Molecular and Cellular Pathobiology Lung Tumor Suppressor GPRC5A Binds EGFR and Restrains Its Effector Signaling

GPRC5A is a G-protein–coupled receptor expressed in lung tissue but repressed in most human lung cancers. Studies in Gprc5a / mice have established its role as a tumor-suppressor function in this setting, but the basis for its role has been obscure. Here, we report that GPRC5A functions as a negative modulator of EGFR signaling. Mouse tracheal epithelial cells (MTEC) from Gprc5a / mice exhibited a relative increase in EGFR and downstream STAT3 signaling, whereas GPRC5A expression inhibited EGFR and STAT3 signaling. GPRC5A physically interacted with EGFR through its transmembrane domain, which was required for its EGFR inhibitory activity. Gprc5a / MTEC were much more susceptible to EGFR inhibitors than wild-type MTEC, suggesting their dependence on EGFR signaling for proliferation and survival. Dysregulated EGFR and STAT3 were identified in the normal epithelia of small and terminal bronchioles as well as tumors of Gprc5a / mouse lungs. Moreover, in these lungs EGFR inhibitor treatment inhibited EGFR and STAT3 activation along with cell proliferation. Finally, overexpression of ectopic GPRC5A in human non–small cell lung carcinoma cells inhibited both EGF-induced and constitutively activated EGFR signaling. Taken together, our results show how GPRC5A deficiency leads to dysregulated EGFR and STAT3 signaling and lung tumorigenesis. Cancer Res; 75(9); 1–14. 2015 AACR. Introduction EGFR (also known as ERBB1 or HER1) belongs to the ERBB family of cell-surface receptor tyrosine kinases. Activation of EGFR in normal lung tissue is regulatable. EGF binding to EGFR triggers homodimerization or heterodimerization of this receptor with other ERBB members, leading to receptor phosphorylation and activation of downstream effectors such as ERK– MAPK, PI3K–AKT, and STAT3. Activation of the EGFR pathway provides a robust signal for cell proliferation and survival in response to extracellular stimuli; such signal fades away after normal organogenesis and tissue injury/repair to maintain homeostasis (1–3). However, dysregulated EGFR activation was found in the lungs with neoplastic and preneoplastic changes, including bronchial preneoplasia (4), the indolent bronchioalveolar carcinoma (BAC) and non–small cell lung cancer (NSCLC; refs. 4, 5). These observations imply that a desensitization mechanism to restrain or terminate EGFR activation has been disrupted during lung tumorigenesis. The identification of these mechanisms is, therefore, important to understand lung tumorigenesis, and also to design novel and effective approaches for preventing lung cancer development. G-protein–coupled receptor familyC group 5 typeA (GPRC5A), also known as RAIG1 or RAI3, is a retinoic acid-inducible gene. GPRC5A is predominately expressed in lung tissue (6–9), suggesting that it may be important for homeostasis of lung tissue. GPRC5A gene locus is at 12p13. LOH (loss of heterozygosity) of chromosome 12p was found to frequently occur in NSCLCs (10, 11). In addition, GPRC5A was significantly repressed in most of NSCLC (8, 12) and all of chronic obstructive pulmonary disease Key Laboratory of Cell Differentiation and Apoptosis of Chinese Minister of Education, Shanghai Jiao Tong University School of Medicine, Shanghai, China. Department of Pathophysiology, Shanghai Jiao Tong University School of Medicine, Shanghai, China. Shanghai Key Laboratory for Tumor Microenvironment and Inflammation, Shanghai Jiao Tong University School of Medicine, Shanghai, China. Department of Thoracic Surgery, Shanghai Chest Hospital, Shanghai Jiao Tong University, Shanghai, China. Department of Oncology, Shanghai First People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China. Translation Medicine Center, Shanghai Chest Hospital, Shanghai Jiao Tong University, Shanghai, China. Insitute of Health Science, Shanghai Institute of Biological Science, Chinese Academy of Science, Shanghai, China. Department of Oral and Maxillofacial—Head and Neck Oncology, Ninth People's Hospital, College of Stomatology, Shanghai Jiao Tong University School of Medicine, Shanghai, China. Department of Oncology, Shanghai East Hospital, Tongji University, Shanghai, China. Department of Molecular and Cellular Biochemistry, Markey Cancer Center, University of Kentucky College of Medicine, Lexington, Kentucky. Note: Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/). S. Zhong, H. Yin, Y. Liao, F. Yao, Q. Li, and J. Zhang contributed equally to this article. Corresponding Authors: Jiong Deng, Shanghai Jiao Tong University School of Medicine, 280 South Chongqing Road, Shanghai 200025, China. Phone: 86-216466-6338; Fax: 86-216-415-4900; E-mail: [email protected]; Binhua P. Zhou, University of Kentucky School of Medicine, Lexington, KY. Email: [email protected]; and Y. Eugene Chin, Shanghai Institute of Biological Science, Chinese Academy of Science, Shanghai, China. Email: [email protected] doi: 10.1158/0008-5472.CAN-14-2005 2015 American Association for Cancer Research. Cancer Research www.aacrjournals.org OF1 Research. on April 13, 2017. © 2015 American Association for Cancer cancerres.aacrjournals.org Downloaded from Published OnlineFirst March 5, 2015; DOI: 10.1158/0008-5472.CAN-14-2005