Cytoskeletal Modulation of Plasma Membrane Events Induced by Interferon-α

Cytochalasin B, a drug that alters microfilament structure, was found to modulate interferon-α (IFN-α)-induced changes in ion fluxes, in motional freedom of spin probes, and lateral diffusion of surface antigens. These changes occur in Daudi cells inherently sensitive to the antiproliferative signal of IFN-α, but not in insensitive cells, and were associated with the antiproliferative signal previously. The biophysical effects of cytochalasin B were detected by flow cytometric quantitation of membrane potential using an oxonol dye, by electron spin resonance (ESR) spectrometry, and by measurements of fluorescence recovery after photobleaching (FRAP) of surface antigens using a laser-interactive cell imaging system. Cytochalasin B treatment increased an IFN-α-induced membrane potential shift by −5 mV. The motional freedom of 5-doxyl-stearic acid changed from 0.67 to 0.63, as expressed by the order parameter, S, with IFN-α treatment and was prevented by cytochalasin B. Changes in the lateral diffusion of surface antigens induced by IFN-α treatment, D = 5.3 × 10⁻¹⁰ without treatment and D = 7.8 × 10⁻¹⁰ cm²/s with treatment, was blocked by cytochalasin B. In contrast, the microtubule stabilizers taxol and D₂O and the microtubule depolymerizing colcemid were ineffective at dose levels sufficient to cause the characteristic cell physiological alterations of these agents. These results implicate microfilaments but not the microtubule system in transduction of the antiproliferative signal by IFN-α in Daudi cells.