Abstract 2443: Novel role of glucose-regulated protein 78 mediating lipid metabolism through controlling stearoyl-CoA desaturase 1
Authors: Cook Katherine L. , Clarke Pamela A.G. , Axelrod Margaret , Wärri Anni , Clarke Robert 
Published: May 2015

Over 230,000 new cases of invasive breast cancer are diagnosed annually within the United States. Of these cases, 70% express the estrogen receptor-α and may be treated with antiestrogens or aromatase inhibitors. While these drugs exhibit clinical benefits, over 50% will develop or not respond to antiestrogen therapy, making understanding the molecular mechanism of antiestrogen resistance critical to preventing and treating endocrine resistant breast cancer. Recently, we have determined a key role of the unfolded protein response endoplasmic reticulum (EnR) protein chaperone, glucose regulated protein 78 (GRP78), in mediating antiestrogen resistance. A sole designation of GRP78 as a protein chaperone controlling UPR signaling is limiting because GRP78 is multifunctional. We now expand the role of GRP78 to include its novel actions regulating lipid metabolism. Metabolic analysis of antiestrogen sensitive LCC1 and antiestrogen resistant LCC9 breast cancer cells indicate that inhibition of GRP78 through RNAi results in an increase in the intracellular concentrations of the polyunsaturated fats (PUFA) linoleate (18:2n6), linolenate [alpha or gamma; (18:3n3 or 6)], dihomo-linolenate (20:3n3 or n6), and dihomo-linoleate (20:2n6). GRP78 knockdown results in an increase in delta-6 desaturase in the LCC9 cells corresponding with the observed increase in PUFA. Moreover, knockdown of GRP78 decreased stearoyl-CoA desaturase 1 (SCD1) and fatty acid synthase (FASN) protein levels, further supporting a role for GRP78 in lipid metabolism. Treatment of breast cancer cells with increasing doses of PUFA linoleic acid results in the inhibition of SCD1, suggesting that GRP78 regulation of PUFA metabolism mediates GRP78 actions on SCD1 and lipid biogenesis. Antiestrogen resistant cells express higher levels of SCD1. Moreover, elevated SCD1 is associated with breast cancer reoccurrence and reduced survival in breast cancer patient-derived data sets, suggesting a critical role of SCD1 in mediating antiestrogen resistance. LCC9 orthotopic tumors treated with GRP78 targeting morpholino were re-sensitized to tamoxifen. Targeting GRP78 in vivo resulted in reduced SCD1 protein in GRP78 morpholino+tamoxifen treated tumors, demonstrating a key role of GRP78/SCD1 interaction in drug resistance. Inhibition of GRP78 also increased short-chained acyl-CoA dehydrogenase (ACADS) protein expression and decreased the fatty acid metabolite butyrylcarnitine, indicating a stimulation of beta-oxidation. These data suggest that the effect of GRP78 knockdown on fatty acid metabolism and biogenesis may represent a new homeostatic ability of GRP78 to modify fatty acid metabolism. The consequences of these activities may help reduce EnR stress by providing an additional energy source for protein folding/refolding and so help alleviate the accumulation of unfolded/misfolded proteins accumulation within the EnR.

Citation Format: Katherine L. Cook, Pamela A.G. Clarke, Margaret Axelrod, Anni Wärri, Robert Clarke. Novel role of glucose-regulated protein 78 mediating lipid metabolism through controlling stearoyl-CoA desaturase 1. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2443. doi:10.1158/1538-7445.AM2014-2443