A “drug holiday” modifies the expression of MITF and pigmentation-related genes but does not induce cell death in resistant melanoma cells. (a) PARP cleavage, MITF-M, and DCT protein levels assessed by immunoblot analysis. β-actin or GAPDH was used as loading control. The proteins were visualized on a medical X-ray film or by using ChemiDoc Imaging System (Biorad). The images are cropped, which is indicated by white spaces. (b) The mRNA levels of MITF-M and pigmentation-related genes in resistant cells and after drug discontinuation (“drug holiday”) relative to their levels in the respective drug-naïve cells (horizontal lines). ((c)-(d)) Representative density plots of MITF-positive cells (c) and Melan-A-positive cells (d) are shown. In addition, percentages of MITF- and Melan-A-positive cells in resistant cell populations, either exposed to drugs (TRAR, PLXR), or after 10 days of “drug holiday” (TRAR DH, PLXR DH), or again reexposed to drugs (TRAR DH+TRA, PLXR DH+PLX) for 2 days, are shown as bars. Data are presented as mean of two independent experiments ± SD.