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Contribution of Src-FAK signaling to the induction of connective tissue growth factor in renal fibroblasts
A Graness, I Cicha and M Goppelt-Struebe
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Figure 1.
Colchicine alters fibroblast morphology and CTGF expression. Renal fibroblasts were grown on collagen-coated glass coverslips. Co: unstimulated cells, 24 h after seeding; Colch: 24 h after seeding, the cells were stimulated with 1 
M colchicine for 90 min. F-actin filaments were visualized with rhodamine phalloidin, FAK and CTGF were detected by specific antibodies by indirect immunofluorescence with secondary antibodies conjugated with Alexa Fluor 488. Photographs were obtained by fluorescence microscopy under original magnification 
1000 and are representative of at least three independent experiments.
Figure 2.
Inhibition of Src-family kinases reduces tyrosine phosphorylation but has no effect on CTGF expression in fibroblasts cultured on collagen-coated plates. (a) Renal fibroblasts grown on collagen-coated dishes were preincubated with PP2 (10
M, 1 h) and stimulated with colchicine (1
M, 20 min). Proteins with apparent molecular weights of 125–130 kDa were detected by an antibody directed against phosphotyrosine (p-Tyr). The position of the molecular weight markers p130 and p72 is indicated by arrows. Vinculin was detected to confirm equal loading of the blot. (b) Renal fibroblasts were preincubated with PP2 (10
M, 1 h) and stimulated with colchicine for 20 min or 2 h as indicated. Tyrosine phosphorylation of the p130 band was quantified by luminescent imager analysis. Values of untreated cells were set to 1; data are means
s.d. of three experiments. Tyrosine phosphorylation of PP2-treated cells was significantly lower than that of control or colchicine-treated cells (P<0.01, Student's t-test). (c) Renal fibroblasts were preincubated with PP2 (10
M, 1 h) and stimulated with colchicine for 2 h as indicated. CTGF expression was detected using goat anti-human CTGF antibody. Blots were reprobed for tubulin to confirm equal protein loading. (d) CTGF expression was quantified by luminescent imager analysis. The graph shows meanss.d. of five experiments.
Figure 3.
Colchicine-induced morphological alterations in cells cultured in soft collagen matrices are dependent on RhoA signaling. Renal fibroblasts were cultured (a) in collagen-I or (b–d) on top of preformed collagen-I gels overnight and were then stimulated with colchicine (1
M) for 90 min as indicated. The immunofluorescent images were taken by (a, b, d) fluorescence microscopy and by (c) confocal microscopy. Photographs shown were analyzed under orignial magnification (a, b) 1000, (d) 400, and (c) using a 63 oil objective, zoom 1.8 for confocal microscopy. Photographs are representative of at least three independent experiments. (a) F-actin was visualized by rhodamine-phalloidin staining. (b) FAK was detected by indirect immunofluorescence. (c) F-actin was visualized by rhodamine-phalloidin staining and phosphotyrosine was detected by indirect immunofluorescence. (d) Fibroblasts were cultured on preformed collagen gels and then treated with Y27632 (10
M for 1 h) and/or colchicine (1
M) for additional 90 min as indicated. F-actin was stained with Alexa 488 phalloidin.
Figure 4.
Upregulation of CTGF in cells cultured in soft matrices is dependent on RhoA-mediated structural alterations. (a) Renal fibroblasts cultured on top of preformed collagen gels were treated with colchicine (1
M, 2 h). CTGF was detected by indirect immunofluorescence (original magnification 1000). The images are representative of at least three experiments with cells cultured in or on top of collagen gels overnight. (b) Fibroblasts were grown in collagen gels for 24 h, preincubated with Y27632 (10
M) or taxol (Tax, 1
M) for 1 h, and then further incubated with colchicine (Colch 1
M) for 2 h. CTGF expression was analyzed by Western blotting.
Figure 5.
Inhibition of Src-family kinases alters tyrosine phosphorylation but has no effect on colchicine-mediated changes in cell morphology. (a) Renal fibroblasts were cultured on preformed collagen gels. After preincubation with PP2 (10
M) for 1 h, the cells were stimulated with colchicine for 20 min. Proteins with apparent molecular weights of 125–130 kDa were detected by an antibody directed against phosphotyrosine (p-Tyr). The position of the molecular weight marker p130 is indicated by an arrow. Phosphorylated FAK was detected with an antibody specific for FAK[pY397]. (b) Renal fibroblasts were stimulated with colchicine for 20 min or 2 h with or without PP2 preincubation, as indicated. Tyrosine phosphorylation of the p130 band was quantified by luminescent imager analysis. Values of unstimulated cells were set to 1; data are meanss.d. of four experiments. *
P<0.05 compared to cells treated with PP2, Student's t-test. (c) Phosphotyrosine was detected in fibroblasts cultured on top of preformed collagen gels (preincubation with PP2 for 1 h, stimulation with colchicine for 2 h). Immunofluorescent images (original magnification 1000) are representative of three experiments.
Figure 6.
Interference with Src-family kinases prevents upregulation of CTGF in fibroblasts cultured in soft matrices. (a) Renal fibroblasts were grown in collagen gels overnight. After preincubation with PP2 (10
M, 1 h), the cells were stimulated with colchicine (Colch 1
M) for 2 h. CTGF expression was detected by Western blotting. The graph shows meanss.d. of five experiments with cells cultured in or on top of preformed collagen gels. NS, no significant difference between control cells and cells treated with PP2 and colchicine. (b) Renal fibroblasts were preincubated with PD98059 (PD, 50
M) for 1 h, and stimulated with 1
M colchicine for 2 h. CTGF was detected by Western blot analysis and quantified by densitometry. To compare different experiments, stimulation with colchicine was set to 100%. Data are meanss.d. of three experiments. (c) Renal fibroblasts were cultured on preformed collagen gels overnight. After pretreatment with PP2 (10
M) or PD98059 (PD, 50
M) for 1 h, the cells were stimulated with 1
M colchicine for 10 min. The expression of phospho-ERK was detected by Western blotting. The blot is representative of three independent experiments. (d) Fibroblasts were cultured in collagen gels (upper panel) or on collagen-coated plates (lower panel) overnight. After pretreatment with LY294002 (50
M) or wortmannin (100 nM) for 1 h, the cells were stimulated with 1
M colchicine for 2 h. CTGF expression was detected by Western blotting. (e) Colchicine-stimulated expression of CTGF was quantified by luminescent imager analysis. To compare different experiments, colchicine-stimulated CTGF expression was set to 100%. Renal fibroblasts were cultured on collagen-coated dishes (black bars) or in or on top of collagen gels (gray bars). Data are means of two experiments half range for wortmannin and meanss.d. of five experiments for LY294002. **
P<0.01, cells cultured on plastic compared to cells cultured in/on collagen gels, Student's t-test.
Figure 7.
Regulation of CTGF expression by cytoskeletal dynamics. Signaling pathways analyzed in fibroblasts grown in collagen gels are indicated by bold lines. Dotted lines indicate signaling pathways described in the literature as outlined in the discussion. In the cells firmly attached to collagen-coated plates, alterations of F-actin will not lead to clustering and activation of adhesion proteins.
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