Multiple Forms of the 26S Proteasome-Associated Protein Ecm29 in the Mouse Brain

摘要

Ecm29 is an ~200-K HEAT-repeat protein that associates with the 26S proteasome in yeast and HeLa cells.Whereas in most mouse organs Ecm29 is present as a single 200-K protein,in the brain there are eleven species,ranging from 55 K to greater than 250 K,that react with anti-Ecm29 antibodies.Since the largest brain-specific Ecm29 variant reacts with antibodies to sequences within the N-ter-minal and C-terminal regions of the protein,but not to the antibody directed to its central region,this putative isoform likely arises by alternative splicing.Some of the smaller Ecm29-positive forms appear to arise by proteolytic processing,but extraction of minced brain fragments in boiling SDS-PAGE sample buffer reveals that all forms are present prior to homogenization.Only the 220-K Ecm29 species is clearly associated with the 26S proteasome;with one exception,the other variants sediment slower than 20S.Direct dissection and immunohistochemistry reveal that these putative Ecm29 isoforms are present throughout the central nervous system.However,anti-Ecm29 immunoreactivity is differentially distributed within subregions of the mouse brain and among cell types,suggesting that Ecm29 isoform distribution contributes to the complexity and regional specificity of brain function.