Nsp14 of SARS-CoV-2 inhibits mRNA processing and nuclear export by targeting the nuclear cap-binding complex

To facilitate selfish replication, viruses halt host gene expression in various ways. The nuclear export of mRNA is one such process targeted by many viruses. SARS-CoV-2, the etiological agent of severe acute respiratory syndrome, also prevents mRNA nuclear export. In this study, Nsp14, a bifunctional viral replicase subunit, was identified as a novel inhibitor of mRNA nuclear export. Nsp14 induces poly(A)+ RNA nuclear accumulation and the dissolution/coalescence of nuclear speckles. Genome-wide gene expression analysis revealed the global dysregulation of splicing and 3'-end processing defects of replication-dependent histone mRNAs by Nsp14. These abnormalities were also observed in SARS-CoV-2-infected cells. A mutation introduced at the guanine-N7-methyltransferase active site of Nsp14 diminished these inhibitory activities. Targeted capillary electrophoresis-mass spectrometry analysis (CE-MS) unveiled the production of N7-methyl-GTP in Nsp14-expressing cells. Association of the nuclear cap-binding complex (NCBC) with the mRNA cap and subsequent recruitment of U1 snRNP and the stem-loop binding protein (SLBP) were impaired by Nsp14. These data suggest that the defects in mRNA processing and export arise from the compromise of NCBC function by N7-methyl-GTP, thus exemplifying a novel viral strategy to block host gene expression.

The linker of nucleoskeleton and cytoskeleton complex is required for X-ray-induced epithelial-mesenchymal transition

The linker of nucleoskeleton and cytoskeleton (LINC) complex has been implicated in various functions of the nuclear envelope, including nuclear migration, mechanotransduction and DNA repair. We previously revealed that the LINC complex component Sad1 and UNC84 domain containing 1 (SUN1) is required for sublethal-dose X-ray-enhanced cell migration and invasion. This study focused on epithelial-mesenchymal transition (EMT), which contributes to cell migration. Hence, the present study aimed to examine whether sublethal-dose X-irradiation induces EMT and whether LINC complex component SUN1 is involved in low-dose X-ray-induced EMT. This study showed that low-dose (0.5 Gy or 2 Gy) X-irradiation induced EMT in human breast cancer MDA-MB-231 cells. Additionally, X-irradiation increased the expression of SUN1. Therefore, SUN1 was depleted using siRNA. In SUN1-depleted cells, low-dose X-irradiation did not induce EMT. In addition, although the SUN1 splicing variant SUN1_916-depleted cells (containing 916 amino acids [AA] of SUN1) were induced EMT by low-dose X-irradiation like as non-transfected control cells, SUN1_888-depleted cells (which encodes 888 AA) were not induced EMT by low-dose X-irradiation. Moreover, since the Wnt/β-catenin signaling pathway regulates E-cadherin expression via the expression of the E-cadherin repressor Snail, the expression of β-catenin after X-irradiation was examined. After 24 hours of irradiation, β-catenin expression increased in non-transfected cells or SUN1_916-depleted cells, whereas β-catenin expression remained unchanged and did not increase in SUN1- or SUN1_888-depleted cells. Therefore, in this study, we found that low-dose X-irradiation induces EMT, and LINC complex component SUN1, especially SUN1_888, is required for X-ray-induced EMT via activation of the Wnt/β-catenin signaling pathway.

Natural history of severe aortic stenosis in elderly heart failure patients who declined transcatheter aortic valve implantation

Background

Transcatheter aortic valve implantation (TAVI) is an established minimally invasive treatment for elderly patients with severe aortic stenosis (AS). Although it is a relatively minimally invasive procedure, many elderly patients cannot undergo TAVI due to advanced age, advanced dementia, significantly impaired ADL, or because the patient or family does not wish to undergo TAVI. In general, severe AS patients died 5 years after an angina attack, 3 years after syncope symptoms, and 2 years after heart failure symptoms. However, few studies have investigated the prognosis of elderly patients with severe AS who declined TAVI.

Purpose

This study aimed to comprehend the natural history of elderly severe AS patients who declined aortic valve intervention and identify risk factors for death in the TAVI era.

Methods

We retrospectively reviewed 2,786 echocardiographic data from our hospital between 2017 and 2021. We identified 504 patients with AS in the echocardiography database. The severe AS was defined by the following echocardiography parameters: peak aortic flow velocity ≥4.0 m/s, aortic valve mean gradient ≥40 mmHg, aortic valve area (AVA)<1.0 cm2, or AVA index<0.6 cm2/m2. Patients with mild and moderate AS and patients who underwent surgical or transcatheter aortic valve intervention were excluded. Eventually, 82 patients fulfilled the study criteria and were analyzed in this study. Clinical events were investigated, and Cox proportional hazards analysis was performed to elucidate risk factors for mortality.

Results

The mean age was 89±6 years, and 63 (77%) were women. AHA/ACC classification was Stage A/B/C/D: 0%/52.4%/39.0%/8.5%. As event occurrence, we detected 34 (41.5%) all-cause deaths, 41 (50.0%) major adverse cardiovascular events, 32 (39.0%) development of heart failure, 13 (15.9%) chest pain attacks, and 3 (3.7%) syncope. The time from diagnosis of severe AS to all-cause death was 227±273 days, and the 1-, 2-, and 3-year survival rates were 61.5%, 46.2%, and 36.9%, respectively. Of the heart failure-onset population, 16 (50.0%) were found to have severe AS on initial heart failure admission. The incidence of heart failure at 1, 2, and 3 years after diagnosis of severe AS was 60.1%, 56.7%, and 45.4%, respectively. The time from heart failure to death was 107±147 days. Cox proportional hazards analysis adjusted with age, sex, comorbidities revealed that dementia (HR 4.5, P=0.014) and Katz index <5 (HR7.8, P=0.009) were independent risk factors for mortality.

Conclusions

Compared to the comprehension of the natural history of AS patients, the prognosis in severe AS patients who declined TAVI was extremely poor. Although the elderly patients did not have a high rate of angina attacks or syncope symptoms, probably due to their reduced ADL, the results suggest that dementia prevention and maintenance of exercise tolerance are essential since dementia and reduced ADL (Katz<5) are independent risk factors for mortality.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): Clinical Research Promotion Foundation Reiwa 2 Michinari Hieda

Inner Nuclear Membrane Protein, SUN1, is Required for Cytoskeletal Force Generation and Focal Adhesion Maturation

The linker of nucleoskeleton and cytoskeleton (LINC) complex is composed of the inner nuclear membrane-spanning SUN proteins and the outer nuclear membrane-spanning nesprin proteins. The LINC complex physically connects the nucleus and plasma membrane via the actin cytoskeleton to perform diverse functions including mechanotransduction from the extracellular environment to the nucleus. Mammalian somatic cells express two principal SUN proteins, namely SUN1 and SUN2. We have previously reported that SUN1, but not SUN2, is essential for directional cell migration; however, the underlying mechanism remains elusive. Because the balance between adhesive force and traction force is critical for cell migration, in the present study, we focused on focal adhesions (FAs) and the actin cytoskeleton. We observed that siRNA-mediated SUN1 depletion did not affect the recruitment of integrin β1, one of the ubiquitously expressed focal adhesion molecules, to the plasma membrane. Consistently, SUN1-depleted cells normally adhered to extracellular matrix proteins, including collagen, fibronectin, laminin, and vitronectin. In contrast, SUN1 depletion reduced the activation of integrin β1. Strikingly, the depletion of SUN1 interfered with the incorporation of vinculin into the focal adhesions, whereas no significant differences in the expression of vinculin were observed between wild-type and SUN1-depleted cells. In addition, SUN1 depletion suppressed the recruitment of zyxin to nascent focal adhesions. These data indicate that SUN1 is involved in the maturation of focal adhesions. Moreover, disruption of the SUN1-containing LINC complex abrogates the actin cytoskeleton and generation of intracellular traction force, despite the presence of SUN2. Thus, a physical link between the nucleus and cytoskeleton through SUN1 is required for the proper organization of actin, thereby suppressing the incorporation of vinculin and zyxin into focal adhesions and the activation of integrin β1, both of which are dependent on traction force. This study provides insights into a previously unappreciated signaling pathway from the nucleus to the cytoskeleton, which is in the opposite direction to the well-known mechanotransduction pathways from the extracellular matrix to the nucleus.

Impact of hypertension on clinical outcome in patients treated with vascular endothelial growth factor inhibitors

Background

Vascular endothelial growth factor (VEGF) family is overexpressed in the tumor microenvironment and induces tumor angiogenesis.1 VEGF signaling pathway (VSP) inhibitors are essential therapeutic drugs for solid cancer patients.2 However, VSP inhibitors often provoke drug-specific anti-angiogenesis in normal tissues, which was referred to as on-target toxicity.2 Hypertension (HTN) is one of the most frequent adverse events caused by VSP inhibitors. A previous report demonstrated that VSP inhibitor-induced hypertension is a favorable prognostic factor, contrarily.3However, multiple VSP inhibitors are administered in various cancer types, and then the relation between VSP inhibitor-associated hypertension and clinical outcome is still controversial.

Purpose

The aim of this study is to elucidate the impacts of HTN and the timing of onset on clinical outcome during cancer therapy with VSP inhibitors.

Method

We reviewed 2,348 patients who were treated with VSP inhibitors from the LIFE Study database, consisting of 14 municipality-level information from claims data between 2016 and 2020. According to the timing of HTN onset mode, the patients were stratified into 3 groups; (1) new-onset HTN group (n=334): de novo development after VSP inhibitor administration, (2) pre-existing HTN group (n=1,363): existing HTN at baseline, including aggravation after VSP inhibitor initiation, and (3) no HTN group (n=651) (Figure 1). The time to treatment failure (TTF) was applied as a surrogate clinical indicator of overall survival. Event-free survival analysis with the log-rank test was conducted for time to first treatment failure amongst the 3 groups. In addition, Cox proportional hazard models adjusted with clinical characteristics were performed to investigate independent factors for TTF.

Results

In the event-free survival analysis, both the new-onset HTN and the pre-existing HTN were associated with prolongation of TTF, compared to the non-HTN (p<0.001 and p<0.001, respectively, by Bonferroni correction) (Figure 2). The New-onset HTN was significantly associated with longer TTF than pre-existing HTN (p<0.001). In Cox proportional hazard model adjusted with age, sex, past medical history, primary cancer lesion, and type of VSP inhibitors, the new-onset HTN and the pre-existing HTN were independent favorable factors, compared to the non-HTN [new-onset HTN: Hazard ratio (HR) 0.62, 95% confidence interval (CI) 0.54 - 0.71, p<0.001; and pre-existing HTN: HR 0.85, 95% CI 0.77 - 0.94, p<0.005]. Moreover, the New-onset HTN was also a significant factor for longer TTF, compared to the pre-existing HTN [HR 0.72, 95% CI 0.64 - 0.82, p<0.001].

Conclusion

In patients treated with VSP inhibitors, both new-onset and pre-existing HTN are independent factors for a favorable clinical outcome, especially new-onset HTN after VSP inhibitors administration.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Japan Society for the Promotion of Science (JSPS) Grants-in-Aid for Scientific Research (KAKENHI) Figure 1. Patient screening and enrollmentFigure 2. HTN & TTF

The SUN1 splicing variants SUN1_888 and SUN1_916 differentially regulate nucleolar structure

The nucleolar structure is highly dynamic and strictly regulated in response to internal cues, such as metabolic rates, and to external cues, such as mechanical forces applied to cells. Although the multilayered nucleolar structure is largely determined by the liquid-like properties of RNA and proteins, the mechanisms regulating the morphology and number of nucleoli remain elusive. The linker of the nucleoskeleton and cytoskeleton (LINC) complex comprises inner nuclear membrane Sad1/UNC-84 (SUN) proteins and outer nuclear membrane-localized nesprins. We previously showed that the depletion of SUN1 proteins affects nucleolar morphologies. This study focuses on the function of SUN1 splicing variants in determining nucleolar morphology. An RNA interference strategy showed that the predominantly expressed variants, SUN1_888 and SUN1_916, were crucial for nucleolar morphology but functionally distinct. In addition, the depletion of either SUN1_888 or SUN1_916 altered the chromatin structure and affected the distribution of histone modifications. Based on these results, we propose a model in which the LINC complex plays a role in modulating nucleolar morphology and numbers via chromatin.

Human THO maintains the stability of repetitive DNA

The evolutionarily conserved multiprotein complex THO/TREX is required for pre-mRNA processing, mRNA export and the maintenance of genome stability. In this study, we analyzed the genome-wide distribution of human THOC7, a component of human THO, by chromatin immunoprecipitation sequencing. The analysis revealed that human THOC7 occupies repetitive sequences, which include microsatellite repeats in genic and intergenic regions and telomeric repeats. The majority of the THOC7 ChIP peaks overlapped with those of the elongating form of RNA polymerase II and R-loops, indicating that THOC7 accumulates in transcriptionally active repeat regions. Knocking down THOC5, an RNA-binding component of human THO, by siRNA induced the accumulation of γH2AX in the repeat regions. We also observed an aberration in the telomeres in the THOC5-depleted condition. These results suggest that human THO restrains the transcription-associated instability of repeat regions in the human genome.

SPOP is essential for DNA-protein cross-link repair in prostate cancer cells: SPOP-dependent removal of topoisomerase 2A from the topoisomerase 2A-DNA cleavage complex

SPOP, speckle-type POZ protein is a substrate adaptor protein of the Cullin-3/RING ubiquitin E3 complex. The spop gene is the most commonly point mutated in human primary prostate cancers, but the pathological contribution of the SPOP mutations remains unclear. In this study, we investigated several known factors that are critical in the DNA–­protein cross-link repair process. The depletion of SPOP or overexpression of a prostate cancer–associated SPOP mutant, F133V, in androgen receptor-positive prostate cancer cells increased the amount of topoisomerase 2A (TOP2A) in the nuclei together with the increased amount of γH2AX, an indication of DNA breaks. Tyrosyl–DNA phosphodiesterases (TDPs) and an endo/exonuclease MRE11 are enzymes that liberate TOP2A from the TOP2A–DNA cleavage complex, and thus is essential for the completion of the DNA repair process. We found that the amount of TDP1 and TDP2 was decreased in SPOP-depleted cells, and that of TDP2 and MRE11 was decreased in F133V-overexpressing cells. These results suggest that the F133V mutant exerts dominant-negative and gain-of-function effects in down-regulation of TDP2 and MRE11, respectively. We conclude that SPOP is involved in the DNA–protein cross-link repair process through the elimination of TOP2A from the TOP2A cleavage complex, which may contribute to the genome stability.

Signal Transduction across the Nuclear Envelope: Role of the LINC Complex in Bidirectional Signaling

The primary functions of the nuclear envelope are to isolate the nucleoplasm and its contents from the cytoplasm as well as maintain the spatial and structural integrity of the nucleus. The nuclear envelope also plays a role in the transfer of various molecules and signals to and from the nucleus. To reach the nucleus, an extracellular signal must be transmitted across three biological membranes: the plasma membrane, as well as the inner and outer nuclear membranes. While signal transduction across the plasma membrane is well characterized, signal transduction across the nuclear envelope, which is essential for cellular functions such as transcriptional regulation and cell cycle progression, remains poorly understood. As a physical entity, the nuclear envelope, which contains more than 100 proteins, functions as a binding scaffold for both the cytoskeleton and the nucleoskeleton, and acts in mechanotransduction by relaying extracellular signals to the nucleus. Recent results show that the Linker of Nucleoskeleton and Cytoskeleton (LINC) complex, which is a conserved molecular bridge that spans the nuclear envelope and connects the nucleoskeleton and cytoskeleton, is also capable of transmitting information bidirectionally between the nucleus and the cytoplasm. This short review discusses bidirectional signal transduction across the nuclear envelope, with a particular focus on mechanotransduction.

X-ray-enhanced cancer cell migration requires the linker of nucleoskeleton and cytoskeleton complex

The linker of nucleoskeleton and cytoskeleton (LINC) complex is a multifunctional protein complex that is involved in various processes at the nuclear envelope, including nuclear migration, mechanotransduction, chromatin tethering and DNA damage response. We recently showed that a nuclear envelope protein, Sad1 and UNC84 domain protein 1 (SUN1), a component of the LINC complex, has a critical function in cell migration. Although ionizing radiation activates cell migration and invasion in vivo and in vitro, the underlying molecular mechanism remains unknown. Here, we examined the involvement of the LINC complex in radiation‐enhanced cell migration and invasion. A sublethal dose of X‐ray radiation promoted human breast cancer MDA‐MB‐231 cell migration and invasion, whereas carbon ion beam radiation suppressed these processes in a dose‐dependent manner. Depletion of SUN1 and SUN2 significantly suppressed X‐ray‐enhanced cell migration and invasion. Moreover, depletion or overexpression of each SUN1 splicing variant revealed that SUN1_888 containing 888 amino acids of SUN1 but not SUN1_916 was required for X‐ray‐enhanced migration and invasion. In addition, the results suggested that X‐ray irradiation affected the expression level of SUN1 splicing variants and a SUN protein binding partner, nesprins. Taken together, our findings supported that the LINC complex contributed to photon‐enhanced cell migration and invasion.

SUN1 splice variants, SUN1_888, SUN1_785, and predominant SUN1_916, variably function in directional cell migration

The LINC complex is a multifunctional protein complex that is involved in various processes at the nuclear envelope, such as nuclear migration, mechanotransduction and chromatin tethering in the meiotic phase. However, it remains unknown how these functions are regulated in different cell contexts. An inner nuclear membrane component of the LINC complex, SUN1, is ubiquitously expressed. The human SUN1 gene produces over 10 variants by alternative splicing. Although functions of SUN1 are relatively well characterized, functional differences among SUN1 splice variants are poorly characterized. LINC complex components are associated with a wide range of human diseases; therefore, it is important to understand the functional diversity among SUN1 splice variants. Here, we identified a novel human SUN1 splice variant, SUN1_888. overexpression of the SUN1 splice variants, SUN1_888 or SUN1_785, but not the predominant isoform, SUN1_916, activated directional cell migration. Knockdown of SUN1_888 suppressed cell migration; in contrast depletion of SUN1_916 activated cell migration. In addition, all of investigated SUN1 splicing variants rescued cell migration in SUN1 knock out cell. These results indicate that redundant and non-redundant functions of SUN1 splice variant in directional cell migration and suggest that variable LINC complexes with distinct task may exit. Furthermore, in contrast to previous studies, we showed association between SUN1 and B-type lamins. Interestingly, B-type lamin preferentially interacts with SUN1 but not SUN2. These results suggest that tissue-specific SUN1 variants variably interact with nucleoplasmic partners and allow variable assembly of LINC complexes that can be assigned to distinct tasks.

Implications for Diverse Functions of the LINC Complexes Based on the Structure

The linker of nucleoskeleton and cytoskeleton (LINC) complex is composed of the outer and inner nuclear membrane protein families Klarsicht, Anc-1, and Syne homology (KASH), and Sad1 and UNC-84 (SUN) homology domain proteins. Increasing evidence has pointed to diverse functions of the LINC complex, such as in nuclear migration, nuclear integrity, chromosome movement and pairing during meiosis, and mechanotransduction to the genome. In metazoan cells, the nuclear envelope possesses the nuclear lamina, which is a thin meshwork of intermediate filaments known as A-type and B-type lamins and lamin binding proteins. Both of lamins physically interact with the inner nuclear membrane spanning SUN proteins. The nuclear lamina has also been implicated in various functions, including maintenance of nuclear integrity, mechanotransduction, cellular signalling, and heterochromatin dynamics. Thus, it is clear that the LINC complex and nuclear lamins perform diverse but related functions. However, it is unknown whether the LINC complex-lamins interactions are involved in these diverse functions, and their regulation mechanism has thus far been elusive. Recent structural analysis suggested a dynamic nature of the LINC complex component, thus providing an explanation for LINC complex organization. This review, elaborating on the integration of crystallographic and biochemical data, helps to integrate this research to gain a better understanding of the diverse functions of the LINC complex.

Loss of the integral nuclear envelope protein SUN1 induces alteration of nucleoli

A supervised machine learning algorithm, which is qualified for image classification and analyzing similarities, is based on multiple discriminative morphological features that are automatically assembled during the learning processes. The algorithm is suitable for population-based analysis of images of biological materials that are generally complex and heterogeneous. Here we used the algorithm wndchrm to quantify the effects on nucleolar morphology of the loss of the components of nuclear envelope in a human mammary epithelial cell line. The linker of nucleoskeleton and cytoskeleton (LINC) complex, an assembly of nuclear envelope proteins comprising mainly members of the SUN and nesprin families, connects the nuclear lamina and cytoskeletal filaments. The components of the LINC complex are markedly deficient in breast cancer tissues. We found that a reduction in the levels of SUN1, SUN2, and lamin A/C led to significant changes in morphologies that were computationally classified using wndchrm with approximately 100% accuracy. In particular, depletion of SUN1 caused nucleolar hypertrophy and reduced rRNA synthesis. Further, wndchrm revealed a consistent negative correlation between SUN1 expression and the size of nucleoli in human breast cancer tissues. Our unbiased morphological quantitation strategies using wndchrm revealed an unexpected link between the components of the LINC complex and the morphologies of nucleoli that serves as an indicator of the malignant phenotype of breast cancer cells.

Global loss of a nuclear lamina component, lamin A/C, and LINC complex components SUN1, SUN2, and nesprin-2 in breast cancer

Cancer cells exhibit a variety of features indicative of atypical nuclei. However, the molecular mechanisms underlying these phenomena remain to be elucidated. The linker of nucleoskeleton and cytoskeleton (LINC) complex, a nuclear envelope protein complex consisting mainly of the SUN and nesprin proteins, connects nuclear lamina and cytoskeletal filaments and helps to regulate the size and shape of the nucleus. Using immunohistology, we found that a nuclear lamina component, lamin A/C and all of the investigated LINC complex components, SUN1, SUN2, and nesprin-2, were downregulated in human breast cancer tissues. In the majority of cases, we observed lower expression levels of these analytes in samples' cancerous regions as compared to their cancer-associated noncancerous regions (in cancerous regions, percentage of tissue samples exhibiting low protein expression: lamin A/C, 85% [n = 73]; SUN1, 88% [n = 43]; SUN2, 74% [n = 43]; and nesprin-2, 79% [n = 53]). Statistical analysis showed that the frequencies of recurrence and HER2 expression were negatively correlated with lamin A/C expression (P < 0.05), and intrinsic subtype and ki-67 level were associated with nesprin-2 expression (P < 0.05). In addition, combinatorial analysis using the above four parameters showed that all patients exhibited reduced expression of at least one of four components despite the tumor's pathological classification. Furthermore, several cultured breast cancer cell lines expressed less SUN1, SUN2, nesprin-2 mRNA, and lamin A/C compared to noncancerous mammary gland cells. Together, these results suggest that the strongly reduced expression of LINC complex and nuclear lamina components may play fundamental pathological functions in breast cancer progression.

Histone modifications associated with cancer cell migration and invasion

Genome-wide aberrant histone modifications are present in a wide range of cancers, and they are associated with carcinogenesis and cancer progression. Aberrant histone modification patterns affect transcriptional regulation, chromosome stability, chromatin structure, chromatin remodeling, and DNA methylation; furthermore, these patterns can predict clinical outcome in many types of cancer. The main cause of poor clinical outcome is metastasis, which is strongly associated with tissue invasion at the primary tumor site. Invasion of cancer cells into surrounding tissue and the vasculature is an important initial step in tumor metastasis, and cell migration is a critical requirement for metastasis. Here, we describe the advantages of detecting global histone modifications by immunohistochemical analysis and provide a collection of protocols for assaying cell migration, invasion, and cell-extracellular matrix adhesion in vitro.

Loss of histone H4K20 trimethylation predicts poor prognosis in breast cancer and is associated with invasive activity

Introduction

Loss of histone H4 lysine 20 trimethylation (H4K20me3) is associated with multiple cancers, but its role in breast tumors is unclear. In addition, the pathological effects of global reduction in H4K20me3 remain mostly unknown. Therefore, a major goal of this study was to elucidate the global H4K20me3 level in breast cancer tissue and investigate its pathological functions.

Methods

Levels of H4K20me3 and an associated histone modification, H3 lysine 9 trimethylation (H3K9me3), were evaluated by immunohistochemistry in a series of breast cancer tissues. Univariate and multivariate clinicopathological and survival analyses were performed. We also examined the effect of overexpression or knockdown of the histone H4K20 methyltransferases, SUV420H1 and SUV420H2, on cancer-cell invasion activity in vitro.

Results

H4K20me3, but not H3K9me3, was clearly reduced in breast cancer tissue. A reduced level of H4K20me3 was correlated with several aspects of clinicopathological status, including luminal subtypes, but not with HER2 expression. Multivariate analysis showed that reduced levels of H4K20me3 independently associated with lower disease-free survival. Moreover, ectopic expression of SUV420H1 and SUV420H2 in breast cancer cells suppressed cell invasiveness, whereas knockdown of SUV420H2 activated normal mammary epithelial-cell invasion in vitro.

Conclusions

H4K20me3 was reduced in cancerous regions of breast-tumor tissue, as in other types of tumor. Reduced H4K20me3 level can be used as an independent marker of poor prognosis in breast cancer patients. Most importantly, this study suggests that a reduced level of H4K20me3 increases the invasiveness of breast cancer cells in a HER2-independent manner.

Cancer-associated upregulation of histone H3 lysine 9 trimethylation promotes cell motility in vitro and drives tumor formation in vivo

Global histone modification patterns correlate with tumor phenotypes and prognostic factors in multiple tumor types. Recent studies suggest that aberrant histone modifications play an important role in cancer. However, the effects of global epigenetic rearrangements on cell functions remain poorly understood. In this study, we show that the histone H3 lysine 9 (H3K9) methyltransferase SUV39H1 is clearly involved in regulating cell migration in vitro. Overexpression of wild-type SUV39H1, but not enzymatically inactive SUV39H1, activated migration in breast and colorectal cancer cells. Inversely, migration was reduced by knockdown of SUV39H1 or chemical inhibition by chaetocin. In addition, H3K9 trimethylation (H3K9me3) was specifically increased in invasive regions of colorectal cancer tissues. Moreover, the presence of H3K9me3 positively correlated with lymph node metastasis in colorectal cancer patients. Furthermore, overexpression of SUV39H1 drove tumorigenesis in mouse, resulting in a considerable decrease in survival rate. These data indicate that H3K9 trimethylation plays an important role in human colorectal cancer progression, possibly by promoting collective cell invasion.

The cytoplasmic tail of heparin-binding EGF-like growth factor regulates bidirectional intracellular trafficking between the plasma membrane and ER

Heparin-binding epidermal growth factor (EGF)- like growth factor (HB-EGF) is synthesized in the ER, transported along the exocytic pathway, and expressed on the plasma membrane as a type I transmembrane protein. Upon extracellular stimulation, HB-EGF, either proHB-EGF or the shed form HB-EGF-CTF, undergoes endocytosis and is then transported retrogradely to the ER. In this study, we showed the essential contribution of the short cytoplasmic tail of HB-EGF (HB-EGF-cyto) to the bidirectional intracellular trafficking between the ER and plasma membrane and revealed several critical amino acids residues that are responsible for internalization from the plasma membrane and ER targeting. We suggest that these anterograde and retrograde sorting signals within HB-EGF-cyto are strictly regulated by protein modification and conformation.

Nuclear envelope-localized EGF family protein amphiregulin activates breast cancer cell migration in an EGF-like domain independent manner

Amphiregulin (AREG), an EGF family protein, is synthesized as a type I transmembrane precursor (proAREG) and expressed on the cell surface with an extracellular EGF-like domain and an intracellular short cytoplasmic tail. The ectodomain shedding yields a soluble EGF receptor ligand (soluble AREG) which binds to EGF receptor (EGFR) and concomitantly induces migration of unshed proAREG from the plasma membrane to the nuclear envelope (NE). AREG is known to play a potential role in breast cancer and has been intensively investigated as an EGF receptor ligand, while the function of the NE-localized proAREG remains unknown. In this study we used a truncated mutant that mimics NE-localized proAREG without shedding stimuli to discriminate between the functions of NE-localized and plasma membrane-localized proAREG and demonstrate that NE-localized proAREG activates breast cancer cell migration, but suppresses cell growth. Moreover, the present study shows that induction of cell migration by NE-localized proAREG does not require the extracellular growth factor domain or EGF receptor function. Collectively these data demonstrate a novel function mediated by the intracellular domain of proAREG and suggest a significant role for NE-localized proAREG in driving human breast cancer progression.

Platelet-derived growth factor regulates breast cancer progression via β-catenin expression

OBJECTIVE

The knowledge on the association between platelet-derived growth factor (PDGF) signaling and epithelial cancers is scarce, although overexpression of PDGF and PDGF receptors has been reported in some human mesenchymal tumors. Thus, we studied the effect of PDGF on breast cancer cells in vitro and the distribution of PDGF in breast cancer tissues.

METHODS

The effect of PDGF-BB on breast cancer cells was assessed by Western blotting, immunofluorescence, WST and 5-bromo-2-deoxyuridine incorporation experiments. PDGF-B and β-catenin expression was investigated in breast cancer tissues by immunohistochemistry.

RESULTS

PDGF-BB induces β-catenin expression in breast cancer cells, and immunohistochemically the distribution of PDGF-B was similar to β-catenin in breast cancer cells. PDGF-B-positive cancer cells were more frequent in cases of ductal carcinoma in situ (87.5%) than invasive carcinoma (61.2%). In addition, PDGF-B staining was stronger in intraductal than invasive cancer cells. PDGF-BB tended to induce nuclear translocation of β-catenin, cell proliferation and DNA incorporation in MDA-MB231 cells, while these results were not found in MCF-7 cells.

CONCLUSION

Our results suggest that PDGF-BB regulates protein expression of β-catenin and is associated with cancer cell behavior.

Plasma-membrane-anchored growth factor pro-amphiregulin binds A-type lamin and regulates global transcription

Amphiregulin (AR), a member of the EGF family, is synthesized as a type I transmembrane protein precursor (proAR) and expressed on the cell surface. Shedding of proAR yields a transmembrane-cytoplasmic fragment (AR-CTF), as well as a soluble AR. Here we demonstrate that the proAR-shedding stimuli trigger endocytosis of both AR-CTF and un-shed proAR. ProAR translocates from the plasma membrane to the inner nuclear membrane, whereas AR-CTF is translocated to the lysosome via retrograde membrane trafficking. Nuclear envelope localization of proAR involves truncation of the C-terminus, which subsequently activates the ER-retrieval signal. The truncated form of proAR interacts with A-type lamin and is retained at the inner nuclear membrane. Heterochromatin formation is then induced and global transcription is transiently suppressed. This study gives new insight into epigenetic chromatin organization in mammalian cells: a plasma-membrane-anchored growth factor is targeted to the inner nuclear membrane where it participates in dynamic chromatin organization and control of transcription.

Localized regulation of axonal RanGTPase controls retrograde injury signaling in peripheral nerve

Peripheral sensory neurons respond to axon injury by activating an importin-dependent retrograde signaling mechanism. How is this mechanism regulated? Here, we show that Ran GTPase and its associated effectors RanBP1 and RanGAP regulate the formation of importin signaling complexes in injured axons. A gradient of nuclear RanGTP versus cytoplasmic RanGDP is thought to be fundamental for the organization of eukaryotic cells. Surprisingly, we find RanGTP in sciatic nerve axoplasm, distant from neuronal cell bodies and nuclei, and in association with dynein and importin-alpha. Following injury, localized translation of RanBP1 stimulates RanGTP dissociation from importins and subsequent hydrolysis, thereby allowing binding of newly synthesized importin-beta to importin-alpha and dynein. Perturbation of RanGTP hydrolysis or RanBP1 blockade at axonal injury sites reduces the neuronal conditioning lesion response. Thus, neurons employ localized mechanisms of Ran regulation to control retrograde injury signaling in peripheral nerve.

Membrane-anchored growth factors, the epidermal growth factor family: beyond receptor ligands

The epidermal growth factor (EGF) family and the EGF receptor (EGFR, ErbB) tyrosine kinase family have been spearheading the studies of signal transduction events that determine cell fate and behavior in vitro and in vivo. The EGFR family and their signaling pathways are giving us tremendous advantages in developing fascinating molecular target strategies for cancer therapy. Currently, two important types of EGFR inhibitors are in clinical use: neutralizing antibodies of EGFR or ErbB2, and synthetic small compounds of tyrosine kinase inhibitors designed for receptors. On the other hand, basic research of the EGF family ligands presents new challenges as membrane-anchored growth factors. All members of the EGF family have important roles in development and diseases and are shed from the plasma membrane by metalloproteases. The ectodomain shedding of the ligands has emerged as a critical component in the functional transactivation of EGFRs in interreceptor cross-talk in response to various shedding stimulants such as G-protein coupled receptor agonists, growth factors, cytokines, and various physicochemical stresses. Among the EGFR-ligands, heparin-binding EGF-like growth factor (HB-EGF) is a prominent ligand in our understanding of the pathophysiological roles of ectodomain shedding in cancer, wound healing, cardiac diseases, etc. Here we focus on ectodomain shedding of the EGF family ligands, especially HB-EGF by disintegrin and metalloproteases, which are not only key events of receptor cross talk, but also novel intercellular signaling by their carboxy-terminal fragments to regulate gene expression directly.

Membrane-anchored growth factor, HB-EGF, on the cell surface targeted to the inner nuclear membrane

Heparin-binding EGF-like growth factor (HB-EGF) is synthesized as a type I transmembrane protein (proHB-EGF) and expressed on the cell surface. The ectodomain shedding of proHB-EGF at the extracellular region on the plasma membrane yields a soluble EGF receptor ligand and a transmembrane-cytoplasmic fragment (HB-EGF-CTF). The cytoplasmic domain of proHB-EGF (HB-EGF-cyto) interacts with transcriptional repressors to reverse their repressive activities. However, how HB-EGF-cyto accesses transcriptional repressors is yet unknown. The present study demonstrates that, after exposure to shedding stimuli, both HB-EGF-CTF and unshed proHB-EGF translocate to the nuclear envelope. Immunoelectron microscopy and digitonin-permeabilized cells showed that HB-EGF-cyto signals are at the inner nuclear membrane. A short sequence element within the HB-EGF-cyto allows a transmembrane protein to localize to the nuclear envelope. The dominant-active form of Rab5 and Rab11 suppressed nuclear envelope targeting. Collectively, these data demonstrate that membrane-anchored HB-EGF is targeted to the inner nuclear membrane via a retrograde membrane trafficking pathway.

Endovascular therapy for massive haemothorax caused by ruptured extracranial vertebral artery aneurysm with neurofibromatosis Type 1

Extracranial vertebral artery aneurysm is uncommon, and the common cause is penetrating trauma. Rupture of extracranial vertebral artery aneurysm into the thoracic cavity is extremely rare and fatal due to haemorrhagic shock by massive haemothorax. We report an intrathoracic rupture of the extracranial vertebral artery aneurysm with neurofibromatosis Type 1, successfully treated by coil and liquid embolisation.

The carboxyl-terminal fragment of pro-HB-EGF reverses Bcl6-mediated gene repression

Heparin-binding epidermal growth factor-like growth factor (HB-EGF), a member of the EGF family, is synthesized as a type I transmembrane precursor (pro-HB-EGF). Ectodomain shedding of pro-HB-EGF yields an amino-terminal soluble ligand of EGF receptor (HB-EGF) and a carboxyl-terminal fragment (HB-EGF-CTF) consisting of the transmembrane and cytoplasmic domains. We previously showed that the HB-EGF-CTF translocates from the plasma membrane to the nucleus and plays a role as a signaling molecule. Immunoprecipitation showed that HB-EGF-CTF can associate with Bcl6, a transcriptional repressor in mammalian cells. A glutathione S-transferase pulldown assay revealed that HB-EGF-CTF interacted efficiently with zinc fingers 4-6 of Bcl6. A luciferase reporter assay showed that the nuclear translocation of HB-EGF-CTF following shedding reversed transcriptional repression of cyclin D2 by Bcl6. Additionally, the level of cyclin D2 protein increased and Bcl6 interaction with the cyclin D2 promoter decreased in parallel with the shedding of pro-HB-EGF at all endogenous levels. These findings suggest that HB-EGF-CTF is a potent regulator of gene expression via its interaction with the transcriptional repressor Bcl6.

Preoperative portal vein embolization with a mixture of gelatin sponge and iodized oil: efficacy and safety

PURPOSE

To evaluate whether portal vein embolization (PVE) using a mixture of gelatin sponge (GS) pieces and iodized oil is safe and effective in inducing hypertrophy of the future liver remnants (FLR).

MATERIAL AND METHODS

PVE was performed in 14 patients (eight male and six female, mean age 65 years, range 35-81 years) diagnosed with malignant liver tumor before surgery, whose FLR volumes were judged too small to allow for safe resection. Liver volume change, biochemical data change, complications related to PVE, and postoperative complications were retrospectively evaluated.

RESULTS

PVE was successful in all patients, and there were no procedural complications. Absolute FLR volume and FLR/total liver volume (TLV) ratio increased by 102 cm3 and 8% (mean values), respectively. Planned hepatectomies were cancelled in three patients due to extrahepatic metastasis or bile duct infection. Five of the 11 patients (45%) who underwent hepatectomies had major postoperative complications. However, complications due to hepatic failure were not seen. In 10 patients, except one whose outcome was fatal outcome, the mean hospitalization days with and without major complications were 73 and 33 days, respectively.

CONCLUSION

PVE using a mixture of GS and iodized oil seems to be effective and safe in inducing hypertrophy of the FLR.

Phosphorylation of RanGAP1 stabilizes its interaction with Ran and RanBP1

Ran is a nuclear Ras-like GTPase that is required for various nuclear events including the bi-directional transport of proteins and ribonucleoproteins through the nuclear pore complex, spindle formation, and reassembly of the nuclear envelope. One of the key regulators of Ran is RanGAP1, a Ran specific GTPase activating protein. The question of whether a mechanism exists for controlling nucleocytoplasmic transport through the regulation of RanGAP1 activity continues to be debated. Here we show that RanGAP1 is phosphorylated in vivo and in vitro. Serine-358 (358S) was identified as the major phosphorylation site, by MALDI-TOF-MS spectrometry. Site directed mutagenesis at this position abolished the phosphorylation. Experiments using purified recombinant kinase and specific inhibitors such as DRB and apigenin strongly suggest that casein kinase II (CK2) is the responsible kinase. Although the phosphorylation of 358S of RanGAP1 did not significantly alter its GAP activity, the phosphorylated wild type RanGAP1, but not a mutant harboring a mutation at the phosphorylation site 358S, efficiently formed a stable ternary complex with Ran and RanBP1 in vivo, suggesting that the 358S phosphorylation of RanGAP1 affects the Ran system.

Endovascular therapy for abdominal pseudoaneurysms: analysis from technical and clinical aspects

PURPOSE

To clarify the factors of outcomes by endovascular therapy for abdominal pseudoaneurysm (PSA) from both technical and clinical aspects.

MATERIAL AND METHODS

Sixteen patients with PSAs underwent embolization. Embolic methods were classified into two groups: proximal and distal embolization (PDE) and proximal embolization alone (PE). The patients were classified into four groups by shock index. Pre-embolization hemoglobin (Hb) level and decrease in Hb level were evaluated. Outcomes were classified into two groups: successful recovery and failure despite successful PSA embolization.

RESULTS

There were no statistical differences in success, recurrence, and complication rate, and outcomes between the two embolic methods. There was a statistically significant correlation between the grades of shock indices and outcomes (P<0.05). There was no statistical difference between the Hb levels and outcomes.

CONCLUSION

Outcomes were not dependent on the embolic methods. Shock index reflecting clinical status may be a simple predictor of outcome. PSA should therefore be treated by optimal embolic methods as quickly as possible to avoid rupture.

Different populations of RNA polymerase II in living mammalian cells

RNA polymerase II is responsible for transcription of most eukaryotic genes, but, despite exhaustive analysis, little is known about how it transcribes natural templates in vivo. We studied polymerase dynamics in living Chinese hamster ovary cells using an established line that expresses the largest (catalytic) subunit of the polymerase (RPB1) tagged with the green fluorescent protein (GFP). Genetic complementation has shown this tagged polymerase to be fully functional. Fluorescence loss in photobleaching (FLIP) reveals the existence of at least three kinetic populations of tagged polymerase: a large rapidly-exchanging population, a small fraction resistant to 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) but sensitive to a different inhibitor of transcription (i.e. heat shock), and a third fraction sensitive to both inhibitors. Quantitative immunoblotting shows the largest fraction to be the inactive hypophosphorylated form of the polymerase (i.e. IIA). Results are consistent with the second (DRB-insensitive but heat-shock-sensitive) fraction being bound but not engaged, while the third (sensitive to both DRB and heat shock) is the elongating hyperphosphorylated form (i.e. IIO).

Importin alpha can migrate into the nucleus in an importin beta- and Ran-independent manner

A classical nuclear localization signal (NLS)-containing protein is transported into the nucleus via the formation of a NLS-substrate/importin alpha/beta complex. In this study, we found that importin alpha migrated into the nucleus without the addition of importin beta, Ran or any other soluble factors in an in vitro transport assay. A mutant importin alpha lacking the importin beta-binding domain efficiently entered the nucleus. Competition experiments showed that this import pathway for importin alpha is distinct from that of importin beta. These results indicate that importin alpha alone can enter the nucleus via a novel pathway in an importin beta- and Ran-independent manner. Furthermore, this process is evolutionarily conserved as similar results were obtained in Saccharomyces cerevisiae. Moreover, the import rate of importin alpha differed among individual nuclei of permeabilized cells, as demonstrated by time-lapse experiments. This heterogeneous nuclear accumulation of importin alpha was affected by the addition of ATP, but not ATPgammaS. These results suggest that the nuclear import machinery for importin alpha at individual nuclear pore complexes may be regulated by reaction(s) that require ATP hydrolysis.

Nuclear import of the U1A splicesome protein is mediated by importin alpha /beta and Ran in living mammalian cells

U1A is a component of the uracil-rich small nuclear ribonucleoprotein. The molecular mechanism of nuclear import of U1A was investigated in vivo and in vitro. When recombinant deletion mutants of U1A are injected into the BHK21 cell cytoplasm, the nuclear localization signal (NLS) of U1A is found in the N-terminal half of the central domain (residues 100-144 in mouse U1A). In an in vitro assay, it was found that the U1A-NLS accumulated in only a portion of the nuclei in the absence of cytosolic extract. In contrast, the addition of importin alpha/beta and Ran induced the uniform nuclear accumulation of U1A-NLS in all cells. Furthermore, U1A was found to bind the C-terminal portion of importin alpha. In addition, the in vitro nuclear migration of full-length U1A was found to be exclusively dependent on importin alpha/beta and Ran. Moreover, in living cells, the full-length U1A accumulated in the nucleus in a Ran-dependent manner, and nuclear accumulation was inhibited by the importin beta binding domain of importin alpha. These results suggest that the nuclear import of U1A is mediated by at least two distinct pathways, an importin alpha/beta and Ran-dependent and an -independent pathway in permeabilized cells, and that the latter pathway may be suppressed in intact cells.

Slippage of nonsuperfluid helium films

We measured the mechanical response of 3He and 4He films on an oscillating substrate using an ultrasonic technique. Up to the coverage at which the fluid state appears at absolute zero, a part of the nonsuperfluid 3He and 4He films underwent slipping relative to the substrate at low temperatures. From the temperature dependence of the slippage, it was found that a thermally activated process plays an important role in the frictional force of this system.

Recycling of importin alpha from the nucleus is suppressed by loss of RCC1 function in living mammalian cells

We previously reported that the nuclear import of substrates containing SV40 T antigen nuclear localization signal (NLS) was suppressed in a temperature-sensitive RCC1 mutant cell line, tsBN2, at nonpermissive temperature. Moreover, it was shown that import into wild type BHK21 cell-derived nuclei gradually decreased in heterokaryons between the tsBN2 and BHK21 cells, although the BHK21 nuclei retained wild type RCC1 and should contain RanGTP (Tachibana et al., 1994). In this study, it was found that in the heterokaryons cultured at non-permissive temperature, endogenous importin alpha was not detected immunocytochemically in the cytoplasm or BHK21 nuclei but only in the tsBN2 nuclei, suggesting that importin alpha cannot be exported from the RCC1-depleted nuclei. In fact, importin alpha microinjected into the nucleus of tsBN2 cells at non-permissive temperature remained in the nucleus. These results strongly support the hypothesis that the recycling of importin alpha from the nucleus requires nuclear RanGTP. Moreover, it was found that cytoplasmic injection of importin alpha restored the import of SV40 T-NLS substrates in the BHK21 nuclei but not the tsBN2 nuclei in the heterokaryons. This indicates that the decrease of importin alpha from the cytoplasm in the heterokaryons leads to a suppression of the efficiency of nuclear import of the T-NLS substrate and provides support for the view that nuclear RanGTP is essential for the nuclear entry of the substrates.

Nucleocytoplasmic protein transport and recycling of Ran

The active transport of proteins into and out of the nucleus is mediated by specific signals, the nuclear localization signal (NLS) and nuclear export signal (NES), respectively. The best characterized NLS is that of the SV40 large T antigen, which contains a cluster of basic amino acids. The NESs were first identified in the protein kinase inhibitor (PKI) and HIV Rev protein, which are rich in leucine residues. The SV40 T-NLS containing transport substrates are carried into the nucleus by an importin alpha/beta heterodimer. Importin alpha recognizes the NLS and acts as an adapter between the NLS and importin beta, whereas importin beta interacts with importin alpha bound to the NLS, and acts as a carrier of the NLS/importin alpha/beta trimer. It is generally thought that importin alpha and beta are part of a large protein family. The leucine rich NES-containing proteins are exported from the nucleus by one of the importin beta family molecules, CRM1/exportin 1. A Ras-like small GTPase Ran plays a crucial role in both import/export pathways and determines the directionality of nuclear transport. It has recently been demonstrated in living cells that Ran actually shuttles between the nucleus and the cytoplasm and that the recycling of Ran is essential for the nuclear transport. Furthermore, it has been shown that nuclear transport factor 2 (NTF2) mediates the nuclear import of RanGDP. This review largely focuses on the issue concerning the functional divergence of importin alpha family molecules and the role of Ran in nucleocytoplasmic protein transport.

Urinary excretion of aquaporin-2 water channel differentiates psychogenic polydipsia from central diabetes insipidus

The present study was undertaken to determine whether urinary excretion of aquaporin-2 (AQP-2) water channel under ad libitum water intake is of value to differentiate polyuria caused by psychogenic polydipsia from central diabetes insipidus. A 30-min urine collection was made at 0900 h in 3 groups of: 11 patients with central diabetes insipidus (22-68 yr old), 10 patients with psychogenic polydipsia (28-60 yr old), and 15 normal subjects (21-38 yr old). In the patients with central diabetes insipidus, the plasma arginine vasopressin level was low despite hyperosmolality, resulting in hypotonic urine. Urinary excretion of AQP-2 was 37 +/- 15 fmol/mg creatinine, a value one-fifth less than that in the normal subjects. In the patients with psychogenic polydipsia, plasma arginine vasopressin and urinary osmolality were as low as those in the patients with central diabetes insipidus. However, urinary excretion of AQP-2 of 187 +/- 45 fmol/mg creatinine was not decreased, and its excretion was equal to that in the normal subjects. These results indicate that urinary excretion of AQP-2, under ad libitum water drinking, participates in the differentiation of psychogenic polydipsia from central diabetes insipidus.

A monoclonal antibody to the COOH-terminal acidic portion of Ran inhibits both the recycling of Ran and nuclear protein import in living cells

A small GTPase Ran is a key regulator for active nuclear transport. In immunoblotting analysis, a monoclonal antibody against recombinant human Ran, designated ARAN1, was found to recognize an epitope in the COOH-terminal domain of Ran. In a solution binding assay, ARAN1 recognized Ran when complexed with importin beta, transportin, and CAS, but not the Ran-GTP or the Ran-GDP alone, indicating that the COOH-terminal domain of Ran is exposed via its interaction with importin beta-related proteins. In addition, ARAN1 suppressed the binding of RanBP1 to the Ran-importin beta complex. When injected into the nucleus of BHK cells, ARAN1 was rapidly exported to the cytoplasm, indicating that the Ran-importin beta-related protein complex is exported as a complex from the nucleus to the cytoplasm in living cells. Moreover, ARAN1, when injected into the cultured cells induces the accumulation of endogenous Ran in the cytoplasm and prevents the nuclear import of SV-40 T-antigen nuclear localization signal substrates. From these findings, we propose that the binding of RanBP1 to the Ran-importin beta complex is required for the dissociation of the complex in the cytoplasm and that the released Ran is recycled to the nucleus, which is essential for the nuclear protein transport.

Up-regulation of nuclear protein import by nuclear localization signal sequences in living cells

Using an in vivo assay system, nuclear import ability in individual cells was determined by examining the nuclear import rate. It was found that when a small (not excess) amount of SV40 T-NLS peptides was co-injected, the nuclear import rate of SV40 T-NLS-containing substrates apparently increased. This up-regulation was reproduced by the co-injection of peptides containing bipartite type NLS of CBP80, but not mutated non-functional NLS peptides, which suggests that these phenomena are specific for functional NLSs. It was further shown that although, in growth-arrested cells, the nuclear import rate was down-regulated compared to growing cells, the elevation of the functional import rate by co-injected NLS peptides reached the same level as in proliferating cells. This up-regulation was abolished by the addition of a protein kinase inhibitor, staurosporine. These results suggest that although potential nuclear import ability does not vary in each cell, the rate of nuclear import may be controlled by the amount of karyophilic proteins, which need to be carried into the nucleus from the cytoplasm, possibly via an NLS-dependent phosphorylation reaction.

Molecular cloning and functional analysis of cynomolgus monkey CYP1A2

Complementary DNA fragments encoding cynomolgus monkey CYP1A2 were amplified by the reverse transcriptase-polymerase chain reaction (RT-PCR) method from the liver total RNA of a 3-methylcholanthrene (3-MC)-treated cynomolgus monkey. The nucleotide sequence determined was 1630 bp long and contained an open reading frame for a polypeptide of 516 residues. The nucleotide and the deduced amino acid sequences of cynomolgus monkey CYP1A2 showed 95.1 and 92.8% identities to those of human CYP1A2, respectively. The level of CYP1A2 mRNA in the liver of untreated cynomolgus monkey was very low. Treatment with 3-MC increased it. Still, it was one-fortieth that of CYP1A1. Cynomolgus monkey CYP1A2 expressed in recombinant yeasts activated 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-3,8dimethylimidazo[4,5-flquinoxaline (MeIQx) at efficient rates in the umu mutagenicity test. This cytochrome P450 (CYP) also activated 2-amino-l-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), but less efficiently. These results indicate that cynomolgus monkeys have a functionally active CYPIA2 gene, but its expression level is very low in the liver of untreated cynomolgus monkeys.

Marmoset CYP1A2: primary structure and constitutive expression in livers

Complementary DNA of marmoset CYP1A2 was isolated by means of screening the cDNA library and reverse-transcriptase polymerase chain reaction. The deduced amino acid sequence of marmoset CYP1A2 consisted of 516 residues and showed 88.2 and 90.0% identities to corresponding forms in human and cynomolgus monkey, respectively. S1 nuclease protection assay demonstrated that CYP1A2 mRNA was expressed constitutively in the liver, but not in the lung, kidney and small intestine. The level of CYP1A2 mRNA in the liver was increased by treatment with 3-methylcholanthrene and polychlorinated biphenyls. Marmoset CYP1A2 expressed in recombinant yeast activated 2-amino-3-methylimidazo [4,5-f]quinoline (IQ) and 2-amino-3,8-dimethylimidazo [4,5-f]quinoxaline (MeIQx) efficiently, and also activated 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine (PhIP), but at a relatively lower rate in the umu mutagenicity test. Marmoset CYP1A2 also showed ethoxyresorufin O-de-ethylase activity. Based on these results, we demonstrate that marmosets constitutively express CYP1A2 in the liver as in humans.

Exogenously injected nuclear import factor p10/NTF2 inhibits signal-mediated nuclear import and export of proteins in living cells

p10/NTF2 is a cytosolic factor which is required for the translocation step in nuclear protein import in an in vitro assay with digitonin-permeabilized cells. To study the functional roles of p10/NTF2 on protein transport between the nucleus and cytoplasm in living cells, recombinant p10/NTF2 was micro-injected into cultured mammalian cells. Cytoplasmically injected p10/NTF2 strongly inhibited the nuclear import of co-injected NLS-containing substrates in a dose-dependent manner but had no effect on the diffusive import of small non-nuclear proteins. Moreover, when injected into the cell nucleus, p10/NTF2 inhibited the nuclear export of NES-containing substrates. The results suggest that the nuclear import factor p10/NTF2 may also be involved in the nuclear export of proteins and that the protein transport efficiency between the nucleus and cytoplasm may be regulated by the intracellular level of p10/NTF2.