Splicing factor SRSF3 represses translation of p21cip1/waf1 mRNA.

Serine/arginine-rich splicing factor 3 (SRSF3) is an RNA binding protein that most often regulates gene expression at the splicing level. Although the role of SRSF3 in mRNA splicing in the nucleus is well known, its splicing-independent role outside of the nucleus is poorly understood. Here, we found that SRSF3 exerts a translational control of p21 mRNA. Depletion of SRSF3 induces cellular senescence and increases the expression of p21 independent of p53. Consistent with the expression patterns of SRSF3 and p21 mRNA in the TCGA database, SRSF3 knockdown increases the p21 mRNA level and its translation efficiency as well. SRSF3 physically associates with the 3'UTR region of p21 mRNA and the translational initiation factor, eIF4A1. Our study proposes a model in which SRSF3 regulates translation by interacting with eIF4A1 at the 3'UTR region of p21 mRNA. We also found that SRSF3 localizes to the cytoplasmic RNA granule along with eIF4A1, which may assist in translational repression therein. Thus, our results provide a new mode of regulation for p21 expression, a crucial regulator of the cell cycle and senescence, which occurs at the translational level and involves SRSF3.

Avenanthramide-C Restores Impaired Plasticity and Cognition in Alzheimer's Disease Model Mice.

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by cognitive decline and dementia with no effective treatment. Here, we investigated a novel compound from oats named avenanthramide-C (Avn-C), on AD-related memory impairment and behavioral deficits in transgenic mouse models. Acute hippocampal slices of wild-type or AD transgenic mice were treated with Avn-C in the presence or absence of oligomeric Aß42. LTP analyses and immunoblotting were performed to assess the effect of Avn-C on Aß-induced memory impairment. To further investigate the effect of Avn-C on impaired memory and Aß pathology, two different AD transgenic mice (Tg2576 and 5XFAD) models were orally treated with either Avn-C or vehicle for 2 weeks. They were then assessed for the effect of the treatment on neuropathologies and behavioral impairments. Avn-C reversed impaired LTP in both ex vivo- and in vivo-treated AD mice hippocampus. Oral administration (6 mg/kg per day) for 2 weeks in AD mice leads to improved recognition and spatial memory, reduced caspase-3 cleavage, reversed neuroinflammation, and to accelerated glycogen synthase kinase-3ß (pS9GSK-3ß) and interleukin (IL-10) levels. Avn-C exerts its beneficial effects by binding to α1A adrenergic receptors to stimulate adenosine monophosphate-activated kinase (AMPK). All of the beneficial effects of Avn-C on LTP retrieval could be blocked by prazosin hydrochloride, a specific inhibitor of α1A adrenergic receptors. Our findings provide evidence, for the first time, that oats' Avn-C reverses the AD-related memory and behavioral impairments, and establish it as a potential candidate for Alzheimer's disease drug development.

NEDDylation promotes stress granule assembly.

Stress granules (SGs) harbour translationally stalled messenger ribonucleoproteins and play important roles in regulating gene expression and cell fate. Here we show that neddylation promotes SG assembly in response to arsenite-induced oxidative stress. Inhibition or depletion of key components of the neddylation machinery concomitantly inhibits stress-induced polysome disassembly and SG assembly. Affinity purification and subsequent mass-spectrometric analysis of Nedd8-conjugated proteins from translationally stalled ribosomal fractions identified ribosomal proteins, translation factors and RNA-binding proteins (RBPs), including SRSF3, a previously known SG regulator. We show that SRSF3 is selectively neddylated at Lys85 in response to arsenite. A non-neddylatable SRSF3 (K85R) mutant do not prevent arsenite-induced polysome disassembly, but fails to support the SG assembly, suggesting that the neddylation pathway plays an important role in SG assembly.

Direct confirmation of quiescence of CD34+CD38- leukemia stem cell populations using single cell culture, their molecular signature and clinicopathological implications.

BACKGROUND: The proliferating activity of a single leukemia stem cell and the molecular mechanisms for their quiescent property remain unknown, and also their prognostic value remains a matter of debate. Therefore, this study aimed to demonstrate the quiescence property and molecular signature of leukemia stem cell and their clinicopathological implications. METHODS: Single cell sorting and culture were performed in the various sets of hematopoietic stem cells including CD34+CD38- acute myeloid leukemia (AML) cell population (ASCs) from a total of 60 patients with AML, and 11 healthy controls. Their quiescence related-molecular signatures and clinicopathological parameters were evaluated in AML patients. RESULTS: Single cell plating efficiency of ASCs was significantly lower (8.6%) than those of normal hematopoietic stem cells i.e.: cord blood, 79.0%; peripheral blood, 45.3%; and bone marrow stem cell, 31.1%. Members of the TGFß super-family signaling pathway were most significantly decreased; as well as members of the Wnt, Notch, pluripotency maintenance and hedgehog pathways, compared with non ASC populations. mtDNA copy number of ASCs was significantly lower than that of corresponding other cell populations. However, our data couldn't support the prognostic value of the ASCs in AML. CONCLUSIONS: ASCs showed remarkable lower plating efficiency and slower dividing properties at the single cell level. This quiescence is represented as a marked decrease in the mtDNA copy number and also linked with down-regulation of genes in various molecular pathways.

Regulation of cellular RNA nano-particle assembly by splicing factor SRp20.

Cellular RNA nano-particles (RNA granules) such as stress granule (SG) and P-body (PB) are translationally silenced mRNA-protein complexes. Previously, a genome-wide loss-of-function screen using oligomeric siRNAs targeting potential drug target genes was performed to identify genes that are involved in SG and PB assembly. SRp20 (SRSF3), a splicing regulator, was identified as a potential regulator for the RNA granule assembly. Here, we show that SRp20 is a bona-fide RNA granule component using antibody against SRp20 as well as Flag-tagged SRp20 through immunofluorescence microscopy. More importantly, upon knockdown of SRp20 using siRNA, RNA granule formation was potently disrupted indicating that SRp20 is one of the major structural components of SGs and PBs. Interestingly, polysome profiling analyses displayed that SRp20 is distributed in all ribosomal fractions suggesting a potential role of SRp20 as a post-transcriptional mRNA regulator. These results broaden the functional role of SRp20 from the nuclear RNA processing events to the cytoplasmic post-transcriptional mRNA regulatory events through RNA granules that are critical for the regulation of gene expression.

HOXB13 promotes androgen independent growth of LNCaP prostate cancer cells by the activation of E2F signaling.

BACKGROUND: Androgen signaling plays a critical role in the development of prostate cancer and its progression. However, androgen-independent prostate cancer cells emerge after hormone ablation therapy, resulting in significant clinical problems. We have previously demonstrated that the HOXB13 homeodomain protein functions as a prostate cancer cell growth suppressor by inhibiting androgen-mediated signals. However, the role of the HOXB13 in androgen-independent growth of prostate cancer cells remains unexplained. RESULTS: In this report, we first demonstrated that HOXB13 was highly overexpressed in hormone-refractory tumors compared to tumors without prostate-specific antigen after initial treatment. Functionally, in an androgen-free environment minimal induction of HOXB13 in LNCaP prostate cancer cells, to the level of the normal prostate, markedly promoted cell proliferation while suppression inhibited cell proliferation. The HOXB13-mediated cell growth promotion in the absence of androgen, appears to be mainly accomplished through the activation of RB-E2F signaling by inhibiting the expression of the p21waf tumor suppressor. Indeed, forced expression of HOXB13 dramatically decreased expression of p21waf; this inhibition largely affected HOXB13-mediated promotion of E2F signaling. CONCLUSIONS: Taken together, the results of this study demonstrated the presence of a novel pathway that helps understand androgen-independent survival of prostate cancer cells. These findings suggest that upregulation of HOXB13 is associated with an additive growth advantage of prostate cancer cells in the absence of or low androgen concentrations, by the regulation of p21-mediated E2F signaling.

Differential CARM1 expression in prostate and colorectal cancers.

BACKGROUND: Coactivator-associated arginine methyltransferase 1 (CARM1) functions as a transcriptional coactivator of androgen receptor (AR)-mediated signaling. Correspondingly, overexpression of CARM1 has been associated with the development of prostate cancer (PCa) and its progression to androgen-independent PCa. In our preliminary study, however, the promoting effects of CARM1, with regard to androgen-stimulated AR target gene expression were minimal. These results suggested that the AR target gene expression associated with CARM1 may result primarily from non-hormone dependent activity. The goal of this study was to confirm the pattern of expression of CARM1 in human tumors and determine the mechanism of action in CARM1 overexpressed tumors. METHODS: Tissue microarray was used to determine the pattern of expression of CARM1 in human cancers by immunohistochemistry. CARM1 expression was also evaluated in prostate and colorectal surgical specimens and the clinical records of all cases were reviewed. In addition, a reporter transcription assay using the prostate-specific antigen (PSA) promoter was used to identify the signaling pathways involved in non-hormone-mediated signal activation associated with CARM1. RESULTS: The tissue microarray showed that CARM1 was particularly overexpressed in the colorectal cancers while CARM1 expression was not prevalent in the prostate and breast cancers. Further studies using surgical specimens demonstrated that CARM1 was highly overexpressed in 75% of colorectal cancers (49 out of 65) but not in the androgen-independent PCa. In addition, CARM1's coactivating effect on the entire PSA promoter was very limited in both androgen-dependent and androgen-independent PCa cells. These results suggest that there are other factors associated with CARM1 expression in PSA regulation. Indeed, CARM1 significantly regulated both p53 and NF-kappaB target gene transcription. CONCLUSIONS: The results of this study suggest that, in addition to its role in activation of steroid receptors, CARM1 functions as a transcriptional modulator by altering the activity of many transcriptional factors, especially with regard to androgen independent PCa and colorectal cancers.

HOXB13 is co-localized with androgen receptor to suppress androgen-stimulated prostate-specific antigen expression.

During the prostate cancer (PCa) development and its progression into hormone independency, androgen receptor (AR) signals play a central role by triggering the regulation of target genes, including prostate-specific antigen. However, the regulation of these AR-mediated target genes is not fully understood. We have previously demonstrated a unique role of HOXB13 homeodomain protein as an AR repressor. Expression of HOXB13 was highly restricted to the prostate and its suppression dramatically increased hormone-activated AR transactivation, suggesting that prostate-specific HOXB13 was a highly potent transcriptional regulator. In this report, we demonstrated the action mechanism of HOXB13 as an AR repressor. HOXB13 suppressed androgen-stimulated AR activity by interacting with AR. HOXB13 did neither bind to AR responsive elements nor disturb nuclear translocation of AR in response to androgen. In PCa specimen, we also observed mutual expression pattern of HOXB13 and AR. These results suggest that HOXB13 not only serve as a DNA-bound transcription factor but play an important role as an AR-interacting repressor to modulate hormone-activated androgen receptor signals. Further extensive studies will uncover a novel mechanism for regulating AR-signaling pathway to lead to expose new role of HOXB13 as a non-DNA-binding transcriptional repressor.

Differential expression of osteocalcin during the metastatic progression of prostate cancer.

Osteocalcin expression is restricted to osteoblasts and serum osteocalcin level is elevated in metastatic bone tumors including prostate tumors, which predominantly metastasizes to the bone and causes typical osteoblastic lesions. Previously, we have reported that osteocalcin RNA is widely expressed but incompletely spliced in the prostate including prostate tumors. Considering that many studies using osteocalcin-driven gene therapy have been conducted to treat hormone refractory metastatic tumors, detailed mechanisms controlling osteocalcin expression needs to be clarified. We aim to learn how osteocalcin expression is regulated during the metastatic process of prostate cancer. We applied assays of immunohistochemistry and RNA in situ hybridization in prostate tumors acquired from prostate (15) and metastatic sites, 13 from lymph node and 14 from bone. RT-PCR analysis in various cultured prostate cells was also performed. As predicted, osteocalcin RNA was highly expressed in most prostate epithelial cells of tumors, regardless of metastatic status of the tumor. However, osteocalcin protein was undetectable in tumors acquired from the primary site or lymph nodes whereas protein was highly expressed in the majority of bone-metastasized prostate tumors. RT-PCR analysis demonstrated that there was more completely spliced form of osteocalcin RNA present in bone-derived prostate cancer cells. Our data suggest that osteocalcin RNA was expressed but not completely spliced in non-bone environment, ultimately resulting in improper production of osteocalcin protein. This study explains why serum osteocalcin level is increased in patients with bone-metastasized prostate cancers. Yet, it remains to be clarified what regulates bone-specific osteocalcin RNA splicing in prostate tumors.

Vibrio vulnificus metalloprotease VvpE is essentially required for swarming.

Bacterial swarming constitutes a good in vitro model for surface adherence and colonization, and is accompanied by expressions of virulence factors related to invasiveness. In this study, it was determined that Vibrio vulnificus swarming was abolished by mutation of the vvpE gene encoding a metalloprotease VvpE and this swarming defect was recovered by complementation of the vvpE gene. Expression of the vvpE gene began simultaneously with the beginning of swarming and increased along with expression of the luxS gene encoding the synthase of the precursor of quorum-sensing signal molecule autoinducer 2, and this increased vvpE expression was decreased by mutation of the luxS gene. Moreover, VvpE destroyed IgA and lactoferrins, which are responsible for mucosal immunity. These results suggest that VvpE may play important roles in the surface adherence and colonization of V. vulnificus by facilitating swarming and in the mucosal invasion of V. vulnificus by destroying IgA and lactoferrin.

Ferrophilic characteristics of Vibrio vulnificus and potential usefulness of iron chelation therapy.

We determined the ferrophilic characteristics of Vibrio vulnificus to evaluate the potential usefulness of iron chelation therapy for the prevention of V. vulnificus infection. Readily available non-transferrin-bound iron (NTBI) is required for the initiation of V. vulnificus growth under in vitro iron-limited conditions and human ex vivo conditions. NTBI aided efficient transferrin-bound iron (TBI) use by V. vulnificus, and the vulnibactin-mediated iron-uptake system was expressed after bacterial growth had been started by NTBI. V. vulnificus required higher NTBI levels for the initiation of growth, produced siderophores at lower levels, and used TBI less efficiently than other bacteria. In addition, the growth of V. vulnificus was inhibited by deferiprone, a clinically available iron chelator. These results show that V. vulnificus is a ferrophilic bacterium that requires higher NTBI levels than other pathogens and that iron chelation therapy might be an effective means of preventing the in vivo growth of V. vulnificus in susceptible patients.

Pseudomonas aeruginosa alkaline protease can facilitate siderophore-mediated iron-uptake via the proteolytic cleavage of transferrins.

In order to determine whether Pseudomonas aeruginosa alkaline protease AprA is involved in facilitating siderophore-mediated iron-acquisition from human transferrins, we measured bacterial growth, the production of siderophore and AprA, iron-acquisition from transferrins, and the proteolytic cleavage of transferrins in an alkaline minimal medium (pH 8.3) containing human transferrins as an iron source and compared these on a time scale. The growth of P. aeruginosa was found to be stimulated in proportion to the iron-saturation levels of transferrins. AprA production and the proteolytic cleavage of transferrins began concomitantly with siderophore production from the early growth phase when P. aeruginosa was actively growing and consuming most iron for growth. However, the AprA-free, but siderophore-containing, culture ultrafiltrates could also remove iron from transferrin. These results indicate that alkaline protease AprA can facilitate the siderophore-mediated iron-uptake of P. aeruginosa via the proteolytic cleavage of transferrins. However, the proteolytic cleavage by AprA is not essentially required for iron-acquisition from transferrins.

Suppression and inactivation of Vibrio vulnificus hemolysin in cirrhotic ascites, a human ex vivo experimental system.

To elucidate the mechanisms underlying the in vivo suppression and inactivation of Vibrio vulnificus hemolysin (VvhA), we used cirrhotic ascites fluid as a human ex vivo experimental system. VvhA expression was suppressed in proportion to the amount of cirrhotic ascites. The expression of vvhA in undiluted cirrhotic ascites could be suppressed further by the addition of glucose, a constituent of cirrhotic ascites. VvhA was readily inactivated in the presence of cirrhotic ascites by a cholesterol-mediated oligomerization and interaction with an undefined constituent(s) of cirrhotic ascites. These results indicate that the expression of vvhA can be suppressed and that any VvhA produced is inactivated by the constituents of cirrhotic ascites. Our results suggest that only a very small portion of the VvhA that is produced in human body fluids may actually contribute to the pathogenesis of V. vulnificus septicemia. It is suggested that cirrhotic ascites could be used as a human ex vivo experimental system for the studies on the in vivo expression and the significance of V. vulnificus virulence factors.

Swarming differentiation of vibrio vulnificus downregulates the expression of the vvhBA hemolysin gene via the LuxS quorum-sensing system.

Swarming has proven to be a good in vitro model for bacterial surface adherence and colonization, and the swarming differentiation of a bacterium has been shown to be coupled with changes in the expression of virulence factors associated with its invasiveness, particularly in the early stages of infection. In this study, we attempted to determine whether the expression of vvhA, which encodes for hemolysin/cytolysin (VvhA), is either upregulated or downregulated during the swarming differentiation of V. vulnificus. The insertional inactivation of vvhA itself exerted no detectable effect on the expression of V. vulnificus swarming motility. However, in our lacZ-fused vvhA transcriptional reporter assay, vvhA expression decreased in swarming V. vulnificus as compared to non-swarming or planktonic V. vulnificus. The reduced expression of vvhA in swarming V. vulnificus increased as a result of the deletional inactivation of luxS, a gene associated with quorum sensing. These results show that vvhA expression in swarming V. vulnificus is downregulated via the activity of the LuxS quorum-sensing system, suggesting that VvhA performs no essential role in the invasiveness of V. vulnificus via the adherence to and colonization on the body surfaces required in the early stages of the infection. However, VvhA may play a significant role in the pathophysiological deterioration occurring after swarming V. vulnificus is differentiated into planktonic V. vulnificus.

Vibrio vulnificus vulnibactin, but not metalloprotease VvpE, is essentially required for iron-uptake from human holotransferrin.

The roles of metalloprotease (VvpE) and catechol-siderophore (vulnibactin) in the uptake of iron from human transferrins by Vibrio vulnificus have been determined using different experimental conditions and methods. Therefore, in this study, we attempted to elucidate the roles of VvpE and vulnibactin using the same methods and experimental conditions, in an in vitro and a human ex vivo system, and in accordance with the molecular version of Koch's postulates. Neither vvpE mutation nor in trans vvpE complementation affected vulnibactin production, iron-assimilation from human holotransferrin (HT), and bacterial growth in a HT-containing deferrated Heart-Infusion medium (HT-DF-HI) or a HT-containing cirrhotic ascites (HT-CA). In contrast, the mutation of fur gene encoding Fur, a repressor regulating expression of the vulnibactin-mediated iron-uptake system, derepressed vulnibactin production, and facilitated iron-assimilation from HT and bacterial growth in HT-DF-HI or HT-CA. The mutation of vis gene encoding isochorismate synthase required for vulnibactin synthesis abolished vulnibactin production, iron-assimilation from HT and bacterial growth in HT-DF-HI or HT-CA. These results demonstrate that vulnibactin is essentially required for iron-assimilation from transferrin, and that VvpE has no direct effect on facilitating vulnibactin-mediated iron-assimilation from transferrin in vitro or in a human ex vivo system.

Proteases of a Bacillus subtilis clinical isolate facilitate swarming and siderophore-mediated iron uptake via proteolytic cleavage of transferrin.

We isolated a highly serine protease-producing Bacillus subtilis strain (PRY) from a clinical sample and identified it through biochemical testing and ribosomal DNA sequencing. The PRY strain exhibited a robust swarming behavior and was able to digest human transferrin efficiently, concomitantly with the production of catechol-siderophore in the exponential growth phase. The growth of PRY was in proportion to increased iron availability resulting from transferrin destruction. These results suggest that proteases of the B. subtilis PRY strain may play a significant role in the pathogenesis of human infections by facilitating siderophore-mediated iron uptake from transferrin and swarming motility.

Effect of the crp mutation on the utilization of transferrin-bound iron by Vibrio vulnificus.

Cyclic AMP-cAMP receptor protein (CRP) complex plays an essential role in the global regulation of Vibrio vulnificus virulence. We found that growth retardation of V. vulnificus caused by mutation of the crp gene encoding CRP was exacerbated under iron-limited conditions. Accordingly, we investigated the effect of crp mutation on the expression of the vulnibactin-mediated iron-uptake system and the ability of V. vulnificus to utilize transferrin-bound iron, and thus to grow in cirrhotic ascites, a human ex vivo system. The production of vulnibactin was suppressed, and the transcription of the vis and vuuA genes, which encode an enzyme required for vulnibactin synthesis and vulnibactin receptor protein, was also suppressed in the crp mutant. Moreover, the crp mutant could not utilize transferrin-bound iron, and its growth was severely suppressed both on transferrin-bound iron and in cirrhotic ascites. All the defects in the crp mutant were recovered by the in trans complementation of the wild-type crp gene. Putative CRP-binding sequences were found in the regulatory regions of the fur, vis and vuuA genes. These results indicate that crp mutation attenuates the ability to grow on transferrin-bound iron and in a human body fluid by down-regulating the vulnibactin-mediated iron-uptake system.

X-gal inhibits the swarming of Vibrio species.

The expressional levels of genes in swarmer cells can be determined by a simple method using X-gal-containing semisolid agars and lacZ-fusion transcription reporter strains of the genes concerned. However, X-gal alone inhibited the swarming of Vibrio, regardless of their ability to digest X-gal. Moreover, X-gal inhibited the growth of V. vulnificus containing functional lacZ. These effects of X-gal itself should be carefully considered when trying to determine the expression levels of genes in swarming cells using X-gal-containing semisolid agar.

Human serum albumin enhances the hemolytic activity of Vibrio vulnificus.

Vibrio vulnificus hemolysin (VvhA) is inactivated in the late growth phase by its oligomerization. Albumin is known to affect the activities of many bacterial toxins. In this study, we investigated the effects of human or bovine serum albumin (HSA or BSA) on the production and activity of VvhA. HSA did not affect V. vulnificus growth and vvhA transcription. However, VvhA hemolytic activity in culture supernatants was significantly higher in the presence of HSA than in the absence of HSA. By Western blot analysis, the oligomerization of VvhA was inhibited and the remaining active VvhA monomer was increased in culture supernatants containing HSA. BSA produced similar results. These findings indicate that both HSA and BSA stabilize VvhA and delay VvhA inactivation by oligomerization, and thus enhance VvhA activity.

Inactivation of Vibrio vulnificus hemolysin by oligomerization but not proteolysis.

Vibrio vulnificus extracellular protease (VvpE) is believed to destroy its hemolysin (VvhA) in the late growth phase, without obvious experimental evidence. So, we attempted to elucidate the mechanism. The hemolytic activity steeply increased with the expression of the VvhA in the early growth phase, and then abruptly declined with the expression of VvpE in the late growth phase. However, the VvhA activity also abruptly declined in a VvpE-deficient mutant. In Western blot, the degradation of VvhA was not observed; instead, the oligomerization of VvhA increased with the concomitant loss of hemolytic activity. These results evidently indicate that the inactivation of VvhA is due to the novel oligomerization of VvhA by unknown mechanism, but not to the destruction of VvhA by VvpE, so that the routine functional assay measuring hemolytic activity cannot reflect the actual production of VvhA.