Self–Induction of Lacritin in Human Corneal and Conjunctival Cells

Abstract

Abstract: : Purpose: The extracellular glycoprotein lacritin is highly expressed in the human lacrimal gland. It is also expressed in human cornea, salivary glands, and breast tissues. Functions of lacritin include promotion of ductal cell proliferation and tear secretion. Lacritin might be an important factor in maintaining ocular surfaces. However, regulation of lacritin expression is unknown. The purpose of the present experiment was to investigate the regulation of lacritin expression in human corneal and conjuctival cells. Methods: Total RNA was extracted from cultured human cell lines (corneal epithelium and conjunctiva) and from primary cultures of human corneal epithelium. Cells were harvested at several time points after addition of lacritin or EGF, and RT–PCR was performed. Recombinant human lacritin with a histidine–tag was expressed in E. coli and purified by standard methods. Results: Recombinant lacritin increased expression of mRNA for lacritin in cultured corneal and conjunctival cells. Expression of the housekeeping gene GAPDH was not changed. EGF did not increase expression of mRNA for lacritin even though EGF is a strong stimulator of corneal cell proliferation. Conclusions: The results suggested that lacritin protein has a specific effect on expression of mRNA for lacritin. Self–induction of lacritin might one of the factors for continuously maintaining ocular surfaces.

Keywords: conjunctiva • cornea: epithelium • glycoconjugates/glycoproteins