Abstract
BackgroundTransforming growth factor (TGF)-β plays a pivotal role in cancer progression through regulating cancer cell proliferation, invasion, and remodeling of the tumor microenvironment. Cancer-associated fibroblasts (CAFs) are the predominant type of stromal cell, in which TGF-β signaling is activated. Among the strategies for TGF-β signaling inhibition, RNA interference (RNAi) targeting of TGF-β ligands is emerging as a promising tool. Although preclinical studies support the efficacy of this therapeutic strategy, its effect on the tumor microenvironment in vivo remains unknown. In addition, differential effects due to knockdown of various TGF-β ligand isoforms have not been examined. Therefore, an experimental model that recapitulates tumor–stromal interaction is required for validation of therapeutic agents.MethodsWe have previously established a three-dimensional co-culture model of lung cancer, and demonstrated the functional role of co-cultured fibroblasts in enhancing cancer cell invasion and differentiation. Here, we employed this model to examine how knockdown of TGF-β ligands affects the behavior of different cell types. We developed lentivirus vectors carrying artificial microRNAs against human TGF-β1 and TGF-β2, and tested their effects in lung cancer cells and fibroblasts.ResultsLentiviral vectors potently and selectively suppressed the expression of TGF-β ligands, and showed anti-proliferative effects on these cells. Furthermore, knockdown of TGF-β ligands attenuated fibroblast-mediated collagen gel contraction, and diminished lung cancer cell invasion in three-dimensional co-culture. We also observed differential effects by targeting different TGF-β isoforms in lung cancer cells and fibroblasts.ConclusionsOur findings support the notion that RNAi-mediated targeting of TGF-β ligands may be beneficial for lung cancer treatment via its action on both cancer and stromal cells. This study further demonstrates the usefulness of this three-dimensional co-culture model to examine the effect of therapeutic agents on tumor–stromal interaction.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2407-14-580) contains supplementary material, which is available to authorized users.
Highlights
Transforming growth factor (TGF)-β plays a pivotal role in cancer progression through regulating cancer cell proliferation, invasion, and remodeling of the tumor microenvironment
Transforming growth factor-β (TGF-β) signaling is activated in lung Cancer-associated fibroblasts (CAFs) CAFs are a major constituent of the tumor stroma, and we have previously shown that lung CAFs are more potent in enhancing cancer cell invasion and collagen gel contraction than normal lung fibroblasts (NFs) [17]
These analyses demonstrated that the TGF-β-regulated genes identified through our analysis are highly enriched in CAFs, suggesting that TGF-β signaling is activated in lung CAFs (Figure 1A)
Summary
Transforming growth factor (TGF)-β plays a pivotal role in cancer progression through regulating cancer cell proliferation, invasion, and remodeling of the tumor microenvironment. Cancer-associated fibroblasts (CAFs) are the predominant type of stromal cell, in which TGF-β signaling is activated. Among the strategies for TGF-β signaling inhibition, RNA interference (RNAi) targeting of TGF-β ligands is emerging as a promising tool. Among the soluble factors involved in the tumor–stromal interaction, transforming growth factor (TGF)-β plays a pivotal role. TGF-β acts as a tumor suppressor by inhibiting proliferation and apoptotic induction in epithelial cells. Epithelial cells become refractory to the growth inhibitory effect of TGFβ and begin to secrete high levels of TGF-β, which in turn exhibits tumor-promoting activity, such as angiogenesis, immune evasion, fibroblast activation, and ECM accumulation [6,7,8]. In contrast to cancer cells, the role of TGF-β signaling in the tumor stroma is poorly understood, at least partly due to technical limitations in detecting TGF-β signaling activation in situ
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