p80 ROKα binding protein is a novel splice variant of CRMP‐1 which associates with CRMP‐2 and modulates RhoA‐induced neuronal morphology

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Abstract
Using antibody against the Rho binding domain of ROKα, two neuronal phosphoproteins of 62 and 80 kDa were co‐immunoprecipitated from brain extracts. Peptide analysis revealed their identity as collapsin response mediator proteins (CRMPs); p62 was CRMP‐2 whereas p80 was a novel splice form of CRMP‐1 with an extended N‐terminus. p80 CRMP‐1 was able to complex with CRMP‐2, suggesting that p80 CRMP‐1 and CRMP‐2 form oligomers. CRMP‐2 was the major substrate of ROK. p80 CRMP‐1 interacted with the kinase domain of ROKα, resulting in inhibition of the catalytic activity towards other substrates. Over‐expression of p80 CRMP‐1 and CRMP‐2 together counteracted the effects of RhoA on neurite retraction, an effect enhanced by mutation of the ROK phosphorylation site in CRMP‐2. p80 CRMP‐1 and CRMP‐2 may be modulators of RhoA‐dependent signaling, through interaction with and regulation of ROKα.