PtdIns4KIIα generates endosomal PtdIns(4)P and is required for receptor sorting at early endosomes

Phosphatidylinositol 4-kinase II alpha (PtdIns4KII alpha) localizes to the trans-Golgi network and endosomal compartments and has been implicated in the regulation of endosomal traffic, but the roles of both its enzymatic activity and the site of its action have not been elucidated. This study shows that PtdIns4KII alpha is required for production of endosomal phosphatidylinositol 4-phosphate (PtdIns(4)P) on early endosomes and for the sorting of transferrin and epidermal growth factor receptor into recycling and degradative pathways. Depletion of PtdIns4KII alpha with small interfering RNA significantly reduced the amount of vesicular PtdIns(4) P on early endosomes but not on Golgi membranes. Cells depleted of PtdIns4KII alpha had an impaired ability to sort molecules destined for recycling from early endosomes. We further identify the Eps15 homology domain-containing protein 3 (EHD3) as a possible endosomal effector of PtdIns4KII alpha. Tubular endosomes containing EHD3 were shortened and became more vesicular in PtdIns4KII alpha-depleted cells. Endosomal PtdIns(4,5)P-2 was also significantly reduced in PtdIns4KII alpha-depleted cells. These results show that PtdIns4KII alpha regulates receptor sorting at early endosomes through a PtdIns(4) P-dependent pathway and contributes substrate for the synthesis of endosomal PtdIns(4,5)P-2.