Expression of 14-3-3sigma, p16 and p53 proteins in anal squamous intraepithelial neoplasm and squamous cell carcinoma.

14-3-3sigma is a p53-regulated G2/M inhibitor involved in numerous cellular signaling pathways related to cell cycle, DNA repair and apoptosis. Recent studies have showed that 14-3-3sigma was silenced transcriptionally through promoter hypermethylation mainly in HPV-negative vulvar squamous cell carcinoma (SCC). However, the expression of 14-3-3sigma protein has not yet been studied in anal SCC and its precursor, anal intraepithelial neoplasm (AIN). In this study, we evaluated the expression of 14-3-3sigma, p16 and p53 in 34 cases of normal perianal squamous mucosa, 5 cases of squamous hyperplasia and 62 cases of AIN, including 54 bowenoid and 8 differentiated AINs. Fourteen cases of invasive anal SCC were also included in the study, including 8 cases associated with bowenoid AIN and 6 cases associated with differentiated AIN. Expression of p16, p53 and 14-3-3sigma proteins was not seen in normal squamous epithelium. Weak staining for 14-3-3sigma was seen in anal squamous hyperplasia. Strong and diffuse p16 immunoreactivity was seen in 98.1% of bowenoid AIN, but only in 12.5% of differentiated AIN. In contrast, increased basal staining with suprabasal extension of p53 was seen in 100% of differentiated AIN, but in none of the bowenoid AIN. Expression of p16 and p53 was essentially mutually exclusive except in one case. Overexpression of 14-3-3sigma was detected in 97% (60/62) of AIN cases, including 96.3% of bowenoid AIN and 100% of differentiated AIN. Expression of 14-3-3sigma was independent of immunoreactivity status for p16 and p53. In conclusion, two histopathologic types of AIN, bowenoid and differentiated, have distinct immunoprofiles for p16 and p53, which suggests dual molecular pathways during anal carcinogenesis. Increased expression of 14-3-3sigma protein was found in approximately 97% of AIN lesions, regardless of histopathologic type and independent of p16 and p53 expression. Our study indicates that immunohistochemical detection of 14-3-3sigma in conjunction with p16 and p53 may be useful in histopathologic recognization of AIN.