MMP13-mediated BACE1 regulation involves PI3K signalling and is unrelated to BACE1 transcription and protein degradation. (A) BACE1 protein levels in SH-SY5Y cells treated with 5 μM CL82198 (CL) for 48 h in the absence (CTRL) or presence of the RTK inhibitor 341610 (4 μM). (B) SH-SY5Y cells were transfected with either control or MMP13 vector for 48 h in the absence or presence of 5 μM CL82198 (CL) and 4 μM 341610. (C) SH-SY5Y cells were transfected with either control or MMP13 vector for 48 h in the absence or presence of 4 μM 341610, and PI3K activity was measured by ELISA. (D) p-Akt protein in SH-SY5Y cells transfected with either control or MMP13 vector for 48 h in the absence or presence of 4 μM 341610. (E) BACE1 protein levels in SH-SY5Y cells treated with 5 μM CL82198 (CL) for 48 h in the absence (CTRL) or presence of the PI3K inhibitor LY294002 (LY, 5 and 10 μM). (F) SH-SY5Y cells were transfected with either control or MMP13 vector for 48 h in the absence or presence of 5 μM CL82198 (CL) and LY294002 (LY, 5 and 10 μM). (G) Relative BACE1 mRNA levels in SH-SY5Y cells treated with 5 μM CL82198 (CL) for 48 h in the absence (CTRL) or presence of LY294002 (LY, 5 and 10 μM). (H) Relative Bace1 mRNA levels in HT22 cells treated with vehicle (CTRL) or Mmp13 shRNA-1 for 72 h. (I and J) BACE1 protein levels in SH-SY5Y cells treated with 5 μM CL82198 (CL) for 48 h in the absence (CTRL) or presence of 1 μM MG132 (G) or 100 μM CQ (H). (K) BACE1 protein levels in SH-SY5Y cells treated with 5 μM CL82198 (CL) for 48 h in the absence (CTRL) or presence of the transcriptional inhibitor actinomycin D (ActD, 0.1 μM) or the protein synthesis inhibitor cycloheximide (CHX, 5 μM). All values were normalized to CTRL (1.0) within each experiment. The error bars are the SEM. n.s. = no significant difference; *P < 0.05, **P < 0.01, ***P < 0.001 (ANOVA, n = 3 or 4).