Medullary Thyroid Carcinoma Cell Lines Contain a Self-Renewing CD133+ Population that Is Dependent on RET Activity.

Abstract

Medullary thyroid carcinoma (MTC) is a cancer of the parafollicular C cells commonly caused by an inherited or acquired RET protooncogene mutation. Therapeutic resistance and recurrence of the disease imply the presence of cancer stem cells in MTC. In this study, we sought to identify and characterize cancer stem cell-like cells in MTC. The characterization of stem cell properties was performed using immunostaining, flow cytometry, sphere formation assay, rederivation assay, Western blotting, and quantitative RT-PCR of defined markers of neural stem and progenitor cells. The role of RET activation was assessed through RNA interference knockdown. CD133 positivity was identified by immunostaining patient MTC. Flow cytometry confirmed a subpopulation of CD133+ cells in two MTC cell lines. The CD133+ cells could be expanded by sphere formation assay, passaged multiple times, and expressed neural progenitor markers β-tubulin 3 and glial fibrillary acidic protein. The MZ-CRC-1 cell line, which harbors a M918T RET mutation, had greater CD133+ cell numbers and sphere-forming ability than the TT cell line, which harbors the less active C634W mutation. Sphere formation was more dependent on RET activity than epidermal growth factor or fibroblast growth factor. Our data support the existence of cancer stem-like cells in MTC, which exhibit the features of self-renewal and of multiple lineage differentiation that is dependent on RET receptor activity. These findings may provide new insights to develop more promising therapy for MTC.