BDNF VAL66MET Polymorphism Elevates the Risk of Bladder Cancer via MiRNA-146b in Micro-Vehicles.

BACKGROUND/AIMS: Emerging studies on brain-derived neurotrophic factor (BDNF) have shown that might be novel biomarkers and therapeutic targets for cancer. We explore the role of BDNF in the tumorigenesis of bladder cancer and the underlying molecular mechanism.

METHODS: 368 patients with diagnosed bladder cancer and 352 healthy controls were enrolled to evaluate the association of BDNF and the miR-146b. Bioinformatics algorithm analysis and luciferase assay were performed to identify the target genes of miR-146b. Real-time PCR and western-blot were carried out to validate the relationship between miR-146b and CRK. MTT assay and FACS were used to evaluated the proliferation and apoptosis of cancer cells. MVs were isolated and transfect into the culture cells to confirm the above observation.

RESULTS: The clinical study shows that BDNF Met/Met was significantly associated with the risk of bladder cancer. In addition, comparing with Val/Val and Val/Met, Met/Met has lower miR-146b level. Luciferase assay shows that BDNF Val/Val is apparently enhanced miR-146b promoter-luciferase, but not BDNF Met/Met. Based on luciferase assay, CRK is a direct target gene of miR-146b. MiR-146b mimics significantly inhibited the expression of CRK and activation of AKT level. The expression of CRK and the activation of AKT (p-AKT) were significantly inhibited by MV-BDNF Val/Val-miR-146b or MV-BDNF Val/Met-miR-146b, but not MV-BDNF Met/Met-miR-146b. MV-BDNF Val/Val-miR-146b or Val/Met-miR-146b obviously inhibited cell proliferation, which eliminated by CRK. Meanwhile, with MV-BDNF Met/Met-miR-146b or Met/Met-miR-146b+CRK did not affect the proliferation. MV-BDNF Val/Val-miR-146b or Val/Met-miR-146b enhanced cell apoptosis, which could be eliminated by CRK. Meanwhile, MV-BDNF Met/Met-miR-146b or Met/Met-miR-146b+CRK did not promote apoptosis.

CONCLUSION: BDNF VAL66MET polymorphism is associated with miR-146b and its target gene CRK. MiR-146b and CRK mediated BDNF VAL66MET polymorphism associated proliferation and apoptosis via activation of AKT. Thus, BDNF Val66Met is associated with the risk of bladder cancer, and the BDNF variant could be used a biomarker for the diagnosis of bladder cancer.