p53 expression and relation to human papillomavirus infection in pingueculae, pterygia, and limbal tumors

Background: The tumor suppressor gene p53 is expressed without apoptosis in the limbal basal stem cells of all pterygia and limbal tumors and most pin gueculae from which these growths seem to originate. Oncogenic human papill omaviruses (HPVs) have been found in pterygia and limbal tumors, and HPV an d p53 overexpression commonly coexist in oropharyngeal and penile carcinoma s. Objective: To search for HPV DNA as a cofactor in the development of pingue culae, pterygia, and limbal tumors. Methods: We examined specimens-1 of pinguecula, 13 of pterygia (7 primary, 1 recurrent, 1 with dysplasia, and 4 primary not tested for p53), and 10 of limbal tumors (2 with actinic keratosis dysplasia, 1 with conjunctival int raepithelial neoplasia, 3 with carcinoma in situ, and 4 with squamous cell carcinoma)-expressing p53. Specimens were tested for the presence of HPV DN A by the polymerase chain reaction using degenerate consensus primers for t he highly conserved portion of the L1 region that encodes a capsid protein of the virus. This assay has a wide spectrum with capability of detecting e ssentially all known HPV types. Nested polymerase chain reaction was perfor med on all specimens. Primers of the cystic fibrosis gene were used to conf irm the presence of genomic DNA and to rule out inhibitors. Purified HPV DN A type 11 was the positive control, and HPV-negative genomic DNA was the ne gative control. Results: Using consensus primers for the highly conserved portion of the L1 region, all specimens of pingueculae, pterygia, and limbal tumors studied were negative for HPV DNA by nested polymerase chain reaction. Conclusions: Human papillomavirus DNA is not required as a cofactor in the development of pterygia and limbal tumors. These data support the theory th at increased p53 expression in the limbal epithelia of pingueculae, pterygi a, and limbal tumors indicates the probable existence of p53 mutations in t hese cells as an early event in their development, which is consistent with UV irradiation causation. Thus, due to a damaged p53-dependent programmed cell death mechanism, mutations in other genes may be progressively acquire d. This would allow for the multistep development of pterygia and limbal tu mor cells from p53-mutated limbal epithelial basal stem cells overlying pin gueculae.