Oxidative stress in cancer associated fibroblasts drives tumor-stroma co-evolution

Abstract

Loss of stromal fibroblast caveolin-1 (Cav-1) is a powerful single independent predictor of poor prognosis in human breast cancer patients, and is associated with early tumor recurrence, lymph node metastasis and tamoxifen-resistance. We developed a novel co-culture system to understand the mechanism(s) by which a loss of stromal fibroblast Cav-1 induces a "lethal tumor microenvironment." Here, we propose a new paradigm to explain the powerful prognostic value of stromal Cav-1. In this model, cancer cells induce oxidative stress in cancer-associated fibroblasts, which then acts as a "metabolic" and "mutagenic" motor to drive tumor-stroma co-evolution, DNA damage and aneuploidy in cancer cells. More specifically, we show that an acute loss of Cav-1 expression leads to mitochondrial dysfunction, oxidative stress and aerobic glycolysis in cancer associated fibroblasts. Also, we propose that defective mitochondria are removed from cancer-associated fibroblasts by autophagy/mitophagy that is induced by oxidative stress. As a consequence, cancer associated fibroblasts provide nutrients (such as lactate) to stimulate mitochondrial biogenesis and oxidative metabolism in adjacent cancer cells (the "Reverse Warburg effect"). We provide evidence that oxidative stress in cancer-associated fibroblasts is sufficient to induce genomic instability in adjacent cancer cells, via a bystander effect, potentially increasing their aggressive behavior. Finally, we directly demonstrate that nitric oxide (No) over-production, secondary to Cav-1 loss, is the root cause for mitochondrial dysfunction in cancer associated fibroblasts. In support of this notion, treatment with anti-oxidants (such as N-acetyl-cysteine, metformin and quercetin) or No inhibitors (L-NAMe) was sufficient to reverse many of the cancer-associated fibroblast phenotypes that we describe. thus, cancer cells use "oxidative stress" in adjacent fibroblasts (1) as an "engine" to fuel their own survival via the stromal production of nutrients and (ii) to drive their own mutagenic evolution towards a more aggressive phenotype, by promoting genomic instability. We also present evidence that the "field effect" in cancer biology could also be related to the stromal production of RoS and No species. eNoS-expressing fibroblasts have the ability to downregulate Cav-1 and induce mitochondrial dysfunction in adjacent fibroblasts that do not express eNoS. As such, the effects of stromal oxidative stress can be laterally propagated, amplified and are effectively "contagious"-spread from cell-to-cell like a virus-creating an "oncogenic/mutagenic" field promoting widespread DNA damage. Oxidative stress in cancer associated fibroblasts drives tumor-stroma co-evolutionA new paradigm for understanding tumor metabolism, the field effect and genomic instability in cancer cells ROS are eliminated by anti-oxidant enzymes, such as superoxide dismutases, the peroxiredoxins and glutathione peroxidases. High ROS levels may result in significant cellular damage and induce oxidative stress, which i...

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“…Cancer cells first secreted hydrogen peroxide (H 2 O 2 ) to induce oxidative stress in adjacent fibroblasts as a form of accelerated aging; [30][31][32] at the same time, the cancer cells mounted an antioxidant defense by upregulating antioxidant proteins, such as TIGAR and peroxiredoxins. 29,33,34 Oxidative stress in the cancer-associated fibroblasts increased stromal ROS production, activating two major transcription factors, namely, HIF1a and NFκB, which both function as master regulators of autophagy, mitophagy, aerobic glycolysis as well as inflammation. 30,[33][34][35][36] As a consequence, the stromal fibroblasts would produce high-energy nutrients (L-lactate, ketones and glutamine).…”

A microfluidic co-culture system to monitor tumor-stromal interactions on a chip

“…49,50 We measured the change of total area covered by HuH7 using phase contrast images of the co-culture chip, which was processed by ImageJ software (detailed procedure illustrated in Figure S3, supplementary material). 52 It was observed that the coverage of tumor cells increased significantly after day 4 ( Figure 6(a)).…”