Rabbit anti-ATP8B1 antibody was characterized previously.7 Other antibodies used were rabbit

anti-calreticulin (Alexis Biochemicals, San Diego, CA), mouse anti-transferrin receptor (Zymed, San Francisco, CA), rabbit anti-VSV-G (vesicular stomatitis virus glycoprotein Alpelisib G) (Abcam, Cambridge, UK), mouse anti-V5, mouse anti-V5, fluorescein isothiocyanate (FITC)-conjugated, goat anti-rabbit Cy3-conjugated (Invitrogen, San Diego, CA), goat anti-rabbit, horseradish peroxidase–conjugated (DAKO, Carpinteria, CA), goat anti-mouse, horseradish peroxidase–conjugated (Pierce, Rockford, IL). Rabbit anti-Na/K ATPase was a generous gift from Dr. J. Koenderink (Nijmegen, The Netherlands). ATP8B1 constructs with a VSV-G epitope tag at the amino-terminus were constructed by polymerase chain reaction (PCR) using human ATP8B1 complementary DNA (cDNA) as template and cloned into the AscI and NheI sites of pCB7-VSV. This construct PI3K inhibitor was used as template for site-directed mutagenesis according to the manufacturer’s protocol (Stratagene), to create seven mutations previously identified in patients with ATP8B1 deficiency.11 Human

CDC50A was cloned into pCDNA3-V5 by PCR or into pmKate2-N to create a carboxyl-terminal tagged constructs (see Supporting Table 1 for primer sequences.) Human bone osteosarcoma epithelial cells (U2OS)12 and human embryonic kidney 293T (HEK293T)13 cells were cultured in Dulbecco’s modified Eagle medium supplemented with 10% fetal bovine serum and antibiotics. Transient transfections were performed using calcium phosphate or polyethylenimine using standard procedures, and cells were harvested after 1–3 days. Cells were incubated at 27°C, 30°C, or 40°C, treated with 3 μM MG132 (Calbiochem, San Diego, CA), 100 nM epoxomycin (Sigma, St. Louis, Plasmin MO), or 5 mM 4-phenyl butyric acid (Sigma, St. Louis, MO) for 40, 16, and 40 hours, respectively. Cells transiently transfected

with pCB7-ATP8B1 and pcDNA3-CDC50A were lysed in 20 mM Tris-HCl; pH 7.4, 5 mM Na-ethylene diamine tetraacetic acid, 135 mM NaCl, 1.0% (vol/vol), Nonidet P-40, and 10% (wt/vol) sucrose and centrifuged at 16,000g for 15 minutes. Supernatants were subjected to western blot analysis or incubated with mouse anti-V5 antibodies immobilized on protein A–agarose beads (Sigma, St. Louis, MO) for 2 hours at 4°C, followed by western blot analysis. HEK293T cells were transiently cotransfected with pCB7-ATP8B1 and pcDNA3-CDC50A using calcium phosphate. After 3 days, RNA was isolated using TRIZOL (Invitrogen), and residual DNA in the samples was degraded by deoxyribonuclease I treatment according to the manufacturer’s protocol (Invitrogen).