DDIT3 and cancer: As a ribosome binding protein, RRBP1 is a member of the ER stress response (16), some ER stress biomarkers, such as the transcription factor C/EBP homologous protein (CHOP) and the double-stranded RNA-dependent protein kinase (PKR)-like ER kinase (PERK), were then assessed in MC3T3-E1 cells cultured by CMs from shRRBP1-transduced two-type cancer cells.