PCBP1 regulates LIFR through FAM3C to maintain BCSC self-renewal and invasiveness

The poly(rC) binding protein 1 gene (PCBP1) encodes the heterogenous nuclear ribonucleoprotein E1 (hnRNPE1), a nucleic acid binding protein that plays a tumor-suppressive role in mammary epithelium by regulating phenotypic plasticity and cell fate. Following loss of PCBP1 function, the FAM3C gene (encoding the Interleukin-like EMT inducer, or “ILEI” protein) and the leukemia inhibitory factor receptor (LIFR) gene are upregulated. Interaction between FAM3C and LIFR in the extracellular space induces phosphorylation of the signal transducer and activator of transcription 3 (pSTAT3). The overexpression and/or hyperactivity of STAT3 has been detected in 40% of breast cancer cases and is associated with poor prognosis. Herein, we characterize feed-forward regulation of LIFR expression in response to FAM3C/LIFR/pSTAT3 signaling in mammary epithelial cells, and show that PCBP1 upregulates LIFR transcription through FAM3C, involving activity at the LIFR promoter. Additionally, our bioinformatic analysis reveals a signature of transcriptional regulation associated with FAM3C/LIFR interaction and identifies the TWIST1 transcription factor as a downstream effector that participates in maintenance of LIFR expression. Finally, we characterize the effect of LIFR expression in cell-based experiments that demonstrate promotion of invasion, migration, and breast cancer stem cell (BCSC) self-renewal, consistent with previous studies that link LIFR expression to tumor initiation and metastasis in mammary epithelial cells. Overall design: Comparative gene expression profiling of bulk RNA extracts from pooled cell populations. Comparisons made between normal murine mammary gland cells (NMuMG) and derivative cell lines, using two independent datasets. Dataset 1: compares (A) NMuMG shPCBP1 with (B) NMuMG shPCBP1 FAM3C KO and (A) with (C) NMuMG shPCBP1 LIFR KO Dataset 2: A pre-existing dataset that compares (D) NMuMG with (E) NMuMG shPCBP1