Persistent Inflammatory Stimulation Drives the Conversion of MSCs to Inflammatory CAFs That Promote Pro-Metastatic Characteristics in Breast Cancer Cells

Abstract

The pro-inflammatory cytokines tumor necrosis factor α (TNFα) and interleukin 1β (IL-1β) are expressed simultaneously and have tumor-promoting roles in breast cancer. In parallel, mesenchymal stem cells (MSCs) undergo conversion at the tumor site to cancer-associated fibroblasts (CAFs), which are generally connected to enhanced tumor progression. Here, we determined the impact of consistent inflammatory stimulation on stromal cell plasticity. MSCs that were persistently stimulated by TNFα + IL-1β (generally 14–18 days) gained a CAF-like morphology, accompanied by prominent changes in gene expression, including in stroma/fibroblast-related genes. These CAF-like cells expressed elevated levels of vimentin and fibroblast activation protein (FAP) and demonstrated significantly increased abilities to contract collagen gels. Moreover, they gained the phenotype of inflammatory CAFs, as indicated by the reduced expression of α smooth muscle actin (αSMA), increased proliferation, and elevated expression of inflammatory genes and proteins, primarily inflammatory chemokines. These inflammatory CAFs released factors that enhanced tumor cell dispersion, scattering, and migration; the inflammatory CAF-derived factors elevated cancer cell migration by stimulating the chemokine receptors CCR2, CCR5, and CXCR1/2 and Ras-activating receptors, expressed by the cancer cells. Together, these novel findings demonstrate that chronic inflammation can induce MSC-to-CAF conversion, leading to the generation of tumor-promoting inflammatory CAFs.

The Role of Chronic Inflammation in the Development of Breast Cancer

“…Mesenchymal stromal cells (MSCs) are adult, fibroblast-like multipotent cells characterized by the ability to differentiate into tissues of mesodermal origin, such as adipocytes, chondroblasts, osteoblasts [99], and, importantly, into cancer-associated fibroblasts [135]. MSC may arise from a variety of sites, including adipose tissue, skin, tendon, muscle, dental pulp and others [99,136].…”

“…In the presence of an inflammatory environment (high levels of TNFα and IFNγ), MSCs become activated and adopt an immune-suppressive phenotype (MSC2) by secreting high levels of soluble factors, including IDO, PGE2, NO, TGFβ, Hepatocyte Growth Factor (HGF) and hemoxygenase (HO), that suppress T cell proliferation [99,101]. Importantly, potent proinflammatory cytokines (tumor necrosis factor and interleukin 1) lead to the conversion of mesenchymal stem cells (MSCs) to inflammatory cancer-associated fibroblasts (CAFs) [135]. Rubenstein, et al [135] have shown that these inflammation-driven CAFs secrete metastasis-promoting factors that elevate the dispersion, scattering, and migration of breast cancer cells via activation of tumor cell receptors that signal through Ras proteins and via GαI proteins; the latter receptors were identified as the chemokine receptors CCR2, CCR5, and CXCR1/2.…”

“…Importantly, potent proinflammatory cytokines (tumor necrosis factor and interleukin 1) lead to the conversion of mesenchymal stem cells (MSCs) to inflammatory cancer-associated fibroblasts (CAFs) [135]. Rubenstein, et al [135] have shown that these inflammation-driven CAFs secrete metastasis-promoting factors that elevate the dispersion, scattering, and migration of breast cancer cells via activation of tumor cell receptors that signal through Ras proteins and via GαI proteins; the latter receptors were identified as the chemokine receptors CCR2, CCR5, and CXCR1/2. MSCs are thus highly versatile cells with the ability to respond to a spectrum of stimuli and with the potential to influence multiple aspects of breast carcinogenesis.…”

The Breast Tumor Microenvironment: A Key Player in Metastatic Spread

“…Although mainly derived from resident fibroblasts [ 28 ], BC-associated fibroblasts (BCAFs) can also originate from other cell types such as mesenchymal stem cells, cancer cells, cancer stem cells, and endothelial cells through a process known as trans-differentiation [ 20 ]. The exposure of mesenchymal stem cells to the proinflammatory cytokines, tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β) can lead to the development of the cancer-associated fibroblast (CAF) phenotype [ 29 ]. These CAFs in turn secrete inflammatory factors and chemokines which can enhance BC migration [ 29 ].…”

“…The exposure of mesenchymal stem cells to the proinflammatory cytokines, tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β) can lead to the development of the cancer-associated fibroblast (CAF) phenotype [ 29 ]. These CAFs in turn secrete inflammatory factors and chemokines which can enhance BC migration [ 29 ]. Moreover, when BC cells are in constant interaction with normal fibroblasts, these hitherto “normal fibroblasts” permanently transition to CAFs [ 28 , 30 ].…”