Figure 3: SB216763 is involved in transcriptional regulation of ligase IV in retinal neurons. (A) SB216763 pretreatment significantly upregulated p-CREB1 expression in serum-starved retinal neurons, as evidenced by western blot analysis. Additionally, SB216763 did not affect CREB1 expression. (B) Relative protein expression of p-CREB1 is presented as a histogram. (C) One mutation was introduced into ATF sites in the –601/+164 constructs. (D) Levels of luciferase activity were normalized to that of Renilla luciferase. SB216763 pretreatment significantly increased luciferase activity of the ligase IV promotor compared with control cells. p-CREB1 mutations dramatically reduced luciferase activity relative to the WT promoter sequence. Data are expressed as mean ± SEM compared with the control group. n = 3 for each group. *P < 0.05, **P < 0.01, vs. control (Con) group (Student's t-test). ATF: Activating transcription factor; Gapdh: glyceraldehyde 3-phosphate dehydrogenase; Mt: mutant; p-CREB1: phosphorylated CREB1; SB216763: a glycogen synthase kinase-3β inhibitor; WT: wild type.