FIG. 5.

Suppression of S phase in HBP1-expressing cells upon serum deprivation. The HBP1-expressing cell lines (B1-C2 and B2-C2) and the control lines were assayed for the ability to exit the cell cycle upon serum deprivation. BrdU incorporation was used as a measure of the S phase, and quiescent cells should exhibit a reduction in BrdU-positive cells. All cell lines were grown on coverslips in differentiation medium for the indicated time period followed by a 1-h pulse of BrdU labeling. Cells were subsequently fixed and immunostained for BrdU. The percentages of BrdU-positive cells were determined by counting the cells from several random fields; approximately 200 to 300 cells were counted for each column. As controls, normal C2 and control hygromycin-resistant C2 cell lines were utilized. The open, filled, and diagonal striped bars represent the proliferating, 6-day-deprived, and 9-day-deprived cell populations for each cell line, respectively.