Receptor protein tyrosine phosphatases (RPTPs) are involved in a broad list of cellular, developmental, and physiological functions. Altering their expression leads to significant changes in protein ...phosphorylation linked to a growing list of human diseases, including cancers and neurological disorders. In this issue of
, Qian and colleagues (pp. 743-759) present the identification of a monoclonal antibody targeting PTPRD extracellular domain-inducing dimerization and inhibition of the phosphatase activities, causing the proteolysis of dimeric PTPRD by a mechanism involving intracellular degradation pathways. Their study supports the potential of modulating PTPRD via its extracellular domains. This opens a new framework in the clinical manipulation of PTPRD and its closely related family members.
While several clinical studies have shown that HIV-1 infection is associated with increased permeability of the intestinal tract, there is very little understanding of the mechanisms underlying ...HIV-induced impairment of mucosal barriers. Here we demonstrate that exposure to HIV-1 can directly breach the integrity of mucosal epithelial barrier, allowing translocation of virus and bacteria. Purified primary epithelial cells (EC) isolated from female genital tract and T84 intestinal cell line were grown to form polarized, confluent monolayers and exposed to HIV-1. HIV-1 X4 and R5 tropic laboratory strains and clinical isolates were seen to reduce transepithelial resistance (TER), a measure of monolayer integrity, by 30-60% following exposure for 24 hours, without affecting viability of cells. The decrease in TER correlated with disruption of tight junction proteins (claudin 1, 2, 4, occludin and ZO-1) and increased permeability. Treatment of ECs with HIV envelope protein gp120, but not HIV tat, also resulted in impairment of barrier function. Neutralization of gp120 significantly abrogated the effect of HIV. No changes to the barrier function were observed when ECs were exposed to Env defective mutant of HIV. Significant upregulation of inflammatory cytokines, including TNF-alpha, were seen in both intestinal and genital epithelial cells following exposure to HIV-1. Neutralization of TNF-alpha reversed the reduction in TERs. The disruption in barrier functions was associated with viral and bacterial translocation across the epithelial monolayers. Collectively, our data shows that mucosal epithelial cells respond directly to envelope glycoprotein of HIV-1 by upregulating inflammatory cytokines that lead to impairment of barrier functions. The increased permeability could be responsible for small but significant crossing of mucosal epithelium by virus and bacteria present in the lumen of mucosa. This mechanism could be particularly relevant to mucosal transmission of HIV-1 as well as immune activation seen in HIV-1 infected individuals.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Leptin plays a central role in weight control by suppressing food intake and increasing energy expenditure. The concept of leptin resistance emerged to explain the seemingly paradoxical elevated ...leptin levels in obesity. Recent discoveries reveal that protein tyrosine phosphatases are key players in leptin resistance by globally suppressing leptin signaling.
Dendritic cells have been at the forefront of cancer-immunotherapy research for over 2 decades. They elicited that attention by having an unprecedented capacity to mount T cells responses against ...tumors. However, the clinical use of DC-based vaccination against established malignancies has resulted in limited clinical benefits. Several factors are responsible for limiting the efficacy of DC-based immunotherapy, such as the harmful influence of the tumor microenvironment on DCs activity. New insights into the inner process of DC-mediated T cell activation have supported the development of new strategies that potentiate DCs-based therapies. Herein, we identify signaling cascades that have recently been targeted by small molecules and biologicals to promote the activation of monocyte-derived DCs and decrease their susceptibility to becoming tolerogenic. While Statins can markedly enhance antigen presentation, protein kinase inhibitors can be used to increase the expression of co-receptors and adhesion molecules. STAT3 and IDO can be modulated to limit the production of regulatory factors that work against differentiation and activation. The targeting of multiple pathways simultaneously has also been found to produce synergism and drastically enhance DCs activity. Some of these strategies have recently yielded positive results in clinical settings against established malignancies such as non-small cell lung cancer. The emergence of these approaches opens the door for a new generation of potent dendritic cell-based therapeutics to fight cancer.
Several host factors influence HIV-1 infection and replication. The p53-mediated antiviral role in monocyte-derived macrophages (MDMs) was previously highlighted. Indeed, an increase in p53 level ...results in a stronger restriction against HIV-1 early replication steps through SAMHD1 activity. In this study, we investigated the potential role of some p53 isoforms in HIV-1 infection. Transfection of isoform-specific small interfering RNA (siRNA) induced distinctive effects on the virus life cycle. For example, in contrast to an siRNA targeting all isoforms, a knockdown of Δ133p53 transcripts reduced virus replication in MDMs that was correlated with a decrease in phosphorylated inactive SAMHD1. Combination of Δ133p53 knockdown and nutlin-3, a pharmacological inhibitor of MDM2 that stabilizes p53, further reduced susceptibility of MDMs to HIV-1 infection, thus suggesting an inhibitory role of Δ133p53 toward p53 antiviral activity. In contrast, p53β knockdown in MDMs increased the viral production independently of SAMHD1. Moreover, experiments with a Nef-deficient virus showed that this viral protein plays a protective role against the antiviral environment mediated by p53. Finally, HIV-1 infection affected the expression pattern of p53 isoforms by increasing p53β and p53γ mRNA levels while stabilizing the protein level of p53α and some isoforms from the p53β subclass. The balance between the various p53 isoforms is therefore an important factor in the overall susceptibility of macrophages to HIV-1 infection, fine-tuning the p53 response against HIV-1. This study brings a new understanding of the complex role of p53 in virus replication processes in myeloid cells.
As of today, HIV-1 infection is still considered a global pandemic without a functional cure, partly because of the presence of stable viral reservoirs. Macrophages constitute one of these cell reservoirs, contributing to the viral persistence. Studies investigating the host factors involved in cell susceptibility to HIV-1 infection might lead to a better understanding of reservoir formation and will eventually allow the development of an efficient cure. Our team previously showed the antiviral role of p53 in macrophages, which acts by compromising the early steps of HIV-1 replication. In this study, we demonstrate the involvement of p53 isoforms, which regulate p53 activity and define the cellular environment influencing viral replication. In addition, the results concerning the potential role of p53 in antiviral innate immunity could be transposed to other fields of virology and suggest that knowledge in oncology can be applied to HIV-1 research.
Phosphatases of regenerating liver (PRL-1, PRL-2, PRL-3; also known as PTP4A1, PTP4A2, PTP4A3, respectively) control intracellular magnesium levels by interacting with the CNNM magnesium transport ...regulators. Still, the exact mechanism governing magnesium transport by this protein complex is not well understood. Herein, we have developed a genetically encoded intracellular magnesium-specific reporter and demonstrate that the CNNM family inhibits the function of the TRPM7 magnesium channel. We show that the small GTPase ARL15 increases CNNM3/TRPM7 protein complex formation to reduce TRPM7 activity. Conversely, PRL-2 overexpression counteracts ARL15 binding to CNNM3 and enhances the function of TRPM7 by preventing the interaction between CNNM3 and TRPM7. Moreover, while TRPM7-induced cell signaling is promoted by PRL-1/2, it is reduced when CNNM3 is overexpressed. Lowering cellular magnesium levels reduces the interaction of CNNM3 with TRPM7 in a PRL-dependent manner, whereby knockdown of PRL-1/2 restores the protein complex formation. Cotargeting of TRPM7 and PRL-1/2 alters mitochondrial function and sensitizes cells to metabolic stress induced by magnesium depletion. These findings reveal the dynamic regulation of TRPM7 function in response to PRL-1/2 levels, to coordinate magnesium transport and reprogram cellular metabolism.
The two faces of PTP1B in cancer Lessard, Laurent; Stuible, Matthew; Tremblay, Michel L.
Biochimica et biophysica acta,
March 2010, 2010-Mar, 2010-03-00, Letnik:
1804, Številka:
3
Journal Article
Recenzirano
PTP1B is a classical non-transmembrane protein tyrosine phosphatase that plays a key role in metabolic signaling and is a promising drug target for type 2 diabetes and obesity. Accumulating evidence ...also indicates that PTP1B is involved in cancer, but contrasting findings suggest that it can exert both tumor suppressing and tumor promoting effects depending on the substrate involved and the cellular context. In this review, we will discuss the diverse mechanisms by which PTP1B may influence tumorigenesis as well as recent in vivo data on the impact of PTP1B deficiency in murine cancer models. Together, these results highlight not only the great potential of PTP1B inhibitors in cancer therapy but also the need for a better understanding of PTP1B function prior to use of these compounds in human patients.
Members of the protein tyrosine phosphatase (Ptp) family dephosphorylate target proteins and counter the activities of protein tyrosine kinases that are involved in cellular phosphorylation and ...signalling. As such, certain PTPs might be tumour suppressors. Indeed, PTPs play an important part in the inhibition or control of growth, but accumulating evidence indicates that some PTPs may exert oncogenic functions. Recent large-scale genetic analyses of various human tumours have highlighted the relevance of PTPs either as putative tumour suppressors or as candidate oncoproteins. Progress in understanding the regulation and function of PTPs has provided insights into which PTPs might be potential therapeutic targets in human cancer.
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Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Flavaglines are a family of natural products from the genus Aglaia that exhibit anti-cancer activity in vitro and in vivo and inhibit translation initiation. They have been shown to modulate the ...activity of eIF4A, the DEAD-box RNA helicase subunit of the eukaryotic initiation factor (eIF) 4F complex, a complex that stimulates ribosome recruitment during translation initiation. One flavagline, silvestrol, is capable of modulating chemosensitivity in a mechanism-based mouse model.
Among a number of flavagline family members tested herein, we find that silvestrol is the more potent translation inhibitor among these. We find that silvestrol impairs the ribosome recruitment step of translation initiation by affecting the composition of the eukaryotic initiation factor (eIF) 4F complex. We show that silvestrol exhibits significant anticancer activity in human breast and prostate cancer xenograft models, and that this is associated with increased apoptosis, decreased proliferation, and inhibition of angiogenesis. We demonstrate that targeting translation by silvestrol results in preferential inhibition of weakly initiating mRNAs.
Our results indicate that silvestrol is a potent anti-cancer compound in vivo that exerts its activity by affecting survival pathways as well as angiogenesis. We propose that silvestrol mediates its effects by preferentially inhibiting translation of malignancy-related mRNAs. Silvestrol appears to be well tolerated in animals.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Transcription of the several hundred of mouse and human Ribosomal RNA (rRNA) genes accounts for the majority of RNA synthesis in the cell nucleus and is the determinant of cytoplasmic ribosome ...abundance, a key factor in regulating gene expression. The rRNA genes, referred to globally as the rDNA, are clustered as direct repeats at the Nucleolar Organiser Regions, NORs, of several chromosomes, and in many cells the active repeats are transcribed at near saturation levels. The rDNA is also a hotspot of recombination and chromosome breakage, and hence understanding its control has broad importance. Despite the need for a high level of rDNA transcription, typically only a fraction of the rDNA is transcriptionally active, and some NORs are permanently silenced by CpG methylation. Various chromatin-remodelling complexes have been implicated in counteracting silencing to maintain rDNA activity. However, the chromatin structure of the active rDNA fraction is still far from clear. Here we have combined a high-resolution ChIP-Seq protocol with conditional inactivation of key basal factors to better understand what determines active rDNA chromatin. The data resolve questions concerning the interdependence of the basal transcription factors, show that preinitiation complex formation is driven by the architectural factor UBF (UBTF) independently of transcription, and that RPI termination and release corresponds with the site of TTF1 binding. They further reveal the existence of an asymmetric Enhancer Boundary Complex formed by CTCF and Cohesin and flanked upstream by phased nucleosomes and downstream by an arrested RNA Polymerase I complex. We find that the Enhancer Boundary Complex is the only site of active histone modification in the 45kbp rDNA repeat. Strikingly, it not only delimits each functional rRNA gene, but also is stably maintained after gene inactivation and the re-establishment of surrounding repressive chromatin. Our data define a poised state of rDNA chromatin and place the Enhancer Boundary Complex as the likely entry point for chromatin remodelling complexes.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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