Non-canonical function of transferrin receptor-1 promotes breast cancer metastasis by activating HCK‒STAT3‒MMP9...

Transferrin receptor 1 (TfR-1), a key mediator of cellular iron uptake, is significantly upregulated across a broad spectrum of malignancies, and its overexpression highly correlated with poor clinical outcomes, such as in breast cancer. However, its precise role in breast cancer progression remains unclear.

We integrated clinical breast cancer tissue specimens and public transcriptomic datasets to analyse the clinical correlation between TfR-1 expression and tumour metastasis. A series of in vitro cell functional assays and in vivo xenograft tumour metastasis models were performed to validate the regulatory effect of TfR-1 on breast cancer proliferation and metastasis. Co‑immunoprecipitation, phosphorylation detection and protein stability assays were further applied to dissect the intermolecular regulatory network among TfR-1, Hematopoietic Cell Kinase (HCK) and Ubiquitin Specific Peptidase 32 (USP32).

Clinical data analysis revealed that elevated TfR-1 expression was tightly linked to metastatic phenotype in breast cancer. Functional experiments confirmed that upregulated TfR-1 robustly boosted the proliferative and metastatic capacity of breast cancer cells in vitro and in vivo. Mechanistically, TfR-1 dual‑regulates HCK, it directly induces HCK phosphorylation, while simultaneously activating USP32 to block HCK protein degradation and sustain HCK abundance. Activated HCK further triggers STAT3 transcription factor signalling, which drives the upregulation and secretion of matrix metalloproteinase 9 (MMP9). In addition, HCK reciprocally phosphorylates TfR-1 to establish a positive feedback circuit amplifying the prometastatic signalling.

This work identifies a previously uncharacterized prometastatic function of TfR-1 independent of its canonical iron transport activity in breast cancer. We uncover a reciprocal TfR‑1/HCK positive feedback axis that activates the USP32‑HCK‑STAT3‑MMP9 signalling cascade to facilitate breast cancer metastasis, which provides novel candidate therapeutic targets for metastatic breast cancer intervention.