Vimentin as a Marker of Early Differentiating, Highly Motile Corneal Epithelial Cells

Vimentin (Vim), a cytoskeletal intermediate filament, is part of a naturally occurring reversible program, the Epithelial-Mesenchymal Transition (EMT), which converts epithelial cells into mesenchymal-like derivatives. Based on previous results showing that epithelial cells co-express Vim and keratin (Krt) as part of a cytoskeletal network which confers them a highly motile phenotype, we explored the role of Vim in rabbit corneal epithelial cells or RCE1(5T5) cells, an established model of corneal epithelial differentiation. Vim and keratin filaments were co-expressed in cells localized at the proliferative/migratory rim of the growing colonies, but not in basal cells from the center of the colonies nor at suprabasal cell layers. Flow cytometry and qPCR demonstrated that there was a decrease in Krt⁺ /Vim⁺ cell number and ΔNp63α expression when cells reached confluence and formed a 4-5 layered epithelium, while there was a concomitant increase of both Pax-6 expression and Krt⁺ /Vim^- cells. Inhibition of cell proliferation with mitomycin C did not modify cell motility nor the expression of Vim. We studied the distribution and expression of α6 integrin, a protein also involved in cell migration. The results demonstrated that α6 integrin had a distribution which was, in part, co-linear with Vim at the proliferative/migratory rim of cell colonies, suggesting an indirect interaction between these proteins. Immunoprecipitation and immunostaining assays indicated that plectin might be mediating such interaction. These data suggest that Vim expression in corneal epithelium is found in a cell population composed of highly motile cells with a Vim⁺ /Krt⁺ /ΔNp63α⁺ /Pax-6^low /α6 integrin⁺ phenotype. J. Cell. Physiol. 232: 818-830, 2017. © 2016 Wiley Periodicals, Inc.