Hypoxia upregulate TPM4 expression to strengthen epithelial-mesenchymal transition that promotes lymph node metastasis of papillary thyroid cancer.

Papillary thyroid cancer (PTC) exhibits a high propensity for lymph node metastasis (LNM), significantly impacting postoperative recurrence and patient prognosis. The hypoxic microenvironment critically drives tumor progression by promoting PTC dedifferentiation. Through integrated bioinformatics analysis combining weighted gene co-expression network analysis and machine learning approaches on TCGA data, we identified TPM4 as a key hypoxia-responsive gene in PTC and validated its association with LNM using GEO datasets. Gene set enrichment analysis demonstrated that patients with high TPM4 expression in both TCGA and GEO databases showed significant enrichment in hypoxia and epithelial-mesenchymal transition (EMT) pathways. Single-cell pseudotime analysis revealed concurrent increases in hypoxia pathway enrichment, TPM4 expression, and EMT pathway activation during cell differentiation. Experimental validation using RT-qPCR and Western blot analyses confirmed that hypoxia-induced TPM4 upregulation activated EMT signaling. Functional assays demonstrated that TPM4 enhanced cellular invasion and migration capabilities. Our findings illuminate a novel mechanism whereby the hypoxic tumor microenvironment promotes lymph node metastasis in PTC through TPM4-mediated activation of EMT signaling, providing new insights into LNM of PTC.