Fig. 6. Role of TGF-ß1 in UVB-induced SIPS. (A) Steady-state mRNA level of TGF-ß1 in skin HDFs exposed (UVB) or not (CTL) to 10 repeated subcytotoxic doses of UVB at 250 mJ/cm². Total RNA samples were extracted at 24, 48 or 72 hours after the last stress. Results were obtained by real-time RT-PCR with GAPDH mRNA as reference. The steady-state mRNA level of TGF-ß1 in control cells after 24 hours was considered as 100%. Results are given as mean ± s.d. of three independent experiments. (B) Steady-state mRNA level of TGF-ß2 and TGF-ß3 at 72 hours after a series of 10 exposures to UVB at 250 mJ/cm2. Results are given as mean ± s.d. of three independent experiments. (Ca) Effects of the stimulation of skin HDFs with TGF-ß1 at 1, 5 and 10 ng/ml on the percentage of cells positive for SA ß-gal activity after 72 hours of stimulation. Results are given as mean ± s.d. of three independent experiments. (Cb) Effect of anti-TGFß-1 receptor II and anti-TGF-ß1-neutralizing antibodies on the proportion of cells positive for SA ß-gal activity at 72 hours after exposure of skin HDFs to 10 subcytotoxic stress with 250 mJ/cm² UVB. Control (CTL) cells had no UVB exposure. The concentration and incubation conditions of antibodies are given in the Materials and Methods. (D) Steady-state mRNA level of apolipoprotein J (apo J), fibronectin (fibro), osteonectin (osteo), SM22, p21^WAF-1, p53 and TGF-ß1 after 72 hours of stimulation with TGF-ß1 at 5 ng/ml. Total RNA was extracted at 72 hours after the last stress. The GAPDH steady-state mRNA level was considered as reference level with real time RT-PCR. The results are expressed as 100% for the steady-state mRNA level in control cells (CTL) not exposed to UVB. Results are given as mean ± s.d. of three independent experiments. Statistical analysis was carried out with the Student's t-test. ns, non-significant (P>0.05); ^*, 0.05>P>0.01; ^**, 0.01>P>0.001; ^***, P<0.001.