| Summary: | Thyroid cancer is the most frequent endocrine malignancy, with an incidence constantly increasing. Despite well-differentiated thyroid tumors are generally cured by conventional therapy, a fraction of them relapses and progresses towards undifferentiated forms, characterized by a poor prognosis. Target therapies introduced in clinical testing are often unsuccessful; therefore, novel therapeutic strategies are needed. To identify critical nodal points for therapeutic intervention, our laboratory faced the “non-oncogene addiction” (NOA) paradigm, which asserts that the tumorigenic state relies on the activity of genes that are essential to support the phenotype of cancer cells but not required to the same degree for normal cell viability. By screening a siRNA library on normal and tumor thyroid cell lines, we identified 15 genes whose silencing interfered with the growth of tumor but not normal thyroid cells. The overall aim of this project was to validate NOA genes to identify thyroid tumor cell vulnerabilities and to explore their role in the regulation of thyroid tumor cell biology. Among the 15 hit genes, we selected MASTL, Cyclin D1 and COPZ1 for validation studies. We confirmed the growth inhibitory effect of their silencing in tumor but not normal thyroid cells and observed that these effects were common to a panel of thyroid tumor cell lines, irrespective of the histotype or genetic lesion. Functional studies on MASTL demonstrated that its depletion in thyroid tumor cells inhibited cell growth, led to mitotic catastrophe and induced DNA damage and cell death. COPZ1 depletion induced abortive autophagy, endoplasmic reticulum stress and apoptotic cell death in thyroid tumor cells, as well as tumor growth inhibition in vivo. Together, our studies identified MASTL and COPZ1 as vulnerability genes for thyroid tumor cells and provided the rationale for future studies aimed to explore their targeting for potential therapeutic intervention.
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