Loss of cyclin D2 expression in the majority of breast cancers is associated with promoter hypermethylation

Cyclin D2 is a member of the D-type cyclins, implicated in cell cycle regul ation, differentiation, and malignant transformation. It was noted previous ly that cyclin D2 is not expressed in the majority of breast cancer cell li nes, whereas abundant expression was detected in finite life span human mam mary epithelial cells. By reverse transcription-PCR and Western blot analys is, we extended this finding to primary breast carcinomas and show that the majority of these tumors lack expression of cyclin D2 mRNA (18 of 24) and protein (10 of 13), In contrast, both luminal and myoepithelial subpopulati ons of normal breast tissues expressed cyclin D2. Hypermethylation of the C pG island in the promoter was detected by methylation-specific PCR in nearl y half of the breast cancers (49 of 106) and was associated with silencing of cyclin D2 gene expression. Promoter hypermethylation was also detected i n ductal carcinoma in situ, suggesting that loss of cyclin D2 expression is an early event in tumorigenesis. Our results suggest that loss of cyclin D 2 expression is associated with the evolution of breast cancer.