Cell cycle dependent expression and stability of the nuclear protein detected by Ki-67 antibody in HL-60 cells.
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.
Bruno
S
S
Cancer Research Institute, New York Medical College, Valhalla.
Darzynkiewicz
Z
Z
D000906:Antibodies; D002453:Cell Cycle / Q000187:drug effects / Q000235:genetics*; D002467:Cell Nucleus / Q000378:metabolism*; D003513:Cycloheximide / Q000494:pharmacology; D004247:DNA / Q000032:analysis; D015870:Gene Expression; D006801:Humans; D019394:Ki-67 Antigen; D009687:Nuclear Proteins / Q000096:biosynthesis* / Q000276:immunology; D014407:Tumor Cells, Cultured / Q000378:metabolism* / Q000473:pathology; D014747:Vinblastine / Q000494:pharmacology
D000906:Antibodies; D019394:Ki-67 Antigen; D009687:Nuclear Proteins; D014747:Vinblastine; D004247:DNA; D003513:Cycloheximide