Mapping of a transcription element critical for expression of the fibroblast growth factor receptor 1 gene

Regulation of fibroblast growth factor receptor-1 (FGFR1) by thyroid hormone: identification of a thyroid hormone response element in the murine Fgfr1 promoter

T(3) is essential for normal skeletal development, acting mainly via the TRalpha1 nuclear receptor. Nevertheless, the mechanisms of T(3) action in bone are poorly defined. Fibroblast growth factor receptor-1 (FGFR1) is also essential for bone formation. Fgfr1 expression and activity are positively regulated by T(3) in osteoblasts, and in mice that harbor a dominant negative PV mutation targeted to TRalpha1 or TRbeta, Fgfr1 expression is sensitive to skeletal thyroid status. To investigate mechanisms underlying T(3) regulation of FGFR1, we obtained primary calvarial osteoblasts from wild-type and TRbeta(PV/PV) littermate mice. T(3) treatment increased Fgfr1 expression 2-fold in wild-type cells, but 8-fold in TRbeta(PV/PV) osteoblasts. The 4-fold increased T(3) sensitivity of TRbeta(PV/PV) osteoblasts was associated with a markedly increased ratio of TRalpha1:TRbeta1 expression that resulted from reduced TRbeta1 expression in TRbeta(PV/PV) osteoblasts compared with wild-type. Bioinformatics and gel shift studies, and mutational analysis, identified a specific TR binding site 279-264 nucleotides upstream of the murine Fgfr1 promoter transcription start site. Transient transfection analysis of a series of Fgfr1 promoter 5'-deletion constructs, of a mutant reporter construct, and a series of heterologous promoter constructs, confirmed that this region of the promoter mediates a TR-dependent transcriptional response to T(3). Thus, in addition to indirect regulation of FGFR1 expression by T(3) reported previously, T(3) also activates the Fgfr1 promoter directly via a thyroid hormone response element located at positions -279/-264.

Mechanism of action in thalidomide teratogenesis

In this commentary, we describe a model to explain the mechanism of the embryopathy of thalidomide. We propose that thalidomide affects the following pathway during development: insulin-like growth factor I (IGF-I) and fibroblast growth factor 2 (FGF-2) stimulation of the transcription of alphav and beta3 integrin subunit genes. The resulting alphavbeta3 integrin dimer stimulates angiogenesis in the developing limb bud, which promotes outgrowth of the bud. The promoters of the IGF-I and FGF-2 genes, the genes for their binding proteins and receptors, as well as the alphav and beta3 genes, lack typical TATA boxes, but instead contain multiple GC boxes (GGGCGG). Thalidomide, or a breakdown product of thalidomide, specifically binds to these GC promoter sites, decreasing transcription efficiency of the associated genes. A cumulative decrease interferes with normal angiogenesis, which results in truncation of the limb. Intercalation into G-rich promoter regions of DNA may explain why certain thalidomide analogs are not teratogenic while retaining their anti-tumor necrosis factor-alpha (TNF-alpha) activity, and suggests that we look elsewhere to explain the action of thalidomide on TNF-alpha. On the other hand, the anti-cancer action of thalidomide may be based on its antiangiogenic action, resulting from specific DNA intercalation. The tissue specificity of thalidomide and its effect against only certain neoplasias may be explained by the fact that various developing tissues and neoplasias depend on different angiogenesis or vasculogenesis pathways, only some of which are thalidomide-sensitive.

IFN regulatory factor-1-mediated transcriptional activation of mouse STAT-induced STAT inhibitor-1 gene promoter by IFN-gamma

STAT-induced STAT inhibitor-1 (SSI-1), also referred to as suppressor of cytokine signaling-1 and JAK-binding protein, is a member of a new family, the members of which are negative regulators of cytokine signals. SSI-1 is induced by various cytokines; however, the transcriptional mechanism of the SSI-1 gene is not fully understood. Here, we showed that transcription of the mouse SSI-1 gene was initiated from six adjoining sites accompanying three GC boxes and a single GC box-like element near them, but not from the TATA box or an initiator sequence. We also showed that IFN-gamma induced SSI-1 mRNA more strongly than IL-6 in NIH-3T3 fibroblasts and that this IFN-gamma effect was mediated by Stat1. To determine the signal pathway downstream of Stat1, transcriptional activities of several mutant promoters were examined. The region mediating stimulatory effect of IFN-gamma to the gene transcription was localized to the -88/-60 region containing three tandem GAAA units, named variant IFN-gamma-responsive element (VIRE), while four IFN-gamma activation site (GAS)-like elements located far upstream were not related to the IFN-gamma response. Gel-shift assays revealed that IFN-gamma induced IFN regulatory factor-1 (IRF-1) binding to VIRE, but not that of IRF-2 or three components of ISGF3. Furthermore, forced expression of IRF-1 mimicked and that of IRF-2 inhibited the stimulatory effect of IFN-gamma on SSI-1 gene transcription. Finally, mouse embryonal fibroblasts lacking IRF-1 showed impaired SSI-1 mRNA induction by IFN-gamma. These results demonstrated that IRF-1, which is induced by activation of Stat1, mediated transcriptional activation of the SSI-1 gene by IFN-gamma via VIRE.

Fibroblast growth factors as multifunctional signaling factors

The fibroblast growth factor (FGF) family consists of at least 15 structurally related polypeptide growth factors. Their expression is controlled at the levels of transcription, mRNA stability, and translation. The bioavailability of FGFs is further modulated by posttranslational processing and regulated protein trafficking. FGFs bind to receptor tyrosine kinases (FGFRs), heparan sulfate proteoglycans (HSPG), and a cysteine-rich FGF receptor (CFR). FGFRs are required for most biological activities of FGFs. HSPGs alter FGF-FGFR interactions and CFR participates in FGF intracellular transport. FGF signaling pathways are intricate and are intertwined with insulin-like growth factor, transforming growth factor-beta, bone morphogenetic protein, and vertebrate homologs of Drosophila wingless activated pathways. FGFs are major regulators of embryonic development: They influence the formation of the primary body axis, neural axis, limbs, and other structures. The activities of FGFs depend on their coordination of fundamental cellular functions, such as survival, replication, differentiation, adhesion, and motility, through effects on gene expression and the cytoskeleton.

Molecular mechanism of androgen-dependent growth in transformed cells. Pathway from basic science to clinical application

Shionogi carcinoma 115 (SC 115) has been extensively used to analyze the mechanism of androgen-dependent cancer growth. This tumor exhibits marked androgen-dependent growth in vivo and one cell line whose growth is markedly stimulated by androgen in serum-free culture condition is isolated from SC 115 tumor. This androgen-dependent growth is mediated through an induction of heparin binding growth factor termed as androgen-induced growth factor (AIGF). In addition, fibroblast growth factor receptor 1 (FGFR 1) is identified as a receptor for AIGF. The expression of FGFR 1 mRNA is up-regulated by androgen in SC 115 cells, indicating that this androgen-inducible autocrine loop is potentiated at two sites by androgen. An androgen-independent cell line is also established from this androgen-dependent SC 115 tumor. The growth of these androgen-independent cells is stimulated by AIGF, indicating that AIGF acts not only as an autocrine growth factor to androgen-dependent cells but also as a paracrine growth factor to androgen-independent cells. In addition, transfection of AIGF expression vector into androgen-dependent cells results in a facilitation of conversion from androgen-dependent to -independent phenotype. Thus, AIGF might play a role from tumor progression. These results indicate that a blockade of AIGF activity is an important therapeutic target. Actually, some compounds such as heparin and suramin are found to inhibit this androgen-induced autocrine loop. These basic observations will be discussed in relation to their possible clinical application.