Enhanced endoplasmic reticulum （ER）-associated protein degradation （ERAD） activity by the unfolded protein response （UPR） represents one of the mechanisms for restoring ER homeostasis. In vitro evidence indicate...Enhanced endoplasmic reticulum （ER）-associated protein degradation （ERAD） activity by the unfolded protein response （UPR） represents one of the mechanisms for restoring ER homeostasis. In vitro evidence indicates that the mammalian gp78 protein is an E3 ubiquitin ligase that facilitates ERAD by polyubiquitinating and targeting proteins for proteasomal degradation under both physiologic and stress conditions. However, the in vivo function of gp78 in maintaining ER protein homeostasis remains untested. Here we show that like its mammalian counterpart, the zebrafish gp78 is also an E3 ubiquitin ligase as revealed by in vitro ubiquitination assays. Expression analysis uncovered that gp78 is highly expressed in several organs, including liver and brain, of both larval and adult fish. Treatment of larvae or adult fish with tunicamycin induces ER stress and upregulates the expression of several key components of the gp78 ERAD complex in the liver. Moreover, liver-specific overexpression of the dominant-negative form of gp78 （gp78-R2M） renders liver more sensitive to tunicamycin-induced ER stress and enhances the expression of sterol response element binding protein （Srebp）-target genes, which was largely suppressed in fish overexpressing wild-type gp78. Together, these data indicate that gp78 plays a critical role in protecting against ER stress in liver.展开更多
The hepatic endoplasmic reticulum(ER)-anchored cytochromes P450(P450s)are mixedfunction oxidases engaged in the biotransformation of physiologically relevant endobiotics as well as of myriad xenobiotics of therapeutic...The hepatic endoplasmic reticulum(ER)-anchored cytochromes P450(P450s)are mixedfunction oxidases engaged in the biotransformation of physiologically relevant endobiotics as well as of myriad xenobiotics of therapeutic and environmental relevance.P450 ER-content and hence function is regulated by their coordinated hemoprotein syntheses and proteolytic turnover.Such P450 proteolytic turnover occurs through a process known as ER-associated degradation(ERAD)that involves ubiquitindependent proteasomal degradation(UPD)and/or autophagic-lysosomal degradation(ALD).Herein,on the basis of available literature reports and our own recent findings of in vitro as well as in vivo experimental studies,we discuss the therapeutic and pathophysiological implications of altered P450 ERAD and its plausible clinical relevance.We specifically(i)describe the P450 ERAD-machinery and how it may be repurposed for the generation of antigenic P450 peptides involved in P450 autoantibodypathogenesis in drug-induced acute hypersensitivity reactions and liver injury,or viral hepatitis;(ⅱ)discuss the relevance of accelerated or disrupted P450-ERAD to the pharmacological and/or toxicological effects of clinically relevant P450 drug substrates;and(ⅲ)detail the pathophysiological consequences of disrupted P450 ERAD,contributing to non-alcoholic fatty liver disease(NAFLD)/non-alcoholic steatohepatitis(NASH)under certain synergistic cellular conditions.展开更多
基金supported by the National Science Foundation(No.1120833)to SFa research grant (MB-8716-08) from United States-Israel Binational Agriculture Research and Development Fund to SD
文摘Enhanced endoplasmic reticulum （ER）-associated protein degradation （ERAD） activity by the unfolded protein response （UPR） represents one of the mechanisms for restoring ER homeostasis. In vitro evidence indicates that the mammalian gp78 protein is an E3 ubiquitin ligase that facilitates ERAD by polyubiquitinating and targeting proteins for proteasomal degradation under both physiologic and stress conditions. However, the in vivo function of gp78 in maintaining ER protein homeostasis remains untested. Here we show that like its mammalian counterpart, the zebrafish gp78 is also an E3 ubiquitin ligase as revealed by in vitro ubiquitination assays. Expression analysis uncovered that gp78 is highly expressed in several organs, including liver and brain, of both larval and adult fish. Treatment of larvae or adult fish with tunicamycin induces ER stress and upregulates the expression of several key components of the gp78 ERAD complex in the liver. Moreover, liver-specific overexpression of the dominant-negative form of gp78 （gp78-R2M） renders liver more sensitive to tunicamycin-induced ER stress and enhances the expression of sterol response element binding protein （Srebp）-target genes, which was largely suppressed in fish overexpressing wild-type gp78. Together, these data indicate that gp78 plays a critical role in protecting against ER stress in liver.
基金supported by NIDDK Center Grant DK26743supported by NIH Grants GM44037 and DK26506(USA)to Maria Almira Correia.
文摘The hepatic endoplasmic reticulum(ER)-anchored cytochromes P450(P450s)are mixedfunction oxidases engaged in the biotransformation of physiologically relevant endobiotics as well as of myriad xenobiotics of therapeutic and environmental relevance.P450 ER-content and hence function is regulated by their coordinated hemoprotein syntheses and proteolytic turnover.Such P450 proteolytic turnover occurs through a process known as ER-associated degradation(ERAD)that involves ubiquitindependent proteasomal degradation(UPD)and/or autophagic-lysosomal degradation(ALD).Herein,on the basis of available literature reports and our own recent findings of in vitro as well as in vivo experimental studies,we discuss the therapeutic and pathophysiological implications of altered P450 ERAD and its plausible clinical relevance.We specifically(i)describe the P450 ERAD-machinery and how it may be repurposed for the generation of antigenic P450 peptides involved in P450 autoantibodypathogenesis in drug-induced acute hypersensitivity reactions and liver injury,or viral hepatitis;(ⅱ)discuss the relevance of accelerated or disrupted P450-ERAD to the pharmacological and/or toxicological effects of clinically relevant P450 drug substrates;and(ⅲ)detail the pathophysiological consequences of disrupted P450 ERAD,contributing to non-alcoholic fatty liver disease(NAFLD)/non-alcoholic steatohepatitis(NASH)under certain synergistic cellular conditions.
