MAPK3 and melanoma: To test whether TRF2 phosphorylation on S323 occurred in vivo, a tetracycline-inducible system was used to overexpress a wild-type form of TRF2 (WT-TRF2) in the human melanoma cell line A375 which carries a BRAFV600E activating mutation and displays strong ERK1/2 activity.