RTN4IP1 Contributes to ESCC via Regulation of Amino Acid Transporters.

Esophageal squamous cell carcinoma (ESCC) accounts for about 90% of esophageal cancer cases. The lack of effective therapeutic targets makes it difficult to improve the overall survival of patients with ESCC. Reticulon 4 Interacting Protein 1 (RTN4IP1) is a novel mitochondrial oxidoreductase. Here, a notable upregulation of RTN4IP1 is demonstrated, which is associated with poor survival in patients with ESCC. RTN4IP1 depletion impairs cell proliferation and induces apoptosis of ESCC cells. Furthermore, c-Myc regulates RTN4IP1 expression via iron regulatory protein 2 (IRP2) at the post-transcriptional level. Mechanistically, RTN4IP1 mRNA harbors functional iron-responsive elements (IREs) in the 3' UTR, which can be targeted by IRP2, resulting in increased mRNA stability. Finally, RTN4IP1 depletion abrogates amino acid uptake and induces amino acid starvation via downregulation of the amino acid transporters SLC1A5, SLC3A2, and SLC7A5, indicating a possible pathway through which RTN4IP1 contributes to ESCC carcinogenesis and progression. In vivo studies using cell-derived xenograft and patient-derived xenograft mouse models as well as a 4-nitroquinoline 1-oxide-induced ESCC model in esophageal-specific Rtn4ip1 knockout mice demonstrate the essential role of RTN4IP1 in ESCC development. Thus, RTN4IP1 emerges as a key cancer-promoting protein in ESCC, suggesting therapeutic RTN4IP1 suppression as a promising strategy for ESCC treatment.