Tumor Microenvironmental Signaling Elicits Epithelial-Mesenchymal Plasticity through Cooperation with Transforming Genetic Events

Abstract

Epithelial-to-mesenchymal transition (EMT) facilitates the escape of epithelial cancer cells from the primary tumor site, which is a key event early in metastasis. Here, we explore how extrinsic, tumor microenvironmental cytokines cooperate with intrinsic, genetic changes to promote EMT in human mammary epithelial cells (HMECs). Viral transduction of transforming genetic events into HMECs routinely generated two distinct cell populations. One population retained epithelial characteristics, while an emergent population spontaneously acquired a mesenchymal morphology and properties associated with cancer stem cells (CSCs). Interestingly, the spontaneous mesenchymal/CSCs were unable to differentiate and lacked epithelial-mesenchymal plasticity. In contrast, exposure of the transformed HMECs retaining epithelial characteristics to exogenous transforming growth factor-β (TGF-β) generated a mesenchymal/CSC population with remarkable plasticity. The TGF-β-induced mesenchymal/CSC population was dependent on the continued presence of TGF-β. Removal of TGF-β or pharmacologic or genetic inhibition of TGF-β/SMAD signaling led to the reversion of mesenchymal/CSC to epithelial/non-CSC. Our results demonstrate that targeting exogenous cytokine signaling disrupts epithelial-mesenchymal plasticity and may be an effective strategy to inhibit the emergence of circulating tumor cells. The model of epithelial-mesenchymal plasticity we describe here can be used to identify novel tumor microenvironmental factors and downstream signaling that cooperate with intrinsic genetic changes to drive metastasis. Understanding the interaction between extrinsic and intrinsic factors that regulate epithelial-mesenchymal plasticity will allow the development of new therapies that target tumor microenvironmental signals to reduce metastasis.

Potent EMT and CSC Phenotypes Are Induced By Oncostatin-M in Pancreatic Cancer

“…Western blots were conducted as described previously (12). Primary antibodies used were Actin (#MS-1295-P; Thermo Scientific), E-Cadherin (#sc-27191; Santa Cruz, #3195; Cell Signaling), Snail (#3879; Cell Signaling), phosphorylated STAT3 Y705 (#9145; Cell Signaling), STAT3 (#9139; Cell Signaling), and ZEB1 (#3396; Cell Signaling).…”

“…Secondary antibodies used were HRP-linked Anti-Mouse (#7076; Cell Signaling) and HRP-linked Anti-Rabbit (#7074; Cell Signaling). For qPCR, total RNA was isolated as previously described (12). RNA (1 μg) was reverse transcribed by iScript cDNA Synthesis Kit (#170-8891; Bio Rad).…”

“…Emerging evidence suggests a pivotal role for the tumor microenvironment (TME) in promoting epithelial-mesenchymal plasticity (E-M plasticity) and the acquisition of CSC properties (12–15). The TME is composed of secreted factors emanating from infiltrating immune components, fibroblasts, and other stromal cells.…”

Intratumoral heterogeneity: Clonal cooperation in epithelial-to-mesenchymal transition and metastasis

“…Many studies have shown that a tumor's microenvironment can affect the EMT status of the tumor cells (reviewed more thoroughly in), 74,119,120 and factors like TGF-b1, secreted by the microenvironment, have been shown to non-cell autonomously regulate EMT of cells in the primary tumor. 121 Few, if any, studies have asked if a mixed population of cells within the tumor itself, some of which have undergone EMT, can cause the surrounding cells to undergo EMT to affect metastatic progression. However, a number of studies have demonstrated cooperativity between tumor cells that have undergone EMT and those that have not.…”

Redox processes inform multivariate transdifferentiation trajectories associated with TGFβ-induced epithelial–mesenchymal transition

“…The cytokine transforming growth factor beta (TGFβ) induces EMT and has been implicated in increased invasiveness of cancers and in the formation of metastases [3–5]. TGFβ signaling is enhanced within the tumor microenvironment through interactions with cancer-associated fibroblasts, immune cells, and extracellular matrix [6, 7]. Circulating tumor cells from breast cancer patients are enriched for mesenchymal markers and TGFβ signaling, implicating TGFβ-mediated EMT as a mechanism for entry into to the circulatory system [8].…”