Induction of cytoskeleton-associated proteins during differentiation of human myeloid leukemic cell lines

Alterations in the expression of proteins associated with the cytoskeletal framework during differentiation of two human myeloid leukemia cell lines were analyzed by two-dimensional gel electrophoresis of Triton-insoluble cellular framework fractions. During in vitro differentiation of HL60 (human promyelocytic leukemia line) and U937 (human monocytoid leukemia line), several new cytoskeleton-associated (CSK) proteins are induced. All of these CSK proteins are also present in freshly isolated normal granulocytes and macrophages. One of these differentiation-induced proteins comigrates with vimentin. There are several differentiation-sensitive proteins, i.e., those that are no longer synthesized upon differentiation. The changes in CSK protein synthesis during differentiation of HL60 and U937 cells do not seem to be related to drug treatment per se since exposure to conditioned medium from phytohemagglutinin-stimulated lymphocytes as well as to dimethyl sulfoxide and 12-O-tetradecanoylphorbol-13-acetate results in the production of many similar proteins. In vitro conditions that do not result in differentiation of HL60 and U937, such as cultivation in serum-free medium, do not induce the CSK proteins that we describe. A notable finding in this study is that all of the qualitative changes in the proteins synthesized during differentiation are detected in the cytoskeletal (Triton-insoluble) fraction, whereas only minor quantitative alterations are observed in the Triton-insoluble extract. The changes in CSK protein components occur in an orderly fashion. Vimentin, an intermediate-filament protein, is synthesized in large amounts prior to changes in cellular morphology and the induction or loss of other CSK proteins. Vimentin may play an important role in the reorganization of the cytoskeleton to support the process of differentiation. The other CSK proteins are synthesized sequentially along with the morphological and functional changes during differentiation. These model systems, therefore, present an opportunity to investigate the role of specific cytoskeletal components in cellular differentiation.