Carcinoma-astrocyte gap junctions promote brain metastasis by cytosolic dsDNA response transfer

Brain metastasis represents a substantial source of morbidity and mortality in various cancers, and is characterized by high resistance to chemotherapy. Here we define the role of the most abundant cell type in the brain, the astrocyte, in brain metastasis. Cancer cells assemble of carcinoma-astrocyte gap junctions composed of connexin 43 (Cx43). Cx43 in cancer cells support brain metastatic colonization. We employ translating ribosome affinity purification (TRAP) to isolate translating mRNA from cancer cells in mixed asrtocyte co-cultures to determine the mechanism behind this Cx43-mediated brain metastatic growth. Once engaged with the astrocyte gap-junctional network, brain metastatic cancer cells employ these channels to transfer the cytosolic dsDNA response messenger cGAMP to astrocytes, activating the cGAS-STING pathway and production of inflammatory cytokines IFNα and TNFα. As paracrine signals, these factors activate the STAT1 and NF-κB pathways in brain metastatic cells, which support tumour growth and chemoresistance. TRAP mRNAs were isolated from MDA231-BrM2 (control or Cx43-depleted) after co-cultured with astrocytes. Gene expression profiles were generated by deep sequencing, in duplicate, using Illumina Illumina HiSeq 2000. Two independent replicates were done per condition (i.e. rep1 and rep2).