Multiple Inositol Polyphosphate Phosphatase: Evolution as a Distinct Group within the Histidine Phosphatase Family and Chromosomal Localization of the Human and Mouse Genes to Chromosomes 10q23 and 19

Abstract

Multiple inositol polyphosphate phosphatase is the only enzyme known to hydrolyze the abundant metabolites inositol pentakisphosphate and inositol hexakisphosphate. We have previously demonstrated that the chick homolog of multiple inositol polyphosphate phosphatase, designated HiPER1, has a role in growth plate chondrocyte differentiation. The relationship of these enzymes to intracellular signaling is obscure, and as part of our investigation we have examined the murine ((MMU)Minpp1) and human ((HSA)MINPP1) homologs. Northern blot analysis demonstrated expression of ((MMU)Minpp1in a variety of mouse tissues, comparable to the expression of other mammalian homologs, but less restricted than the expression ofHiPER1in chick. A purified (MMU)Minpp1 fusion protein cleaved phosphate from inositol (1,3,4,5)-tetrakisphosphate andpara-nitrophenyl phosphate. When the presumptive active site histidine was altered to alanine by site-directed mutagenesis, enzyme activity was abolished, confirming the classification of (MMU)Minpp1 as a histidine phosphatase. The amino acid sequences of the murine and human MINPP proteins share >80% identity with the rat enzyme and >56% identity with HiPER1, with conservation of the C-terminal consensus sequence that retains proteins in the endoplasmic reticulum. The intron/exon structure of the mammalian (MMU)Minpp1and (HSA)MINPP1genes is also conserved compared to the chickHiPER1gene. Sequence analysis of plant and fruit fly MINPP homologs supports the hypothesis that the MINPP enzymes constitute a distinct evolutionary group within the histidine phosphatase family. We have mapped (HSA)MINPP1to human chromosome 10q23 by fluorescencein situhybridization, YAC screening, and radiation hybrid mapping. This assignment places (HSA)MINPP1in a region of chromosome 10 that is frequently mutated in human cancers and places (HSA)MINPP1proximal to the tumor suppressorPTEN,which maps to 10q23.3. Using a radiation hybrid panel, we localized (MMU)Minpp1to a region of mouse chromosome 19 that includes the murine homolog ofPten.The evolutionary conservation of this novel enzyme within the inositol polyphosphate pathway suggests a significant role for multiple inositol polyphosphate phosphatase throughout higher eukaryotes.