PKCι is a target of 7,8,4′‐trihydroxyisoflavone for the suppression of UVB‐induced MMP‐1 expression

The soy isoflavone daidzein is bioconverted to 7,8,4′‐trihydroxyisoflavone (7,8,4′‐THIF) by microorganisms. Here, we investigated the matrix metalloproteinase (MMP)‐1 inhibitory properties of 7,8,4′‐THIF that arise through the suppression of UVB‐induced MMP‐1 expression. 7,8,4′‐THIF reduced UVB‐induced MMP‐1 expression at the transcriptional level in primary human dermal fibroblasts and inhibited UVB‐induced transcriptional activity of AP‐1, a major activator of MMP‐1 expression. Additionally, it was observed that the mitogen‐activated protein kinase (MAPK) pathway, a crucial signalling cascade for MMP‐1 expression, was suppressed by 7,8,4′‐THIF. Protein kinase C iota (PKCι) was suspected to be a direct target of 7,8,4′‐THIF. The direct interaction between 7,8,4′‐THIF and PKCι was confirmed using pull‐down assays and immobilized metal ion affinity‐based fluorescence polarization assays. Finally, we observed that 7,8,4′‐THIF inhibited UVB‐induced MMP‐1 expression in a human skin equivalent model. Taken together, these results suggest that 7,8,4′‐THIF, a bioconversion product of daidzein, suppresses UVB‐induced MMP‐1 expression.