Transcriptional activation of the minimal human Proalpha1(I) collagen promoter: obligatory requirement for Sp1

IGF-I-induced VEGF expression in HUVEC involves phosphorylation and inhibition of poly(ADP-ribose)polymerase

Insulin-like growth factor-I (IGF-I) has been shown to promote angiogenesis by enhancing vascular endothelial growth factor (VEGF) expression. However, how IGF-I-induces VEGF expression is not yet fully understood. With this investigation, we propose a new possible mechanism involving downregulation of poly(ADP-ribosyl)ation (pADPR). We first demonstrated that IGF-I increased VEGF protein expression in endothelial cells. Inhibitors of mitogen activated kinase (PD 98059), phosphatidyl-3-inositol-kinase (LY 294002), and protein kinase C (staurosporine) diminished the IGF-I effect suggesting the involvement of signal transduction. Since there is an established link between pADPR and transcriptional activity, we focused on a possible role of poly(ADP-ribose)polymerase (PARP). The inhibition of PARP by 3-aminobenzamide or nicotinamide enhanced VEGF expression. Additionally, IGF-I markedly decreased PARP activity. Furthermore, the IGF-I-mediated inhibition of PARP could be demonstrated as a result of protein phosphorylation since phosphorylation of PARP decreased its activity in vitro and IGF-I treatment of endothelial cells induced PARP phosphorylation. The IGF-I-mediated phosphorylation and inhibition of PARP represent a novel mechanism of VEGF protein expression.

Inhibition of basal and transforming growth factor-beta-induced stimulation of COL1A1 transcription by the DNA intercalators, mitoxantrone and WP631, in cultured human dermal fibroblasts

The Sp1 transcription factor plays a crucial role in COL1A1 transcriptional regulation under normal and pathologic conditions and under the effects of transforming growth factor-beta (TGF-beta). Sp1 activity is elevated in numerous diseases characterized by tissue fibrosis. Therefore, inhibition of Sp1 binding to COL1A1 regulatory elements may represent an effective treatment for these diseases. Here we examined the effect of two DNA intercalators that prevent Sp1 binding on the expression of COL1A1 in human dermal fibroblasts. Cultured human adult dermal fibroblasts were treated with WP631 (50 pm/ml to 500 nm/ml) or mitoxantrone (5-500 nm/ml). Cytotoxicity, cellular apoptosis, and collagen deposition were examined by fluorescence microscopy. Collagen production was examined by enzyme-linked immunosorbent assay and metabolic labeling, COL1A1 steady-state mRNA levels, and stability were assessed by Northern hybridizations, and COL1A1 transcription by in vitro nuclear transcription assays and transient transfections. Competition of the drugs for Sp1 binding and their effect on TGF-beta-induced stimulation of COL1A1 transcription was also examined. Both drugs caused a dose-related inhibition of COL1A1 production and mRNA levels without cytotoxicity or apoptosis. COL1A1 transcriptional activity showed a profound reduction mediated by a short proximal promoter region containing an Sp1-binding element at -87 to -82 bp. Furthermore, both drugs inhibited Sp1 DNA complex formation and abrogated the stimulation of COL1A1 transcription induced by TGF-beta. WP631 showed 10-fold higher potency than mitoxantrone. These data indicate that mitoxantrone and WP631 are very potent inhibitors of basal and TGF-beta-stimulated COL1A1 expression and suggest that Sp1-DNA intercalators may be an effective and novel approach for the treatment of fibrotic diseases and modulation of profibrogenic effects of TGF-beta.

Down-regulation of procollagen alpha1[I]] messenger RNA by titanium particles correlates with nuclear factor kappaB (NF-kappaB) activation and increased rel A and NF-kappaB1 binding to the collagen promoter

Previously, we showed that exposure of human osteoblasts to titanium particles stimulates protein tyrosine phosphorylation (PTP), activates the transcription factor nuclear factor kappaB (NF-kappaB), and causes an approximately 50% decrease in the steady-state messenger RNA (mRNA) level of procollagen alpha1[I]. In this study, we identify three NF-kappaB binding sites within the human procollagen alpha1[I] gene promoter, show that titanium particles stimulate their binding of the NF-kappaB subunits Rel A (p65) and NF-kappaB1 (p50), and find NF-kappaB activation correlates with collagen gene suppression by titanium particles in osteoblasts. Protein tyrosine kinase (PTK) inhibitors, which significantly reduce the suppressive effect of titanium particles on collagen gene expression, inhibited NF-kappaB binding activity showing that titanium particle stimulation of PTK signals in osteoblasts are critical for both NF-kappaB activation and collagen gene expression. The antioxidant pyrrolidine dithiocarbamate (PDTC), which also inhibits the titanium particle suppression of collagen, abrogated the titanium particle activation of NF-kappaB, suggesting the involvement of redox signals in NF-kappaB-mediated collagen gene expression. The RNA polymerase II inhibitor actinomycin D (Act D) decreased procollagen alpha1[I] mRNA expression and effectively blocked the titanium-induced suppressive effect, suggesting that titanium particles activate a cascade of signals in osteoblasts, which result in a suppression of procollagen alpha1[I] mRNA. Collectively, these results show that titanium particles can activate NF-kappaB signaling in osteoblasts and suggest that NF-kappaB binding to the collagen gene promoter has a functional role in the down-regulation of procollagen alpha1[I] gene transcription.

Particulate wear debris activates protein tyrosine kinases and nuclear factor kappaB, which down-regulates type I collagen synthesis in human osteoblasts

Particulate wear debris generated mechanically from prosthetic materials is phagocytosed by a variety of cell types within the periprosthetic space including osteoblasts, which cells with an altered function may contribute to periprosthetic osteolysis. Exposure of osteoblast-like osteosarcoma cells or bone marrow-derived primary osteoblasts to either metallic or polymeric particles of phagocytosable sizes resulted in a marked decrease in the steady-state messenger RNA (mRNA) levels of procollagen alpha1[I] and procollagen alpha1[III]. In contrast, no significant effect was observed for the osteoblast-specific genes, such as osteonectin and osteocalcin (OC). In kinetic studies, particles once phagocytosed, maintained a significant suppressive effect on collagen gene expression and type I collagen synthesis for up to five passages. Large particles of a size that cannot be phagocytosed also down-regulated collagen gene expression suggesting that an initial contact between cells and particles can generate gene responsive signals independently of the phagocytosis process. Concerning such signaling, titanium particles rapidly increased protein tyrosine phosphorylation and nuclear transcription factor kappaB (NF-kappaB) binding activity before the phagocytosis of particles. Protein tyrosine kinase (PTK) inhibitors such as genistein and the NF-kappaB inhibitor pyrrolidine dithiocarbamate (PDTC) significantly reduced the suppressive effect of titanium on collagen gene expression suggesting particles suppress collagen gene expression through the NF-kappaB signaling pathway. These results provide a mechanism by which particulate wear debris can antagonize the transcription of the procollagen alpha1[I] gene in osteoblasts, which may contribute to reduced bone formation and progressive periprosthetic osteolysis.

Members of the Sp transcription factor family regulate rat calmodulin gene expression

We have previously demonstrated that insulin positively regulates transcription of the rat calmodulin (CaM) I gene and that both basal and insulin stimulation of this gene are critically dependent on Sp1. Furthermore, a 392 bp CaM promoter was stimulated by insulin equal to the full promoter but lost activity with deletion of any of the three Sp1 sites (Solomon SS, Palazzolo MR, Takahashi T, Raghow R. Endocrinology 1997;138:5052-5054). Herein we document that Sp1 preferentially binds to the upstream sites Sp1(2) and Sp1(3) but not Sp1(1). Furthermore, gel-mobility super-shift assays demonstrate that both Sp1 and Sp3 protein are found in these complexes. When pPac-Spl, pPac-Sp3, pPac-USp3, and pPac-Sp4 were cotransfected with rCaM 1-392 promoter into Drosophila SL2 cells and challenged with 10,000 microU/mL insulin, we discovered that (1) Sp1 enhanced both basal and insulin-stimulated CaM I gene expression; (2) USp3, a "long" form of the Sp3 molecule, had a stimulatory effect on CaM I gene expression; (3) Sp1 or USp3 is involved in mediating insulin-stimulation of the CaM I gene in SL2 cells; and (4) Sp3, a "short" form of the Sp3 molecule, and Sp4 inhibited Spl-stimulated and insulin-stimulated Sp1-mediated CaM I gene expression. Together these data corroborate and extend our previous observations on Sp1 and elucidate that other members of the Sp family of transcription factors may also be involved in regulating the activity of the CaM promoter.

Alterations in the regulation of expression of the alpha 1(I) collagen gene (COL1A1) in systemic sclerosis (scleroderma)

At present, the mechanisms that regulate the expression of collagen genes in normal and pathologic fibroblasts are not known. Thus, the detailed study of transcriptional regulation of COL1A1 in SSc cells will increase our current understanding of the pathophysiology of fibrotic diseases. These studies will yield valuable information regarding the important biological process of regulation of collagen gene expression under normal and pathologic conditions, a process that has remained elusive despite intense recent investigations. It is now evident that persistent overproduction of collagen is responsible for the progressive nature of tissue fibrosis in SSc. Up-regulation of collagen gene expression in SSc fibroblasts appears to be a critical event in this process. The coordinate transcriptional activation of numerous collagen genes suggests a fundamental alteration in the regulatory control of gene expression in SSc fibroblasts. Trans-acting nuclear factors which bind to cis-acting elements in enhancer (intronic) and promoter regions of the genes modulate the basal and inducible transcriptional activity of the collagen genes. The identification of the nuclear transcription factors that regulate normal collagen gene expression may provide promising approaches to the therapy of this incurable disease.

The molecular basis of glucocorticoid-induced skin atrophy: topical glucocorticoid apparently decreases both collagen synthesis and the corresponding collagen mRNA level in human skin in vivo

The effects of topical betamethasone-17-valerate on collagen propeptide levels, collagen mRNA level, lysyl oxidase mRNA and matrix metalloproteinase (MMP)-1 and MMP-2 mRNA levels were studied in human skin. Three days' treatment of healthy skin with topical betamethasone caused a 70-80% decrease in type I and III collagen propeptides in suction blister fluid. A similar decrease was found in type I collagen mRNA when assayed by either slot-blot hybridization or a quantitative polymerase chain reaction method, indicating that the decrease in collagen synthesis after topical glucocorticoid treatment is apparently due to a decrease in corresponding mRNA. mRNA of lysyl oxidase, which is an important enzyme catalysing the cross-linking of collagen chains, and collagen-degrading enzyme MMP-1 and MMP-2 mRNAs were not decreased in the same skin samples. This suggests that in vivo, glucocorticoids modulate variably the genes involved in collagen synthesis and degradation. Our study provides a solid molecular basis for glucocorticoid-induced dermal atrophy, which results from the decrease in functional collagen mRNA in the skin.

Modulation of human alpha1(I) procollagen gene activity by interaction with Sp1 and Sp3 transcription factors in vitro

In previous work, we delineated a proximal region of the human alpha1(I) collagen gene (COL1A1) promoter necessary to direct its basal transcription in fibroblasts. This region has potential recognition sites for a variety of DNA-binding proteins. Here, we show that the -129/-107-bp sequence in this region of the promoter, which harbors an inverted CCAAT motif closely linked to a GC-rich direct repeat and is perfectly conserved between mouse and human, specifically bound the transcription factors Sp1, Sp3, and CTF/NF-1 in nuclear extracts from human skin and lung fibroblasts. Drosophila Schneider L2 cells lacking endogenous Sp activity were used to investigate the effect of expression of Sp or CTF/NF-1 transcription factors on COLlAl promoter activity. Expression of Sp1 caused potent trans-activation of a COL1A1 promoter (-174 to +42bp). In contrast, expression of Sp3, which binds to the same recognition sites as Sp1, and CTF/NF-1 stimulated COL1A1 promoter activity only at higher concentrations, and Sp2 did not transactivate. Expression of a 10-fold excess of Sp3, but not CTF/NF-1 or Sp2, abrogated the stimulation of COL1A1 promoter activity induced by Sp1. TGF-beta at concentrations previously shown to increase COL1A1 transcription caused a decrease in the relative amount of Sp3 in fibroblast nuclear extracts. These results suggest that both Sp1 and Sp3 bind to the proximal COL1A1 promoter and stimulate its activity; however, their interaction with each other may result in repression of Sp1-induced COL1A1 transcription. Alterations in the relative amounts or DNA-binding activities of these transcription factors in a cell- or signal-specific manner may contribute to the control of transcription from the COL1A1 promoter. The present findings, and recent observations implicating Sp1 and its homologs in regulating the expression of several collagen genes, suggest that the family of Sp1 transcription factors play a role in physiological and pathological modulation of connective tissue accumulation.