14-3-3γ regulates Copinel-mediated neuronal differentiation in HiB5 hippocampal progenitor cells

Copinel (CPNE1), known as a calcium-dependent membrane-binding protein, has tandem C2 domains and an A domain. We previously demonstrated that CPNE1 directly induces neuronal differentiation via Protein kinase B (AKT) phosphorylation in the hippocampal progenitor cell line, HiB5. To better understand its cellular function, we carried out a yeast two-hybrid screening to find CPNE1 binding partners. Among the identified proteins, 14-3-3 gamma appears to directly interact with CPNE1. Between CPNE1 and 14-3-3 gamma, the physical interaction as well as the specific binding regions of CPNE1 was confirmed in vitro and in vivo. Furthermore, among the seven 14-3-3 isotypes, only 14-3-3 gamma directly interacts with CPNE1. Our results also demonstrate that AKT phosphorylation, neurite outgrowth and expression of the neuronal marker protein are increased when 14-3-3 gamma is overexpressed in CPNE1 high expressed HiB5 cells. Furthermore, the neighboring Ser54 amino acids residue of C2A domain in CPNE1 has an important role in binding with 14-3-3 gamma, and in differentiation-related function of CPNE1. Moreover, mutation of Ser54 amino acids residue in CPNE1 effectively decreased association with 14-3-3 gamma and neuronal differentiation of HiB5 cells. Collectively, our findings indicate that 14-3-3 gamma regulates the differentiation ability of CPNE1 through the binding with C2A domain of CPNE1 in HiB5 cells.