A Role for Rat Inositol Polyphosphate Kinases rIPK2 and rIPK1 in Inositol Pentakisphosphate and Inositol Hexakisphosphate Production in Rat-1 Cells

Fujii, Makoto; York, John D.

doi:10.1074/jbc.m412006200

Cited by 51 publications

(46 citation statements)

References 51 publications

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“…In the absence of stimulation by Wnt3a, cells display little change in intracellular IP 3 or IP 5 levels when IPMK is suppressed by siRNA. Earlier studies report dramatic reductions in IP 5 accu- mulation in HEK293 and HeLa cells (45), as well as in Rat-1 cells (38), when IPMK expression was suppressed with siRNA. Unlike these earlier studies performed with serum-fed cells, our studies required that we eliminate serum to study the Wnt response, likely the basis for the differences in the effects observed in response to IPMK suppression.…”

Section: Resultsmentioning

confidence: 99%

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Inositol Pentakisphosphate Mediates Wnt/β-Catenin Signaling

Gao

Wang

2007

Journal of Biological Chemistry

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Section: Resultsmentioning

confidence: 99%

“…4A) (37)(38)(39)(40)(41)(42). Aurintricarboxylic acid (ATA, 2 M) has been shown in vitro to inhibit IP3K and IPMK; whereas adriamycin (20 M) has been shown in vitro to inhibit IP3K and CGA (40 M) has been shown in vitro to inhibit IPMK (43,44).…”

Section: Resultsmentioning

confidence: 99%

Inositol Pentakisphosphate Mediates Wnt/β-Catenin Signaling

Gao

Wang

2007

Journal of Biological Chemistry

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“…However, the extent to which ITPK1 contributes to higher order inositol phosphate synthesis in mammals remains to be demonstrated in a range of conditions and cell types. For example, it has been shown that two other inositol kinases, IPK1 and IPK2, are sufficient to recapitulate InsP 6 synthesis from Ins(1,4,5)P 3 (38,39). In contrast, the function of gmITPK4 in soybean is likely restricted to the synthesis of higher inositol polyphosphates.…”

Section: )P 3 Does Not Stimulate Thismentioning

confidence: 99%

Integration of Inositol Phosphate Signaling Pathways via Human ITPK1

Chamberlain

Qian

Stiles

et al. 2007

Journal of Biological Chemistry

105

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Inositol 1,3,4-trisphosphate 5/6-kinase (ITPK1) is a reversible, poly-specific inositol phosphate kinase that has been implicated as a modifier gene in cystic fibrosis. Upon activation of phospholipase C at the plasma membrane, inositol 1,4,5-trisphosphate enters the cytosol and is inter-converted by an array of kinases and phosphatases into other inositol phosphates with diverse and critical cellular activities. In mammals it has been established that inositol 1,3,4-trisphosphate, produced from inositol 1,4,5-trisphosphate, lies in a branch of the metabolic pathway that is separate from inositol 3,4,5,6-tetrakisphosphate, which inhibits plasma membrane chloride channels. We have determined the molecular mechanism for communication between these two pathways, showing that phosphate is transferred between inositol phosphates via ITPK1-bound nucleotide. Intersubstrate phosphate transfer explains how competing substrates are able to stimulate each others' catalysis by ITPK1. We further show that these features occur in the human protein, but not in plant or protozoan homologues. The high resolution structure of human ITPK1 identifies novel secondary structural features able to impart substrate selectivity and enhance nucleotide binding, thereby promoting intersubstrate phosphate transfer. Our work describes a novel mode of substrate regulation and provides insight into the enzyme evolution of a signaling mechanism from a metabolic role.Cellular inositol phosphate metabolism is an intricate web of kinase and phosphatase reactions that produces a number of important signaling molecules (for review see Ref. 1). A now classic example of these signaling activities is the release of Ca 2ϩ into the cytoplasm through an intracellular channel that is gated by inositol 1,4,5-trisphosphate (Ins(1,4,5)P 3 ) 4 (2). Additional roles are continually being discovered: inositol phosphates have recently been shown to be critical to the activity of RNA-editing enzymes (3), to participate in telomere maintenance (4), and to be the phosphate donors in certain protein phosphorylation events (5). It is of critical interest, therefore, to establish the regulatory mechanisms that govern the metabolism of inositol phosphates.An interesting feature of inositol phosphate metabolism is the promiscuity with which several key kinases phosphorylate multiple substrates (6). For example, ITPK1 (also known as inositol 1,3,4-trisphosphate 5/6-kinase) adds either a 5-or 6-phosphate to Ins(1,3,4)P 3 and also attaches a 1-phosphate to Ins(3,4,5,6)P 4 (6, 7) (inositol phosphate structures shown in Fig. 2). These reactions have been demonstrated to be reversible: ITPK1 can also dephosphorylate Ins(1,3,4,5,6)P 5 back to Ins(3,4,5,6)P 4 (8). An especially puzzling aspect of this phenomenon is that dephosphorylation of Ins(1,3,4,5,6)P 5 by human ITPK1 is stimulated, rather than competitively inhibited, by one of its alternate substrates, Ins(1,3,4)P 3 (8).The fact that mammalian ITPK1 reversibly phosphorylates both Ins(3,4,5,6)P 4 and Ins(1,3,4)P 3 takes on...

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“…The cDNA for human G␣ q QL in pcDNA was from UMR cDNA Resource Center (Rolla, MO). The construction of the rat IPMK cDNA construct pBabePuro-GFP-rIPMK was described previously (57). The human Vip1 kinase domain (residues 1-387) CFP fusion construct pmCFPhsVIP1-KD has been described (27).…”

Section: Methodsmentioning

confidence: 99%

Alterations in an inositol phosphate code through synergistic activation of a G protein and inositol phosphate kinases

Otto

Kelly

Chiou

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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In mammals, many cellular stimuli evoke a response through G protein activation of phospholipase C, which results in the lipidderived production of inositol 1,4,5-trisphosphate (IP3). Although it is well established that IP3 is converted to numerous inositol phosphates (IPs) and pyrophosphates (PP-IPs) through the action of up to six classes of inositol phosphate kinases (IPKs), it is not clear that these metabolites are influenced by G protein signaling. Here we report that activation of G␣q leads to robust stimulation of IP3 to IP8 metabolism. To expose flux through these pathways, genetic perturbation was used to alter IP homeostasis. Coupled expression of a constitutively active G␣qQL and one or more IPK gene products synergistically generated dramatic changes in the patterns of intracellular IP messengers. Many distinct IP profiles were observed through the expression of different combinations of IPKs, including changes in previously unappreciated pools of IP 5 and IP6, two molecules widely viewed as stable metabolites. Our data link the activation of a trimeric G protein to a plethora of metabolites downstream of IP3 and provide a framework for suggesting that cells possess the machinery to produce an IPK-dependent IP code. We imply, but do not prove, that agonist-induced alterations in such a code would theoretically be capable of enhancing signaling complexity and specificity. The essential roles for IPKs in organism development and cellular adaptation are consistent with our hypothesis that such an IP code may be relevant to signaling pathways.Gq ͉ metabolomics ͉ phospholipase C ͉ signal transduction ͉ G protein-coupled receptor I n mammals, hundreds of G protein-coupled receptors (GPCR) and receptor tyrosine kinases (RTKs) are present and link to numerous intracellular signaling modules that, in combination, enable selective cellular responses. One of the most commonly activated signaling modules is the generation of the second messengers inositol 1,4,5-trisphosphate (IP 3 ) and 1,2-diacylglycerol by the action of phospholipase C isozymes (PLCs) on phosphatidylinositol 4,5-bisphosphate (PIP 2 ) (1-5). The ubiquity of PLC activation in response to a wide range of stimuli supports its central role in signaling, but also emphasizes that the production of two messengers alone, IP 3 and diacylglycerol, is insufficient to encode the breadth of specific cellular responses necessary for survival and adaptation. Therefore, it has been postulated that further signaling diversity could theoretically arise from the conversion of IP 3 to numerous inositol tetrakisphosphate (IP 4 ), inositol pentakisphosphate (IP 5 ), inositol hexakisphosphate (IP 6 ), and inositol pyrophosphate (PP-IP) molecules (2, 6-9). The production of these regulators occurs through the action of up to six classes of evolutionarily conserved IP kinase (IPK) gene products that include: IPMK/IPK2 (10-14), IPK1 (15-17), , ITPK/IP56K (21, 22), IP6K/ IHPK (23-25), and VIP1 (25-27) (Fig. 1). Genetic and biochemical studies of IPKs have provided v...

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A Role for Rat Inositol Polyphosphate Kinases rIPK2 and rIPK1 in Inositol Pentakisphosphate and Inositol Hexakisphosphate Production in Rat-1 Cells

Cited by 51 publications

References 51 publications

Inositol Pentakisphosphate Mediates Wnt/β-Catenin Signaling

Inositol Pentakisphosphate Mediates Wnt/β-Catenin Signaling

Integration of Inositol Phosphate Signaling Pathways via Human ITPK1

Alterations in an inositol phosphate code through synergistic activation of a G protein and inositol phosphate kinases

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