Differential Roles of JIP Scaffold Proteins in the Modulation of Amyloid Precursor Protein Metabolism

Hidenori Taru,Yutaka Kirino,Toshiharu Suzuki

doi:10.1074/jbc.m203713200

Abstract

We previously found that the JNK-interacting proteins JIP1b and JIP2 associate with the cytoplasmic domain of the Alzheimer's amyloid precursor protein (APP) (Taru, H., Iijima, K., Hase, M., Kirino, Y., Yagi, Y., and Suzuki, T. (2002) J. Biol. Chem. 277, 20070-20078). This interaction involves the carboxyl-terminal phosphotyrosine interaction (PI) domain of JIP1b or JIP2 and the GYENPTY motif in the APP cytoplasmic domain. The expression of JIP1b stabilizes immature APP and suppresses the production of a secreted large extracellular amino-terminal domain of APP, the generation of a cleaved intracellular carboxyl-terminal fragment of APP, and the secretion of beta-amyloid 40 and 42. Deletion of the PI domain or alteration of PI amino acid residues prevents JIP1b from interacting with APP and affecting its metabolism, but deletion of the JNK-binding domain of JIP1b has no effect. JIP2, a weaker APP-binding protein, does not influence the processing of APP, although it is known that both JIP1b and JIP2 equally regulate the JNK signaling cascade. The present results suggest that JIP1b can directly modulate APP metabolism by interacting with the APP cytoplasmic domain, independent of its regulation of the JNK signaling cascade.

Highlights

The ␤-amyloid peptide (A␤)1 is a component of amyloid plaques, one of the major hallmarks of Alzheimer’s disease (AD), and is implicated in the pathology of AD
1 The abbreviations used are: A␤, ␤-amyloid peptide; AD, Alzheimer’s disease; APP, ␤-amyloid precursor protein; APPcyt, the cytoplasmic domain of APP; CHAPS, 3-[(3-cholamidpropyl)dimethylammonio]-1propane-sulfonic acid; JNK, c-Jun amino-terminal kinase; JIP, JNKinteracting protein; PI, phosphotyrosine interaction; GST, glutathione S-transferase; N2a, mouse neuroblastoma Neuro-2a cells; CTF, intracellular carboxyl-terminal fragment of APP truncated at ␣- (CTF␣) or ␤-site (CTF␤); sAPP, the secreted large amino-terminal ectodomain of APP cleaved at the ␣- or ␤-site; DMEM, Dulbecco’s modified Eagle’s medium; FBS, fetal bovine serum; ELISA, enzyme-linked immunosorbent assay; Tricine, N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]glycine; APPL, APP-like; HA, hemagglutinin
To define the region of APPcyt required for its interaction with JIP proteins, we examined the ability of JIP1b, a stronger APP-binder than JIP2, to bind various APPcyt protein constructs (Fig. 1, A and B)

Summary

The abbreviations used are

A␤, ␤-amyloid peptide; AD, Alzheimer’s disease; APP, ␤-amyloid precursor protein; APPcyt, the cytoplasmic domain of APP; CHAPS, 3-[(3-cholamidpropyl)dimethylammonio]-1propane-sulfonic acid; JNK, c-Jun amino-terminal kinase; JIP, JNKinteracting protein; PI, phosphotyrosine interaction; GST, glutathione S-transferase; N2a, mouse neuroblastoma Neuro-2a cells; CTF, intracellular carboxyl-terminal fragment of APP truncated at ␣- (CTF␣) or ␤-site (CTF␤); sAPP, the secreted large amino-terminal ectodomain of APP cleaved at the ␣- or ␤-site; DMEM, Dulbecco’s modified Eagle’s medium; FBS, fetal bovine serum; ELISA, enzyme-linked immunosorbent assay; Tricine, N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]glycine; APPL, APP-like; HA, hemagglutinin. The majority of APP is cleaved by ␣-secretase within the A␤ domain to produce sAPP␣ and CTF␣, either at the plasma membrane or in the secretary pathway [4, 12, 13] This non-amyloidogenic processing of APP results not in the secretion of A␤ peptides but rather of a small peptide (p3) that consists of the carboxyl-terminal half of A␤ generated by further cleavage of CTF␣ at the ␥-site. The present results suggest that the regulation of APP metabolism by JIP1b is dependent on its direct interaction with APPcyt rather than on an interaction with JNK, with a subsequent activation of the JNK signaling cascade These observations suggest that JIP family proteins are not functionally equivalent with respect to APP metabolism, they act on the JNK system in an identical manner

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION