Rho Kinase II Phosphorylation of the Lipoprotein Receptor LR11/SORLA Alters Amyloid-β Production

Abstract

LR11, also known as SorLA, is a mosaic low-density lipoprotein receptor that exerts multiple influences on Alzheimer disease susceptibility. LR11 interacts with the amyloid-␤ precursor protein (APP) and regulates APP traffic and processing to amyloid-␤ peptide (A␤). The functional domains of LR11 suggest that it can act as a cell surface receptor and as an intracellular sorting receptor for trans-Golgi network to endosome traffic. We show that LR11 over-expressed in HEK293 cells is radiolabeled following incubation of cells with [ 32 P i ]orthophosphate. Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) was used to discover putative LR11 interacting kinases. Rho-associated coiled-coil containing protein kinase (ROCK) 2 was identified as a binding partner and a candidate kinase acting on LR11. LR11 and ROCK2 co-immunoprecipitate from post-mortem human brain tissue and drug inhibition of ROCK activity reduces LR11 phosphorylation in vivo. Targeted knockdown of ROCK2 with siRNA decreased LR11 ectodomain shedding while simultaneously increasing intracellular LR11 protein level. Site-directed mutagenesis of serine 2206 in the LR11 cytoplasmic tail reduced LR11 shedding, decreased LR11 phosphorylation in vitro, and abrogated LR11 mediated A␤ reduction. These findings provide direct evidence that LR11 is phosphorylated in vivo and indicate that ROCK2 phosphorylation of LR11 may enhance LR11 mediated processing of APP and amyloid production.

SORLA regulates calpain‐dependent degradation of synapsin

“…Phosphorylation of SORLA in vivo was described before [16][17][18]. Our phosphorylation analysis further detected phosphorylation of synapsin 1 and 2 at the putative 14-3-3 binding sites (Ser666 and Ser546) in mouse cortex, a prerequisite for 14-3-3 binding to these sites (Fig.…”

Sorting receptor SORLA – a trafficking path to avoid Alzheimer disease

“…2B). In addition, SORLA is phosphorylated by protein kinase C and ROCK2 (rho-activated coiled-coil kinase 2) (Lane et al, 2010a;Herskowitz et al, 2011), enzymes that have previously been implicated in amyloidogenic processing, because inhibition of the activity of these kinases by knockdown or pharmacological intervention increased the production of Ab (Zhou et al, 2003;Leuchtenberger et al, 2006). Reducing ROCK2 activity impairs the trafficking of SORLA and decreases ectodomain shedding of the receptor .…”

Rho Kinase Inhibition as a Therapeutic for Progressive Supranuclear Palsy and Corticobasal Degeneration

“…Pharmacologic inhibition of ROCKs can induce protein degradation pathways, including autophagy, in mammalian cells (Bauer et al, 2009;Koch et al, 2014). However, whether ROCKs influence tau synthesis or protein homeostasis is unclear.…”

“…Autophagy (macroautophagy) mediates protein aggregate degradation and represents the major cellular pathway for soluble tau disposal in primary neuron cultures (Verhoef et al, 2002;Krüger et al, 2012). Autophagy can be pharmacologically induced with rapamycin through the inhibition of mammalian target of rapamycin (mTOR), and treatment with rapamycin reduced insoluble tau levels in Drosophila models of tauopathy (Berger et al, 2006;Bakhoum et al, 2014). Other studies revealed that mTOR and the mTOR effector p70 S6 kinase (S6K) likely have direct effects on tau synthesis, phosphorylation, and aggregation Tang et al, 2013).…”

“…PSP and CBD are neuropathologically characterized by preferential accumulation of 4R tau isoform in neurons, astrocytes, and oligodendroglia, and both diseases share genetic features, including a higher frequency of the microtubule associated protein tau (MAPT ) H1 haplotype (Conrad et al, 1997;Houlden et al, 2001).…”