The Kupffer cell-specifying factor Id3 endows macrophages with antimetastatic activity

The anti-tumor activity of macrophages is mediated in part via phagocytosis and controlled by a balance between the recognition of live cells by activating receptors and inhibitory receptors. The latter protects host tissues during infection but allows tumoral cells to escape phagocytosis and promotes metastasis. We investigated the mechanisms that control anti-metastatic activity of macrophages and found that the transcriptional repressor and Kupffer cells (KC)-specifying factor ID3 is required and sufficient to orchestrate tumor cell killing by macrophages in vivo and in vitro and reduces by ~50% liver and lung colonization by metastatic-initiating cells invading from the portal vein in long-term orthotopic pancreatic cancer models. Loss-of-function and gain -of functions experiments indicate that ID3 controls expression of activating and inhibitory receptors, in particular the inhibitory receptor SIRPa, which boost their phagocytic activity against tumor cells. Mechanistically, ID3 prevents binding of ELK1 and the E-Box factor E2A to promoter/enhancer regions of the inhibitory receptor Sirpa gene, which limits expression of SIRPa at levels compatible with efficient phagocytosis of tumor cells and prevents its upregulation by inflammatory stimuli. This mechanism endows macrophages with anti-metastatic activity. Overall design: KPC-1 tumor cells DNA profiles from R26LSL-DTR and Clec4fCre;R26LSL-DTR mice. DNA samples were extracted with QIAamp DNA Micro Kit, DNA were used for library construction using the KAPA Hyper Prep Kit (Kapa Biosystems KK8504) with 8 cycles of PCR. After sample barcoding, 100-110ng of each library were pooled and captured by hybridization with the mm_IMPACT (Integrated Mutation Profiling of Actionable Cancer Targets) assay.