LIMK2d, a truncated isoform of Lim kinase 2 regulates neurite growth in absence of the LIM kinase domain.

Lim kinase 2 isoforms, LIMK2a and LIMK2b, phosphorylate cofilin leading to remodeling of actin cytoskeleton during neuronal differentiation. The expression and function of the LIMK2d isoform, missing the kinase domain, remain unknown. We analyzed the expression of LIMK2 splice variants in adult rat brain and in cultures of rat neural stem cells by RT-QPCR. All three splice variants were expressed in adult cortex, hippocampus and cerebellum. Limk2a and Limk2d expression, but not Limk2b, increased during neuronal differentiation. We studied the localization and function of LIMK2d isoform by transfecting Hela, NSC-34, and hippocampal rat neuron cultures. Similarly to LIMK2b, LIMK2d was expressed in the cytoplasm, neurites and dendritic spines, but not in the nucleus. Similarly to LIMK2a, LIMK2d over-expression in NSC-34 cells increased neurite length, but independently of cofilin phosphorylation or of direct interaction with actin. Overall, these results indicate that LIMK2d is a third LIMK2 isoform which regulates neurite extension and highlights the possible existence of a kinase independent function of LIMK2.

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