Selective presence of ubiquitin in intracellular inclusions

The authors have shown previously that ubiquitin, a protein involved in the degradation of short-lived and abnormal proteins, is present in several cytoplasmic inclusions of neurons. This study used a library of antibodies to ubiquitin and immunohistochemically examined for the presence of ubiquitin in nonviral intracytoplasmic inclusions that form in different cell types under various pathologic conditions. Membrane-bound lysosomal and nonlysosomal inclusions such as those of storage disease, Russell bodies, alpha-1-antitrypsin and alpha-fetoprotein as well as nonmembrane-bound inclusions were examined. Ubiquitin epitopes were detected in some of the nonmembrane-bound inclusions only. The ubiquitin-containing inclusions were the Rosenthal fibers, Mallory bodies, Crooke bodies, Lafora bodies, amyloid bodies, and the giant axons of giant axonal neuropathy. Nemaline bodies and the inclusions of juvenile digital fibromatosis, both of which contain actin and actinbinding proteins, did not show immunoreaction. These findings, as well as those of the previous study, show that the presence of ubiquitin in cellular inclusions is selective. The ubiquitin-containing inclusions are not membrane bound; they are fibrillary and most contain also intermediate filament-related proteins. The role of ubiquitin in the formation of these inclusions remains to be elucidated.