Structural functional analysis of disabled-1 in regulation of reelin signaling

 
 
 
 

Structural functional analysis of disabled-1 in regulation of reelin signaling

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Title: Structural functional analysis of disabled-1 in regulation of reelin signaling
Author: Huang, Yongcheng
Description: Reelin is a critical protein required for proper lamination of the brain. Dab1 relays Reelin signaling through its interaction with the Reelin receptors VLDLR and ApoER2 via a PTB domain. One hallmark feature of Reelin signaling is the highly elevated tyrosine phosphorylation and subsequent degradation of Dab1 following Reelin stimulation. This tyrosine phosphorylation is required for Dab1 functions in brain development. However, how it is regulated and how it contributes to Reelin signaling are not fully understood. We show phosphotyrosines attract SH2 domain-containing proteins such as CrkI and CrkII, which interact with Dab1 in a Reelin-dependent manner. This interaction requires SH2 domains of CrkI/II and phosphotyrosines Y220 and Y232 of Dab1. While binding to Dab1, CrkI/II could stimulate Dab1 phosphorylation through Src family kinases. Furthermore, we show Y220 and Y232 mediate Reelin-dependent degradation of Dab1, indicating that Y220 and Y232 of Dab1 have multiple functions in Reelin signaling. The PTB domain of Dab1 has simultaneous bindings to the Reelin receptors and PIP2. We show that PIP2-binding is required for Reelin-independent Dab1 membrane localization and basal tyrosine phosphorylation. We also show that it is required for efficient Reelin-Dab1 signal transduction in neurons. While PIP2 on plasma membrane is important for Reelin signaling, change of PIP2 level affects response of Dab1 to Reelin. We show that depletion of PIP2 by neomycin or activated PLC significantly compromised Reelin-induced Dab1 phosphorylation. Our results indicate that well-maintained PIP2 level is critical for efficient transduction of Reelin signaling. In addition to tyrosine phosphorylation, Dab1 undergoes serine phosphorylation. We show that serine 19 (Ser19) is phosphorylated by PKC independently of Reelin. Consistently, mutation of Ser19 showed no effect on Reelin-induced Dab1 tyrosine phosphorylation and degradation. Although PKC does not change response of Dab1 to Reelin by phosphorylating Ser19, we found it regulates Dab1 degradation through an unknown mechanism. Our data suggest that PKC regulates Reelin signaling in a mechanism independently of Reelin-independent Ser19 phosphorylation. Overall, our research data presented here indicate that phosphorylation events of Dab1 are important for Reelin signaling and they are finely regulated.
Permanent Link: http://rave.ohiolink.edu/etdc/view?acc_num=osu1193754102
http://hdl.handle.net/2374.OX/6103
Date: 2007

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