Growth cone collapse stimulated by both calpain- and rho-mediated pathways

The signal transduction pathways regulating growth cone motility remain poorly defined. Previously, we have characterized the inhibitory molecule, motuporamine C (MotC), as a robust stimulator of growth cone collapse. Utilizing MotC as a research tool to elucidate pathways involved with collapse, we have previously shown that the Rho-Rho kinase (ROCK) pathway is partially required for collapse. In this study, we report MotC induces a high-amplitude rise in intracellular free Ca2+ concentration levels in chicks, resulting in the activation of the Ca2+-sensitive protease, calpain. Furthermore, we show that while calpain is necessary for collapse, inhibition of calpain only partially attenuates MotC-mediated collapse. Instead, concomitant inhibition of both the Rho-ROCK and calpain pathways has an additive effect in attenuating the collapse response to MotC. To our knowledge, this is the first demonstration of concurrent activation of calpain and Rho-ROCK signaling during growth cone collapse. Our data support a model of growth cone collapse that requires the combinatorial regulation of multiple signal transduction cascades that likely target different cellular mechanisms to induce this motile response. (c) 2008 IBRO. Published by Elsevier Ltd. All rights reserved.