SEC61B and bone osteosarcoma: In human bone osteosarcoma epithelial cells (U-2 OS), immunofluorescence staining confirmed localisation of the endogenous ARL6IP1 protein to the tubular ER, with ARL6IP1 staining observed throughout ER tubules where it exhibits strong overlap with the ER marker Sec61β in peripheral ER tubules (Fig. 4a).