THE LABELING OF PROLIFERATING CELLS BY KI67 AND MIB-1 ANTIBODIES DEPENDS ON THE BINDING OF A NUCLEAR-PROTEIN TO THE DNA

The antigen Ki-67 Ag, regarded as a marker for proliferating cells, was identified as a protein(s) (pKi-67) which can exist free or associated with DNA as evidenced by DNA digestion of cells before or after immunolabeling with Ki-67. The dual nature of this antigen was also supported by reconstitution of Ki-67 Ag from purified DNA and nuclear proteins extracted from the K562 cell line. The immunoreactivity of the resulting complexes was examined in solution using Ki-67 and MIB-1 antibodies. The interaction between Ki-67 or MIB-1 antibodies and pKi-67 was enhanced in the presence of undegraded ds DNA, indicating that ds DNA modulates the conformation of pKi- 67 and that the altered conformation of pKi-67 is more reactive than the pure protein to both Ki-67 and MIB-1 antibodies. © 1994 Academic Press, Inc.