Growth phase‐dependent changes in the subcellular localization of pre‐B‐cell colony‐enhancing factor¹

A cDNA encoding the homolog of the human pre-B-cell colony-enhancing factor (PBEF), a cytokine-like secreted protein, was isolated from a rat cDNA library. This protein existed in both the cytoplasm and nucleus of the cells, and the amount was higher in the cytoplasm than in the nucleus of proliferating PC-12 and Swiss 3T3 cells but higher in the nucleus than in the cytoplasm of the PC-12 cells treated with nerve growth factor and the 3T3 cells grown to a confluent state. Thus, the so-called PBEF is not a cytokine-like secreted protein but an intracellular protein associated with the cell cycle.