The Correlation between the Expression of CD99 and the Cell Cycle

ABSTRACT

PURPOSE: The cell cycle control system is necessary for the normal growth and differentiation of cells. The purposes of this study were to compare CD99 expression with a known intracellular marker of a specific cell cycle and to evaluate the potential of CD99 as surface marker for this cell cycle. METHODS: We induced arrest of the cell cycle in fetal lung fibroblast by contact inhibition or serum deprivation from culture media. We activated peripheral blood lymphocytes with the treatment of phytohemagglutinin (PHA) and interleukin-2 (IL-2). Next, we synchronized the cell cycle of peripheral blood lymphocytes to the late G1 phase with rapamycin. According to their CD99 expression, the peripheral blood lymphocytes were separated by magnetic bead and analyzed by Western blotting. RESULTS: CD99 expression in fetal lung fibroblast rapidly decreased in cell cycle arrest and recovered soon after G1 activation of the cell cycle. By analyzing chronologic changes of CD99 expression and PI-histogram, we found CD99 expression decreased after passing the G1 checkpoint. G1/S transition was interrupted by potent immunosuppresant, rapamycin. IL-2 receptor remained high after rapamycin treatment in the activated lymphocytes, whereas CD99 expression and propium iodide decreased as compared with the same condition without rapamycin. This suggested that CD99 expression was decreased in the late G1 phase. Retinoblastoma gene (Rb) and CDK-2 are necessary for G1/S transition. We found both of these in CD99+ lymphocyte through Western blotting only. Cyclin B, which has an important role in S/G2/M transition, was only found in CD99-activated lymphocytes. CONCLUSION: CD99 may be a G1 phase specific surface marker.