Analysis of OSW-1-Induced Stress Responses in HT-29 Cells

Abstract

OSW-1, a promising compound that is toxic to diverse tumor cell lines, is a saponin from Ornithogalum saundersia. In this study, we analyzed the stress responses induced by OSW-1 using the human colon cancer cell line HT-29 cells and compared it with the commonly used ER and Golgi stress inducers brefeldin A (BFA), thapsigargin (Tg), and tunicamycin (Tm). OSW-1 induced few ER stress-related factors, but there was an increase in expression of TFE3 protein, one of the Golgi stress response factors. A shift in the molecular weight of TFE3 was also found, likely attributable to dephosphorylation. Conversely, the impact of OSW-1 on the expression of the TFEB protein, another member of the MiTF/TFE family, was minimal. Cleavage of CREB3, another Golgi stress sensor, was apparently induced only by BFA. LC3-II and p62, autophagy-related factors, were increased in all drug treatments. Unexpectedly, OSBP protein levels, one of the targets of OSW-1, were increased by not only three reagents but also OSW-1. Taken together, OSW-1 treatment of HT-29 cells induced atypical Golgi stress that strongly activated the TFE3 pathway and did not involve the CREB3 pathway or the ER stress response. Although OSW-1 was also found to affect the autophagy system, it was suggested that the effects of OSW-1 may not be mediated by OSBP depletion. These findings will contribute to the development of OSW-1-based cancer therapies and to our understanding of Golgi stress responses.