Pericentrin contains five NESs and an NLS essential for its nucleocytoplasmic trafficking during the cell cycle

Cathepsin V regulates cell cycle progression and histone stability in the nucleus of breast cancer cells

Introduction: We previously identified that Cathepsin V (CTSV) expression is associated with poor prognosis in ER+ breast cancer, particularly within the Luminal A subtype. Examination of the molecular role of the protease within Luminal A tumours, revealed that CTSV promotes tumour cell invasion and proliferation, in addition to degradation of the luminal transcription factor, GATA3, via the proteasome. Methods: Cell line models expressing CTSV shRNA or transfected to overexpress CTSV were used to examine the impact of CTSV on cell proliferation by MTT assay and flow cytometry. Western blotting analysis was used to identify the impact of CTSV on histone and chaperone protein expression. Cell fractionation and confocal microscopy was used to illustrate the presence of CTSV in the nuclear compartment. Results: In this work we have identified that CTSV has an impact on breast cancer cell proliferation, with CTSV depleted cells exhibiting delayed progression through the G2/M phase of the cell cycle. Further investigation has revealed that CTSV can control nuclear expression levels of histones H3 and H4 via regulating protein expression of their chaperone sNASP. We have discovered that CTSV is localised to the nuclear compartment in breast tumour cells, mediated by a bipartite nuclear localisation signal (NLS) within the CTSV sequence and that nuclear CTSV is required for cell cycle progression and histone stability in breast tumour cells. Discussion: Collectively these findings support the hypothesis that targeting CTSV may have utility as a novel therapeutic target in ER+ breast cancer by impairing cell cycle progression via manipulating histone stabilisation.

Novel compound heterozygous mutations of PCNT gene in MOPD type II with central precocious puberty

We report on a 6-year and 11-month old girl with short stature, microcephaly, proboscis nose, small teeth, left breast Tanner stage II, and nasopharynx adenoid hypertrophy. Her gestational age was 37 weeks and birth weight was 800 g. Her growth hormone peak was higher than 35.2 ng/ml, luteinizing hormone peak 8.97 IU/l, and blood glucose of 120 min 7.82 mmol/l in oral glucose tolerance test. Genetic testing revealed two novel heterozygous mutations in the PCNT gene, an insertion mutation at c.1828dupT (p.S610Ffs*32), and a splice site mutation at c.1207 + 1G>A, which were inherited from healthy carrier patients. This case shows that MOPDII can be associated with central precocious puberty and impaired glucose tolerance in addition to intrauterine growth restriction, postpartum growth defect, and microcephaly.

Development of EST-Molecular Markers from RNA Sequencing for Genetic Management and Identification of Growth Traits in Potato Grouper (Epinephelus tukula)

Simple Summary

The potato grouper is a novel aquaculture species in Taiwan. Due to the lack of genetic information concerning this species, we have developed molecular markers based on transcriptome sequencing and further characterized their association with gene diversity and growth traits of this species. Ultimately, these markers could be utilized as accurate and efficient tools for genetic management and marker-assisted selection of potato grouper with distinct growth traits.

Abstract

The accuracy and efficiency of marker-assisted selection (MAS) has been proven for economically critical aquaculture species. The potato grouper (Epinephelus tukula), a novel cultured grouper species in Taiwan, shows large potential in aquaculture because of its fast growth rate among other groupers. Because of the lack of genetic information for the potato grouper, the first transcriptome and expressed sequence tag (EST)-derived simple sequence repeat (SSR) and single nucleotide polymorphism (SNP) markers were developed. Initially, the transcriptome was obtained from seven cDNA libraries by using the Illumina platform. De novo transcriptome of the potato grouper yielded 51.34 Gb and 111,490 unigenes. The EST-derived SSR and SNP markers were applied in genetic management, in parentage analysis, and to discover the functional markers of economic traits. The F₁ juveniles were identified as siblings from one pair of parents (80 broodstocks). Fast- and slow-growth individuals were analyzed using functional molecular markers and through their association with growth performance. The results revealed that two SNPs were correlated with growth traits. The transcriptome database obtained in this study and its derived SSR and SNP markers may be applied not only for MAS but also to maintain functional gene diversity in the novel cultured grouper.

Linker region is required for efficient nuclear localization of polynucleotide kinase phosphatase

Polynucleotide kinase phosphatase (PNKP) is a DNA repair factor with dual enzymatic functions, i.e., phosphorylation of 5’-end and dephosphorylation of 3’-end, which are prerequisites for DNA ligation and, thus, is involved in multiple DNA repair pathways, i.e., base excision repair, single-strand break repair and double-strand break repair through non-homologous end joining. Mutations in PNKP gene causes inherited diseases, such as microcephaly and seizure (MCSZ) by neural developmental failure and ataxia with oculomotor apraxia 4 (AOA4) and Charcot-Marie-Tooth disease 2B2 (CMT2B2) by neurodegeneration. PNKP consists of the Forkhead-associated (FHA) domain, linker region, phosphatase domain and kinase domain. Although the functional importance of PNKP interaction with XRCC1 and XRCC4 through the FHA domain and that of phosphatase and kinase enzyme activities have been well established, little is known about the function of linker region. In this study, we identified a functional putative nuclear localization signal (NLS) of PNKP located in the linker region, and showed that lysine 138 (K138), arginine 139 (R139) and arginine 141 (R141) residues therein are critically important for nuclear localization. Furthermore, double mutant of K138A and R35A, the latter of which mutates arginine 35, central amino acid of FHA domain, showed additive effect on nuclear localization, indicating that the FHA domain as well as the NLS is important for PNKP nuclear localization. Thus, this study revealed two distinct mechanisms regulating nuclear localization and subnuclear distribution of PNKP. These findings would contribute to deeper understanding of a variety of DNA repair pathway, i.e., base excision repair, single-strand break repair and double-strand break repair.

RanGTP and importin β regulate meiosis I spindle assembly and function in mouse oocytes

Homologous chromosome segregation during meiosis I (MI) in mammalian oocytes is carried out by the acentrosomal MI spindles. Whereas studies in human oocytes identified Ran GTPase as a crucial regulator of the MI spindle function, experiments in mouse oocytes questioned the generality of this notion. Here, we use live-cell imaging with fluorescent probes and Förster resonance energy transfer (FRET) biosensors to monitor the changes in Ran and importin β signaling induced by perturbations of Ran in mouse oocytes while examining the MI spindle dynamics. We show that unlike RanT24N employed in previous studies, a RanT24N, T42A double mutant inhibits RanGEF without perturbing cargo binding to importin β and disrupts MI spindle function in chromosome segregation. Roles of Ran and importin β in the coalescence of microtubule organizing centers (MTOCs) and MI spindle assembly are further supported by the use of the chemical inhibitor importazole, whose effects are partially rescued by the GTP hydrolysis-resistant RanQ69L mutant. These results indicate that RanGTP is essential for MI spindle assembly and function both in humans and mice.

Nuclear roles for cilia-associated proteins

Cilia appear to be derived, evolutionarily, from structures present in the ancestral (pre-ciliary) eukaryote, such as microtubule-based vesicle trafficking and chromosome segregation systems. Experimental observations suggest that the ciliary gate, the molecular complex that mediates the selective molecular movement between cytoplasmic and ciliary compartments, shares features with nuclear pores. Our hypothesis is that this shared transport machinery is at least partially responsible for the observation that a number of ciliary and ciliogenesis-associated proteins are found within nuclei where they play roles in the regulation of gene expression, DNA repair, and nuclear import and export. Recognizing the potential for such nuclear roles is critical when considering the phenotypic effects that arise from the mutational modification of ciliary proteins.

CDK4 protein is degraded by anaphase-promoting complex/cyclosome in mitosis and reaccumulates in early G1 phase to initiate a new cell cycle in HeLa cells

CDK4 regulates G₁/S phase transition in the mammalian cell cycle by phosphorylating retinoblastoma family proteins. However, the mechanism underlying the regulation of CDK4 activity is not fully understood. Here, we show that CDK4 protein is degraded by anaphase-promoting complex/cyclosome (APC/C) during metaphase-anaphase transition in HeLa cells, whereas its main regulator, cyclin D1, remains intact but is sequestered in cytoplasm. CDK4 protein reaccumulates in the following G₁ phase and shuttles between the nucleus and the cytoplasm to facilitate the nuclear import of cyclin D1. Without CDK4, cyclin D1 cannot enter the nucleus. Point mutations that disrupt CDK4 and cyclin D1 interaction impair the nuclear import of cyclin D1 and the activity of CDK4. RNAi knockdown of CDK4 also induces cytoplasmic retention of cyclin D1 and G₀/G₁ phase arrest of the cells. Collectively, our data demonstrate that CDK4 protein is degraded in late mitosis and reaccumulates in the following G₁ phase to facilitate the nuclear import of cyclin D1 for activation of CKD4 to initiate a new cell cycle in HeLa cells.

Nuclear Localized LSR: A Novel Regulator of Breast Cancer Behavior and Tumorigenesis

Lipolysis-stimulated lipoprotein receptor (LSR) has been found in the plasma membrane and is believed to function in lipoprotein endocytosis and tight junctions. Given the impact of cellular metabolism and junction signaling pathways on tumor phenotypes and patient outcome, it is important to understand how LSR cellular localization mediates its functions. We conducted localization studies, evaluated DNA binding, and examined the effects of nuclear LSR in cells, xenografts, and clinical specimens. We found LSR within the membrane, cytoplasm, and the nucleus of breast cancer cells representing multiple intrinsic subtypes. Chromatin immunoprecipitation (ChIP) showed direct binding of LSR to DNA, and sequence analysis identified putative functional motifs and post-translational modifications of the LSR protein. While neither overexpression of transcript variants, nor pharmacologic manipulation of post-translational modification significantly altered localization, inhibition of nuclear export enhanced nuclear localization, suggesting a mechanism for nuclear retention. Coimmunoprecipitation and proximal ligation assays indicated LSR-pericentrin interactions, presenting potential mechanisms for nuclear-localized LSR. The clinical significance of LSR was evaluated using data from over 1,100 primary breast tumors, which showed high LSR levels in basal-like tumors and tumors from African-Americans. In tumors histosections, nuclear localization was significantly associated with poor outcomes. Finally, in vivo xenograft studies revealed that basal-like breast cancer cells that overexpress LSR exhibited both membrane and nuclear localization, and developed tumors with 100% penetrance, while control cells lacking LSR developed no tumors. These results show that nuclear LSR alters gene expression and may promote aggressive cancer phenotypes.

IMPLICATIONS

LSR functions in the promotion of aggressive breast cancer phenotypes and poor patient outcome via differential subcellular localization to alter cell signaling, bioenergetics, and gene expression. Mol Cancer Res; 15(2); 165-78. ©2016 AACR.

The RanGTP Pathway: From Nucleo-Cytoplasmic Transport to Spindle Assembly and Beyond

The small GTPase Ran regulates the interaction of transport receptors with a number of cellular cargo proteins. The high affinity binding of the GTP-bound form of Ran to import receptors promotes cargo release, whereas its binding to export receptors stabilizes their interaction with the cargo. This basic mechanism linked to the asymmetric distribution of the two nucleotide-bound forms of Ran between the nucleus and the cytoplasm generates a switch like mechanism controlling nucleo-cytoplasmic transport. Since 1999, we have known that after nuclear envelope breakdown (NEBD) Ran and the above transport receptors also provide a local control over the activity of factors driving spindle assembly and regulating other aspects of cell division. The identification and functional characterization of RanGTP mitotic targets is providing novel insights into mechanisms essential for cell division. Here we review our current knowledge on the RanGTP system and its regulation and we focus on the recent advances made through the characterization of its mitotic targets. We then briefly review the novel functions of the pathway that were recently described. Altogether, the RanGTP system has moonlighting functions exerting a spatial control over protein interactions that drive specific functions depending on the cellular context.

The GTPase RAN regulates multiple steps of the centrosome life cycle

Growing lines of evidence implicate the small GTPase RAN, its regulators and effectors--predominantly, nuclear transport receptors--in practically all aspects of centrosome biology in mammalian cells. These include duplication licensing, cohesion, positioning, and microtubule-nucleation capacity. RAN cooperates with the protein nuclear export vector exportin 1/CRM1 to recruit scaffolding proteins containing nuclear export sequences that play roles in the structural organization of centrosomes. Together, they also limit centrosome reduplication by regulating the localization of key "licensing" proteins during the centrosome duplication cycle. In parallel, RAN also regulates the capacity of centrosomes to nucleate and organize functional microtubules, and this predominanlty involves importin vectors: many factors regulating microtubule nucleation or function harbor nuclear localization sequences that interact with importin molecules and such interaction inhibits their activity. Active RANGTP binding to importin molecules removes the inhibition and releases microtubule regulatory factors in the free productive form. A dynamic scenario emerges, in which RAN is pivotal in linking spatiotemporal control of centrosome regulators to the cell cycle machinery.

Calumenin-15 facilitates filopodia formation by promoting TGF-β superfamily cytokine GDF-15 transcription

Filopodia, which are actin-rich finger-like membrane protrusions, have an important role in cell migration and tumor metastasis. Here we identify 13 novel calumenin (Calu) isoforms (Calu 3-15) produced by alternative splicing, and find that Calu-15 promotes filopodia formation and cell migration. Calu-15 shuttles between the nucleus and cytoplasm through interacting with importin α, Ran GTPase, and Crm1. The phosphorylation of the threonine at position 73 (Thr-73) by casein kinase 2 (CK2) is essential for the nuclear import of Calu-15, and either Thr-73 mutation or inhibition of CK2 interrupts its nuclear localization. In the nucleus, Calu-15 increases the transcription of growth differentiation factor-15 (GDF-15), a member of the transforming growth factor-β (TGF-β) superfamily, via binding to its promoter region. Furthermore, Calu-15 induces filopodia formation mediated by GDF-15. Together, we identify that Calu-15, a novel isoform of Calu with phosphorylation-dependent nuclear localization, has a critical role in promoting filopodia formation and cell migration by upregulating the GDF-15 transcription.

Strategies on the nuclear-targeted delivery of genes

To improve the nuclear-targeted delivery of non-viral vectors, extensive effort has been carried out on the development of smart vectors which could overcome multiple barriers. The nuclear envelope presents a major barrier to transgene delivery. Viruses are capable of crossing the nuclear envelope to efficiently deliver their genome into the nucleus through the specialized protein components. However, non-viral vectors are preferred over viral ones because of the safety concerns associated with the latter. Non-viral delivery systems have been designed to include various types of components to enable nuclear translocation at the periphery of the nucleus. This review summarizes the progress of research regarding nuclear transport mechanisms. "Smart" non-viral vectors that have been modified by peptides and other small molecules are able to facilitate the nuclear translocation and enhance the efficacy of gene expression. The resulting technology may also enhance delivery of other macromolecules to the nucleus.

Potential effects of CRM1 inhibition in mantle cell lymphoma

Mantle cell lymphoma (MCL) is an aggressive histotype of B-cell non-Hodgkin lymphoma. The disease has no known cure, which prompts the urgent need for novel therapeutic agents. Chromosomal region maintenance 1 (CRM1) may play a role in human neoplasia and serve as a novel target of cancer treatment. This study summarizes MCL pathogenesis and determines the involvement of CRM1 in the regulation of several vital signaling pathways contributing to MCL pathogenesis, including the pathways of cell cycle progression, DNA damage response, phosphoinositide kinase-3, nuclear factor-κB activation, and chromosomal stability. A preclinical study is also presented to compare the CRM1 status in MCL cell lines and primary MCL cells with normal B cells, as well as the therapeutic efficiency of CRM1 inhibition in MCL in vitro and in vivo, which make these agents potential targets of novel MCL treatments.

Chromatin-bound NLS proteins recruit membrane vesicles and nucleoporins for nuclear envelope assembly via importin-α/β

The mechanism for nuclear envelope (NE) assembly is not fully understood. Importin-β and the small GTPase Ran have been implicated in the spatial regulation of NE assembly process. Here we report that chromatin-bound NLS (nuclear localization sequence) proteins provide docking sites for the NE precursor membrane vesicles and nucleoporins via importin-α and -β during NE assembly in Xenopus egg extracts. We show that along with the fast recruitment of the abundant NLS proteins such as nucleoplasmin and histones to the demembranated sperm chromatin in the extracts, importin-α binds the chromatin NLS proteins rapidly. Meanwhile, importin-β binds cytoplasmic NE precursor membrane vesicles and nucleoporins. Through interacting with importin-α on the chromatin NLS proteins, importin-β targets the membrane vesicles and nucleoporins to the chromatin surface. Once encountering Ran-GTP on the chromatin generated by RCC1, importin-β preferentially binds Ran-GTP and releases the membrane vesicles and nucleoporins for NE assembly. NE assembly is disrupted by blocking the interaction between importin-α and NLS proteins with excess soluble NLS proteins or by depletion of importin-β from the extract. Our findings reveal a novel molecular mechanism for NE assembly in Xenopus egg extracts.

A global survey of CRM1-dependent nuclear export sequences in the human deubiquitinase family

The mechanisms that regulate the nucleocytoplasmic localization of human deubiquitinases remain largely unknown. The nuclear export receptor CRM1 binds to specific amino acid motifs termed NESs (nuclear export sequences). By using in silico prediction and experimental validation of candidate sequences, we identified 32 active NESs and 78 inactive NES-like motifs in human deubiquitinases. These results allowed us to evaluate the performance of three programs widely used for NES prediction, and to add novel information to the recently redefined NES consensus. The novel NESs identified in the present study reveal a subset of 22 deubiquitinases bearing motifs that might mediate their binding to CRM1. We tested the effect of the CRM1 inhibitor LMB (leptomycin B) on the localization of YFP (yellow fluorescent protein)- or GFP (green fluorescent protein)-tagged versions of six NES-bearing deubiquitinases [USP (ubiquitin-specific peptidase) 1, USP3, USP7, USP21, CYLD (cylindromatosis) and OTUD7B (OTU-domain-containing 7B)]. YFP-USP21 and, to a lesser extent, GFP-OTUD7B relocated from the cytoplasm to the nucleus in the presence of LMB, revealing their nucleocytoplasmic shuttling capability. Two sequence motifs in USP21 had been identified during our survey as active NESs in the export assay. Using site-directed mutagenesis, we show that one of these motifs mediates USP21 nuclear export, whereas the second motif is not functional in the context of full-length USP21.

Characterization of molecular determinants for nucleocytoplasmic shuttling of PRV UL54

The pseudorabies virus (PRV) early protein UL54 is a homologue of the herpes simplex virus 1 (HSV-1) immediate-early protein ICP27, which is a multifunctional protein and essential for HSV-1 infection. To determine if UL54 might shuttle between the nucleus and cytoplasm, as has been shown for its homologues in human herpesviruses, the molecular determinants for its nucleocytoplasmic shuttling were investigated. Heterokaryon assays demonstrated that UL54 was a nucleocytoplasmic shuttling protein and this property could not be blocked by leptomycin B, an inhibitor of chromosome region maintenance 1 (CRM1). However, TAP/NXF1 promoted the nuclear export of UL54 and interacted with UL54, suggesting that UL54 shuttles between the nucleus and the cytoplasm via a TAP/NXF1, but not CRM1, dependent nuclear export pathway. Furthermore, UL54 was demonstrated to target to the nucleus through a classic Ran-, importin β1- and α5-dependent nuclear import mechanism.