Effects of serum deprivation on Ki-67-reactive antigen. Expression in HeLa cells

In order to elucidate the relationship between the level of cellular Ki-67-reactive antigen and cell proliferation activity, the effects of serum deprivation on the antigen expression and cell proliferation of HeLa cells were investigated using flow cytometry. The antigen was constitutively expressed in almost all cells cultured in normal medium containing 10% calf serum. In the serum- deprived cells, the antigen-negative fraction increased with culture time, and the level of Ki-67-reactive antigen fell rapidly during the first 24 h. The reduction in the antigen caused by serum deprivation was independent of the cell cycle phase. Both BrdUrd incorporation and the S phase fraction were diminished during the experiment with evidence of cell growth retardation. However, after refeeding with fresh normal medium, the antigen level that had been reduced by serum deprivation recovered to the level of the control cells within 24 h. These results suggest that the level of Ki-67-reactive antigen in cells reflects their growth condition.