Altered gene expression in immunogenic poorly differentiated thyroid carcinomas from RET/PTC3p53−/− mice

Abstract

Cancers develop and progress via activation of oncogenes and loss of tumor suppressor genes, a progression that can be recapitulated through cross breeding mouse strains harboring genetic mutations. To de®ne the role of RET/PTC3, p53 and Fhit in thyroid carcinogenesis, we intercrossed RET/PTC3 transgenics with p537/7 mice. This new strain, RET/PTC3 p537/7 , succumb to rapidly growing and strikingly large multilobed thyroid tumors containing mixtures of both well and poorly di erentiated, highly proliferative follicular epithelial cells. Interestingly, transplanted tumors from RET/ PTC3 p537/7 mice grew in SCID but not syngeneic immunocompetent mice indicating that these advanced tumors were immunogenic. RET/PTC3 protein expression was reduced to undetectable levels in tumors of older mice suggesting that the continued elevated expression of RET/PTC3 may not be necessary for tumor progression. Similarly, expression of Fhit protein was reduced in early tumors and undetected in older tumors irrespective of tumor histopathology. In contrast to RET/PTC3 p537/7 mice, RET/PTC3 Fhit7/7 mice did not develop advanced thyroid carcinomas. These studies support a model of human thyroid cancer whereby thyroid epithelium expresses RET/PTC3 protein at early stages of tumor development, followed by the reduction of RET/PTC3 and loss of p53 function with progressive reduction of Fhit protein expression coincident with malignant progression. Oncogene (2001) 20, 3235 ± 3246.

A Thyroid Tumor-Specific Antigen Formed by the Fusion of Two Self Proteins

“…Likewise, somatic rearrangement of c-RET has been observed in irradiated human thyroid tissue grafts in SCID mice, supporting the notion that ionizing radiation is an etiologic agent for thyroid cancer (12). Tumor progression to advanced stages (poorly differentiated or undifferentiated thyroid cancer) in humans and in animal models does not correlate with persistent RET/PTC expression (4,13,14), a finding inconsistent with other models of multistep carcinogenesis (15).…”

“…Consistent with this idea, we find high level expression of a number of key proinflammatory mediators by developed thyroid carcinomas, but fewer and lower amounts of these mediators in preneoplastic thyroid lesions of RP3 transgenic mice. 4 Early neoplastic lesions may thus represent an immunological crossroad between tolerance to self and immunity to tumor, with direction being determined by the extent and amount of cytokines produced from stressed or transformed cells. In addition to these inflammatory mediators, the state of newly grafted tissue, tumor fragments vs single thyroid lobes excised en bloc, may also influence the effector response because increased cellular apoptosis and necrosis may facilitate Ag uptake and cross-presentation by professional APCs, resulting in thyroid tissue rejection.…”

“…RP3 mice that have been crossed to p53 null mutants (RP3 p53Ϫ/Ϫ ) develop large, fast-growing, poorly differentiated thyroid carcinomas (4). Although RP3 expression is eventually lost in these advanced tumors, thyroid tumors from 6-mo-old RP3 p53Ϫ/Ϫ mice still express uniformly detectable levels of RP3, as previously demonstrated (4). To address the possibility that the inflammatory properties of malignant growth may enhance the induction of antithyroid responses in vivo, 3-mm 3 thyroid tumor fragments from 6-mo-old RP3 p53Ϫ/Ϫ mice were transplanted s.c. into haplocompatible recipient mice and monitored weekly for tumor outgrowth.…”

“…Homozygous RP3 mice were crossed with C57BL/6-Tpr53 mice and double heterozygotes crossed to generate RP3 p53Ϫ/Ϫ mice (4). Progeny were genotyped using RP3-and p53-specific primers in a standard DNA amplification reaction (PCR), as previously described (4). Six-to 8-wk-old C57BL/6J-Prkdc scid / SzJ (C57BL/6 SCID) mice (The Jackson Laboratory, Bar Harbor, ME) were used for the growth of tumor tissue and to determine specimen viability.…”

“…Similar treatments in thyroid cancer patients may cause autoimmune thyroid disease, the leading cause of hypothyroidism in the U.S. Consequently, we have been interested in determining whether thyroid cancers express tumorspecific targets distinguishable from self that may limit immunization-induced autoimmune disease. Because differentiated thyroid carcinomas originating from the thyroid epithelium frequently express tumor-specific rearranged during transfection/papillary thyroid carcinoma (RET/PTC) 3 fusion proteins (3), we hypothesized that inflammation along with immune responses to these unique Ags during the early stages of thyroid transformation may lead to immune recognition (4) and, by directing immune cells to target RET/PTC proteins, may provide an ideal antitumor therapy. To begin to address such a hypothesis, we set out to measure the nature of RET/PTC immunogenicity.…”