Electrophoretic analysis of the cytoplasmic and nuclear protein changes after induction of differentiation in WEHI‐3B myelomonocytic leukemia cells

Abstract

In response to a differentiation factor (G‐CSF) the myelomonocytic leukemia cell line (WEHI‐3B(D⁺) differentiates to form mature macrophages and neutrophils. The effect of G‐CSF on WEHI‐3B(D⁺) differentiation was augmented by low concentrations (5 ng/ml) of actinomycin D. Quantitative binding of an antineutrophil serum was used to segregate the differentiated cells from the leukemic blast cells. Molecular markers of later myeloid differentiation were detected in myelocytes and macrophages purified from differentiating WEHI‐3B(D⁺ ) cells. To study the initial molecular processes associated with the initiation of WEHI‐3B(D⁺) cells to differentiation, the protein changes were analyzed using gel electrophoresis. Quantitative analysis of the fluorographs from the two‐dimensional (2D) electrophorograms of the ³⁵S‐labeled proteins revealed major changes in the biosynthetic rates for 16 proteins within 5 hr: The biosynthesis of six proteins was increased and another ten proteins were synthesized at a reduced rate. Two of the proteins (17K and 36K daltons) were located in the nucleus. Pulse‐chase experiments indicated that protein turnover for these proteins was rapid but the degradation of four proteins was suppressed. At least six of the proteins (16K to 120K daltons) were acidic and were associated with the cytoplasm. Electrophoretic analysis of the ³⁵S‐labeled proteins indicated that a 35K protein induced by G‐CSF was found in high abundance only in purified cells of intermediate differentiation (eg, myelocytes). Other proteins (eg, a very high molecular weight protein, and a 16K dalton protein) were obviously late markers of differentiated neutrophils or macrophages.