Progressive metastasis is the proximate cause of cancer-related mortality for the majority of patients with solid tumors. Identifying gatekeepers of late stage progression and defining their mechanisms of action is therefore crucial. Thyroid cancer provides an outstanding model to identify regulators of late stage cancer progression due to its typical long latency and the often rapid pace of end-stage progression. We have focused on defining unique genomic alterations in distant metastatic lesions in thyroid cancer and identified Regulator of Calcineurin 1.4 (RCAN1.4) as a new metastasis suppressor. This function has subsequently been reported in other solid tumors. Through a combination of unbiased genomic analysis and confirmatory studies of human tissues, and functional studies in human cell lines, mouse xenografts, and newly-developed genetically engineered mouse models, we have identified the Cap-N-Collar transcription factor, NFE2L3 (Nrf3) as a critical downstream functional regulator induced by RCAN1.4 loss. In addition, NFE2L3 itself functions to promote thyroid cancer cell growth and invasion and is associated with poor prognosis. We also have shown that RCAN1.4 loss and NFE2L3 overexpression are associated with immune activation in vitro and in vivo, that overexpression of NFE2L3 is associated with a permissive type 1 immune environment in human thyroid cancer, that IL-8 release and gene expression are regulated by NFE2L3, and that NFE2L3 directly binds to the IL8 promoter and regulates its activity, suggesting a mechanistic role in regulation the tumor-immune interface in thyroid cancer. Progressive thyroid cancers are typically not associated with overexpression of PD1/PDL1 or microsatellite instability, despite often robust immune cell infiltrate, thus, checkpoint inhibitors have been largely ineffective. These data highlight the importance of defining regulators of the immune environment that regulate progression of this tumor type. The overall hypothesis is that RCAN1.4 loss and NFE2L3 overexpression induce a tumorigenic and pro-metastatic immune environment that facilitates thyroid cancer progression.
Metastatic progressive differentiated thyroid cancer is an incurable disease. We have identified a new metastasis suppression signaling pathway in thyroid cancer and other solid tumors mediated by loss of RCAN 1.4 and activation of the transcription factor NFE2L3. Our preliminary data suggest that this pathway regulates the development of a tumor-promoting immune environment; the proposed experiments will determine the mechanism by which activation of this pathway occurs and how it promotes cancer progression with an emphasis on future therapeutic targets.
