ARMS interacts with ARMS interacts with -syntrophin: -syntrophin: implications for EphA4 signaling at the implications for EphA4 signaling at the

neuromuscular synapseneuromuscular synapse

Yu CHENYu CHEN

Department of BiochemistryDepartment of Biochemistry

Hong Kong University of Science and TechnologyHong Kong University of Science and Technology

Sub-synapticnucleus

Schwann cell

Neurotransmitterreceptor

Pre-synaptic Motor Neuron

Post-synapticMuscle

Pre-synaptic Neuron

Post-synaptic Neuron

AcetylcholinereceptorNeurotransmitter

Acetylcholine

Ion Influx

CNS synapse Neuromuscular junctionCNS synapse Neuromuscular junction

Axon & dendritic growth

Axon guidance and neuronal migration

Neuronal survival and differentiation

Synapse formation and plasticity

Nerve regeneration

Functions of receptor tyrosine kinasesFunctions of receptor tyrosine kinasesFunctions of receptor tyrosine kinasesFunctions of receptor tyrosine kinases

Plasma membrane

Nucleus

RTK

P

Trophic factors

Raf

MEK

ERK

ERK

c-Fos

Elk-1

BDNF

TrkB

Ephrin

EphA4

AChR clustering and NMJ stability Development/maturation of NMJ

Muscle fiber

ARMS (ARMS (aankyrin nkyrin rrepeat- rich epeat- rich mmembrane embrane sspanninpannin

gg))

● Activation of Eph receptor results in the rapid tyrosine phosphorylation of ARMS (Kong et al.,2001)

● ARMS interacts with TrkB and potentiates TrkB-mediated sustained MAPK activation (Arévalo et al.,2004)

ARMS localized at the neuromuscular junctionARMS localized at the neuromuscular junction

ARMS colocalized with EphA4 and TrkB at the NMJARMS colocalized with EphA4 and TrkB at the NMJ

Library screening for ARMS interacting proteinsLibrary screening for ARMS interacting proteins

Bait: C-terminal 100 amino acids of ARMSBait: C-terminal 100 amino acids of ARMS

Library: P12 mouse muscle cDNA libraryLibrary: P12 mouse muscle cDNA library

EERESIL

1616 1715

PH1a PDZ PH1b PH2 SU

PH1a PDZ PH1b PH2 SU

GI->AA

-syntrophin

-syntrophin mutant

ARMS

+

―

ARMS interacted with ARMS interacted with -syntrophin-syntrophin

ARMS and syntrophin colocalized in muscleARMS and syntrophin colocalized in muscle

ARMS PDZ binding motif and ARMS PDZ binding motif and -syntrophin PDZ do-syntrophin PDZ domain were necessary for ARMS clusteringmain were necessary for ARMS clustering

Muscle fiber

Ephrin

EphA4ARMS

Syn

?

ARMS interacted with EphA4 receptorARMS interacted with EphA4 receptor

Muscle fiber

Ephrin

STAT

Subsynaptic gene transcription

EphA4ARMS

Syn

JAK JAK?

?

ARMS and ARMS and -syntrophin potentiates EphA4--syntrophin potentiates EphA4-mediated signalingmediated signaling

Ephrin

STAT

Subsynaptic gene transcription

EphA4ARMS

Syn

JAK JAK

? ?Muscle fiber

Junctional localization of ARMS was Junctional localization of ARMS was aberrant in syntrophin knockout miceaberrant in syntrophin knockout mice

Junctional localization of EphA4 was Junctional localization of EphA4 was aberrant in syntrophin knockout miceaberrant in syntrophin knockout mice

Ephrin

STAT

Subsynaptic gene transcription

EphA4ARMS

Syn

JAK JAK Muscle fiber