Abstract: 【Abstract】 Objective To investigate the effect of miRNA （miR）-193b-5p on melanogenesis and its possible mechanisms. Methods Human primary melanocytes were isolated from discarded normal foreskin tissues of healthy males after circumcision, and cultured in vitro. miR-NC mimics （miR-NC mimic group） and miR-193b-5p mimics （miR-193b-5p mimic group） were transfected into human primary melanocytes and human MNT1 melanoma cells, separately. After transfection, real-time quantitative PCR （RT-qPCR） was performed to determine the overexpression efficiency of miR-193b-5p at 48 hours, Western blot analysis to determine the expression of melanogenesis-related proteins tyrosinase （TYR） and microphthalmia-associated transcription factor （MITF） in human primary melanocytes and human MNT1 melanoma cells at 72 hours, and the melanin content in the above cells was determined by a sodium hydroxide solubilization method at 1 week. The target gene of miR-193b-5p was predicted by using Targetscan algorithms and verified by dual-luciferase reporter assay, and RT-qPCR and Western blot analysis were performed to analyze changes in mRNA and protein expression of the target gene respectively after the overexpression of miR-193b-5p. Two-independent-samples t test was used for comparisons between two groups. Results In human primary melanocytes and human MNT1 melanoma cells, the miR-193b-5p expression levels were significantly higher in the miR-193b-5p mimic groups than in the miR-NC mimic groups （t = 65.57, 22.49, respectively, both P < 0.001）, and the melanin content was significantly lower in the miR-193b-5p mimic groups （0.091 ± 0.007, 0.130 ± 0.004, respectively） than in the miR-NC mimic groups （0.117 ± 0.002, 0.188 ± 0.032, t = 5.98, 3.24, P < 0.01, < 0.05, respectively）. Western blot analysis showed that the expression of melanogenesis-related proteins TYR and MITF in both human primary melanocytes and human MNT1 melanoma cells was significantly lower in the miR-193b-5p mimic groups than in the miR-NC mimic groups （all P < 0.01）. TargetScan analysis and dual-luciferase reporter assay revealed a binding site for miR-193b-5p in the 3′ untranslated region of the transcriptional regulator CITED2. After up-regulation of miR-193b-5p expression in human primary melanocytes and human MNT1 melanoma cells, the CITED2 mRNA and protein expression levels significantly decreased compared with the miR-NC mimic groups （all P < 0.05）. Conclusion miR-193b-5p overexpression can down-regulate the expression of melanogenesis-related proteins TYR and MITF, and then inhibit melanogenesis, which may be related to the targeted inhibition of CITED2 expression.

Key words: Melanocytes, Melanoma cells, Melanogenesis, CITED2, miRNA-193b-5p