Tip110, the Human Immunodeficiency Virus Type 1 (HIV-1) Tat-interacting Protein of 110 kDa as a Negative Regulator of Androgen Receptor (AR) Transcriptional Activation

SART3 reads methylarginine-marked glycine- and arginine-rich motifs

Glycine- and arginine-rich (GAR) motifs, commonly found in RNA-binding and -processing proteins, can be symmetrically (SDMA) or asymmetrically (ADMA) dimethylated at the arginine residue by protein arginine methyltransferases. Arginine-methylated protein motifs are usually read by Tudor domain-containing proteins. Here, using a GFP-Trap, we identify a non-Tudor domain protein, squamous cell carcinoma antigen recognized by T cells 3 (SART3), as a reader for SDMA-marked GAR motifs. Structural analysis and mutagenesis of SART3 show that aromatic residues lining a groove between two adjacent aromatic-rich half-a-tetratricopeptide (HAT) repeat domains are essential for SART3 to recognize and bind to SDMA-marked GAR motif peptides, as well as for the interaction between SART3 and the GAR-motif-containing proteins fibrillarin and coilin. Further, we show that the loss of this reader ability affects RNA splicing. Overall, our findings broaden the range of potential SDMA readers to include HAT domains.

Metformin Treatment Leads to Increased HIV Transcription and Gene Expression through Increased CREB Phosphorylation and Recruitment to the HIV LTR Promoter

Antiretroviral therapy has effectively suppressed HIV infection and replication and prolonged the lifespan of HIV-infected individuals. In the meantime, various complications including type 2 diabetes associated with the long-term antiviral therapy have shown steady increases. Metformin has been the front-line anti-hyperglycemic drug of choice and the most widely prescribed medication for the treatment of type 2 diabetes. However, little is known about the effects of Metformin on HIV infection and replication. In this study, we showed that Metformin treatment enhanced HIV gene expression and transcription in HIV-transfected 293T and HIV-infected Jurkat and human PBMC. Moreover, we demonstrated that Metformin treatment resulted in increased CREB expression and phosphorylation, and TBP expression. Furthermore, we showed that Metformin treatment increased the recruitment of phosphorylated CREB and TBP to the HIV LTR promoter. Lastly, we showed that inhibition of CREB phosphorylation/activation significantly abrogated Metformin-enhanced HIV gene expression. Taken together, these results demonstrated that Metformin treatment increased HIV transcription, gene expression, and production through increased CREB phosphorylation and recruitment to the HIV LTR promoter. These findings may help design the clinical management plan and HIV cure strategy of using Metformin to treat type 2 diabetes, a comorbidity with an increasing prevalence, in people living with HIV.

SART3, regulated by p53, is a biomarker for diagnosis, prognosis and immune infiltration in hepatocellular carcinoma

OBJECTIVE

This study aimed to investigate the role of squamous cell carcinoma antigen recognized by T cells 3 (SART3) in hepatocellular carcinoma (HCC).

METHODS

SART3 expression and prognostic value were analyzed in TCGA and GEO datasets. The diagnostic value and prognostic significance of SART3 were determined using immunohistochemistry in the Guangxi cohort. The whole-exome mutation spectrum of SART3 was analyzed in high and low expression groups in both TCGA and Guangxi cohorts. The biological functions of the SART3 gene were validated through in vitro experiments using small interfering RNA technology to downregulate SART3 expression in HCC cell lines.

RESULTS

SART3 expression was significantly higher in HCC tissues than in adjacent noncancerous liver tissues in TCGA, GEO and Guangxi cohorts. High expression of SART3 was significantly associated with poor prognosis in HCC patients. In TCGA and Guangxi cohorts, the expression of SART3 in the TP53 mutation group was significantly higher than that in the non-mutation group. Downregulation of SART3 expression significantly inhibited the migration and proliferation of HCC cells. SART3 may be involved mainly in immune infiltration of Th2 cells and macrophages in HCC. Additionally, SART3 can upregulate the expression of immune checkpoints (PD-L1 and TIM-3) and predict potential therapeutic agents for HCC.

CONCLUSION

The findings of this study demonstrate the diagnostic and prognostic value of SART3 in HCC. SART3 may be associated with immune infiltration of Th2 cells and macrophages in HCC, highlighting its potential role in the development and progression of HCC.

HIV Nef Expression Down-modulated GFAP Expression and Altered Glutamate Uptake and Release and Proliferation in Astrocytes

HIV infection of astrocytes leads to restricted gene expression and replication but abundant expression of HIV early genes Tat, Nef and Rev. A great deal of neuroHIV research has so far been focused on Tat protein, its effects on astrocytes, and its roles in neuroHIV. In the current study, we aimed to determine effects of Nef expression on astrocytes and their function. Using transfection or infection of VSVG-pseudotyped HIV viruses, we showed that Nef expression down-modulated glial fibrillary acidic protein (GFAP) expression. We then showed that Nef expression also led to decreased GFAP mRNA expression. The transcriptional regulation was further confirmed using a GFAP promoter-driven reporter gene assay. We performed transcription factor profiling array to compare the expression of transcription factors between Nef-intact and Nef-deficient HIV-infected cells and identified eight transcription factors with expression changes of 1.5-fold or higher: three up-regulated by Nef (Stat1, Stat5, and TFIID), and five down-regulated by Nef (AR, GAS/ISRE, HIF, Sp1, and p53). We then demonstrated that removal of the Sp1 binding sites from the GFAP promoter resulted in a much lower level of the promoter activity and reversal of Nef effects on the GFAP promoter, confirming important roles of Sp1 in the GFAP promoter activity and for Nef-induced GFAP expression. Lastly, we showed that Nef expression led to increased glutamate uptake and decreased glutamate release by astrocytes and increased astrocyte proliferation. Taken together, these results indicate that Nef leads to down-modulation of GFAP expression and alteration of glutamate metabolism in astrocytes, and astrocyte proliferation and could be an important contributor to neuroHIV.

Tip110/SART3-Mediated Regulation of NF-κB Activity by Targeting IκBα Stability Through USP15

To date, there are a small number of nuclear-restricted proteins that have been reported to play a role in NF-κB signaling. However, the exact molecular mechanisms are not fully understood. Tip110 is a nuclear protein that has been implicated in multiple biological processes. In a previous study, we have shown that Tip110 interacts with oncogenic ubiquitin specific peptidase 15 (USP15) and that ectopic expression of Tip110 leads to re-distribution of USP15 from the cytoplasm to the nucleus. USP15 is known to regulate NF-κB activity through several mechanisms including modulation of IκBα ubiquitination. These findings prompted us to investigate the role of Tip110 in the NF-κB signaling pathway. We showed that Tip110 regulates NF-κB activity. The expression of Tip110 potentiated TNF-α-induced NF-κB activity and deletion of the nuclear localization domain in Tip110 abrogated this potentiation activity. We then demonstrated that Tip110 altered IκBα phosphorylation and stability in the presence of TNF-α. Moreover, we found that Tip110 and USP15 opposingly regulated NF-κB activity by targeting IκBα protein stability. We further showed that Tip110 altered the expression of NF-κB-dependent proinflammatory cytokines. Lastly, by using whole-transcriptome analysis of Tip110 knockout mouse embryonic stem cells, we found several NF-κB and NF-κB-related pathways were dysregulated. Taken together, these findings add to the nuclear regulation of NF-κB activity by Tip110 through IκBα stabilization and provide new evidence to support the role of Tip110 in controlling cellular processes such as cancers that involve proinflammatory responses.

Tip110 Expression Facilitates the Release of HEXIM1 and pTEFb from the 7SK Ribonucleoprotein Complex Involving Regulation of the Intracellular Redox Level

HIV-1 Tat-interacting protein of 110 kDa (Tip110; p110^nrb/SART3) has been identified to be important for HIV gene transcription and several host gene expression. In this study, we showed that Tip110 was present in the 7SK snRNP through direct binding to MEPCE, a component of the 7SK snRNP complex. In addition, we found a positive association between Tip110 expression, change of HEXIM1 from dimer/oligomer to monomer, and release of HEXIM1 and P-TEFb from the 7SK snRNP complex. A similar association was also noted specifically in nuclear matrix as well as in chromatin where the free HEXIM1 and 7SK snRNP-bound HEXIM1 are located. Moreover, we demonstrated that Tip110 expression was linked to the glutathione metabolic pathway and the intracellular redox level, which in turn regulated HEXIM1 dimerization/oligomerization. Lastly, we performed the FRET microscopic analysis and confirmed the direct relationship between Tip110 expression and HEXIM1 dimerization/oligomerization in vivo. Taken together, these results identified a new mechanism governing HEXIM1 dimerization/oligomerization and the release of HEXIM1 and P-TEFb from the 7SK snRNP complex. These results also yield new insights to the roles of Tip110 in HIV gene transcription and replication.

The spliceosome factor sart3 regulates hematopoietic stem/progenitor cell development in zebrafish through the p53 pathway

Hematopoietic stem cells (HSCs) possess the potential for self-renew and the capacity, throughout life, to differentiate into all blood cell lineages. Yet, the mechanistic basis for HSC development remains largely unknown. In this study, we characterized a zebrafish smu471 mutant with hematopoietic stem/progenitor cell (HSPC) defects and found that sart3 was the causative gene. RNA expression profiling of the sart3^smu471 mutant revealed spliceosome and p53 signaling pathway to be the most significantly enriched pathways in the sart3^smu471 mutant. Knock down of p53 rescued HSPC development in the sart3^smu471 mutant. Interestingly, the p53 inhibitor, mdm4, had undergone an alternative splicing event in the mutant. Restoration of mdm4 partially rescued HSPC deficiency. Thus, our data suggest that HSPC proliferation and maintenance require sart3 to ensure the correct splicing and expression of mdm4, so that the p53 pathway is properly inhibited to prevent definitive hematopoiesis failure. This study expands our knowledge of the regulatory mechanisms that impact HSPC development and sheds light on the mechanistic basis and potential therapeutic use of sart3 in spliceosome-mdm4-p53 related disorders.

Regulation of Constitutive Tip110 Expression in Human Cord Blood CD34+ Cells Through Selective Usage of the Proximal and Distal Polyadenylation Sites Within the 3'Untranslated Region

Tip110 plays important roles for stem cell pluripotency and hematopoiesis. However, little is known about the regulatory mechanisms of Tip110 expression in this process. In this study, we first showed that constitutive Tip110 expression was cell proliferation and differentiation dependent and self-regulated in both human cord blood CD34⁺ cells. Using a series of molecular techniques, we found that ectopic Tip110 expression led to increased constitutive Tip110 expression through its 3'-untranslated region (3'UTR), specifically through preferential usage of proximal polyadenylation sites within its 3'UTR in cells, including human cord blood CD34⁺ cells, which indeed led to an increased number of CD34⁺ cells during differentiation of those cells. Lastly, we showed that Tip110 protein interacted with cleavage stimulation factor 64 (CstF64) protein and that more CstF64 was recruited to the promixal polyadenylation site than the distal polyadenylation site within its 3'UTR. These finding together demonstrates that constitutive Tip110 expression is regulated, at least in part, through its interaction with CstF64, recruitment of CstF64 to, and selective usage of those two polyadenylation sites within its 3'UTR.

Tip110 Deletion Impaired Embryonic and Stem Cell Development Involving Downregulation of Stem Cell Factors Nanog, Oct4, and Sox2

HIV-1 Tat-interacting protein of 110 kDa, Tip110, plays important roles in multiple biological processes. In this study, we aimed to characterize the function of Tip110 in embryonic development. Transgenic mice lacking expression of a functional Tip110 gene (Tip110^-/- ) died post-implantation, and Tip110^-/- embryos exhibited developmental arrest between 8.5 and 9.5 days post coitum. However, in vitro cultures of Tip110^-/- embryos showed that Tip110 loss did not impair embryo growth from the zygote to the blastocyst. Extended in vitro cultures of Tip110^-/- blastocysts showed that Tip110 loss impaired both blastocyst outgrowth and self-renewal and survival of blastocyst-derived embryonic stem cells. Microarray analysis of Tip110^-/- embryonic stem cells revealed that Tip110 loss altered differentiation, pluripotency, and cycling of embryonic stem cells and was associated with downregulation of several major stem cell factors including Nanog, Oct4, and Sox2 through a complex network of signaling pathways. Taken together, these findings document for the first time the lethal effects of complete loss of Tip110 on mammalian embryonic development and suggest that Tip110 is an important regulator of not only embryonic development but also stem cell factors. Stem Cells 2017;35:1674-1686.

Role of Tat-interacting protein of 110 kDa and microRNAs in the regulation of hematopoiesis

PURPOSE OF REVIEW

Hematopoiesis is regulated by cellular factors including transcription factors, microRNAs, and epigenetic modifiers. Understanding how these factors regulate hematopoiesis is pivotal for manipulating them to achieve their desired potential. In this review, we will focus on HIV-1 Tat-interacting protein of 110 kDa (Tip110) and its regulation of hematopoiesis.

RECENT FINDINGS

There are several pathways in hematopoiesis that involve Tip110 regulation. Tip110 is expressed in human cord blood CD34 cells; its expression decreases when CD34 cells begin to differentiate. Tip110 is also expressed in mouse marrow hematopoietic stem cells (HSC) and hematopoietic progenitor cells (HPC). Tip110 expression increases the number, survival, and cell cycling of HPC. Tip110-mediated regulation of hematopoiesis has been linked to its reciprocal control of proto-oncogene expression. Small noncoding microRNAs (miRs) have been shown to play important roles in regulation of hematopoiesis. miR-124 specifically targets 3'-untranslated region of Tip110 and subsequently regulates Tip110 expression in HSC.

SUMMARY

Our recent findings for manipulating expression levels of Tip110 in HSC and HPC could be useful for expanding HSC and HPC and for improving engraftment of cord blood HSC/HPC.

Tip110: Physical properties, primary structure, and biological functions

HIV-1 Tat-interacting protein of 110kDa (Tip110), also referred to as squamous cell carcinoma antigen recognized by T cells 3 (Sart3), p110 or p110(nrb), was initially identified as a cDNA clone (KIAA0156) without annotated functions. Over the past twenty years, several functions have been attributed to this protein. The proposed biological functions include roles for Tip110 in pre-mRNA splicing, gene transcription, stem cell biology, and development. Dysregulation of Tip110 is also a contributing factor in the development of cancer and other human diseases. It is clear that our understanding of this protein is rapidly evolving. In this review, we aimed to provide a summary of all the existing literature on this gene/protein and its proposed biological functions.

Tip110 binding to U6 small nuclear RNA and its participation in pre-mRNA splicing

Background

RNA–protein interactions play important roles in gene expression control. These interactions are mediated by several recurring RNA-binding motifs including a well-known and characterized ribonucleoprotein motif or so-called RNA recognition motif (RRM).

Results

In the current study, we set out to identify the RNA ligand(s) of a RRM-containing protein Tip110, also known as p110^nrb, SART3, or p110, using a RNA-based yeast three-hybrid cloning strategy. Six putative RNA targets were isolated and found to contain a consensus sequence that was identical to nucleotides 34–46 of U6 small nuclear RNA. Tip110 binding to U6 was confirmed to be specific and RRM-dependent in an electrophoretic mobility shift assay. Both in vitro pre-mRNA splicing assay and in vivo splicing-dependent reporter gene assay showed that the pre-mRNA splicing was correlated with Tip110 expression. Moreover, Tip110 was found in the spliceosomes containing pre-spliced pre-mRNA and spliced mRNA products. Nonetheless, the RRM-deleted mutant (ΔRRM) that did not bind to U6 showed promotion in vitro pre-mRNA splicing, whereas the nuclear localization signal (NLS)-deleted mutant ΔNLS that bound to U6 promoted the pre-mRNA splicing both in vitro and in vivo. Lastly, RNA-Seq analysis confirmed that Tip110 regulated a number of gene pre-mRNA splicing including several splicing factors.

Conclusions

Taken together, these results demonstrate that Tip110 is directly involved in constitutive eukaryotic pre-mRNA splicing, likely through its binding to U6 and regulation of other splicing factors, and provide further evidence to support the global roles of Tip110 in regulation of host gene expression.

Tip110 Regulates the Cross Talk between p53 and Hypoxia-Inducible Factor 1α under Hypoxia and Promotes Survival of Cancer Cells

Hypoxia often occurs under various physiological and pathophysiological conditions, including solid tumors; it is linked to malignant transformation, metastatic progression, and treatment failure or resistance. Tip110 protein plays important roles in several known physiological and pathophysiological processes, including cancers. Thus, in the present study we investigated the regulation of Tip110 expression under hypoxia. Hypoxia led to Tip110 protein degradation through the ubiquitin-proteasome system. Under hypoxia, Tip110 stabilized p53, which in return destabilized Tip110. In addition, Tip110 regulated hypoxia-inducible factor 1α (HIF-1α), likely through enhancement of its protein stability. Furthermore, Tip110 upregulated p300, a known coactivator for both p53 and HIF-1α. Expression of a p53(22/23) mutant deficient in p300 binding accelerated Tip110 degradation under hypoxia. Tip110 knockdown resulted in the inhibition of cell proliferation and cell death in the presence of p53. Finally, significantly less Tip110, p53, and HIF-1α was detected in the hypoxic region of bone metastasis tumors in a mouse model of human melanoma cells. Taken together, these results suggest Tip110 is an important mediator in the cross talk between p53 and HIF-1α in response to hypoxic stress.

The ribonucleotidyl transferase USIP-1 acts with SART3 to promote U6 snRNA recycling

The spliceosome is a large molecular machine that serves to remove the intervening sequences that are present in most eukaryotic pre-mRNAs. At its core are five small nuclear ribonucleoprotein complexes, the U1, U2, U4, U5 and U6 snRNPs, which undergo dynamic rearrangements during splicing. Their reutilization for subsequent rounds of splicing requires reversion to their original configurations, but little is known about this process. Here, we show that ZK863.4/USIP-1 (U Six snRNA-Interacting Protein-1) is a ribonucleotidyl transferase that promotes accumulation of the Caenorhabditis elegans U6 snRNA. Endogenous USIP-1–U6 snRNA complexes lack the Lsm proteins that constitute the protein core of the U6 snRNP, but contain the U6 snRNP recycling factor SART3/B0035.12. Furthermore, co-immunoprecipitation experiments suggest that SART3 but not USIP-1 occurs also in a separate complex containing both the U4 and U6 snRNPs. Based on this evidence, genetic interaction between usip-1 and sart-3, and the apparent dissociation of Lsm proteins from the U6 snRNA during spliceosome activation, we propose that USIP-1 functions upstream of SART3 to promote U6 snRNA recycling.

Regulation of neuronal survival and morphology by the E3 ubiquitin ligase RNF157

Neuronal health is essential for the long-term integrity of the brain. In this study, we characterized the novel E3 ubiquitin ligase ring finger protein 157 (RNF157), which displays a brain-dominant expression in mouse. RNF157 is a homolog of the E3 ligase mahogunin ring finger-1, which has been previously implicated in spongiform neurodegeneration. We identified RNF157 as a regulator of survival in cultured neurons and established that the ligase activity of RNF157 is crucial for this process. We also uncovered that independently of its ligase activity, RNF157 regulates dendrite growth and maintenance. We further identified the adaptor protein APBB1 (amyloid beta precursor protein-binding, family B, member 1 or Fe65) as an interactor and proteolytic substrate of RNF157 in the control of neuronal survival. Here, the nuclear localization of Fe65 together with its interaction partner RNA-binding protein SART3 (squamous cell carcinoma antigen recognized by T cells 3 or Tip110) is crucial to trigger apoptosis. In summary, we described that the E3 ligase RNF157 regulates important aspects of neuronal development.

Regulation of ubiquitin-proteasome system-mediated Tip110 protein degradation by USP15

Tip110 is a nuclear protein and has been shown to function in tumor antigenicity, regulation of gene transcription, pre-mRNA splicing, stem cell proliferation and differentiation, and embryonic development. To characterize the in vivo functions of Tip110, a transgene cassette expressing human Tip110 protein (hTip110) was used to generate hTip110 transgenic (Tg) mice. Unexpectedly, only Tip110 mRNA but not Tip110 protein was expressed in Tg MEF and tissues. Treatment of Tg MEF with proteasome inhibitors led to detection of hTip110 protein, which prompted us to investigate the regulatory mechanisms of Tip110 degradation in mouse cells. We found that hTip110 was more sensitive to ubiquitin-proteasome system (UPS)-mediated protein degradation than mouse Tip110 (mTip110), likely resulting from more hTip110 ubiquitination. Using affinity chromatography and proteomics, we identified USP15, a deubiquitinating enzyme, to be associated with Tip110. Tip110 expression led to re-distribution of USP15 from the cytoplasm to the nucleus and complete co-localization of Tip110 with USP15 in the nucleus, whereas USP15 expression resulted in hTip110 deubiquitination. Interestingly, USP15 knockdown restored hTip110 protein expression in Tg MEF and USP15 expression had little effects. Taken together, these results provide insights into the regulatory mechanism of human Tip110 degradation by USP15.

Tip110 protein binds to unphosphorylated RNA polymerase II and promotes its phosphorylation and HIV-1 long terminal repeat transcription

Transcription plays an important role in both HIV-1 gene expression and replication and mandates complicated but coordinated interactions between the host and virus. Our previous studies have shown that an HIV-1 Tat-interacting protein of 110 kDa, Tip110, binds to and enhances Tat function in Tat-mediated HIV-1 gene transcription and replication (Liu, Y., Li, J., Kim, B. O., Pace, B. S., and He, J. J. (2002) HIV-1 Tat protein-mediated transactivation of the HIV-1 long terminal repeat promoter is potentiated by a novel nuclear Tat-interacting protein of 110 kDa, Tip110. J. Biol. Chem. 277, 23854-23863). However, the underlying molecular mechanisms by which this takes place were not understood. In this study, we demonstrated that Tip110 bound to unphosphorylated RNA polymerase II (RNAPII) in a direct and specific manner. In addition, we detected Tip110 at the HIV-1 long terminal repeat (LTR) promoter and found that Tip110 expression was associated with increased phosphorylation of serine 2 of the heptapeptide repeats within the RNAPII C-terminal domain and increased recruitment of positive transcription elongation factor b to the LTR promoter. Consistent with these findings, we showed that Tip110 interaction with Tat directly enhanced transcription elongation of the LTR promoter. Taken together, these findings have provided additional and mechanistic evidence to support Tip110 function in HIV-1 transcription.

Tip110 interacts with YB-1 and regulates each other's function

Background

Tip110 plays important roles in tumor immunobiology, pre-mRNA splicing, expression regulation of viral and host genes, and possibly protein turnover. It is clear that our understanding of Tip110 biological function remains incomplete.

Results

Herein, we employed an immunoaffinity-based enrichment approach combined with protein mass spectrometry and attempted to identify Tip110-interacting cellular proteins. A total of 13 major proteins were identified to be complexed with Tip110. Among them was Y-box binding protein 1 (YB-1). The interaction of Tip110 with YB-1 was further dissected and confirmed to be specific and involve the N-terminal of both Tip110 and YB-1 proteins. A HIV-1 LTR promoter-driven reporter gene assay and a CD44 minigene in vivo splicing assay were chosen to evaluate the functional relevance of the Tip110/YB-1 interaction. We showed that YB-1 potentiates the Tip110/Tat-mediated transactivation of the HIV-1 LTR promoter while Tip110 promotes the inclusion of the exon 5 in CD44 minigene alternative splicing.

Conclusions

Tip110 and YB-1 interact to form a complex and mutually regulate each other’s biological functions.

Enhancing engraftment of cord blood cells via insight into the biology of stem/progenitor cell function

Cord blood (CB) transplantation has been used over the last 24 years to treat patients with malignant and nonmalignant disorders. CB has its advantages and disadvantages compared with other sources of hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs) for transplantation. More knowledge of the cytokines and intracellular signaling molecules regulating HSCs and HPCs could be used to modulate these regulators for clinical benefit. This review provides information about the general field of CB transplantation and about studies from the author's laboratory that focus on regulation of HSCs and HPCs by CD26/DPPIV, SDF-1/CXCL12, the Rheb2-mTOR pathway, SIRT1, DEK, cyclin-dependent kinase inhibitors, and cytokines/growth factors. Cryopreservation of CB HSCs and HPCs is also briefly discussed.

Tip110 maintains expression of pluripotent factors in and pluripotency of human embryonic stem cells

HIV-1 Tat-interacting protein of 110 kDa [Tip110; p110(nrb)/SART3/p110] is an RNA binding nuclear protein implicated in regulation of HIV-1 gene and host gene transcription, pre-mRNA splicing, and cancer immunology. Recently, we demonstrated a role for Tip110 in regulation of hematopoiesis. Here, we show that TIP110 is also expressed in human embryonic stem cells (hESCs) and expression was decreased with differentiation of these ESCs. TIP110 was found, through up- and down-modulation of expression of Tip110, to be important in maintaining pluripotent factor (NANOG, OCT4, and SOX2) expression in and pluripotency of hESCs, although the mechanisms involved and whether the Tip110 effects are direct remain to be determined.

Proteasomal degradation of p53 by human papillomavirus E6 oncoprotein relies on the structural integrity of p53 core domain

The E6 oncoprotein produced by high-risk mucosal HPV stimulates ubiquitinylation and proteasome-dependent degradation of the tumour suppressor p53 via formation of a trimeric complex comprising E6, p53, and E6-AP. p53 is also degraded by its main cellular regulator MDM2. The main binding site of p53 to MDM2 is situated in the natively unfolded N-terminal region of p53. By contrast, the regions of p53 implicated in the degradation by viral E6 are not fully identified to date. Here we generated a series of mutations (Y103G, Y107G, T155A, T155V, T155D, L264A, L265A) targeting the central folded core domain of p53 within a region opposite to its DNA-binding site. We analysed by in vitro and in vivo assays the impact of these mutations on p53 degradation mediated by viral E6 oncoprotein. Whereas all mutants remained susceptible to MDM2-mediated degradation, several of them (Y103G, Y107G, T155D, L265A) became resistant to E6-mediated degradation, confirming previous works that pointed to the core domain as an essential region for the degradation of p53. In parallel, we systematically checked the impact of the mutations on the transactivation activity of p53 as well as on the conformation of p53, analysed by Nuclear Magnetic Resonance (NMR), circular dichroism (CD), and antibody probing. These measurements suggested that the conformational integrity of the core domain is an essential parameter for the degradation of p53 by E6, while it is not essential for the degradation of p53 by MDM2. Thus, the intracellular stability of a protein may or may not rely on its biophysical stability depending on the degradation pathway taken into consideration.

An unhealthy relationship: viral manipulation of the nuclear receptor superfamily

The nuclear receptor (NR) superfamily is a diverse group of over 50 proteins whose function is to regulate the transcription of a vast array of cellular genes. These proteins are able to tune transcription over an extremely dynamic range due to the fact that they may act as either transcriptional activators or repressors depending on promoter context and ligand status. Due to these unique properties, diverse families of viruses have evolved strategies to exploit NRs in order to regulate expression of their own genes and to optimize the cellular milieu to facilitate the viral lifecycle. While the specific NRs targeted by these viruses vary, the strategies used to target them are common. This is accomplished at the cis-level by incorporation of nuclear receptor response elements into the viral genome and at the trans-level by viral proteins that target NRs directly or indirectly to modulate their function. The specific NR(s) targeted by a particular virus are likely to be reflective of the tissue tropism of the virus in question. Thus, the essential role played by NRs in the replication cycles of such diverse viruses underscores the importance of understanding their functions in the context of specific infections. This knowledge will allow appropriate considerations to be made when treating infected individuals with hormone-associated diseases and will potentially assist in the rational design of novel antiviral therapeutics.

TIP110/p110nrb/SART3/p110 regulation of hematopoiesis through CMYC

Intracellular factors are involved in and essential for hematopoiesis. HIV-1 Tat-interacting protein of 110 kDa (TIP110; p110(nrb)/SART3/p110) is an RNA-binding nuclear protein implicated in the regulation of HIV-1 gene and host gene transcription, pre-mRNA splicing, and cancer immunology. In the present study, we demonstrate a role for TIP110 in the regulation of hematopoiesis. TIP110 was expressed in human CD34(+) cells and decreased with differentiation of CD34(+) cells. TIP110 mRNA was also expressed in phenotyped mouse marrow hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs). Using TIP110 transgenic (TIP110(TG)) and haploinsufficient (TIP110(+/-)) mice, we found that increased TIP110 expression enhanced HPC numbers, survival, and cell cycling, whereas decreased TIP110 expression had the opposite effects. Moreover, TIP110(+/-) bone marrow HPCs responded more effectively, and TIP110(TG) HPCs less effectively, than those of wild-type control mice to recovery from the cell-cycle-active drug 5-fluorouracil (5-FU). Unexplained sex differences were noted in HSC competitive repopulating ability, but not HPC numbers, in TIP110(TG) mice. Intracellularly, TIP110 regulated CMYC and GATA2 expression at the transcriptional level, and TIP110 and CMYC reciprocally regulated the expression of each other. These results demonstrate a role for TIP110 in the regulation of hematopoiesis, effects that are likely linked to TIP110 regulation of CMYC.

Inhibition of HIV-1 entry by extracts derived from traditional Chinese medicinal herbal plants

Background

Highly active anti-retroviral therapy (HAART) is the current HIV/AIDS treatment modality. Despite the fact that HAART is very effective in suppressing HIV-1 replication and reducing the mortality of HIV/AIDS patients, it has become increasingly clear that HAART does not offer an ultimate cure to HIV/AIDS. The high cost of the HAART regimen has impeded its delivery to over 90% of the HIV/AIDS population in the world. This reality has urgently called for the need to develop inexpensive alternative anti-HIV/AIDS therapy. This need has further manifested by recent clinical trial failures in anti-HIV-1 vaccines and microbicides. In the current study, we characterized a panel of extracts of traditional Chinese medicinal herbal plants for their activities against HIV-1 replication.

Methods

Crude and fractionated extracts were prepared from various parts of nine traditional Chinese medicinal herbal plants in Hainan Island, China. These extracts were first screened for their anti-HIV activity and cytotoxicity in human CD4+ Jurkat cells. Then, a single-round pseudotyped HIV-luciferase reporter virus system (HIV-Luc) was used to identify potential anti-HIV mechanisms of these extracts.

Results

Two extracts, one from Euphorbiaceae, Trigonostema xyphophylloides (TXE) and one from Dipterocarpaceae, Vatica astrotricha (VAD) inhibited HIV-1 replication and syncytia formation in CD4+ Jurkat cells, and had little adverse effects on host cell proliferation and survival. TXE and VAD did not show any direct inhibitory effects on the HIV-1 RT enzymatic activity. Treatment of these two extracts during the infection significantly blocked infection of the reporter virus. However, pre-treatment of the reporter virus with the extracts and treatment of the extracts post-infection had little effects on the infectivity or gene expression of the reporter virus.

Conclusion

These results demonstrate that TXE and VAD inhibit HIV-1 replication likely by blocking HIV-1 interaction with target cells, i.e., the interaction between gp120 and CD4/CCR5 or gp120 and CD4/CXCR4 and point to the potential of developing these two extracts to be HIV-1 entry inhibitors.

Androgen receptor (AR) coregulators: a diversity of functions converging on and regulating the AR transcriptional complex

Androgens, acting through the androgen receptor (AR), are responsible for the development of the male phenotype during embryogenesis, the achievement of sexual maturation at puberty, and the maintenance of male reproductive function and behavior in adulthood. In addition, androgens affect a wide variety of nonreproductive tissues. Moreover, aberrant androgen action plays a critical role in multiple pathologies, including prostate cancer and androgen insensitivity syndromes. The formation of a productive AR transcriptional complex requires the functional and structural interaction of the AR with its coregulators. In the last decade, an overwhelming and ever increasing number of proteins have been proposed to possess AR coactivating or corepressing characteristics. Intriguingly, a vast diversity of functions has been ascribed to these proteins, indicating that a multitude of cellular functions and signals converge on the AR to regulate its function. The current review aims to provide an overview of the AR coregulator proteins identified to date and to propose a classification of these AR coregulator proteins according to the function(s) ascribed to them. Taken together, this approach will increase our understanding of the cellular pathways that converge on the AR to ensure an appropriate transcriptional response to androgens.

Systematic analysis of the protein interaction network for the human transcription machinery reveals the identity of the 7SK capping enzyme

We have performed a survey of soluble human protein complexes containing components of the transcription and RNA processing machineries using protein affinity purification coupled to mass spectrometry. Thirty-two tagged polypeptides yielded a network of 805 high-confidence interactions. Remarkably, the network is significantly enriched in proteins that regulate the formation of protein complexes, including a number of previously uncharacterized proteins for which we have inferred functions. The RNA polymerase II (RNAP II)-associated proteins (RPAPs) are physically and functionally associated with RNAP II, forming an interface between the enzyme and chaperone/scaffolding proteins. BCDIN3 is the 7SK snRNA methylphosphate capping enzyme (MePCE) present in an snRNP complex containing both RNA processing and transcription factors, including the elongation factor P-TEFb. Our results define a high-density protein interaction network for the mammalian transcription machinery and uncover multiple regulatory factors that target the transcription machinery.