Alteration in Neuronal Architecture Resulting from the Chemical Inhibition of CDK5 during Neuronal Differentiation

Abstract

Cyclin-dependent kinases (CDK) are a large family of proteins that regulate the progression of the cell cycle. CDK5, a member of this family, is active only in terminally differentiated (non dividing) neurons. This neuronal restricted activity is due to the neuron-specific location of its activating partners, p35 and p39. CDK5 has been shown to perform a number of functions in neurons, including phosphorylation of neurofilament and tau proteins; proteins important for neuronal architecture. We are interested in better understanding the function of CDK5 in the growth and maintenance of neurites by observing the phenotypic response of PC12 cells when CDK5 is inhibited. To this end, we exploited the PC12 cell line as it exhibits a neuronal-like phenotype in response to either NGF and FGF. Previously we have investigated CDK5 in the NGF-induced differentiation of these cells. Here we focus on the FGF-induced differentiation response as it is similar but not identical to NGF-induced differentiation. We exploit both the temporal and morphological differences that occur in these two similar, but distinct growth factor-induced differentiation pathways to elucidate the role that cdk5 plays in the neuronal differentiation process. Our results showed that inhibition of CDK5 activity by the chemical inhibitor olomoucine produced both morphological and temporal alterations in the response of the cells to FGF. Specifically we examined a number of physical attributes, such as the number, length and branching of neuritic extensions, and applied a quantitative analysis method. Our data reveals that CDK5 plays a role in the establishment of the FGF-induced neuronal phenotype in PC12 cells and demonstrates a function of this enzyme in neuronal architecture.