Expression of survivin protein in pterygium and relationship with oxidative DNA damage

Abstract

Ultraviolet radiation is known to cause oxidative DNA damage and is thought to be a major factor implicated in the pathogenesis of pterygium. Among all the photo-oxidative DNA products, the 8-hydroxydeoxyguanosine (8-OHdG) is regarded a sensitive and stable biomarker for evaluating the degree of DNA damage. The protein p53 is a major cell stress regulator that acts to integrate signals from a wide range of cellular stresses. UV radiation has a carcinogenic effect resulting in DNA damaged cells with loss of normal growth control. This assumption is supported by the association between UV-B exposure and activation of survivin, a member of the inhibitor of apoptosis protein family (IAP), highly up-regulated in almost all types of human malignancy. In this study we demonstrate, for the first time in pterygium, the immunohistochemical presence of survivin, and investigate the correlation between survivin, p53 and 8-OHdG. Our results demonstrate that oxidative stress could lead to a significant activation of survivin expression, suggesting that this might be an important event in the development of pterygium, inducing and supporting a hyperproliferative condition. Survivin expression in pterygium would counteract UV-B-induced apoptosis and would cooperate with loss of p53. The co-operation between survivin and functional loss of p53 might provide a general mechanism for aberrant inhibition of apoptosis that could be responsible for the development of pterygium and its possible progression to neoplasia.

Figure 1

Immunohistochemical staining for 8-OHdG (A, B) and p53 (C, D). In pterygium 8-OHdG (A) and p53 expression (C) was localized to the nuclei of the epithelial layer. No differences in the pattern of staining between 8-OHdG and p53 were observed. No immunostaining for 8-OHdG (B) or p53 (D) in normal conjunctiva samples was observed. Each section was counterstained with haematoxylin. Original magnification: A, B, D, 400X; C, 630x.

Figure 3

Immunohistochemical staining for 8-OHdG (A), p53 (B), survivin (C). Sections from normal human skin (A) and human cutaneous malignant melanoma (B, C) were included as positive controls. Sections incubated without a primary antibody (inset B¹), or with an isotype control antibody (insets A¹ and C¹) displayed no immunoreactivity. Each section was counterstained with haematoxylin. Original magnification: A, B, and insets A¹, B¹, C¹, 400x; C, 630x.

Figure 2

Immunohistochemical staining for survivin. The immunoreactiv-ity was localized to the nuclei and cytoplasm of the epithelial cells. Note in B a cell with immunoreactivity in both nucleus and cytoplasm (arrow). No immunostaining in normal conjunctiva was detected (C). Each section was counterstained with haematoxylin. Original magnification: A-C, 400x.