Genetic Deficiency in Plasma Protein HRG Enhances Tumor Growth and Metastasis by Exacerbating Immune Escape and Vessel Abnormalization

Abstract

Histidine-rich glycoprotein (HRG) is a 75-kDa heparin-binding plasma protein implicated in the regulation of tumor growth and vascularization. In this study, we show that hrg À/À mice challenged with fibrosarcoma or pancreatic carcinoma grow larger tumors with increased metastatic properties. Compared with wild-type mice, fibrosarcomas in hrg À/À mice were more hypoxic, necrotic, and less perfused, indicating enhanced vessel abnormalization. HRG deficiency was associated with a suppressed antitumor immune response, with both increased infiltration of M2 marker-expressing macrophages and decreased infiltration of dendritic cells and cytotoxic T cells. Analysis of transcript expression in tumor-associated as well as peritoneal macrophages from hrg À/À mice revealed an increased expression of genes associated with a proangiogenic and immunoinhibitory phenotype. In accordance, expression arrays conducted on HRG-treated peritoneal macrophages showed induction of genes involved in extracellular matrix biology and immune responsiveness. In conclusion, our findings show that macrophages are a direct target of HRG. HRG loss influences macrophage gene regulation, leading to excessive stimulation of tumor angiogenesis, suppression of tumor immune response, and increased tumor growth and metastatic spread. Cancer Res; 72(8); 1953-63. Ó2012 AACR.

Histidine-Rich Glycoprotein Uptake and Turnover Is Mediated by Mononuclear Phagocytes

“…The specific binding of HRG to CD45 + inflammatory cells and the important role for CSF1R (CD115)-positive inflammatory cells in uptake and turnover of HRG that we report here, is in agreement with the finding that mononuclear phagocytes are key mediators of HRGs effects on tumor growth and metastasis [1]. Importantly, hrg gene targeting in mice profoundly affects peritoneal mononuclear cells, which are polarized towards a pro-angiogenic/immunosuppressive phenotype [16]. Identification of the exact phenotype of the HRG-binding monocyte/macrophage awaits characterization of the HRG receptor.…”

“…These data combined with our previous report that HRG induces gene regulation in peritoneal monocytes [16] make plausible the suggestion that HRG binds to a cell surface signaling receptor on mononuclear phagocytes (see Figure 8). The exact expression pattern of an HRG receptor awaits its molecular identification.…”

“…Moreover, HRG is essential in mounting inflammatory and immune responses against bacterial and fungal infections [2], [15]. In cancer, HRG polarizes tumor-associated macrophages from a pro-angiogenic, immune-suppressive M2 phenotype towards an anti-tumor, immunity-promoting, M1 phenotype [1], [16]. It has been suggested that HRG's bioactivity correlates with fragmentation of the protein [17], [18].…”

Impact of tumour associated macrophages in pancreatic cancer

“…The role of TAMs in promoting pancreatic metastasis was also shown in tumour mouse models. Pharmacological inhibition of macrophage recruitment to the pancreatic tumour microenvironment using the CSF1R inhibitors reduced metastatic spreading to the liver (37), while increased macrophage conversing towards a M2 phenotype by the loss of HRG increased metastatic spreading (49). A reduction of macrophage numbers due to inhibition of their migration and reduced metastatic spreading of pancreatic cancer cells was also described in response to the focal adhesion kinase (FAK) inhibitor PF-562,271.…”

“…In contrast, conversion of macrophages towards a more pronounced pro-angiogenic phenotype by depleting histidine rich glycoprotein (HRG) resulted in increased pancreatic tumour growth. Accelerated tumour formation in HRG deficient mice was in part associated with increased infiltration of M2 marker?expressingmacrophages and their increased pro-angiogenic gene expression profile resulting in excessive stimulation of tumour angiogenesis (49).…”