BINDING OF AP-1 GOLGI ADAPTERS TO MEMBRANES REQUIRES PHOSPHORYLATED CYTOPLASMIC DOMAINS OF THE MANNOSE 6-PHOSPHATE INSULIN-LIKE GROWTH FACTOR-II RECEPTOR/

In mammalian cells, clathrin-coated vesicles mediate transport of the lysosomal enzyme receptors from the trans-Golgi network to the endocyt ic pathway. A critical step of this process is the recruitment of Golg i-specific adaptors onto Golgi membranes for efficient clathrin polyme rization. An in vitro assay was used here to quantitate this event in streptolysin-O-permeabilized NRK cells. At 37-degrees-C, these interac tions are cytosol- and energy-dependent, sensitive to GTP(gamma)S (gua nosine 5'-O-(thiotriphosphate)) and brefeldin A. We report that Golgi- specific adaptor binding is enhanced in mannose 6-phosphate/insulin-li ke growth factor II (IGF II) receptor-overexpressing cells and reduced in mannose 6-phosphate receptor-deficient cells. Furthermore, adaptor binding is partially inhibited after addition of soluble cytoplasmic domains of the mannose 6-phosphate/GF II receptor. Almost complete inh ibition is only observed when this domain is phosphorylated on serines 2421 and 2492, a major modification acquired during exit of the recep tor from the Golgi. These results show that the mannose 6-phosphate/IG F II receptor is part of the components that recruit the Golgi-specifi c adaptors and that its phosphorylation is an important feature for hi gh affinity interactions with sorting components.