PIASy represses CCAAT/enhancer-binding protein delta (C/EBPdelta) transcriptional activity by sequestering C/EBPdelta to the nuclear periphery

SUMO and PIAS repress NF-κB activation in a basal chordate

Small ubiquitin-like modifier (SUMO) regulates various biological processes, including the MyD88/TICAMs-IRAKs-TRAF6-NF-κB pathway, one of the core immune pathways. However, its functions are inconsistent between invertebrates and vertebrates and have rarely been investigated in lower chordates, including amphioxus and fishes. Here, we investigated the SUMOylation gene system in the amphioxus, a living basal chordate. We found that amphioxus has a SUMOylation system that has a complete set of genes and preserves several ancestral traits. We proceeded to study their molecular functions using the mammal cell lines. Both amphioxus SUMO1 and SUMO2 were shown to be able to attach to NF-κB Rel and to inhibit NF-κB activation by 50-75% in a dose-dependent fashion. The inhibition by SUMO2 could be further enhanced by the addition of the SUMO E2 ligase UBC9. In comparison, while human SUMO2 inhibited RelA, human SUMO1 slightly activated RelA. We also showed that, similar to human PIAS1-4, amphioxus PIAS could serve as a SUMO E3 ligase and promote its self-SUMOylation. This suggests that amphioxus PIAS is functionally compatible in human cells. Moreover, we showed that amphioxus PIAS is not only able to inhibit NF-κB activation induced by MyD88, TICAM-like, TRAF6 and IRAK4 but also able to suppress NF-κB Rel completely in the presence of SUMO1/2 in a dose-insensitive manner. This suggests that PIAS could effectively block Rel by promoting Rel SUMOylation. In comparison, in humans, only PIAS3, but not PIAS1/2/4, has been reported to promote NF-κB SUMOylation. Taken together, the findings from amphioxus, together with those from mammals and other species, not only offer insights into the functional volatility of the animal SUMO system, but also shed light on its evolutionary transitions from amphioxus to fish, and ultimately to humans.

SUMO Proteomics Analyses Identify Protein Inhibitor of Activated STAT-Mediated Regulatory Networks Involved in Cell Cycle and Cell Proliferation

Protein inhibitor of activated STAT (PIAS) proteins are E3 SUMO ligases playing important roles in protein stability and signaling transduction pathways. PIAS proteins are overexpressed in the triple-negative breast cancer cell line MDA-MB-231, and PIAS knockout (KO) results in a reduction in cell proliferation and cell arrest in the S phase. However, the molecular mechanisms underlying PIAS functions in cell proliferation and cell cycle remain largely unknown. Here, we used quantitative SUMO proteomics to explore the regulatory role of PIAS SUMO E3 ligases upon CRISPR/Cas9 KO of individual PIAS. A total of 1422 sites were identified, and around 10% of SUMO sites were regulated following KO of one or more PIAS genes. We identified protein substrates that were either specific to individual PIAS ligase or regulated by several PIAS ligases. Ki-67 and TOP2A, which are involved in cell proliferation and epithelial-to-mesenchymal transition, are SUMOylated at several lysine residues by all PIAS ligases, suggesting a level of redundancy between these proteins. Confocal microscopy and biochemical experiments revealed that SUMOylation regulated TOP2A protein stability, while this modification is involved in the recruitment of Ki-67 nucleolar proteins containing the SUMO interacting motif. These results provide novel insights into both the redundant and specific regulatory mechanisms of cell proliferation and cell cycle mediated by PIAS SUMO E3 ligases.

CCAAT/Enhancer-Binding Proteins in Fibrosis: Complex Roles Beyond Conventional Understanding

CCAAT/enhancer-binding proteins (C/EBPs) are a family of at least six identified transcription factors that contain a highly conserved basic leucine zipper domain and interact selectively with duplex DNA to regulate target gene expression. C/EBPs play important roles in various physiological processes, and their abnormal function can lead to various diseases. Recently, accumulating evidence has demonstrated that aberrant C/EBP expression or activity is closely associated with the onset and progression of fibrosis in several organs and tissues. During fibrosis, various C/EBPs can exert distinct functions in the same organ, while the same C/EBP can exert distinct functions in different organs. Modulating C/EBP expression or activity could regulate various molecular processes to alleviate fibrosis in multiple organs; therefore, novel C/EBPs-based therapeutic methods for treating fibrosis have attracted considerable attention. In this review, we will explore the features of C/EBPs and their critical functions in fibrosis in order to highlight new avenues for the development of novel therapies targeting C/EBPs.

Cancer-Associated Dysregulation of Sumo Regulators: Proteases and Ligases

SUMOylation is a post-translational modification that has emerged in recent decades as a mechanism involved in controlling diverse physiological processes and that is essential in vertebrates. The SUMO pathway is regulated by several enzymes, proteases and ligases being the main actors involved in the control of sumoylation of specific targets. Dysregulation of the expression, localization and function of these enzymes produces physiological changes that can lead to the appearance of different types of cancer, depending on the enzymes and target proteins involved. Among the most studied proteases and ligases, those of the SENP and PIAS families stand out, respectively. While the proteases involved in this pathway have specific SUMO activity, the ligases may have additional functions unrelated to sumoylation, which makes it more difficult to study their SUMO-associated role in cancer process. In this review we update the knowledge and advances in relation to the impact of dysregulation of SUMO proteases and ligases in cancer initiation and progression.

Linking nuclear matrix-localized PIAS1 to chromatin SUMOylation via direct binding of histones H3 and H2A.Z

As a conserved posttranslational modification, SUMOylation has been shown to play important roles in chromatin-related biological processes including transcription. However, how the SUMOylation machinery associates with chromatin is not clear. Here, we present evidence that multiple SUMOylation machinery components, including SUMO E1 proteins SAE1 and SAE2 and the PIAS (protein inhibitor of activated STAT) family SUMO E3 ligases, are primarily associated with the nuclear matrix rather than with chromatin. We show using nuclease digestion that all PIAS family proteins maintain nuclear matrix association in the absence of chromatin. Of importance, we identify multiple histones including H3 and H2A.Z as directly interacting with PIAS1 and demonstrate that this interaction requires the PIAS1 SAP (SAF-A/B, Acinus, and PIAS) domain. We demonstrate that PIAS1 promotes SUMOylation of histones H3 and H2B in both a SAP domain– and an E3 ligase activity–dependent manner. Furthermore, we show that PIAS1 binds to heat shock–induced genes and represses their expression and that this function also requires the SAP domain. Altogether, our study reveals for the first time the nuclear matrix as the compartment most enriched in SUMO E1 and PIAS family E3 ligases. Our finding that PIAS1 interacts directly with histone proteins also suggests a molecular mechanism as to how nuclear matrix–associated PIAS1 is able to regulate transcription and other chromatin-related processes.

Chordate PIAS proteins act as conserved repressors of the TRAF6 self-polyubiquitination

In mammals, PIAS proteins are important SUMO E3 ligases and act as versatile regulators of over sixty different proteins, including components from the NF-κB pathways. But the PIAS functions are not well-understood due to complicated molecular mechanisms and multiple gene paralogs with overlapping roles, which is especially true in lower vertebrates where dedicated studies are scarce. As a basal chordate with a single PIAS gene, amphioxus is a convenient model to study PIAS from the evolutionary perspective. TRAF6 is a critical adaptor of the NF-κB pathways but it is not known whether TRAF6 is regulated by PIAS. Here we discover that in mammalian cells, amphioxus PIAS inhibited NF-κB activation by co-localizing and binding with TRAF6. The interaction relied on the N-terminal SAP and PINIT domains of PIAS. TRAF6 is an E3 ubiquitin ligase, which initiates downstream NF-κB signaling by promoting its self-ubiquitination. Both amphioxus SUMO1 and Ubc9 (SUMO E2 ligase) could suppress TRAF6 self-ubiquitination and NF-κB activation, suggesting that the SUMOylation activity competed away the ubiquitination activity of TRAF6. However, we show that the wild-type PIAS and the mutant PIAS without SUMO E3 ligase activity both could inhibit TRAF6-mediated NF-κB activation by reducing TRAF6 self-ubiquitination. This implies that SUMO ligase activity is not the only mechanism for PIAS to negatively regulate TRAF6. Finally, we tested the interactions between human PIAS1-4 and TRAF6. It reveals that human PIAS1, 3 and 4, but not 2, were able to repress NF-κB activation by reducing TRAF6 self-ubiquitination. Taken together, our study discovers a conserved regulatory interaction between chordate PIAS and TRAF6. It therefore sheds light on the complicated role of PIAS in immune regulation, and may help to understand the PIAS functions in other lower chordate taxa, such as jawless and jawed fishes.

The E3 SUMO ligase PIASγ is a novel interaction partner regulating the activity of diabetes associated hepatocyte nuclear factor-1α

The transcription factor hepatocyte nuclear factor-1α (HNF-1A) is involved in normal pancreas development and function. Rare variants in the HNF1A gene can cause monogenic diabetes, while common variants confer type 2 diabetes risk. The precise mechanisms for regulation of HNF-1A, including the role and function of post-translational modifications, are still largely unknown. Here, we present the first evidence for HNF-1A being a substrate of SUMOylation in cellulo and identify two lysine (K) residues (K205 and K273) as SUMOylation sites. Overexpression of protein inhibitor of activated STAT (PIASγ) represses the transcriptional activity of HNF-1A and is dependent on simultaneous HNF-1A SUMOylation at K205 and K273. Moreover, PIASγ is a novel HNF-1A interaction partner whose expression leads to translocation of HNF-1A to the nuclear periphery. Thus, our findings support that the E3 SUMO ligase PIASγ regulates HNF-1A SUMOylation with functional implications, representing new targets for drug development and precision medicine in diabetes.

CEBPE-Mutant Specific Granule Deficiency Correlates With Aberrant Granule Organization and Substantial Proteome Alterations in Neutrophils

Specific granule deficiency (SGD) is a rare disorder characterized by abnormal neutrophils evidenced by reduced granules, absence of granule proteins, and atypical bilobed nuclei. Mutations in CCAAT/enhancer-binding protein-ε (CEBPE) are one molecular etiology of the disease. Although C/EBPε has been studied extensively, the impact of CEBPE mutations on neutrophil biology remains elusive. Here, we identified two SGD patients bearing a previously described heterozygous mutation (p.Val218Ala) in CEBPE. We took this rare opportunity to characterize SGD neutrophils in terms of granule distribution and protein content. Granules of patient neutrophils were clustered and polarized, suggesting that not only absence of specific granules but also defects affecting other granules contribute to the phenotype. Our analysis showed that remaining granules displayed mixed protein content and lacked several glycoepitopes. To further elucidate the impact of mutant CEBPE, we performed detailed proteomic analysis of SGD neutrophils. Beside an absence of several granule proteins in patient cells, we observed increased expression of members of the linker of nucleoskeleton and cytoskeleton complex (nesprin-2, vimentin, and lamin-B2), which control nuclear shape. This suggests that absence of these proteins in healthy individuals might be responsible for segmented shapes of neutrophilic nuclei. We further show that the heterozygous mutation p.Val218Ala in CEBPE causes SGD through prevention of nuclear localization of the protein product. In conclusion, we uncover that absence of nuclear C/EBPε impacts on spatiotemporal expression and subsequent distribution of several granule proteins and further on expression of proteins controlling nuclear shape.

Chromatin remodeling: demethylating H3K4me3 of type I IFNs gene by Rbp2 through interacting with Piasy for transcriptional attenuation

Type I IFNs (IFNIs) are involved in the course of antiviral and antimicrobial activities; however, robust inductions of these can lead to host immunopathology. We have reported that the Pias (protein inhibitor of activated signal transducer and activator of transcription) family member, Piasy, possesses the ability to suppress IFNI transcriptions in mouse embryonic fibroblasts (MEFs), yet the specific molecular mechanism by which it acts remains elusive. Here, we identify that the H3K4me3 levels, one activation mark of genes, in MEFs that were stimulated by poly(I:C) were impaired by Piasy in the IFN-β gene. Piasy bound to the promoter region of the IFN-β gene in MEFs. Meanwhile, retinoblastoma binding protein 2 (Rbp2) was proven to be the only known and novel H3K4me3 demethylase that interacted with Piasy. Overexpression of Rbp2, but not its enzymatically inactive mutant Rbp2^H483G/E485Q, retarded the transcription activities of IFNI, whereas small interfering RNA-mediated or short hairpin RNA-mediated knockdown of Rbp2 enhanced IFNI promoter responses. Above all, coexpression of Piasy and Rbp2 led to statistically less IFNI induction than overexpression of either Piasy or Rbp2 alone. Mechanistically, Piasy bound to the Jmjc domain (451-503 aa) of Rbp2 via its PINIT domain (101-218 aa), which is consistent with the domain required for their attenuation of transcription and H3K4me3 levels of IFNI genes. Our study demonstrates that Piasy may prevent exaggerated transcription of IFNI by Rbp2-mediated demethylation of H3K4me3 of IFNI, avoiding excessive immune responses.-Yu, X., Chen, H., Zuo, C., Jin, X., Yin, Y., Wang, H., Jin, M., Ozato, K., Xu, S. Chromatin remodeling: demethylating H3K4me3 of type I IFNs gene by Rbp2 through interacting with Piasy for transcriptional attenuation.

The conserved ancient role of chordate PIAS as a multilevel repressor of the NF-κB pathway

In vertebrates, PIAS genes encode versatile cellular regulators, with functions extremely complex and redundant. Here we try to understand their functions from an evolutionary perspective. we evaluate the sequences, expression and molecular functions of amphioxus PIAS genes and compare them with their vertebrate counterparts. Phylogenetic analysis suggests a single PIAS gene in ancestral chordates, which has been duplicated into four families (PIAS1-4) in vertebrates by 2R-WGD but remained single in a basal chordate (amphioxus). Amphioxus PIAS encodes two variants with and without a Serine/Threonine-rich tail, which are retained in human PIAS1-3 but lost in PIAS4. We show that amphioxus PIAS binds C-terminus of NF-κB Rel and blocks the DNA binding activity. In humans, such function is retained in PIAS1, altered in PIAS4, and lost in PIAS2-3. Instead, PIAS3 has evolved new ability to inhibit Rel by binding RHD and promoting SUMOylation. We show that amphioxus PIAS also inhibits NF-κB by binding with upstream signalling adaptor TICAM-like and MyD88. Finally, we verify that human PIAS1, 3 and 4, but not 2, were capable of these newly-discovered functions. Our study offers insight into the sub- and neo-functionalization of PIAS genes and suggests a conserved ancient role for chordate PIAS in NF-κB signalling.

Protein Inhibitor of Activated STAT3 Regulates Migration, Invasion, and Activation of Fibroblast-like Synoviocytes in Rheumatoid Arthritis

The aggressive phenotype displayed by fibroblast-like synoviocytes (FLSs) is a critical factor of cartilage destruction in rheumatoid arthritis (RA). Increased FLSs migration and subsequent degradation of the extracellular matrix are essential to the pathology of RA. Protein inhibitor of activated STAT (PIAS), whose family members include PIAS1, PIAS2 (PIASx), PIAS3, and PIAS4 (PIASy), play important roles in regulating various cellular events, such as cell survival, migration, and signal transduction in many cell types. However, whether PIAS proteins have a role in the pathogenesis of RA is unclear. In this study, we evaluated the role of PIAS proteins in FLSs migration, invasion, and matrix metalloproteinases (MMPs) expression in RA. We observed increased expression of PIAS3, but not PIAS1, PIAS2, or PIAS4, in FLSs and synovial tissues from patients with RA. We found that PIAS3 knockdown by short hairpin RNA reduced migration, invasion, and MMP-3, MMP-9, and MMP-13 expression in FLSs. In addition, we demonstrated that PIAS3 regulated lamellipodium formation during cell migration. To gain insight into molecular mechanisms, we evaluated the effect of PIAS3 knockdown on Rac1/PAK1 and JNK activation. Our results indicated that PIAS3-mediated SUMOylation of Rac1 controlled its activation and modulated the Rac1 downstream activity of PAK1 and JNK. Furthermore, inhibition of Rac1, PAK1, or JNK decreased migration and invasion of RA FLSs. Thus, our observations suggest that PIAS3 suppression may be protective against joint destruction in RA by regulating synoviocyte migration, invasion, and activation.

C/EBPβ and C/EBPδ transcription factors: Basic biology and roles in the CNS

CCAAT/enhancer binding protein (C/EBP) β and C/EBPδ are transcription factors of the basic-leucine zipper class which share phylogenetic, structural and functional features. In this review we first describe in depth their basic molecular biology which includes fascinating aspects such as the regulated use of alternative initiation codons in the C/EBPβ mRNA. The physical interactions with multiple transcription factors which greatly opens the number of potentially regulated genes or the presence of at least five different types of post-translational modifications are also remarkable molecular mechanisms that modulate C/EBPβ and C/EBPδ function. In the second part, we review the present knowledge on the localization, expression changes and physiological roles of C/EBPβ and C/EBPδ in neurons, astrocytes and microglia. We conclude that C/EBPβ and C/EBPδ share two unique features related to their role in the CNS: whereas in neurons they participate in memory formation and synaptic plasticity, in glial cells they regulate the pro-inflammatory program. Because of their role in neuroinflammation, C/EBPβ and C/EBPδ in microglia are potential targets for treatment of neurodegenerative disorders. Any strategy to reduce C/EBPβ and C/EBPδ activity in neuroinflammation needs to take into account its potential side-effects in neurons. Therefore, cell-specific treatments will be required for the successful application of this strategy.

Transcriptional activity of erythroid Kruppel-like factor (EKLF/KLF1) modulated by PIAS3 (protein inhibitor of activated STAT3)

Erythroid Kruppel-like factor (EKLF or KLF1) is a transcription factor crucial for red cell development that is directly involved in regulation of a large number of erythroid genes. EKLF serves mostly as an activator of expression of these genes; however, it can act also as a repressor. Here, we present evidence that EKLF interacts with proteins from the PIAS (protein inhibitor of activated STAT) family that convey repressive activity to EKLF in the absence of sumoylation. Our studies identify PIAS3 as a transcriptional corepressor of EKLF for at least a subset of its target genes during erythropoiesis (e.g. β-globin, α-hemoglobin stabilizing protein). We demonstrate an interaction between EKLF and PIAS proteins confirmed by in vivo coimmunoprecipitation assays with both exogenous and endogenous proteins. We identified an LXXLL signature motif located near the N terminus of PIAS proteins that, although not involved in the EKLF-PIAS3 interaction, is required for the transrepression activity. Knockdown of endogenous PIAS3 accelerates differentiation of both murine erythroleukemia cells, as well as fetal liver cells, whereas an increase in PIAS3 levels inhibits this increase. Using chromatin immunoprecipitation assays, we show that PIAS3 preferentially occupies the β-globin promoter in undifferentiated murine erythroleukemia cells. Together these results demonstrate that an interaction between EKLF and PIAS3 provides a novel mode of regulation of EKLF activity in the absence of sumolylation and furthermore shows an important involvement of PIAS proteins in erythropoiesis.

Identification of a non-covalent ternary complex formed by PIAS1, SUMO1, and UBC9 proteins involved in transcriptional regulation

Post-translational modifications with ubiquitin-like proteins require three sequentially acting enzymes (E1, E2, and E3) that must unambiguously recognize each other in a coordinated fashion to achieve their functions. Although a single E2 (UBC9) and few RING-type E3s (PIAS) operate in the SUMOylation system, the molecular determinants regulating the interactions between UBC9 and the RING-type E3 enzymes are still not well defined. In this study we use biochemical and functional experiments to characterize the interactions between PIAS1 and UBC9. Our results reveal that UBC9 and PIAS1 are engaged both in a canonical E2·E3 interaction as well as assembled into a previously unidentified non-covalent ternary complex with SUMO as evidenced by bioluminescence resonance energy transfer, nuclear magnetic resonance spectroscopy, and isothermal titration calorimetry studies. In this ternary complex, SUMO functions as a bridge by forming non-overlapping interfaces with UBC9 and PIAS1. Moreover, our data suggest that phosphorylation of serine residues adjacent to the PIAS1 SUMO-interacting motif favors formation of the non covalent PIAS1·SUMO·UBC9 ternary complex. Finally, our results also indicate that the non-covalent ternary complex is required for the known transcriptional repression activities mediated by UBC9 and SUMO1. Taken together, the data enhance our knowledge concerning the mode of interaction of enzymes of the SUMOylation machinery as well as their role in transcriptional regulation and establishes a framework for investigations of other ubiquitin-like protein systems.

The many faces of C/EBPδ and their relevance for inflammation and cancer

The CCAAT/enhancer binding protein delta (CEBPD, C/EBPδ) is a transcription factor that modulates many biological processes including cell differentiation, motility, growth arrest, proliferation, and cell death. The diversity of C/EBPδ's functions depends in part on the cell type and cellular context and can have opposing outcomes. For example, C/EBPδ promotes inflammatory signaling, but it can also inhibit pro-inflammatory pathways, and in a mouse model of mammary tumorigenesis, C/EBPδ reduces tumor incidence but promotes tumor metastasis. This review highlights the multifaceted nature of C/EBPδ's functions, with an emphasis on pathways that are relevant for cancer and inflammation, and illustrates how C/EBPδ emerged from the shadow of its family members as a fascinating “jack of all trades.” Our current knowledge on C/EBPδ indicates that, rather than being essential for a specific cellular process, C/EBPδ helps to interpret a variety of cues in a cell-type and context-dependent manner, to adjust cellular functions to specific situations. Therefore, insights into the roles and mechanisms of C/EBPδ signaling can lead to a better understanding of how the integration of different signaling pathways dictates normal and pathological cell functions and physiology.

PIASy mediates hypoxia-induced SIRT1 transcriptional repression and epithelial-to-mesenchymal transition in ovarian cancer cells

Epithelial-mesenchymal transition (EMT) has an essential role in organogenesis and contributes to a host of pathologies, including carcinogenesis. Hypoxia (low oxygen supply) aids tumor metastasis in part by promoting EMT in cancer cells. The underlying mechanism whereby hypoxia orchestrates EMT remains poorly defined. Here we report that SIRT1, a multifaceted player in tumorigenesis, opposed ovarian cancer metastasis in vitro and in vivo by impeding EMT. Hypoxic stress downregulated the expression of SIRT1, primarily at the transcriptional level, by reducing the occupancy of the transcriptional activator Sp1 on the proximal promoter of the SIRT1 gene in a SUMOylation-dependent manner. Further analysis revealed that the SUMO E3 ligase PIASy (also known as PIAS4) was induced by hypoxia and prevented Sp1 from binding to the SIRT1 promoter. Conversely, knockdown of PIASy by small interfering RNA (siRNA) restored Sp1 binding and SIRT1 expression in cancer cells challenged with hypobaric hypoxia, reversed cancer cell EMT, and attenuated metastasis in vivo in nude mice. Importantly, analysis of human ovarian tumor specimens indicated that PIASy expression was positively, whereas SIRT1 expression was inversely, correlated with cancer aggressiveness. In summary, our work has identified a new pathway that links downregulation of SIRT1 to hypoxia-induced EMT in ovarian cancer cells and, as such, sheds light on the development of novel anti-tumor therapeutics.

PML, SUMOylation, and Senescence

Since its discovery, 25 years ago, promyelocytic leukemia (PML) has been an enigma. Implicated in the oncogenic PML/RARA fusion, forming elusive intranuclear domains, triggering cell death or senescence, controlled by and perhaps controlling SUMOylation… there are multiple PML-related issues. Here we review the reciprocal interactions between PML, senescence, and SUMOylation, notably in the context of cellular transformation.

HSF2BP represses BNC1 transcriptional activity by sequestering BNC1 to the cytoplasm

Basonuclin (BNC1), a zinc finger transcriptional factor, is essential for mouse spermatogenesis. However, the regulatory mechanisms of BNC1 in spermatogenesis are poorly understood. In this study, we identified HSF2BP, a testis-specific binding protein of HSF2, as a binding partner of BNC1 by using yeast two-hybrid screening. HSF2BP could interact with and inhibit BNC1 transcriptional activity without affecting its expression level. Moreover, coexpression of HSF2BP with BNC1 resulted in a striking redistribution of BNC1 to the cytoplasm. These data suggest that HSF2BP may play a pivotal role in regulating BNC1 transcriptional activity and subcellular localization during spermatogenesis.

A SUMOylation-dependent pathway regulates SIRT1 transcription and lung cancer metastasis

BACKGROUND

Epithelial-to-mesenchymal transition (EMT) plays a pivotal role in lung cancer metastasis. The class III deacetylase sirtuin 1 (SIRT1) possesses both pro- and anticarcinogenic properties. The role of SIRT1 in lung cancer EMT is largely undefined.

METHODS

The effect of SIRT1 on migration of lung cancer cells was evaluated by wound healing assay in vitro and metastasis assay in nude mice in vivo. Protein expression in human lung cancers and cultured lung cancer cells was assessed by western blotting and immunohistochemistry. Interaction between protein and DNA was measured by chromatin immunoprecipitation assay. SIRT1 promoter activity was determined by reporter assay.

RESULTS

SIRT1 activation antagonized migration of lung cancer cells by suppressing EMT in vitro. Activation of SIRT1 by resveratrol also statistically significantly hampered (by 68.33%; P < .001, two-sided test) lung cancer cell metastasis in vivo. Hypoxia repressed SIRT1 transcription through promoting the competition between Sp1 and HIC1 on the SIRT1 proximal promoter in a SUMOylation-dependent manner. Disruption of SUMOylation by targeting either Ubc9 or PIASy restored SIRT1 expression in and favored an epithelial-like phenotype of cancer cells, thereby preventing metastasis. Decreased SIRT1 combined with elevated PIASy expression was implicated in more-invasive types of lung cancers in humans.

CONCLUSIONS

We have identified a novel pathway that links SIRT1 down-regulation to hypoxia-induced EMT in lung cancer cells and may shed light on the development of novel antitumor therapeutics.

Protein inhibitors of activated STAT (Pias1 and Piasy) differentially regulate pituitary homeobox 2 (PITX2) transcriptional activity

Protein inhibitors of activated STAT (Pias) proteins can act independent of sumoylation to modulate the activity of transcription factors and Pias proteins interacting with transcription factors can either activate or repress their activity. Pias proteins are expressed in many tissues and cells during development and we asked if Pias proteins regulated the pituitary homeobox 2 (PITX2) homeodomain protein, which modulates developmental gene expression. Piasy and Pias1 proteins are expressed during craniofacial/tooth development and directly interact and differentially regulate PITX2 transcriptional activity. Piasy and Pias1 are co-expressed in craniofacial tissues with PITX2. Yeast two-hybrid, co-immunoprecipitation and pulldown experiments demonstrate Piasy and Pias1 interactions with the PITX2 protein. Piasy interacts with the PITX2 C-terminal tail to attenuate its transcriptional activity. In contrast, Pias1 interacts with the PITX2 C-terminal tail to increase PITX2 transcriptional activity. The E3 ligase activity associated with the RING domain in Piasy is not required for the attenuation of PITX2 activity, however, the RING domain of Pias1 is required for enhanced PITX2 transcriptional activity. Bimolecular fluorescence complementation assays reveal PITX2 interactions with Piasy and Pias1 in the nucleus. Piasy represses the synergistic activation of PITX2 with interacting co-factors and Piasy represses Pias1 activation of PITX2 transcriptional activity. In contrast, Pias1 did not affect the synergistic interaction of PITX2 with transcriptional co-factors. Last, we demonstrate that Pias proteins form a complex with PITX2 and Lef-1, and PITX2 and β-catenin. Lef-1, β-catenin, and Pias interactions with PITX2 provide new molecular mechanisms for the regulation of PITX2 transcriptional activity and the activity of Pias proteins.

Targeting the JAK-STAT pathway in lymphoma: a focus on pacritinib

INTRODUCTION

The Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway mediates signaling by cytokine, chemokine and growth factor receptors on cell surface to the nucleus. JAK/STAT pathway is aberrantly activated in a variety of lymphomas, with a dual role of promoting cell survival/proliferation and immune evasion.

AREAS COVERED

This review describes the preclinical rationale behind the development of JAK inhibitors in lymphoma, some of which are being evaluated in Phase I/II studies, and summarizes the characteristics and clinical results of different JAK inhibitors in clinical development. Available preclinical and clinical data about JAK inhibition in lymphoid malignancies were reviewed using a PubMed access. To date, pacritinib (SB1518), a selective JAK2/FLT3 inhibitor is the first and only JAK inhibitor that has been evaluated in patients with relapsed lymphoma.

EXPERT OPINION

The preclinical rationale behind the development of pacritinib in lymphoproliferative neoplasms is strong, as the deregulation of the JAK/STAT pathway is involved in the pathogenesis of multiple lymphoma subtypes, although with different mechanisms. Pacritinib demonstrated safety and early clinical efficacy in a variety of lymphoma histologic types, providing the first proof of principle of the potential clinical value of targeting JAK/STAT pathway in lymphoma.

Genomic analysis of the role of transcription factor C/EBPδ in the regulation of cell behaviour on nanometric grooves

C/EBPδ is a tumour suppressor transcription factor that induces gene expression involved in suppressing cell migration. Here we investigate whether C/EBPδ-dependent gene expression also affects cell responses to nanometric topology. We found that ablation of the C/EBPδ gene in mouse embryonal fibroblasts (MEFs) decreased cell size, adhesion and cytoskeleton spreading on 240 nm and 540 nm nanometric grooves. ChIP-SEQ and cDNA microarray analyses demonstrated that many binding sites for C/EBPδ, and the closely related C/EBPβ, exist throughout the mouse genome and control the upregulation or downregulation of many adjacent genes. We also identified a group of C/EBPδ-dependent, trans-regulated genes, whose promoters contained no C/EBPδ binding sites and yet their activity was regulated in a C/EBPδ-dependent manner. These genes include signalling molecules (e.g. SOCS3), cytoskeletal components (Tubb2, Krt16 and Krt20) and cytoskeletal regulators (ArhGEF33 and Rnd3) and are possibly regulated by cis-regulated diffusible mediators, such as IL6. Of particular note, SOCS3 was shown to be absolutely required for efficient cell spreading and contact guidance on 240 nm and 540 nm nanometric grooves. C/EBPδ is therefore involved in the complex regulation of multiple genes, including cytoskeletal components and signalling mediators, which influence the nature of cell interactions with nanometric topology.

Protein inhibitor of activated STAT, PIASy regulates α-smooth muscle actin expression by interacting with E12 in mesangial cells

Phenotypic transformation of mesangial cells (MCs) is implicated in the development of glomerular disease; however, the mechanisms underlying their altered genetic program is still unclear. α-smooth muscle actin (α-SMA) is known to be a crucial marker for phenotypic transformation of MCs. Recently, E-boxes and the class I basic helix-loop-helix proteins, such as E12 have been shown to regulateα-SMA expression. Therefore, we tried to identify a novel E12 binding protein in MCs and to examine its role in glomerulonephritis. We found that PIASy, one of the protein inhibitors of activated STAT family protein, interacted with E12 by yeast two-hybrid screens and coimmunopreciptation assays. Overexpression of E12 significantly enhanced theα-SMA promoter activity, and the increase was blocked by co-transfection of PIASy, but not by a PIASy RING mutant. In vivo sumoylation assays revealed that PIASy was a SUMO E3 ligase for E12. Furthermore, transforming growth factor-β (TGF-β) treatment induced expression of both PIASy and E12, consistent with α-SMA expression. Moreover, reduced expression of PIASy protein by siRNA specific for PIASy resulted in increased TGF-β-mediated α-SMA expression. In vivo, PIASy and E12 were dramatically upregulated along with α-SMA and TGF-β in the proliferative phase of Thy1 glomerulonephritis. Furthermore, an association between PIASy and E12 proteins was observed at day 6 by IP-western blotting, but not at day 0. These results suggest that TGF-β up-regulates PIASy expression in MCs to down-regulateα-SMA gene transcription by the interaction with E12.

CCAAT/Enhancer Binding Protein-delta (C/EBP-delta) regulates cell growth, migration and differentiation

BACKGROUND

CCAAT/enhancer binding protein-delta (C/EBP-delta) is a member of the highly conserved C/EBP family of basic region leucine zipper transcription factors. C/EBP family members regulate cell growth and differentiation and "loss of function" alterations in C/EBPs have been reported in a variety of human cancers. C/EBP-delta gene expression is upregulated by G0 growth arrest, IL-6 family cytokines and endotoxin treatments. C/EBP-delta exhibits properties of a tumor suppressor gene, including reduced expression and promoter methylation-induced silencing in transformed cell lines and primary tumors. In addition, C/EBP-delta gene expression is repressed by c-Myc, an oncogene that is over-expressed in a wide range of human cancers. "ChIP-chip" studies demonstrated that C/EBP-delta functions as a transcriptional activator of target genes that function in intracellular signal transduction, transcription, DNA binding/repair, cell cycle control, cell adhesion, and apoptosis. Despite progress in determining the biochemical functions of C/EBP-delta, the specific cellular defects that are induced by C/EBP-delta "loss of function" alterations are poorly understood. This study investigated the impact of C/EBP-delta "loss of function" alterations on growth arrest, migration/invasion and differentiation in nontransformed mouse mammary epithelial cells (MECs) and primary mouse embryo fibroblasts (MEFs).

RESULTS

C/EBP-delta siRNA transfected MECs exhibited ~90% reduction in C/EBP-delta mRNA and protein levels. C/EBP-delta siRNA treatment resulted in defective growth arrest as demonstrated by persistently elevated BrdU labeling, 3H-thymidine incorporation and cyclin D1 levels in response to growth arrest treatments. C/EBP-delta siRNA treatment also resulted in increased migration/invasion and defective differentiation. C/EBP-delta knockout MEFs exhibited defective growth arrest and increased proliferation/migration. Re-introduction of C/EBP-delta expression restored the growth arrest response of C/EBP-delta knockout MEFs. Finally, deletion of the C/EBP-delta DNA binding domain or the C/EBP-delta bZIP domain resulted in the loss of C/EBP-delta growth inhibition in clonogenic assays.

CONCLUSIONS

This study demonstrates that C/EBP-delta functions in the regulation of critical cell fate determining programs such as growth arrest, migration, and differentiation. These results support the tumor suppressor function of C/EBP-delta and identify potential mechanisms in which "loss of function" alterations in C/EBP-delta could promote cell transformation and tumorigenesis.

Myc interacts with Max and Miz1 to repress C/EBPdelta promoter activity and gene expression

BACKGROUND

"Loss of function" alterations in CCAAT/Enhancer Binding Proteindelta (C/EBPdelta) have been reported in a number of human cancers including breast, prostate and cervical cancer, hepatocellular carcinoma and acute myeloid leukemia. C/EBPdelta gene transcription is induced during cellular quiescence and repressed during active cell cycle progression. C/EBPdelta exhibits tumor suppressor gene properties including reduced expression in cancer cell lines and tumors and promoter methylation silencing. We previously reported that C/EBPdelta expression is inversely correlated with c-Myc (Myc) expression. Aberrant Myc expression is common in cancer and transcriptional repression is a major mechanism of Myc oncogenesis. A number of tumor suppressor genes are targets of Myc transcriptional repression including C/EBPalpha, p15INK4, p21CIP1, p27KIP1 and p57KIP2. This study investigated the mechanisms underlying Myc repression of C/EBPdelta expression.

RESULTS

Myc represses C/EBPdelta promoter activity in nontransformed mammary epithelial cells in a dose-dependent manner that requires Myc Box II, Basic Region and HLH/LZ domains. Chromatin Immunoprecipitation (ChIP) assays demonstrate that Myc, Miz1 and Max are associated with the C/EBPdelta promoter in proliferating cells, when C/EBPdelta expression is repressed. EMSAs demonstrate that Miz1 binds to a 30 bp region (-100 to -70) of the C/EBPdelta promoter which contains a putative transcription initiator (Inr) element. Miz1 functions exclusively as a repressor of C/EBPdelta promoter activity. Miz1 siRNA expression or expression of a Miz1 binding deficient Myc (MycV394D) construct reduces Myc repression of C/EBPdelta promoter activity. Max siRNA expression, or expression of a Myc construct lacking the HLH/LZ (Max interacting) region, also reduces Myc repression of C/EBPdelta promoter activity. Miz1 and Max siRNA treatments attenuate Myc repression of endogenous C/EBPdelta expression. Myc Box II interacting proteins RuvBl1 (Pontin, TIP49) and RuvBl2 (Reptin, TIP48) enhances Myc repression of C/EBPdelta promoter activity.

CONCLUSION

Myc represses C/EBPdelta expression by associating with the C/EBPdelta proximal promoter as a transient component of a repressive complex that includes Max and Miz1. RuvBl1 and RuvBl2 enhance Myc repression of C/EBPdelta promoter activity. These results identify protein interactions that mediate Myc repression of C/EBPdelta, and possibly other tumor suppressor genes, and suggest new therapeutic targets to block Myc transcriptional repression and oncogenic function.

PIAS proteins: pleiotropic interactors associated with SUMO

The interactions and functions of protein inhibitors of activated STAT (PIAS) proteins are not restricted to the signal transducers and activators of transcription (STATs), but PIAS1, -2, -3 and -4 interact with and regulate a variety of distinct proteins, especially transcription factors. Although the majority of PIAS-interacting proteins are prone to modification by small ubiquitin-related modifier (SUMO) proteins and the PIAS proteins have the capacity to promote the modification as RING-type SUMO ligases, they do not function solely as SUMO E3 ligases. Instead, their effects are often independent of their Siz/PIAS (SP)-RING finger, but dependent on their capability to noncovalently interact with SUMOs or DNA through their SUMO-interacting motif and scaffold attachment factor-A/B, acinus and PIAS domain, respectively. Here, we present an overview of the cellular regulation by PIAS proteins and propose that many of their functions are due to their capability to mediate and facilitate SUMO-linked protein assemblies.

The Stat family of transcription factors have diverse roles in mammary gland development

The Stat family of transcription factors have diverse roles in mammary gland development. Genetic studies in mice have revealed an essential requirement for Stat5a in development of secretory alveolar cells during pregnancy while Stat6, which is normally associated with differentiation of T helper cells, is important in the commitment of luminal cells to this alveolar lineage. In contrast, Stat3 is specifically activated at the initiation of post-lactational regression when it has an essential function in the regulation of cell death and tissue remodelling. Stat1 and Stat4 have been shown to be regulated during a mammary developmental cycle although whether they have specific, non-redundant roles is not clear. Thus, the adult mammary gland is somewhat unusual in that it is a tissue where different Stats are sequentially activated to orchestrate the processes of functional differentiation, cell death and tissue remodelling.