Abstract
Memapsin 2 (BACE, beta-secretase) is a membrane-associated aspartic protease that initiates the hydrolysis of beta-amyloid precursor protein (APP) leading to the production of amyloid-beta (A beta) and the progression of Alzheimer disease. Both memapsin 2 and APP are transported from the cell surface to endosomes where APP is cleaved by memapsin 2. We described previously that the cytosolic domain of memapsin 2 contains an acid cluster-dileucine motif (ACDL) that binds the VHS (Vps-27, Hrs, and STAM) domain of Golgi-localized gamma-ear-containing ARF-binding (GGA) proteins (He, X., Zhu, G., Koelsch, G., Rodgers, K. K., Zhang, X. C., and Tang, J. (2003) Biochemistry 42, 12174-12180). Here we report that GGA proteins colocalize in the trans-Golgi network and endosomes with memapsin 2 and a memapsin 2 chimera containing a cytosolic domain of a mannose-6-phosphate receptor. Depleting cellular GGA proteins with RNA interference or mutation of serine 498 to stop the phosphorylation of ACDL resulted in the accumulation of memapsin 2 in early endosomes. A similar change of memapsin 2 localization also was observed when a retromer subunit, VPS26, was depleted. These observations suggest that GGA proteins function with the phosphorylated ACDL in the memapsin 2-recycling pathway from endosomes to trans-Golgi on the way back to the cell surface.
Highlights
Memapsin 2 (EC 3.4.23.46) (1), called -secretase, BACE (2), and ASP-2 (3, 4), is the protease that initiates the cleavage of -amyloid precursor protein (APP).1 After a second cleavage by another protease, ␥-secretase, a 40- or 42-residue peptide called amyloid- (A) is produced
M2-mannose-6-phosphate receptors (MPRs), in which the memapsin 2 cytosolic domain was replaced by the cytosolic domain of CD-MPR (Fig. 1A) that contained an acid clusterdileucine motif (ACDL) motif
The ACDL motif in the cytosolic domain of memapsin 2 was presumably phosphorylated and interacted with GGA proteins to facilitate its transport from endosomes via TGN to cell surface
Summary
Memapsin 2 (EC 3.4.23.46) (1), called -secretase, BACE (2), and ASP-2 (3, 4), is the protease that initiates the cleavage of -amyloid precursor protein (APP). After a second cleavage by another protease, ␥-secretase, a 40- or 42-residue peptide called amyloid- (A) is produced. The region of memapsin 2 cytosolic domain that mediates cellular trafficking has been traced to a motif with the sequence DISLL This motif, which belongs to the acidic cluster-dileucine (ACDL) sorting signal (DXXLL, where X denotes a nonconserved residue) (for review, see Ref. 13), binds the VHS (Vps-27, Hrs, and STAM) domains of Golgilocalized ␥-ear-containing ARF-binding (GGA) proteins (14, 15). Phosphorylation of the memapsin 2 ACDL motif is essential for its recycling pathway from early endosomes to the cell surface (11). These observations open the possibility that the interaction of GGA proteins with the phosphorylated memapsin 2 may mediate the recycling of the protease from endosomes. We report in this paper that GGA proteins are involved in the cellular transport of memapsin 2 from endosomes to the cell surface in the recycle pathway
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