The expression of Ki-67, MCM3, and p27 defines distinct subsets of proliferating, resting, and differentiated cells

The mini-chromosome maintenance proteins (MCM), which are involved in the c ontrol of DNA replication, and the cyclin-dependent kinase inhibitors, such as p27/KIP1, represent two groups of proteins that are currently under inv estigation as diagnostic tumour markers. The expression of p27 and MCM3 was compared with: the expression of the Ki-67 protein, an approved marker for proliferating cells, extensively used in histopathology and cancer researc h. The expression pattern of all three proteins was assessed on germinal ce ntres and oral mucosa, which display a well-defined spatio-temporal organiz ation. The expression of the p27 protein was closely related to differentia ted cells, whereas MCM3 and Ki-67 were predominantly localized to the regio ns of proliferating cells. However, it is important to note that considerab le numbers of cells that were growth-arrested, as confirmed by the absence of the Ki-67 protein, stained positive for the MCM3 protein. These results were verified in vitro using growth-arrested Swiss 3T3. The MCM3 protein is therefore expressed in cells that have ceased to proliferate, but are not terminally differentiated, according to the absence of p27 protein expressi on. In conclusion, a combined analysis of Ki-67, MCM3, and p27 protein expr ession may provide a more detailed insight into the cell proliferation and differentiation processes that determine individual tumour growth. Copyrigh t (C) 2001 John Wiley & Sons, Ltd.