Increased γ-tubulin expression and P16INK4A promoter methylation occur together in preinvasive lesions and carcinomas of the breast

Abstract

BackgroundLoss of p16INK4A due to promoter hypermethylation is correlated with the ability to acquire centrosomal abnormalities in variant human mammary epithelial cells. γ-Tubulin is a highly conserved component of centrosome in most animal cells and γ-tubulin protein overexpression could lead to centrosome aberration. Materials and methodsA large series of breast premalignant lesions and carcinoma was analyzed. Real-time quantitative PCR and immunohistochemistry were carried out to measure γ-tubulin copy numbers and protein expression. MethyLight and immunohistochemistry were carried out to determine p16INK4A methylation and protein expression. Resultsγ-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 p16INK4a methylation increased while protein expression displayed a decreasing trend. P16INK4a methylation showed a firm association with γ-tubulin gene amplification. Conclusionγ-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. P16INK4a methylation and γ-tubulin gene amplification had a synergistic effect on tumor progression. The synergism might arise as a result of the combined influence that p16INK4a and γ-tubulin have on the G1–S cell cycle checkpoints and centrosome.