Rwl. Lim et S. Halpain, Regulated association of microtubule-associated protein 2 (MAP2) with Src and Grb2: Evidence for MAP2 as a scaffolding protein, J BIOL CHEM, 275(27), 2000, pp. 20578-20587
Microtubule-associated protein 2 (MAP2) and tan, which is involved in Alzhe
imer's disease, are major cytoskeletal proteins in neurons. These proteins
are involved in microtubule assembly and stability, To further characterize
MAP2, we took a strategy of identifying potential MAP2 binding partners. T
he low molecular weight MAP2c protein has 11 PXXP motifs that are conserved
across species, and these PXXP motifs could be potential ligands for Src h
omology 3 (SH3) domains. We tested for MAP2 interaction with SH3 domain-con
taining proteins. All neuronal MAP2 isoforms bound specifically to the SH3
domains of c-Src and Grb2 in an in vitro glutathione S-transferase-SH3 pull
-down assay. Interactions between endogenous proteins were confirmed by co-
immunoprecipitation using brain lysate, All three proteins were also found
co-expressed in neuronal cell bodies and dendrites. Surprisingly, the SH3 d
omain-binding site was mapped to the microtubule-binding domain that contai
ns no PXXP motif. Src bound primarily the soluble, non-microtubule-associat
ed MAP2c in vitro. This specific MAP2/SH3 domain interaction was inhibited
by phosphorylation of MAP2c by the mitogen-activated protein kinase extrace
llular signal-regulated kinase 2 but not by protein kinase A. This phosphor
ylation-regulated association of MAP2 with proteins of intracellular signal
transduction pathways suggests a possible link between cellular signaling
and neuronal cytoskeleton, with MAP2 perhaps acting as a molecular scaffold
upon which cytoskeleton-modifying proteins assemble and dissociate in resp
onse to neuronal activity.