Y. Aikawa et al., Involvement of PITPnm, a mammalian homologue of Drosophila rdgB, in phosphoinositide synthesis on Golgi membranes, J BIOL CHEM, 274(29), 1999, pp. 20569-20577
Phosphatidylinositol transfer protein (PITP) is involved in phospholipase C
-mediated signaling and membrane trafficking. We previously reported clonin
g and characterization of a gene encoding for membrane-bound PITP, named PI
TPnm, that is a mammalian homologue of the Drosophila retinal degeneration
B (rdgB) gene (Aikawa, Y., Hara, H., and Watanabe, T. (1997) Biochem. Bioph
ys. Res. Commun, 236, 559-564). Here we report the subcellular localization
of PITPnm protein and provide evidence for its involvement in phosphatidyl
inositol 4-phosphate (PtdIns 4-P) synthesis. PITPnm is an integral membrane
protein that largely localized in close association with membranes of Golg
i vacuoles and the endoplasmic reticulum (ER). The amino terminus region of
PITPnm was exposed to cytoplasmic side. Interaction with various phosphoin
ositides was observed in the amino terminus region spanning from 196 amino
acids to 257 amino acids of PITPnm. At the amino terminus regions of 1-372
amino acids, PITPnm formed a complex with type III PtdIns 4-kinase. The tra
nsmembrane and carboxyl-terminal portions (residues 418-1242) functioned to
retain the PITPnm in the Golgi vacuole. These results suggest that PITPnm
plays a role in phosphoinositide synthesis on the Golgi vacuoles and possib
ly in the PtdIns signaling pathway in mammalian cells.