Genetic and Functional Evidence Links Germline Biallelic Inactivating Variants in <i>WWOX</i> to Histological Mixed‐Type Thyroid Cancer

Despite WWOX's established role as a tumor suppressor, conclusive evidence linking germline WWOX loss-of-function variants to oncogenesis remains scarce. Two germline homozygous WWOX missense variants (p.P252A and p.P282A) are identified in a patient with histological mixed-type thyroid cancer. In vitro and in vivo functional assays demonstrate that both WWOX^P252A and WWOX^P282A mutants exhibit complete loss of tumor-suppressive activity, failing to inhibit tumor cell growth and invasion. The WWOX^P252A mutant undergo accelerated degradation via HSC70 chaperone-mediated autophagy in the lysosome. Furthermore, both P252A and P282A variants impair the WWOX protein's critical role in DNA damage repair. A nucleotide excision repair-related protein, POLE4, is identified to interact with WWOX, but not with the WWOX^P282A mutant. Finally, low WWOX expression is found to be associated with epithelial-mesenchymal transition and aggressive phenotype in thyroid cancer. These findings provide the first genetic and functional evidence that germline WWOX loss-of-function variants drive cancer pathogenesis by perturbing multiple tumor-suppressive mechanisms.