RalA, PLD and mTORC1 Are Required for Kinase-Independent Pathways in DGKβ-Induced Neurite Outgrowth.

Takuya Kano,Akio Nakashima,Yasuhito Shirai,Nobuyuki Takei,Ushio Kikkawa,Shuji Ueda,Ryosuke Tsumagari,Minoru Yamanoue

doi:10.3390/biom11121814

Abstract

Diacylglycerol kinase β (DGKβ) is an enzyme that converts diacylglycerol to phosphatidic acid and is mainly expressed in the cerebral cortex, hippocampus and striatum. We previously reported that DGKβ induces neurite outgrowth and spinogenesis, contributing to higher brain functions, including emotion and memory. To elucidate the mechanisms involved in neuronal development by DGKβ, we investigated the importance of DGKβ activity in the induction of neurite outgrowth using human neuroblastoma SH-SY5Y cells. Interestingly, both wild-type DGKβ and the kinase-negative (KN) mutant partially induced neurite outgrowth, and these functions shared a common pathway via the activation of mammalian target of rapamycin complex 1 (mTORC1). In addition, we found that DGKβ interacted with the small GTPase RalA and that siRNA against RalA and phospholipase D (PLD) inhibitor treatments abolished DGKβKN-induced neurite outgrowth. These results indicate that binding of RalA and activation of PLD and mTORC1 are involved in DGKβKN-induced neurite outgrowth. Taken together with our previous reports, mTORC1 is a key molecule in both kinase-dependent and kinase-independent pathways of DGKβ-mediated neurite outgrowth, which is important for higher brain functions.

Highlights

Diacylglycerol kinase (DGK) phosphorylates diacylglycerol (DG) to produce phosphatidic acid (PA)
We have recently found that Diacylglycerol kinase β (DGKβ) induces neurite outgrowth and spinogenesis by activating mammalian target of rapamycin complex 1 (mTORC1) in a kinase-dependent pathway [14]
Our previous results suggested that the kinase-negative (KN) mutant of DGKβ induced neurite outgrowth in SH-SY5Y cells, the effect was weaker than wild-type (WT) DGKβ [13]

Summary

Introduction

Diacylglycerol kinase (DGK) phosphorylates diacylglycerol (DG) to produce phosphatidic acid (PA). This enzyme is considered to play an important role in signal transduction by regulating the balance between two lipid messengers since DG is an activator of protein kinase C (PKC) and PA can regulate the functions of several enzymes, including mTOR [1]. Of the 10 mammalian DGK subtypes [2,3,4], DGKα is necessary for anergy [5,6], and DGKδ is involved in diabetes [7]. The β subtype of DGK (DGKβ) is abundantly expressed in neurons, especially in the cerebral cortex, hippocampus and striatum, and its expression increases on the postnatal day when neural networks are formed [8]. We found that a unique localization of DGKβ at the plasma membrane was critical for its functions

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Results

Conclusion