Cholera toxin

Fibroblasts were cultured in Dulbecco–Vogt modification of Eagle’s medium (DMEM) supplemented with 10% bovine growth serum (HyClone^®, Thermo Fisher Scientific, Ottawa, ON, Canada), 100 UI/mL penicillin G (Sigma, Oakville, ON, Canada), and 25 µg/mL gentamicin (Schering, Pointe-Claire, QC, Canada). Keratinocytes were cultured in a combination of DMEM with Ham’s F12 (3:1), supplemented with 5% Fetal Clone II serum (Hyclone), 5 µg/mL insulin (Sigma), 0.4 µg/mL hydrocortisone (Calbiochem, EMD Biosciences, Gibbstown, NJ, USA), 10⁻¹⁰ M cholera toxin (MP Biomedicals, Montreal, QC, Canada), 10 ng/mL human epidermal growth factor (EGF; Austral Biological, San Ramon, CA, USA), 100 UI/mL penicillin G (Sigma), and 25 µg/mL gentamicin (Schering).

Fibroblasts (passage 4) were seeded at 4 × 10³ cells/cm² and cultured in Dulbecco’s Modified Eagle’s Medium (DMEM) supplemented with 10% fetal calf serum (FCS, Invitrogen, Burlington, ON, Canada), 100 IU/mL penicillin G (Sigma, Oakville, ON, Canada) and 25 μg/mL gentamicin (Schering, Pointe-Claire, QC, Canada). Keratinocytes (passage 1) were seeded at 4 × 10³ cells/cm² on a feeder layer of irradiated 3T3 murine fibroblasts and cultured in a combination of DMEM with Ham’s F12 (3:1) (DMEMH), supplemented with 5% Fetal Clone II serum (Hyclone, Scarborough, ON, Canada), 5 μg/mL insulin (Sigma, Oakville, ON, Canada), 0.4 μg/mL hydrocortisone (Galenova, Saint-Hyacinthe, QC, Canada), 10⁻¹⁰ M cholera toxin (MP Biomedicals, Montreal, QC, Canada), 10 ng/mL human epidermal growth factor (EGF; Austral Biological, San Ramon, CA, USA), 100 IU/mL penicillin G (Sigma) and 25 μg/mL gentamicin (Schering). All cell cultures were incubated at 37 °C in an 8% carbon dioxide (CO₂) atmosphere, and the cell culture medium was changed three times per week.