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Histochemistry and Cell Biology

, Volume 118, Issue 5, pp 415–422 | Cite as

The proliferation marker pKi-67 becomes masked to MIB-1 staining after expression of its tandem repeats

  • Mirko H. Schmidt
  • Rainer Broll
  • Hans-Peter Bruch
  • Michael Duchrow
Original Paper

Abstract.

The Ki-67 antigen, pKi-67, is one of the most commonly used markers of proliferating cells. The protein can only be detected in dividing cells (G1-, S-, G2-, and M-phase) but not in quiescent cells (G0). The standard antibody to detect pKi-67 is MIB-1, which detects the so-called 'Ki-67 motif' FKELF in 9 of the protein's 16 tandem repeats. To investigate the function of these repeats we expressed three of them in an inducible gene expression system in HeLa cells. Surprisingly, addition of a nuclear localization sequence led to a complete absence of signal in the nuclei of MIB-1-stained cells. At the same time antibodies directed against different epitopes of pKi-67 did not fail to detect the protein. We conclude that the overexpression of the 'Ki-67 motif', which is present in the repeats, can lead to inability of MIB-1 to detect its antigen as demonstrated in adenocarcinoma tissue samples. Thereafter, in order to prevent the underestimation of Ki-67 proliferation indices in MIB-1-labeled preparations, additional antibodies (for example, MIB-21) should be used. Additionally, we could show in a mammalian two-hybrid assay that recombinant pKi-67 repeats are capable of self-associating with endogenous pKi-67. Speculating that the tandem repeats are intimately involved in its protein–protein interactions, this offers new insights in how access to these repeats is regulated by pKi-67 itself.

Cell proliferation Mammalian two-hybrid system MIB-1 pKi-67 Proliferation index 

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Copyright information

© Springer-Verlag 2002

Authors and Affiliations

  • Mirko H. Schmidt
    • 2
  • Rainer Broll
    • 1
  • Hans-Peter Bruch
    • 1
  • Michael Duchrow
    • 1
  1. 1.Surgical Research Laboratory, Department of Surgery, Medical University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany
  2. 2.Henry Ford Hospital, Hermelin Brain Tumor Center, Department of Neurosurgery, 2799 W. Grand Blvd., Detroit, MI 48202 USA

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