Inositol Hexakisphosphate Kinase-2 in Cerebellar Granule Cells Regulates Purkinje Cells and Motor Coordination via Protein 4.1N

Abstract

Inositol hexakisphosphate kinases (IP6Ks) regulate various biological processes. Among pyrophosphates generated by IP6Ks, diphosphoinositol pentakisphosphate (IP7), and bis-diphosphoinositol tetrakisphosphate have been extensively characterized. IP7 is produced in mammals by a family of inositol hexakisphosphate kinases, IP6K1, IP6K2, and IP6K3, which have distinct biological functions. We report that IP6K2 binds protein 4.1.N with high affinity and specificity. Nuclear translocation of 4.1N, which is required for its principal functions, is dependent on IP6K2. Both of these proteins are highly expressed in granule cells of the cerebellum where their interaction regulates Purkinje cell morphology and cerebellar synapses. The deletion of IP6K2 in male/female mice elicits substantial defects in synaptic influences of granule cells upon Purkinje cells as well as notable impairment of locomotor function. Moreover, the disruption of IP6K2-4.1N interactions impairs cell viability. Thus, IP6K2 and its interaction with 4.1N appear to be major determinants of cerebellar disposition and psychomotor behavior. Inositol phosphates are produced by a family of inositol hexakisphosphate kinases (IP6Ks)-IP6K1, IP6K2, and IP6K3. Of these, the physiological roles of IP6K2 in the brain have been least characterized. In the present study, we report that IP6K2 binds selectively to the neuronal protein 4.1N. Both of these proteins are highly expressed in granule cells of the cerebellum. Using IP6K2 knock-out (KO) mice, we establish that IP6K2-4.1N interactions in granule cells regulate Purkinje cell morphology, the viability of cerebellar neurons, and psychomotor behavior.

Inositol Pyrophosphates: Signaling Molecules with Pleiotropic Actions in Mammals

“…Both IP6K2 and 4.1N are highly enriched in cerebellar granule cells. Their interaction controls the morphology of Purkinje cells and cerebellar synapses [57]. Therefore, the contribution of 5-IP7 to the cerebellar control by IP6K2 warrants further investigation.…”

“…IP6K1 KO mice exhibit impaired locomotion without unaffected motor coordination under basal conditions [55]; however, the locomotion of IP6K2 KO mice is impaired locomotive, including a reduced latency to fall off the rotarod, notable decrease in stride length, and speed of movement [57]. This indicates defective motor coordination.…”

“…This indicates defective motor coordination. IP6K2 determines the nuclear translocation of 4.1N, a high-affinity IP6K2-binding protein [57], which is the key for its functions. Both IP6K2 and 4.1N are highly enriched in cerebellar granule cells.…”

4.1N-Mediated Interactions and Functions in Nerve System and Cancer

“…Many molecules, including α7 acetylcholine receptor (α7AChr) ( Kanno et al, 2013 ), inositol 1,4,5-trisphosphate receptor type 1 (IP3R1) ( Zhang et al, 2003 ; Fukatsu et al, 2004 ; Fukatsu et al, 2006 ; Fiedler and Nathanson, 2011 ), GluR1/4 13,14 , GluK1/2/3 15,16 , metabotropic glutamate receptor 8 (mGluR8) ( Rose et al, 2008 ), K-Cl co-transporter 2 (KCC2) ( Li et al, 2007 ; Horn et al, 2010 ), D2 and D3 dopamine receptors (D2/3Rs) ( Binda et al, 2002 ; Kabbani and Levenson, 2006 ), Ca2 + -calmodulin serine kinase (CASK) ( Cohen et al, 1998 ; Biederer and Sudhof, 2001 ; Mburu et al, 2006 ), nuclear mitotic apparatus (NuMA) ( Ye et al, 1999 ; Ilies et al, 2012 ), phosphoinositide 3 kinase enhancer (PIKE) ( Ye et al, 2000 ), inositol hexakisphosphate kinase 2 (IP6K2) ( Nagpal et al, 2018 ), cell adhesion molecule (CAM) 1/3 29,30 , βII spectrin ( Wang et al, 2018 ), flotillin-1 32 , pp1 ( Wang et al, 2016 ), and 14-3-3 34-36 , have been identified as 4.1N binding partners. Although 4.1N performs different functions depending on specific tissue localization, 4.1N predominantly functions as a scaffolding protein in signaling transduction by locating, supporting, and coordinating multiple partners.…”

Expression of 1L-myo-Inositol -1-Phosphate Synthase (EC 5.5.1.4) is Deregulated in the Cerebellum of Curly Tail Mutant Mice

“…In addition, elevated concentrations of myo-inositol were detected in the anterior cingulated of bipolar adolescents when compared to healthy individuals [4]. Remarkably, highly increased levels of myoinositol were found in cerebral white matter in a new Vsyndrome characterized by hypomyelination with atrophy of the basal ganglia and the cerebellum [5], while others have recently shown that a phosphorylator of inositol, inositol hexakisphosphate kinase-2 in cerebellar granule cells, regulates Purkinje cell morphology and cerebellar synapses [6]. Determining myo-inositol concentration during human brain development provides essential clues concerning its functions in the cerebellum [7,8] and allows subsequent, non-invasive therapeutic intervention.…”