Regulation Of Hepatic Cholesteryl Ester Transfer Protein Expression And Reverse Cholesterol Transport By Inhibition Of DNA Topoisomerase Ⅱ

Cardiovascular disease is still a global threat to human health and life.Atherosclerosis is a major pathological basis of cardiovascular disease,and a complex pathological process which is involved by accumulation of lipids,inflammatory reaction,cell necrosis and fibrosis in the artery.Among which the abnormal lipid metabolism plays a key role in the formation and development of atherosclerotic lesions.In fact,enhancing reverse cholesterol transport(RCT)or cholesterol metabolism and lowering plasma lipid levels have demonstrated an inhibitory effect on atherosclerosis.Cholesteryl ester transfer protein(CETP)transfers cholesteryl ester(CE)from high-density lipoprotein(HDL)to apoB-containing lipoproteins,such as low-density lipoprotein(LDL)and very low-density lipoprotein(VLDL),in exchange for triglycerides(TG).Then the CE in LDL can be uptake by the liver for subsequent metabolism though action of the LDL receptor.Moreover,CETP can increase a direct removal of HDL-CE in the liver in the manners which are independent of the established lipoprotein receptors.Thus,CETP has an important role in RCT and cholesterol metabolism.CETP is predominantly expressed by the liver and then secreted into plasma where CETP is mainly associated with HDL and apoB-containing lipoproteins.CETP expression can be transcriptionally activated by liver X receptors α and β(LXR),the ligand-activated transcription factors,because of the existence of the LXR responsive element(LXRE)in the CETP promoter.DNA topoisomerases ⅡA and ⅡB(Topo Ⅱ)are ubiquitous enzymes and regulates topological rearrangement of DNA during replication,transcription and separation of daughter chromosomes at mitosis.Since Topo Ⅱ is vital for cell survival and tumor cells always exert an abnormal Topo Ⅱ activity,Topo Ⅱ is a promising molecular target for cancer chemotherapy,and some Topo Ⅱ inhibitors,such as etoposide(VP-16)and teniposide(VM-26),have been used to treat various cancers for many years.In spite of the functions of etoposide and teniposide in cancer biology and immunology have been well defined,the importance of Topo Ⅱ inhibitors in other fields still remains unknown.Etoposide has been reported to reduce atherosclerotic lesions in cholesterol-fed rabbits with un-fully elucidated mechanisms.We hypothesized that DNA topoisomerase Ⅱ inhibitors are able to promote cholesterol efflux and metabolism,thereby inhibiting the development of atherosclerosis.In this study,we determined if Topo Ⅱ activity can influence cholesterol metabolism by regulating hepatic CETP expression.We found that inactivation of Topo Ⅱ by etoposide or teniposide and inhibition of Topo Ⅱ expression by siRNA increased CETP expression in human hepatic cell line,HepG2 cells,which was associated with increased CETP secretion and mRNA expression.Meanwhile,inhibition of LXR expression by siRNA attenuated CETP expression induced by etoposide and teniposide.Etoposide and teniposide induced LXRα expression and LXRα/β nuclear translocation while inhibiting expression of receptor interacting protein 140(RIP140),an LXR co-repressor gene.In vivo,administration of teniposide moderately reduced serum lipid profiles,induced CETP expression in the liver,and activated RCT in CETP transgenic mice.Taken together,our study demonstrates that etoposide and teniposide can induce heptic CETP expression,which may promote RCT and reduce the lipid levels in peripheral tissues thereby lowering the risk of atheroslclerosis.Our study reveals an important function of Topo Ⅱ in regulating cholesterol metabolism,and provides new theory in the application of Topo Ⅱ inhibitor in the treatment of the atherosclerosis.