The adaptor protein Dab2 sorts LDL receptors into coated pits independently of AP-2 and ARH.
Clathrin-mediated endocytosis requires cargo-specific adaptor proteins that recognize specific receptors and recruit them into coated pits. ARH [also called low-density lipoprotein receptor (LDLR) adaptor protein] serves as an adaptor for LDLR endocytosis in liver. However, ARH is dispensable for LDL uptake by some other cell types. Here, we show that the adaptor Dab2 plays a major role in LDLR internalization in HeLa cells and fibroblasts. Dab2 mediates internalization of LDLRs but not transferrin receptors independently of ARH and the classic clathrin adaptor AP-2. If Dab2 is absent, ARH can mediate LDLR endocytosis, but its action requires AP-2. Furthermore, the rate of LDLR endocytosis is decreased when Dab2 is absent and Dab2, but not ARH, catalyzes the efficient clustering of LDLR into coated pits. Dab2 activity requires its binding to clathrin, LDLR and phospholipids. Dab2 is also involved in moving LDLRs off filopodia. We suggest that Dab2 is a cargo-specific endocytic adaptor protein, stably associating with phospholipids and clathrin to sort LDLR to nascent-coated pits, whereas ARH might accelerate later steps in LDLR endocytosis in cooperation with AP-2.
Maurer
Meghan E
ME
Molecular and Cellular Biology Program, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue N, Seattle, WA 98109, USA.
Cooper
Jonathan A
JA
D033962:Adaptor Protein Complex 2 / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D051017:Apoptosis Regulatory Proteins; D002966:Clathrin / Q000378:metabolism; D003034:Coated Pits, Cell-Membrane / Q000378:metabolism*; D004705:Endocytosis / Q000502:physiology; D020868:Gene Silencing; D006367:HeLa Cells; D006801:Humans; D008954:Models, Biological; D018995:Myosin Heavy Chains / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism; D011485:Protein Binding; D021381:Protein Transport / Q000502:physiology; D034741:RNA, Small Interfering / Q000235:genetics; D011973:Receptors, LDL / Q000378:metabolism*; D035361:Transcription Factor TFIIIB / Q000378:metabolism; D025521:Tumor Suppressor Proteins
D033962:Adaptor Protein Complex 2; D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; C427472:BDP1 protein, human; D002966:Clathrin; C102885:DAB2 protein, human; C469745:LDLRAP1 protein, human; D010743:Phospholipids; D034741:RNA, Small Interfering; D011973:Receptors, LDL; D035361:Transcription Factor TFIIIB; D025521:Tumor Suppressor Proteins; C089785:myosin VI; D018995:Myosin Heavy Chains