Distinct roles for plasma membrane PtdIns 4 P and PtdIns 4 5 P2 during yeast receptor mediated endocytosis

Clathrin-mediated endocytosis requires the coordinated assembly of various endocytic proteins and lipids at the plasma membrane. Accumulating evidence demonstrates a crucial role for phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2) in endocytosis, but specific roles for PtdIns(4)P other than as the biosynthetic precursor of PtdIns(4,5)P2 have not been clarified. In this study we investigated the role of PtdIns(4)P or PtdIns(4,5)P2 in receptor-mediated endocytosis through the construction of temperature-sensitive (ts) mutants for the PI 4-kinases Stt4p and Pik1p and the PtdIns(4) 5-kinase Mss4p. Quantitative analyses of endocytosis revealed that both the stt4(ts)pik1(ts) and mss4(ts) mutants have a severe defect in endocytic internalization. Live-cell imaging of endocytic protein dynamics in stt4(ts)pik1(ts) and mss4(ts) mutants revealed that PtdIns(4)P is required for the recruitment of the alpha-factor receptor Ste2p to clathrin-coated pits whereas PtdIns(4,5)P2 is required for membrane internalization. We also found that the localization to endocytic sites of the ENTH/ANTH domain-bearing clathrin adaptors, Ent1p/Ent2p and Yap1801p/Yap1802p, is significantly impaired in the stt4(ts)pik1(ts) mutant, but not in the mss4(ts) mutant. These results suggest distinct roles in successive steps for PtdIns(4)P and PtdIns(4,5)P2 during receptor-mediated endocytosis.