Wilson MS, Jessen HJ, Saiardi A.
J Biol Chem. 2019 Jun 11. pii: jbc.RA119.007848. doi: 10.1074/jbc.RA119.007848. [Epub ahead of print] PMID: 31186349
Phosphate's central role in most biochemical reactions in a living
organism requires carefully maintained phosphate homeostasis. Although
phosphate homeostasis in mammals has long been studied at the organismal
level, the intracellular mechanisms controlling phosphate metabolism
are not well understood. Inositol pyrophosphates (PP-IPx) have emerged as
important regulatory elements controlling yeast phosphate homeostasis.
To verify whether inositol pyrophosphates also regulate mammalian
cellular phosphate homeostasis, here we knocked out inositol
hexakisphosphate kinase (IP6K) 1 and IP6K2
to generate human HCT116 cells devoid of any inositol pyrophosphates.
Using PAGE and HPLC analysis, we observed that the IP6K1/2-knockout
cells have non-detectable levels of the IP6-derived IP7 and IP8 and also exhibit reduced synthesis of the IP5-derived PP-IP4
Nucleotide analysis showed that the knockout cells contain increased
amounts of ATP, while the Malachite green assay found elevated levels of
free intracellular phosphate. Furthermore, [32Pi] pulse
labeling experiments uncovered alterations in phosphate flux, with both
import and export of phosphate being decreased in the knockout cells.
Functional analysis of the phosphate exporter xenotropic and polytropic
retrovirus receptor 1 (XPR1) revealed that it is regulated by inositol
pyrophosphates, which can bind to its SPX domain. We conclude that IP6K1
and -2 together control inositol pyrophosphate metabolism and thereby
physiologically regulate phosphate export and other aspects of mammalian
cellular phosphate homeostasis.
2.
Nagpal L, Fu C, Snyder SH.
J Neurosci. 2018 Aug 22;38(34):7409-7419. doi: 10.1523/JNEUROSCI.1165-18.2018. Epub 2018 Jul 13. Abstract
Inositol hexakisphosphate kinases
(IP6Ks) regulate various biological processes. Among pyrophosphates
generated by IP6Ks, diphosphoinositol pentakisphosphate (IP7/PP-InsP5), and
bis-diphosphoinositol tetrakisphosphate (PP-InsP4) 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.SIGNIFICANCE STATEMENT 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.
Free Article
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.SIGNIFICANCE STATEMENT 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.
Free Article
3.
Puhl-Rubio AC, Stashko MA, Wang H, Hardy PB, Tyagi V, Li B, Wang X, Kireev D, Jessen HJ, Frye SV, Shears SB, Pearce KH.
SLAS Discov. 2018 Oct;23(9):982-988. doi: 10.1177/2472555218775323. Epub 2018 May 29. PMID: 29842835
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