Increased gamma-tubulin expression and P16INK4A promoter methylation occur together in preinvasive lesions and carcinomas of the breast.
BACKGROUND
Loss of p16(INK4A) due to promoter hypermethylation is correlated with the ability to acquire centrosomal abnormalities in variant human mammary epithelial cells. gamma-Tubulin is a highly conserved component of centrosome in most animal cells and gamma-tubulin protein overexpression could lead to centrosome aberration.


METHODS
A large series of breast premalignant lesions and carcinoma was analyzed. Real-time quantitative PCR and immunohistochemistry were carried out to measure gamma-tubulin copy numbers and protein expression. MethyLight and immunohistochemistry were carried out to determine p16(INK4A) methylation and protein expression.


RESULTS
gamma-Tubulin protein expression was concordant with gene amplification; both of them were found to increase with atypical ductal hyperplasia-carcinoma sequence. The median value and positive rate of p16(INK4a) methylation increased while protein expression displayed a decreasing trend. P16(INK4a) methylation showed a firm association with gamma-tubulin gene amplification.


CONCLUSIONS
gamma-Tubulin gene amplification and the concomitant protein overexpression present not only in invasive carcinoma but also in a significant fraction of atypical hyperplasia and in situ carcinomas. P16(INK4a) methylation and gamma-tubulin gene amplification had a synergistic effect on tumor progression. The synergism might arise as a result of the combined influence that p16(INK4a) and gamma-tubulin have on the G1-S cell cycle checkpoints and centrosome.
Liu
T
T
Breast Cancer Research Key Laboratory of National Education Ministry, Cancer Institute and Hospital, Tianjin Medical University, Tianjin, China.
Niu
Y
Y
Yu
Y
Y
Liu
Y
Y
Zhang
F
F
D001483:Base Sequence; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology; D019175:DNA Methylation; D017931:DNA Primers; D019942:Genes, p16; D006801:Humans; D007150:Immunohistochemistry; D009361:Neoplasm Invasiveness; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D014404:Tubulin / Q000235:genetics / Q000378:metabolism*
D017931:DNA Primers; D014404:Tubulin