Presenilin/γ-Secretase-mediated Cleavage Regulates Association of Leukocyte-Common Antigen-related (LAR) Receptor Tyrosine Phosphatase with β-Catenin

Annakaisa Haapasalo,Doo Yeon Kim,Bryce W Carey,Mari K Turunen,Warren H Pettingell,Dora M Kovacs

doi:10.1074/jbc.m611324200

Abstract

Leukocyte-common antigen-related (LAR) receptor tyrosine phosphatase regulates cell adhesion and formation of functional synapses and neuronal networks. Here we report that LAR is sequentially cleaved by alpha- and presenilin (PS)/gamma-secretases, which also affect signaling and/or degradation of type-I membrane proteins including the Alzheimer disease-related beta-amyloid precursor protein. Similar to the previously characterized PS/gamma-secretase substrates, inhibition of gamma-secretase activity resulted in elevated LAR C-terminal fragment (LAR-CTF) levels in stably LAR-overexpressing Chinese hamster ovary (CHO) cells, human neuroglioma cells, and mouse cortical neurons endogenously expressing LAR. Furthermore, LAR-CTF levels increased in cells lacking functional PS, indicating that gamma-secretase-mediated cleavage of LAR was PS-dependent. Inhibition of alpha-secretase activity by TAPI-1 treatment blocked LAR-CTF accumulation, demonstrating that prior ectodomain shedding was prerequisite for PS/gamma-secretase-mediated cleavage of LAR. Moreover, we identified the product of PS/gamma-secretase cleavage, LAR intracellular domain (LICD), both in vitro and in cells overexpressing full-length (FL) LAR or LAR-CTFs. LAR localizes to cadherin-beta-catenin-based cellular junctions. Assembly and disassembly of these junctions are regulated by tyrosine phosphorylation. We found that endogenous tyrosine-phosphorylated beta-catenin coimmunoprecipitated with LAR in CHO cells. However, when PS/gamma-secretase activity was inhibited, the association between LAR and beta-catenin significantly diminished. In addition to cell adhesion, beta-catenin is involved in transcriptional regulation. We observed that LICD significantly decreased transcription of cyclin D1, one of the beta-catenin target genes. Thus, our results show that PS/gamma-secretase-mediated cleavage of LAR controls LAR-beta-catenin interaction, suggesting an essential role for PS/gamma-secretase in the regulation of LAR signaling.

Highlights

Presenilin (PS)2/␥-secretase is a high molecular weight enzymatic complex composed of PS1 or PS2, nicastrin, Aph-1, and Pen-2 (1–5)
We show that LICD is involved in the regulation of ␤-catenin-mediated transcription of the cyclin D1 gene, suggesting that LAR proteolytic processing by PS/␥-secretase affects LAR signaling
Using a BLAST search based on the homology at the amyloid precursor protein (APP) ⑀-cleavage site and the S3 cleavage site of Notch, we have identified a number of type-I membrane proteins with homologous amino acid sequences at their membrane-cytosol interface, including nectin-1␣ (20) and ␤2-subunit of the voltage-gated sodium channel (VGSC) (21)

Summary

Introduction

Presenilin (PS)2/␥-secretase is a high molecular weight enzymatic complex composed of PS1 or PS2, nicastrin, Aph-1, and Pen-2 (1–5). Treatment of the cells together with TPA and any of the three ␥-secretase inhibitors resulted in a prominent accumulation of LAR-CTFs of ϳ72 kDa in size (Fig. 1A). We observed that LAR-CTFs accumulated in cells overexpressing either of these mutants in a similar manner to the WT LAR after TPA and DAPT treatment (supplemental Fig. S1).

Results

Conclusion