Immune Suppression Mediated by Myeloid and Lymphoid Derived Immune Cells in the Tumor Microenvironment Facilitates Progression of Thyroid Cancers Driven by HrasG12V and Pten Loss

Abstract

Thyroid cancer is the most common endocrine malignancy and is predicted to be the 4th most commonly diagnosed cancer by 2030. Approximately one-half of follicular thyroid carcinomas (FTC) contain genetic alterations in RAS family members. Furthermore, Cowden's disease, which is characterized by loss of PTEN, predisposes for the development of FTC in humans. We have shown that thyroid specific expression of HrasG12V at endogenous levels and Pten inactivation (HrasG12V/Pten−/−/TPO-cre mice) leads to the development of FTCs that closely recapitulate human disease, with complete penetrance at one year. In patients, FTCs metastasize via the bloodstream to distant sites, frequently the lungs, bones and brain. The first objective of the study was to determine if these mice developed de novo metastasis to relevant sites. Indeed, spontaneous metastasis to the lungs was observed in 56% of HrasG12V/Pten−/−/TPO-cre mice. We next sought to identify the cellular components within the tumor microenvironment (TME) of FTC that contribute to tumor progression and metastasis via FACS analysis. Surprisingly, a large amount of immune infiltrate was observed. HrasG12V/Pten−/−/TPO-Cre thyroid tumors were comprised of 68.5 ± 11.79% CD45+ cells, in stark contrast to wild-type (WT) thyroids which were comprised of 17.6% CD45+ cells. Further, 53.1 ± 10.9% of the CD45+ cells from HrasG12V/Pten−/−/TPO-Cre thyroid tumors were of myeloid-lineage (CD11b+), consisting of macrophages (F4/80+Gr-1−) and myeloid-derived suppressor cells (F4/80−Gr-1+). Further, HrasG12V/Pten−/−/TPO-cre tumors contained Arginase-1 positive cells as determined by immunohistochemical analysis, supporting an immunosuppressive TME in HrasG12V/Pten−/−/TPO-Cre thyroid tumors. We next evaluated whether or not cytotoxic (CD8+) or helper T cells (CD4+) were recruited to HrasG12V/Pten−/−/TPO-Cre tumors. The majority of T cells in these tumors were double positive for CD4 and CD25, markers of immune suppressive regulatory T cells (Treg). Additionally, we identified Foxp3 positive cells by immunohistochemical analysis of tumor sections, indicating a functional suppressive Treg phenotype in vivo. HrasG12V/Pten−/−/TPO-Cre tumor cell lines displayed increased secretion of SDF-1, I-TAC, CCL9/10, and MCP5, cytokines that have been reported to play a direct role in the chemotaxis of immune cells and thus could contribute to the increased recruitment of myeloid and lymphoid derived cells in HrasG12V/Pten−/−/TPO-Cre tumors. These studies are the first to identify and implicate the interaction between tumor cells and immune cells in Ras-driven thyroid cancer progression, which we hope will lead to the development of more effective therapeutic approaches for aggressive forms of thyroid cancer that target the TME.

PTEN Function at the Interface between Cancer and Tumor Microenvironment: Implications for Response to Immunotherapy

“…In a HRAS G12V /PTEN −/− follicular thyroid carcinoma mouse model immunosuppressive Tregs and M2 macrophages were significantly upregulated. Moreover, cell lines isolated by HRAS G12V /PTEN −/− express higher levels of chemotactic factors for MDSCs, T cells and macrophages as compared to BRAF V600E /PTEN −/− tumors, highlighting the tight association between genetic background and tumor immune infiltrate [113]. Tumor genetic background influences immune/inflammatory infiltrate into the TME not only in the primary tumor, but also in metastatic lesions, as demonstrated by Vidotto et al Indeed, the authors showed that in PTEN-loss prostate cancer, higher levels of Tregs were observed in liver metastases as compared to the primary lesion, and high levels of CD8 + cells were present in bone metastases [114].…”

LINC00852 Promotes Lung Adenocarcinoma Spinal Metastasis by Targeting S100A9

“…Under physiological conditions, S100A9 and other S100 family proteins are intracellular proteins. However, tumor cells constantly secrete S100A9 to recruit myeloid-derived suppressor cells, thereby promoting cancer growth via inflammatory pathways and forming a special pre-metastatic immunosuppressive niche 12 . Therefore, the S100A9 protein plays a critical role in cancer metastasis 13 - 15 .…”

Single-Molecule Study Reveals How Receptor and Ras Synergistically Activate PI3Kα and PIP3 Signaling

“…2) The membrane-anchored, small G-protein H-Ras is employed as a representative Ras isoform. H-Ras is central to leukocyte transmigration and is linked to at least 65 oncogenic mutations ( http://cancer.sanger.ac.uk/cosmic ; https://www.cancer.gov/research/key-initiatives/ras/about ) ( 20 , 21 ). More broadly, mutations in this and other Ras isoforms are linked to >25% of human cancers ( http://cancer.sanger.ac.uk/cosmic ; https://www.cancer.gov/research/key-initiatives/ras/about ) ( 17 ).…”