The Mechanism Of Peroxisome-mediated Lipid Degradation On Serine Deprivation Sensitivity Of Tumor Cells

BackgroundSerine is essential for the rapid proliferation of tumor cells.Serine is an important one-carbon unit donor that participates in the folate cycle and supports tumor cell proliferation by participating in biomolecule synthesis and maintaining cellular redox homeostasis.Therefore,serine deprivation strategies show potential for clinical application,but the related drugs and dietary therapies had not been practically used in clinical treatment.Further studies have revealed that tumor cells can adapt to serine deprivation microenvironment through their own genetic and metabolic alterations.For example,tumor cells containing TP53 reduce the sensitivity of tumor cells to serine deprivation by inhibiting the cell cycle and maintaining cellular redox homeostasis.Thus,it is crucial that explore new mechanisms of tumor cell resistance to serine deprivation.It can help serine deprivation therapy be more effectively applied to the clinical.Current studies on tumors escaping from serine deprivation have mainly focused on tumor cells of the same tissue origin,while there are few studies on the effects of serine deprivation on tumor cells of different tissue origin.Purpose of the studyThe purpose of this study was to elucidate the differences in the response of tumor cells of different tissue origins to serine deprivation,to reveal new mechanisms by which tumor cells resist serine deprivation,and to explore new methods to enhance the therapeutic effects of serine deprivation on tumors.Experimental methods and resultsTo investigate the sensitivity of tumor cells derived from different tissues to serine deprivation,we first established a cell model of serine deprivation,i.e.A549,HT1080,HCT116,HeLa and HepG2 cells cultured in serine deficient medium.First,we performed preliminary exploration using crystalline violet staining,CCK8,flow cytometry,RT-PCR,and Western blot.The results showed that HepG2 cells were insensitive to serine deprivation.And ATP and total NADP were maintained normal in HepG2 cells after serine deprivation,while A549,HT1080,HCT116 and HeLa cells had significantly lower levels of ATP as well as total NADP.In-depth studies by flow cytometry and immunofluorescence revealed that the lipid content in HepG2 was significantly higher than that in other tumor cells.Moreover,TCGA database analysis revealed that the expression of lipid droplets(LDs)marker proteins was also higher in LIHC than in other tumor tissues.Finally,rescue experiments confirmed that the exogenous addition of lipids could reduce the sensitivity of A549 to serine deprivation and maintain their energy and redox homeostasis.Meanwhile blocking the fatty acid oxidation process in HepG2 could enhance their sensitivity to serine deprivation and disrupt the energy and redox homeostasis of the cells.To identify the sites of fatty acid metabolism,we used lipid metabolism sequencing,immunofluorescence,lipid tracing,Western blot and TCGA database analysis to explore,which showed that serine deprivation promoted lipid transport from LDs to peroxisomes in HepG2 cells and that peroxisomal marker proteins were significantly higher in HepG2 cells than in other tumor cells,which indicated that peroxisomes might involve in serine deprivation-induced fatty acid oxidation.Further experiments confirmed that decreasing the number of peroxisomes enhanced the sensitivity of HepG2 to serine deprivation and increasing the number of peroxisomes decreased the sensitivity of A549 to serine deprivation.Conclusions and implications1.This study found that the sensitivity of different types of tumor cells to serine deprivation is different and intervention in fatty acid oxidation influences the sensitivity of tumor cells to serine deprivation.2.Peroxisome is involved in the degradation of fatty acids in tumor cells under serine deprivation,and reducing the number of peroxisomes in tumor cells also enhances the sensitivity of tumor cells to serine deprivation.Thus,our study provides a theoretical basis for the application of serine deprivation in tumor therapy,which,in particular,is important for the treatment of lipid-rich tumors.Limitations1.The specific molecular mechanism by which serine deprivation promotes peroxisomal-mediated fatty acid degradation was not elucidated.2.No relevant animal experiments were conducted in this study.3.The present study failed to distinguish the mitochondrial and peroxisomalmediated lipid degradation processes in detail.