Cancer Letters

Cancer Letters

Volume 344, Issue 1, 1 March 2014, Pages 28-39
Cancer Letters

Metastasis-associated protein S100A4 induces a network of inflammatory cytokines that activate stromal cells to acquire pro-tumorigenic properties

https://doi.org/10.1016/j.canlet.2013.10.036Get rights and content

Highlights

  • Stroma bordering metastatic lesions is enriched with the S100A4 protein.

  • S100A4 stimulates tumor cells to secrete a variety of pro-inflammatory factors.

  • The secreted factors educate stromal cells to acquire tumor-supportive properties.

  • We propose that S100A4 modulated tumor-stromal crosstalk promotes metastasis.

Abstract

Tumor cells have the ability to exploit stromal cells to facilitate metastasis. By using malignant melanoma as a model, we show that the stroma adjacent to metastatic lesions is enriched in the known metastasis-promoting protein S100A4. S100A4 stimulates cancer cells to secrete paracrine factors, such as inflammatory cytokines IL8, CCL2 and SAA, which activate stromal cells (endothelial cells and monocytes) so that they acquire tumor-supportive properties. Our data establishes S100A4 as an inducer of a cytokine network enabling tumor cells to engage angiogenic and inflammatory stromal cells, which might contribute to pro-metastatic activity of S100A4.

Introduction

Metastasis is the major cause of death in cancer patients, signifying the need for a better understanding of the metastasis process leading to more effective therapies [1]. Recently it has been acknowledged that not only cancer cells, but also factors in the tumor microenvironment, particularly those related to inflammation, contribute to metastasis [2]. It has been demonstrated that tumor cells, via crosstalk with stromal cells, can establish permissive and protective milieu or a niche at distant sites to facilitate growth and survival of metastatic cells [3], [4], [5]. Such tumor-stroma cell crosstalk often involves myeloid cells and is based on secreted factors, like pro-inflammatory cytokines [5], [6], [7]. Among the factors found to be executing such paracrine crosstalk are also members of the S100 family of Ca2+-binding proteins [5], [7]. S100 proteins are known to be involved in both cancer and inflammatory disorders [8], [9], suggesting a link between pro-inflammatory functions of S100 proteins and promotion of metastasis [7], [10]. In recent years the inflammation-associated proteins S100A8 and S100A9 have emerged as important signaling molecules in the formation of a pre-metastatic niche. Hiratsuka et al. [7] have shown that S100A8/A9 produced by stroma cells in pre-metastatic lung induce other inflammatory factors (such as serum amyloid A, SAA) and recruit myeloid cells which together facilitate niche formation. Furthermore, Acharyya et al. [5] have demonstrated that tumor-recruited myeloid cells produce S100A8/A9, which facilitate survival and chemoresistance of metastatic breast cancer cells. Taken together, these studies strengthen the notion that S100 proteins play a role in the tumor-stromal cell crosstalk thereby facilitating metastasis and drug-resistance.

Another member of the family, S100A4, is also strongly linked to metastasis and poor prognosis [11], [12], [13], and is known to play a role in inflammatory disorders [14], [15]. The exact mechanisms of how S100A4 executes its pro-metastatic functions are not completely elucidated, but several lines of evidence suggest that this function is associated with the protein present in the tumor microenvironment. First, many types of stromal cells, such as fibroblasts, endothelial cells and immune cells express S100A4 [16]. Further, S100A4-positive stromal cells were shown to facilitate the development of a primary tumor and lung metastases in breast cancer models in vivo [3], [17]. Finally, S100A4 released from the cells was shown to act as an extracellular factor modulating the microenvironment i.e. stimulating angiogenesis [18], [19], recruiting immune cells [20], [21] and promoting neurite outgrowth [22]. Collectively, these studies suggest S100A4 as an important player in the tumor microenvironment.

In the present study we investigate the effect of extracellular S100A4 on melanoma cells and how this potentiates interactions with stromal cells. We show that S100A4 stimulates tumor cells to release pro-inflammatory cytokines and other paracrine factors that activate endothelial cells and monocytes to acquire pro-tumorigenic properties. This suggests that extracellular S100A4 may assist tumor cells in engaging tumor-supportive stromal cells, and implies the importance of an inflammatory cytokine network in mediating pro-metastatic S100A4 effects.

Section snippets

Cell lines and reagents

The malignant melanoma cell lines Melmet 1 and Melmet 5 (and FEMX-1) were established from subcutaneous and lymph node metastases, respectively, at the Norwegian Radium Hospital (Norway) as described previously [23], [24]. Green fluorescent protein (GFP)-luciferase (Luc) labeled melanoma cells were generated by transducing the cells with lentivirus carrying a human ferritin promoter-driven GFP-Luc construct described previously [25] (kindly provided by Dr. Glen Merlino, NIH, MD). WM239 and

The metastases-adjacent stroma is enriched in S100A4

To evaluate association between S100A4 expression and metastatic melanoma lesions in vivo, we generated experimental metastases by injecting Melmet 1 and Melmet 5 cells L.V. into nude mice. The established brain metastases (from Melmet 1 and Melmet 5) and lung metastases (initiated only by Melmet 5) were analyzed by IHC, revealing that tumor cells express low levels of S100A4 (Fig. 1A and C). Conversely, S100A4 positivity was associated with stromal cells adjacent to the tumors (Fig. 1A (i) and

Discussion

Tumor-associated stromal cells play an important role in promoting metastasis. Here we demonstrate an association between metastases-related stroma and a known pro-metastatic protein S100A4, which can act as an initiator of a tumor-stroma interaction loop supporting the tumor cells (Fig. 10). We show that S100A4 facilitates “education” of stromal cells by stimulating tumor cells to secrete numerous paracrine factors, cytokines. The most induced cytokines IL8 and CCL2 could act as central

Conflict of Interest

None.

Acknowledgements

We thank Alexandr Kristian and Karianne Giller Fleten for assistance with experimental metastasis models in vivo, the genotyping and bioinformatics core facilities, with Geir Frode Øy and Vegard Nygaard, for protein-array experiments and data analysis, Tove Øyjord for assistance with qRT-PCR and Dr. Hari Prasad Dhakal and Ellen Hellesylt for help with IHC. This work was supported by the Norwegian Cancer Society and Jeanette and Søren Bothners Legacy.

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