Protein expression in relation to the cell cycle of exponentially growing human prostatic epithelial cells.

This report concerns the study of the relationship between protein expression and the cell cycle in exponentially proliferating benign and malignant human prostate epithelial cells in short-term cultures. Multiparameter flow cytometric measurements were performed to correlate the expression of prostate-specific acid phosphatase, epithelial membrane antigen and epitectin with cell cycle progression. The expression of the three proteins was heterogeneous in G1 cells. The early post-mitotic cells exhibited the lowest levels when compared with late G1 cells, wherein the expression was many times greater. There was no further increase as the cells progressed through S and G2 + M. These findings, corroborating prior observations in other systems, suggest the possibility that the levels of the proteins studied increase during the G1 phase of the cell cycle and drop during or immediately after cytokinesis. As an alternate explanation, the heterogeneity of protein expression characteristic of G1 cells may be due, at least in part, to an asymmetric apportionment of cell constituents at mitosis.