Nucleocytoplasmic Gynodioecy

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.

SIRT1 activation synergizes with FXR agonism in hepatoprotection via governing nucleocytoplasmic shuttling and degradation of FXR

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.

FHA domain of AGGF1 is essential for its nucleocytoplasmic transport and angiogenesis

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.

Calcium regulation of nucleocytoplasmic transport

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.

The nuclear export receptor OsXPO1 is required for rice development and involved in abiotic stress responses

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.

Mechanism underlying carbon tetrachloride-inhibited protein synthesis in liver

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.

Circadian Rhythms in Doxorubicin Nuclear Uptake and Clock Control of C6 Glioma Cells

Alterations of drug efficacy by the circadian clock are a concern when assessing drug therapies. Circadian rhythms persist in some cancer cells and are repressed in others. A better understanding of circadian activities generated within cancer cells could indicate therapeutic approaches that selectively disrupt rhythms and deprive cells of any benefits provided by circadian timing. Another option is to induce expression of the core clock gene Per2 to suppress cancer cell proliferation. We used the C6 rat glioblastoma cell line to identify rhythmic cancer cell properties that could provide improved therapeutic targets. Nuclear uptake of the anti-cancer agent doxorubicin by C6 cells showed a circadian rhythm that was shifted six hours from the rhythm in Per2 expression. We also observed circadian expression of the Crm1 (Xpo1) gene that is responsible for a key component of molecular transport through nuclear pores. C6 cultures include glioma stem cells (GSCs) that have elevated resistance to chemotherapeutic agents. We examined C6 tumorsphere cultures formed from GSCs to determine whether Hes1 and Bmi1 genes that maintain GSCs are under circadian clock control. Unlike Per2 gene expression in tumorspheres, Hes1 and Bmi1 expression did not oscillate in a circadian rhythm. These results highlight the importance of the nuclear pore complex in cancer treatments and suggest that the nuclear export mechanism and genes maintaining the cancer stem cell state could be inhibited therapeutically at a particular phase of the circadian cycle while preserving the tumor-suppressing abilities of Per2 gene expression.

Nucieocytoplasmic Shuttling of Geminivirus C4 Protein Mediated by Phosphorylation and Myristoylation Is Critical for Viral Pathogenicity

Many geminivirus C4 proteins induce severe developmental abnormalities in plants.We previously demon- strated that Tomato leaf curl Yunnan virus (TLCYnV)C4 induces plant developmental abnormalities at least partically by decreasing the accumulation of NbSKη,an ortholog of Arabidopsis BIN2 kinase involved in the brassinosteroid signaling pathway,in the nucleus through directing it to the plasma membrane.However, the molecular mechanism by which the membrane-associated C4 modifies the localization of NbSKη in the host cell remains unclear.Here,we show that TLCYnV C4 is a nucleocytoplasmic shuttle protein,and that C4 shuttling is accompanied by nuclear export of NbSKTI.TLCYnV C4 is phosphorylated by NbSKη in the nucleus,which promotes myristoylation of the viral protein.Myristoylation of phosphorylated C4 favors its interaction with exportin-α(XPO I);which in turn facilitates nuclear export of the C4/NbSKTI complex. Supporting this model,chemical inhibition of N-myristoyltransferases or exportin-α enhanced nuclear retention of C4,and mutations of the putative phosphorylation or myristoylation sites in C4 resulted in increased nuclear retention ofrC4 and thus decreased severity of C4-induced developmental abnormalities. The impact of C4 on development is also lessened when a nuclear localization signal or a nuclear export signal is added to its C-terminus,restricting it to a specific cellular niche and therefore impairing nucleocytoplasmic shuttling.Taken together,our results suggest that nucleocytoplasmic shuttling of TLCYnV C4,enabled by phosphorylation by NbSKη,myristoylation,and interaction with exportin-α is critical for its function as a pathogenicity factor.

Putting things in place for fertilization： discovering roles for importin proteins in cell fate and spermatogenesis

Importin proteins were originally characterized for their central role in protein transport through the nuclear pores, the only intracellular entry to the nucleus. This vital function must be tightly regulated to control access by transcription factors and other nuclear proteins to genomic DNA, to achieve appropriate modulation of cellular behaviors affecting cell fate. Importin-mediated nucleocytoplasmic transport relies on their specific recognition of cargoes, with each importin binding to distinct and overlapping protein subsets. Knowledge of importin function has expanded substantially in regard to three key developmental systems： embryonic stem cells, muscle cells and the germ line. In the decade since the potential for regulated nucleocytoplasmic transport to contribute to spermatogenesis was proposed, we and others have shown that the importins that ferry transcription factors into the nucleus perform additional roles, which control cell fate. This review presents key findings from studies of mammalian spermatogenesis that reveal potential new pathways by which male fertility and infertility arise. These studies of germline genesis illuminate new ways in which importin proteins govern cellular differentiation, includ ng v a d rect ng proteins to d st nct ntrace ular compartments and by determining cellular stress responses.

Nuclear translocation of OsMFT1 that is impeded by OsFTIP1 promotes drought toleranee in rice

Drought is the leading environmental threat affecting crop productivity,and plants have evolved a series of mechanisms to adapt to drought stress.The FT-interacting proteins(FTIPs)and phosphatidylethanola mine.binding proteins(PEBPs)play key roles in developmental processes,whereas their roles in the regulation of stress response are still largely unknown.Here,we report that OsFTIP1 negatively regulates drought response in rice.We showed that OsFTIP1 interacts with rice MOTHER OF FT AND TFL1(OsMFT1),a PEBP that promotes rice tolerance to drought treatment.Further studies discovered that OsMFT1 interacts with two key drought-related transcription factors,OsbZIP66 and OsMYB26,regulating their binding capacity on drought-related genes and thereby enhancing drought toleranee in rice.Interestingly,we found that OsFTIP1 impedes the nucleocytoplasmic translocation of OsMFT1,implying that dynamic modulation of drought-responsive genes by the OsMFT1-OsMYB26 and OsMFT1-OsbZIP66 complexes is integral to OsFTIP1-modulated nuclear accumulation of OsMFT1.Our findings also suggest that OsMFT1 might act as a hitherto unknown nucleocytoplasmic trafficking signal that regulates drought tolerance in rice in response to environmental signals.

The OsFTIP6-OsHB22-OsMYBR57 module regulates drought response in rice

Plants have evolved a sophisticated set of mechanisms to adapt to drought stress.Transcription factors play crucial roles in plant responses to various environmental stimuli by modulating the expression of numerous stress-responsive genes.However,how the crosstalk between different transcription factor families orchestrates initiation of the key transcriptional network and the role of posttranscriptional modification of transcription factors,especially in cellular localization/trafficking in response to stress in rice,remain still largely unknown.In this study,we isolated an Osmybr57 mutant that displays a drought-sensitive phenotype through a genetic screen for drought stress sensitivity.We found that OsMYBR57,an MYB-related protein,directly regulates the expression of several key drought-related OsbZ/Ps in response to drought treatment.Further studies revealed that OsMYBR57 interacts with a homeodomain transcription factor,OsHB22,which also plays a positive role in drought signaling.We further demonstrate that OsFTIP6 interacts with OsHB22 and promotes the nucleocytoplasmic translocation of OsHB22 into the nucleus,where OsHB22 cooperates with OsMYBR57 to regulate the expression of drought-responsive genes.Our findings have revealed a mechanistic framework underlying the OsFTIP6-0sHB22-0sMYBR57 module-mediated regulation of drought response in rice.The OsFTIP6-mediated OsHB22 nucleocytoplasmic shuttling and OsMYBR57-0sHB22 regulation of OsbZIP transcription ensure precise control of expression of OsLEA3 and Rab21,and thereby regulate the response to water deficiency in rice.

A karyopherin constrains nuclear activity of the NLR protein SNC1 and is essential to prevent autoimmunity in Arabidopsis

The nucleotide-binding and leucine-rich repeat(NLR)proteins comprise a major class of intracellular immune receptors that are capable of detecting pathogen-derived molecules and activating immunity and cell death in plants.The activity of some NLRs,particularly the Toll-like/interleukin-1 receptor(TIR)type,is highly correlated with their nucleocytoplasmic distribution.However,whether and how the nucleocytoplasmic homeostasis of NLRs is coordinated through a bidirectional nuclear shuttling mechanism remains unclear.Here,we identified a nuclear transport receptor,KA120,which is capable of affecting the nucleocytoplasmic distribution of an NLR protein and is essential in preventing its autoactivation.We showed that the ka120 mutant displays an autoimmune phenotype and NLR-induced transcriptome features.Through a targeted genetic screen using an artificial NLR microRNA library,we identified the TIR-NLR gene SNC1 as a genetic interactor of KA120.Loss-of-function snc1 mutations as well as compromising SNC1 protein activities all substantially suppressed ka120-induced autoimmune activation,and the enhanced SNC1 activity upon loss of KA120 functionappeared to occur at the protein level.Overexpression of KA120 efficiently repressed SNC1 activity and led to a nearly complete suppression of the autoimmune phenotype caused by the gain-of-function snc1-1 mutation or SNC1 overexpression in transgenic plants.Further florescence imaging analysis indicated that SNC1 undergoes altered nucleocytoplasmic distribution with significantly reduced nuclear signal when KA120 is constitutively expressed,supporting a role of KA120 in coordinating SNC1 nuclear abundance and activity.Consistently,compromising the SNC1 nuclear level by disrupting the nuclear pore complex could also partially rescue ka120-induced autoimmunity.Collectively,our study demonstrates that KA120 is essential to avoid autoimmune activation in the absence of pathogens and is required to constrain the nuclear activity of SNC1,possibly through coordinating SNC1 nucleocytoplasmic homeostasis as a potential mechanism.

Protein trafficking during plant innate immunity

Plants have evolved a sophisticated immune system to fight against pathogenic microbes. Upon detection of pathogen invasion by immune receptors, the immune system is turned on, resulting in production of antimicrobial molecules including pathogenesis-related（PR） proteins.Conceivably, an efficient immune response depends on the capacity of the plant cell＇s protein/membrane trafficking network to deploy the right defense-associated molecules in the right place at the right time. Recent research in this area shows that while the abundance of cell surface immune receptors is regulated by endocytosis, many intracellular immune receptors, when activated, are partitioned between the cytoplasm and the nucleus for induction of defense genes and activation of programmed cell death, respectively. Vesicle transport is an essential process for secretion of PR proteins to the apoplastic space and targeting of defense-related proteins to the plasma membrane or other endomembrane compartments. In this review, we discuss the various aspects of protein trafficking during plant immunity, with a focus on the immunity proteins on the move and the major components of the trafficking machineries engaged.

Hitting a moving target:inhibition of the nuclear export receptor XPO1/CRM1 as a therapeutic approach in cancer

Cellular homeostasis crucially relies on the correct nucleocytoplasmic distribution of a vast number of proteins and RNA molecules,which are shuttled in and out of the nucleus by specialized transport receptors.The nuclear export receptor XPO1,also called CRM1,mediates the translocation of hundreds of proteins and several classes of RNA to the cytoplasm,and thus regulates critical signaling pathways and cellular functions.The normal function of XPO1 appears to be often disrupted in malignant cells due to gene mutations or,most commonly,aberrant overexpression.Due to its important physiological roles and its frequent alteration in human tumors,XPO1 is a promising target for cancer therapy.XPO1 inhibitors have undergone extensive testing as therapeutic agents in preclinical models of cancer,with promising results.One of these inhibitors,Selinexor,is currently being evaluated in multiple clinical trials of different types of solid tumors and hematological malignancies.Here,we review several key aspects of XPO1 function,as well as the mechanisms that may lead to its alteration in cancer,and provide an update on the status of XPO1 inhibitors being developed as drugs for cancer therapy,including the definitive results of the first clinical trials with Selinexor that have been recently published.