Abstract P2-25-03: β-arrestin1, a potential tumour suppressor in breast cancer is downregulated in PERK/ATF4-dependent manner

Abstract

Abstract Introduction: β-Arrestin1 (ARRB1) belongs to the arrestin family originally identified as a multifunctional adaptor protein that negatively regulates the desensitization and internalization of G-protein-coupled receptors. Recent studies have indicated that ARRB1 can form multiprotein complexes with transcription regulators, thereby indirectly inhibiting the function of some transcription factors, e.g., NF-kB, and promoting the activity of others, e.g., p53. Further, arrestins function as multifunctional adaptors in many signalling pathways, such as the Hedgehog (Hh), Wingless, Notch, and transforming growth factor-β (TGF-β) pathways. Expression of ARRB1 is downregulated in TNBC patients and ARRB1 expression level is inversely correlated with the histological grade of the breast cancer and positively associated with TNBC patient survival, suggestive of a tumour-suppressive function of ARRB1 in breast cancer. Loss of ARRB1 expression is associated with a poor prognosis for non-small cell lung cancer patients. However, the mechanisms regulating the expression of ARRB1 in human cancers remain unclear. We hypothesized that metabolic endoplasmic reticulum (EnR) stressors including low glucose and hypoxia that activate an unfolded protein response (UPR) in tumour cells might regulate the expression of ARRB1 in human cancers. Methods: Expression of ARRB1 was determined by a combination of real-time RT-PCR, western blotting along with promoter reporter assays. Computational target prediction analysis was done to identify miRNAs targeting ARRB1 as well as transcription factors regulating ARRB1 expression. ARRB1overexpressing breast cancer clones were generated by lentiviral transduction to investigate its functional role in tumour progression and drug sensitivity. Results: We observed that ARRB1 expression was significantly reduced in several cancers including breast tumours as compared to normal tissue and decreased expression of ARRB1 was associated with poor prognosis in Luminal A subtype. We found significant downregulation of ARRB1 mRNA and protein during conditions of EnR stress in multiple ER-positive breast cancer cell lines. Using PERK, ATF6 and XBP1 knockdown sub-clones of MCF7 we observed that PERK signalling was required for the downregulation of ARRB1. ATF4 and miR-204/211 downstream of PERK were identified as key regulators of ARRB1 expression. Conclusion: Our results show that ATF4 and miR-204/211 downstream of the PERK signalling pathway repress ARRB1 expression in breast cancer cells. Our results suggest that the downregulation of ARRB1 by EnR stressors in the tumour microenvironment may contribute to breast cancer progression. Citation Format: Afrin Sultana, Ananya Gupta, Sanjeev Gupta. β-arrestin1, a potential tumour suppressor in breast cancer is downregulated in PERK/ATF4-dependent manner [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-25-03.