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.