Abstract 1696: Regulation of sensitivity to the platinum-containing drugs by the sec61 translocon

Abstract The Sec61 protein translocon is a multimeric complex that allows the transport of proteins across or laterally into a lipid bilayer. Components of the sec61 complex are involved in retrotranslocation, Golgi structure and vesicle transport. We have discovered that one component of this complex, the sec61β subunit, modulates cellular sensitivity to the platinum-containing drugs. As part of an effort to enhance sensitivity to the platinum drugs we sought to determine the mechanism of this effect. Sec61β expression in human 2008 ovarian cancer cells was constitutively knocked down by infection with a lentivirus producing an shRNA targeting sec61β, and knockdown was confirmed by qRT-PCR and western blot analysis which demonstrated a 96% reduction in mRNA expression and 87% reduction at the protein level. Effects on drug sensitivity were measured using an SRB assay, and platinum drug accumulation was quantified by inductively coupled plasma mass spectrometry. Sec61β knockdown (KD) did not alter cell viability or growth rate but resulted in 8-, 16.8- and 9-fold resistance to cisplatin, carboplatin, and oxaliplatin, respectively. Resistance to several other clinically relevant chemotherapeutics including paclitaxel, doxorubicin, vincristine, and etoposide was also increased but to a smaller extent (1.7 to 7-fold). Sec61β KD reduced the cellular accumulation of cisplatin to 67% of that in the parental cells. Given that transporters and chaperones that manage copper homeostasis regulate platinum drug accumulation and efflux, their expression in 2008 sec61β KD cells was analyzed by western blot. Among these, ATP7A was found to be 2-fold over-expressed while no change in ATP7B, ATOX1, or CTR2 could be detected. This increase in ATP7A expression was not altered by pretreatment with copper, cisplatin, or the copper chelator bathocuproine disulfonate. We conclude that the sec61β translocon modulates the cytotoxicity of many chemotherapeutic agents with the largest effect being on sensitivity to the platinum drugs. Sec61β regulates expression of the copper export transporter ATP7A that we have previously shown to control platinum drug sequestration and efflux. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1696. doi:10.1158/1538-7445.AM2011-1696