Expression of External‐Surface Membrane Proteins in Differentiated and Undifferentiated Mouse Neuroblastoma Cells

Abstract

Murine neuroblastoma cultures [clones N-18, N1E-115, and N1A-103] were labeled externally with the cationic reagent N,N,N-[3H]-trimethylamino-.beta.-alanyl-N-hydroxy-succinimide ester ([3H]Me3N-.beta.Ala-NSuc) or with 125I/lactoperoxidase. The cells were labeled in the logarithmic and confluent growth phases and in a highly differentiated state following treatment with 2% dimethylsulfoxide (DMSO). The labeled exterior membrane proteins were analyzed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. Major changes in the exterior membrane proteins were observed during maturation and differentiation of the cells. Most of these changes were clonal-specific, while others were common to several clones. Two proteins of MW 55,000 and 65,000 were labeled by both 125I/lactoperoxidase and Me3-N-[3H]-.beta.Ala-NSuc. The level of labeling was dependent on the clonal lines used and the state of the cell maturation. A group of proteins displaying a MW of 150,000-200,000 was related to the transition of a culture from logarithmic to confluent growth phases. An additional protein with an apparent MW of 95,000 was common to differentiated cells of the 2 inducible clones used. In general the maturation of logarithmic phase cells into confluent cells resulted in a less complex electrophoretic distribution of the pattern of labeling. After DMSO treatment further reduction in the complexity of the externally labeled proteins was observed.