[Molecular mechanism of erythroid differentiation in mouse Friend cells]

The mechanism of in vitro erythroid differentiation in mouse Friend cells was studied by employing cell fusion between two genetically marked Friend cells and other nonerythroid cells. Erythroid differentiation was induced indirectly by fusing Friend cells that had been exposed briefly to dimethyl sulfoxide prior to fusion with nonerythroid cells that had been treated with ultraviolet light(or other DNA-damaging agents). The results suggest that two distinct reactions are involved in erythroid differentiation in Friend cells in vitro. One reaction, originating from the damaged DNA (or inhibition of DNA replication as a consequence), exhibits an inducible nature, is nonspecific to Friend cells, and is trans-acting. The other reaction is specific to Friend cells. Evidence that a typical tumor promoter, 12-O-tetradecanoylphorbol 13-acetate, inhibits erythroid differentiation by affecting the latter reaction is also presented. Brief exposure of Friend cells to DMSO was found to induce an early cellular activity required fusion for erythroid differentiation which is detected only by with UV irradiated cells. The induction process of this activity consists of at least two distinct stages. In the first stage, the reaction proceeds without supply of metabolites from the medium and exhibits sensitivity to tumor promoters. The second stage is closed involved with cellular metabolic activity, notably protein synthesis. Under normal conditions, the induced activity is short-lived, suggesting that turnover of the molecules responsible for this activity. There appears to be a signal produced following DMSO pulse which acts as an inducer for this activity. The signal remains active as long as 40 hr when protein synthesis is blocked. When permeabilized Friend cells, which had been briefly treated by DMSO, were exposed to cell-free extracts from UV irradiated cells, a small but significant number of the cells became reactive to benzidine, a characteristic of erythroid differentiation. The activity in the extracts was apparently induced following UV irradiation, reaching a maximum 25 to 30 hr after irradiation. After partial purification, the active factor seems to be a protein with a molecular weight of 35,000 to 40,000.