THE CELLULAR-DISTRIBUTION OF THE ADENOMATOUS POLYPOSIS-COLI TUMOR-SUPPRESSOR PROTEIN IN NEUROBLASTOMA-CELLS IS REGULATED BY MICROTUBULE DYNAMICS

The adenomatous polyposis coli tumour suppressor protein is highly exp ressed in developing rodent brain, but its function is unclear. Recent studies have suggested a role for this protein in regulating microtub ule dynamics. Neuro 2A mouse neuroblastoma cells were previously thoug ht not to express this protein. Using immunochemical techniques, this report corrects this observation. Immunoreactive bands of a size consi stent with that of the full-length protein were observed by western bl otting. Using immunocytochemistry, punctate immunoreactivity localized to areas of the cell containing microtubules, particularly neurite gr owth cones, in a distribution suggesting a role in neuritogenesis and growth cone extension. The protein did not localize to actin-rich cell ular structures, and perturbation of the actin cytoskeleton had no eff ect upon this distribution. Treatment of cells with taxol to stabilize microtubules caused the concentration of the immunoreactive puncta to the tips of microtubules and areas along the axis of potential microt ubule assembly. Treatment of cells with the microtubule disrupting rea gent nocodazole showed that over shorter times the punctate distributi on was not dependent upon polymerized microtubules. However, al longer incubation times a decrease in punctate immunostaining was observed. These results indicate that the intracellular distribution of the aden omatous polyposis coil protein is dependent upon microtubule but not a ctin dynamics. A role for this protein in the regulation of directed m icrotubule assembly is suggested. (C) 1997 IBRO. Published by Elsevier Science Ltd.