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)Minpp1 in a variety of mouse tissues, comparable to the expression of other mammalian homologs, but less restricted than the expression of HiPER1 in chick. A purified (MMU)Minpp1 fusion protein cleaved phosphate from inositol (1,3,4,5)-tetrakisphosphate and para-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)Minpp1 and (HSA)MINPP1 genes is also conserved compared to the chick HiPER1 gene. 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)MINPP1 to human chromosome 10q23 by fluorescence in situ hybridization, YAC screening, and radiation hybrid mapping. This assignment places (HSA)MINPP1 in a region of chromosome 10 that is frequently mutated in human cancers and places (HSA)MINPP1 proximal to the tumor suppressor PTEN, which maps to 10q23.3. Using a radiation hybrid panel, we localized (MMU)Minpp1 to a region of mouse chromosome 19 that includes the murine homolog of Pten. The evolutionary conservation of this novel enzyme within the inositol polyphosphate pathway suggests a significant role for multiple inositol polyphosphate phosphatase throughout higher eukaryotes.
Copyright 1999 Academic Press.