Overexpression of murine phosphatidylinositol 4-phosphate 5-kinase type Ibeta disrupts a phosphatidylinositol 4,5 bisphosphate regulated endosomal pathway.
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)P2]. PI(4,5)P2 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)P2 for the specific cellular processes have not been rigorously defined. Murine PI4P5K type Ibeta (mPIP5K-Ibeta) 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-Ibeta 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)P2-binding pleckstrin homology (PH) domain of phospholipase-Cdelta (PLC-delta). Analysis of the conserved domains of mPIP5K-Ibeta 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-Ibeta and the PLC-delta-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-Ibeta acts through PI(4,5)P2 to regulate endosomal trafficking and/or fusion.
Galiano
Floyd J
FJ
Department of Biochemistry and Molecular Biology and the Feist-Weiller Cancer Center, Louisiana State University Health Sciences Center, School of Medicine in Shreveport, Shreveport, Louisiana 71130, USA.
Ulug
Emin T
ET
Davis
J Nathan
JN
D002460:Cell Line; D019281:Dimerization; D011992:Endosomes / Q000378:metabolism*; D015870:Gene Expression / Q000502:physiology; D006801:Humans; D007527:Isoenzymes / Q000096:biosynthesis* / Q000235:genetics; D008561:Membrane Fusion / Q000502:physiology; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism*; D054803:Phospholipase C delta; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000502:physiology; D021381:Protein Transport / Q000502:physiology*; D010738:Type C Phospholipases / Q000096:biosynthesis* / Q000235:genetics
D007527:Isoenzymes; D019269:Phosphatidylinositol 4,5-Diphosphate; D017853:Phosphotransferases (Alcohol Group Acceptor); C020077:1-phosphatidylinositol-4-phosphate 5-kinase; D010738:Type C Phospholipases; D054803:Phospholipase C delta