Expression of the pro-angiogenic factors vascular endothelial growth factor and interleukin-8/CXCL8 by human breast carcinomas is responsive to nutrient deprivation and endoplasmic reticulum stress.
BACKGROUND
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. 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-kappaB). 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-kappaB 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.


RESULTS
We 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).


CONCLUSIONS
These 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.
Marjon
Philip L
PL
University of New Mexico, School of Medicine, Department of Biochemistry and Molecular Biology, Albuquerque, NM 87131, USA. pmarjon@salud.unm.edu
Bobrovnikova-Marjon
Ekaterina V
EV
Abcouwer
Steve F
SF
D000230:Adenocarcinoma / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism; D001943:Breast Neoplasms / Q000378:metabolism*; D022762:CCAAT-Enhancer-Binding Proteins / Q000096:biosynthesis; D015687:Cell Hypoxia / Q000187:drug effects / Q000502:physiology; D003035:Cobalt / Q000494:pharmacology; D004249:DNA Damage / Q000187:drug effects / Q000502:physiology; D004273:DNA, Neoplasm / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D005947:Glucose / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D006801:Humans; D016209:Interleukin-8 / Q000096:biosynthesis* / Q000378:metabolism; D009389:Neovascularization, Pathologic; D012333:RNA, Messenger / Q000096:biosynthesis; D012334:RNA, Neoplasm / Q000096:biosynthesis; D051742:Transcription Factor CHOP; D014157:Transcription Factors / Q000096:biosynthesis; D014407:Tumor Cells, Cultured; D014415:Tunicamycin / Q000494:pharmacology; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology; D042442:Vascular Endothelial Growth Factors / Q000096:biosynthesis* / Q000378:metabolism
D000596:Amino Acids; D022762:CCAAT-Enhancer-Binding Proteins; C497249:DDIT3 protein, human; D004273:DNA, Neoplasm; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D016209:Interleukin-8; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D014157:Transcription Factors; D042442:Vascular Endothelial Growth Factors; D005973:Glutamine; D014415:Tunicamycin; D051742:Transcription Factor CHOP; D003035:Cobalt; C018021:cobaltous chloride; D005947:Glucose