No abstract

Cancer-associated systemic inflammation is strongly linked with poor disease outcome in cancer patients 1,2. For most human epithelial tumour types, high systemic neutrophil-tolymphocyte ratios are associated with poor overall survival 3 , and experimental studies have demonstrated a causal relationship between neutrophils and metastasis 4,5. However, the cancer cell-intrinsic mechanisms dictating the substantial heterogeneity in systemic neutrophilic inflammation between tumour-bearing hosts are largely unresolved. Using a panel of 16 distinct genetically engineered mouse models (GEMMs) for breast cancer, we have uncovered a novel role for cancer cell-intrinsic p53 as a key regulator of pro-metastatic neutrophils. Mechanistically, p53 loss in cancer cells induced secretion of Wnt ligands that stimulate IL-1β production by tumour-associated macrophages, which drives systemic inflammation. Pharmacological and genetic blockade of Wnt secretion in p53-null cancer cells reverses IL-1β expression by macrophages and subsequent neutrophilic inflammation, resulting in reduced metastasis formation. Collectively, we demonstrate a novel mechanistic link between loss of p53 in cancer cells, Wnt ligand secretion and systemic neutrophilia that potentiates metastatic progression. These insights illustrate the importance of the genetic makeup of breast tumours in dictating pro-metastatic systemic inflammation, and set the stage for personalized immune intervention strategies for cancer patients. 4 Main text To determine how pro-metastatic systemic inflammation is influenced by genetic aberrations in tumours, we studied 16 GEMMs for breast cancer carrying different tissue-specific mutations. These GEMMs represent most subtypes of human breast cancer, including ductal and lobular carcinoma, oestrogen receptor-positive (luminal A), HER2 + , triple-negative and basal-like breast cancer. Because we and others have demonstrated that neutrophils expand systemically and promote metastasis 5-10 , we evaluated circulating neutrophil levels as a marker for systemic inflammation in mammary tumour-bearing mice with end-stage disease. As expected, most tumour-bearing mice displayed an increase in circulating neutrophils as compared to non-tumour-bearing animals (wild-type [WT]) (Fig. 1a). Like the inter-patient heterogeneity in systemic inflammation in human breast cancer 11 , we observed a striking variability in the extent of neutrophilia between the different tumour-bearing GEMMs (Fig. 1a, Extended Data Fig. 1a). We found that the models exhibiting high neutrophil expansion displayed a subset of neutrophils expressing the stem cell marker cKIT (Fig. 1b), indicative of an immature neutrophil phenotype 5. We subsequently searched for commonalities and differences among the 16 GEMMs with regards to high versus low systemic neutrophil levels. Strikingly, mice bearing tumours with a p53 deletion exhibited the most pronounced circulating neutrophil levels (Fig. 1a). The difference in magnitude of systemic inflammation between p53proficient and p...

The leucine-rich repeat-containing heterotrimeric guanine nucleotide-binding protein-coupled receptor 5 (LGR5) has been identified as a marker of cycling stem cells in several epithelial tissues, including small intestine, colon, stomach and hair follicle. To investigate whether LGR5 also marks mammary epithelial stem cells, we performed in situ lineage-tracing studies and mammary gland reconstitutions with LGR5-expressing mammary epithelial cells. Interestingly, the LGR5 progeny population in mammary epithelium switches from the luminal to the myoepithelial compartment during the first 12 days of postnatal development, likely reflecting local changes in Wnt signalling. Together, our findings point to a stage-specific contribution of LGR5-expressing cells to luminal and basal epithelial lineages during postnatal mammary gland development.