Integrins play a role in fibroblast growth factor (FGF) signaling through cross-talk with FGF receptors (FGFRs), but the mechanism underlying the cross-talk is unknown. We discovered that FGF1 directly bound to soluble and cell-surface integrin ␣v␤3 (K D about 1 M). Antagonists to ␣v␤3 (monoclonal antibody 7E3 and cyclic RGDfV) blocked this interaction. ␣v␤3 was the predominant, if not the only, integrin that bound to FGF1, because FGF1 bound only weakly to several ␤1 integrins tested. We presented evidence that the CYDMKTTC sequence (the specificity loop) within the ligand-binding site of ␤3 plays a role in FGF1 binding. We found that the integrin-binding site of FGF1 overlaps with the heparin-binding site but is distinct from the FGFR-binding site using docking simulation and mutagenesis. We identified an FGF1 mutant (R50E) that was defective in integrin binding but still bound to heparin and FGFR. R50E was defective in inducing DNA synthesis, cell proliferation, cell migration, and chemotaxis, suggesting that the direct integrin binding to FGF1 is critical for FGF signaling. Nevertheless, R50E induced phosphorylation of FGFR1 and FRS2␣ and activation of AKT and ERK1/2. These results suggest that the defect in R50E in FGF signaling is not in the initial activation of FGF signaling pathway components, but in the later steps in FGF signaling. We propose that R50E is a useful tool to identify the role of integrins in FGF signaling. Fibroblast growth factors (FGFs)2 constitute a family of heparin-binding polypeptides involved in the regulation of biological responses such as growth, differentiation, and angiogenesis (1-4). The FGF family currently consists of 22 members with FGF1 (acidic FGF) and FGF2 (basic FGF) the most extensively studied. The biological effects of FGFs are mediated by four structurally related receptor tyrosine kinases designated FGFR1-4. The binding of FGF to its receptor results in receptor dimerization and subsequent autophosphorylation of specific tyrosine residues within the cytoplasmic domain (1-4). Activation of the receptor allows proteins containing Src homology 2 or phosphotyrosine binding domains to bind to sequence recognition motifs in the FGFR, resulting in phosphorylation and activation of these proteins (5). This leads to the activation of intracellular signaling cascades. The main signaling cascade activated through the stimulation of FGFR is the Ras/MAPK pathway.FGF signaling enhances multiple biological processes that promote tumor progression (6). Therapies targeting FGF receptors and/or FGF signaling not only affect the growth of the tumor cells but also modulate tumor angiogenesis (7). FGF1 and FGF2 are responsible for resistance to chemotherapeutic agents in cancer (8 -11) and are also pro-inflammatory growth factors that play a role in pathological angiogenesis in chronic inflammatory diseases (12). Thus FGF signaling is a potential therapeutic target for cancer and pathological angiogenesis in chronic inflammatory diseases.It has been proposed that cross-talk between i...

Galectin-7 is normally expressed in all types of stratified epithelia, but is significantly down-regulated in squamous cell carcinomas. This protein was recently found to be highly inducible by p53 in a colon carcinoma cell line, DLD-1, and designated as PIG1 (for p53-induced gene 1). We studied transfectants of HeLa and DLD-1 cells ectopically expressing this protein and found that they were more susceptible to apoptosis than control transfectants. This was observed in apoptosis induced by mechanistically distinct stimuli, suggesting that galectin-7 acts on a common point in the apoptosis signaling pathways. Further analyses of actinomycin Dinduced apoptosis demonstrated that galectin-7 expression causes enhanced caspase-3 activity and poly(ADPribose) polymerase cleavage, and the potentiation of apoptosis by galectin-7 was completely abrogated by a caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone. In addition, galectin-7 transfectants displayed accelerated mitochondrial cytochrome c release and up-regulated JNK activity upon apoptosis induction. Several lines of evidence indicate that the effect on apoptosis is not due to the lectin functioning extracellularly through interactions with cell surface glycoconjugates. In fact, this lectin is found to localize in nuclei and cytoplasm of the transfectants and the transformed keratinocyte line HaCaT. Therefore, galectin-7 is a pro-apoptotic protein that functions intracellularly upstream of JNK activation and cytochrome c release. DNA microarray analysis revealed genes that are differentially expressed between galectin-7 and control transfectants. Some of them are potentially contributory to this lectin's proapoptotic function and these include redox-related genes monoamine oxidase B, ryanodine receptor 2, and glutathione S-transferase Mu 3.

We have studied murine models of asthma using FcεRIα-chain-deficient (FcεRIα−/−) mice to investigate the role of IgE-dependent mast cell activation in these models. When mice were either 1) immunized once with OVA in alum i.p. and then challenged with OVA intranasally, or 2) repeatedly immunized with OVA in the absence of adjuvant and subsequently challenged with nebulized OVA, FcεRα−/− mice had significantly fewer eosinophils and lower IL-4 levels in their bronchoalveolar lavage fluid compared with wild-type mice. When mice were given anti-IL-5 antibody before OVA challenge in protocol 1, eosinophilic infiltration into the airways was significantly suppressed in both genotypes, but only FcεRIα−/− mice showed significantly reduced airway hyperresponsiveness (AHR). In addition, when mice immunized and challenged with OVA also received a late OVA provocation at a higher concentration and were then exposed to methacholine, only wild-type mice developed a substantial increase in AHR. Since FcεRI is expressed mainly on mast cells in mouse airways, we conclude that IgE-dependent activation of this cell type plays an important role in the development of allergic airway inflammation and AHR in mice. The models used may be of value for testing inhibitors of IgE or mast cells for development of therapeutic agents for human asthma.

Tensin family is a group of focal adhesion proteins that interact with integrins, actin, and phosphotyrosine-containing proteins. To explore the in vivo functions of a new member of the family, tensin3, we have generated mutant mice with a disrupted tensin3 gene. Inactivation of tensin3 resulted in growth retardation and postnatal lethality in one third of the homozygous mutants. Histological analysis of those mutants showed incomplete development of the small intestine, lung, and bone. Villus formation in the small intestine was affected and cells migrated slower in the runt mutants. Their lungs also displayed enlarged air space suggesting defects in alveogenesis. In addition, the resting zone was thicker and fewer proliferating cells were present in the growth plates of tensin3(-/-) tibiae. These observations indicate that tensin3 is essential for normal development and functions of the small intestine, lung, and bone. These phenotypes of the runt tensin3(-/-) mice are similar to some clinical features of Silver-Russell syndrome (SRS) which is a genetically inherited defect. About 10% of SRS cases have been linked to abnormality in chromosome 7p11.2-13, where human tensin3 gene is located, suggesting a potential link between tensin3 and SRS.

Keratinocytes undergo apoptosis in a variety of physiological and pathological conditions. Galectin-3 is a member of a family of beta-galactoside-binding animal lectins expressed abundantly in keratinocytes and other epithelial cells. Here, we have studied the regulatory role of galectin-3 in keratinocyte apoptosis by using cells from gene-targeted galectin-3 null (gal3(-/-)) mice. We showed that galectin-3 mRNA was transiently upregulated in ultraviolet-B (UVB)-irradiated wild-type keratinocytes. We found that gal3(-/-) keratinocytes were significantly more sensitive to apoptosis induced by UVB as well as various other stimuli, both in vitro and in vivo, than wild-type cells. Moreover, we demonstrated that increased apoptosis in gal3(-/-) keratinocytes was attributable to higher extracellular signal-regulated kinase (ERK) activation and lower AKT activation after UVB irradiation. We conclude that endogenous galectin-3 is an anti-apoptotic molecule in keratinocytes functioning by suppressing ERK activation and enhancing AKT activation and may play a role in the development of apoptosis-related skin diseases.