Identification of novel drug targets to overcome anti-HER2 therapy resistance is an unmet need. Since G protein-coupled receptors (GPCRs) are known to cross-talk with the HER superfamily, it is possible that some GPCRs may signal to modulate the HER2 pathway. We have identified GPR110 (also known as ADGFR1, Adhesion G Protein-Coupled Receptor F1) as a potential target in HER2+ breast cancer (BC) based on its expression in tumorigenic and anti-HER2-resistant cells. We have also shown that GPR110 knockdown in HER2+ BC cells inhibits colony formation in soft agar assay, mammosphere formation, and invasion/migration in trans-well assay, suggesting its potential role in tumorigenesis and tumor cell dissemination. To further characterize the role of GPR110 in HER2+ BC, we generated stable cell lines of BT474 and SKBR3, two HER2+ BC cell line models, that overexpress GPR110 in Doxycycline (Dox)-inducible manner. GPR110 overexpression enhanced colony formation in soft agar assay, mammosphere formation, and number of Aldefluor+ tumorigenic cells, substantiating its role in tumorigenesis. In addition, Dox-induced GPR110 overexpression increased invasion/migration potential of clones in trans-well assay, further supporting its role in cancer cell dissemination. To understand the mechanism of GPR110-mediated tumorigenesis and tumor cell dissemination in HER2+ BC, we carried out transcriptomic and proteomic analysis of selected cell lines (with or without Dox) using RNAseq and RPPA respectively. This analysis uncovered a previously unanticipated role of GPR110 in cancer cell regulation and maintaining quiescence. Overexpression of GPR110 by Dox treatment led to downregulation of various cell cycle pathways and targets such as E2F targets, G2M checkpoint pathway and MYC targets at the transcriptomic level. Validation of RNA-Seq and RPPA candidates demonstrated lower number of proliferative Ki67+ cells and reduced NF-kB staining, and inhibited STAT3 phosphorylation. In support of these results, GPR110 overexpression also led to cell cycle arrest at G0/G1 phase, when analyzed by the DNA content analysis with propidium iodide using flow cytometry. Ongoing in vivo studies will further elucidate the exact and overall role of GPR110 in HER2+ BC. In summary, our results demonstrate a previously uncovered role of GPR110 in tumorigenesis and metastasis as well as cell cycle regulation in HER2+ BC.

Citation Format: Raksha Bhat, Lanfang Qin, Carmine De Angelis, Suhas Vasaikar, Hariprasad Thangavel, Noor AbdulKareem, Bing Zhang, Rachel Schiff, Meghana V. Trivedi. The role of GPR110 in tumorigenicity, tumor cell dissemination, and cell cycle regulation in HER2+ breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3044.