The Ki-67 protein interacts with members of the heterochromatin protein 1 (HP1) family: a potential role in the regulation of higher-order chromatin structure

The expression of the nuclear protein Ki‐67 (pKi‐67) is strictly correlated with cell proliferation. Because of this, anti‐Ki‐67 antibodies can be used as operational markers to estimate the growth fraction of human neoplasia in situ. For a variety of tumours, the assessment of pKi‐67 expression has repeatedly been proven to be of prognostic value for survival and tumour recurrence, but no cellular function has yet been ascribed to the Ki‐67 protein. This study shows that a C‐terminal domain of pKi‐67 (Kon21) is able to bind to all three members of the mammalian heterochromatin protein 1 (HP1) family in vitro and in vivo. This interaction can be manipulated in living cells, as evidenced by ectopic expression of GFP‐tagged HP1 proteins in HeLa cells, which results in a dramatic relocalization of endogenous pKi‐67. Taken together, the data presented in this study suggest a role for pKi‐67 in the control of higher‐order chromatin structure. Copyright © 2001 John Wiley & Sons, Ltd.