To study the expression and cellular distribution of multiple S100A genes and proteins in normal corneal-limbal epithelium and ocular surface squamous cell carcinoma (SCC) tissue.
Normal corneal-limbal tissue was obtained from the Lions Eye Bank, Tampa, FL. Ocular surface SCC tissues were excised from patients undergoing surgery at Singapore National Eye Centre. S100A mRNA expression was measured by quantitative PCR. S100 protein distribution was determined by immunofluorescent staining analysis.
Twelve S100 mRNAs were identified in human corneal and limbal epithelial cells. S100A2, A6, A8, A9, A10, and A11 mRNA was expressed at high level, while S100A1, A3, A4, A5, A6, A7, and A12 mRNA expression was low. The intracellular localization of S100A2, A6, A8, A9, A10 and A11 protein was determined in normal corneal-limbal and SCC tissues. S100A2 and S100A10 proteins were enriched in basal limbal epithelial cells of the normal tissue. S100A8 and S100A9 were found only at the surface of peripheral corneal and limbal epithelium. S100A6 was uniformly found at the plasma membrane of corneal and limbal epithelial cells. S100A11 was found at the supralayer limbal epithelial cells adjacent to the conjunctiva. SCC tissue showed typical pathological changes with expression of cytokeartin (CK) 14 and CK4 in the epithelial cells. All SCC epithelial cells were positive of S100A2, S100A10, S100A6 and S100A11 staining. Intracellular staining of S100A8 and S100A9 was found in several layers of SCC epithelium. Expression of S100A2 and S100A10 decreased dramatically in cultured limbal epithelial cells with increased passaging, which was accompanied by a small increase of S100A9 mRNA, with no changes of S100A8 gene expression. Serum and growth hormone depletion of the culture serum caused a small reduction of S100A2 and S100A10 gene expression, which was accompanied by a small increase of S100A9 mRNA while no changes of S100A8 expression was measured.
Normal corneal and limbal epithelial cells express a broad spectrum of S100 genes and proteins. Ocular surface SCC express high levels of S100A2, S100A10, S100A8 and S100A9 proteins. The expression of S100A2 and S100A10 is associated with limbal epithelial cell proliferation and differentiation.

Pterygium is an ocular surface disease of unknown etiology associated with epithelial and fibrovascular outgrowth from the conjunctiva onto the cornea. S100 proteins are calcium-activated signaling proteins that interact with other proteins to modulate biological functions such as cell migration, proliferation, and differentiation. The aim of this study was to investigate the presence of various S100 proteins in pterygium compared to normal conjunctiva.
Immunofluorescent staining using antibodies against S100A4, S100A6, S100A8, S100A9, and S100A11 were conducted to investigate the expression and tissue distribution. S100 protein secretions and expressions were confirmed using western blot and quantitative real-time polymerase chain reaction (RT-PCR), respectively.
Immunofluorescent staining demonstrated the presence of S100A4, S100A6, S100A8, S100A8, S100A9, and S100A11 in both conjunctival and pterygial epithelium. No significant difference was found in the localization and expression of S100A4. In both conjunctiva and pterygium, S100A4-positive cells were found in superficial and suprabasal layers. S100A6 expression was strong in the superficial layer of pterygium epithelium but relatively weaker in the suprabasal and superficial cells of normal conjunctiva epithelium. S100A8 and S100A9 were localized in the superficial layer of both pterygium and normal conjunctiva epithelium, with higher levels in pterygium than uninvolved conjunctiva. S100A11 was expressed in the basal cells of conjunctival epithelium but in the suprabasal layers of pterygium epithelium. Western blot and RT-PCR confirmed the presence of S100A4, S100A6, S100A8, S100A9, and S100A11 in pterygium and conjunctiva tissue.
Higher levels of S100A6, S100A8, and S100A9 expressions were detected in the pterygium tissue relative to normal conjunctiva. In addition, a distinct alteration of localization of S100A11 expression was observed in pterygium epithelium compared to the conjunctiva. Therefore, these S100 proteins may be associated with the formation of pterygium.