Nonapoptotic cell death caused by the inhibition of RNA polymerase disrupts organelle distribution.

It is controversial whether the mode of cell death induced by CAG repeat diseases is apoptotic. One technical problem that affects this issue is that the very methods used for DNA injection may induce artificial apoptosis. A recent study demonstrated that the functions of RNA polymerase II are disrupted in spinocerebellar ataxia type 1 (SCA 1) pathology, one of the CAG repeat diseases, and that alpha-amanitin can inhibit the activity of RNA polymerase. To examine the cell death mechanisms involved in CAG repeat diseases, we treated cultured rat neurons with alpha-amanitin to avoid the artifacts caused by DNA transfection. Mature and immature rat neurons were treated with alpha-amanitin for 4-6 days and the effects of the treatment on the elongation of neurites, the distribution or morphology of organelles, and the nature of cell death were assessed by immunocytochemistry and quantitative analysis. Neurons exhibited a disruption of neurite elongation and eventually died by day 15 of the treatment. However, apoptosis was not detected. When the neurons survived well, but showed altered neurites, Golgi complexes and lysosomes exhibited changes in their normal intracellular distribution or morphology, but the endoplasmic reticulum and mitochondria did not. The distribution of phosphorylated Trk receptors was also disrupted in the neurites of treated neurons. The signal intensity of the dynein intermediate chain was markedly decreased in the treated neurons. Thus, organelle transport systems, particularly a minus-end-directed microtubule-dependent pathway, would be disrupted by the inhibition of RNA polymerase, and this change is likely to be an early event involved in SCA 1 pathology.