Tumor cells induce the cancer associated fibroblast phenotype via caveolin-1 degradation: Implications for breast cancer and DCIS therapy with autophagy inhibitors

Abstract

Loss of stromal caveolin 1 (Cav-1) is a novel biomarker for cancer-associated fibroblasts that predicts poor clinical outcome in breast cancer and DCIS patients. We hypothesized that epithelial cancer cells may have the ability to drive Cav-1 downregulation in adjacent normal fibroblasts, thereby promoting the cancer associated fibroblast phenotype. To test this hypothesis directly, here we developed a novel co-culture model employing (i) human breast cancer cells (MCF7), and (ii) immortalized fibroblasts (hTERT-BJ1), which are grown under defined experimental conditions. Importantly, we show that co-culture of immortalized human fibroblasts with MCF7 breast cancer cells leads to Cav-1 downregulation in fibroblasts. These results were also validated using primary cultures of normal human mammary fibroblasts co-cultured with MCF7 cells. In this system, we show that Cav-1 downregulation is mediated by autophagic/lysosomal degradation, as pre-treatment with lysosome-specific inhibitors rescues Cav-1 expression. Functionally, we demonstrate that fibroblasts co-cultured with MCF7 breast cancer cells acquire a cancer associated fibroblast phenotype, characterized by Cav-1 downregulation, increased expression of myofibroblast markers and extracellular matrix proteins, and constitutive activation of TGFβ/Smad2 signaling. siRNA-mediated Cav-1 downregulation mimics several key changes that occur in co-cultured fibroblasts, clearly indicating that a loss of Cav-1 is a critical initiating factor, driving stromal fibroblast activation during tumorigenesis. As such, this co-culture system can now be used as an experimental model for generating "synthetic" cancer associated fibroblasts (CAFs). More specifically, these "synthetic" CAFs could be used for drug screening to identify novel therapeutics that selectively target the Cav-1-negative tumor micro-environment. Our findings also suggest that chloroquine, or other autophagy/lysosome inhibitors, may be useful as anti-cancer agents, to therapeutically restore the expression of stromal Cav-1 in cancer associated fibroblasts. We discuss this possibility, in light of the launch of a new clinical trial that uses chloroquine to treat DCIS patients: PINC (Preventing Invasive Breast Neoplasia with Cholorquine) [See http://clinicaltrials.gov/show/NCT01023477].

Curcumin attenuates high glucose-induced podocyte apoptosis by regulating functional connections between caveolin-1 phosphorylation and ROS

“…Chen et al showed that reduced cav-1 expression correlated with increased ROS production in the adventitia of hypertensive PA [36] . Martinez-Outschoorn et al demonstrated that a loss of stromal cav-1 in fibroblasts was sufficient to induce ROS production and oxidative stress, indicating that a loss of cav-1 provided a feed-forward mechanism for promoting oxidative stress and the autophagic program [37][38][39] . Zhang et al showed that glucose-induced ROS generation was significantly attenuated by the chemical disruption of caveolae in knockout mesangial cells [30] .…”

Organ-Specific Cancer Metabolism and Its Potential for Therapy

“…The reverse Warburg effect in estrogen receptor positive breast cancers includes the metabolic interaction between tumor cells and stromal cells. Thereby, cancer cells promote the metabolic reprogramming of stromal cells such as fibroblasts into cancer-associated fibroblasts [58]. Specifically, fibroblasts co-cultured with breast cancer cells displayed decreased caveolin 1 expression, and induction of HIF1 and NF B [59].…”

Ketone body utilization drives tumor growth and metastasis

“…As ketone bodies are preferentially used only during periods of starvation, we envision that limited RePORT RePORT Cav-1 expression under these co-culture conditions is due to its autophagic digestion, which is lysosome-dependent. 6,7 Fibroblasts overexpressing ketogenic enzymes induce mitochondrial biogenesis in MCF7 cells, as well as cell growth. To examine the paracrine effects of HMGCS2-and BDH1-overexpressing fibroblasts on adjacent cancer cells, they were coculultured with MCF7 cells under low mitogen conditions.…”