A pro-tumorigenic function of S100A8/A9 in carcinogen-induced hepatocellular carcinoma.

Human hepatocellular carcinoma (HCC) is a heterogeneous disease, driven by different risk factors and presenting diverse clinicopathological features and outcomes. Epidemiological and experimental data indicate that the damage-associated molecular pattern molecules S100A8 and S100A9, forming a heterodimer called calprotectin, might be critically involved in HCC development. However, deletion of S100a9 in an inflammation- and cirrhosis-driven mouse model did not show any impairment in liver tumorigenesis, most likely due to functional compensation by other inflammatory cytokines. Here, we investigated the effect of calprotectin ablation in mice treated with diethylnitrosamine, a carcinogen-driven HCC model mimicking cancer development caused by acute liver damage in the absence of prominent chronic inflammation and tissue damage. We found that tumor cell proliferation was diminished in the absence of S100A8/A9, leading to significant reduction of tumor size. Our results demonstrate that calprotectin is required for the progression of non-inflammation driven liver tumor and might represent a therapeutic target for the treatment of HCC formed in non-cirrhotic liver.

Chronic liver inflammation and hepatocellular carcinogenesis are independent of S100A9.

The S100A8/A9 heterodimer (calprotectin) acts as a danger signal when secreted into the extracellular space during inflammation and tissue damage. It promotes proinflammatory responses and drives tumor development in different models of inflammation-driven carcinogenesis. S100A8/A9 is strongly expressed in several human tumors, including hepatocellular carcinoma (HCC). Apart from this evidence, the role of calprotectin in hepatocyte transformation and tumor microenvironment is still unknown. The aim of this study was to define the function of S100A8/A9 in inflammation-driven HCC. Mice lacking S100a9 were crossed with the Mdr2(-/-) model, a prototype of inflammation-induced HCC formation. S100a9(-/-) Mdr2(-/-) (dKO) mice displayed no significant differences in tumor incidence or multiplicity compared to Mdr2(-/-) animals. Chronic liver inflammation, fibrosis and oval cell activation were not affected upon S100a9 deletion. Our data demonstrate that, although highly upregulated, calprotectin is dispensable in the onset and development of HCC, and in the maintenance of liver inflammation.

Hepatocyte-specific S100a8 and S100a9 transgene expression in mice causes Cxcl1 induction and systemic neutrophil enrichment.

BACKGROUND: Calprotectin consists of the Ca2+-binding proteins S100a8 and S100a9 that are induced in epithelial cells in response to tissue damage and infection. Both proteins are also secreted by activated innate immune cells and numerous studies demonstrate their crucial role in pathological conditions of acute and chronic inflammation. RESULTS: Here, we established a conditional mouse model with simultaneous S100a8 and S100a9 transgene expression in hepatocytes (TgS100a8a9hep) under the control of doxycycline to unravel the role of epithelial-derived Calprotectin on tissue homeostasis and inflammation. TgS100a8a9hep mice displayed a significant enrichment of neutrophils in peripheral blood and tissues with high blood content. Interestingly, Cxcl1 transcription was significantly induced in the liver of TgS100a8a9hep mice and primary hepatocytes derived thereof as compared to Control mice, accompanied by an increase of Cxcl1 serum levels. However, expression of other chemokines with a known function in neutrophil mobilization from the bone marrow, e.g. Csf3 and Cxcl2, was not altered. Doxycycline treatment of TgS100a8a9hep mice reduced Cxcl1 expression in the liver and resulted in normal numbers of neutrophils. CONCLUSION: In summary, our data demonstrate for the first time that hepatocyte-specific S100a8 and S100a9 expression induces a systemic mobilization of neutrophils by a specific activation of Cxcl1 transcription in the liver.