Selective down-regulation of 440 kDa ankyrinB associated with neurite retraction

Brain-specific isoforms of ankyrin, 440 kDa and 220 kDa ankyrinB, which are generated from a single gene by alternative splicing of pre-mRNA, are both expressed in human neuroblastoma NB-1 cells and the expression of the larger isoform is increased upon induction of neurite outgrowth. Exposure to methylmercury, a potent neurotoxic substance, at a sublethal dose induced dramatic retraction of neurites in NB-1 cells. Concomitantly, synthesis of 440 kDa ankyrinB polypeptide and mRNA were selectively attenuated in methylmercury-treated cells, while the 220 kDa isoform was not affected. These results indicate that the expression of 440 kDa ankyrinB is intimately associated not only with the neurite outgrowth but also with neurite retraction in neuronal cells, and is regulated at mRNA level.