Nuclear accumulation of active Smad complexes is crucial for transduction of transforming growth factor β （TGF-β）- superfamily signals from transmembrane receptors into the nucleus. It is now clear that the nucleo...Nuclear accumulation of active Smad complexes is crucial for transduction of transforming growth factor β （TGF-β）- superfamily signals from transmembrane receptors into the nucleus. It is now clear that the nucleocytoplasmic distributions of Smads, in both the absence and the presence of a TGF-β-superfamily signal, are not static, but instead the Smads are continuously shuttling between the nucleus and the cytoplasm in both conditions. This article presents the evidence for continuous nucleocytoplasmic shuttling of Smads. It then reviews different mechanisms that have been proposed to mediate Smad nuclear import and export, and discusses how the Smad steady-state distributions in the absence and the presence of a TGF-β-superfamily signal are established. Finally, the biological relevance of continuous nucleocytoplasmic shuttling for signaling by TGF-β superfamily members is discussed.展开更多
P68 RNA helicase is a prototypical DEAD box RNA helicase. The protein plays a very important role in early organ development and maturation. Consistent with the function of the protein in transcriptional regulation an...P68 RNA helicase is a prototypical DEAD box RNA helicase. The protein plays a very important role in early organ development and maturation. Consistent with the function of the protein in transcriptional regulation and pre-mRNA splicing, p68 was found to predominately localize in the cell nucleus. However, recent experiments demon- strate a transient cytoplasmic localization of the protein. We report here that p68 shuttles between the nucleus and the cytoplasm. The nucleocytoplasmic shuttling of p68 is mediated by two nuclear localization signal and two nuclear exporting signal sequence elements. Our experiments reveal that p68 shuttles via a classical RanGTPase-dependent pathway.展开更多
We study the evolution of a gynodioecious species under mixed-mating through a nucleocytoplasmic male sterility model. We consider two cytoplasmic types and a nuclear locus with two alleles. Here, the interaction betw...We study the evolution of a gynodioecious species under mixed-mating through a nucleocytoplasmic male sterility model. We consider two cytoplasmic types and a nuclear locus with two alleles. Here, the interaction between one cytoplasmic type and a recessive nuclear male-sterility factor gives rise to only one female genotype, while the remaining types correspond to hermaphroditic plants. We include two fitness paramaters: the advantageous female fitness t of females relative to that of hermaphrodites;and a silent and dominant cost of restoration, that is, a diminished fitness for plants carrying a dominant restorer gene relative to that of hermaphrodites. The parameter related to the cost of restoration is assumed to be present on outcrossing male fertility only. We find that every population converges to a stable population. We also determine the nature of the attracting stable population, which could be a nucleocytoplasmic polymorphism, a nuclear polymorphism or another population with some genotypes absent. This depends on the position of t with respect to critical values expressed in terms of the other parameters and also on the initial population.展开更多
Farnesoid X receptor(FXR)is widely accepted as a promising target for various liver diseases;however,panels of ligands in drug development show limited clinical benefits,without a clear mechanism.Here,we reveal that a...Farnesoid X receptor(FXR)is widely accepted as a promising target for various liver diseases;however,panels of ligands in drug development show limited clinical benefits,without a clear mechanism.Here,we reveal that acetylation initiates and orchestrates FXR nucleocytoplasmic shuttling and then enhances degradation by the cytosolic E3 ligase CHIP under conditions of liver injury,which represents the major culprit that limits the clinical benefits of FXR agonists against liver diseases.Upon inflammatory and apoptotic stimulation,enhanced FXR acetylation at K217,closed to the nuclear location signal,blocks its recognition by importin KPNA3,thereby preventing its nuclear import.Concomitantly,reduced phosphorylation at T442 within the nuclear export signals promotes its recognition by exportin CRM1,and thereby facilitating FXR export to the cytosol.Acetylation governs nucleocytoplasmic shuttling of FXR,resulting in enhanced cytosolic retention of FXR that is amenable to degradation by CHIP.SIRT1 activators reduce FXR acetylation and prevent its cytosolic degradation.More importantly,SIRT1 activators synergize with FXR agonists in combating acute and chronic liver injuries.In conclusion,these findings innovate a promising strategy to develop therapeutics against liver diseases by combining SIRT1 activators and FXR agonists.展开更多
Angiogenic factor with G-patch and FHA domains 1(AGGF1) exhibits a dynamic distribution from the nucleus to the cytoplasm in endothelial cells during angiogenesis, but the biological significance and underlying mechan...Angiogenic factor with G-patch and FHA domains 1(AGGF1) exhibits a dynamic distribution from the nucleus to the cytoplasm in endothelial cells during angiogenesis, but the biological significance and underlying mechanism of this nucleocytoplasmic transport remains unknown. Here, we demonstrate that the dynamic distribution is essential for AGGF1 to execute its angiogenic function. To search the structural bases for this nucleocytoplasmic transport, we characterized three potential nuclear localization regions, one potential nuclear export region, forkhead-associated(FHA), and G-patch domains to determine their effects on nucleocytoplasmic transport and angiogenesis, and we show that AGGF1 remains intact during the dynamic subcellular distribution and the region from 260 to 288 amino acids acts as a signal for its nuclear localization. The distribution of AGGF1 in cytoplasm needs both FHA domain and 14-3-3α/β. Binding of AGGF1 via FHA domain to 14-3-3α/β is required to complete the transport. Thus, we for the first time established structural bases for the nucleocytoplasmic transport of AGGF1 and revealed that the FHA domain of AGGF1 is essential for its nucleocytoplasmic transport and angiogenesis.展开更多
Bidirectional trafficking of macromolecules between the cytoplasm and the nucleus is mediated by the nuclear pore complexes(NPCs)embedded in the nuclear envelope(NE)of eukaryotic cell.The NPC functions as the sole pat...Bidirectional trafficking of macromolecules between the cytoplasm and the nucleus is mediated by the nuclear pore complexes(NPCs)embedded in the nuclear envelope(NE)of eukaryotic cell.The NPC functions as the sole pathway to allow for the passive diffusion of small molecules and the facilitated translocation of larger molecules.Evidence shows that these two transport modes and the conformation of NPC can be regulated by calcium stored in the lumen of nuclear envelope and endoplasmic reticulum.However,the mechanism of calcium regulation remains poorly understood.In this review,we integrate data on the observations of calciumregulated structure and function of the NPC over the past years.Furthermore,we highlight challenges in the measurements of dynamic conformational changes and transient transport kinetics in the NPC.Finally,an innovative imaging approach,single-molecule superresolution fluorescence microscopy,is introduced and expected to provide more insights into the mechanism of calcium-regulated nucleocytoplasmic transport.展开更多
The transport of proteins to and from the nucleus is necessary for many cellular processes and is one of the ways plants respond to developmental signals and environmental stresses.Nucleocytoplasmic trafficking of pro...The transport of proteins to and from the nucleus is necessary for many cellular processes and is one of the ways plants respond to developmental signals and environmental stresses.Nucleocytoplasmic trafficking of proteins is mediated by the nuclear transport receptor(NTR).Although NTR has been extensively studied in humans and Arabidopsis,it has rarely been identified and functionally characterized in rice.In this study,we identified exportin 1 in rice(OsXPO1)as a nuclear export receptor.OsXPO1shares high protein identity with its functional homologs in Arabidopsis and other organisms.OsXPO1localized to both the nucleus and the cytoplasm,directly interacted with the small GTPases OsRAN1and OsRAN2 in the nucleus,and mediated their nuclear export.Loss-of-function osxpo1 mutations were lethal at the seedling stage.Suppression of OsXPO1 expression in RNA interference lines produced multifaceted developmental defects,including arrested growth,premature senescence,abnormal inflorescence,and brown and mouth-opened spikelets.Overexpression of OsXPO1 in rice reduced plant height and seed-setting rate,but increased plant tolerance in response to PEG-mimicked drought stress and salt stress.These results indicate that OsXPO1 is a nuclear export receptor and acts in regulating plant development and abiotic stress responses.展开更多
AIM: To study the mechanism underlying carbon tetrachloride (CCl4)-induced alterations of protein synthesis in liver. METHODS: Male Sprague-Dawley rats were given CCl4 (1 mL/100 g body weight) and 3H-leucine incorpora...AIM: To study the mechanism underlying carbon tetrachloride (CCl4)-induced alterations of protein synthesis in liver. METHODS: Male Sprague-Dawley rats were given CCl4 (1 mL/100 g body weight) and 3H-leucine incorporation. Malondialdehyde (MDA) level in the liver, in vitro response of hepatocyte nuclei nucleotide triphosphatase (NTPase) to free radicals, and nuclear export of total mRNA with 3'-poly A+ were measured respectively. Survival response of HepG2 cells to CCl4 treatment was assessed by methyl thiazolyl tetrazolium. Km and Vmax values of nuclear envelope NTPase activity in liver of rats treated with CCl4 were assayed by a double-reciprocal plot. RESULTS: The protein synthesis was inhibited while the MDA level was signif icantly increased in liver of rats treated with CCl4. In addition, CCl4 decreased the NTPase binding capacity of nuclear envelope (Km value) in cultured HepG2 cells. Moreover, in vitro ferrous radicals from Fenton's system suppressed the NTPase activity of liver nuclear envelope in a dose-dependent manner. Down-regulation of the nuclear envelope NTPase activity indicated a lower energy provision for nucleocytoplasmic transport of mRNA molecules, an evidence in CCl4-treated HepG2 cells correspondingly supported by the nuclear sequestration of poly (A)+ mRNA molecules in morphological hybridization research. CONCLUSION: Inhibition of mRNA transport, suggestive of decreased NTPase activity of the nuclear envelope, may be involved in carbon tetrachloride-inhibited protein synthesis in liver.展开更多
There is a continuing need for novel antivirals to treat hepatitis B virus (HBV) infection, as it remains a major health problem worldwide. Ideally new classes of antivirals would target multiple steps in the viral li...There is a continuing need for novel antivirals to treat hepatitis B virus (HBV) infection, as it remains a major health problem worldwide. Ideally new classes of antivirals would target multiple steps in the viral lifecycle. In this review, we consider the steps in which HBV RNAs are processed, exported from the nucleus and translated. These are often overlooked steps in the HBV life-cycle. HBV, like retroviruses, incorporates a number of unusual steps in these processes, which use a combination of viral and host cellular machinery. Some of these unusual steps deserve a closer scrutiny. They may provide alternative targets to existing antiviral therapies, which are associated with increasing drug resistance. The RNA post-transcriptional regulatory element identified 20 years ago promotes nucleocytoplasmic export of all unspliced HBV RNAs. There is evidence that inhibition of this step is part of the antiviral action of interferon. Similarly, the structured RNA epsilon element situated at the 5’ end of the polycistronic HBV pregenomic RNA also performs key roles during HBV replication. The pregenomic RNA, which is the template for translation of both the viral core and polymerase proteins, is also encapsidated and used in replication. This complex process, regulated at the epsilon element, also presents an attractive antiviral target. These RNA elements that mediate and regulate gene expression are highly conserved and could be targeted using novel strategies employing RNAi, miRNAs or aptamers. Such approaches targeting these functionally constrained genomic regions should avoid escape mutations. Therefore understanding these regulatory elements, along with providing potential targets, may also facilitate the development of other new classes of antiviral drugs.展开更多
文摘Nuclear accumulation of active Smad complexes is crucial for transduction of transforming growth factor β （TGF-β）- superfamily signals from transmembrane receptors into the nucleus. It is now clear that the nucleocytoplasmic distributions of Smads, in both the absence and the presence of a TGF-β-superfamily signal, are not static, but instead the Smads are continuously shuttling between the nucleus and the cytoplasm in both conditions. This article presents the evidence for continuous nucleocytoplasmic shuttling of Smads. It then reviews different mechanisms that have been proposed to mediate Smad nuclear import and export, and discusses how the Smad steady-state distributions in the absence and the presence of a TGF-β-superfamily signal are established. Finally, the biological relevance of continuous nucleocytoplasmic shuttling for signaling by TGF-β superfamily members is discussed.
文摘P68 RNA helicase is a prototypical DEAD box RNA helicase. The protein plays a very important role in early organ development and maturation. Consistent with the function of the protein in transcriptional regulation and pre-mRNA splicing, p68 was found to predominately localize in the cell nucleus. However, recent experiments demon- strate a transient cytoplasmic localization of the protein. We report here that p68 shuttles between the nucleus and the cytoplasm. The nucleocytoplasmic shuttling of p68 is mediated by two nuclear localization signal and two nuclear exporting signal sequence elements. Our experiments reveal that p68 shuttles via a classical RanGTPase-dependent pathway.
文摘We study the evolution of a gynodioecious species under mixed-mating through a nucleocytoplasmic male sterility model. We consider two cytoplasmic types and a nuclear locus with two alleles. Here, the interaction between one cytoplasmic type and a recessive nuclear male-sterility factor gives rise to only one female genotype, while the remaining types correspond to hermaphroditic plants. We include two fitness paramaters: the advantageous female fitness t of females relative to that of hermaphrodites;and a silent and dominant cost of restoration, that is, a diminished fitness for plants carrying a dominant restorer gene relative to that of hermaphrodites. The parameter related to the cost of restoration is assumed to be present on outcrossing male fertility only. We find that every population converges to a stable population. We also determine the nature of the attracting stable population, which could be a nucleocytoplasmic polymorphism, a nuclear polymorphism or another population with some genotypes absent. This depends on the position of t with respect to critical values expressed in terms of the other parameters and also on the initial population.
基金supported by the National Natural Science Foundation of China(grants 81720108032 and 81930109 to Haiping Hao,82073926 to Hong Wang,and 82073928 to Guangji Wang)the National Key Research and Development Programme of China(2021YFA1301300 to Haiping Hao)+2 种基金Leading Technology Foundation Research Project of Jiangsu Province(grant BK20192005 to Guangji Wang,China)the Project Program of State Key Laboratory of Natural Medicines(China Pharmaceutical University,SKLNMZZ202202 to Haiping Hao)Sanming Project of Medicine in Shenzhen(SZSM201801060 to Guangji Wang,China)。
文摘Farnesoid X receptor(FXR)is widely accepted as a promising target for various liver diseases;however,panels of ligands in drug development show limited clinical benefits,without a clear mechanism.Here,we reveal that acetylation initiates and orchestrates FXR nucleocytoplasmic shuttling and then enhances degradation by the cytosolic E3 ligase CHIP under conditions of liver injury,which represents the major culprit that limits the clinical benefits of FXR agonists against liver diseases.Upon inflammatory and apoptotic stimulation,enhanced FXR acetylation at K217,closed to the nuclear location signal,blocks its recognition by importin KPNA3,thereby preventing its nuclear import.Concomitantly,reduced phosphorylation at T442 within the nuclear export signals promotes its recognition by exportin CRM1,and thereby facilitating FXR export to the cytosol.Acetylation governs nucleocytoplasmic shuttling of FXR,resulting in enhanced cytosolic retention of FXR that is amenable to degradation by CHIP.SIRT1 activators reduce FXR acetylation and prevent its cytosolic degradation.More importantly,SIRT1 activators synergize with FXR agonists in combating acute and chronic liver injuries.In conclusion,these findings innovate a promising strategy to develop therapeutics against liver diseases by combining SIRT1 activators and FXR agonists.
基金This work was supported by grants from the National Natural Science Foundation of China(30730047,81070262,81130003 and 81630034).
文摘Angiogenic factor with G-patch and FHA domains 1(AGGF1) exhibits a dynamic distribution from the nucleus to the cytoplasm in endothelial cells during angiogenesis, but the biological significance and underlying mechanism of this nucleocytoplasmic transport remains unknown. Here, we demonstrate that the dynamic distribution is essential for AGGF1 to execute its angiogenic function. To search the structural bases for this nucleocytoplasmic transport, we characterized three potential nuclear localization regions, one potential nuclear export region, forkhead-associated(FHA), and G-patch domains to determine their effects on nucleocytoplasmic transport and angiogenesis, and we show that AGGF1 remains intact during the dynamic subcellular distribution and the region from 260 to 288 amino acids acts as a signal for its nuclear localization. The distribution of AGGF1 in cytoplasm needs both FHA domain and 14-3-3α/β. Binding of AGGF1 via FHA domain to 14-3-3α/β is required to complete the transport. Thus, we for the first time established structural bases for the nucleocytoplasmic transport of AGGF1 and revealed that the FHA domain of AGGF1 is essential for its nucleocytoplasmic transport and angiogenesis.
基金We thank the grant support from National Institutes of Health(GM094041-01)the Research Capacity Enhancement Grant(Bowling Green State University).
文摘Bidirectional trafficking of macromolecules between the cytoplasm and the nucleus is mediated by the nuclear pore complexes(NPCs)embedded in the nuclear envelope(NE)of eukaryotic cell.The NPC functions as the sole pathway to allow for the passive diffusion of small molecules and the facilitated translocation of larger molecules.Evidence shows that these two transport modes and the conformation of NPC can be regulated by calcium stored in the lumen of nuclear envelope and endoplasmic reticulum.However,the mechanism of calcium regulation remains poorly understood.In this review,we integrate data on the observations of calciumregulated structure and function of the NPC over the past years.Furthermore,we highlight challenges in the measurements of dynamic conformational changes and transient transport kinetics in the NPC.Finally,an innovative imaging approach,single-molecule superresolution fluorescence microscopy,is introduced and expected to provide more insights into the mechanism of calcium-regulated nucleocytoplasmic transport.
基金supported by the National Key Research and Development Program(2020YFA0907600)the Laboratory of Lingnan Modern Agriculture Project(NZ2021004)+1 种基金the Natural Science Foundation of Guangdong Province(2020A1515010157)the Science and Technology Program of Guangzhou(202102080499)。
文摘The transport of proteins to and from the nucleus is necessary for many cellular processes and is one of the ways plants respond to developmental signals and environmental stresses.Nucleocytoplasmic trafficking of proteins is mediated by the nuclear transport receptor(NTR).Although NTR has been extensively studied in humans and Arabidopsis,it has rarely been identified and functionally characterized in rice.In this study,we identified exportin 1 in rice(OsXPO1)as a nuclear export receptor.OsXPO1shares high protein identity with its functional homologs in Arabidopsis and other organisms.OsXPO1localized to both the nucleus and the cytoplasm,directly interacted with the small GTPases OsRAN1and OsRAN2 in the nucleus,and mediated their nuclear export.Loss-of-function osxpo1 mutations were lethal at the seedling stage.Suppression of OsXPO1 expression in RNA interference lines produced multifaceted developmental defects,including arrested growth,premature senescence,abnormal inflorescence,and brown and mouth-opened spikelets.Overexpression of OsXPO1 in rice reduced plant height and seed-setting rate,but increased plant tolerance in response to PEG-mimicked drought stress and salt stress.These results indicate that OsXPO1 is a nuclear export receptor and acts in regulating plant development and abiotic stress responses.
基金Supported by The National Natural Science Foundation of China,No.30470846
文摘AIM: To study the mechanism underlying carbon tetrachloride (CCl4)-induced alterations of protein synthesis in liver. METHODS: Male Sprague-Dawley rats were given CCl4 (1 mL/100 g body weight) and 3H-leucine incorporation. Malondialdehyde (MDA) level in the liver, in vitro response of hepatocyte nuclei nucleotide triphosphatase (NTPase) to free radicals, and nuclear export of total mRNA with 3'-poly A+ were measured respectively. Survival response of HepG2 cells to CCl4 treatment was assessed by methyl thiazolyl tetrazolium. Km and Vmax values of nuclear envelope NTPase activity in liver of rats treated with CCl4 were assayed by a double-reciprocal plot. RESULTS: The protein synthesis was inhibited while the MDA level was signif icantly increased in liver of rats treated with CCl4. In addition, CCl4 decreased the NTPase binding capacity of nuclear envelope (Km value) in cultured HepG2 cells. Moreover, in vitro ferrous radicals from Fenton's system suppressed the NTPase activity of liver nuclear envelope in a dose-dependent manner. Down-regulation of the nuclear envelope NTPase activity indicated a lower energy provision for nucleocytoplasmic transport of mRNA molecules, an evidence in CCl4-treated HepG2 cells correspondingly supported by the nuclear sequestration of poly (A)+ mRNA molecules in morphological hybridization research. CONCLUSION: Inhibition of mRNA transport, suggestive of decreased NTPase activity of the nuclear envelope, may be involved in carbon tetrachloride-inhibited protein synthesis in liver.
基金Supported by Thailand Research Fundthe Commission on Higher Education Fund grant(to Nattanan Panjaworayan T-Thienprasert),No.MRG5680051and NZ Health Research Council Grant 05/195(to Augustine Chen and Chris M Brown)
文摘There is a continuing need for novel antivirals to treat hepatitis B virus (HBV) infection, as it remains a major health problem worldwide. Ideally new classes of antivirals would target multiple steps in the viral lifecycle. In this review, we consider the steps in which HBV RNAs are processed, exported from the nucleus and translated. These are often overlooked steps in the HBV life-cycle. HBV, like retroviruses, incorporates a number of unusual steps in these processes, which use a combination of viral and host cellular machinery. Some of these unusual steps deserve a closer scrutiny. They may provide alternative targets to existing antiviral therapies, which are associated with increasing drug resistance. The RNA post-transcriptional regulatory element identified 20 years ago promotes nucleocytoplasmic export of all unspliced HBV RNAs. There is evidence that inhibition of this step is part of the antiviral action of interferon. Similarly, the structured RNA epsilon element situated at the 5’ end of the polycistronic HBV pregenomic RNA also performs key roles during HBV replication. The pregenomic RNA, which is the template for translation of both the viral core and polymerase proteins, is also encapsidated and used in replication. This complex process, regulated at the epsilon element, also presents an attractive antiviral target. These RNA elements that mediate and regulate gene expression are highly conserved and could be targeted using novel strategies employing RNAi, miRNAs or aptamers. Such approaches targeting these functionally constrained genomic regions should avoid escape mutations. Therefore understanding these regulatory elements, along with providing potential targets, may also facilitate the development of other new classes of antiviral drugs.
