Adaptive response and apoptosis in HCT116 cells upon endoplasmic reticulum stress

Abstract

Objective: To investigate the interconnection between adaptive and apoptotic responses in tumor cells undergoing ER stress, a situation frequently observed during tumor growth. Material and Methods: the human tumor colorectal HCT116 cell line was used as model system. Knockdown of FLIPL, TRAF2 and RIPK1 were accomplished using small-interference RNA. Cells overexpressing FLIPL were generated by retrovirus infection and selection with puromycin. Multicellular tumor spheroids were prepared by the hanging drop method and grown in 96 well plates coated with agarose until treatment. Results: we have identified FLIPL as an important regulator in the balance between apoptosis and survival in conventional 2D cultures of HCT116 cells. FLIPL downregulation or overexpression provokes sensitization or protection to ER stress, respectively. We have also demonstrated that RIPK1 and TRAF2, two negative modulators of TRAIL-induced apoptosis, have a protective role against ER stress-induced apoptosis. In addition, we show that HCT116 3D spheroids, whose architecture resemble solid tumours, are more resistant to ER stress-induced UPR signalling and apoptosis although more experiments are needed to decipher the molecular and cellular basis of this resistance. Conclusions: (1) FLIPL, TRAF2 and RIPK1 play an adaptive role to delay ER stress-induced apoptosis in HCT116 cells and (2) HCT116-derived spheroids are more resistant to ER stress than standard 2D cultures.