Mechanism Of PPARδ On Cancer Cell Autophagy Suppression

Backgroud:Peroxisome-proliferator-activated receptors（PPARs）consist of PPARα,PPARγ,PPARδ,which play an important role in regulating metabolism,inflammation,and tumorigenesis.Ligand binding and activated PPARs form a PPARs/RXRs heterodimer that regulates downstream targeted gene expressions.Our previous studies show that PPARδpromotes cancer cell metabolism and colitis-associated colon cancer.In contrast,PPARαinhibits tumor growth by autophagy induction,while it is unclear the effect of PPARδon cancer cell autophagy.Autophagy is a conserved catabolic process in eukaryotic cells,which delivers cytoplasmic materials（proteins,lipids）or organelles（mitochondria,nuclei and ribosomes）into lysosome for degradation.In addition,ATG7 plays an important role in autophagy formation.Therefore,the interaction of PPARδwith ATG7 on the effect of cancer cell autophagy was investigated.Methods:PPARδ^-/-SW480 cells were performed by CRISPR/Cas9.PPARδsh RNA or PPARδplasmids were constructed and transfected into cancer cells.Immunofluorescence analysis was used to detect autophagosome.Western blot and fluorescence quantitative PCR analysis were used to detect protein and gene expressions.Xenograft tumor model was used to analyze tumor growth.Results:Western blot analysis showed that PPARδknockout or silenced cancer cells increased LC3-II accumulation and autophagosome formation.In contrast,overexpression of PPARδreversed this event.Fluorescence quantitative PCR analysis showed that overexpression of PPARδinhibited ATG7 gene expression,consequently,reduced ATG7 protein expression.In contrast,PPARδknockout or silenced cancer cells reversed this event.Xenograft tumor model analysis showed that PPARδpromoted tumor growth and reduced ATG7 expression and LC3-II accumulation in tumor lysastes.Furthermore,PPARδagonist GW501516 decreased ATG7 expression and LC3-II accumulation in cancer cells.Xenograft tumor model analysis showed that PPARδagonist GW501516 promoted tumor growth and reduced ATG7 expression and LC3-II accumulation in tumor lysates by Western blot analysis.Conclusions:PPARδpromoted tumor gowth,which was involved in autophagy inhibition by reducing ATG7 expression.In addition,PPARδagonist GW501516enhanced this event.