Cytoplasmic chaperonin complexes enter neurites developing in vitro and differ in subunit composition within single cells

Chaperonins containing t-complex polypeptide-1 (CCT) are cytosolic molecular chaperone particles implicated especially in the biogenesis of cytoskeletal proteins by promoting the correct folding of the major ubiquitous cytoskeletal components, tubulin and actin. We have purified cytosolic chaperonins from the ND7/23 cell line, determined their subunit composition and examined changes in the intracellular locations of their components during differentiation of ND7/23 cells to a neuronal phenotype by using immunocytochemistry and immunoblots. Chaperonins containing the CCTα (TCP1? subunit enter neuritic processes and are particularly noticeable at the leading edge of growth cone-like structures where they co-localise with actin. Chaperonins containing three other components (CCTβ, ε and γ), however, remain predominantly restricted to perikaryal cytoplasm. These findings suggest a heterogeneous population of chaperonin particles within single differentiated ND7/23 cells and this may reflect specialisation of chaperonin function in different cytoplasmic compartments of a neurone. Further, since ribosomes do not enter neurites while CCTα-containing chaperonins do, the latter may play roles, subsequent to translation, which influence cytoskeletal elaboration during neuritogenesis.