Notch3 expression correlates with thyroid cancer differentiation, induces apoptosis, and predicts disease prognosis

BACKGROUND Thyroid tumorigenesis is characterized by a progressive loss of differentiation exhibited by a range of disease variants. The Notch receptor family (1‐4) regulates developmental progression in both normal and cancerous tissues. This study sought to characterize the third Notch isoform (Notch3) across the various differentiated states of thyroid cancer, and determine its clinical impact. METHODS Notch3 expression was analyzed in a tissue microarray of normal and pathologic thyroid biopsies from 155 patients. The functional role of Notch3 was then investigated by upregulating its expression in a follicular thyroid cancer (FTC) cell line. RESULTS Notch3 expression regressed across decreasingly differentiated, increasingly malignant thyroid specimens, correlated with clinicopathological attributes reflecting poor prognosis, and independently predicted survival following univariate and multivariate analyses. Overexpression of the active Notch3 intracellular domain (NICD3) in a gain‐of‐function FTC line led to functional activation of centromere‐binding protein 1, while increasing thyroid‐specific gene transcription. NICD3 induction also reduced tumor burden in vivo and initiated the intrinsic apoptotic cascade, alongside suppressing cyclin and B‐cell lymphoma 2 family expression. CONCLUSIONS Loss of Notch3 expression may be fundamental to the process of dedifferentiation that accompanies thyroid oncogenesis. Conversely, activation of Notch3 in thyroid cancer exerts an antiproliferative effect and restores elements of a differentiated phenotype. These findings provide preclinical rationale for evaluating Notch3 as a disease prognosticator and therapeutic target in advanced thyroid cancer. Cancer 2017;123:769–82. © 2016 American Cancer Society. Expression of the Notch family's third isoform (Notch3) is progressively lost across lesser differentiated, more malignant thyroid cancer subtypes, and correlates directly with disease prognosis. Conversely, activation of Notch3 suppresses thyroid cancer cell proliferation and upregulates thyroid‐specific differentiated features. These findings warrant further investigation into therapeutic targeting of Notch3 for treating advanced disease.