LAUSR

Our lab has previously identified a mechanism of transforming growth factor beta (TGFβ)-mediated epithelial-to-mesenchymal transition (EMT) in normal murine mammary gland (NMuMG) cells. Reduced expression of heterogenous nuclear ribonucleoprotein E1 (hnRNP E1, hereafter “E1”) in NMuMG cells induces EMT, tumorigenesis, and metastasis. Our experimental data has revealed that increased expression of interleukin-like EMT inducer (ILEI) and of leukemia inhibitory factor receptor (LIFR) proteins occurs following E1 knockdown (E1KD). ILEI and LIFR have been shown to interact by coimmunoprecipitation/radiography experiments, and there is a correlation between ILEI expression and phosphorylation of the LIFR effector STAT3. ILEI is necessary to induce EMT in NMuMG cells, and spheroid formation capacity in non-adherent serum-depleted cell culture conditions is attenuated following either ILEI or LIFR knockdown. Loss of spheroid formation following ILEI knockdown is rescued by treatment with exogenous recombinant ILEI protein (rILEI); however, spheroid formation is not rescued by rILEI following LIFR knockdown. In immunocompromised mice, orthotopic grafts of NMuMG cells with E1KD (E1KD cells) with additional knockdown of either ILEI or LIFR display a decrease in tumor initiation, growth, and metastasis relative to control cells. These data suggest that ILEI-induced spheroid formation capacity involves LIFR, and that an ILEI/LIFR signaling axis promotes breast cancer stem cell (BCSC) phenotype. Characterization of the mechanisms that allow BCSCs to persist during chemotherapeutic interventions will advance our understanding of drug resistant and dormant breast cancer. The precise mechanisms involved in ILEI-mediated EMT and ILEI/LIFR-mediated BCSC induction are unknown. Semi-quantitative PCR data demonstrates that the increase in LIFR expression in E1KD cells is regulated at the transcriptional level. Additionally, E1KD cells with CRISPR-Cas9-mediated ILEI knockout (E1KD-ILEI-KO cells) show decreased luciferase signal relative to control cells following transfection of LIFR promoter DNA sequences placed upstream of a luciferase gene. Further, E1KD-ILEI-KO cells show attenuation of spheroid formation when compared to unaltered E1KD cells. Our data allow us to conclude that ILEI participates in the regulation of LIFR gene transcription, which plays a role in ILEI-induced maintenance of spheroid formation and self-renewal. Continued investigation will allow development of studies aimed at revealing the mechanisms involved in ILEI/LIFR axis-mediated disease progression in vivo. Citation Format: William S. Streitfeld, Annamarie C. Dalton, Philip H. Howe. ILEI regulates LIFR expression and CSC self-renewal [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3080.