The human homologue of yeast ArgRIII protein is an inositol phosphate multikinase with predominantly nuclear localization

Abstract

The function of the transcription regulator ArgRIII in the expression of several genes involved in the metabolism of arginine in yeast has been well studied. It was previously reported that it is also an inositol phosphate multikinase and an important factor of the mRNA export pathway [reviewed by Shears (2000) Bioessays 22, 786-789]. In the present study we report the cloning of a full-length 1248-bp cDNA encoding a human inositol phosphate multikinase (IPMK). This protein has a calculated molecular mass of 47.219 kDa. Functionally important motifs [inositol phosphate-binding site, ATP-binding site, catalytically important SSLL (Ser-Ser-Leu-Leu) domain] are conserved between the human IPMK and yeast ArgRIII. Bacterially expressed protein demonstrated an inositol phosphate multikinase activity similar to that of yeast ArgRIII. Ins(1,4,5)P3 is phosphorylated at positions 3 and 6 up to Ins(1,3,4,5,6)P5. The human IPMK fused with a fluorescent protein tag is localized predominantly in the nucleus when transiently expressed in mammalian cells. A basic cluster in the protein's C-terminus is positively involved in nuclear targeting. These findings are consistent with the concept of a nuclear inositol phosphate signalling and phosphorylation pathway in mammalian cells.

Molecular and Biochemical Characterization of Two Plant Inositol Polyphosphate 6-/3-/5-Kinases

“…evident is exactly how I(1,3,4)P 3 would be produced in Arabidopsis given that there does not appear to be a specific I(1,4,5)P 3 3-kinase gene (which as mentioned earlier is the canonical member of the IPK family defined by the PXXX-DXKXG motif). We did not detect significant IP 3 3-kinase activity in AtIpk2s; however, the Shears and Mayr groups have reported (18,30,31) that other Ipk2s do synthesize I(1,3,4,5)P 4 as an intermediate of the IP 3 to IP 5 reaction. Under the conditions described in this study, we have not been able to detect I(1,3,4,5)P 4 as a product but it is certainly possible that under different conditions AtIpk2s would generate I(1,3,4,5)P 4 , which could then be dephosphorylated by a 5-phosphatase to make I(1,3,4)P 3 .…”

Arginine Transcriptional Response Does Not Require Inositol Phosphate Synthesis

“…Different studies have shown that IPMK accumulates preferentially in the nucleus (10,31,32). This is a strong indication that some of its inositol phosphate products may be involved in regulating gene expression.…”

Stabilization of protein–protein interactions by small molecules

“…In humans, D-myo-inositol 1,4,5,6-tetrakisphosphate [Ins(1,4,5, 6)P 4 ; Table 1] is produced by inositol phosphate multikinase (IMPK) that phosphorylates Ins(1,4,5)P 3 to form Ins(1,3,4,5,6)P 4 [64]. The yeast homolog of IMPK -the kinase Arg82 -has been shown to be involved in transcriptional regulation suggesting a functional role of Ins(1,3,4,5,6)P 4 in regulation of gene expression.…”