SUPPRESSION OF KIF2 IN PC12 CELLS ALTERS THE DISTRIBUTION OF A GROWTHCONE NONSYNAPTIC MEMBRANE-RECEPTOR AND INHIBITS NEURITE EXTENSION

In the present study, we present evidence about the cellular functions of KIF2, a kinesin-like superfamily member having a unique structure in that its motor domain is localized at the center of the molecule (N oda Y., Y. Sato-Yoshitake, S. Kondo, M. Nangaku, and N. Hirokawa, 1995 . J. Cell Biol, 129:157-167.). Using subcellular fractionation techniq ues, isopicnic sucrose density centrifugation of microsomal fractions from developing rat cerebral cortex, and immunoisolation with KIF2 ant ibodies, we have now identified a type of nonsynaptic vesicle that ass ociates with KIF2. This type of organelle lacks synaptic vesicle marke rs (synapsin, synaptophysin), amyloid precursor protein, GAP-43, or N- cadherin, On the other hand, it contains beta(gc), which is a novel va riant of the beta subunit of the IGF-1 receptor, which is highly enric hed in growth cone membranes. Both beta(gc) and KIF2 are upregulated b y NGF in PC12 cells and highly concentrated in growth cones of develop ing neurons. We have also analyzed the consequences of KIF2 suppressio n by antisense oligonucleotide treatment on nerve cell morphogenesis a nd the distribution of synaptic and nonsynaptic vesicle markers. KIF2 suppression results in a dramatic accumulation of beta(gc) within the cell body and in its complete disappearance from growth cones; no alte rations in the distribution of synapsin, synaptophysin, GAP-43, or amy loid percursor protein are detected in KIF2-suppressed neurons. Instea d, all of them remained highly enriched at nerve terminals. KIF2 suppr ession also produces a dramatic inhibition of neurite outgrowth; this phenomenon occurs after beta(gc) has disappeared from growth cones. Ta ken collectively, our results suggest an important role for KIF2 in ne urite extension, a phenomenon that may be related with the anterograde transport of a type of nonsynaptic vesicle that contains as one of it s components a growth cone membrane receptor for IGF-1, a growth facto r implicated in nerve cell development.