Growth factor regulation of cytoplasmic dynein intermediate chain subunit expression preceding neurite extension

Cytoplasmic dynein is a motor protein responsible for intracellular movements toward the minus ends of microtubules. The intermediate chains are one of the subunits important for binding dynein to cargo. The intermediate chains are encoded by two genes and are translated into at least five different polypeptide isoforms in rat brain. In rat optic nerve, dynein with only one of the intermediate chain polypeptides is found associated with membrane bounded organelles in fast anterograde transport. Dynein containing the other intermediate chain polypeptides associates with a different set of proteins, in the slow transport component. To determine if the intermediate chain expression levels are regulated during neurite differentiation, we analyzed the protein levels by two-dimensional SDS-PAGE and intermediate chain mRNA by RT-PCR in cultured rat pheochromocytoma (PC12) cells. In the absence of nerve growth factor, the major intermediate chain isoform is the IC74-2C polypeptide. IC74-2C is ubiquitous and is utilized for constitutive dynein function and association with membrane bounded organelles. Within 24 hr of the addition of nerve growth factor to the cultures, there is an increased expression of the developmentally regulated isoforms that are associated with the actin cytoskeleton. This change in intermediate chain isoform expression preceded neurite growth. Nerve growth factor induced differentiation also results in increased light intermediate chain phosphorylation. The growth factor induced changes in the expression of dynein intermediate chains suggests that specific intermediate chain isoforms are utilized during axon growth.