Oncoprotein Signaling Mediates Tumor-Specific Inflammation and Enhances Tumor Progression

The RET/PTC3 (RP3) fusion protein is an oncogene expressed during the development of thyroid cancer and in thyroid epithelial cells of patients with Hashimoto's thyroiditis. RP3 has two immunological properties: 1) it encodes a chimeric protein including peptides that may be targets of antitumor immune responses and 2) it is a tyrosine kinase that can activate NF-kappaB transcriptional programs, induce secretion of proinflammatory mediators, and stimulate innate immunity. To distinguish the antigenic properties of the RP3 oncoprotein from its signaling function, a transplantable tumor system was developed. Tumors expressing the functional, but not mutant, form of RP3 show enhanced infiltration of CD8(+) lymphocytes, myeloid-derived CD11b(+)Gr1(+) cells, and enhanced growth in immunocompetent mice. In contrast, RP3 signaling mutant-expressing tumors maintained enhanced infiltration of CD8(+) lymphocytes did not enhance recruitment of CD11b(+)Gr1(+) cells and showed a decreased tumor incidence. These results implicate a role for RP3 function in enhancing a tumor-suppressive innate inflammatory response. These experiments support a mechanism whereby oncogenes can directly recruit and activate innate and adaptive immune cells, resulting in enhanced tumor progression.