Abstract
A tight junction (TJ) makes a physical barrier in the epidermal cells of skin. Ultraviolet (UV) light may disrupt the TJ barrier, but the mechanism has not been well clarified. Weak UVB (5 mJ/cm2) caused mislocalization of claudin-1 (CLDN1), a component of the TJ strand, and disruption of TJ barrier in human keratinocyte-derived HaCaT cells. The UVB-induced mislocalization of CLDN1 was inhibited by monodansylcadaverine (MDC), a clathrin-dependent endocytosis inhibitor, suggesting that UVB enhances the internalization of CLDN1. Transepidermal electrical resistance and paracellular flux of lucifer yellow, a fluorescent hydrophilic marker, were rescued by MDC. UVB changed neither the total nor phosphorylation levels of CLDN1, but it increased both mono-ubiquitination and tyrosine nitration levels of CLDN1. Fluorescence measurements revealed that UVB increased intracellular free Ca2+, nitric oxide (NO), and peroxynitrite contents, which were inhibited by Opsin2 (OPN2) siRNA, suggesting that OPN2 functions as a UVB sensor. The effects of UVB were inhibited by an antagonist of transient receptor potential type vanilloid 1 (TRPV1) and Ca2+ chelator. Both NO donor and peroxynitrite donor induced the mislocalization of CLDN1 and disruption of TJ barrier, which were rescued by a NO synthase (NOS) inhibitor and a peroxynitrite scavenger. Weak UVB irradiation induced the disruption of TJ barrier mediated by mislocalization of CLDN1 in HaCaT cells. The OPN2/TRPV1/NOS signaling pathway may be a novel target for preventing destruction of the TJ barrier by UVB irradiation.
Highlights
Skin has a function of maintaining a physical barrier between the inside and outside of the body
CLDN1 was mainly localized in the cell–cell contact that is located at the apical region of lateral membranes, the so-called tight junction (TJ), under control conditions (Figure 1B, Figure S1 and S7)
In Western blotting, the protein level of CLDN1 was constant after UVB irradiation, whereas that of CLDN4 was transiently increased after 6 h and decreased after 48 h (Figure 1D)
Summary
Skin has a function of maintaining a physical barrier between the inside and outside of the body. The protein expressions of NOS1-3 are detected in the human skin [16] and human keratinocyte-derived HaCaT cells [17,18]. Peroxynitrite is a potent nitrating and oxidizing agent, leading to the nitration of tyrosine residue of target proteins and aberrations of their expression, localization, and function [19]. It is unknown what regulatory mechanism is involved in the elevation of NOS expression by UVB irradiation. We investigated the effect of low dose of UVB (5 mJ/cm2) on the expression and function of CLDN1 using HaCaT cells. The molecular mechanism of tight junctional localization of CLDN1 was assessed by immunoblotting, as well as immunofluorescence staining, RNS assay, and paracellular permeability measurements
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