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.

Materials And 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.

Conclusion: 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.