ABSTRACT
IκB kinase ε (IKKε) is a key molecule at the crossroads of inflammation and cancer. Known to regulate cytokine secretion via NFκB and IRF3, the kinase is also a breast cancer oncogene, overexpressed in a variety of tumours. However, to what extent IKKε remodels cellular metabolism is currently unknown. Here, we used metabolic tracer analysis to show that IKKε orchestrates a complex metabolic reprogramming that affects mitochondrial metabolism and consequently serine biosynthesis independently of its canonical signalling role. We found that IKKε upregulates the serine biosynthesis pathway (SBP) indirectly, by limiting glucose-derived pyruvate utilisation in the TCA cycle, inhibiting oxidative phosphorylation. Inhibition of mitochondrial function induces activating transcription factor 4 (ATF4), which in turn drives upregulation of the expression of SBP genes. Importantly, pharmacological reversal of the IKKε-induced metabolic phenotype reduces proliferation of breast cancer cells. Finally, we show that in a highly proliferative set of ER negative, basal breast tumours, IKKε and PSAT1 are both overexpressed, corroborating the link between IKKε and the SBP in the clinical context.
Subject(s)
Breast Neoplasms , I-kappa B Kinase , Mitochondria , Serine/biosynthesis , Breast Neoplasms/genetics , Female , Humans , I-kappa B Kinase/genetics , Mitochondria/genetics , Mitochondria/metabolism , Oncogenes/geneticsABSTRACT
OBJECTIVES: The objective of this study was to investigate how mast cell tryptase may influence intestinal permeability and tight junction (TJ) proteins in vitro and explore translation to irritable bowel syndrome (IBS). METHODS: We investigated the effect of: (1) tryptase on Caco-2 monolayers, (2) mast cell degranulation in a Caco-2/human mast cell-1 (HMC-1) co-culture model, (3) mast cell degranulation±tryptase inhibition with nafamostat mesilate (NM). Epithelial integrity was assessed by transepithelial resistance (TER), permeability to fluorescein isothiocyanate (FITC)-dextran and transmission electron microscopy (TEM). The expression of junctional proteins zonula occludens-1 (ZO-1), junctional adhesion molecule-A (JAM-A), claudin-1 (CLD-1), CLD-2, CLD-3, occludin and E-cadherin was determined by western blot analysis and immunofluorescence confocal microscopy. Based on the in vitro results, we further assessed JAM-A expression in biopsy tissue (cecum) from 34 IBS patients, 12 controls, and 8 inflammatory controls using immunofluorescence confocal microscopy and explored associations between JAM-A and IBS symptoms. RESULTS: ptase disrupted epithelial integrity in Caco-2 monolayers as shown by a significant decrease in TER, an increase in permeability to FITC-dextran, and a decrease in the expression of junctional proteins JAM-A, CLD-1, and ZO-1 within 24 h. Correspondingly, in the Caco-2/HMC-1 co-culture model we showed a significant decrease in TER, an increase in permeability to FITC-dextran, and the presence of open TJs (TEM) in response to mast cell degranulation within 24 h. In this co-culture model, mast cell degranulation significantly decreased JAM-A and CLD-1 protein expression at 24 h. Tryptase inhibition (NM) significantly reduced the effect of mast cell degranulation on the junctional protein JAM-A, TER, and FITC-dextran flux. In IBS, epithelial JAM-A protein expression was significantly reduced in IBS tissue compared with controls. Lower JAM-A expression was associated with more severe abdominal pain (rs=-0.69, P=0.018) and longer duration of symptoms (rs=-0.7, P=0.012) in IBS-alternating subtype. CONCLUSIONS: uced JAM-A expression in vitro appears to contribute to the underlying mechanisms of altered epithelial integrity in response to tryptase released from degranulating mast cells. In IBS, JAM-A expression was significantly reduced in the cecal epithelium and associated with abdominal pain severity. JAM-A may provide new insights into the underlying mechanisms in IBS.
Subject(s)
Cell Adhesion Molecules/metabolism , Dextrans/pharmacokinetics , Fluorescein-5-isothiocyanate/analogs & derivatives , Irritable Bowel Syndrome/metabolism , Irritable Bowel Syndrome/physiopathology , Mast Cells/enzymology , Receptors, Cell Surface/metabolism , Tryptases/metabolism , Abdominal Pain/etiology , Adult , Caco-2 Cells/metabolism , Cadherins/metabolism , Claudins/metabolism , Coculture Techniques , Female , Fluorescein-5-isothiocyanate/pharmacokinetics , Humans , Intercellular Junctions/metabolism , Irritable Bowel Syndrome/complications , Male , Microscopy, Electron, Transmission , Middle Aged , Occludin/metabolism , Permeability , Severity of Illness Index , Time Factors , Zonula Occludens-1 Protein/metabolismABSTRACT
During obesity, macrophages infiltrate the breast tissue leading to low-grade chronic inflammation, a factor considered responsible for the higher risk of breast cancer associated with obesity. Here, we formally demonstrate that breast epithelial cells acquire malignant properties when exposed to medium conditioned by macrophages derived from human healthy donors. These effects were mediated by the breast cancer oncogene IKKε and its downstream target-the serine biosynthesis pathway as demonstrated by genetic or pharmacological tools. Furthermore, amlexanox, an FDA-approved drug targeting IKKε and its homologue TBK1, delayed in vivo tumour formation in a combined genetic mouse model of breast cancer and high-fat diet-induced obesity/inflammation. Finally, in human breast cancer tissues, we validated the link between inflammation-IKKε and alteration of cellular metabolism. Altogether, we identified a pathway connecting obesity-driven inflammation to breast cancer and a potential therapeutic strategy to reduce the risk of breast cancer associated with obesity.