Cloning, expression and nuclear localization of human NPM3, a member of the nucleophosmin/nucleoplasmin family of nuclear chaperones

Pumilio1 regulates NPM3/NPM1 axis to promote PD-L1-mediated immune escape in gastric cancer

Abnormal regulation of RNA binding proteins (RBPs) plays an essential role in tumorigenesis and progression, but their functions and mechanisms remain largely elusive. Previously, we reported that Pumilio 1 (PUM1), a RBP, could regulate glycolysis metabolism and promote the progression of gastric cancer (GC). However, the role of PUM1 in tumor immune regulation remains largely elusive. In this study, we report that PUM1 induces immune escape through posttranscriptional regulation of PD-L1 in GC. We used multiplexed immunohistochemistry to analyze the correlation between PUM1 expression and immune microenvironment in GC. The effect of PUM1 deficiency on tumor killing of T cells was examined in vitro and in vivo. The molecular mechanism of PUM1 was evaluated via RNA immunoprecipitation, chromatin immunoprecipitation, Western blot, co-immunoprecipitation, and RNA stability assays. Clinically, elevated PUM1 expression is associated with high-expression of PD-L1, lack of CD8+ T cell infiltration and poor prognosis in GC patients. PUM1 positively regulates PD-L1 expression and PUM1 reduction enhances T cell killing of tumors. Mechanistically, PUM1 directly binds to nucleophosmin/nucleoplasmin 3 (NPM3) mRNA and stabilizes NPM3. NPM3 interacts with NPM1 to promote NPM1 translocation into the nucleus and increase the transcription of PD-L1. PUM1 inhibits the anti-tumor activity of T cells through the PUM1/NPM3/PD-L1 axis. In summary, this study reveals the critical post-transcriptional effect of PUM1 in the modulation of PD-L1-dependent GC immune escape, thus provides a novel indicator and potential therapeutic target for cancer immunotherapy.

Insights on the nuclear shuttling of H2A-H2B histone chaperones

All cellular processes that involve the unwinding of DNA also lead to the systematic shuttling of histones. Histone shuttling across the nuclear membrane is facilitated by a class of proteins known as - histone chaperones. Histone chaperones are classified based on their binding to H3/H4 histones or H2A/H2B histones. During the shuttling process, two types of signals - NLS and NES are recognized by the nuclear transport proteins. However, this is the nuclear transport protein and the mechanism of signal recognition by the protein is still unknown. Thus, in this piece of work, the NLS and NES signals are predicted on important H2A/H2B binding histone chaperones. In addition, cellular localization and potential DNA binding regions of histone chaperones are predicted. Mapping of predicted regions on the histone chaperone's structure suggested that the critical binding regions mainly lie on the disordered region of the histone chaperones. NLS and NES are present in the N- and C-terminal of the histone chaperones. Most histone chaperones contain bipartiate NLS signals. This article sheds light on the crucial aspect that in addition of being directly engaged in nucleosome synthesis and disassembly in vivo, histone chaperone also performs various specific roles via histone binding activity.

Pan-cancer analysis of the prognostic and immunological role of nucleophosmin/nucleoplasmin 3 (NPM3) and its potential significance in lung adenocarcinoma

Background

Nucleophosmin/nucleoplasmin 3 (NPM3), a member of the NPM protein family, is widely expressed in various human tissues. Although previous studies identified elevated NPM3 expression in several cancers, a systematic pan-cancer analysis remains lacking. In this study, we conducted a comprehensive analysis of NPM3 to determine its role in tumorigenesis and tumor development.

Methods

Using data from The Cancer Genome Atlas (TCGA) and various bioinformatics analysis tools, we conducted a pan-cancer analysis of NPM3. Additionally, we collected gene expression and clinical data from 890 patients with lung adenocarcinoma (LUAD) from TCGA and the Gene Expression Omnibus database. We performed Cox regression analyses to explore the independent prognostic value of NPM3 expression in LUAD and plotted a nomogram to predict patient survival. We also used real-time quantitative polymerase chain reaction (RT-qPCR) to examine the expression levels of NPM3 in seven pairs of LUAD and paraneoplastic tissue samples.

Results

NPM3 expression was significantly increased in 20 types of cancer and was associated with poor prognosis in five types (P < 0.05). NPM3 expression was negatively correlated with DNA methylation and positively correlated with copy number variation. NPM3 was also significantly associated with immune cell infiltration in various cancers. Cox regression analyses revealed that NPM3 expression could serve as an independent prognostic marker of LUAD. Moreover, our nomogram demonstrated good predictive ability for the prognosis of patients with LUAD. Finally, the high expression of NPM3 in LUAD was verified using RT-qPCR.

Conclusion

NPM3 is a promising biomarker for predicting pan-cancer prognosis and immunotherapeutic efficacy.

NPM3 as a novel oncogenic factor and poor prognostic marker contributes to cell proliferation and migration in lung adenocarcinoma

BACKGROUND

Lung cancer is the leading cause of cancer-related deaths worldwide, and despite recent advances in targeted therapies and immunotherapies, the clinical benefit remains limited. Therefore, there is an urgent need to further investigate the molecular mechanisms underlying lung cancer. The aim of this study was to investigate the expression and function of NPM3 in the tumor microenvironment of lung adenocarcinoma (LUAD).

METHODS

We utilized bioinformatics tools and databases, including UALCAN, GEPIA2, HPA, and Sangerbox, to analyze NPM3 expression in LUAD samples and its association with prognosis and mutational landscape. NPM3 expression in various cell types was assessed at the single cell level using the TISCH database. We also used algorithms such as TIMER and EPIC to explore the crosstalk between NPM3 expression and immune features. KEGG enrichment analysis was performed to identify potential signaling pathways of NPM3. Finally, we employed siRNA knockdown strategy to investigate the effect of NPM3 on LUAD cell proliferation and migration in vitro.

RESULTS

NPM3 was significantly upregulated in LUAD tissues and was strongly associated with poor prognosis and TP53 gene mutations. Single-cell sequencing analysis revealed that NPM3 was expressed in immune cells (dendritic cells and monocytes/macrophages) in the tumor microenvironment. Moreover, NPM3 expression was negatively associated with immune B cell and CD4 T cell infiltration, as well as with several immune-related genes (including CCL22, CXCR2, CX3CR1, CCR6, HLA-DOA, HLA-DQA2). KEGG enrichment analysis indicated that NPM3 expression was associated with cell cycle, CAMs, and NSCLC pathway genes. Finally, in vitro experiments showed that NPM3 knockdown inhibited LUAD cell proliferation and migration in NCI-H1299 and SPC-A1 cells, and suppressed the expression of CCNA2 and MAD2L1.

CONCLUSION

Elevated NPM3 expression predicts poor clinical outcome and an immunosuppressive microenvironment in LUAD tissues. NPM3 promotes LUAD progression by promoting cell proliferation and migration, and targeting NPM3 may represent a novel therapeutic strategy for LUAD.

Vertebrate nucleoplasmin and NASP: egg histone storage proteins with multiple chaperone activities

Recent reviews have focused on the structure and function of histone chaperones involved in different aspects of somatic cell chromatin metabolism. One of the most dramatic chromatin remodeling processes takes place immediately after fertilization and is mediated by egg histone storage chaperones. These include members of the nucleoplasmin (NPM2/NPM3), which are preferentially associated with histones H2A-H2B in the egg and the nuclear autoantigenic sperm protein (NASP) families. Interestingly, in addition to binding and providing storage to H3/H4 in the egg and in somatic cells, NASP has been shown to be a unique genuine chaperone for histone H1. This review revolves around the structural and functional roles of these two families of chaperones whose activity is modulated by their own post-translational modifications (PTMs), particularly phosphorylation. Beyond their important role in the remodeling of paternal chromatin in the early stages of embryogenesis, NPM and NASP members can interact with a plethora of proteins in addition to histones in somatic cells and play a critical role in processes of functional cell alteration, such as in cancer. Despite their common presence in the egg, these two histone chaperones appear to be evolutionarily unrelated. In contrast to members of the NPM family, which share a common monophyletic evolutionary origin, the different types of NASP appear to have evolved recurrently within different taxa.

Spatiotemporal expression profile of no29/nucleophosmin3 in the intestine of Xenopus laevis during metamorphosis

A Xenopus laevis homolog of nucleophosmin/nucleoplasmin3 (NPM3), no29, has been previously identified as a thyroid hormone (TH)-response gene during TH-induced metamorphosis. X. laevis has another NPM3 homolog (npm3) in the pseudo-tetraploid genome, whereas X. tropicalis possesses one ortholog in the diploid genome. To assess the possible roles of these NPM3 homologs in amphibian metamorphosis, we have analyzed their expression profiles in X. laevis tadpoles. Levels of no29 and npm3 mRNA are rapidly up-regulated by exogenous TH in various organs of the premetamorphic tadpoles. Notably, in the small intestine, no29 and npm3 mRNA levels are transiently up-regulated during metamorphic climax, when progenitor/stem cells of the adult epithelium appear and actively proliferate. In situ hybridization analysis has revealed that the no29 transcript is specifically localized in adult epithelial progenitor/stem cells of the intestine during natural and TH-induced metamorphosis. Double-staining for in situ hybridization and immunohistochemistry has shown co-expression of no29 mRNA and no38 protein (an ortholog of NPM1), which is known to interact with NPM3 and to regulate cell proliferation in mammals. Thus, no29/npm3 might serve as a stem cell marker in the intestine during metamorphosis.

The Multifunctional Nucleolar Protein Nucleophosmin/NPM/B23 and the Nucleoplasmin Family of Proteins

The nucleophosmin (NPM)/nucleoplasmin family of nuclear chaperones has three members: NPM1, NPM2, and NPM3. Nuclear chaperones serve to ensure proper assembly of nucleosomes and proper formation of higher order structures of chromatin. In fact, this family of proteins has such diverse functions in cellular processes such as chromatin remodeling, ribosome biogenesis, genome stability, centrosome replication, cell cycle, transcriptional regulation, apoptosis, and tumor suppression. Of the members of this family, NPM1 is the most studied and is the main focus of this review. NPM2 and NPM3 are less well characterized, and are also discussed wherever appropriate. The structure–function relationship of NPM proteins has largely been worked out. Other than the many processes in which NPM1 takes part, the major interest comes from its involvement in human cancers, particularly acute myeloid leukemia (AML). Its significance stems from the fact that AML with mutated NPM1 accounts for ∼30% of all AML cases and usually has good prognosis. Its clinical importance also comes from its involvement in virus replication, particularly in the era of outbreaks of infectious diseases.

NPM1/B23: A Multifunctional Chaperone in Ribosome Biogenesis and Chromatin Remodeling

At a first glance, ribosome biogenesis and chromatin remodeling are quite different processes, but they share a common problem involving interactions between charged nucleic acids and small basic proteins that may result in unwanted intracellular aggregations. The multifunctional nuclear acidic chaperone NPM1 (B23/nucleophosmin) is active in several stages of ribosome biogenesis, chromatin remodeling, and mitosis as well as in DNA repair, replication and transcription. In addition, NPM1 plays an important role in the Myc-ARF-p53 pathway as well as in SUMO regulation. However, the relative importance of NPM1 in these processes remains unclear. Provided herein is an update on the expanding list of the diverse activities and interacting partners of NPM1. Mechanisms of NPM1 nuclear export functions of NPM1 in the nucleolus and at the mitotic spindle are discussed in relation to tumor development. It is argued that the suggested function of NPM1 as a histone chaperone could explain several, but not all, of the effects observed in cells following changes in NPM1 expression. A future challenge is to understand how NPM1 is activated, recruited, and controlled to carry out its functions.

Identification and characterization of nucleoplasmin 3 as a histone-binding protein in embryonic stem cells

Embryonic stem (ES) cells are thought to have unique chromatin structures responsible for their capacity for self-renewal and pluripotency. To examine this possibility, we sought nuclear proteins in mouse ES cells that specifically bind to histones using a pull-down assay with synthetic peptides of histone H3 and H4 tail domain as baits. Nuclear proteins preferentially bound to the latter. We identified 45 proteins associated with the histone H4 tail and grouped them into four categories: 10 chromatin remodeling proteins, five histone chaperones, two histone modification-related proteins, and 28 other proteins. mRNA expression levels of 20 proteins selected from these 45 proteins were compared between undifferentiated and retinoic acid (RA)-induced differentiated ES cells. All of the genes were similarly expressed in both states of ES cells, except nucleoplasmin 3 (NPM3) that was expressed at a higher level in the undifferentiated cells. NPM3 proteins were localized in the nucleoli and nuclei of the cells and expression was decreased during RA-induced differentiation. When transfected with NPM3 gene, ES cells significantly increased their proliferation compared with control cells. The present study strongly suggests that NPM3 is a chromatin remodeling protein responsible for the unique chromatin structure and replicative capacity of ES cells.

Sperm nucleosomes disassembly is a requirement for histones proteolysis during male pronucleus formation

We had previously reported that a cysteine-protease catalyzes the sperm histones (SpH) degradation associated to male chromatin remodeling in sea urchins. We found that this protease selectively degraded the SpH leaving maternal cleavage stage (CS) histone variants unaffected, therefore we named it SpH-protease. It is yet unknown if the SpH-protease catalyzes the SpH degradation while these histones are organized as nucleosomes or if alternatively these histones should be released from DNA before their proteolysis. To investigate this issue we had performed an in vitro assay in which polynucleosomes were exposed to the active purified protease. As shown in this report, we found that sperm histones organized as nucleosomes remains unaffected after their incubation with the protease. In contrast the SpH unbound and free from DNA were readily degraded. Interestingly, we also found that free DNA inhibits SpH proteolysis in a dose-dependent manner, further strengthening the requirement of SpH release from DNA before in order to be degraded by the SpH-protease. In this context, we have also investigated the presence of a sperm-nucleosome disassembly activity (SNDA) after fertilization. We found a SNDA associated to the nuclear extracts from zygotes that were harvested during the time of male chromatin remodeling. This SNDA was undetectable in the nuclear extracts from unfertilized eggs and in zygotes harvested after the fusion of both pronuclei. We postulate that this SNDA is responsible for the SpH release from DNA which is required for their degradation by the cysteine-protease associated to male chromatin remodeling after fertilization.

New insights into the nucleophosmin/nucleoplasmin family of nuclear chaperones

Basic proteins and nucleic acids are assembled into complexes in a reaction that must be facilitated by nuclear chaperones in order to prevent protein aggregation and formation of non-specific nucleoprotein complexes. The nucleophosmin/nucleoplasmin (NPM) family of chaperones [NPM1 (nucleophosmin), NPM2 (nucleoplasmin) and NPM3] have diverse functions in the cell and are ubiquitously represented throughout the animal kingdom. The importance of this family in cellular processes such as chromatin remodeling, genome stability, ribosome biogenesis, DNA duplication and transcriptional regulation has led to the rapid growth of information available on their structure and function. The present review covers different aspects related to the structure, evolution and function of the NPM family. Emphasis is placed on the long-term evolutionary mechanisms leading to the functional diversification of the family members, their role as chaperones (particularly as it pertains to their ability to aid in the reprogramming of chromatin), and the importance of NPM2 as an essential component of the amphibian chromatin remodeling machinery during fertilization and early embryonic development.

Post-meiotic shifts in HSPA2/HSP70.2 chaperone activity during mouse spermatogenesis

HSPA2 (formerly HSP70.2) is a testis-specific member of the HSP70 family known to play a critical role in the completion of meiosis during male germ cell differentiation. Although abundantly present in post-meiotic cells, its function during spermiogenesis remained obscure. Here, using a global proteomic approach to identify genome-organizing proteins in condensing spermatids, we discovered an unexpected role for HSPA2, which acquires new functions and becomes tightly associated with major spermatid DNA-packaging proteins, transition proteins 1 and 2. Hence, HSPA2 is identified here as the first transition protein chaperone, and these data shed a new light on the yet totally unknown process of genome-condensing structure assembly in spermatids.

Post-meiotic shifts in HSPA2/HSP70.2 chaperone activity during mouse spermatogenesis

HSPA2 (formerly HSP70.2) is a testis-specific member of the HSP70 family known to play a critical role in the completion of meiosis during male germ cell differentiation. Although abundantly present in post-meiotic cells, its function during spermiogenesis remained obscure. Here, using a global proteomic approach to identify genome-organizing proteins in condensing spermatids, we discovered an unexpected role for HSPA2, which acquires new functions and becomes tightly associated with major spermatid DNA-packaging proteins, transition proteins 1 and 2. Hence, HSPA2 is identified here as the first transition protein chaperone, and these data shed a new light on the yet totally unknown process of genome-condensing structure assembly in spermatids.

Long-term evolution and functional diversification in the members of the nucleophosmin/nucleoplasmin family of nuclear chaperones

The proper assembly of basic proteins with nucleic acids is a reaction that must be facilitated to prevent protein aggregation and formation of nonspecific nucleoprotein complexes. The proteins that mediate this orderly protein assembly are generally termed molecular (or nuclear) chaperones. The nucleophosmin/nucleoplasmin (NPM) family of molecular chaperones encompasses members ubiquitously expressed in many somatic tissues (NPM1 and -3) or specific to oocytes and eggs (NPM2). The study of this family of molecular chaperones has experienced a renewed interest in the past few years. However, there is a lack of information regarding the molecular evolution of these proteins. This work represents the first attempt to characterize the long-term evolution followed by the members of this family. Our analysis shows that there is extensive silent divergence at the nucleotide level suggesting that this family has been subject to strong purifying selection at the protein level. In contrast to NPM1 and NPM-like proteins in invertebrates, NPM2 and NPM3 have a polyphyletic origin. Furthermore, the presence of selection for high frequencies of acidic residues as well as the existence of higher levels of codon bias was detected at the C-terminal ends, which can be ascribed to the critical role played by these residues in constituting the acidic tracts and to the preferred codon usage for phosphorylatable amino acids at these regions.

Identification of evolutionarily conserved regulatory elements in the mouse Fgf8 locus

The secreted signaling molecule fibroblast growth factor 8 (Fgf8) is an essential component of certain embryonic signaling centers including the mid-hindbrain (isthmic) organizer, the first branchial arch (BA1), and the apical ectodermal ridge (AER). In these signaling centers Fgf8 transcripts are expressed in a dynamic and transient fashion, but the mechanism by which this highly specific expression pattern is established remains largely unknown. We used DNA sequence comparisons coupled to transgenic approaches to obtain insight into the structure and function of regulatory elements in the Fgf8 locus. First, a bacterial artificial chromosome (BAC) containing the mouse Fgf8 gene partially rescues the embryonic lethality of Fgf8-deficient mice and controls Fgf8-specific gene expression of a coinjected lacZ reporter transgene. Second, sequence comparison of vertebrate Fgf8 loci revealed evolutionarily highly conserved noncoding sequences that were unexpectedly located mainly 3' of the Fgf8 coding region. Third, in transgenic mice some of these elements were sufficient to target expression to the AER, tail bud, and brain, including the isthmic organizer, indicating that they may represent Fgf8 cis-acting elements. Collectively, these data identify novel regulatory elements of the Fgf8 gene sufficient to drive expression to regions of known Fgf8 activity.

Essential role of the B23/NPM core domain in regulating ARF binding and B23 stability

How cells coordinate inhibition of growth and division during genotoxic events is fundamental to our understanding of the origin of cancer. Despite increasing interest and extensive study, the mechanisms that link regulation of DNA synthesis and ribosomal biogenesis remain elusive. Recently, the tumor suppressor p14(ARF) (ARF) has been shown to interact functionally with the nucleolar protein B23/NPM (B23) and inhibit rRNA biogenesis. However, the molecular basis of the ARF-B23 interaction is hitherto unclear. Here we show that a highly conserved motif in the B23 oligomerization domain is essential for mediating ARF binding in vivo. Mutagenesis of conserved B23 core residues (L102A, G105A, G107A) prevented B23 from interacting with ARF. Modeling of the B23 core indicated that substitutions in the GSGP loop motif could trigger conformational changes in B23 thereby obstructing ARF binding. Interestingly, the GSGP loop mutants were unstable, defective for oligomerization, and delocalized from the nucleolus to the nucleoplasm. B23 core mutants displayed increased ubiquitination and proteasomal degradation. We conclude that the functional integrity of the B23 core motif is required for stability, efficient nucleolar localization as well as ARF binding.

The characterization of amphibian nucleoplasmins yields new insight into their role in sperm chromatin remodeling

Background

Nucleoplasmin is a nuclear chaperone protein that has been shown to participate in the remodeling of sperm chromatin immediately after fertilization by displacing highly specialized sperm nuclear basic proteins (SNBPs), such as protamine (P type) and protamine-like (PL type) proteins, from the sperm chromatin and by the transfer of histone H2A-H2B. The presence of SNBPs of the histone type (H type) in some organisms (very similar to the histones found in somatic tissues) raises uncertainty about the need for a nucleoplasmin-mediated removal process in such cases and poses a very interesting question regarding the appearance and further differentiation of the sperm chromatin remodeling function of nucleoplasmin and the implicit relationship with SNBP diversity The amphibians represent an unique opportunity to address this issue as they contain genera with SNBPs representative of each of the three main types: Rana (H type); Xenopus (PL type) and Bufo (P type).

Results

In this work, the presence of nucleoplasmin in oocyte extracts from these three organisms has been assessed using Western Blotting. We have used mass spectrometry and cloning techniques to characterize the full-length cDNA sequences of Rana catesbeiana and Bufo marinus nucleoplasmin. Northern dot blot analysis shows that nucleoplasmin is mainly transcribed in the egg of the former species. Phylogenetic analysis of nucleoplasmin family members from various metazoans suggests that amphibian nucleoplasmins group closely with mammalian NPM2 proteins.

Conclusion

We have shown that these organisms, in striking contrast to their SNBPs, all contain nucleoplasmins with very similar primary structures. This result has important implications as it suggests that nucleoplasmin's role in chromatin assembly during early zygote development could have been complemented by the acquisition of a new function of non-specifically removing SNBPs in sperm chromatin remodeling. This acquired function would have been strongly determined by the constraints imposed by the appearance and differentiation of SNBPs in the sperm.

A proteomic approach for dissecting H-Ras signaling networks in NIH/3T3 mouse embryonic fibroblast cells

To elucidate an understanding into H-Ras protein network, we have established various oncogene H-Ras-expressing NIH/3T3 mouse embryonic fibroblast cell clones, which are expressing G12V H-Ras, G12R H-Ras, and G12V/T35S H-Ras proteins under the tight control of expression by an antibiotic doxycycline. Here we provide a catalog of proteome profiles in total cell lysate derived from the oncogenic and partial loss of function H-Ras-expressing NIH/3T3 cells. In this biological context, we compared total proteome changes by the combined methods of 2-DE, quantitative image analysis and MALDI-TOF-MS analysis both commonly in oncogenic and partial loss of function H-Ras expression system. Thus, we tried to dissect H-Ras signaling pathway, especially a downstream effector molecule, Raf in NIH/3T3 cells using proteomics tools. In this study, we centralized upon the proteome profile changes as common targets for oncogenic H-Ras and a partial loss of function H-Ras in the H-Ras-expressing cells. Thirteen protein spots were selected as what the staining intensities on the gels for 2-DE images from both kinds of cells were consistently changed in their protein expression level. Differentially regulated expression was further confirmed for some subsets of candidates by semiquantitative RT-PCR and Western blot analysis using specific antibodies. Taken together, our results obtained and present here show that the comparative analysis of proteome from oncogenic and partial loss of function H-Ras-expressing cells has yielded interpretable data to elucidate the protein network directly and/or indirectly.

A proteomic approach for unraveling the oncogenic H-Ras protein networks in NIH/3T3 mouse embryonic fibroblast cells

To elucidate the oncogenic H-Ras network, we have established various stable and inducible oncogenic H-Ras-expressing NIH/3T3 mouse embryonic fibroblast cell clones, which express G12V H-Ras and G12R H-Ras proteins under the influence of a strong cytomegalovirus promoter and under the tight control of expression by an antibiotic, doxycycline, respectively. Here we provide a catalogue of proteome profiles in total cell lysates derived from oncogenic H-Ras-expressing NIH/3T3 cells. In this biological context, we compared total proteome changes by the combined methods of 2-DE, quantitative image analysis and MALDI-TOF MS analysis using both a stable expression system as well as an inducible expression system. There were a large number of common targets for oncogenic H-Ras, which were identified in both cell lines and consisted of 64 proteins (36 up-regulated and 28 down-regulated). Differentially regulated expression was further confirmed for some subsets of candidates by Western blot analysis using specific antibodies. Taken together, the results presented here show that comparative analysis of the proteome from the oncogenic H-Ras-expressing cells yielded interpretable data to elucidate protein networks directly and/or indirectly.

Further evidence on the role of heparan sulfate as protamine acceptor during the decondensation of human spermatozoa

BACKGROUND

Human spermatozoa decondense in vitro upon exposure to heparin and glutathione. Glutathione is also the disulfide bond reducer in vivo, and heparan sulfate, a functional analogue of heparin, has been proposed as the protamine acceptor. The aim of this study was to evaluate the decondensing ability of chemically modified heparins and different glycosaminoglycans (GAGs) on isolated sperm nuclei in vitro, and to analyse the possible role of different GAGs as protamine acceptors.

METHODS

Capacitated spermatozoa and isolated sperm nuclei from normospermic semen samples were decondensed in the presence of heparin (or its equivalent) and glutathione. After fixation with glutaraldehyde, the percentage of decondensed spermatozoa and nuclei was determined under phase-contrast. Proteins were extracted from sperm nuclei previously incubated in the presence of gluhathione and different GAGs by incubation with urea-beta-meracptoethanol-NaCl, and analysed by acid polyacrylamide gel electrophoresis.

RESULTS

The ability of desulfated heparins and other GAGs to decondense isolated nuclei mirrored exactly the decondensation of capacitated spermatozoa, the only difference being the level of maximum decondensation achieved. Heparan sulfate and heparin, but not other GAGs, were able to release protamines from sperm chromatin.

CONCLUSIONS

Heparan sulfate could be functioning as protamine acceptor in vivo during human sperm nuclear decondensation.

The structure and function of Xenopus NO38-core, a histone chaperone in the nucleolus

Xenopus NO38 is an abundant nucleolar chaperone and a member of the nucleoplasmin (Np) family. Here, we report high-resolution crystal structures of the N-terminal domain of NO38, as a pentamer and a decamer. As expected, NO38 shares the Np family fold. In addition, NO38- and Np-core pentamers each use highly conserved residues and numerous waters to form their respective decamers. Further studies show that NO38 and Np each bind equal amounts of the four core histones. However, NO38 prefers the (H3-H4)(2) tetramer, while Np probably prefers H2A-H2B dimers. We also show that NO38 and Np will each bind noncognate histones when the preferred partner is absent. We suggest that these chaperones must form decamers in order to bind histones and differentiate between histone tetramers and dimers. When taken together, these data imply that NO38 may function as a histone chaperone in the nucleolus.

Protein NPM3 interacts with the multifunctional nucleolar protein B23/nucleophosmin and inhibits ribosome biogenesis

Protein B23/nucleophosmin is a multifunctional protein that plays roles in ribosome biogenesis, control of centrosome duplication, and regulation of p53 expression. A yeast two-hybrid screen was performed in a search for interaction partners of B23. The complementary DNA for a highly acidic protein, nucleoplasmin 3 (NPM3), was found in multiple positive clones. Protein NPM3 and its interaction with B23 were further characterized. Endogenous B23 was able to be co-immunoprecipitated with NPM3, and this complex was resistant to ribonuclease treatment and high concentrations of salt. The N-terminal 35-90 amino acids of B23 were found to be required for their interaction. Separate co-immunoprecipitation studies of B23 and NPM3 suggested the existence of two different complexes, one containing B23 and 28 S ribosomal RNA (rRNA) and another composed of B23, NPM3, and other proteins, but no RNA. NPM3 was localized in the nucleolus, and its nucleolar localization depended on active rRNA transcription. In the cells overexpressing NPM3, there were decreased rates of pre-rRNA synthesis and processing. Overexpression of a mutant of NPM3 that did not interact with B23 did not alter pre-rRNA synthesis and processing, suggesting that the interaction of NPM3 with B23 plays a role in the ribosome biogenesis.

Millions of years of evolution preserved: a comprehensive catalog of the processed pseudogenes in the human genome

Processed pseudogenes were created by reverse-transcription of mRNAs; they provide snapshots of ancient genes existing millions of years ago in the genome. To find them in the present-day human, we developed a pipeline using features such as intron-absence, frame-disruption, polyadenylation, and truncation. This has enabled us to identify in recent genome drafts approximately 8000 processed pseudogenes (distributed from http://pseudogene.org). Overall, processed pseudogenes are very similar to their closest corresponding human gene, being 94% complete in coding regions, with sequence similarity of 75% for amino acids and 86% for nucleotides. Their chromosomal distribution appears random and dispersed, with the numbers on chromosomes proportional to length, suggesting sustained "bombardment" over evolution. However, it does vary with GC-content: Processed pseudogenes occur mostly in intermediate GC-content regions. This is similar to Alus but contrasts with functional genes and L1-repeats. Pseudogenes, moreover, have age profiles similar to Alus. The number of pseudogenes associated with a given gene follows a power-law relationship, with a few genes giving rise to many pseudogenes and most giving rise to few. The prevalence of processed pseudogenes agrees well with germ-line gene expression. Highly expressed ribosomal proteins account for approximately 20% of the total. Other notables include cyclophilin-A, keratin, GAPDH, and cytochrome c.

The crystal structure of Drosophila NLP-core provides insight into pentamer formation and histone binding

The nucleoplasmin-like protein from Drosophila (dNLP) functions as a chaperone for core histones and may remodel chromatin in embryos. We now report the crystal structure of a dNLP-core pentamer at 1.5 A resolution. The monomer has an eight-stranded, beta barrel topology that is similar to nucleoplasmin (Np). However, a signature beta hairpin is tucked in along the lateral surface of the dNLP-core pentamer, while it extends outward in the Np-core decamer. Drosophila NLP and Np both assemble histone octamers. This process may require each chaperone to form a decamer, which would create symmetric binding sites for the histones. Conformational differences between dNLP and Np may reflect their different oligomeric states, while a conserved, nonpolar subunit interface may allow conformational plasticity during histone binding.

Mouse Wnt9b transforming activity, tissue-specific expression, and evolution

The members of the Wnt family of secreted factors have oncogenic potential and important roles as developmental regulators. We report an analysis of mouse Wnt9b (also called Wnt15 and Wnt14b), including its cDNA sequence, chromosomal mapping, epithelial cell transforming activity, adult and embryonic tissue expression patterns, and evolution. We also deduced the full-length amino acid sequence of its close relative, Wnt9a (also called Wnt14), from unannotated genomic DNA sequences in GenBank. Full-length comparisons among Wnt amino acid sequences provide evidence that Wnt9b and Wnt9a are close paralogs of each other and are orthologs of Wnt9 genes from shark and hagfish. Mapping Wnt9b to The Jackson Laboratory BSS interspecific backcross panel places it at 63.0 cM on chromosome 11. Sequence comparisons of two pairs of linked Wnt genes (the Wnt9a-Wnt3a pair and the Wnt9b-Wnt3 pair) suggest that they arose from the relatively recent duplication of a single ancestral Wnt gene pair, confirming the close paralogous relationship of Wnt9a and Wnt9b. Wnt9b expression is primarily restricted to the kidney in the adult mouse, with lower levels detected in the preputial gland, liver, and mammary gland. Testing of staged whole mouse embryos from 9.5 to 17.5 days of gestation showed expression at all stages with a peak at day 10.5. In situ hybridization analysis showed expression in most but not all tissues of the 16.5-day embryo. No significant elevation of Wnt9b expression was detected in 29 mouse mammary tumor virus-induced tumors. Overexpression of Wnt9b in C57MG mammary epithelial cells caused small transformed foci in cell monolayers and a moderate morphological transformation in pooled colonies compared with Wnt1.

Nucleomorphin. A novel, acidic, nuclear calmodulin-binding protein from dictyostelium that regulates nuclear number

Probing of Dictyostelium discoideum cell extracts after SDS-PAGE using (35)S-recombinant calmodulin (CaM) as a probe has revealed approximately three-dozen Ca(2+)-dependent calmodulin binding proteins. Here, we report the molecular cloning, expression, and subcellular localization of a gene encoding a novel calmodulin-binding protein (CaMBP); we have called nucleomorphin, from D. discoideum. A lambdaZAP cDNA expression library of cells from multicellular development was screened using a recombinant calmodulin probe ((35)S-VU1-CaM). The open reading frame of 1119 nucleotides encodes a polypeptide of 340 amino acids with a calculated molecular mass of 38.7 kDa and is constitutively expressed throughout the Dictyostelium life cycle. Nucleomorphin contains a highly acidic glutamic/aspartic acid inverted repeat (DEED) with significant similarity to the conserved nucleoplasmin domain and a putative transmembrane domain in the carboxyl-terminal region. Southern blotting reveals that nucleomorphin exists as a single copy gene. Using gel overlay assays and CaM-agarose we show that bacterially expressed nucleomorphin binds to bovine CaM in a Ca(2+)-dependent manner. Amino-terminal fusion to the green fluorescence protein (GFP) showed that GFP-NumA localized to the nucleus as distinct arc-like patterns similar to heterochromatin regions. GFP-NumA lacking the acidic DEED repeat still showed arc-like accumulations at the nuclear periphery, but the number of nuclei in these cells was increased markedly compared with control cells. Cells expressing GFP-NumA lacking the transmembrane domain localized to the nuclear periphery but did not affect nuclear number or gross morphology. Nucleomorphin is the first nuclear CaMBP to be identified in Dictyostelium. Furthermore, these data present the first identification of a member of the nucleoplasmin family as a calmodulin-binding protein and suggest nucleomorphin has a role in nuclear structure in Dictyostelium.