Targeting the HIF1A-UCA1-PTBP3 axis: a potential therapeutic strategy for head and neck cancer

Long non-coding RNAs (lncRNAs) are multifunctional regulators of gene expression and play a vital role in various physiological and pathological processes. The urothelial cancer-associated 1 (UCA1) lncRNA is involved in the development and progression of bladder, colon, stomach, lung, and breast cancers. Pharyngeal cancer, especially those in the hypopharynx (HPC), is a devastating subtype of head and neck cancer often detected in late stages. Although some patients survive under curative treatments, they are still prone to having the disease relapse or metastatic spread. Upregulation of UCA1 expression is associated with disease progression and poor prognosis in HPC patients, but the molecular mechanism by which UCA1 functions in HPC remains unclear. We used genetic silencing and ectopic expression approaches to examine the effect of UCA1 dysregulation on the proliferation, colony formation, migration, and invasion of head and neck cancer cells in vitro. Using a xenograft animal model, we employed UCA1-depleted cells to evaluate UCA1’s role in tumor growth and metastasis. RNA pulldown followed by mass spectrometry was used to identify UCA1-interacting proteins. We also examined the downstream effectors and upstream mediator(s) of the UCA1-mediated signaling axis by using RT-qPCR, Western blotting, promoter-driven luciferase, and transendothelial migration assays. Ectopic UCA1 expression increased cell migration and invasion but reduced the proliferation of head and neck cancer cells. The increases in migration and invasion are accompanied by elevated levels of epithelial and mesenchymal markers, reminiscent of incomplete epithelial-mesenchymal transition (EMT). In contrast, depletion of UCA1 had opposite effects. Animal xenograft studies also supported the role of UCA1 in promoting lymph node metastasis. UCA1 was predominantly nuclear localized, where polypyrimidine tract binding protein 3 (PTBP3) binds UCA1 lncRNA. Manipulating PTBP3 expression reversed the effect of UCA1 expression on cell migration and invasion. Moreover, increased UCA1 expression, mimicking the regulatory effect of TGF-β on cyclin D1, p21, and Smad2 phosphorylation, could promote trans-endothelial migration. Significantly, hypoxia induced UCA1 expression partly through an HIF1A-dependent manner. We conclude that HIF1A-induced nuclear UCA1 stimulated cell migration and invasion via interacting with PTBP3, increasing lymph node metastasis in head and neck cancer.