S-nitrosylation of ARH is required for LDL uptake by the LDL receptor

Abstract

This article is available online at http://www.jlr.org (ARH) and the disabled-like protein 2 (dab2). Both ARH and dab2 target LDLRs to coated pits through binding sites for the LDLR, clathrin, and the adaptor protein 2 (AP-2) complex. ARH binds to the FDNPVY 807 sequence of the LDLR through a phosphotyrosine-binding (PTB) domain, to the heavy chain of clathrin through a clathrin box sequence, and to the ␤ 2-subunit of AP-2 through a sequence with strong homology to the AP-2-binding sequences of ␤ -arrestins ( 5-8 ) ( Fig. 1A ). Y807 of the FDNPVY 807 plays a critical role in the interaction of ARH and dab2 with the LDLR, and mutation of Y807 to either cysteine or alanine cripples LDLR-dependent LDL uptake ( 3,5,8,9 ). By contrast, uptake of VLDL remnants does not require ARH, dab2, or a functional FDNPVY sequence because binding of VLDL remnants to the LDLR induces a separate endocytic process that involves a second internalization motif on the LDLR cytoplasmic domain ( 10 ). It is not clear why the LDLR needs an induced process for VLDL remnant uptake when the FDNPVY-dependent process can internalize both LDL and VLDL remnants, nor why the FDNPVY process utilizes both the ARH and dab2 adaptors when either adaptor is suffi cient to support lipoprotein uptake by the LDLR.A key question is why an ARH is necessary. ARH has highest expression in kidney, liver, and placenta ( 11 ); however, dab2 is also highly expressed in both kidney and placenta, and it is dab2, not ARH, that is required for normal placental and kidney function ( 12 ). Hepatocytes and peripheral blood leukocytes lack dab2 ( 13,14 ), and ARH defi ciency in both humans and mice sharply reduces LDL clearance rates, resulting in hypercholesterolemia ( 15-18 ). Why hepatocytes and leukocytes normally rely upon ARH is unclear because both cell types lose their dependence on ARH for LDL uptake when dab2 expression is induced Abstract The LDL receptor (LDLR) relies upon endocytic adaptor proteins for internalization of lipoproteins. The results of this study show that the LDLR adaptor autosomal recessive hypercholesterolemia protein (ARH) requires nitric oxide to support LDL uptake. Nitric oxide nitrosylates ARH at C199 and C286, and these posttranslational modifi cations are necessary for association of ARH with the adaptor protein 2 (AP-2) component of clathrin-coated pits. In the absence of nitrosylation, ARH is unable to target LDL-LDLR complexes to coated pits, resulting in poor LDL uptake. The role of nitric oxide on LDLR function is specifi c for ARH because inhibition of nitric oxide synthase activity impairs ARH-supported LDL uptake but has no effect on other LDLR-dependent lipoprotein uptake processes, including VLDL remnant uptake and dab2-supported LDL uptake. These fi ndings suggest that cells that depend upon ARH for LDL uptake can control which lipoproteins are internalized by their LDLRs through changes in nitric oxide. -Zhao, Z., S. Pompey, H. Dong, J. Weng, R. Garuti, and P. Michaely. The LDL receptor (LDLR) internalizes a broad spectrum ...

Research update for articles published in EJCI in 2012

“…Zhao et al and several others have reported that uptake of certain fractions of lipoproteins, especially, VLDL remnant does not require LDL receptor adaptor protein 1 (LDLRAP1) [78]. Those basic data support our findings that clearance of remnant lipoproteins is preserved in autosomal recessive hypercholesterolaemia (ARH), which is caused by the loss of function mutations in LDLRAP1 gene.…”

Endocytic adaptors Arh and Dab2 control homeostasis of circulatory cholesterol

“…2B). It was uncertain if these variants are related to the posttranslational modifications such as S-nitrosylation of Arh (31). In contrast, arh deletion did not cause a compensatory expression of Dab2 or LDLR proteins in either MEFs or hepatic tissues (Fig.…”

Endocytosis in the adaptation to cellular stress

“…Alternatively, modifications of specific adaptor proteins might be employed to trigger changes in the endocytosis of select cargos. For example, ARH, the endocytic adaptor that facilitates the internalization of ligand-bound LDLRs, needs to be S-nitrosylated to interact with AP-2 [32]. This type of modification could conceivably be modulated by cellular redox state and, thus, be responsive to certain types of stress.…”