DNA replication licensing and cell cycle kinetics of normal and neoplastic breast.
Mcm2-7 (MCM) proteins are part of the origin licensing machinery that regulates initiation of DNA replication. Geminin is a licensing repressor and prevents reinitiation of DNA replication during S-G2-M phase by blocking reloading of Mcm2-7 at replication origins. Here, we have analysed these replication licensing factors (RLFs) to determine whether the pathway becomes deregulated during mammary carcinogenesis, and have assessed their potential value as prognostic markers. Protein expression profiles were generated for Ki67, Mcm2, geminin, HER-2, ER and PR in a series of reduction mammoplasty (n=18) and breast cancer specimens (n=120), and compared to clinicopathological parameters. A large proportion of epithelial cells of the terminal duct lobular unit reside in a primed 'replication licensed' but not proliferating state. This state is characterised by Mcm2 expression and absence of Ki67 and the S/G2/M marker geminin. In breast cancers, increasing tumour grade is associated with increased Ki67, Mcm2 and geminin expression. The Mcm2/Ki67 ratio decreases through the grades, indicating a shift from a predominantly licensed state to an actively proliferating state. This shift is associated with an increase in the geminin/Ki67 ratio, signifying a shortening of G1 phase in breast cancer cells. Ki67, Mcm2 and the Mcm2/Ki67 ratio are statistically significantly associated with the Nottingham Prognostic Index (NPI), but geminin and the geminin/Ki67 ratio are not. Ki67, Mcm2 and Mcm2/Ki67 are highly correlated with one another, with Mcm2 being the single most important predictor of NPI score (P<0.001). However, only 12% of variation in NPI is explained by Mcm2, as the labelling index for this marker is approaching 100% for many of the high-grade tumours. The origin licensing phenotypes of normal breast and breast cancers therefore relate to their cellular differentiation status, and high-level MCM expression in more poorly differentiated tumours severely constrains their use as prognostic markers in breast cancer.
Shetty
A
A
Department of Pathology, University College London, UK.
Loddo
M
M
Fanshawe
T
T
Prevost
A T
AT
Sainsbury
R
R
Williams
G H
GH
Stoeber
K
K
D000328:Adult; D014408:Biomarkers, Tumor / Q000032:analysis; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology*; D016022:Case-Control Studies; D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000032:analysis / Q000096:biosynthesis*; D002454:Cell Differentiation; D004261:DNA Replication; D005260:Female; D064248:Geminin; D020869:Gene Expression Profiling; D006801:Humans; D007150:Immunohistochemistry; D019394:Ki-67 Antigen / Q000032:analysis / Q000096:biosynthesis*; D007700:Kinetics; D016462:Mammaplasty; D008875:Middle Aged; D064111:Minichromosome Maintenance Complex Component 2; D009687:Nuclear Proteins / Q000032:analysis / Q000096:biosynthesis*; D010641:Phenotype; D011379:Prognosis
D014408:Biomarkers, Tumor; D018797:Cell Cycle Proteins; C577995:GMNN protein, human; D064248:Geminin; D019394:Ki-67 Antigen; D009687:Nuclear Proteins; C084859:MCM2 protein, human; D064111:Minichromosome Maintenance Complex Component 2