Hras ^G12V induces follicular thyroid cancer with attenuated MAPK activation and increased latency compared to Kras...

RAS mutations are found in nearly 50% of follicular thyroid cancers (FTCs), frequently accompanied by secondary mutations in the PI3K/AKT pathway as tumors advance to more poorly differentiated states. To examine the role that oncogenic Hras plays in thyroid tumor initiation and progression, we developed murine models with thyroid-specific expression of Hras ^G12V combined with heterozygous or homozygous loss of Pten. Loss of Pten cooperated with Hras ^G12V in a dose-dependent manner to induce the development of follicular thyroid carcinoma and poorly-differentiated thyroid carcinoma. Histopathology of Hras ^G12V /Pten ^Hom tumors closely resembled those from the established Kras ^G12D /Pten ^Hom model, but tumor onset was significantly delayed in Hras ^G12V /Pten ^Hom mice. At three weeks of age, downregulation of MAPK pathway inhibitors was observed in Kras ^G12D /Pten ^Hom thyroids, accompanied by increased MAPK pathway activation compared to Hras ^G12V /Pten ^Hom mice. Furthermore, amplification of oncogenic Ras was found in Hras ^G12V tumors and cell lines, while allelic balance was maintained in Kras ^G12D models. These studies demonstrate clear phenotypic differences between mutant Hras and Kras in the thyroid and suggest that delayed MAPK activation may mediate the increased tumor latency observed in the Hras ^G12V /Pten ^Hom model.