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The Journal of Neuroscience, August 27, 2008, 28(35):8789-8800; doi:10.1523/JNEUROSCI.2738-08.2008
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Development/Plasticity/Repair
CD2AP and Cbl-3/Cbl-c Constitute a Critical Checkpoint in the Regulation of Ret Signal Transduction
Cynthia C. Tsui1,3 andBrian A. Pierchala2,3 1Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan 48109-0680, 2Department of Biologic and Materials Sciences, School of Dentistry, University of Michigan, Ann Arbor, Michigan 48109-1078, and 3Department of Biological Sciences, The State University of New York at Buffalo, Buffalo, New York 14260
Correspondence should be addressed to Brian A. Pierchala, Department of Biologic and Materials Sciences, School of Dentistry, University of Michigan, 1011 North University, Ann Arbor, MI 48109-1078. Email: pierchal{at}umich.edu
The glial cell line-derived neurotrophic factor (GDNF) family ligands (GFLs) are critical for nervous system development and maintenance. GFLs promote survival and growth via activation of the receptor tyrosine kinase (RTK) Ret. In sympathetic neurons, the duration of Ret signaling is governed by how rapidly Ret is degraded after its activation. In an effort to elucidate mechanisms that control the half-life of Ret, we have identified two novel Ret interactors, CD2-associated protein (CD2AP) and Cbl-3. CD2AP, an adaptor molecule involved in the internalization of ubiquitinated RTKs, is associated with Ret under basal, unstimulated conditions in neurons. After Ret activation by GDNF, CD2AP dissociates. Similarly, the E3-ligase Cbl-3 interacts with unphosphorylated Ret and dissociates from Ret after Ret activation. In contrast to their dissociation from autophosphorylated Ret, an interaction between CD2AP and Cbl-3 is induced by GDNF stimulation of sympathetic neurons, suggesting that CD2AP and Cbl-3 dissociate from Ret as a complex. In neurons, the overexpression of CD2AP enhances the degradation of Ret and inhibits GDNF-dependent survival, and gene silencing of CD2AP blocks Ret degradation and promotes GDNF-mediated survival. Surprisingly, Cbl-3 overexpression dramatically stabilizes activated Ret and enhances neuronal survival, even though Cbl-family E3 ligases normally function to trigger RTK downregulation. In combination with CD2AP, however, Cbl-3 promotes Ret degradation rapidly and almost completely blocks survival promotion by GDNF, suggesting that Cbl-3 acts as a switch that is triggered by CD2AP and oscillates between inhibition and promotion of Ret degradation. Consistent with the hypothesis, Cbl-3 silencing in neurons only inhibited Ret degradation and enhanced neuronal survival in combination with CD2AP silencing. CD2AP and Cbl-3, therefore, constitute a checkpoint that controls the extent of Ret downregulation and, thereby, the sensitivity of neurons to GFLs.
Key words: GDNF; Ret; sympathetic neuron; neurotrophic factor; degradation; E3-ligase
Received June 15, 2008; accepted July 22, 2008.
Correspondence should be addressed to Brian A. Pierchala, Department of Biologic and Materials Sciences, School of Dentistry, University of Michigan, 1011 North University, Ann Arbor, MI 48109-1078. Email: pierchal{at}umich.edu
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[Abstract] [Full Text] [PDF]
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