Abstract P5-04-28: A potential role for IL6ST mediating endocrine resistance in breast cancer via interaction with the ER signaling pathway
Authors: Mosly DH , Turnbull AK , Langdon SP , Sims AH 
Published: May 2019

Abstract
Background
Interest in the ubiquitously expressed transmembrane receptor IL6ST (gp130) has developed as it has been identified as a predictive biomarker of endocrine treatment response in breast cancer patients and is included in the 'Endopredict' test. At least seven cytokines (IL-6, OSM, LIF, IL-11, CNTF, IL-27, CT-1) signal via IL6ST. Interleukin-6 (IL-6) can mediate effects via two signaling pathways; classic signaling (through the membrane-bound IL-6 receptor, IL-6R) and trans-signaling (via non-signaling membrane-bound soluble IL-6R, sIL-6R). Both pathways may occur in parallel and activate cells. Crosstalk between the ER signaling pathway and IL6ST through STAT3 has been identified and implicated in the conversion from ER responsiveness to non-responsiveness.
Method
A panel of 3 ERa+ luminal breast cancer cell lines (MCF-7, T47D, ZR-75-1) were chosen to examine IL6ST expression by western blot, gel electrophoresis and qRT-PCR. Proliferation assays (SRB) were carried out to investigate the effects of seven cytokines (IL-6, OSM, LIF, IL-11, CNTF, IL-27, CT-1) on cell growth. The action of both IL-6 and Oncostatin M (OSM) on cell migration and downstream signaling pathways (pSTAT3 and pERK1/2) was studied. The extent of trans-signaling occurrence and interaction between cytokines and estrogen was investigated using proliferation assays.
Results
Three cell lines (MCF-7, T47D, ZR-75-1 were shown to express varying levels of full-length IL6ST, with MCF-7 having the least expression. Gel electrophoresis and qRT-PCR confirmed the presence of all previously described IL6ST soluble forms in the three cell lines. Surprisingly, the growth response to the cytokines was variable across the cell lines. IL6 caused a modest increase in growth in MCF-7 but produced inhibition in ZR-75-1. OSM and LIF stimulated growth in MCF-7, whereas OSM inhibited ZR-75-1 and LIF had no effect. Interestingly, no significant effect on growth was seen in T47D with any of the cytokines except IL-11 which generated a significant growth effect on T47D cells. Both STAT3 and MAPK/ERK pathways were activated to different extents in the three cell lines as a result of OSM and IL-6 activation, whereas cells migration was only stimulated in ZR-75-1. The trans-signaling pathway significantly enhanced the growth inhibition in ZR-75-1. Estrogen eliminated the effect of both IL-6 and OSM on MCF-7 growth, while both cytokines decreased estrogen-induced cell proliferation in ZR-75-1. There was no effect in T47D.
Conclusion
These results indicate:
· The presence of both classic and trans-signaling occurrence in breast cancer cell lines.
· Differential patterns of pSTAT3 and pERK1/2 signaling which could help explain the variation in responses to the cytokines.
· IL6ST full-length form is the most abundant form in all three cell lines under basal conditions.
· The levels and roles of the different IL6ST soluble forms will be further studied after estrogen stimulation.
· The effect of IL6ST silencing in the presence of estrogen and tamoxifen on cell growth and the gene expression currently being examined.
Citation Format: Mosly DH, Turnbull AK, Langdon SP, Sims AH. A potential role for IL6ST mediating endocrine resistance in breast cancer via interaction with the ER signaling pathway [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-04-28.