Protein kinase N1 critically regulates cerebellar development and long-term function

Abstract

Increasing evidence suggests that synapse dysfunctions are a major determinant of several neurodevelopmental and neurodegenerative diseases. Here we identify protein kinase N1 (PKN1) as a novel key player in fine-tuning the balance between axonal outgrowth and presynaptic differentiation in the parallel fiber–forming (PF-forming) cerebellar granule cells (Cgcs). Postnatal Pkn1–/– animals showed a defective PF–Purkinje cell (PF-PC) synapse formation. In vitro, Pkn1–/– Cgcs exhibited deregulated axonal outgrowth, elevated AKT phosphorylation, and higher levels of neuronal differentiation-2 (NeuroD2), a transcription factor preventing presynaptic maturation. Concomitantly, Pkn1–/– Cgcs had a reduced density of presynaptic sites. By inhibiting AKT with MK-2206 and siRNA-mediated knockdown, we found that AKT hyperactivation is responsible for the elongated axons, higher NeuroD2 levels, and reduced density of presynaptic specifications in Pkn1–/– Cgcs. In line with our in vitro data, Pkn1–/– mice showed AKT hyperactivation, elevated NeuroD2 levels, and reduced expression of PF-PC synaptic markers during stages of PF maturation in vivo. The long-term effect of Pkn1 knockout was further seen in cerebellar atrophy and mild ataxia. In summary, our results demonstrate that PKN1 functions as a developmentally active gatekeeper of AKT activity, thereby fine-tuning axonal outgrowth and presynaptic differentiation of Cgcs and subsequently the correct PF-PC synapse formation.

PKN1 kinase-negative knock-in mice develop splenomegaly and leukopenia at advanced age without obvious autoimmune-like phenotypes

“…Additionally, PKN1 is an effector protein kinase of Rho family GTPases, such as RhoA, RhoB, RhoC, and Rac 1, in mammalian tissues 7–13 . PKN1 is expressed ubiquitously and involved in various functions, including cell-cell adhesion 14,15 , cell migration 16–19 , vesicle transport 20,21 , cell survival 22–26 , cell cycle regulation 18,27–31 , transcriptional regulation 32–36 , tumorigenesis 19,32,33,37,38 , myogenic differentiation 39 , parallel fiber-Purkinje-cell synapse formation in the cerebellum 40 , and pyrin inflammasome formation 41,42 . In some cases, PKN1 reportedly plays important roles independent of its kinase activity, such as activation of phospholipase D1 43 , scaffolding for p38γ mitogen-activated protein kinase signaling 44 , and increasing the survival of cardiac muscle cells following ischemia/reperfusion 24 .…”

PKN1 promotes synapse maturation by inhibiting mGluR-dependent silencing through neuronal glutamate transporter activation

“…Considering that many synapses are not covered by glial processes in the hippocampus 44 , 45 , EAAT3 may be more important in synapses specifically in the developing hippocampus. A recent study suggested a role of PKN1 in development of cerebellar circuits 24 . In this study we identify PKN1 as an important promoter of synapse maturation through upregulation of neuronal glutamate transporters and inhibition of mGluR-dependent synapse silencing in the hippocampus.…”

“…PKN has been implicated in cell proliferation or metastasis of many types of tumor including prostate and bladder cancers, and PKN inhibitors may treat them 20 , 23 . Very recently, PKN1 has been reported to be involved in axonal outgrowth and presynaptic differentiation of parallel fibers of cerebellar granule cells 24 ; however, the physiological roles of PKN in the brain have not been fully clarified yet. Therefore, we investigated the function of PKN1 in the hippocampus by generating PKN1a knockout (KO) mice (Supplementary Fig.…”

Identification of Differentially Expressed Genes Associated With Precocious Puberty by Suppression Subtractive Hybridization in Goat Pituitary Tissues

“…PKN1 (protein kinase N1) is a stress-responsive kinase and a member of the protein kinase novel (PKN) family also known as protein kinase C-related kinases (PRKs) [20,21]. The interaction of Rho with PKN1 induces a conformational change in PKN1 leading to activation loop phosphorylation by 3-Phosphoinositide-Dependent Kinase-1(PDK1) on Thr 774 in the case of human PKN1 (Thr 778 in mouse/rat) which is necessary for the catalytic activation of PKN1/2 14 and critical for the stability of the protein [22,23]. PKN1 is shown to provide a basal cardioprotective function in the face of I/R injury [24].…”