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NIDA Proteomics Center
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Investigators
> Elizabeth A. Eipper
Effects of Cocaine Treatment on
Kalirin Phosphorylation and Function
Elizabeth A. Eipper, Department of Neuroscience,
University of Connecticut Health Center
Chronic cocaine exposure results in structural
changes in the medium spiny neurons of the brain reward centers. Significant
progress has been made in understanding the signaling pathways involved in
short-term responses to cocaine. Our long-term goal is to build on this
knowledge to understand how chronic cocaine exposure leads to the changes in
spine number that presumably underlie the associated behavioral changes. Spine
formation, which requires carefully coordinated changes in the actin
cytoskeleton, is a complex process known to involve the activation of Rac, a
small GTPase of the Rho subfamily. Recent proteomic studies identified Kalirin7
as the major guanine nucleotide exchange factor for Rac in the PSD. The fact
that levels of Kalirin7 increase in response to chronic cocaine, led to the
hypothesis that Kalirin7 plays an essential role in the structural changes
observed. Consistent with this, mice lacking Kalirin7 (Kal7KO) have
fewer dendritic spines and exhibit increased sensitivity to chronic cocaine.
The technologies available to us through the Neuroproteomics Center will allow
us to determine the phosphorylation state of Kalirin7 in the mouse
striatum/nucleus accumbens under basal conditions and after acute and chronic
exposure to cocaine. A multiple reaction monitoring method will be developed so
that phosphorylation at all key sites can be determined simultaneously. Cdk5,
whose role in addiction is studied by Center Investigator James Bibb, alters
Kalirin7 function by phosphorylating a single site near its C-terminus. Methods
for assessing the phosphorylation state of activated Kalirin7 and Kalirin7 that
is engaged in interactions with the NR2B subunit of the NMDA receptor will be
developed. Lfc, a RhoGEF found in dendritic spines but not concentrated at the
PSD, is studied by Center Director Angus Nairn; comparisons of Kalirin7 and Lfc
will be especially informative. The 8-plex iTraq capabilities developed in the
Center will allow us to compare the composition of PSDs isolated from wildtype
and Kal7KO mice under control conditions and after chronic exposure to cocaine.
Kalirin7, with its nine spectrin-like repeats and PDZ-binding motif, is known to
interact with multiple proteins; its absence may result in the loss of specific
components of the PSD. The Kal7KO mice, with their heightened
sensitivity to cocaine, should provide a valuable resource to Center
Investigators studying synaptic maintenance, protein complexes that mediate
synapse formation and NMDA Receptor complexes.
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