ECD co-operates with ERBB2 to promote tumorigenesis through upregulation of unfolded protein response and glycolysis

The ecdysoneless (ECD) mRNA and protein are overexpressed in breast cancer (BC), correlating with poor prognosis and shorter patient survival, particularly in ERBB2/HER2-positive BC. This study investigates the co-operative oncogenic mechanism of ECD and ERBB2 by deriving transgenic mice overexpressing ECD and/or ERBB2 (huHER2) in mammary epithelium under the MMTV promoter, as well as immortal human mammary epithelial cell lines (hMECs) overexpressing ECD and/or ERBB2. While the tumor latency and percentage of mice with tumors were similar between single and double-transgenic mice, we observed more and larger tumors in double transgenic mice in comparison to ECD or huHER2 single transgenic mice. Compared to huHER2Tg mice, which developed more homogenous solid nodular carcinomas, double transgenic mice (ECD;huHER2Tg) developed heterogenous and histologically aggressive mammary tumors with basal-like phenotype and epithelial mesenchymal transition (EMT) features, as seen in ECDTg mice and those reported in patients. ECD and ERBB2 overexpressing hMECs showed significant increase in oncogenic traits as compared to single gene expressing cells. Transcriptomic analysis revealed upregulation of two major oncogenic pathways, unfolded protein response (UPR) and glycolysis in ECD;huHER2Tg tumors as well as in ECD + ERBB2-overexpressing hMECs. ECD + ERBB2-overexpressing hMECs exhibited an increase in glucose uptake and enhanced glycolytic rate as compared to ECD or ERBB2-overexpressing hMECs. ECD as an RNA binding protein directly associated with mRNAs of three key glycolytic enzymes (LDHA, PKM2 and HK2) and mRNA of a major UPR regulated gene HSPA5, and increased mRNA stability. Knockdown of these genes resulted in decreased oncogenic traits of ECD + ERBB2 overexpressing hMECs. Taken together, our findings support a co-operative role of ECD and ERBB2 in oncogenesis by enhancing two major oncogenic pathways, UPR and glycolysis.