Protective TGFβ2/SMAD3 axis identified by TWAS in papillary thyroid cancer.

Papillary thyroid carcinoma (PTC) is the most common endocrine malignancy. Although generally indolent, a subset shows aggressive behaviour. Furthermore, the genetic heterogeneity of PTC is not fully explained by known driver mutations, underscoring the need to identify additional susceptibility genes and regulatory mechanisms. To identify additional susceptibility genes and regulatory mechanisms, we integrated transcriptome-wide association studies (TWAS) with summary-data-based Mendelian randomisation (SMR), joint/conditional testing (JCT), and colocalisation analyses across multiple independent cohorts, followed by heterogeneity in dependent instruments (HEIDI) test. Gene prioritisation analyses consistently highlighted TGFB2 and SMAD3 as candidate susceptibility genes for PTC, with SMR supporting putative protective effects. Besides, GEPIA confirmed the positive correlation between TGFB2 and SMAD3 expression in TCGA-THCA. Functional experiments in TPC-1 cells showed that TGFβ2 treatment inhibited cell proliferation and migration, induced apoptosis, and resulted in G0/G1 cell-cycle arrest, accompanied by increased SMAD3 phosphorylation, suggesting activation of canonical TGFβ signalling. Collectively, these findings bridge population-based genetic inference with mechanistic validation and suggest convergent evidence supporting a tumour-suppressive role of the TGFβ2/SMAD3 axis in PTC.