Mechanism Of AMPK/PPARδ Signaling Pathway Inhibits Tumor Growth

PPARδ belongs to the peroxisome-proliferator-activated receptors(PPARs)family,which promotes tumorigenesis.Our previous studies show that PPARδ promotes the development of colon cancer,which is associated with increased glucose and glutamine metabolic pathway.As a serine/threonine kinase,AMPK can induce substrate phosphorylation and regulate the metabolism of cells and organisms in eukaryotes,while it is still unclear the effect of AMPK/PPARδ pathway on cancer cell metabolism and tumor progression.Here we found that AMPK induced PPARδ-S50 phosphorylation leading to inhibition of p62/SQSTM1-mediated misfolded PPARδ autophagic degradation,subsequently,suppressed PPARδ activity and tumor growth.The significant findings were as follows.1.Metformin treatment activated AMPK and increased PPARδ protein levels.Immunoprecipitation analysis showed that activated AMPK bound to PPARδ and induced PPARδ phosphorylation.Further detection by using LC/MS/MS,site-directed mutagenesis and in vitro kinase assay showed that AMPK induced PPARδ-S50 phosphorylation.2.Analysis by using half-life and extraction of soluble and insoluble protein showed that AMPK induced insoluble PPARδ-S50 phosphorylation leading to inhibiton of misfolded PPARδ protein degradation by p62/SQSTM1.3.AMPK-induced PPARδ-S50 phosphorylation decreased the activity of PPARδ leading to inhibition of Glut1 and SLC1A5 expressions,subsequently reduced cancer cell glucose consumption,glutamine uptake and lactate release.4.The analysis of soft agar and xenograft mice model showed that PPARδ-S50 phosphorylation significantly inhibited cancer cell proliferation and tumor growth,which was related to the inhibition of metabolic pathway in cancer cells.In summary,this study has determined that AMPK induced PPARδ-S50 phosphorylation resulting in the accumulation of misfolded PPARδ protein and inhibition of PPARδ activity,subsequently,suppressed PPARδ-mediated cancer cell metabolism and tumor growth.These findings revealed a new mechanism of AMPK/PPARδ pathway-mediated tumor suppression.