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HIF1-alpha functions as a tumor promoter in cancer associated fibroblasts, and as a tumor suppressor in breast cancer cells: Autophagy drives compartment-specific oncogenesis.

ABSTRACT: Our recent studies have mechanistically implicated a loss of stromal Cav-1 expression and HIF1-alpha-activation in driving the cancer-associated fibroblast phenotype, through the paracrine production of nutrients via autophagy and aerobic glycolysis. However, it remains unknown if HIF1a-activation is sufficient to confer the cancer-associated fibroblast phenotype. To test this hypothesis directly, we stably-expressed activated HIF1a in fibroblasts and then examined their ability to promote tumor growth using a xenograft model employing human breast cancer cells (MDA-MB-231). Fibroblasts harboring activated HIF1a showed a dramatic reduction in Cav-1 levels and a shift towards aerobic glycolysis, as evidenced by a loss of mitochondrial activity, and an increase in lactate production. Activated HIF1a also induced BNIP3 and BNIP3L expression, markers for the autophagic destruction of mitochondria. Most importantly, fibroblasts expressing activated HIF1a increased tumor mass by ?2-fold and tumor volume by ?3-fold, without a significant increase in tumor angiogenesis. In this context, HIF1a also induced an increase in the lymph node metastasis of cancer cells. Similar results were obtained by driving NF?B activation in fibroblasts, another inducer of autophagy. Thus, activated HIF1a is sufficient to functionally confer the cancer-associated fibroblast phenotype. It is also known that HIF1a expression is required for the induction of autophagy in cancer cells. As such, we next directly expressed activated HIF1a in MDA-MB-231 cells and assessed its effect on tumor growth via xenograft analysis. Surprisingly, activated HIF1a in cancer cells dramatically suppressed tumor growth, resulting in a 2-fold reduction in tumor mass and a 3-fold reduction in tumor volume. We conclude that HIF1a activation in different cell types can either promote or repress tumorigenesis. Based on these studies, we suggest that autophagy in cancer-associated fibroblasts promotes tumor growth via the paracrine production of recycled nutrients, which can directly "feed" cancer cells. Conversely, autophagy in cancer cells represses tumor growth via their "self-digestion". Thus, we should consider that the activities of various known oncogenes and tumor-suppressors may be compartment and cell-type specific, and are not necessarily an intrinsic property of the molecule itself. As such, other "classic" oncogenes and tumor suppressors will have to be re-evaluated to determine their compartment specific effects on tumor growth and metastasis. Lastly, our results provide direct experimental support for the recently proposed "Autophagic Tumor Stroma Model of Cancer".

SUBMITTER: Chiavarina B

PROVIDER: S-EPMC3047618 | biostudies-literature | 2010 Sep

REPOSITORIES: biostudies-literature

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HIF1-alpha functions as a tumor promoter in cancer associated fibroblasts, and as a tumor suppressor in breast cancer cells: Autophagy drives compartment-specific oncogenesis.

Chiavarina Barbara B Whitaker-Menezes Diana D Migneco Gemma G Martinez-Outschoorn Ubaldo E UE Pavlides Stephanos S Howell Anthony A Tanowitz Herbert B HB Casimiro Mathew C MC Wang Chenguang C Pestell Richard G RG Grieshaber Philip P Caro Jaime J Sotgia Federica F Lisanti Michael P MP

Cell cycle (Georgetown, Tex.) 20100904 17

Our recent studies have mechanistically implicated a loss of stromal Cav-1 expression and HIF1-alpha-activation in driving the cancer-associated fibroblast phenotype, through the paracrine production of nutrients via autophagy and aerobic glycolysis. However, it remains unknown if HIF1a-activation is sufficient to confer the cancer-associated fibroblast phenotype. To test this hypothesis directly, we stably-expressed activated HIF1a in fibroblasts and then examined their ability to promote tumor ...[more]

PMID: 20864819

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Project description:Recently, using a co-culture system, we demonstrated that MCF7 epithelial cancer cells induce oxidative stress in adjacent cancer-associated fibroblasts, resulting in the autophagic/lysosomal degradation of stromal caveolin-1 (Cav-1). However, the detailed signaling mechanism(s) underlying this process remain largely unknown. Here, we show that hypoxia is sufficient to induce the autophagic degradation of Cav-1 in stromal fibroblasts, which is blocked by the lysosomal inhibitor chloroquine. Concomitant with the hypoxia-induced degradation of Cav-1, we see the upregulation of a number of well-established autophagy/mitophagy markers, namely LC3, ATG16L, BNIP3, BNIP3L, HIF-1? and NF?B. In addition, pharmacological activation of HIF-1? drives Cav-1 degradation, while pharmacological inactivation of HIF-1 prevents the downregulation of Cav-1. Similarly, pharmacological inactivation of NF?B--another inducer of autophagy-prevents Cav-1 degradation. Moreover, treatment with an inhibitor of glutathione synthase, namely BSO, which induces oxidative stress via depletion of the reduced glutathione pool, is sufficient to induce the autophagic degradation of Cav-1. Thus, it appears that oxidative stress mediated induction of HIF1- and NF?B-activation in fibroblasts drives the autophagic degradation of Cav-1. In direct support of this hypothesis, we show that MCF7 cancer cells activate HIF-1?- and NF?B-driven luciferase reporters in adjacent cancer-associated fibroblasts, via a paracrine mechanism. Consistent with these findings, acute knock-down of Cav-1 in stromal fibroblasts, using an siRNA approach, is indeed sufficient to induce autophagy, with the upregulation of both lysosomal and mitophagy markers. How does the loss of stromal Cav-1 and the induction of stromal autophagy affect cancer cell survival? Interestingly, we show that a loss of Cav-1 in stromal fibroblasts protects adjacent cancer cells against apoptotic cell death. Thus, autophagic cancer-associated fibroblasts, in addition to providing recycled nutrients for cancer cell metabolism, also play a protective role in preventing the death of adjacent epithelial cancer cells. We demonstrate that cancer-associated fibroblasts upregulate the expression of TIGAR in adjacent epithelial cancer cells, thereby conferring resistance to apoptosis and autophagy. Finally, the mammary fat pads derived from Cav-1 (-/-) null mice show a hypoxia-like response in vivo, with the upregulation of autophagy markers, such as LC3 and BNIP3L. Taken together, our results provide direct support for the "Autophagic Tumor Stroma Model of Cancer Metabolism", and explain the exceptional prognostic value of a loss of stromal Cav-1 in cancer patients. Thus, a loss of stromal fibroblast Cav-1 is a biomarker for chronic hypoxia, oxidative stress and autophagy in the tumor microenvironment, consistent with its ability to predict early tumor recurrence, lymph node metastasis and tamoxifen-resistance in human breast cancers. Our results imply that cancer patients lacking stromal Cav-1 should benefit from HIF-inhibitors, NF?B-inhibitors, anti-oxidant therapies, as well as autophagy/lysosomal inhibitors. These complementary targeted therapies could be administered either individually or in combination, to prevent the onset of autophagy in the tumor stromal compartment, which results in a "lethal" tumor microenvironment.

Project description:BackgroundClaudin-18.2 (CLDN18.2) has emerged as an alluring therapeutic target against gastrointestinal tumors in recent years. However, a thorough understanding of its regulatory mechanism in gastric cancer remains elusive.MethodsWe presented a comprehensive study comprising 185 gastric cancer patients, which included 112 cases with high CLDN18.2 expression and 73 cases with low CLDN18.2 expression as determined by immunohistochemistry. After overdressed CLDN18.2 in AGS and NUGC4 cell lines, we elucidated the functions of CLDN18.2 in connecting gastric cancer cells and cancer-associated fibroblasts (CAFs) through an in vitro adhesion models and in vivo lung colonization models. The molecular mechanism underlying CLDN18.2-mediated interaction between gastric cancer cells and CAFs was identified through RNA sequencing and protein-proximity labeling techniques in vivo.ResultsIn our own cohort, a correlation was observed between high levels of CLDN18.2 expression and advanced cancer stage, poor prognosis, and heightened infiltration of CAFs. We elucidated a pivotal role of CLDN18.2 in mediating adhesion between gastric cancer cells and CAFs, which leads to the adhesion of cancer cells to stroma tissue and facilitates the clustering of cancer cells and CAFs into embolus, enhancing gastric cancer's metastatic progression and the risk of embolic death. Mechanistically, it was discovered that CAFs can activate adhesion and metastasis-related signaling pathways in CLDN18.2-positive gastric cancer cells. Furthermore, using an in vivo protein-proximity labeling approach, we identified S100 calcium binding protein A4 (S100A4) as a distinctive marker of CAFs that interacts with CLDN18.2 to enhance gastric cancer progression.ConclusionsOur findings illuminated the role of the CLDN18.2-mediated interaction between cancer cells and CAFs in promoting gastric cancer progression and embolism, thereby providing insight into potential therapeutic avenues for CLDN18.2 positive cancers. Video Abstract.

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Dataset Information

HIF1-alpha functions as a tumor promoter in cancer associated fibroblasts, and as a tumor suppressor in breast cancer cells: Autophagy drives compartment-specific oncogenesis.

Publications

HIF1-alpha functions as a tumor promoter in cancer associated fibroblasts, and as a tumor suppressor in breast cancer cells: Autophagy drives compartment-specific oncogenesis.

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