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A PDZ protein regulates the distribution of the transmembrane semaphorin, M-SemF
L H Wang1, R G Kalb, S M Strittmatter
1Department of Neurology, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
Abstract:
M-SemF is a membrane-associated, neurally enriched member of the semaphorin family of axon guidance signals. We considered whether the cytoplasmic domain of M-SemF might possess a signaling function and/or might control the distribution of M-SemF on the cell surface. We identify a PDZ-containing neural protein as an M-SemF cytoplasmic domain-associated protein (SEMCAP-1). SEMCAP-2 is a closely related nonneuronal protein. SEMCAP-1 has recently also been identified as GIPC, by virtue of its interaction with the RGS protein GAIP in vitro (De Vries, L., Lou, X., Zhao, G., Zheng, B., and Farquhar, M. G. (1998) Proc. Natl. Acad. Sci. U. S. A. 95, 12340-12345). Expression studies support the notion that SEMCAP-1(GIPC) interacts with M-SemF, but not GAIP, in brain. Lung SEMCAP-2 and SEMCAP-1(GIPC) are potential partners for both GAIP and M-SemF. The protein interaction requires the single PDZ domain of SEMCAP-1(GIPC) and the carboxyl-terminal four residues of M-SemF, ESSV. While SEMCAP-1(GIPC) also interacts with SemC, it does not interact with other proteins containing a class I PDZ binding motif, nor does M-SemF interact with other class I PDZ proteins. Co-expression of SEMCAP-1(GIPC) induces the redistribution of dispersed M-SemF into detergent-resistant aggregates in HEK293 cells. Thus, SEMCAP-1(GIPC) appears to regulate the subcellular distribution of M-SemF in brain, and SEMCAPs could link M-SemF to G protein signal transduction pathways.
Insights
Researchers identified SEMCAP-1 (also known as GIPC) as a protein that binds to M-SemF, a neural semaphorin. This interaction regulates M-SemF
Area of Science:
- Neuroscience
- Cell Biology
- Molecular Biology
Background:
- M-SemF is a membrane-associated protein involved in axon guidance.
- The cytoplasmic domain of M-SemF may have signaling functions or regulate cell surface distribution.
- PDZ domain-containing proteins are known to interact with various cellular targets.
Purpose of the Study:
- To investigate potential signaling functions of the M-SemF cytoplasmic domain.
- To identify proteins that interact with the M-SemF cytoplasmic domain.
- To understand how M-SemF is regulated on the cell surface.
Main Methods:
- Yeast two-hybrid screening to identify M-SemF interacting proteins.
- Co-immunoprecipitation and Western blotting to confirm protein interactions.
- Expression studies in HEK293 cells to analyze subcellular localization.
Main Results:
- Identified SEMCAP-1 (GIPC) as an M-SemF cytoplasmic domain-associated protein.
- SEMCAP-1 interacts with M-SemF via its PDZ domain and M-SemF's C-terminal residues (ESSV).
- SEMCAP-1 co-expression causes M-SemF redistribution into detergent-resistant aggregates, suggesting regulation of subcellular distribution.
Conclusions:
- SEMCAP-1 (GIPC) plays a role in regulating the subcellular distribution of M-SemF in the brain.
- SEMCAP proteins may link M-SemF to G protein signal transduction pathways.
- The interaction between M-SemF and SEMCAP-1 is specific and involves a unique PDZ domain interaction motif.