Fig. 4: BDNF makes cap-independent translation of DSCR1.4 mRNA more actively by increasing DAP5 expression.

a, b BDNF treatment on DIV 3 hippocampal neuron increases protein levels of DAP5 and DSCR1.4 but not DSCR1.4 mRNA level. Vehicle (DDW) or 30 μM BDNF were treated for 1 h. a The protein levels were confirmed by Western blot. GAPDH and phosphorylation of ERK were used as a loading control and marker of BDNF activity, respectively. b Endogenous DSCR1.4 mRNA levels were analyzed by qRT-PCR and were normalized to β-actin. The bars represent the mean ± SEM (n = 3). c Cap-independent translation is essential for DSCR1.4 protein accumulation by BDNF. DIV 3 hippocampal neurons were treated with vehicle (DMSO), 100 μM RAD001(RAD) or 50 mg/ml cycloheximide (CHX) for 3 h followed by BDNF treatment for 1 h. The levels of each protein were confirmed by Western blot. The numbers at the bottom indicate the fold relative to a vehicle. The amount of DSCR1.4 was normalized to GAPDH. d, e BDNF raises cap-independent translation activity of DSCR1.4 mRNA. At 24 h after d pRF hDSCR1.4 5′UTR or e pRF mDSCR1.4 5′UTR vectors were transfected into DIV 2 hippocampal neurons, Vehicle (DDW) and BDNF were treated to the neurons for 1 h. The bars represent the mean ± SEM (e; n = 5, F; n = 3). f BDNF increases the interaction between DAP5 and DSCR1.4 5′UTR. In vitro transcribed biotin-DSCR1.4 5′UTR was incubated with extracts of the vehicle (DDW) or 30 μM BDNF-treated DIV 3 mouse hippocampal neurons. DAP5 binding was measured by Western blot. Phospho-ERK was used to confirm the activity of BDNF. GADPH was used as a loading control and negative control. g, h BDNF increases the cap-independent local translation of DSCR1.4 mRNA in axon as well as soma. EGFP and pRF mDSCR1.4 5′ 3′ UTR vectors were co-transfected into DIV 2 mouse hippocampal neurons. At 24 h later, 100 μM anisomycin was treated for 3 h and then 30 μM BDNF was treated for 1 h, followed by 5 μM puromycin treatment for 40 min. To detect newly synthesized FLUC proteins, Puro-PLA assay was conducted. g Representative image obtained from confocal microscopy. h The graph shows relative fluorescence intensity measured by Image J. The bars represent the mean ± SEM (Vehicle; n = 11, Anisomycin; n = 12, BDNF; n = 11, BDNF + Anisomycin; n = 11). Scale bar, 30 μm. Data information: In d, e, h, ^*P < 0.05, ^****P < 0.0001 (two-way ANOVA, Student’s t test)