Fas is ubiquitously expressed on a variety of cells and triggers apoptosis, which have critical roles in the immune system. MicroRNAs (miRNAs) have been recently identified as regulators that modulate target gene expression and are involved in diverse biological processes, such as cell proliferation and apoptosis. This study was undertaken to investigate the contribution of miRNA in the regulation of Fas expression and Fas-mediated apoptosis. Bioinformatics analysis indicated that Fas was a potential target of let-7/miR-98 family. Indeed ectopic expression of let-7/miR-98 reduced, whereas knockdown of endogenous let-7/miR-98 increased the expression of Fas at both mRNA and protein levels. Let-7/miR-98 was verified to target Fas 3 0 untranslated region directly by site-directed gene mutagenesis and reporter gene assay. More importantly, introduction of let-7/miR-98 could decrease the sensitivity to Fas-induced apoptosis. Furthermore, let-7/miR-98 expression was reduced in activation-induced cell death process, accompanied by increased expression of Fas. In conclusion, our study first demonstrated that let-7/miR-98 regulated Fas expression and the sensitivity of Fas-mediated apoptosis.

Background Minimal erythema dose (MED) has substantial inter‐ and intraindividual variations, reflecting the influence of very diverse factors. However, related studies showed little consistency probably because of their limited sample size. Objective To identify the factors associated with MED variations in a large‐scale population study. Methods The MED test was performed by following the international standard procedure on 22 146 subjects. The results were analysed in adjusted multivariable linear and logistic regression models. Results This large‐scale study revealed that lower MED was consistently associated with lighter skin [β‐coefficient = −0.33, 95% confidence interval ( CI ) −0.36 to 0.30, P = 6.41 × 10 −84 ]. Females had significantly higher MED than male (β = 0.91, 0.32–1.50, P = 2.93 × 10 −3 ). Stratified analyses showed that MED was not associated with age [female: odds ratio ( OR ) = 0.99, 0.98–1.01; male: OR = 0.99, 0.97–1.00]. MED was lower in summer than in other seasons (spring: OR = 1.08, 1.06–1.11; autumn: OR = 1.11, 1.08–1.13; winter: OR = 1.20, 1.18–1.22). Furthermore, MED was associated with air temperature (β = −0.36, −0.49 to 0.23, P = 4.81 × 10 −8 ) and air pressure (β = −0.64, −0.82 to 0.46, P = 8.01 × 10 −12 ) in summer only while not in other seasons. Conclusions This study provides unprecedented evidence that MED is associated with skin colour, sex, season and meteorological factors, but not with age.

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