4.1. Cell Culture and Stable Cell Lines Establishment

HeLa and 293T cells were cultured in DMEM (Corning Cellgro, 15-017-CVR, Manassas, VA, USA) supplemented with 10% Fetal Bovine Serum (CLARK Bioscience, Richmond, VA, USA), 2 mM GlutaMAX (Gibco, Carlsbad, CA, USA), 100 units/mL of Penicillin-100 µg/mL of Streptomycin (HyClone, Logan, UT, USA). HeLa-DRD1-GFP-3FLAG, HeLa-DRD2-GFP-3FLAG, HeLa-GFP-DRD3-3FLAG, HeLa-DRD5-GFP-3FLAG, HeLa-GIPC1-GFP-3FLAG cells were maintained in DMEM complete medium with 1 μg/mL puromycin (Selleck, Washington, DC, USA). HeLa-GFP-DRD3-3FLAG cells were established as previously described [32,58]. In addition, HeLa-DRD1/DRD2/DRD5/GIPC1-GFP-3FLAG cells were established similarly. The cDNA for DRD1/DRD2/DRD5/GIPC1 were amplified from HeLa cells and cloned into MSCV vector with GFP-3FLAG in their C-terminus.