ITEM METADATA RECORD
Title: The role of PHD2 in breast cancer metastasis.
Other Titles: De rol van PHD2 in borstkanker metastase
Authors: Kuchnio, Anna
Issue Date: 29-Apr-2015
Abstract: Breast cancer (BC) is the most frequently diagnosed cancer in women in the US and Europe, affecting one in eight women. Despite improvements in radiotherapy, cytotoxic, hormonal, and targeted therapies, BC remains the second leading cause of cancer deaths in women, exceeded only by lung cancer. Metastatic relapse is a main cause of this high mortality, and occurs up to long periods of time after the removal of the primary tumor. Understanding the mechanisms that control metastasis is therefore pivotal for the design of improved and safe breast cancer treatment regimen.
Hypoxia is a characteristic feature of most solid tumors, including BC, and is a strong stimulus of tumor cell invasion and metastasis. Hypoxia signaling regulates nearly every single step of the metastatic cascade, including epithelial-to-mesenchymal transition (EMT), intravasation, survival in the circulation, formation of the pre-metastatic niche, and growth from micro- to macro-metastatic lesions. Furthermore, hypoxic tumors display lower sensitivity to treatment, leading to poor prognosis. The hypoxia-inducible transcription factors (HIFs) mediate a variety of cellular adaptations to hypoxia. Prolyl-hydroxylases (PHD1-3) are oxygen sensors that regulate HIF levels in normoxia by targeting it for proteasomal degradation. Despite the crucial role of PHD2 as an oxygen sensor, its role in tumor growth and metastasis in general and of BC in particular, remains largely debated. Studies from our and other research teams on PHD2 in cancer yielded interesting results, highlighting different possible roles of PHD2 that may be cell-type dependent. On the one hand, the host lab demonstrated that haplodeficiency of PHD2 selectively in endothelial cells (ECs) reduced metastasis without affecting tumor growth, by normalizing the abnormal tumor vessels and reducing tumor cell intravasation, suggesting that PHD2 could be an anti-BC drug target. Using transplantable tumor models, others reported that silencing of PHD2 in cancer cells either increased or decreased tumor growth with different underlying mechanisms. Dissection of the role of PHD2 in conditions that allow the evaluation of cell-intrinsic effects as well as the impact of bidirectional tumor / stroma cross-talk, remains strongly warranted. This is particularly relevant in light of pharmacological PHD2 blockade, which would target PHD2 in all cells inside the tumor. Furthermore, the studies mentioned above only used transplantable tumor models. The role of PHD2 in breast cancer using a clinically more relevant spontaneously arising BC model thus remains undefined.
In this study, we utilized the spontaneously arising PyMT-oncogene driven breast cancer model and intercrossed this transgenic line with mice with heterozygous gene deficiency of PHD2 (PHD2+/- mice; named PyMT+/- mice upon intercross with the the PyMT line). Tumor growth was unaffected, but metastasis and intravasation were reduced in PyMT+/- mice as compared to control mice (PyMT mice intercrossed with PHD2 wild type mice; named PyMT+/+ mice). Applying genetic strategies in vivo and in vitro, we show that this reduction in metastasis and intravasation can be ascribed to two independent mechanisms. First, we show that global “genetic targeting” of PHD2 in the entire tumor in PyMT+/- mice induces tumor vessel normalization (a.o. tighter endothelial lining, improved pericyte coverage, better perfused), similar to selective PHD2 haplodeficiency in ECs in xenograft models. Secondly, reduction in metastasis was also attributable to reduced activation of cancer-associated fibroblasts (CAFs). As compared to PyMT+/+ tumors, PyMT+/- tumors contained fewer activated CAFs, which deposited less cross-linked collagen matrix and contracted the collagen matrix less. These processes are known to induce cancer cell invasion. We showed that reduced CAF activation was independent of PHD2 level in fibroblasts, but reliant on the level of PHD2 in cancer cells. PHD2 haplodeficiency in cancer cells lowered the release of TGF-b1 and diminished the differentiation of normal fibroblasts to activated CAFs.
Taken together, these results provide evidence that PHD2 is a potential therapeutical target; the inhibition of which can offer substantial anti-metastatic benefit. Additionally, improved vessel function in spontaneously developing tumor model by PHD2 haplodeficiency could increase chemotherapy delivery and thus provide an advantage during surgical tumor resection.
Hypoxia is a characteristic feature of most solid tumors, including BC, and is a strong stimulus of tumor cell invasion and metastasis. Hypoxia signaling regulates nearly every single step of the metastatic cascade, including epithelial-to-mesenchymal transition (EMT), intravasation, survival in the circulation, formation of the pre-metastatic niche, and growth from micro- to macro-metastatic lesions. Furthermore, hypoxic tumors display lower sensitivity to treatment, leading to poor prognosis. The hypoxia-inducible transcription factors (HIFs) mediate a variety of cellular adaptations to hypoxia. Prolyl-hydroxylases (PHD1-3) are oxygen sensors that regulate HIF levels in normoxia by targeting it for proteasomal degradation. Despite the crucial role of PHD2 as an oxygen sensor, its role in tumor growth and metastasis in general and of BC in particular, remains largely debated. Studies from our and other research teams on PHD2 in cancer yielded interesting results, highlighting different possible roles of PHD2 that may be cell-type dependent. On the one hand, the host lab demonstrated that haplodeficiency of PHD2 selectively in endothelial cells (ECs) reduced metastasis without affecting tumor growth, by normalizing the abnormal tumor vessels and reducing tumor cell intravasation, suggesting that PHD2 could be an anti-BC drug target. Using transplantable tumor models, others reported that silencing of PHD2 in cancer cells either increased or decreased tumor growth with different underlying mechanisms. Dissection of the role of PHD2 in conditions that allow the evaluation of cell-intrinsic effects as well as the impact of bidirectional tumor / stroma cross-talk, remains strongly warranted. This is particularly relevant in light of pharmacological PHD2 blockade, which would target PHD2 in all cells inside the tumor. Furthermore, the studies mentioned above only used transplantable tumor models. The role of PHD2 in breast cancer using a clinically more relevant spontaneously arising BC model thus remains undefined.
In this study, we utilized the spontaneously arising PyMT-oncogene driven breast cancer model and intercrossed this transgenic line with mice with heterozygous gene deficiency of PHD2 (PHD2+/- mice; named PyMT+/- mice upon intercross with the the PyMT line). Tumor growth was unaffected, but metastasis and intravasation were reduced in PyMT+/- mice as compared to control mice (PyMT mice intercrossed with PHD2 wild type mice; named PyMT+/+ mice). Applying genetic strategies in vivo and in vitro, we show that this reduction in metastasis and intravasation can be ascribed to two independent mechanisms. First, we show that global “genetic targeting” of PHD2 in the entire tumor in PyMT+/- mice induces tumor vessel normalization (a.o. tighter endothelial lining, improved pericyte coverage, better perfused), similar to selective PHD2 haplodeficiency in ECs in xenograft models. Secondly, reduction in metastasis was also attributable to reduced activation of cancer-associated fibroblasts (CAFs). As compared to PyMT+/+ tumors, PyMT+/- tumors contained fewer activated CAFs, which deposited less cross-linked collagen matrix and contracted the collagen matrix less. These processes are known to induce cancer cell invasion. We showed that reduced CAF activation was independent of PHD2 level in fibroblasts, but reliant on the level of PHD2 in cancer cells. PHD2 haplodeficiency in cancer cells lowered the release of TGF-B1 and diminished the differentiation of normal fibroblasts to activated CAFs.
Taken together, these results provide evidence that PHD2 is a potential therapeutical target; the inhibition of which can offer substantial anti-metastatic benefit. Additionally, improved vessel function in spontaneously developing tumor model by PHD2 haplodeficiency could increase chemotherapy delivery and thus provide an advantage during surgical tumor resection.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Laboratory of Angiogenesis and Vascular Metabolism (Vesalius Research Center) (+)

Files in This Item:
File Status SizeFormat
Thesis AK final RS.pdf Published 3459KbAdobe PDFView/Open Request a copy

These files are only available to some KU Leuven Association staff members

 




All items in Lirias are protected by copyright, with all rights reserved.