The Synthesis of Inositol Hexakisphosphate

Verbsky, John W.; Wilson, Monita P.; Kisseleva, Marina V.; Majerus, Philip W.; Wente, Susan R.

doi:10.1074/jbc.m205682200

Cited by 87 publications

(42 citation statements)

References 29 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…1F) and no other inositol polyphosphates we tested (data not shown). These data are consistent with the recently reported characterization of human IPK1 (13). Fig.…”

Section: Resultssupporting

confidence: 83%

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

Fujii

York

2005

Journal of Biological Chemistry

View full text Add to dashboard Cite

Over 30 inositol polyphosphates are known to exist in mammalian cells; however, the majority of them have uncharacterized functions. In this study we investigated the molecular basis of synthesis of highly phosphorylated inositol polyphosphates (such as inositol tetrakisphosphate, inositol pentakisphosphate (IP 5 ), and inositol hexakisphosphate (IP 6 )) in rat cells. We report that heterologous expression of rat inositol polyphosphate kinases rIPK2, a dual specificity inositol trisphosphate/inositol tetrakisphosphate kinase, and rIPK1, an IP 5 2-kinase, were sufficient to recapitulate IP 6 synthesis from inositol 1,4,5-trisphosphate in mutant yeast cells. Overexpression of rIPK2 in Rat-1 cells increased inositol 1,3,4,5,6-pentakisphosphate (I(1,3,4,5,6)P 5 ) levels about 2-3-fold compared with control. Likewise in Rat-1 cells, overexpression of rIPK1 was capable of completely converting I(1,3,4,5,6)P 5 to IP 6 . Simultaneous overexpression of both rIPK2 and rIPK1 in Rat-1 cells increased both IP 5 and IP 6 levels. To reduce IPK2 activity in Rat-1 cells, we introduced vector-based short interference RNA against rIPK2. Cells harboring the short interference RNA had a 90% reduction of mRNA levels and a 75% decrease of I(1,3,4,5,6)P 5 . These data confirm the involvement of IPK2 and IPK1 in the conversion of inositol 1,4,5-trisphosphate to IP 6 in rat cells. Furthermore these data suggest that rIPK2 and rIPK1 act as key determining steps in production of IP 5 and IP 6 , respectively. The ability to modulate the intracellular inositol polyphosphate levels by altering IPK2 and IPK1 expression in rat cells will provide powerful tools to study the roles of I(1,3,4,5,6)P 5 and IP 6 in cell signaling.Most of the over 30 inositol polyphosphates present in mammalian cells have unknown physiological functions (1-3). One of the well characterized inositol polyphosphates is a second messenger, inositol 1,4,5-trisphosphate (I(1,4,5)P 3 ), 1 which participates in intracellular Ca 2ϩ mobilization (4) and also serves as a precursor of highly phosphorylated inositol polyphosphates such as inositol tetrakisphosphate (IP 4 ), inositol pentakisphosphate (IP 5 ), and inositol hexakisphosphate (IP 6 ) (1-3). Recently the inositol polyphosphate synthetic pathway in budding yeast, Saccharomyces cerevisiae, has been identified (5-8). In yeast, I(1,4,5)P 3 , which is hydrolyzed from phosphatidylinositol 4,5-bisphosphate by phospholipase C, is sequentially phosphorylated to IP 6 by two inositol polyphosphate kinases, a multiple specificity IP 3 /IP 4 kinase (inositol polyphosphate kinase 2 (Ipk2)) and an IP 5 2-kinase (inositol polyphosphate kinase 1 (Ipk1)). On the other hand, a synthetic pathway of IP 6 from I(1,4,5)P 3 in mammalian cells is thought to be more complex and to be a sequence of I(1,4,5)P 3 3 I(1,3,4,5)P 4 3 I(1,3,4)P 3 3 I(1,3,4,6)P 4 3 I(1,3,4,5,6)P 5 3 IP 6 (2, 3). In this pathway, IP 3 3-kinases (2), inositol polyphosphate 5-phosphatases (9), and I(1,3,4)P 3 5/6-kinase (3) appear to catalyze the first three steps to produ...

show abstract

“…1F) and no other inositol polyphosphates we tested (data not shown). These data are consistent with the recently reported characterization of human IPK1 (13). Fig.…”

Section: Resultssupporting

confidence: 83%

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

Fujii

York

2005

Journal of Biological Chemistry

View full text Add to dashboard Cite

show abstract

“…The pathways that produce the higher soluble inositol phosphates in human cells have been elucidated recently (1)(2)(3). The action of phospholipase C on phosphatidylinositol 4,5-bisphosphate, yields inositol 1,4,5-trisphosphate (InsP 3 ) 1 and diacylglycerol.…”

mentioning

confidence: 99%

Increased Levels of Inositol Hexakisphosphate (InsP6) Protect HEK293 Cells from Tumor Necrosis Factor α- and Fas-induced Apoptosis

Verbsky

Majerus

2005

Journal of Biological Chemistry

Self Cite

View full text Add to dashboard Cite

The overexpression of inositol 1,3,4-trisphosphate 5/6-kinase has recently been shown to protect HEK293 cells from tumor necrosis factor ␣ (TNF␣)-induced apoptosis. This overexpression leads to an increase in the levels of both inositol 1,3,4,5,6-pentakisphosphate (InsP 5 ) and inositol 1,2,3,4,5,6-hexakisphosphate (InsP 6 ). Cells that overexpress InsP 5 2-kinase have increased levels of InsP 6 and are also protected from TNF␣-induced apoptosis; furthermore, cells that express an RNA interference construct to the 2-kinase are deficient in InsP 6 and are sensitized to TNF␣-induced apoptosis. Therefore the protective effect of 5/6-kinase on TNF␣-mediated apoptosis is due to an increase of InsP 6 or to a metabolite derived from InsP 6 . Furthermore, we find that the InsP 6 also protects from Fas-mediated apoptosis. No effect was seen in the endocytic rate of transferrin receptor, caspase 8 activity, or TNF receptor number at the cell surface. Cells that overexpress 2-kinase do show an increase in the amount of receptor-interacting protein (RIP), while cells with reduced InsP 6 levels show relatively less RIP, providing a possible mechanism for the effect on apoptosis.The pathways that produce the higher soluble inositol phosphates in human cells have been elucidated recently (1-3). The action of phospholipase C on phosphatidylinositol 4,5-bisphosphate, yields inositol 1,4,5-trisphosphate (InsP 3 ) 1 and diacylglycerol. In mammalian cells, InsP 3 is phosphorylated to inositol 1,3,4,5-tetrakisphosphate by an InsP 3 3-kinase and dephosphorylated to inositol 1,3,4-trisphosphate (Ins(1,3,4)P 3 ) by a 5-phosphatase (4). Ins(1,3,4)P 3 is then phosphorylated to inositol 1,3,4,6-tetrakisphosphate (Ins(1,3,4,6)P 4 ) by the Ins(1,3,4)P 3 5/6-kinase, to inositol 1,3,4,5,6-pentakisphosphate (InsP 5 ) by Ins(1,3,4,6)P 4 5-kinase, and to inositol 1,2,3,4,5,6-hexakisphosphate (InsP 6 ) by InsP 5 2-kinase (1, 5). In cell culture, production of InsP 6 is regulated by the activity of 5/6-kinase, which is rate-limiting (6) producing the committed isomer in the synthesis of InsP 6 , Ins(1,3,4,6)P 4 . Overexpression of 5/6-kinase results in an increase in InsP 5 and InsP 6 , while depletion of 5/6-kinase results in the loss of InsP 5 and InsP 6 .Another function for the inositol (1,3,4)P 3 5/6-kinase other than phosphorylating inositol phosphates was recently discovered. Wilson et al. (7) have shown that 5/6-kinase co-purifies with the COP9 signalosome from cow brain. This complex of nine proteins has been shown to have the ability to phosphorylate c-Jun, IB␣, and p53 (8 -10). Wilson et al. (7) subsequently showed that 5/6-kinase purified from insect cells also phosphorylates c-Jun, p53, and IB␣, making it likely that in part the protein kinase activity of the COP9 signalosome may be attributed to 5/6-kinase.c-Jun and IB are both involved in TNF␣ signaling and apoptosis. TNF␣ is involved in numerous processes including cell death and development and oncogenesis and immune, inflammatory, and stress responses (11). TNF␣ acts in opposing...

show abstract

“…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)(7)(8)(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)(11)(12)(13)(14), IPK1 (15)(16)(17), IP3K (18)(19)(20), ITPK/IP56K (21,22), IP6K/ IHPK (23)(24)(25), and VIP1 (25)(26)(27) (Fig. 1).…”

mentioning

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.

View full text Add to dashboard Cite

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...

show abstract

The Synthesis of Inositol Hexakisphosphate

Cited by 87 publications

References 29 publications

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

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

Increased Levels of Inositol Hexakisphosphate (InsP6) Protect HEK293 Cells from Tumor Necrosis Factor α- and Fas-induced Apoptosis

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

Contact Info

Product

Resources

About