ABSTRACT
Fibroblast growth factors (FGFs) and fibroblast growth factor receptors (FGFRs) are major regulators of skeletal growth and development. Signal transduction via FGFRs is complex and mediates proliferation, differentiation, or migration depending upon the cellular context. Members of the Spry gene family antagonize the FGFR signal transduction pathway and inhibit lung morphogenesis, angiogenesis, and chondrogenesis. We examined the expression of Spry2 in the osteoblastic MC3T3-E1 cell line. MC3T3-E1 cells express Spry2 in response to FGF1 stimulation. Treatment of MC3T3-E1 cells with FGF1 results in the expression of Spry2 in a manner consistent with an early response gene. Pharmacological inhibitors of mitogen-activated protein kinase activation inhibit FGF1-induced expression of Spry2 mRNA. Transient overexpression of Spry2 in MC3T3-E1 resulted in decreased FGF1-mediated extracellular signal-regulated kinase phosphorylation and FGF1-stimulated osteopontin promoter activity. Furthermore, we show that Spry2 interacts with Raf-1 in a glutathione-S-transferase pulldown assay and that this interaction may involve multiple sites. Finally, Spry2 expression precedes the onset of the expression of osteoblast differentiation markers in an in vitro assay of primary osteoblast differentiation. Taken together, these results indicate that Spry2 expression is an early response to stimulation by FGF1 in MC3T3-E1 cells and acts as a feedback inhibitor of FGF1-induced osteoblast responses, possibly through interaction with Raf1.
Subject(s)
Fibroblast Growth Factors/metabolism , Osteoblasts/metabolism , Proteins/genetics , Adaptor Proteins, Signal Transducing , Animals , Cell Differentiation , Cell Line , Feedback, Physiological , Immunoblotting , Intracellular Signaling Peptides and Proteins , Membrane Proteins , Mice , Osteoblasts/cytology , Protein Kinase Inhibitors/pharmacology , Protein Serine-Threonine Kinases , Proto-Oncogene Proteins c-raf/metabolism , RNA, Messenger/analysis , Reverse Transcriptase Polymerase Chain ReactionABSTRACT
Exposure of a small skin area of volunteers to UV light in 1 minimal erythemal dose is accompanied by rapid appearance in the circulating blood of soluble factors able to restore proliferation of X-ray-damaged autologous lymphocytes, to decrease frequency of chromosome breaks, and to stimulate unscheduled DNA synthesis. The appearance of such an activity in the blood can be also induced without skin irradiation. For this, one volume of a directly UV-irradiated blood is to be mixed in vitro with 10-fold volumes of intact blood, thus modeling the in vivo situation, when a small amount of transcutaneously UV-irradiated blood mixes with intact blood in the circulation. It has been found that the platelet-derived growth factor and epidermal growth factor, added at physiological concentrations to the culture medium, decrease chromosome break frequency in X-damaged cells.
