The Pathway for the Production of Inositol Hexakisphosphate in Human Cells

Verbsky, John W.; Chang, Shao-Chun; Wilson, Monita P.; Mochizuki, Yasuhiro; Majerus, Philip W.

doi:10.1074/jbc.m411528200

Cited by 75 publications

(74 citation statements)

References 31 publications

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“…If IP3K were not participating in this metabolism, adriamycin likely would have little effect, but in this case adriamycin treatment abolishes the IP 5 response to Wnt3a. We propose that IP3K is the major enzyme to convert IP 3 to IP 4 as it was found in human (45).…”

Section: Resultsmentioning

confidence: 99%

“…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%

Section: Resultsmentioning

confidence: 99%

Inositol Pentakisphosphate Mediates Wnt/β-Catenin Signaling

Gao

Wang

2007

Journal of Biological Chemistry

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“…This function may be superimposed upon a more general role of ITPK1 homologues in eukaryotes: contributing to the synthesis of higher inositol polyphosphates such as InsP 6 (33,37). 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.…”

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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“…We did not use RNA interference to reduce expression of the InsP 5 kinase that synthesizes InsP 6 . This decision was based on previous experiments showing that "knockdown" of mammalian InsP 5 2-kinase expression induces gross changes in nuclear morphology (41), is pro-apoptotic (42), and generally toxic (43,44). Instead, we overexpressed MINPP, an InsP 6 phosphatase.…”

Section: The Effect Of Minpp Upon Insp 6 Levels and Nucleolinmentioning

confidence: 99%

The Nucleolus Exhibits an Osmotically Regulated Gatekeeping Activity That Controls the Spatial Dynamics and Functions of Nucleolin

Yang

Reece²,

Cho

et al. 2008

Journal of Biological Chemistry

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We demonstrate that physiologically relevant perturbations in the osmotic environment rheostatically regulate a gatekeeping function for the nucleolus that controls the spatial dynamics and functions of nucleolin. HeLa cells and U2-OS osteosarcoma cells were osmotically challenged with 100 -200 mM sorbitol, and the intranuclear distribution of nucleolin was monitored by confocal microscopy. Nucleolin that normally resides in the innermost fibrillar core of the nucleolus, where it assists rDNA transcription and replication, was expelled within 30 min of sorbitol addition. The nucleolin was transferred into the nucleoplasm, but it distributed there non-uniformly; locally high levels accumulated in 4,6-diamidino-2-phenylindole-negative zones containing euchromatic (transcriptionally active) DNA. Inositol pyrophosphates also responded within 30 min of hyperosmotic stress: levels of bisdiphosphoinositol tetrakisphosphate increased 6-fold, and this was matched by decreased levels of its precursor, diphosphoinositol pentakisphosphate. Such fluctuations in inositol pyrophosphate levels are of considerable interest, because, according to previously published in vitro data, they regulate the degree of phosphorylation of nucleolin through a novel kinase-independent phosphotransferase reaction (Saiardi, A., Bhandari, A., Resnick, R., Cain, A., Snowman, A. M., and Snyder, S. H. (2004) Science 306, 2101-2105). However, by pharmacologically intervening in inositol pyrophosphate metabolism, we found that it did not supervise the osmotically driven switch in the biological activities of nucleolin in vivo.

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The Pathway for the Production of Inositol Hexakisphosphate in Human Cells

Cited by 75 publications

References 31 publications

Inositol Pentakisphosphate Mediates Wnt/β-Catenin Signaling

Inositol Pentakisphosphate Mediates Wnt/β-Catenin Signaling

Integration of Inositol Phosphate Signaling Pathways via Human ITPK1

The Nucleolus Exhibits an Osmotically Regulated Gatekeeping Activity That Controls the Spatial Dynamics and Functions of Nucleolin

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