Cell cycle dependent expression and stability of the nuclear protein detected by Ki-67 antibody in HL-60 cells

• Published in: Cell proliferation Vol. 25; no. 1; p. 31
• Main Authors: Bruno, S, Darzynkiewicz, Z
• Format: Journal Article
• Language: English
• Published: England 01.01.1992
• Subjects: Antibodies; Cell Cycle - drug effects; Cell Cycle - genetics; Cell Nucleus - metabolism; Cycloheximide - pharmacology; DNA - analysis; Gene Expression; Humans; Ki-67 Antigen; Nuclear Proteins - biosynthesis; Nuclear Proteins - immunology; Tumor Cells, Cultured - metabolism; Tumor Cells, Cultured - pathology; Vinblastine - pharmacology
• ISSN: 0960-7722
• DOI: 10.1111/j.1365-2184.1992.tb01435.x

The expression and stability of the proliferation-associated nuclear antigen detected by Ki-67 antibody have been investigated in human promyelocytic leukaemic HL-60 cells in relation to their progression through the cell cycle. Expression of this antigen was minimal in late G1 and early S phase cells. The antigen accumulated in the cells predominantly during S phase, and its rate of increase per cell accelerated during the second half of this phase. The accumulation of Ki-67 antigen during S exceeded the increase in DNA content, and thus the Ki-67/DNA ratio rose 80% from late G1 to G2 + M. This antigen rapidly disappeared from post-mitotic cells. The half-life of this protein estimated in post-mitotic cells during stathmokinesis induced by vinblastine appeared to be shorter than 1 h. This rapid turnover should be compared with the relatively long (6-8 h) duration of G1 of the studied cells. In cells in which de novo protein synthesis was inhibited by 0.1 microgram/ml cycloheximide, the half-life of the Ki-67 antigen was also found to be about 1 h regardless of the cell position in the cell cycle. Thus, the data suggest that variations in the level of this protein during the cell cycle are a consequence of its different synthesis rate rather than phase-specific changes in the rate of its degradation. Because the late G1 and very early S phase cells express the antigen at levels only slightly above background, it is possible that, when using Ki-67 antibody as a marker of the cell growth fraction, some late G1 cells can be erroneously classified as non-cycling cells.