Akt regulates the expression of MafK, synaptotagmin I, and syntenin-1, which play roles in neuronal function

Abstract

BackgroundAkt regulates various cellular processes, including cell growth, survival, and metabolism. Recently, Akt's role in neurite outgrowth has also emerged. We thus aimed to identify neuronal function-related genes that are regulated by Akt.MethodsWe performed suppression subtractive hybridization on two previously established PC12 sublines, one of which overexpresses the wild-type (WT) form and the other, the dominant-negative (DN) form of Akt. These sublines respond differently to NGF's neuronal differentiation effect.ResultsA variety of genes was identified and could be classified into several functional groups, one of which was developmental processes. Two genes involved in neuronal differentiation and function were found in this group. v-Maf musculoaponeurotic fibrosarcoma oncogene homolog K (MafK) induces the neuronal differentiation of PC12 cells and immature telencephalon neurons, and synaptotagmin I (SytI) is essential for neurotransmitter release. Another gene, syntenin-1 (Syn-1) was also recognized in the same functional group into which MafK and SytI were classified. Syn-1 has been reported to promote the formation of membrane varicosities in neurons. Quantitative reverse transcription polymerase chain reaction analyses show that the transcript levels of these three genes were lower in PC12 (WT-Akt) cells than in parental PC12 and PC12 (DN-Akt) cells. Furthermore, treatment of PC12 (WT-Akt) cells with an Akt inhibitor resulted in the increase of the expression of these genes and the improvement of neurite outgrowth. These results indicate that dominant-negative or pharmacological inhibition of Akt increases the expression of MafK, SytI, and Syn-1 genes. Using lentiviral shRNA to knock down endogenous Syn-1 expression, we demonstrated that Syn-1 promotes an increase in the numbers of neurites and branches.ConclusionsTaken together, these results indicate that Akt negatively regulates the expression of MafK, SytI, and Syn-1 genes that all participate in regulating neuronal integrity in some way or another.

Synaptotagmin‐1 promotes the formation of axonal filopodia and branches along the developing axons of forebrain neurons

“…These protrusions closely resemble the axonal filopodia observed in chick forebrain neurons. Knockdown of syntenin by RNAi reduces the number of neuritic processes and their branching in PC12 cells treated with NGF (Ro et al,2010). It was reported recently that both syt1 and syntenin‐1 are negatively regulated by the Akt signaling pathway in PC12 cells (Ro etal.,2010).…”

“…Knockdown of syntenin by RNAi reduces the number of neuritic processes and their branching in PC12 cells treated with NGF (Ro et al,2010). It was reported recently that both syt1 and syntenin‐1 are negatively regulated by the Akt signaling pathway in PC12 cells (Ro etal.,2010). The Akt protein kinase is downstream of PI3K and has been shown to be involved in local control of axon branching (Gallo and Letourneau,1998; Kwon et al,2006; Read and Forman,2009; Drinjakovik et al,2010).…”

Small Maf proteins (MafF, MafG, MafK): History, structure and function

“…Hematopoietic GATA factors (GATA1 or GATA2) and cardiac GATA factors (GATA4 or GATA6) bind to GATA motifs in HCEK and regulate MafK gene expression in specific tissues. It has also been shown that NGF (Torocsik et al, 2002), TGF-β (Okita et al, 2013), AKT (Ro et al, 2010) and Wnt signaling (Wang et al, 2015) influence MafK gene expression.…”

Targeting tumor invasion: the roles of MDA-9/Syntenin

“…Additionally, MDA-9/ Syntenin promotes an increase in the numbers and branching patterns of neurites. In PC12 cells, a model for neuron-like cells, Akt inhibition, either through dominant negative (DN) expression or through pharmacological inhibition, led to an increase in MDA-9/Syntenin expression and improvement in neurite outgrowth [46]. Taken together, these findings serve as foundation for a key role of MDA-9/ Syntenin in directional cell movements during early development and regeneration.…”