Although δ-catenin/neural plakophilin-related armadillo protein (NPRAP) was reported to interact with presenilin-1 (PS-1), the effects of PS-1 on δ-catenin have not been established. In this study, we report that overexpression of PS-1 inhibits the δ-catenin-induced dendrite-like morphological changes in NIH 3T3 cells and promotes δ-catenin processing and turnover. The effects of PS-1 on endogenous δ-catenin processing were confirmed in hippocampal neurons overexpressing PS-1, as well as in the transgenic mice expressing the disease-causing mutant PS-1 (M146V). In addition, disease-causing mutant PS-1 (M146V and L286V) enhanced δ-catenin processing, whereas PS-1/γ-secretase inhibitors could block the formation of processed forms of δ-catenin. Together, our findings suggest that PS-1 can affect δ-catenin-induced morphogenesis possibly through the regulation of its processing and stability.
KeywordsAlzheimer's disease; δ-Catenin/NPRAP; Presenilin/γ-secretase Alzheimer's disease (AD) is the most common type of senile dementia and is characterized by progressive loss of memory and cognitive dysfunction [16]. In familial Alzheimer's disease (FAD), over 70 mutations have been significantly associated with presenilin-1 (PS-1) and presenilin-2 (PS-2) [7]. Multiple lines of evidence indicate that PS contributes directly to the intramembranous "γ-secretase" processing of many proteins of diverse functions, including APP [3], the developmental signaling receptor Notch1 [4], and cell adhesion molecules N-and E-cadherin [15]. Interestingly, it is reported that PS-1 interacts with a member of the armadillo/ β-catenin family termed δ-catenin, a protein expressed mostly in the brain and encoded on chromosome 5 [21]. δ-Catenin, or neural plakophilin-related armadillo protein (NPRAP), is a member of the p120 ctn subfamily of armadillo/β-catenin proteins, which are defined as proteins with 10 armadillo (ARM) repeats in characteristic spacing and with diverse NH 2 -and COOH-terminal sequences that flank the ARM repeats [18]. δ-Catenin is a nervous system-specific adherens junction protein involved in cell motility and expressed early in neuronal development [14]. The overexpression of δ-catenin can induce the branching of cellular processes in 3T3 cells In this report, we investigated the effects of PS-1 on δ-catenin. The co-overexpressed PS-1 significantly impaired δ-catenin-induced cellular branching in NIH 3T3 fibroblasts. We also found that PS-1 expression promoted δ-catenin processing when they were co-transfected in 3T3 cells and when PS-1 was overexpressed in hippocampal neurons, which was sensitive to PS-1/γ-secretase inhibition and was facilitated by the Alzheimer's disease-causing PS-1 mutation. Our findings suggest that one function of PS-1 expression is to promote δ-catenin processing and, thereby, affect the function of δ-catenin in cells.
Experimental procedures Plasmid constructionConstruction of full-length-δ-catenin constructs in pEGFP-C1 or pRFP-C1 has been described previously [11]. The wild-type PS-1 and...