Inositol polyphosphate 4-phosphatase type I regulates cell growth downstream of transcription factor GATA-1

^*Institute of Molecular Medicine, John Radcliffe Hospital, Oxford OX3 9AE, United Kingdom; ^†Department of Hematology-Oncology, ^‡Harvard Medical School, Boston, MA 02115; ^**Howard Hughes Medical Institute, Children's Hospital, Boston, MA 02115; ^¶Division of Hematology-Oncology, Departments of Internal Medicine and Biological Chemistry and Molecular Biophysics, Washington University School of Medicine, St Louis, MO 63110; and ^‖Department of Biochemistry and Biophysics, Iowa State University, Ames, IA 50011

Contributed by Philip W. Majerus

Abstract

Megakaryocytes lacking transcription factor GATA-1 fail to complete maturation in vivo and hyperproliferate. To define how GATA-1 regulates megakaryocyte cell growth we searched for mRNA transcripts expressed in primary wild-type, but not GATA-1⁻, megakaryocytes. One differentially expressed transcript encodes inositol polyphosphate 4-phosphatase type I (4-Ptase I). This enzyme hydrolyses phosphatidylinositol 3,4-bisphosphate and also has lesser activity against soluble analogues of this lipid, inositol 3,4-bisphosphate and inositol 1,3,4-triphosphate. Reintroduction of 4-Ptase I into both primary GATA-1⁻ and wild-type megakaryocytes significantly retards cell growth, suggesting that absence of 4-Ptase I may contribute to the hyperproliferative phenotype of GATA-1⁻ megakaryocytes. Overexpression of 4-Ptase I also markedly reduces growth of NIH 3T3 fibroblasts. Taken together, these data indicate that 4-Ptase I is a regulator of cell proliferation.

Footnotes

↵ § P.V. and F.A.N. contributed equally to this work.
↵ ‡‡ To whom reprint requests should be addressed. E-mail: orkin{at}rascal.med.harvard.edu.
Data deposition: The sequence reported in this paper has been deposited in the GenBank database (accession no. AF317838).
Article published online before print: Proc. Natl. Acad. Sci. USA, 10.1073/pnas.250476397.
Article and publication date are at www.pnas.org/cgi/doi/10.1073/pnas.250476397
Abbreviations:

4-Ptase I,

inositol polyphosphate 4-phosphatase type I;

PI 3-kinase,

phosphatidylinositol 3-kinase;

RT-PCR,

reverse transcriptase–PCR;

HPRT,

hypoxanthine phosphoribosyl transferase;

GFP,

green fluorescent protein