REPRESSION OF A G0-ASSOCIATED 65-KILODALTON PROTEIN IN ACTIVELY PROLIFERATING AND SV40-TRANSFORMED MOUSE KIDNEY-CELLS

The pattern of [S-35]methionine-labeled proteins from primary cultures of mouse kidney epithelial cells arrested in G0 phase was analyzed by two-dimensional gel electrophoresis and compared with that observed f rom cultures of actively proliferating and SV40-transformed mouse kidn ey cells. A major polypeptide (p65) migrating with a molecular mass of 65000 daltons and a pI of 5.8 was detected in quiescent cultures of c ells which had exhausted their finite division potential. Under the ex perimental conditions used, these cells had lost sensitivity to growth factors and were irreversibly blocked in G0 phase of the cell cycle. In cultures of actively proliferating mouse kidney cells, the expressi on of p65 was not observed until just prior to arrest. Moreover, proli ferating cultures of immortalized mouse kidney cells that had been rea ctivated from their quiescent state by infection with SV40 did not exp ress p65. Subcellular localization studies suggest that p65 is associa ted with the crude nuclear fraction. In addition, p65 is glycosylated and binds the lectin concanavalin A. Pulse-chase experiments demonstra ted that p65 was short lived with an estimated half life of 10 min. Th us, p65 appears to be a growth-arrest specific gene product whose expr ession is repressed during the proliferative state of mitotically acti ve mouse kidney cells.