2. Materials and methods
2.1. Reagents and antibodies
QUER was purchased from Biospectrum, QU-CAP and caprilic/capric triglycerides (CAP) were obtained from BASF and dimethyl-sulfoxide (DMSO) was obtained from Sigma. LLVY-AMC, MG132, as well as primary proteasomal antibodies against α7 (PW8110; 30 kDa) and β5 (PW8895; 23 kDa) subunits were purchased from BIOMOL. Primary antibodies against GAPDH (sc25778; 37 kDa) and secondary antibodies were purchased from Santa Cruz Biotechnology. Primary antibody against tyrosinase (#MS-800-P0, 70–80 kDa) was obtained from Thermo Scientific.
2.2. Cell lines and culture conditions
HFL-1 human embryonic fibroblasts (obtained by the European Collection of Cell Cultures) and mouse melanocytes (B16F10 cell line) were maintained in Dulbecco's modified Eagle's medium (DMEΜ; Invitrogen) supplemented with 10% foetal bovine serum (v/v; Invitrogen), 2 mM glutamine, and 1% non-essential amino-acids. Cells were subcultured at 37 °C, 5% CO2 and 95% humidity, were fed approximately 16 h prior to each assay and cell number was determined in duplicates using a Coulter Z2 counter (Beckman Coulter). HFL-1 cells were subcultured when they reached confluence at a split ratio of 1:2 until they entered to senescence.