Background and Aim: Cancer cells release a complex of different factors into their environment that can lead to functional changes in cells within the tumor microenvironment and also farther away from the tumor region. The aim of this study is in vitro evaluation of the effects of conditioned medium derived from A375 human melanoma cell line on the function of human melanocytes.

Materials and Methods: The conditioned medium was prepared from A375 melanoma cell line after 48 hours of culture. Melanocytes in the test group were seeded in T-25 flask and treated with the conditioned medium for 22 days. The same number of melanocytes in the control group was cultured in complete medium (DMEM supplemented with 10% FBS). The morphological characteristics by using inverted light microscope, growth rate by direct cell counting, expression levels of melanoma diagnostic markers (S100A4, S100A14, MITF, TYR) and also epithelial-mesenchymal transition (EMT) related markers (CDH1, CDH2, SNAI1, SNAI2, TWIST1, TGF-β) by real-time PCR and migration rate by scratch assay, were studied in both groups. A375 melanoma cell line was used as a positive control.

Results: The results showed that melanocytes treatment with A375-conditioned medium leads to alteration of the cells morphological characteristics, 1.62 fold increase in melanocytes proliferation rate, significant increase in S100A14 (*p=0.003) and TGF-β (*p=0.001) expression, a significant decrease in CDH1 (*p=0.048) gene expression and also increase in migration rate of the treated melanocytes (*p<0.05).

‍Conclusion: Based on results of this study, secreted molecules derived from A375 melanoma cell line, can change the molecular and functional characteristics of melanocytes in order to induce malignant transformation.