Coincident inactivation of 14-3-3σ and p16INK4a is an early event in vulval squamous neoplasia

The structure and expression of 14-3-3 sigma(sigma) was analysed in squamous carcinomas (SCC) of the vulva and in the vulval pre-malignant lesion vulval intraepithetial neoplasia (VIN). Sequence analysis of the sigma coding region did not detect mutations in any case of SCC or VIN III and loss of heterozygosity (LOH) occurred in only 2 out of 27 informative cases. In contrast to the absence of genetic change, methylation-specific PCR (MSP) analysis revealed dense CpG methylation within the a gene in approximately 60% of cases of vulval SCC, but methylation was not detected in matched, normal epithelial tissue. Methylation was associated in all cases with reduced or absent expression of a mRNA. There was no correlation between sigma methylation and HPV or p53 status. Analysis of pre-malignant vulval intraepithelial neoplasia (VIN) revealed that sigma methylation was detectable early in neoplastic development. Coincident methylation, accompanied by loss of expression, of sigma and p16(INK4a) was commonly detected in both SCC and VIN 111, suggesting that epigenetic silencing of these two genes is an early and important event in vulval neoplasia.