We recently characterized the cytotoxic action of a novel phenformin derivative, 2-(2-chlorophenyl)ethylbiguanide (2-Cl-Phen), on HT-29 cells under a serum- and glucose-deprived condition and found that 2-Cl-Phen attenuated ATF4 and GRP78, typical downstream targets of the unfolded protein response (UPR), together with c-Myc protein expression in a transcriptional and posttranscriptional manner. In the current study, we focused on the expression of ER-associated protein degradation (ERAD) components after treatment with 2-Cl-Phen under a serum- and glucose-deprived condition. Among nine ER-localizing factors regulating protein quality control within the ER, the amounts of Herp, GRP78, GRP94, and OS9 proteins were significantly downregulated by treatment with 2-Cl-Phen. In particular, replacement of the culture medium with the serum- and glucose-deprived medium induced the expression of Herp protein at the early phase. This increase in Herp protein was accompanied by an increase in its mRNA, and its induction was significantly dampened by 2-Cl-Phen. However, cotreatment with a proteasome inhibitor, MG132, restored Herp expression only to a limited extent. Taken together, these results show that 2-Cl-Phen changed the expression of several ERAD components, especially by transcriptional inhibition of Herp induction by 2-Cl-Phen when it occurred at an early phase, and this finding provides new insights into understanding the mechanisms of 2-Cl-Phen-mediated cytotoxicity.
Keywords: 2-Cl-Phen; ER stress; ERAD; Herp.