Inhibition of neurite extension by overexpression of individual domains of LIM kinase 1

Lin-11, Isf-1 and Mec-3 (LIM) kinases are serine/threonine kinases that phosphorylate cofilin, an actin depolymerizing protein. LIM kinases have a highly modular structure composed of two N-terminal LIM domains (LIM 1/2), a PSD-95, Dig and ZO-1 (PDZ) domain and a C-terminal protein kinase domain. Here, we overexpressed individual domains of mouse LIM kinase I (LIMK1) in PC12 cells and investigated their effects on neurite outgrowth. Although none of the LIMK1 domains had an effect on spontaneous neurite outgrowth, the N-terminal LIM 1/2 domains strongly inhibited differentiation of PC12 cells after stimulation with both nerve growth factor (NGF) and the Rho-kinase inhibitor Y-27632. In contrast, the overexpressed PDZ domain reduced neurite outgrowth only when differentiation had been induced by Y-27632, but not by NGF. Our data suggest that the different noncatalytic N-terminal domains of LIMK1 contribute to the regulation of neurite extension by using distinct signal transduction pathways.