Expression Pattern and Subcellular Localization of Human Papillomavirus Minor Capsid Protein L2

The expression pattern of human papillomavirus (HPV) capsid antigen L2 is poorly described, and the significance of its localization with both promyelocytic leukemia protein (PML) and Daxx in a subnuclear domain, nuclear domain 10 (ND-10), when ectopically expressed in tissue culture cells is controversial. To address whether ND-10 localization of L2 occurs in natural cervical lesions, we used a HPV16 and HPV18 L2-specific monoclonal antibody (RG-1), in addition to rabbit antiserum to HPV6 L2, to localize L2. Immunohistochemical staining with RG-1 produced diffuse staining in the nuclei of some cells located within the superficial epithelial layers in eight of nine cases of HPV16/18⁺ cervical intraepithelial neoplasia grade 1 (CIN1); however, no staining was observed in HPV16/18⁺ high-grade CIN (0 of 8 cases), normal cervical epithelium (0 of 20 cases), cervical squamous cell carcinoma (0 of 102 cases), adenocarcinoma (0 of 51 cases), or adenosquamous carcinoma (0 of 6 cases). HPV16/18⁺ cervical lesions that express L2 exhibit higher HPV16/18 genome copies per cell compared with those that do not positively stain with RG-1 (P = 0.04). RG-1 staining of HeLa cells transfected with L2 expression constructs was frequently concentrated in the ND-10, particularly in cells expressing high levels of L2, and co-localized with the cellular markers of ND-10, PML, and Daxx. In contrast, L2 was primarily diffuse within the nucleus and distinct from ND-10 as defined by PML immunofluorescent staining in CIN lesions, condylomata, and HPV16-transduced organotypic cultures.