TMF/ARA160 is a BC-box-containing protein that mediates the degradation of Stat3

The Warburg micro syndrome protein RAB3GAP1 modulates neuronal morphogenesis and interacts with axon elongation end ER-Golgi trafficking factors

RAB3GAP1 is GTPase activating protein localized to the ER and Golgi compartments. In humans, mutations in RAB3GAP1 are the most common cause of Warburg Micro syndrome, a neurodevelopmental disorder associated with intellectual disability, microcephaly, and agenesis of the corpus callosum. We found that downregulation of RAB3GAP1 leads to a reduction in neurite outgrowth and complexity in human stem cell derived neurons. To further define the cellular function of RAB3GAP1, we sought to identify novel interacting proteins. We used a combination of mass spectrometry, co-immunoprecipitation and colocalization analysis and identified two novel interactors of RAB3GAP1: the axon elongation factor Dedicator of cytokinesis 7 (DOCK7) and the TATA modulatory factor 1 (TMF1) a modulator of Endoplasmic Reticulum (ER) to Golgi trafficking. To define the relationship between RAB3GAP1 and its two novel interactors, we analyzed their localization to different subcellular compartments in neuronal and non-neuronal cells with loss of RAB3GAP1. We find that RAB3GAP1 is important for the sub-cellular localization of TMF1 and DOCK7 across different compartments of the Golgi and endoplasmic reticulum. In addition, we find that loss of function mutations in RAB3GAP1 lead to dysregulation of pathways that are activated in response to the cellular stress like ATF6, MAPK, and PI3-AKT signaling. In summary, our findings suggest a novel role for RAB3GAP1 in neurite outgrowth that could encompass the regulation of proteins that control axon elongation, ER-Golgi trafficking, as well as pathways implicated in response to cellular stress.

Sodium acetate promotes fat synthesis by suppressing TATA element modulatory factor 1 in bovine mammary epithelial cells

Short-chain fatty acids are important nutrients that regulate milk fat synthesis. They regulate milk synthesis via the sterol regulatory element binding protein 1 (SREBP1) pathway; however, the details are still unknown. Here, the regulation and mechanism of sodium acetate (SA) in milk fat synthesis in bovine mammary epithelial cells (BMECs) were assessed. BMECs were treated with SA supplementation (SA+) or without SA supplementation (SA-), and milk fat synthesis and activation of the SREBP1 pathway were increased (P = 0.0045; P = 0.0042) by SA+ and decreased (P = 0.0068; P = 0.0031) by SA-, respectively. Overexpression or inhibition of SREBP1 demonstrated that SA promoted milk fat synthesis (P = 0.0045) via the SREBP1 pathway. Overexpression or inhibition of TATA element modulatory factor 1 (TMF1) demonstrated that TMF1 suppressed activation of the SREBP1 pathway (P = 0.0001) and milk fat synthesis (P = 0.0022) activated by SA+. Overexpression or inhibition of TMF1 and SREBP1 showed that TMF1 suppressed milk fat synthesis (P = 0.0073) through the SREBP1 pathway. Coimmunoprecipitation analysis revealed that TMF1 interacted with SREBP1 in the cytoplasm and suppressed the nuclear localization of SREBP1 (P = 0.0066). The absence or presence of SA demonstrated that SA inhibited the expression of TMF1 (P = 0.0002) and the interaction between TMF1 and SREBP1 (P = 0.0001). Collectively, our research suggested that TMF1 was a new negative regulator of milk fat synthesis. In BMECs, SA promoted the SREBP1 pathway and milk fat synthesis by suppressing TMF1. This study enhances the current understanding of the regulation of milk fat synthesis and provides new scientific data for the regulation of milk fat synthesis.

Genetic architecture and heritability of early-life telomere length in a wild passerine

Early-life telomere length (TL) is associated with fitness in a range of organisms. Little is known about the genetic basis of variation in TL in wild animal populations, but to understand the evolutionary and ecological significance of TL it is important to quantify the relative importance of genetic and environmental variation in TL. In this study, we measured TL in 2746 house sparrow nestlings sampled across 20 years and used an animal model to show that there is a small heritable component of early-life TL (h²  = 0.04). Variation in TL among individuals was mainly driven by environmental (annual) variance, but also brood and parental effects. Parent-offspring regressions showed a large maternal inheritance component in TL ( h maternal 2  = 0.44), but no paternal inheritance. We did not find evidence for a negative genetic correlation underlying the observed negative phenotypic correlation between TL and structural body size. Thus, TL may evolve independently of body size and the negative phenotypic correlation is likely to be caused by nongenetic environmental effects. We further used genome-wide association analysis to identify genomic regions associated with TL variation. We identified several putative genes underlying TL variation; these have been inferred to be involved in oxidative stress, cellular growth, skeletal development, cell differentiation and tumorigenesis in other species. Together, our results show that TL has a low heritability and is a polygenic trait strongly affected by environmental conditions in a free-living bird.

Luteolin binds Src, promotes STAT3 protein ubiquitination and exerts anti-melanoma effects in cell and mouse models

Signal transducer and activator of transcription 3 (STAT3) has been proposed as a target for melanoma prevention. Luteolin, a bioactive flavonoid abundant inmedicinal herbs, has been reported to have anti-melanoma activity in vitro. However, its in vivo anti-melanoma effects and underlying mechanisms have not been fully elucidated. In this study, ten cell lines and two mouse models (B16F10 allograft and A375 xenograft models) were used for assessing the in vitro and in vivo anti-melanoma effects of luteolin. A STAT3 over-activated stable A375 cell line was used to determine the contribution of STAT3 signaling in luteolin's anti-melanoma effects. Results showed that luteolin dose-dependently reduced viability of melanoma cells. Luteolin also induced apoptosis in, and suppressed migration and invasion of, A375 and B16F10 melanoma cells. Mechanistically, luteolin inhibited phosphorylation of STAT3 and Src (an upstream kinase of STAT3), accelerated ubiquitin-proteasome pathway-mediated STAT3 degradation, and downregulated the expression of STAT3-targeted genes involved in cell survival and invasion in melanoma cells. Molecular modelling and surface plasmon resonance imaging showed that luteolin stably bound to the protein kinase domain of Src. Animal studies demonstrated that prophylactic administration of luteolin restrained melanoma growth and Src/STAT3 signaling in both A375 and B16F10 melanoma-bearing mice. Moreover, luteolin's anti-melanoma effects were diminished by STAT3 over-activation in A375 cells. Our findings indicate that luteolin inhibits STAT3 signaling by suppressing STAT3 activation and promoting STAT3 protein degradation in melanoma cells, thereby exhibiting anti-melanoma effects. This study provides further pharmacological groundwork for developing luteolin as a chemopreventive agent against melanoma.

Getting Sugar Coating Right! The Role of the Golgi Trafficking Machinery in Glycosylation

The Golgi is the central organelle of the secretory pathway and it houses the majority of the glycosylation machinery, which includes glycosylation enzymes and sugar transporters. Correct compartmentalization of the glycosylation machinery is achieved by retrograde vesicular trafficking as the secretory cargo moves forward by cisternal maturation. The vesicular trafficking machinery which includes vesicular coats, small GTPases, tethers and SNAREs, play a major role in coordinating the Golgi trafficking thereby achieving Golgi homeostasis. Glycosylation is a template-independent process, so its fidelity heavily relies on appropriate localization of the glycosylation machinery and Golgi homeostasis. Mutations in the glycosylation enzymes, sugar transporters, Golgi ion channels and several vesicle tethering factors cause congenital disorders of glycosylation (CDG) which encompass a group of multisystem disorders with varying severities. Here, we focus on the Golgi vesicle tethering and fusion machinery, namely, multisubunit tethering complexes and SNAREs and their role in Golgi trafficking and glycosylation. This review is a comprehensive summary of all the identified CDG causing mutations of the Golgi trafficking machinery in humans.

The role of understudied post-translational modifications for the behavior and function of Signal Transducer and Activator of Transcription 3

The Signal Transducer and Activator of Transcription (STAT) family of transcription factors is involved in inflammation, immunity, development, cancer, and response to injury, among other biological phenomena. Canonical STAT signaling is often represented as a 3-step pathway involving the sequential activation of a membrane receptor, an intermediate kinase, and a STAT transcription factor. The rate-limiting phosphorylation at a highly conserved C-terminal tyrosine residue determines the nuclear translocation and transcriptional activity of STATs. This apparent simplicity is actually misleading and can hardly explain the pleiotropic nature of STATs, the existence of various noncanonical STAT pathways, or the key role of the N-terminal domain in STAT functions. More than 80 post-translational modifications (PTMs) have been identified for STAT3, but their functions remain barely understood. Here, we provide a brief but comprehensive overview of these underexplored PTMs and their role on STAT3 canonical and noncanonical functions. A less tyrosine-centric point of view may be required to advance our understanding of STAT signaling.

Aging-dependent regulatory cells emerge in subcutaneous fat to inhibit adipogenesis

Adipose tissue mass and adiposity change throughout the lifespan. During aging, while visceral adipose tissue (VAT) tends to increase, peripheral subcutaneous adipose tissue (SAT) decreases significantly. Unlike VAT, which is linked to metabolic diseases, including type 2 diabetes, SAT has beneficial effects. However, the molecular details behind the aging-associated loss of SAT remain unclear. Here, by comparing scRNA-seq of total stromal vascular cells of SAT from young and aging mice, we identify an aging-dependent regulatory cell (ARC) population that emerges only in SAT of aged mice and humans. ARCs express adipose progenitor markers but lack adipogenic capacity; they secrete high levels of pro-inflammatory chemokines, including Ccl6, to inhibit proliferation and differentiation of neighboring adipose precursors. We also found Pu.1 to be a driving factor for ARC development. We identify an ARC population and its capacity to inhibit differentiation of neighboring adipose precursors, correlating with aging-associated loss of SAT.

DGG-100629 inhibits lung cancer growth by suppressing the NFATc1/DDIAS/STAT3 pathway

DNA damage-induced apoptosis suppressor (DDIAS) promotes the progression of lung cancer and hepatocellular carcinoma through the regulation of multiple pathways. We screened a chemical library for anticancer agent(s) capable of inhibiting DDIAS transcription. DGG-100629 was found to suppress lung cancer cell growth through the inhibition of DDIAS expression. DGG-100629 induced c-Jun NH(2)-terminal kinase (JNK) activation and inhibited NFATc1 nuclear translocation. Treatment with SP600125 (a JNK inhibitor) or knockdown of JNK1 restored DDIAS expression and reversed DGG-100629-induced cell death. In addition, DGG-100629 suppressed the signal transducer and activator of transcription (STAT3) signaling pathway. DDIAS or STAT3 overexpression restored lung cancer cell growth in the presence of DGG-100629. In a xenograft assay, DGG-100629 inhibited tumor growth by reducing the level of phosphorylated STAT3 and the expression of STAT3 target genes. Moreover, DGG-100629 inhibited the growth of lung cancer patient-derived gefitinib-resistant cells expressing NFATc1 and DDIAS. Our findings emphasize the potential of DDIAS blockade as a therapeutic approach and suggest a novel strategy for the treatment of gefitinib-resistant lung cancer.

TMF1 is upregulated by insulin and is required for a sustained glucose homeostasis

Insulin-regulated glucose homeostasis is a critical and intricate physiological process, of which not all regulatory components have been deciphered. One of the key players in modulating glucose uptake by cells is the glucose transporter-GLUT4. In this study, we aimed to explore the regulatory role of the trans-Golgi-associated protein-TATA Element Modulatory Factor (TMF1) in the GLUT4 mediated, insulin-directed glucose uptake. By establishing and using TMF1-/- myoblasts and mice, we examined the effect of TMF1 absence on the insulin driven functioning of GLUT4. We show that TMF1 is upregulated by insulin in myoblasts, and is essential for the formation of insulin responsive, glucose transporter GLUT4-containing vesicles. Absence of TMF1 leads to the retention of GLUT4 in perinuclear compartments, and to severe impairment of insulin-stimulated GLUT4 trafficking throughout the cytoplasm and to the cell plasma membrane. Accordingly, glucose uptake is impaired in TMF1-/- cells, and TMF1-/- mice are hyperglycemic. This is reflected by the mice impaired blood glucose clearance and increased blood glucose level. Correspondingly, TMF1-/- animals are leaner than their normal littermates. Thus, TMF1 is a novel effector of insulin-regulated glucose homeostasis, and dys-functioning of this protein may contribute to the onset of a diabetes-like disorder.

OsTMF attenuates cold tolerance by affecting cell wall properties in rice

Plant cell wall composition and structure can be modified as plants adapt to environmental stresses; however, the underlying regulatory mechanisms remain elusive. Here, we report that OsTMF, a homologue of the human TATA modulatory factor (TMF) in rice (Oryza sativa) and highly conserved in plants, negatively regulates cold tolerance through modification of cell wall properties. Cold stress increased the expression of OsTMF and accumulation of OsTMF in the nucleus, where OsTMF acts as a transcription activator and modulates the expression of genes involved in pectin degradation (OsBURP16), cellulose biosynthesis (OsCesA4 and OsCesA9), and cell wall structural maintenance (genes encoding proline-rich proteins and peroxidases). OsTMF directly activated the expression of OsBURP16, OsCesA4, and OsCesA9 through binding to the TATA cis-elements in their promoters. Under cold stress conditions, OsTMF negatively regulated pectin content and peroxidase activity and positively regulated cellulose content, causing corresponding alterations to cell wall properties, all of which collectively contribute to the negative effect of OsTMF on cold tolerance. Our findings unravel a previously unreported molecular mechanism of a conserved plant TMF protein in the regulation of cell wall changes under cold stress.

Targeting STAT-3 signaling pathway in cancer for development of novel drugs: Advancements and challenges

Signal transducers and activators of transcription 3 (STAT-3) is a transcription factor that regulates the gene expression of several target genes. These factors are activated by the binding of cytokines and growth factors with STAT-3 specific receptors on cell membrane. Few years ago, STAT-3 was considered an acute phase response element having several cellular functions such as inflammation, cell survival, invasion, metastasis and proliferation, genetic alteration, and angiogenesis. STAT-3 is activated by several types of inflammatory cytokines, carcinogens, viruses, growth factors, and oncogenes. Thus, the STAT3 pathway is a potential target for cancer therapeutics. Abnormal STAT-3 activity in tumor development and cellular transformation can be targeted by several genomic and pharmacological methodologies. An extensive review of the literature has been conducted to emphasize the role of STAT-3 as a unique cancer drug target. This review article discusses in detail the wide range of STAT-3 inhibitors that show antitumor effects both in vitro and in vivo. Thus, targeting constitutive STAT-3 signaling is a remarkable therapeutic methodology for tumor progression. Finally, current limitations, trials and future perspectives of STAT-3 inhibitors are also critically discussed.

STAT3 and STAT5 Activation in Solid Cancers

The Signal Transducer and Activator of Transcription (STAT)3 and 5 proteins are activated by many cytokine receptors to regulate specific gene expression and mitochondrial functions. Their role in cancer is largely context-dependent as they can both act as oncogenes and tumor suppressors. We review here the role of STAT3/5 activation in solid cancers and summarize their association with survival in cancer patients. The molecular mechanisms that underpin the oncogenic activity of STAT3/5 signaling include the regulation of genes that control cell cycle and cell death. However, recent advances also highlight the critical role of STAT3/5 target genes mediating inflammation and stemness. In addition, STAT3 mitochondrial functions are required for transformation. On the other hand, several tumor suppressor pathways act on or are activated by STAT3/5 signaling, including tyrosine phosphatases, the sumo ligase Protein Inhibitor of Activated STAT3 (PIAS3), the E3 ubiquitin ligase TATA Element Modulatory Factor/Androgen Receptor-Coactivator of 160 kDa (TMF/ARA160), the miRNAs miR-124 and miR-1181, the Protein of alternative reading frame 19 (p19ARF)/p53 pathway and the Suppressor of Cytokine Signaling 1 and 3 (SOCS1/3) proteins. Cancer mutations and epigenetic alterations may alter the balance between pro-oncogenic and tumor suppressor activities associated with STAT3/5 signaling, explaining their context-dependent association with tumor progression both in human cancers and animal models.

Golgi Structure and Function in Health, Stress, and Diseases

The Golgi apparatus is a central intracellular membrane-bound organelle with key functions in trafficking, processing, and sorting of newly synthesized membrane and secretory proteins and lipids. To best perform these functions, Golgi membranes form a unique stacked structure. The Golgi structure is dynamic but tightly regulated; it undergoes rapid disassembly and reassembly during the cell cycle of mammalian cells and is disrupted under certain stress and pathological conditions. In the past decade, significant amount of effort has been made to reveal the molecular mechanisms that regulate the Golgi membrane architecture and function. Here we review the major discoveries in the mechanisms of Golgi structure formation, regulation, and alteration in relation to its functions in physiological and pathological conditions to further our understanding of Golgi structure and function in health and diseases.

Selected Golgi-Localized Proteins and Carcinogenesis: What Do We Know?

The role of the Golgi apparatus in carcinogenesis still remains unclear. A number of structural and functional cis-, medial-, and trans-Golgi proteins as well as a complexity of metabolic pathways which they mediate may indicate a central role of the Golgi apparatus in the development and progression of cancer. Pleiotropy of cellular function of the Golgi apparatus makes it a "metabolic heart" or a relay station of a cell, which combines multiple signaling pathways involved in carcinogenesis. Therefore, any damage to or structural abnormality of the Golgi apparatus, causing its fragmentation and/or biochemical dysregulation, results in an up- or downregulation of signaling pathways and may in turn promote tumor progression, as well as local nodal and distant metastases. Three alternative or parallel models of spatial and functional Golgi organization within tumor cells were proposed: (1) compacted Golgi structure, (2) normal Golgi structure with its increased activity, and (3) the Golgi fragmentation with ministacks formation. Regardless of the assumed model, the increased activity of oncogenesis initiators and promoters with inhibition of suppressor proteins results in an increased cell motility and migration, increased angiogenesis, significantly activated trafficking kinetics, proliferation, EMT induction, decreased susceptibility to apoptosis-inducing factors, and modulating immune response to tumor cell antigens. Eventually, this will lead to the increased metastatic potential of cancer cells and an increased risk of lymph node and distant metastases. This chapter provided an overview of the current state of knowledge of selected Golgi proteins, their role in cytophysiology as well as potential involvement in tumorigenesis.

STAT3 Interactors as Potential Therapeutic Targets for Cancer Treatment

Signal transducers and activators of transcription (STATs) mediate essential signaling pathways in different biological processes, including immune responses, hematopoiesis, and neurogenesis. Among the STAT members, STAT3 plays crucial roles in cell proliferation, survival, and differentiation. While STAT3 activation is transient in physiological conditions, STAT3 becomes persistently activated in a high percentage of solid and hematopoietic malignancies (e.g., melanoma, multiple myeloma, breast, prostate, ovarian, and colon cancers), thus contributing to malignant transformation and progression. This makes STAT3 an attractive therapeutic target for cancers. Initial strategies aimed at inhibiting STAT3 functions have focused on blocking the action of its activating kinases or sequestering its DNA binding ability. More recently, the diffusion of proteomic-based techniques, which have allowed for the identification and characterization of novel STAT3-interacting proteins able to modulate STAT3 activity via its subcellular localization, interact with upstream kinases, and recruit transcriptional machinery, has raised the possibility to target such cofactors to specifically restrain STAT3 oncogenic functions. In this article, we summarize the available data about the function of STAT3 interactors in malignant cells and discuss their role as potential therapeutic targets for cancer treatment.

STAT3: a multifaceted oncoprotein

Signal transducer and activator of transcription (STAT) 3 is a key signalling protein engaged by a multitude of growth factors and cytokines to elicit diverse biological outcomes including cellular growth, differentiation, and survival. The complete loss of STAT3 is not compatible with life and even partial loss of function mutations lead to debilitating pathologies like hyper IgE syndrome. Conversely, augmented STAT3 activity has been reported in as many as 50% of all human tumours. The dogma of STAT3 activity posits that it is a tyrosine phosphorylated transcription factor which modulates the expression of hundreds of genes. However, the regulation and biological consequences of STAT3 activation are far more complex. In addition to tyrosine phosphorylation, STAT3 is decorated with a plethora of post-translational modifications which regulate STAT3's nuclear function in addition to its non-genomic activities. In addition to these emerging complexities in the biochemical regulation of STAT3 activity, recent studies reveal that STAT3 is either oncogenic or a tumour suppressor. This review will explore these complexities.

PDGFRβ translocates to the nucleus and regulates chromatin remodeling via TATA element-modifying factor 1

PDGFRβ translocates to the nucleus in a ligand-dependent manner tethered by TATA element–modifying factor 1 (TMF-1). Papadopoulos et al. show that PDGFRβ interacts with TMF-1 and Fer kinase in the nucleus, regulating chromatin remodeling by the SWI–SNF complex and controlling proliferation via a p21-dependent mechanism.

Translocation of full-length or fragments of receptors to the nucleus has been reported for several tyrosine kinase receptors. In this paper, we show that a fraction of full-length cell surface platelet-derived growth factor (PDGF) receptor β (PDGFRβ) accumulates in the nucleus at the chromatin and the nuclear matrix after ligand stimulation. Nuclear translocation of PDGFRβ was dependent on PDGF-BB–induced receptor dimerization, clathrin-mediated endocytosis, β-importin, and intact Golgi, occurring in both normal and cancer cells. In the nucleus, PDGFRβ formed ligand-inducible complexes with the tyrosine kinase Fer and its substrate, TATA element–modifying factor 1 (TMF-1). PDGF-BB stimulation decreased TMF-1 binding to the transcriptional regulator Brahma-related gene 1 (Brg-1) and released Brg-1 from the SWI–SNF chromatin remodeling complex. Moreover, knockdown of TMF-1 by small interfering RNA decreased nuclear translocation of PDGFRβ and caused significant up-regulation of the Brg-1/p53-regulated cell cycle inhibitor CDKN1A (encoding p21) without affecting PDGFRβ-inducible immediate-early genes. In conclusion, nuclear interactions of PDGFRβ control proliferation by chromatin remodeling and regulation of p21 levels.

Epigenetic Component p66a Modulates Myeloid-Derived Suppressor Cells by Modifying STAT3

STAT3 plays a critical role in myeloid-derived suppressor cell (MDSC) accumulation and activation. Most studies have probed underlying mechanisms of STAT3 activation. However, epigenetic events involved in STAT3 activation are poorly understood. In this study, we identified several epigenetic-associated proteins such as p66a (Gatad2a), a novel protein transcriptional repressor that might interact with STAT3 in functional MDSCs, by using immunoprecipitation and mass spectrometry. p66a could regulate the phosphorylation and ubiquitination of STAT3. Silencing p66a promoted not only phosphorylation but also K63 ubiquitination of STAT3 in the activated MDSCs. Interestingly, p66a expression was significantly suppressed by IL-6 both in vitro and in vivo during MDSC activation, suggesting that p66a is involved in IL-6-mediated differentiation of MDSCs. Indeed, silencing p66a could promote MDSC accumulation, differentiation, and activation. Tumors in mice injected with p66a small interfering RNA-transfected MDSCs also grew faster, whereas tumors in mice injected with p66a-transfected MDSCs were smaller as compared with the control. Thus, our data demonstrate that p66a may physically interact with STAT3 to suppress its activity through posttranslational modification, which reveals a novel regulatory mechanism controlling STAT3 activation during myeloid cell differentiation.

Porcine Reproductive and Respiratory Syndrome Virus Antagonizes JAK/STAT3 Signaling via nsp5, Which Induces STAT3 Degradation

Signal transducer and activator of transcription 3 (STAT3) is a pleiotropic signaling mediator of many cytokines, including interleukin-6 (IL-6) and IL-10. STAT3 is known to play critical roles in cell growth, proliferation, differentiation, immunity and inflammatory responses. The objective of this study was to determine the effect of porcine reproductive and respiratory syndrome virus (PRRSV) infection on the STAT3 signaling since PRRSV induces a weak protective immune response in host animals. We report here that PRRSV infection of MARC-145 cells and primary porcine pulmonary alveolar macrophages led to significant reduction of STAT3 protein level. Several strains of both PRRSV type 1 and type 2 led to a similar reduction of STAT3 protein level but had a minimal effect on its transcripts. The PRRSV-mediated STAT3 reduction was in a dose-dependent manner as the STAT3 level decreased, along with incremental amounts of PRRSV inocula. Further study showed that nonstructural protein 5 (nsp5) of PRRSV induced the STAT3 degradation by increasing its polyubiquitination level and shortening its half-life from 24 h to ∼3.5 h. The C-terminal domain of nsp5 was shown to be required for the STAT3 degradation. Moreover, the STAT3 signaling in the cells transfected with nsp5 plasmid was significantly inhibited. These results indicate that PRRSV antagonizes the STAT3 signaling by accelerating STAT3 degradation via the ubiquitin-proteasomal pathway. This study provides insight into the PRRSV interference with the JAK/STAT3 signaling, leading to perturbation of the host innate and adaptive immune responses.

IMPORTANCE

The typical features of immune responses in PRRSV-infected pigs are delayed onset and low levels of virus neutralizing antibodies, as well as weak cell-mediated immunity. Lymphocyte development and differentiation rely on cytokines, many of which signal through the JAK/STAT signaling pathway to exert their biological effects. Here, we discovered that PRRSV antagonizes the JAK/STAT3 signaling by inducing degradation of STAT3, a master transcription activator involved in multiple cellular processes and the host immune responses. The nsp5 protein of PRRSV is responsible for the accelerated STAT3 degradation. The PRRSV-mediated antagonizing STAT3 could lead to suppression of a broad spectrum of cytokines and growth factors to allow virus replication and spread in host animals. This may be one of the reasons for the PRRSV interference with the innate immunity and its poor elicitation of protective immunity. This finding provides insight into PRRSV pathogenesis and its interference with the host immune responses.

SUMOylation and SENP3 regulate STAT3 activation in head and neck cancer

Hyperphosphorylation of signal transducer and activator of transcription 3 (STAT3) has been found in various types of human cancers, including head and neck cancer (HNC). Although smoking is critical in the development and progression of HNC, how tobacco components activate STAT3 is unclear. We demonstrated that exposure of HNC cell lines to a tobacco extract induced a rapid Y705 phosphorylation of STAT3 and a rapid increase in the SUMO protease SENP3 that depended on a simultaneous increase in reactive oxygen species. We identified that SUMOylation at the lysine 451 site facilitated STAT3 binding to the phosphatase TC45 through an SUMO-interacting motif of TC45. SENP3 could thus enhance STAT3 phosphorylation by de-conjugating the SUMO2/3 modification of STAT3. Knocking-down of SENP3 greatly impaired basal and induced STAT3 phosphorylation by tobacco extract or interleukin 6. A correlation between SENP3 protein levels and STAT3 Y705 phosphorylation levels in human laryngeal carcinoma specimens was found, which was more significant in the specimens derived from the smoker patients and with poor clinicopathological parameters. Our data identified SUMOylation as a previously undescribed post-translational modification of STAT3 and SENP3 as a critical positive modulator of tobacco- or cytokine-induced STAT3 activation. These findings provide novel insights into the hyperphosphorylation of STAT3 in development of HNC.

TMF/ARA160 Governs the Dynamic Spatial Orientation of the Golgi Apparatus during Sperm Development

TMF/ARA160 is known to be a TATA element Modulatory Factor (TMF). It was initially identified as a DNA-binding factor and a coactivator of the Androgen receptor. It was also characterized as a Golgi-associated protein, which is essential for acrosome formation during functional sperm development. However, the molecular roles of TMF in this intricate process have not been revealed. Here, we show that during spermiogenesis, TMF undergoes a dynamic change of localization throughout the Golgi apparatus. Specifically, TMF translocates from the cis-Golgi to the trans-Golgi network and to the emerging vesicles surface, as the round spermatids develop. Notably, lack of TMF led to an abnormal spatial orientation of the Golgi and to the deviation of the trans-Golgi surface away from the nucleus of the developing round spermatids. Concomitantly, pro-acrosomal vesicles derived from the TMF-/- Golgi lacked targeting properties and did not tether to the spermatid nuclear membrane thereby failing to form the acrosome anchoring scaffold, the acroplaxome, around the cell-nucleus. Absence of TMF also perturbed the positioning of microtubules, which normally lie in proximity to the Golgi and are important for maintaining Golgi spatial orientation and dynamics and for chromatoid body formation, which is impaired in TMF-/- spermatids. In-silico evaluation combined with molecular and electron microscopic analyses revealed the presence of a microtubule interacting domain (MIT) in TMF, and confirmed the association of TMF with microtubules in spermatogenic cells. Furthermore, the MIT domain in TMF, along with microtubules integrity, are required for stable association of TMF with the Golgi apparatus. Collectively, we show here for the first time that a Golgi and microtubules associated protein is crucial for maintaining proper Golgi orientation during a cell developmental process.

Signal transducer and activator of transcription 3 regulation by novel binding partners

Signal transducers and activators of transcription (STATs) mediate essential signals for various biological processes, including immune responses, hematopoiesis, and neurogenesis. STAT3, for example, is involved in the pathogenesis of various human diseases, including cancers, autoimmune and inflammatory disorders. STAT3 activation is therefore tightly regulated at multiple levels to prevent these pathological conditions. A number of proteins have been reported to associate with STAT3 and regulate its activity. These STAT3-interacting proteins function to modulate STAT3-mediated signaling at various steps and mediate the crosstalk of STAT3 with other cellular signaling pathways. This article reviews the roles of novel STAT3 binding partners such as DAXX, zipper-interacting protein kinase, Krüppel-associated box-associated protein 1, Y14, PDZ and LIM domain 2 and signal transducing adaptor protein-2, in the regulation of STAT3-mediated signaling.

Berberine Increases Doxorubicin Sensitivity by Suppressing STAT3 in Lung Cancer

Berberine (BBR), an alkaloid component isolated from Chinese medicinal herb Huang Lian, has aroused broad interests for its antitumor effect in recent years. The signal transducer and activator of transcription 3 (STAT3), plays critical roles in malignant transformation and progression and was found to be constitutively activated in a variety of human cancers. In this study, we show that BBR inhibited cell proliferation, induced apoptosis, and suppressed tumor spheroid formation of lung cancer cell lines. These effects were correlated with BBR-mediated suppression of both phosphorylated and total levels of STAT3 protein. Furthermore, BBR promoted STAT3 degradation by enhancing ubiquitination. Importantly, we demonstrated that BBR was able to inhibit doxorubicin (DOX)-mediated STAT3 activation and sensitize lung cancer cells to the cytotoxic effect of DOX treatment. Given that BBR is widely used in clinic with low toxicity, our results are potentially important for the development of a novel combinatorial therapy with BBR and DOX in the treatment of lung cancer.

Paeoniflorin inhibits human glioma cells via STAT3 degradation by the ubiquitin-proteasome pathway

We investigated the underlying mechanism for the potent proapoptotic effect of paeoniflorin (PF) on human glioma cells in vitro, focusing on signal transducer and activator of transcription 3 (STAT3) signaling. Significant time- and dose-dependent apoptosis and inhibition of proliferation were observed in PF-treated U87 and U251 glioma cells. Expression of STAT3, its active form phosphorylated STAT3 (p-STAT3), and several downstream molecules, including HIAP, Bcl-2, cyclin D1, and Survivin, were significantly downregulated upon PF treatment. Overexpression of STAT3 induced resistance to PF, suggesting that STAT3 was a critical target of PF. Interestingly, rapid downregulation of STAT3 was consistent with its accelerated degradation, but not with its dephosphorylation or transcriptional modulation. Using specific inhibitors, we demonstrated that the prodegradation effect of PF on STAT3 was mainly through the ubiquitin-proteasome pathway rather than via lysosomal degradation. These findings indicated that PF-induced growth suppression and apoptosis in human glioma cells through the proteasome-dependent degradation of STAT3.

The synthetic tryptanthrin analogue suppresses STAT3 signaling and induces caspase dependent apoptosis via ERK up regulation in human leukemia HL-60 cells

Tryptanthrin is a natural product which has been reported to have several medicinal properties. In this study, we tried to investigate the detailed molecular mechanism of its bromo analogue (TBr), a potent cytotoxic agent in the induction of cancer cell death. It was found that TBr primarily targets STAT3 and ERK signaling during the induction of apoptosis in several human leukemia cell lines. In HL-60 cells, TBr treatment caused early down regulation of p-STAT3 with concomitant up regulation of p-ERK which led to the activation of intrinsic and extrinsic pathways of apoptosis. The mechanism of TBr mediated inhibition of p-STAT3 was found to be due to the activation of ubiquitin dependent degradation of tyrosine 705 and serine 727 p-STAT3. As IL-6 is the main driver of the STAT3 pathway, the effect of TBr on cell death was subdued when treated in the combination with IL-6 in HL60 cells. Interestingly, PD98059 significantly reduced the apoptotic effects of TBr, thus showing the direct involvement of p-ERK in TBr mediated cell death. It was further shown that apoptotic protein Bax silencing in HL-60 cells resists TBr mediated ERK dependent apoptosis. In summary, for the first time we report the mechanism of TBr mediated cell death in human leukemia cell lines by targeting STAT3 and ERK pathways.

Critical role for lysine 685 in gene expression mediated by transcription factor unphosphorylated STAT3

STAT3 is a pleiotropic transcription factor that is activated by the phosphorylation of tyrosine 705 in response to many cytokines and growth factors. STAT3 without Tyr-705 phosphorylation (U-STAT3) is also a potent transcription factor, and its concentration in cells increases greatly in response to STAT3 activation because the STAT3 gene can be driven by phosphorylated STAT3 dimers. We have now searched for post-translational modifications of U-STAT3 that might have a critical role in its function. An analysis by mass spectroscopy indicated that U-STAT3 is acetylated on Lys-685, and the integrity of Lys-685 is required for the expression of most U-STAT3-dependent genes. In contrast, we found only a very minor role for Lys-685 in gene expression induced in response to tyrosine-phosphorylated STAT3. U-STAT3 plays an important role in angiotensin II-induced gene expression and in the consequent development of cardiac hypertrophy and dysfunction. Mutation of Lys-685 inhibits this function of STAT3, providing new information on the role of U-STAT3 in augmenting the development of heart failure.

Inducible STAT3 NH2 terminal mono-ubiquitination promotes BRD4 complex formation to regulate apoptosis

Signal Transducers and Activator of Transcription-3 (STAT3) are latent transcription factors that are regulated by post-translational modifications (PTMs) in response to cellular activation by the IL-6 superfamily of cytokines to regulate cell cycle progression and/or apoptosis. Here we observe that STAT3 is inducibly mono-ubiquitinated and investigate its consequences. Using domain mapping and highly specific selected reaction monitoring-mass spectrometric assays, we identify lysine (K) 97 in its NH2-terminal domain as the major mono-ubiquitin conjugation site. We constructed a mono-ubiquitinated mimic consisting of a deubiquitinase-resistant monomeric ubiquitin fused to the NH2 terminus of STAT3 (ubiquitinated-STAT3 FP). In complex assays of ectopically expressed ubi-STAT3-FP, we observed enhanced complex formation with bromodomain-containing protein 4 (BRD4), a component of the activated positive transcriptional elongation factor (P-TEFb) complex. Chromatin immunoprecipitation experiments in STAT3(+/-) and STAT3(-/-) MEFs showed BRD4 recruitment to STAT3-dependent suppressor of cytokine signaling-3 gene (SOCS3). The effect of a selective small molecule inhibitor of BRD4, JQ1, to inhibit SOCS3 expression demonstrated the functional role of BRD4 for STAT3-dependent transcription. Additionally, ectopic ubiquitinated-STAT3 FP expression upregulated BCL2, BCL2L1, APEX1, SOD2, CCND1 and MYC expression indicating the role of ubiquitinated STAT3 in anti-apoptosis and cellular proliferation. Finally we observed that ubiquitinated-STAT3 FP suppressed TNFα-induced apoptotic cell death, indicating the functional importance of mono-ubiquitinated STAT3 in antiapoptotic gene expression. We conclude that STAT3 mono-ubiquitination is a key trigger in BRD4-dependent antiapoptotic and pro-proliferative gene expression programs. Thus, inhibiting the STAT3 mono-ubiquitination-BRD4 pathway may be a novel therapeutic target for the treatment of STAT3-dependent proliferative diseases.

Ubiquitination regulates the morphogenesis and function of sperm organelles

It is now understood that protein ubiquitination has diverse cellular functions in eukaryotes. The molecular mechanism and physiological significance of ubiquitin-mediated processes have been extensively studied in yeast, Drosophila and mammalian somatic cells. Moreover, an increasing number of studies have emphasized the importance of ubiquitination in spermatogenesis and fertilization. The dysfunction of various ubiquitin systems results in impaired sperm development with abnormal organelle morphology and function, which in turn is highly associated with male infertility. This review will focus on the emerging roles of ubiquitination in biogenesis, function and stability of sperm organelles in mammals.

A new model for developmental neuronal death and excitatory/inhibitory balance in hippocampus

The nervous system develops through a program that produces neurons in excess and then eliminates approximately half during a period of naturally occurring death. Neuronal activity has been shown to promote the survival of neurons during this period by stimulating the production and release of neurotrophins. In the peripheral nervous system (PNS), neurons depends on neurotrophins that activate survival pathways, which explains how the size of target cells influences number of neurons that innervate them (neurotrophin hypothesis). However, in the central nervous system (CNS), the role of neurotrophins has not been clear. Contrary to the neurotrophin hypothesis, a recent study shows that, in neonatal hippocampus, neurotrophins cannot promote survival without spontaneous network activity: Neurotrophins recruit neurons into spontaneously active networks, and this activity determines which neurons survive. By placing neurotrophin upstream of activity in the survival signaling pathway, these new results change our understanding of how neurotrophins promote survival. Spontaneous, synchronized network activity begins to spread through both principle neurons and interneurons in the hippocampus as they enter the death period. At this stage, neurotransmission mediated by γ-aminobutyric acid (GABA) is excitatory and drives the spontaneous activity. An important recent observation is that neurotrophins preferentially recruit GABAergic neurons into spontaneously active networks; thus, neurotrophins select for survival only those neurons joined to active networks with strong GABAergic inputs, which would later become inhibitory. A proper excitatory/inhibitory (E/I) balance is critical for normal adult brain function. This balance may be especially important in the hippocampus where impairments in E/I balance are associated with pathologies including epilepsy. Here, I discuss the molecular mechanisms for survival in neonatal neurons, how these mechanisms change during development, and how they may be linked to degenerative diseases.

Signal transducer and activator of transcription 3 (STAT3) degradation by proteasome controls a developmental switch in neurotrophin dependence

Neonatal brains develop through a program that eliminates about half of the neurons. During this period, neurons depend on neurotrophins for their survival. Recently, we reported that, at the conclusion of the naturally occurring death period, neurons become neurotrophin-independent and, further, that this developmental switch is achieved by the emergence of a second survival pathway mediated by signal transducer and activator of transcription 3 (STAT3). Here I show that calcineurin plays a key role in controlling the developmental switch in mouse hippocampal neurons. Calcineurin promotes the degradation of STAT3 via the ubiquitin-proteasome pathway. Inhibition of calcineurin acutely increases total levels of STAT3 as well as its activated forms, resulting in decreased levels of the tumor suppressor p53 and its proapoptotic target, Bax. In vivo and in vitro, calcineurin regulates levels of STAT3 and neurotrophin dependence. TMF/ARA 160 (TATA element modulatory factor/androgen receptor co-activator 160), the key mediator of STAT3 ubiquitination, is required for calcineurin-dependent STAT3 degradation. Thus, these results show that the ubiquitin-proteasome pathway controls the critical developmental switch of neurotrophin dependence in the newborn hippocampus.

Testosterone deficiency accompanied by testicular and epididymal abnormalities in TMF(-/-) mice

TMF/ARA160 is a Golgi-associated protein, which is essential for spermiogenesis. In this study, we show that lack of TMF/ARA160 leads to defects in both the testis and the epididymis. In the testis, spermatid retention and extensive proliferation of Leydig cells were observed. Concomitantly, the serum levels of luteinizing hormone (LH), a stimulator of Leydig cell proliferation, were significantly increased in TMF(-/-) mice. Structural and functional defects were also seen in the epididymis. These included apoptosis of epithelial epididymal cells and sperm stasis in the cauda. Notably, the serum testosterone levels of TMF(-/-) mice were significantly lower than those of wt mice, and external testosterone administration decreased the number of apoptotic epithelial epididymal cells in TMF(-/-) animals. In summary, we show here for the first time that TMF/ARA160 participates in the control of serum testosterone levels in males, and its absence results in major testicular and epididymal defects.

The ubiquitin ligase TRAF6 negatively regulates the JAK-STAT signaling pathway by binding to STAT3 and mediating its ubiquitination

STAT3 is a key transcription factor that mediates various cellular and organismal processes, such as cell growth, apoptosis, immune response and cancer. However, the molecular mechanisms of STAT3 regulation remain poorly understood. Here, we identified TRAF6 as a new STAT3 interactor. TRAF6 augmented the ubiquitination of STAT3 and deactivated its transcriptional activity induced by IFNα stimulation or overexpressed with JAK2. Both the RING domain and the TRAF-type zinc finger domain of TRAF6 were indispensable for STAT3 deactivation. Accordingly, TRAF6 also down-regulated the expression of two known STAT3 target genes, CRP and ACT. Therefore, we showed that TRAF6 is a new regulator of JAK/STAT signaling and provide a new mechanistic explanation for the crosstalk between the NF-κB and the JAK-STAT pathways.

MARCH7 E3 ubiquitin ligase is highly expressed in developing spermatids of rats and its possible involvement in head and tail formation

Spermatogenesis is a highly complicated metamorphosis process of male germ cells. Recent studies have provided evidence that the ubiquitin-proteasome system plays an important role in sperm head shaping, but the underlying mechanism is less understood. In this study, we localized membrane-associated RING-CH (MARCH)7, an E3 ubiquitin ligase, in rat testis. Northern blot analysis showed that March7 mRNA is expressed ubiquitously but highly in the testis and ovary. In situ hybridization of rat testis demonstrated that March7 mRNA is expressed weakly in spermatogonia and its level is gradually increased as they develop. Immunohistochemical analysis detected MARCH7 protein expression in spermiogenic cells from late round spermatids to elongated spermatids and in epididymal spermatozoa. Moreover, MARCH7 was found to be localized to the caudal end of the developing acrosome of late round and elongating spermatids, colocalizing with β-actin, a component of the acroplaxome. In addition, MARCH7 was also detected in the developing flagella and its expression levels were prominent in elongated spermatids. We also showed that MARCH7 catalyzes lysine 48 (K48)-linked ubiquitination. Immunolocalization studies revealed that K48-linked ubiquitin chains were detected in the heads of elongating spermatids and in the acrosome/acroplaxome, neck, midpiece and cytoplasmic lobes of elongated spermatids. These results suggest that MARCH7 is involved in spermiogenesis by regulating the structural and functional integrity of the head and tail of developing spermatids.

STAT3 inhibition, a novel approach to enhancing targeted therapy in human cancers (review)

Signal transducer and activator of transcription 3 (STAT3) regulates many critical functions in human normal and malignant tissues, such as differentiation, proliferation, survival, angiogenesis and immune function. Constitutive activation of STAT3 is implicated in a wide range of human cancers. As such, STAT3 has been studied as a tumour therapeutic target. This review aimed principally to summarise the updated research on STAT3 inhibition studies and their therapeutic potential in solid tumours. Recent literature associated with STAT3 inhibition was reviewed through PubMed and Medline database, followed by critical comparison and analysis. Constitutive activation of STAT3 has been identified as abnormal and oncogenic. The pathway of STAT3 activation and signal transduction identifies 3 approaches for inhibition: modulating upstream positive or negative regulators, regulating RNA (DN-STAT3, anti-sense RNA, siRNA and microRNA) or targeting STAT3 protein at different domains. The last approach using small molecule STAT3 inhibitors has been the most examined so far with both preclinical and clinical studies. Targeting STAT3 using a specific inhibitor may be a useful cancer treatment approach, with the potential for a broad clinical impact.

Loss of TMF/ARA160 protein renders colonic mucus refractory to bacterial colonization and diminishes intestinal susceptibility to acute colitis

TMF/ARA160 is a Golgi-associated protein with several cellular functions, among them direction of the NF-κB subunit, p65 RelA, to ubiquitination and proteasomal degradation in stressed cells. We sought to investigate the role of TMF/ARA160 under imposed stress conditions in vivo. TMF(-/-) and wild-type (WT) mice were treated with the ulcerative agent dextran sulfate sodium (DSS), and the severity of the inflicted acute colitis was determined. TMF(-/-) mice were found to be significantly less susceptible to DSS-induced colitis, with profoundly less bacterial penetration into the colonic epithelia. Surprisingly, unlike in WT mice, no bacterial colonies were visualized in colons of healthy untreated TMF(-/-) mice, indicating the constitutive resistance of TMF(-/-) colonic mucus to bacterial retention and penetration. Gene expression analysis of colon tissues from unchallenged TMF(-/-) mice revealed 5-fold elevated transcription of the muc2 gene, which encodes the major component of the colonic mucus gel, the MUC2 mucin. Accordingly, the morphology of the colonic mucus in TMF(-/-) mice was found to differ from the mucus structure in WT colons. The NF-κB subunit, p65, a well known transcription inducer of muc2, was up-regulated significantly in TMF(-/-) intestinal epithelial cells. However, this did not cause spontaneous inflammation or increased colonic crypt cell proliferation. Collectively, our findings demonstrate that absence of TMF/ARA160 renders the colonic mucus refractory to bacterial colonization and the large intestine less susceptible to the onset of colitis.

PDLIM2 inhibits T helper 17 cell development and granulomatous inflammation through degradation of STAT3

Granuloma formation is an important host defense mechanism against intracellular bacteria; however, uncontrolled granulomatous inflammation is pathologic. T helper 17 (TH17) cells are thought to have a pathogenic role in autoimmune and inflammatory diseases, including in granulomas. Here, we report that the PDZ-LIM domain protein PDLIM2 inhibited TH17 cell development and granulomatous responses by acting as a nuclear ubiquitin E3 ligase that targeted signal transducer and activator of transcription 3 (STAT3), a transcription factor critical for the commitment of naïve CD4+ T cells to the TH17 lineage. PDLIM2 promoted the polyubiquitination and proteasomal degradation of STAT3, thereby disrupting STAT3-mediated gene activation. Deficiency in PDLIM2 resulted in the accumulation of STAT3 in the nucleus, enhanced the extent of TH17 cell differentiation, and exacerbated granuloma formation. This study delineates an essential role for PDLIM2 in inhibiting TH17 cell-mediated inflammatory responses by suppressing STAT3 signaling and provides a potential therapeutic target for the treatment of autoimmune diseases.

Skin-derived precursors differentiating into dopaminergic neuronal cells in the brains of Parkinson disease model rats

OBJECT

In the authors' previous study, they observed that amino acids 157-171 of von Hippel-Lindau protein (VHL peptide) induced neuronal differentiation of skin-derived precursors. They also noted that transplantation of these differentiated cells into the striata of a Parkinson disease (PD) rat model reduced apomorphine-induced rotations. In the present study, they investigated if these cells produce dopamine in the striatum.

METHODS

Skin-derived precursors were differentiated into neurons using VHL peptide and transplanted into the striata of a PD model of rats. Four weeks after transplantation, a probe was inserted into rat striata and extracellular dopamine was extracted by microdialysis. Dopamine levels were measured by high-pressure liquid chromatography. Brain sections were assessed by immunohistochemical analysis for the presence of tyrosine hydroxylase and dopamine transporter.

RESULTS

Increased dopamine levels in the striata of the rats were observed after transplantation (p < 0.01), and these were correlated with a reduction in the number of apomorphine-induced rotations (p < 0.05). Skin-derived precursors observed along the tract of transplantation were positive for tyrosine hydroxylase and dopamine transporter.

CONCLUSIONS

This study suggests that transplantation of skin-derived precursors, differentiated into neuronal cells using VHL peptide, can improve PD-like symptoms by enabling production of dopamine in the striata in a PD model of rats.

Signal transducer and activator of transcription-3, inflammation, and cancer: how intimate is the relationship?

Signal transducer and activator of transcription-3 (STAT-3) is one of six members of a family of transcription factors. It was discovered almost 15 years ago as an acute-phase response factor. This factor has now been associated with inflammation, cellular transformation, survival, proliferation, invasion, angiogenesis, and metastasis of cancer. Various types of carcinogens, radiation, viruses, growth factors, oncogenes, and inflammatory cytokines have been found to activate STAT-3. STAT-3 is constitutively active in most tumor cells but not in normal cells. Phosphorylation of STAT-3 at tyrosine 705 leads to its dimerization, nuclear translocation, DNA binding, and gene transcription. The phosphorylation of STAT-3 at serine 727 may regulate its activity negatively or positively. STAT-3 regulates the expression of genes that mediate survival (survivin, bcl-xl, mcl-1, cellular FLICE-like inhibitory protein), proliferation (c-fos, c-myc, cyclin D1), invasion (matrix metalloproteinase-2), and angiogenesis (vascular endothelial growth factor). STAT-3 activation has also been associated with both chemoresistance and radioresistance. STAT-3 mediates these effects through its collaboration with various other transcription factors, including nuclear factor-kappaB, hypoxia-inducible factor-1, and peroxisome proliferator activated receptor-gamma. Because of its critical role in tumorigenesis, inhibitors of this factor's activation are being sought for both prevention and therapy of cancer. This has led to identification of small peptides, oligonucleotides, and small molecules as potential STAT-3 inhibitors. Several of these small molecules are chemopreventive agents derived from plants. This review discusses the intimate relationship between STAT-3, inflammation, and cancer in more detail.

Signal transducer and activator of transcription-3, inflammation, and cancer: how intimate is the relationship?

Signal transducer and activator of transcription-3 (STAT-3) is one of six members of a family of transcription factors. It was discovered almost 15 years ago as an acute-phase response factor. This factor has now been associated with inflammation, cellular transformation, survival, proliferation, invasion, angiogenesis, and metastasis of cancer. Various types of carcinogens, radiation, viruses, growth factors, oncogenes, and inflammatory cytokines have been found to activate STAT-3. STAT-3 is constitutively active in most tumor cells but not in normal cells. Phosphorylation of STAT-3 at tyrosine 705 leads to its dimerization, nuclear translocation, DNA binding, and gene transcription. The phosphorylation of STAT-3 at serine 727 may regulate its activity negatively or positively. STAT-3 regulates the expression of genes that mediate survival (survivin, bcl-xl, mcl-1, cellular FLICE-like inhibitory protein), proliferation (c-fos, c-myc, cyclin D1), invasion (matrix metalloproteinase-2), and angiogenesis (vascular endothelial growth factor). STAT-3 activation has also been associated with both chemoresistance and radioresistance. STAT-3 mediates these effects through its collaboration with various other transcription factors, including nuclear factor-kappaB, hypoxia-inducible factor-1, and peroxisome proliferator activated receptor-gamma. Because of its critical role in tumorigenesis, inhibitors of this factor's activation are being sought for both prevention and therapy of cancer. This has led to identification of small peptides, oligonucleotides, and small molecules as potential STAT-3 inhibitors. Several of these small molecules are chemopreventive agents derived from plants. This review discusses the intimate relationship between STAT-3, inflammation, and cancer in more detail.

Golgins and GRASPs: holding the Golgi together

The GRASP and golgin families of proteins have emerged as key components of the Golgi apparatus, with major roles in both the structural organisation of this organelle and the trafficking that occurs there. Both types of protein participate in membrane tethering events that occur upstream of membrane fusion as well as contributing to the structural scaffold that defines Golgi architecture, referred to as the Golgi matrix. The importance of these proteins is highlighted by their targeting in mitosis, apoptosis, and pathogenic infections that cause dramatic structural and functional reorganisation of the Golgi apparatus. In this review we will discuss our current understanding of GRASP and golgin function, highlighting some of the common themes that have emerged as well as describing previously unsuspected roles for these proteins in various cellular processes.

TMF/ARA160 downregulates proangiogenic genes and attenuates the progression of PC3 xenografts

TMF/ARA160 is a Golgi-associated protein whose level is downregulated in solid tumors. TMF changes its subcellular localization on exposure of cells to stress cues, thereby, directing proteins, such as the key transcription factor, Stat3, to proteasomal degradation. Here, we show that enforced ectopic expression of HA-TMF in PC3 prostate carcinoma cells, which do not express Stat3, significantly attenuated the development and growth of xenograft tumors elicited by these cells in athymic mice. Immunohistochemical analysis revealed impaired angiogenesis and accelerated onset of apoptosis in the HA-TMF-expressing tumors. RNA expression profiling revealed the downregulation of several proangiogenic genes in HA-TMF-expressing xenografts. Among these were the interleukin-8 and interleukin-1beta genes, whose expression is controlled by nuclear factor-kB. The level of the nuclear factor-kB component, p65/RelA, was decreased in HA-TMF-expressing xenografts, and TMF was found to direct the ubiquitination and proteasomal degradation of p65/RelA in metabolically stressed PC3 clones. Taken together, our findings indicate that TMF/ARA160 is a regulator of key transcription factors under metabolic constraints, thereby affecting angiogenesis and progression of solid tumors, which are subjected to metabolic stress.

Functional involvement of TMF/ARA160 in Rab6-dependent retrograde membrane traffic

The small GTPase Rab6 regulates retrograde membrane traffic from endosomes to the Golgi apparatus and from the Golgi to the endoplasmic reticulum (ER). We examined the role of a Rab6-binding protein, TMF/ARA160 (TATA element modulatory factor/androgen receptor-coactivator of 160 kDa), in this process. High-resolution immunofluorescence imaging revealed that TMF signal surrounded Rab6-positive Golgi structures and immunoelectron microscopy revealed that TMF is concentrated at the budding structures localized at the tips of cisternae. The knockdown of either TMF or Rab6 by RNA interference blocked retrograde transport of endocytosed Shiga toxin from early/recycling endosomes to the trans-Golgi network, causing missorting of the toxin to late endosomes/lysosomes. However, the TMF knockdown caused Rab6-dependent displacement of N-acetylgalactosaminyltransferase-2 (GalNAc-T2), but not beta1,4-galactosyltransferase (GalT), from the Golgi. Analyses using chimeric proteins, in which the cytoplasmic regions of GalNAc-T2 and GalT were exchanged, revealed that the cytoplasmic region of GalNAc-T2 plays a crucial role in its TMF-dependent Golgi retention. These observations suggest critical roles for TMF in two Rab6-dependent retrograde transport processes: one from endosomes to the Golgi and the other from the Golgi to the ER.

Concise Review: Role and Function of the Ubiquitin-Proteasome System in Mammalian Stem and Progenitor Cells

Highly ordered degradation of cell proteins by the ubiquitin-proteasome system, a sophisticated cellular proteolytic machinery, has been identified as a key regulatory mechanism in many eukaryotic cells. Accumulating evidence reveals that the ubiquitin-proteasome system is involved in the regulation of fundamental processes in mammalian stem and progenitor cells of embryonic, neural, hematopoietic, and mesenchymal origin. Such processes, including development, survival, differentiation, lineage commitment, migration, and homing, are directly controlled by the ubiquitin-proteasome system, either via proteolytic degradation of key regulatory proteins of signaling and gene expression pathways or via nonproteolytic mechanisms involving the proteasome itself or posttranslational modifications of target proteins by ubiquitin or other ubiquitin-like modifiers. Future characterization of the precise roles and functions of the ubiquitin-proteasome system in mammalian stem and early progenitor cells will improve our understanding of stem cell biology and may provide an experimental basis for the development of novel therapeutic strategies in regenerative medicine. Disclosure of potential conflicts of interest is found at the end of this article.

Cul4A is required for hematopoietic stem-cell engraftment and self-renewal

Several hematopoietic stem-cell (HSC) regulators are controlled by ubiquitin-mediated proteolysis, so the ubiquitin pathway might modulate HSC function. However, this hypothesis has not been formally tested. Cul4A encodes a core subunit of one ubiquitin ligase. Whereas Cul4A-deficient embryos die in utero, Cul4A-haploinsufficient mice are viable but exhibit abnormal hematopoiesis (fewer erythroid and primitive myeloid progenitors). Given these data, we examined whether Cul4A(+/-) HSCs might also be impaired. Using bone marrow transplantation assays, we determined that Cul4A(+/-) HSCs exhibit defects in engraftment and self-renewal capacity. These studies are the first to demonstrate that ubiquitin-mediated protein degradation is important for HSC function. Further, they indicate that a Cul4A ubiquitin ligase targets for degradation one or multiple HSC regulators.

BCR-ABL activates STAT3 via JAK and MEK pathways in human cells

Chronic myeloid leukaemia (CML) is characterised by a progression from a chronic towards an acute phase. We previously reported that signal transducer and activator of transcription 3 (STAT3), a major oncogenic signalling protein, is the target of p210-BCR-ABL in a murine embryonic stem (ES) cell model and in primary CD34+ CML cells. This activation was associated with inhibition of differentiation in ES cells. The present study found that BCR-ABL greatly phosphorylated STAT3 Ser727 residue and, to a lesser extent, Tyr705 residue in BCR-ABL-expressing cell lines (UT7-p210, MO7E-p210, and K562) and in primary CD34+ CML cells. Using BCR-ABL mutants, it was shown that BCR-ABL tyrosine kinase activity and its Tyr177 residue were necessary for STAT3 Ser727 phosphorylation. Constitutive STAT3 Tyr705 phosphorylation was associated with constitutive phosphorylation of Janus kinase (JAK)1 and JAK2, and was inhibited by the JAK inhibitor AG490, suggesting the involvement of JAK proteins in this process. Specific MEK [mitogen-activated protein (MAP) kinase/extracellular signal-regulated kinase (ERK) kinase] inhibitors PD98056 and UO126, as well as the use of a dominant-negative form of MEK1 abrogated STAT3 Ser727 phosphorylation, suggesting involvement of MAP-Kinase/Erk pathway. Inhibition of BCR-ABL with imatinib mesylate led to a dose-dependent downregulation of total STAT3 protein and mRNA, suggesting that BCR-ABL is involved in the transcriptional regulation of STAT3. Targeting JAK, MEK and STAT3 pathways could therefore be of therapeutic value, especially in advanced stage CML.

trnp: A conserved mammalian gene encoding a nuclear protein that accelerates cell-cycle progression

We herein describe a novel protein encoded by a single exon in a single-copy conserved mammalian gene. This protein, termed TMF regulated nuclear protein (TRNP), was identified in a yeast "two-hybrid" screen in which the "BC box" containing protein-TMF/ARA160 served as a bait. TRNP is a basic protein which accumulates in an insoluble nuclear fraction in mammalian cells. It is 227 aa long in humans and chimps and 223 aa long in mice. Enforced expression of TRNP in cells that do not express this protein significantly increased their proliferation rate by enhancing their cell-cycle progression from the G0/G1 to the S phase. Like another proliferation promoting factor, Stat3, TRNP was directed to proteasomal degradation by TMF/ ARA160. Thus, the trnp gene encodes a novel mammalian conserved nuclear protein that can accelerate cellcycle progression and is regulated by TMF/ARA160.

Luteolin promotes degradation in signal transducer and activator of transcription 3 in human hepatoma cells: an implication for the antitumor potential of flavonoids

In this study, we have investigated the underlying molecular mechanism for the potent proapoptotic effect of luteolin on human hepatoma cells both in vitro and in vivo, focusing on the signal transducer and activator of transcription 3 (STAT3)/Fas signaling. A clear apoptosis was found in the luteolin-treated HLF hepatoma cells in a time- and dosage-dependent manner. In concert with the caspase-8 activation by luteolin, an enhanced expression in functional Fas/CD95 was identified. Consistent with the increased Fas/CD95 expression, a drastic decrease in the Tyr(705) phosphorylation of STAT3, a known negative regulator of Fas/CD95 transcription, was found within 20 minutes in the luteolin-treated cells, leading to down-regulation in the target gene products of STAT3, such as cyclin D1, survivin, Bcl-xL, and vascular endothelial growth factor. Of interest, the rapid down-regulation in STAT3 was consistent with an accelerated ubiquitin-dependent degradation in the Tyr(705)-phosphorylated STAT3, but not the Ser(727)-phosphorylated one, another regulator of STAT3 activity. The expression level of Ser(727)-phosphorylated STAT3 was gradually decreased by the luteolin treatment, followed by a fast and clear down-regulation in the active forms of CDK5, which can phosphorylate STAT3 at Ser(727). An overexpression in STAT3 led to resistance to luteolin, suggesting that STAT3 was a critical target of luteolin. In nude mice with xenografted tumors using HAK-1B hepatoma cells, luteolin significantly inhibited the growth of the tumors in a dosage-dependent manner. These data suggested that luteolin targeted STAT3 through dual pathways-the ubiquitin-dependent degradation in Tyr(705)-phosphorylated STAT3 and the gradual down-regulation in Ser(727)-phosphorylated STAT3 through inactivation of CDK5, thereby triggering apoptosis via up-regulation in Fas/CD95.