Hypoxia inducible NOD2 interacts with 3-O-sulfogalactoceramide and regulates vesicular homeostasis.
BACKGROUND
Oxygen sensing in mammalian cells is a conserved signaling pathway regulated by hypoxia inducible factor type 1 (HIF-1). Inadequate oxygen supply (hypoxia) is common to many pathological disorders where autophagy plays an import role. The aim of this study was the identification and characterization of novel HIF-1 target genes that promote autophagy during hypoxia.


METHODS
Whole genome Chromatin Immune Precipitation from hypoxic HeLa cells was used to identify novel HIF-1 target genes. Hypoxia induced expression and transcription regulation was studied in wild type and HIF-deficient cells. siRNA silencing of candidate genes was used to establish their role during autophagy. Recombinant protein was used for screening immobilized glycosylated lipids to identify potential ligands.


RESULTS
We identified the Nucleotide Oligomerization Domain 2 (NOD2/CARD15) as a novel HIF-1 target and 3-O-sulfo-galactoceramide (sulfatide) and Mycobacterium sp. specific sulfolipid-1 as the first NOD2 ligands that both compete for binding to NOD2. Loss of NOD2 function impaired autophagy upstream of the autophagy inhibitor chloroquine by reducing the number of acidic vesicles. Inhibition of sulfatide synthesis elicited defects in autophagy similar to the NOD2 loss of function but did not influence NOD2-mediated NF-kB signaling.


CONCLUSIONS
Our findings suggest that the interaction of NOD2 with sulfatide may mediate the balance between autophagy and inflammation in hypoxic cells.


GENERAL SIGNIFICANCE
These findings may lead to a better understanding of complex inflammatory pathologies like Crohn's disease and tuberculosis where both NOD2 and hypoxia are implicated.
['Nabatov|Alexey A|AA|', 'Hatzis|Pantelis|P|', 'Rouschop|Kasper M A|KM|', 'van Diest|Paul|P|', 'Vooijs|Marc|M|']
D001343:Autophagy D015687:Cell Hypoxia D002460:Cell Line D045744:Cell Line, Tumor D048749:Cytokinesis D006017:Glycolipids D057809:HEK293 Cells D006367:HeLa Cells D006706:Homeostasis D006801:Humans D051795:Hypoxia-Inducible Factor 1, alpha Subunit D007249:Inflammation D008024:Ligands D016328:NF-kappa B D053473:Nod2 Signaling Adaptor Protein D015398:Signal Transduction D037521:Virulence Factors
Hypoxia NOD2 Autophagy Sulfatide Chloroquine Vesicle CQ LRR MDP Mtb Muramyl dipeptide Mycobacterium tuberculosis Nucleotide-binding oligomerization domain-containing protein 2 PRR SL-1 V-ATPase Vacuolar-type H(+)-ATPase leucine rich repeats mycobacteria specific Sulfolipid-1 pathogen recognition receptors