Hermansky-Pudlak Syndrome Protein Complexes Associate with Phosphatidylinositol 4-Kinase Type II in Neuronal and Non-neuronal Cells

Department of Cell Biology and Medicine, Emory University, Atlanta, Georgia 30322, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 12/2008; 284(3):1790-802. DOI: 10.1074/jbc.M805991200
Source: PubMed


The Hermansky-Pudlak syndrome is a disorder affecting endosome sorting. Disease is triggered by defects in any of 15 mouse gene products, which are part of five distinct cytosolic molecular complexes: AP-3, homotypic fusion and vacuole protein sorting, and BLOC-1, -2, and -3. To identify molecular associations of these complexes, we used in vivo cross-linking followed by purification of cross-linked AP-3 complexes and mass spectrometric identification of associated proteins. AP-3 was co-isolated with BLOC-1, BLOC-2, and homotypic fusion and vacuole protein sorting complex subunits; clathrin; and phosphatidylinositol-4-kinase type II alpha (PI4KIIalpha). We previously reported that this membrane-anchored enzyme is a regulator of AP-3 recruitment to membranes and a cargo of AP-3 ( Craige, B., Salazar, G., and Faundez, V. (2008) Mol. Biol. Cell 19, 1415-1426 ). Using cells deficient in different Hermansky-Pudlak syndrome complexes, we identified that BLOC-1, but not BLOC-2 or BLOC-3, deficiencies affect PI4KIIalpha inclusion into AP-3 complexes. BLOC-1, PI4KIIalpha, and AP-3 belong to a tripartite complex, and down-regulation of either PI4KIIalpha, BLOC-1, or AP-3 complexes led to similar LAMP1 phenotypes. Our analysis indicates that BLOC-1 complex modulates the association of PI4KIIalpha with AP-3. These results suggest that AP-3 and BLOC-1 act, either in concert or sequentially, to specify sorting of PI4KIIalpha along the endocytic route.

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    • "Recruitment of AP-1 onto membranes at the TGN has been reported to be dependent on phosphatidylinositol 4-phosphate (PI4P)24. Similarly, PI4KIIalpha activity has been shown to be necessary for recuitment of AP-3 onto membranes enriched in PI4P25. Some of the earlier studies have identified an important role for other PI4Ks in picornavirus replication and also in heptitis C virus infection26. "
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