Overexpression of murine phosphatidylinositol 4-phosphate 5-kinase type Iβ disrupts a phosphatidylinositol 4,5 bisphosphate regulated endosomal pathway

✍ Scribed by Floyd J. Galiano; Emin T. Ulug; J. Nathan Davis

• Publisher: John Wiley and Sons
• Year: 2002
• Tongue: English
• Weight: 453 KB
• Volume: 85
• Category: Article
• ISSN: 0730-2312
• DOI: 10.1002/jcb.10100

✦ Synopsis

Abstract

The type I phosphatidylinositol 4‐phosphate 5‐kinases (PI4P5K) phosphorylate phosphatidylinositol 4‐phosphate [PI(4)P] to produce phosphatidylinositol 4,5‐bisphosphate [PI(4,5)P~2~]. PI(4,5)P~2~ has been implicated in signal transduction, receptor mediated endocytosis, vesicle trafficking, cytoskeletal structure, and membrane ruffling. However, the specific type I enzymes associated with the production of PI(4,5)P~2~ for the specific cellular processes have not been rigorously defined. Murine PI4P5K type Iβ (mPIP5K‐Iβ) was implicated in receptor mediated endocytosis through the isolation of a truncated and inactive form of the enzyme that blocked the ligand‐dependent downregulation of the colony‐stimulating factor‐1 receptor. The present study shows that enforced expression of mPIP5K‐Iβ in 293T cells resulted in the accumulation of large vesicles that were linked to an endosomal pathway. Similar results were obtained after the expression of the PI(4,5)P~2~‐binding pleckstrin homology (PH) domain of phospholipase‐Cδ (PLC‐δ). Analysis of the conserved domains of mPIP5K‐Iβ led to the identification of dimerization domains in the N‐ and C‐terminal regions. Enforced expression of the individual dimerization domains interfered with the proper subcellular localization of mPIP5K‐Iβ and the PLC‐δ‐PH domain and blocked the accumulation of the endocytic vesicles induced by these proteins. In addition to regulating early steps in endocytosis, these results suggest that mPIP5K‐Iβ acts through PI(4,5)P~2~ to regulate endosomal trafficking and/or fusion. J. Cell. Biochem. 85: 131–145, 2002. © 2002 Wiley‐Liss, Inc.