Supplemental Figure 1. Spectral curve of the UVB light source. The portable UV-lamp (UVM-57) used in this study emits mid-range UV at a nominal wavelength of 302 nm with the emission maximum at 312 nm. The characteristics of the lamp were verified by spectroradiometry (Macam SR9910). The irradiance (W/m2) was measured at 1 nm intervals after stabilizing both the lamp and the spectroradiometer for a minimum of 30 min. The spectral curve represents the means of 4 repeated measurement series.  Supplemental Figure 2. The effect of UVB on cell proliferation. REK monolayers were seeded at 150.000 cells/well on 6-well plates, grown for approximately 24 h and either exposed to 10 mJ/cm2 of UVB or sham-irradiated. The cell numbers were counted after 12-48 h using a hemocytometer. The data represent means and SEM from 3 experiments each with 2 replicates. The effect of UVB on cell proliferation was statistically significant (p < 0.001; 2-way ANOVA). The results of Bonferroni tests for individual comparisons between the controls and UVB-treated specimens are shown for each time point (** p < 0.01 and *** p < 0.001). Supplemental Figure 3. The effect of UVB on CD44 expression analyzed with western blotting. Cultures were either exposed to 10 mJ/cm2 of UVB or sham-irradiated. The cells were lysed 6-36 h after the exposure, as indicated, and analyzed using an antibody specific for rat CD44. The standard form of the protein (90 kDa) was quantified, normalizing band intensities to those of GAPDH. A representative blot is shown in panel A and the results of the quantification in B (means and range from 2 experiments). Statistical significance was analyzed using 2-way ANOVA. Supplemental Figure 4. Effects of protein kinase inhibitors on hyaluronan synthesis. REKs pretreated for 2 h with the inhibitors were exposed to 10 mJ/cm2 of UVB, followed by a 24-h incubation in the presence of the corresponding inhibitor as detailed in Supplemental Table 1. Control cultures contained an equal concentration of DMSO, which was used to dissolve the inhibitors. Hyaluronan accumulation with inhibitors for MEK1/2 (UO126), MEK1 (PD 98059), PI3K (Wortmannin), Akt (Akt inhibitor VIII), JNK (SP600125) and STAT3 (Cpd188) is shown. The data represent means and range from 2 (UO126, PD 98059, SP600125 and Akt VIII), 3 (for Wortmannin) or 4 (Cpd188) independent experiments. Statistical significance was analyzed using univariate analysis of variance, where differences between treatments were tested using the estimated marginal means (LSD) and between controls and treatments using pnorm as described in Experimental Procedures. Supplemental Figure 5. Activation of the signaling pathways by UVB. Actin-normalized band intensities of active pERK, pJNK and pSTAT3 was analyzed with phosphospecific antibodies and western blotting from samples collected at different time points after a single exposure to 10 mJ/cm2 of UVB (means and range of 2 individual experiments). Statistical significance was analyzed using 2-way ANOVA. The results of Bonferroni tests for individual comparisons are shown (* p < 0.05). Supplemental Figure 6. Effect of the EGFR inhibitor AG1478 on Has1-3 expression 8 h post-UVB. The data represent means and SEM from 3 experiments each with 2 replicates. Statistical significance was analyzed using analysis of variance as described in Experimental Procedures (* p < 0.05 and *** p < 0.001).