Tumour-infiltrating regulatory T cells stimulate mammary cancer metastasis through RANKL–RANK signalling

Abstract

Inflammatory mechanisms influence tumor development and metastatic progression1. Of interest is the role of such mechanisms in metastatic spread of tumors whose etiology does not involve pre-existing inflammation or infection, such as breast and prostate cancers. We found that prostate cancer metastasis is associated with lymphocyte infiltration into advanced tumors and elevated expression of the tumor necrosis factor (TNF) family members receptor activator of NF-κB (RANK) ligand (RANKL) and lymphotoxin (LT)2. But the source of RANKL and its role in metastasis were not established. RANKL and its receptor RANK control proliferation of mammary lobuloalveolar cells during pregnancy3 through activation of IκB kinase α (IKKα)4, a protein kinase that is required for self-renewal of mammary cancer progenitors5 and prostate cancer metastasis2. We therefore examined whether RANKL, RANK and IKKα are also involved in mammary/breast cancer metastasis. Indeed, RANK signaling in mammary carcinoma cells that overexpress the ErbB2 (c-Neu) proto-oncogene6, which is frequently amplified in metastatic human breast cancers7,8, was important for pulmonary metastasis. Metastatic spread of ErbB2-transformed carcinoma cells was also dependent on CD4+CD25+ T cells, whose major pro-metastatic function appeared to be RANKL production. RANKL-producing T cells were mainly FoxP3+ and found in close proximity to smooth muscle actin (SMA)-positive stromal cells in mouse and human breast cancers. The T cell-dependence of pulmonary metastasis was replaced by administration of exogenous RANKL, a procedure that also stimulated pulmonary metastasis of RANK-positive human breast carcinoma cells. These results are consistent with the adverse prognostic impact of tumor-infiltrating CD4+ or FoxP3+ T cells on human breast cancer9,10 and suggest that targeting of RANKL-RANK signaling can be used in conjunction with other therapies to prevent subsequent metastatic disease.

Inflammation and skeletal metastasis

“…[163][164][165] Of note, TGFb was found to induce the expression of the FOXP3 transcription factor and to stimulate the transition of naive T cells into Tregs, 166 whereas tumorinfiltrating Tregs produced RANKL to stimulate metastasis in breast cancer. 146 Similarly, findings in metastatic prostate cancer suggest that RANKL derived from inflammatory cells (macrophages and T cells) activates IKKa directly repressing maspin. In addition, maspin suppressed the progression of osteolytic lesions in a model of prostate cancer bone metastasis.…”

“…[144][145][146] In prostate and breast cancer models, the activation of IKKa by the receptor activator of NF-kB ligand (RANKL) signaling through RANK promotes metastasis. 145,146 Upon activation, IKKa translocates to the cancer cell nucleus and directly represses the transcription of the metastasis suppressor maspin (SERPINB5), a mechanism that appears to be independent of NF-kB. Interestingly, the accumulation of inflammatory macrophages and Treg (CD4 þ /CD25 þ /FOXP3 þ ) cells was detected in tumors and further identified as major contributors for RANKL expression.…”

“…Interestingly, the accumulation of inflammatory macrophages and Treg (CD4 þ /CD25 þ /FOXP3 þ ) cells was detected in tumors and further identified as major contributors for RANKL expression. 145,146 Diverse mechanisms of inflammation-induced tumor progression and metastasis stimulate the infiltration and activation of myeloid cells, which mediate the different steps of the metastasis from EMT and dissemination through circulation to distant organ colonization. Myeloid cells induce immunosuppression, promote angiogenesis, survival of tumor cells and prepare distant sites to facilitate tumor growth.…”

Ovarian cancer stem cells promote tumour immune privilege and invasion via CCL5 and regulatory T cells

“…Tumour cells can interact with immune cells in the tumour microenvironment through the expression of immune-associated molecules, such as programmed cell death ligand 1 (PD-L1), IDO1, high-mobility group box-1 protein (HMGB1), CCL5 and CXCL2. Among these molecules, PD-L1 and IDO1 can directly suppress T cells [41,42], HMGB1 and CCL5 can enhance T reg -mediated immunosuppression [43,44] and CXCL2 can lead to immune tolerance by attracting myeloid-derived suppressor cells (MDSCs) to the tumour microenvironment [45].…”

Progesterone signalling in breast cancer: a neglected hormone coming into the limelight

“…Are they activated by ERα or PR expressed by the tumour cells or perhaps by hormone-responsive bone cells? In the MMTV-Erbb2 tumour model, infiltrating T cells have been shown to stimulate metastasis by releasing RANKL 90 , suggesting that paracrine loops also involve an immune cell component, at least in tumorigenesis.…”