Controversial relationship between the expression of the RB pathway components and RB protein phosphorylation in human breast cancer.
Recent data challenge the relevance of the RB pathway to cancer based on RB inactivation, at least in breast tumors. To obtain information on the actual role of the components of the RB pathway in tumor progression we decided to investigate whether their quantitative changes were associated with variations in the level of RB phosphorylation in human breast cancer. A series of 68 human primary breast carcinomas was studied. Five cases were excluded from the study due to their lack of RB expression. In the remaining 63 cases the expression of cyclin D1, cdk4, cyclin E, and INK4a mRNA was assessed by real-time RT-PCR. The level of RB phosphorylated protein (ppRB) and p27 expression was immunohistochemically analyzed by measuring the percentage of stained cells (labeling index, LI). Cell proliferation rate was measured by Ki67 LI evaluation. The ppRB LI ranged from 5.2 to 73.8 and, as expected, was strongly related to the Ki67 LI (r=0.80; p<0.001). The expression of cyclin D1 mRNA, expressed in arbitrary units (a. u.), ranged from 1.15 to 123.0 and was inversely related to the ppRB LI (p=0.021) and Ki67 LI (p<0.001). Neither the cdk4 (range from 0.07 to 1.13 a. u.) nor the cyclin E (range from 0.13 to 9.27 a. u.) mRNA expression was significantly associated with the ppRB LI (p=0.962 and p=0.103, respectively). Cyclin E was related to Ki67 LI (p=0.022). Both INK4a mRNA (range from 0.01 to 0.60 a. u.) and p27 (LI from 0.0 to 73.1) values were inversely related to the ppRB LI (p=0.022 and p=0.014, respectively). Cyclin D1, cdk4, and cyclin E mRNA expressions were not significantly related to one another. In human primary breast cancers, the expression levels of the factors known to facilitate the cell cycle progression by RB protein phosphorylation were not positively related to ppRB-LI. Pathological increases of cyclin D, cdk4, and cyclin E are very likely associated with other biological functions other than their well-established action on cell cycle progression.
Montanaro
L
L
Department of Experimental Pathology, Unit of Clinical Pathology, University of Bologna, Bologna, Italy.
Vici
M
M
Donati
G
G
Ceccarelli
C
C
Santini
D
D
Treré
D
D
Derenzini
M
M
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D018797:Cell Cycle Proteins / Q000032:analysis* / Q000235:genetics; D049109:Cell Proliferation; D056741:Cyclin D; D019927:Cyclin E / Q000032:analysis / Q000235:genetics; D051358:Cyclin-Dependent Kinase 4 / Q000032:analysis / Q000235:genetics; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000032:analysis / Q000235:genetics; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000032:analysis; D016213:Cyclins / Q000032:analysis / Q000235:genetics; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007150:Immunohistochemistry; D019394:Ki-67 Antigen / Q000032:analysis; D008875:Middle Aged; D010766:Phosphorylation; D012333:RNA, Messenger / Q000032:analysis; D011960:Receptors, Estrogen / Q000032:analysis; D016160:Retinoblastoma Protein / Q000032:analysis* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
D018797:Cell Cycle Proteins; D056741:Cyclin D; D019927:Cyclin E; D019941:Cyclin-Dependent Kinase Inhibitor p16; D016213:Cyclins; D019394:Ki-67 Antigen; D012333:RNA, Messenger; D011960:Receptors, Estrogen; D016160:Retinoblastoma Protein; D050760:Cyclin-Dependent Kinase Inhibitor p27; C495900:CDK4 protein, human; D051358:Cyclin-Dependent Kinase 4