MicroRNA involves in regulating behavior of neural stem/precursor cells (NSPCs), thus it offers the potential to treat central nervous system disease. However, the effect of miR-21 on NSPCs remains unknown. In this study, we demonstrated that miR-21 reduced proliferation and promoted neural differentiation in NSPCs via regulating the activation of AKT and GSK-3β signaling pathways in vitro. During differentiation of NSPCs, the expression of miR-21 was increased in a time-dependent manner by qRT-PCR. Synthesized pre-miR-21 or anti-miR-21 was transfected into NSPCs, thereby efficiently overexpressing or knocking down miR-21. Overexpression of miR-21 promoted the neural differentiation of NSPCs, as indicated by Tuj1 and PSA-NCAM staining. Interestingly, knocking down miR-21 had the opposite effect of neural differentiation in NSPCs. However, in proliferation area, overexpression of miR-21 decreased the cell viability by 3-((2-methyl-1,3-thiazol-4-yl)ethynyl)pyridine hydrochloride (MTT) assay, and inhibited the proliferation of NSPCs, as indicated by 5-Bromo-2-deoxyUridine (BrdU) staining. And likewise, knocking down miR-21 had the opposite effect of cell viability and proliferation. Western blot showed that overexpression of miR-21 enhanced the expression of Cyclin D1, however, knocking down miR-21 prevented its expression. Furthermore, we revealed that protein kinase B (AKT) and glycogen synthase kinase-3 beta (GSK-3β) signaling pathways were involved in the proliferation and neural differentiation of NSPCs. Overexpression of miR-21 activated AKT, and the p-GSK-3β was increased. Conversely, knocking down miR-21 blocked the activation of AKT, and decreased the phosphorylation level of GSK-3β. These results demonstrated that miR-21 promotes neural differentiation and reduces proliferation in NSPCs via regulating AKT and GSK-3β pathways. These findings may help to develop strategies for treatment of central nervous system diseases.

The alteration of p21-activated kinase 4 (PAK4) and transforming growth factor-beta (TGF-β) signaling effector Smad2/3 was detected in several types of tumors, which acts as oncogenic factor and tumor suppressor, but the relationship between these events has not been explored. Here, we demonstrate that PAK4 interacts with and modulates phosphorylation of Smad2/3 via both kinase-dependent and kinase-independent mechanisms, which attenuate Smad2/3 axis transactivation and TGF-β-mediated growth inhibition in gastric cancer cells. First, PAK4 interaction with Smad2/3, which is independent of PAK4 kinase activity, blocks TGF-β1-induced phosphorylation of Smad2 Ser465/467 or Smad3 Ser423/425 and the consequent activation. In addition, PAK4 phosphorylates Smad2 on Ser465, leading to the degradation of Smad2 through ubiquitin–proteasome-dependent pathway under hepatocyte growth factor (HGF) stimulation. Interestingly, PAK4 expression correlates negatively with phospho-Ser465/467 Smad2 but positively with phospho-Ser465 Smad2 in gastric cancer tissues. Furthermore, the expressions of HGF, phospho-Ser474 PAK4 and phospho-Ser465 Smad2 are markedly increased in gastric cancer tissues, and the expression of Smad2 is decreased in gastric cancer tissues. Our results document an oncogenic role of PAK4 in repression of Smad2/3 transactivation that involved in tumorigenesis, and suggest PAK4 as a potential therapeutic target for gastric cancer.