Hypoxia-mediated suppression and memory of IFI44L and its interaction with STING in breast cancer metastasis and immune evasion

Solid tumors often contain patches of hypoxic regions that yield aggressive, pro-metastatic phenotypes. Prevention and understanding of metastases is critical for the future of breast cancer research, as metastatic cancer is extremely difficult to manage and treat. Recent work in our lab has shown that long-term hypoxia suppresses type I interferon (IFN) signaling in breast cancer cells. Even upon reoxygenation, these gene expression changes are maintained, indicative of “hypoxic memory.” Breast cancer cells that have disseminated from the primary tumor as circulating tumor cells with this “post-hypoxic” memory phenotype show enhanced metastatic potential. IFNs typically boost and enhance immune cell activity through interferon-stimulated genes (ISGs); thus, hypoxic suppression of IFN signaling yields an immunosuppressive tumor microenvironment. More research is needed to understand how ISGs are downregulated in hypoxia and how those changes in gene expression contribute to immunosuppressive ability of hypoxic and post-hypoxic cells. Interferon-inducible 44-like (IFI44L) is an ISG that has been associated with tumor-suppressive properties, and correlated with presence of tumor-infiltrating lymphocytes in other cancers, but its role in breast cancer has not been studied. We found that IFI44L is significantly suppressed in breast cancer cells in hypoxia and maintained after reoxygenation as a hypoxic memory. To understand the implications of hypoxic memory and suppression of IFI44L, we generated IFI44L overexpression and knockdown models in MCF7 and NT2.5 breast cell lines, and Brx68s, a circulating tumor cell line. We discovered that in adherent MCF7 cells, IFI44L OE significantly increases STING expression, whereas in suspension circulating tumor cells, IFI44L OE suppresses STING expression. We see that IFI44L does not impact canonical STING signaling molecules, pIRF3 and pTBK1. The consequences and mechanisms of STING regulation by IFI44L are unknown and experiments are ongoing in the lab to address these questions; in vivo studies of IFI44L are ongoing to elucidate the impact this gene has on tumor formation and metastasis. We expect to see that IFI44L OE has a tumor suppressive mechanism, and expect the opposite with IFI44L KO. Additionally, we plan to investigate STING regulation by IFI44L and the possible impact that this has on immune evasion and metastasis.