A role of CPEB1 in the modulation of proliferation and neuronal maturation of rat primary neural progenitor cells.

Cytoplasmic polyadenylation binding protein 1 (CPEB1) is a RNA binding protein, which regulates translation of target mRNAs by regulating polyadenylation status. CPEB1 plays important roles in the regulation of germline cell development by modulating cell cycle progression through the polyadenylation of target mRNAs such as cyclin B1. Similar mechanism is reported in proliferating astrocytes by us, although CPEB1 is involved in the transport of target mRNAs as well as local translation at dendritic spines. In this study, we found the expression of CPEB1 in cultured rat primary neural progenitor cells (NPCs). EGF stimulation of cultured NPCs induced rapid phosphorylation of CPEB1, a hallmark of CPEB1-dependent translational control along with cyclin B1 polyadenylation and translation. EGF-induced activation of ERK1/2 and Aurora A kinase was responsible for CPEB1 phosphorylation. Pharmacological inhibition studies suggested that ERK1/2 is involved in the activation of Aurora A kinase and regulation of CPEB1 phosphorylation in cultured NPCs. Long-term incubation in EGF resulted in the down-regulation of CPEB1 expression, which further increased expression of cyclin B1 and cell cycle progression. When we down-regulated the expression of CPEB1 in NPCs by siRNA transfection, the proliferation of NPCs was increased. Increased NPCs proliferation by down-regulation of CPEB1 resulted in eventual up-regulation of neuronal differentiation with increase in both pre- and post-synaptic proteins. The results from the present study may suggest the importance of translational control in the regulation of neuronal development, an emerging concept in many neurodevelopmental and psychiatric disorders such as autism spectrum disorder.