Liprin-α /SYD-2 is a protein known to regulate presynaptic structure and directly interact with the LAR family of receptor tyrosine phosphatases (RPTP) and the GRIP/ABP family of PDZ proteins. Here I study that liprin-α directly interacts with GIT1, a GTPase-activating protein for a small GTP-binding ADP-ribosylation factor (Arf) that is known to regulate protein trafficking and actin cytoskeleton. GIT1 also directly binds to focal adhesion complex (FC) proteins including β-Pix/Cool rac1 GTP exchange factor, focal adhesion kinase (FAK) and paxillin. GIT1 is broadly expressed in rat brain slices. GIT1 is also colocalized with liprin-α and GRIP at both excitatory and inhbitory synaptic sites in hippocampal cultured neurons. GIT1, β-PIX , Pyk2, and FAK but not paxillin are tightly associated with the postsynaptic density along with liprin-α in rat brain. GIT1 was coimmunoprecipitated with liprin-α, β -PIX, FAK and Pyk2, and a GIT1 fusion protein pulled down liprin-α, GRIP and AMPAR in rat brain. Interestingly, disruption of the interaction between GIT1 and liprin-α by a dominant negative construct significantly decreased synaptic clustering of liprin-α, GRIP and AMPA receptor (AMPAR) in hippocampal cultured neurons. Also it was also found that GIT1 could be a potential substrate for the LAR family of receptor protein tyrosine phosphatase(RPTP) in vitro.
These results suggest that GIT1 may modulate the synaptic clustering of AMPAR by interacting with liprin-α/GRIP complex, and that GIT1 may regulate protein trafficking and actin cytoskeleton at synaptic sites by interacting with Arfs and the LAR family of RPTPs.