Distinct roles for plasma membrane PtdIns(4)P and PtdIns(4,5)P 2 during receptor-mediated endocytosis in yeast

Abstract

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)P 2 ] in endocytosis but specific roles for phosphatidylinositol-4-phosphate [PtdIns(4)P], other than as the biosynthetic precursor of PtdIns(4,5)P 2 , have not been clarified. In this study we investigated the roles of PtdIns(4)P and PtdIns (4,5)P 2 in receptor-mediated endocytosis through the construction of temperature-sensitive (ts) mutants for the phosphatidylinositol 4-kinases (PI4-kinases) Stt4p and Pik1p and the 1-phosphatidylinositol- 4-phosphate 5-kinase [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 a-factor receptor Ste2p to clathrin-coated pits, whereas PtdIns (4,5)P 2 is required for membrane internalization. We also found that the localization to endocytic sites of the ENTH/ANTH domain-bearing clathrin adaptors, Ent1p, Ent2p, Yap1801p and 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)P 2 during receptor-mediated endocytosis.