Abstract P4-08-11: Linc01588-V4 is UPR-downregulated lncRNA in a PERK-dependent manner and estrogen-responsive gene mediated cell proliferation and migration of ER+ breast cancer cells

Abstract Background: Physiological or pathological processes that disturb protein folding in the endoplasmic reticulum cause a state known as endoplasmic reticulum stress (ER stress) and then activate a set of signalling pathways termed the Unfolded Protein Response (UPR). This concerted and complex cellular response is mediated by three molecular sensors, PKR-like ER kinase (PERK), activated transcription factor 6 (ATF6), and inositol-requiring enzyme 1 (IRE1). UPR is mostly associated with adaptive signalling, allowing cancer cells to cope with adverse environmental conditions and conferring therapy resistance. Long noncoding RNA (lncRNA) belongs to a class of non-protein coding transcripts longer than 200 nucleotides. However, not much is known about UPR-regulated lncRNA and the causative effect of lncRNA in affecting ER stress responses and cancer development. Recent studies have highlighted the role of interaction between the UPR and the estrogen signaling pathway in contributing to endocrine resistance. Here we have evaluated the role of UPR-regulated and estrogen-responsive lncRNA in breast cancer. Method: Gene Expression Profiling Interactive Analysis, an interactive web server developed to analyze the RNA sequencing expression data, was used to analyze the Linc01588 expression across all cancers and overall survival in breast cancer patients. Expression of all Linc01588 variants V1-V5 in breast cancer cell lines was verified by conventional PCR. Additionally, UPR-induced and estrogen-responsive Linc01588 was assessed using RT-qPCR in ER+ breast cancer cell lines treated with UPR inducers Brefeldin A and Thapsigargin or estrogen (E2) and estrogen receptors-targeted Tamoxifen and Fulvestrant. Furthermore, sub-clones of MCF7 cells deficient in downstream UPR signalling were utilized to further validate the regulatory mechanisms of Linc01588 in response to UPR stimulation. Linc01588 knockdown clones in MCF7 and T47D generated by the lentivirus strategy were used to investigate the functional mechanism of cell proliferation and migration. Results: Linc01588 expression is increased in primary and metastatic breast cancer as compared with normal breast tissue. Increased Linc01588 expression was associated with poor overall survival in ER+ and HER2-amplified breast cancer patients but not in TNBC. There are 5 isoforms of Linc01588 and variant 4 (Linc01588-V4) and variant 5 (Linc01588-V5) were two main predominantly expressed variants in breast cancer cell lines. Linc01588-V4 expression was downregulated upon treatment with UPR inducers in ER+ breast cancer cell lines in a PERK-dependent manner. Furthermore, the expression of Linc01588-V4 was markedly elevated in ER+ breast cancer cell lines upon E2-stimulation and 293T cells transiently transfected with estrogen receptors (ERα). Tamoxifen treatment increased Linc01588-V4 expression in MCF7 cells but not in T47D cells. The Linc01588-V5 was downregulated by UPR inducers but not affected by E2, ERα, Tamoxifen, and Fulvestrant. Knockdown of Linc01588-V4 in MCF7 and T47D cells reduced cell proliferation and migration but had no effect on the expression of ERα protein and induction of E2-responsive genes. Conclusion: We have identified Linc01588-V4 as an estrogen-responsive lncRNA which can regulate cell proliferation and migration of ER+ breast cancer cells. Citation Format: Wen Liu, Sanjeev Gupta, Ananya Gupta, Wenyuan Zhao, Qian Xu. Linc01588-V4 is UPR-downregulated lncRNA in a PERK-dependent manner and estrogen-responsive gene mediated cell proliferation and migration of ER+ breast cancer cells [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P4-08-11.