Primary embryonic lung fibroblasts (MRC-5), human newborn foreskin fibroblasts (HFFs), 293T, and Hela cells were propagated in Dulbecco's modified Eagle medium (DMEM) supplemented with 10% fetal bovine serum, non-essential amino acids, and penicillin-streptomycin. Transient transfection of expression constructs were carried out using lipofectamine according to the manufacturers' instructions.