Objective This study aimed to investigate the characteristic expression of programmed death-ligand 2 (PD-L2) and epithelial-mesenchymal transition (EMT)-related biomarkers in head and neck squamous cell carcinoma (HNSCC) and their mechanism of action in HNSCC metastasis.

Methods Tumor tissue samples from 94 patients with HNSCC were collected from Tianjin Medical University Cancer Hospital from January 2018 to July 2023, and their correlation with clinicopathological parameters, including lymph node metastasis, was statistically assessed. Western blot was used to detect PD-L2 expression in HNSCC tumor tissues. PD-L2 overexpression and knockdown stably-transfected monoclonal cell lines were generated using lentiviral vectors. Transwell assays were performed to explore the effect of PD-L2 on the invasive migration of the HNSCC cell lines. Additionally, RNA sequencing was used to identify downstream target genes regulated by PD-L2. The expression levels of key EMT markers, including E-cadherin, N-cadherin, and Vimentin, were examined by Western blot to elucidate the molecular mechanism by which PD-L2 promotes tumor cell metastasis through EMT pathway activation. Additionally, RNA sequencing was employed to identify downstream target genes regulated by PD-L2. The expression levels of key EMT markers, including E-cadherin, N-cadherin, and Vimentin, were examined with Western blot analysis to elucidate the molecular mechanism by which PD-L2 promotes tumor cell metastasis through the EMT pathway activation.

Results High expression of PD-L2 is positively correlated with N staging (P<0.05), and elevated PD-L2 expression predicts a poor prognosis in HNSCC patients.

Conclusions PD-L2 regulates the EMT pathway to promote HNSCC metastasis. Targeting PD-L2 is expected to provide a new strategy for the treatment of metastatic HNSCC.