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

Cytoplasmic dynein is a motor protein responsible for intracellular movemen ts toward the minus ends of microtubules. The intermediate chains are one o f the subunits important for binding dynein to cargo. The intermediate chai ns 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 on e of the intermediate chain polypeptides is found associated with membrane bounded organelles in fast anterograde transport. Dynein containing the oth er intermediate chain polypeptides associates with a different set of prote ins, in the slow transport component. To determine if the intermediate chai n expression levels are regulated during neurite differentiation, we analyz ed the protein levels by two-dimensional SIDS-PAGE and intermediate chain m RNA by RT-PCR in cultured rat pheochromocytoma (PC12) cells. In the absence of nerve growth factor, the major intermediate chain isoform is the IC74-2 C polypeptide. IC74-2C is ubiquitous and is utilized for constitutive dynei n function and association with membrane bounded organelles. Within 24 hr o f the addition of nerve growth factor to the cultures, there is an increase d expression of the developmentally regulated isoforms that are associated with the actin cytoskeleton. This change in intermediate chain isoform expr ession preceded neurite growth. Nerve growth factor induced differentiation also results in increased light intermediate chain phosphorylation. The gr owth factor induced changes in the expression of dynein intermediate chains suggests that specific intermediate chain isoforms are utilized during axo n growth. (C) 2001 Wiley-Liss, Inc.