediated PCR (LMPCR) and chromatin immunoprecipitation (ChIP) in vivo, we identified a functional target site for the transcription factor, nuclear factor I (NFI), in the basal promoter from the p21 gene. Transfection of recombinant constructs bearing mutations in the p21 NFI site demonstrated that NFI acts as a repressor of p21 gene expression in various types of cultured cells. Inhibition of NFI in human skin fibroblasts through RNAi considerably increased p21 promoter activity suggesting that NFI is a key repressor of p21 transcription. Over-expression of each of the four NFI isoforms in HCT116 cells established that each of them contribute to various extend to the repression of the p21 gene. Most of all, over-expression of NFI-B in doxorubicin, growth-arrested HCT116 increased the proportion of cells in the S-phase of the cell cycle whereas NFI-A and NFI-X reduced it, thereby establishing a role for NFI in the cell cycle dependent expression of p21.