Abstract
BackgroundThe expression of pro-angiogenic cytokines, such as vascular endothelial growth factor (VEGF) and interleukin-8/CXCL8 (IL-8), plays an important role in tumor growth and metastasis. Low oxygen tension within poorly-vascularized tumors is thought to be the prime stimulus causing the secretion of VEGF. The expression of IL-8 by solid tumors is thought to be primarily due to intrinsic influences, such as constitutive activation of nuclear factor kappa B (NF-κB). However, VEGF expression is responsive to glucose deprivation, suggesting that low concentrations of nutrients other than oxygen may play a role in triggering the pro-angiogenic phenotype. Glucose deprivation causes endoplasmic reticulum (ER) stress and alters gene expression through the unfolded protein response (UPR) signaling pathway. A branch of the UPR, known as the ER overload response (EOR), can cause NF-κB activation. Thus, we hypothesized that treatments that cause ER stress and deprivation of other nutrients, such as amino acids, would trigger the expression of angiogenic cytokines by breast cancer cell lines.ResultsWe found that glutamine deprivation and treatment with a chemical inducer of ER stress (tunicamycin) caused a marked induction of the secretion of both VEGF and IL-8 protein by a human breast adenocarcinoma cell line (TSE cells). Glutamine deprivation, glucose deprivation and several chemical inducers of ER stress increased VEGF and IL-8 mRNA expression in TSE and other breast cancer cell lines cultured under both normoxic and hypoxic conditions, though hypoxia generally diminished the effects of glucose deprivation. Of all amino acids tested, ambient glutamine availability had the largest effect on VEGF and IL-8 mRNA expression. The induction of VEGF mRNA expression, but not IL-8, was sustained and closely corresponded with the upregulated expression of the ER stress-responsive genes glucose-regulated protein 78 (GRP78) and growth arrest and DNA damage inducible gene 153 (GADD153).ConclusionThese results suggest that nutrient deprivation within the solid tumor microenvironment might contribute to the activation of a pro-angiogenic phenotype. The angiogenic switch may act to increase blood supply in response to nutrient deprivation as well as hypoxia.
Highlights
The expression of pro-angiogenic cytokines, such as vascular endothelial growth factor (VEGF) and interleukin-8/CXCL8 (IL-8), plays an important role in tumor growth and metastasis
Tunicamycin, and cobalt chloride on the secretion of VEGF and IL-8 protein by TSE cells To determine if VEGF and IL-8 proteins were secreted by TSE cells under stress, as induced by glutamine deprivation, tunicamycin, or hypoxia, triplicate confluent cultures of the various cell types were grown in 6-well plates and incubated with 3 mL per well of complete media containing 4 mM glutamine as a control, 0.25 mM glutamine, 5 μg/mL tunicamycin, or 100 μM CoCl2 for 24 hours
We propose that environmental factors other than hypoxia may contribute to induction of VEGF expression in the tumor environment
Summary
The expression of pro-angiogenic cytokines, such as vascular endothelial growth factor (VEGF) and interleukin-8/CXCL8 (IL-8), plays an important role in tumor growth and metastasis. Neoplastic progression includes genetic alterations that allow malignant cells to ignore normal growth controls For these cells, growth is limited by the delivery rate of oxygen and nutrients (such as glucose and amino acids) and removal rate of waste products (such as CO2 and lactic acid) [1]. As a tumor grows in size, the cancer cells and the stromal cells that surround them both experience progressive hypoxia, nutrient starvation and acidosis until the tumor microenvironment becomes deleterious to growth or even toxic [1] These cells survive and adapt to this ischemic environment by producing pro-angiogenic factors to initiate the formation and attraction of new blood vessels to the tumor [2]. An increase in the synthesis of pro-angiogenic factors is a natural cellular response to an ischemic environment [3]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
