Can, a putative oncogene associated with myeloid leukemogenesis, may be activated by fusion of its 3' half to different genes: characterization of the set gene

The oncoprotein SET promotes serine-derived one-carbon metabolism by regulating SHMT2 enzymatic activity

Cancer cells frequently reprogram one-carbon metabolic pathways to fulfill their vigorous demands of biosynthesis and antioxidant defense for survival and proliferation. Dysfunction of oncogenes or tumor suppressor genes is critically involved in this process, but the precise mechanisms by which cancer cells actively trigger one-carbon metabolic alterations remain incompletely elucidated. Here, by using untargeted metabolomic analysis, we identify the oncoprotein SE translocation (SET) as a key regulator of one-carbon metabolism in cancer cells. SET physically interacts with mitochondrial SHMT2 and facilitates SHMT2 enzymatic activity. Loss of SET profoundly suppresses serine-derived one-carbon metabolic flux, whereas reexpression of ectopic SET leads to the opposite effect. Notably, although the presence of SHMT2 is critical for SET-mediated one-carbon metabolic alterations, the depletion of SHMT2 alone is insufficient to antagonize SET-induced tumor growth, probably due to functional compensation by its cytosolic isozyme SHMT1 upon SHMT2 knockdown. Instead, pharmacological targeting of cellular SHMT (including both SHMT1 and SHMT2) activity results in dramatic suppression of SET-induced tumor growth. Moreover, by using a Kras/Lkb1 mutation-driven lung tumor mouse model, we demonstrate that the loss of SET compromises both tumor formation and intratumoral SHMT2 enzymatic activity. Clinically, the overexpression of SET and SHMT2 is observed in lung tumors, both of which correlate with poor prognosis. Our study reveals a SET-SHMT2 axis in regulating serine-derived one-carbon metabolism and uncovers one-carbon metabolic reprogramming as a mechanism for SET-driven tumorigenesis.

Cancer progression by the okadaic acid class of tumor promoters and endogenous protein inhibitors of PP2A, SET and CIP2A

PURPOSE

Okadaic acid class of tumor promoters are transformed into endogenous protein inhibitors of PP2A, SET, and CIP2A in human cancers. This indicates that inhibition of PP2A activity is a common mechanism of cancer progression in humans. It is important to study the roles of SET and CIP2A vis-à-vis their clinical significance on the basis of new information gathered from a search of PubMed.

RESULTS AND DISCUSSION

The first part of this review introduces the carcinogenic roles of TNF-α and IL-1, which are induced by the okadaic acid class of compounds. The second part describes unique features of SET and CIP2A in cancer progression for several types of human cancer: (1) SET-expressing circulating tumor cells (SET-CTCs) in breast cancer, (2) knockdown of CIP2A and increased PP2A activity in chronic myeloid leukemia, (3) CIP2A and epidermal growth factor receptor (EGFR) activity in erlotinib sensitive- and resistant-non-small cell lung cancer, (4) SET antagonist EMQA plus radiation therapy against hepatocellular carcinoma, (5) PP2A inactivation as a common event in colorectal cancer, (6) prostate cancer susceptibility variants, homeobox transcription factor (HOXB13 T) and CIP2A T, and (7) SET inhibitor OP449 for pre-clinical investigation of pancreatic cancer. In the Discussion, the binding complex of SET is briefly introduced, and overexpression of SET and CIP2A proteins is discussed in relation to age-associated chronic inflammation (inflammaging).

CONCLUSION

This review establishes the concept that inhibition of PP2A activity is a common mechanism of human cancer progression and activation of PP2A activity leads to effective anticancer therapy.

Putative Roles of SETBP1 Dosage on the SET Oncogene to Affect Brain Development

Mutations in SET BINDING PROTEIN 1 (SETBP1) cause two different clinically distinguishable diseases called Schinzel–Giedion syndrome (SGS) or SETBP1 deficiency syndrome (SDD). Both disorders are disorders of protein dosage, where SGS is caused by decreased rate of protein breakdown due to mutations in a proteosome targeting domain, and SDD is caused by heterozygous loss-of-function mutations leading to haploinsufficiency. While phenotypes of affected individuals support a role for SETBP1 in brain development, little is known about the mechanisms that might underlie this. The binding partner which gave SETBP1 its name is SET and there is extensive literature on this important oncogene in non-neural tissues. Here we describe different molecular complexes in which SET is involved as well as the role of these complexes in brain development. Based on this information, we postulate how SETBP1 protein dosage might influence these SET-containing molecular pathways and affect brain development. We examine the roles of SET and SETBP1 in acetylation inhibition, phosphatase activity, DNA repair, and cell cycle control. This work provides testable hypotheses for how altered SETBP1 protein dosage affects brain development.

The Sexual Dimorphic Synapse: From Spine Density to Molecular Composition

A synaptic sexual dimorphism is relevant in the context of multiple neurodevelopmental, neurodegenerative, and neuropsychiatric disorders. Many of these disorders show a different prevalence and progression in woman and man. A similar variance is also present in corresponding animal models. To understand and characterize this dimorphism in pathologies it is important to first understand sex differences in unaffected individuals. Therefore, sexual differences have been studied since 1788, first focusing on brain weight, size, and volume. But as these measures are not directly related to brain function, the investigation of sexual dimorphism also expanded to other organizational levels of the brain. This review is focused on sexual dimorphism at the synaptic level, as these specialized structures are the smallest functional units of the brain, determining cell communication, connectivity, and plasticity. Multiple differences between males and females can be found on the levels of spine density, synaptic morphology, and molecular synapse composition. These differences support the importance of sex-disaggregated data. The specificity of changes to a particular brain region or circuit might support the idea of a mosaic brain, in which each tile individually lies on a continuum from masculinization to feminization. Moreover, synapses can be seen as the smallest tiles of the mosaic determining the classification of larger areas.

Template activating factor-I epigenetically regulates the TERT transcription in human cancer cells

Telomere, the terminus of linear chromosome in eukaryotes, is composed of specific repeat DNA which is mainly synthesized by a protein complex called telomerase. The maintenance of telomere DNA is important for unlimited proliferative capacity of cancer cells. The telomerase activity is controlled by the expression level of telomerase reverse transcriptase (TERT), a catalytic unit of telomerase, in some species including human. Therefore, to reveal the regulatory mechanisms of the transcription of TERT gene is important for understanding the tumor development. We found that template activating factor-I (TAF-I), a multifunctional nuclear protein, is involved in the transcriptional activation of TERT for the maintenance of telomere DNA in HeLa cells. TAF-I maintains the histone H3 modifications involved in transcriptional activation and hypomethylated cytosines in CpG dinucleotides around the transcription start site (TSS) in the TERT gene locus. Collectively, TAF-I is involved in the maintenance of telomere DNA through the regulation of TERT transcription, then consequently the occurrence and/or recurrence of cancer cells.

Deregulation of protein phosphatase 2A inhibitor SET is associated with malignant progression in breast cancer

To understand the mechanism underlying metastasis, identification of a mechanism-based and common biomarker for circulating tumour cells (CTCs) in heterogenous breast cancer is needed. SET, an endogenous inhibitor of protein phosphatase 2A, was overexpressed in all subtypes of invasive breast carcinoma tissues. Treatment with SET-targeted siRNAs reduced the motility of MCF-7 and MDA-MB-231 cells in transwell assay. SET knockdown reduced the number of mammospheres by 60–70% in MCF-7 and MDA-MB-231 cells, which was associated with the downregulation of OCT4 and SLUG. Hence, we analysed the presence of SET-expressing CTCs (SET-CTCs) in 24 breast cancer patients. CTCs were enriched using a size-based method and then immunocytochemically analysed using an anti-SET antibody. SET-CTCs were detected in 6/6 (100%) patients with recurrent breast cancer with a median value of 12 (12 cells/3 mL blood), and in 13/18 (72.2%) patients with stage I–III breast cancer with a median value of 2.5, while the median value of healthy controls was 0. Importantly, high numbers of SET-CTCs were correlated with lymph node metastasis in patients with stage I–III disease. Our results indicate that SET contributes to breast cancer progression and can act as a potential biomarker of CTCs for the detection of metastasis.

Crosstalk between hnRNP K and SET in ATRA-induced differentiation in acute promyelocytic leukemia

HnRNP K protein is a heterogeneous nuclear ribonucleoprotein which has been proposed to be involved in the leukemogenesis of acute promyelocytic leukemia (APL), as well as in differentiation induced by all‐trans retinoic acid (ATRA). We previously demonstrated a connection between SET and hnRNP K function in head and neck squamous cell carcinoma (HNSCC) cells related to splicing processing. The objective of this study was to characterize the participation of hnRNP K and SET proteins in ATRA‐induced differentiation in APL. We observed higher (5‐ to 40‐fold) levels of hnRNP K and SET mRNA in APL patients at the diagnosis phase compared with induction and maintenance phases. hnRNP K knockdown using short‐hairpin RNA led to cell death in ATRA‐sensitive NB4 and resistant NB4‐R2 cells by apoptosis with SET cleavage. In addition, hnRNP K knockdown increased granulocytic differentiation in APL cells, mainly in NB4‐R2 with ATRA. hnRNP K knockdown had an effect similar to that of treatment with U0126 (an meiosis‐specific serine/threonine protein kinase/ERK inhibitor), mainly in NB4‐R2 cells. SET knockdown in APL cells revealed that apoptosis induction in cells with hnRNP K knockdown occurred by SET cleavage rather than by reduction in SET protein. Transplantation of NB4‐R2 cells into nude mice confirmed that arsenic trioxide (ATO) combined with U0126 has higher potential against tumor progression when compared to ATO. Therefore, hnRNP K/SET and ERK are potential therapeutic targets for both antineoplastic leukemia therapy and relapsed APL patients with ATRA resistance.

Interstitial Deletions Generating Fusion Genes

A fusion gene is the physical juxtaposition of two different genes resulting in a structure consisting of the head of one gene and the tail of the other. Gene fusion is often a primary neoplasia-inducing event in leukemias, lymphomas, solid malignancies as well as benign tumors. Knowledge about fusion genes is crucial not only for our understanding of tumorigenesis, but also for the diagnosis, prognostication, and treatment of cancer. Balanced chromosomal rearrangements, in particular translocations and inversions, are the most frequent genetic events leading to the generation of fusion genes. In the present review, we summarize the existing knowledge on chromosome deletions as a mechanism for fusion gene formation. Such deletions are mostly submicroscopic and, hence, not detected by cytogenetic analyses but by array comparative genome hybridization (aCGH) and/or high throughput sequencing (HTS). They are found across the genome in a variety of neoplasias. As tumors are increasingly analyzed using aCGH and HTS, it is likely that more interstitial deletions giving rise to fusion genes will be found, significantly impacting our understanding and treatment of cancer.

SET knockdown attenuated phenotype modulation and calcium channel associated markers of airway smooth muscle cells in asthmatic mice

Background

Dysfunctional phenotype modulation and calcium channels in airway smooth muscle cells (ASMCs) are important characteristics of airway remodeling in chronic asthma. However, the mechanisms underlying these pathological processes remain unclear. SET (I2PP2A, inhibitor-2 of protein phosphatase 2A) has many significant functions and is involved in various physiological and pathological processes. This study aimed to determine the function of SET in chronic asthma.

Methods

BALB/c mice were sensitized by ovalbumin injection and repeated inhalation of ovalbumin. The Penh value was measured using the Buxco whole body plethysmography system. A short hairpin RNA of the SET gene was designed and transfected into ASMCs derived from asthmatic mice. Flow cytometry of Annexin-V/propidium iodide staining was used for evaluating cell apoptosis. Western blot was adopted to measure the expression levels of ASMCs phenotype modulation markers and calcium channel-associated proteins.

Results

The results showed that shRNA targeting SET significantly decreased the expression of SET, and enhanced the apoptosis of ASMCs. SET knockdown promoted the expression of contractile phenotype markers such as α-SMA (alpha smooth muscle Actin), SM-MHC (smooth muscle Myosin heavy chain), and calponin, and inhibited the expression of synthetic phenotype markers including vimentin and CD44. The expression of the calcium channel-related proteins STIM1 (Stromal interaction molecule 1) and Orai1 were also inhibited after SET knockdown.

Conclusions

These data demonstrated that SET participated in the development of airway dysfunction in asthma, suggesting that the silencing of SET may be a new therapeutic target for the treatment of asthma patients.

Targeted CRM1-inhibition perturbs leukemogenic NUP214 fusion proteins and exerts anti-cancer effects in leukemia cell lines with NUP214 rearrangements

Chromosomal translocations fusing the locus of nucleoporin NUP214 each with the proto-oncogenes SET and DEK are recurrent in, largely intractable, acute leukemias. The molecular basis underlying the pathogenesis of SET-NUP214 and DEK-NUP214 are still poorly understood, but both chimeras inhibit protein nuclear export mediated by the β-karyopherin CRM1. In this report, we show that SET-NUP214 and DEK-NUP214 both disturb the localization of proteins essential for nucleocytoplasmic transport, in particular for CRM1-mediated protein export. Endogenous and exogenous SET-NUP214 and DEK-NUP214 form nuclear bodies. These nuclear bodies disperse upon targeted inhibition of CRM1 and the two fusion proteins re-localize throughout the nucleoplasm. Moreover, SET-NUP214 and DEK-NUP214 nuclear bodies reestablish shortly after removal of CRM1 inhibitors. Likewise, cell viability, metabolism, and proliferation of leukemia cell lines harboring SET-NUP214 and DEK-NUP214 are compromised by CRM1 inhibition, which is even sustained after clearance from CRM1 antagonists. Our results indicate CRM1 as a possible therapeutic target in NUP214-related leukemia. This is especially important, since no specific or targeted treatment options for NUP214 driven leukemia are available yet.

DCAF1 (VprBP): emerging physiological roles for a unique dual-service E3 ubiquitin ligase substrate receptor

Cullin-RING ligases (CRLs) comprise a large group of modular eukaryotic E3 ubiquitin ligases. Within this family, the CRL4 ligase (consisting of the Cullin4 [CUL4] scaffold protein, the Rbx1 RING finger domain protein, the DNA damage-binding protein 1 [DDB1], and one of many DDB1-associated substrate receptor proteins) has been intensively studied in recent years due to its involvement in regulating various cellular processes, its role in cancer development and progression, and its subversion by viral accessory proteins. Initially discovered as a target for hijacking by the human immunodeficiency virus accessory protein r, the normal targets and function of the CRL4 substrate receptor protein DDB1–Cul4-associated factor 1 (DCAF1; also known as VprBP) had remained elusive, but newer studies have begun to shed light on these questions. Here, we review recent progress in understanding the diverse physiological roles of this DCAF1 in supporting various general and cell type-specific cellular processes in its context with the CRL4 E3 ligase, as well as another HECT-type E3 ligase with which DCAF1 also associates, called EDD/UBR5. We also discuss emerging questions and areas of future study to uncover the dynamic roles of DCAF1 in normal physiology.

Disclosing the Interactome of Leukemogenic NUP98-HOXA9 and SET-NUP214 Fusion Proteins Using a Proteomic Approach

The interaction of oncogenes with cellular proteins is a major determinant of cellular transformation. The NUP98-HOXA9 and SET-NUP214 chimeras result from recurrent chromosomal translocations in acute leukemia. Functionally, the two fusion proteins inhibit nuclear export and interact with epigenetic regulators. The full interactome of NUP98-HOXA9 and SET-NUP214 is currently unknown. We used proximity-dependent biotin identification (BioID) to study the landscape of the NUP98-HOXA9 and SET-NUP214 environments. Our results suggest that both fusion proteins interact with major regulators of RNA processing, with translation-associated proteins, and that both chimeras perturb the transcriptional program of the tumor suppressor p53. Other cellular processes appear to be distinctively affected by the particular fusion protein. NUP98-HOXA9 likely perturbs Wnt, MAPK, and estrogen receptor (ER) signaling pathways, as well as the cytoskeleton, the latter likely due to its interaction with the nuclear export receptor CRM1. Conversely, mitochondrial proteins and metabolic regulators are significantly overrepresented in the SET-NUP214 proximal interactome. Our study provides new clues on the mechanistic actions of nucleoporin fusion proteins and might be of particular relevance in the search for new druggable targets for the treatment of nucleoporin-related leukemia.

Epigenetics and the dynamics of chromatin during adenovirus infections

The DNA genome of eukaryotic cells is compacted by histone proteins within the nucleus to form chromatin. Nuclear-replicating viruses such as adenovirus have evolved mechanisms of chromatin manipulation to promote infection and subvert host defenses. Epigenetic factors may also regulate persistent adenovirus infection and reactivation in lymphoid tissues. In this review, we discuss the viral proteins E1A and protein VII that interact with and alter host chromatin, as well as E4orf3, which separates host chromatin from sites of viral replication. We also highlight recent advances in chromatin technologies that offer new insights into virus-directed chromatin manipulation. Beyond the role of chromatin in the viral replication cycle, we discuss the nature of persistent viral genomes in lymphoid tissue and cell lines, and the potential contribution of epigenetic signals in maintaining adenovirus in a quiescent state. By understanding the mechanisms through which adenovirus manipulates host chromatin, we will understand new aspects of this ubiquitous virus and shed light on previously unknown aspects of chromatin biology.

Chromatin-bound CRM1 recruits SET-Nup214 and NPM1c onto HOX clusters causing aberrant HOX expression in leukemia cells

We previously demonstrated that CRM1, a major nuclear export factor, accumulates at Hox cluster regions to recruit nucleoporin-fusion protein Nup98HoxA9, resulting in robust activation of Hox genes (Oka et al., 2016). However, whether this phenomenon is general to other leukemogenic proteins remains unknown. Here, we show that two other leukemogenic proteins, nucleoporin-fusion SET-Nup214 and the NPM1 mutant, NPM1c, which contains a nuclear export signal (NES) at its C-terminus and is one of the most frequent mutations in acute myeloid leukemia, are recruited to the HOX cluster region via chromatin-bound CRM1, leading to HOX gene activation in human leukemia cells. Furthermore, we demonstrate that this mechanism is highly sensitive to a CRM1 inhibitor in leukemia cell line. Together, these findings indicate that CRM1 acts as a key molecule that connects leukemogenic proteins to aberrant HOX gene regulation either via nucleoporin-CRM1 interaction (for SET-Nup214) or NES-CRM1 interaction (for NPM1c).

Distribution of SET/I2PP2A protein in gastrointestinal tissues

SET (also called I2PP2A and TIF-1) is a multi-functional protein that regulates a variety of cell signaling including nucleosome assembly, histone binding, and tumorigenesis. Elevated SET protein levels are observed in various human tumors, and are correlated with poor prognosis and drug-resistance. We recently reported that SET protein levels in cancer cells were positively correlated with poor prognosis of gastric cancer patients. Using immunohistochemistry, SET protein was observed not only in cancer cells, but also in some interstitial cells. However, the tissue distribution of SET has not been investigated. Here we performed co-immunofluorescent staining to characterize SET protein distribution in gastrointestinal tissues. We found that even though the positive rate is much lower than epithelial cells, SET protein is also expressed in non-epithelial cells, such as monocytes/macrophages, neural cells, myofibroblasts, and smooth muscle cells. Our results indicate an extensive role of SET in a variety of cell types.

Cyclin-dependent kinase 1-mediated phosphorylation of SET at serine 7 is essential for its oncogenic activity

SE translocation (SET), an inhibitor of protein phosphatase 2A (PP2A), plays important roles in mitosis and possesses oncogenic activity in several types of cancer. However, little is known regarding its regulation. Here we reveal a novel phosphorylation site of SET isoform 1, and we have determined its biological significance in tumorigenesis. We found that the mitotic kinase cyclin-dependent kinase 1 (CDK1) phosphorylates SET isoform 1 in vitro and in vivo at serine 7 during antitubulin drug-induced mitotic arrest and normal mitosis. SET deletion resulted in massive multipolar spindles, chromosome misalignment and missegregation, and centrosome amplification during mitosis. Moreover, mitotic phosphorylation of SET isoform 1 is required for cell migration, invasion, and anchorage-independent growth in vitro and tumorigenesis in xenograft animal models. We further documented that SET phosphorylation affects Akt activity. Collectively, our findings suggest that SET isoform 1 promotes oncogenesis in a mitotic phosphorylation-dependent manner.

Structural basis for the acetylation of histone H3K9 and H3K27 mediated by the histone chaperone Vps75 in Pneumocystis carinii

Rtt109 is a histone acetyltransferase (HAT) that is a potential therapeutic target in conditioned pathogenic fungi Pneumocystis carinii (P. carinii). The histone chaperone Vps75 can stimulate the Rtt109-dependent acetylation of several histone H3 lysines and preferentially acetylates H3K9 and H3K27 within canonical histone (H3-H4)2 tetramers. Vps75 shows two protein conformations assembled into dimeric and tetrameric forms, but the roles played by multimeric forms of Vps75 in Rtt109-mediated histone acetylation remain elusive. In P. carinii, we identified that Vps75 (PcVps75) dimers regulate H3K9 and H3K27 acetylation by directly interacting with histone (H3-H4)2 tetramers, rather than by forming a Vps75-Rtt109 complex. For PcVps75 tetramers, the major histone-binding surface is buried within a walnut-like structure in the absence of a histone cargo. Based on crystal structures of dimeric and tetrameric forms of PcVps75, as well as HAT assay data, we confirmed that residues 192E, 193D, 194E, 195E, and 196E and the disordered C-terminal tail (residues 224-250) of PcVps75 mediate interactions with histones and are important for the Rtt109 in P. carinii (PcRtt109)-mediated acetylation of H3K9 and H3K27, both in vitro and in yeast cells. Furthermore, expressing PcRtt109 alone or in combination with PcVps75 variants that cannot effectively bind histones could not fully restore cellular growth in the presence of genotoxic agents that block DNA replication owing to the absence of H3K9 and H3K27 acetylation. Together, these data indicate that the interaction between PcVps75 and histone (H3-H4)2 tetramers is a critical regulator of the Rtt109-mediated acetylation of H3K9 and H3K27.

The NMR-based characterization of the FTY720-SET complex reveals an alternative mechanism for the attenuation of the inhibitory SET-PP2A interaction

The su(var)3-9, enhancer of zeste, trithorax (SET)/inhibitor 2 of protein phosphatase 2A (PP2A) oncoprotein binds and inhibits PP2A, composed of various isoforms of scaffolding, regulatory, and catalytic subunits. Targeting SET with a sphingolipid analog drug fingolimod (FTY720) or ceramide leads to the reactivation of tumor suppressor PP2A. However, molecular details of the SET-FTY720 or SET-ceramide, and mechanism of FTY720-dependent PP2A activation, remain unknown. Here, we report the first in solution examination of the SET-FTY720 or SET-ceramide complexes by NMR spectroscopy. FTY720-ceramide binding resulted in chemical shifts of residues residing at the N terminus of SET, preventing its dimerization or oligomerization. This then released SET from PP2ACα, resulting in PP2A activation, while monomeric SET remained associated with the B56γ. Our data also suggest that the PP2A holoenzyme, composed of PP2A-Aβ, PP2A-B56γ, and PP2ACα subunits, is selectively activated in response to the formation of the SET-FTY720 complex in A549 cells. Various PP2A-associated downstream effector proteins in the presence or absence of FTY720 were then identified by stable isotope labeling with amino cells in cell culture, including tumor suppressor nonmuscle myosin IIA. Attenuation of FTY720-SET association by point mutations of residues that are involved in FTY720 binding or dephosphorylation of SET at Serine 171, enhanced SET oligomerization and the formation of the SET-PP2A inhibitory complex, leading to resistance to FTY720-dependent PP2A activation.-De Palma, R. M., Parnham, S. R., Li, Y., Oaks, J. J., Peterson, Y. K., Szulc, Z. M., Roth, B. M., Xing, Y., Ogretmen, B. The NMR-based characterization of the FTY720-SET complex reveals an alternative mechanism for the attenuation of the inhibitory SET-PP2A interaction.

Loss of SET reveals both the p53-dependent and the p53-independent functions in vivo

Our previous study showed that the oncoprotein SET acts as a new reader of unacetylated p53 for transcriptional repression. To further elucidate the physiological significance of SET in vivo, we generated set knockout mice. Set knockout mice died during embryonic development between day 11.5 and day 12.5 post coitum, exhibiting cardiac edema and open neural tube, among other developmental defects. Further analyses revealed that loss of SET leads to upregulation of p53 target genes including p21 and puma without any obvious effect on p53 stability in set knockout embryos. Notably, the developmental defects of set knockout mice were significantly, but nonetheless partially, rescued by concomitant deletion of p53. The failure to obtain fully live set/p53 double knockout mice suggested that p53-independent targets of SET also contribute to the embryonic lethality of set knockout mice. Indeed, we found that FOXO1 acts as an important target of SET and that SET-mediated regulation of FOXO1 is also acetylation-dependent. Taken together, these data underscore the importance of SET oncoprotein during embryonic development and reveal both of the p53-dependent and the p53-independent functions of SET in vivo.

NUP214 in Leukemia: It's More than Transport

NUP214 is a component of the nuclear pore complex (NPC) with a key role in protein and mRNA nuclear export. Chromosomal translocations involving the NUP214 locus are recurrent in acute leukemia and frequently fuse the C-terminal region of NUP214 with SET and DEK, two chromatin remodeling proteins with roles in transcription regulation. SET-NUP214 and DEK-NUP214 fusion proteins disrupt protein nuclear export by inhibition of the nuclear export receptor CRM1, which results in the aberrant accumulation of CRM1 protein cargoes in the nucleus. SET-NUP214 is primarily associated with acute lymphoblastic leukemia (ALL), whereas DEK-NUP214 exclusively results in acute myeloid leukemia (AML), indicating different leukemogenic driver mechanisms. Secondary mutations in leukemic blasts may contribute to the different leukemia outcomes. Additional layers of complexity arise from the respective functions of SET and DEK in transcription regulation and chromatin remodeling, which may drive malignant hematopoietic transformation more towards ALL or AML. Another, less frequent fusion protein involving the C terminus of NUP214 results in the sequestosome-1 (SQSTM1)-NUP214 chimera, which was detected in ALL. SQSTM1 is a ubiquitin-binding protein required for proper autophagy induction, linking the NUP214 fusion protein to yet another cellular mechanism. The scope of this review is to summarize the general features of NUP214-related leukemia and discuss how distinct chromosomal translocation partners can influence the cellular effects of NUP214 fusion proteins in leukemia.

Targeting SET to restore PP2A activity disrupts an oncogenic CIP2A-feedforward loop and impairs triple negative breast cancer progression

Background

Triple-negative breast cancer (TNBC) remains difficult to be targeted. SET and cancerous inhibitor of protein phosphatase 2A (CIP2A) are intrinsic protein-interacting inhibitors of protein phosphatase 2A (PP2A) and frequently overexpressed in cancers, whereas reactivating PP2A activity has been postulated as an anti-cancer strategy. Here we explored this strategy in TNBC.

Methods

Data from The Cancer Genome Atlas (TCGA) database was analyzed. TNBC cell lines were used for in vitro studies. Cell viability was examined by MTT assay. The apoptotic cells were examined by flow cytometry and Western blot. A SET-PP2A protein-protein interaction antagonist TD19 was used to disrupt signal transduction. In vivo efficacy of TD19 was tested in MDA-MB-468-xenografted animal model.

Findings

TCGA data revealed upregulation of SET and CIP2A and positive correlation of these two gene expressions in TNBC tumors. Ectopic SET or CIP2A increased cell viability, migration, and invasion of TNBC cells. Notably ERK inhibition increased PP2A activity. ERK activation is known crucial for Elk-1 activity, a transcriptional factor regulating CIP2A expression, we hypothesized an oncogenic feedforward loop consisting of pERK/pElk-1/CIP2A/PP2A. This loop was validated by knockdown of PP2A and ectopic expression of Elk-1, showing reciprocal changes in loop members. In addition, ectopic expression of SET increased pAkt, pERK, pElk-1 and CIP2A expressions, suggesting a positive linkage between SET and CIP2A signaling. Moreover, TD19 disrupted this CIP2A-feedforward loop by restoring PP2A activity, demonstrating in vitro and in vivo anti-cancer activity. Mechanistically, TD19 downregulated CIP2A mRNA via inhibiting pERK-mediated Elk-1 nuclear translocation thereby decreased Elk-1 binding to the CIP2A promoter.

Interpretation

These findings suggested that a novel oncogenic CIP2A-feedforward loop contributes to TNBC progression and targeting SET to disrupt this oncogenic CIP2A loop showed therapeutic potential in TNBC.

The concept of the okadaic acid class of tumor promoters is revived in endogenous protein inhibitors of protein phosphatase 2A, SET and CIP2A, in human cancers

PURPOSE

The okadaic acid class of tumor promoters, which are inhibitors of protein phosphatases 1 and 2A (PP1 and PP2A), induced tumor promotion in mouse skin, rat glandular stomach, and rat liver. Endogenous protein inhibitors of PP2A, SET and CIP2A, were up-regulated in various human cancers, so it is vital to review the essential mechanisms of tumor promotion by the okadaic acid class compounds, together with cancer progression by SET and CIP2A in humans.

RESULTS AND DISCUSSION

The first part of this review introduces the okadaic acid class compounds and the mechanism of tumor promotion: (1) inhibition of PP1 and PP2A activities of the okadaic acid class compounds; (2) some topics of tumor promotion; (3) TNF-α gene expression as a central mediator in tumor promotion; (4) exposure to the okadaic acid class of tumor promoters in relation to human cancer. The second part emphasizes the overexpression of SET and CIP2A in cancer progression, and the anticancer activity of SET antagonists as follows: (5) isolation and characterization of SET; (6) isolation and characterization of CIP2A; (7) progression of leukemia with SET; (8) progression of breast cancer with SET and CIP2A; (9) progression of lung cancer with SET; (10) anti-carcinogenic effects of SET antagonists OP449 and FTY720; and also (11) TNF-α-inducing protein of Helicobacter pylori, which is a clinical example of the okadaic acid pathway.

CONCLUSIONS

The overexpression of endogenous protein inhibitors of PP2A, SET and CIP2A, is tightly linked to the progression of various human cancers, as well as Alzheimer's disease.

GnRH regulates the expression of its receptor accessory protein SET in pituitary gonadotropes

Reproductive function is under the control of the neurohormone GnRH, which activates a G-protein-coupled receptor (GnRHR) expressed in pituitary gonadotrope cells. GnRHR activates a complex signaling network to regulate synthesis and secretion of the two gonadotropin hormones, luteinizing hormone and follicle-stimulating hormone, both regulating gametogenesis and steroidogenesis in gonads. Recently, in an attempt to identify the mechanisms underlying GnRHR signaling plasticity, we identified the first interacting partner of GnRHR, the proto-oncogene SET. We showed that SET binds to intracellular domains of GnRHR to enhance its coupling to cAMP pathway in αT3-1 gonadotrope cells. Here, we demonstrate that SET protein is rapidly regulated by GnRH, which increases SET phosphorylation state and decreases dose-dependently SET protein level. Our results highlight a post-translational regulation of SET protein involving the proteasome pathway. We determined that SET phosphorylation upon GnRH stimulation is mediated by PKC and that PKC mediates GnRH-induced SET down-regulation. Phosphorylation on serine 9 targets SET for degradation into the proteasome. Furthermore, a non-phosphorylatable SET mutant on serine 9 is resistant to GnRH-induced down-regulation. Altogether, these data suggest that GnRH-induced SET phosphorylation on serine 9 mediates SET protein down-regulation through the proteasome pathway. Noteworthy, SET down-regulation was also observed in response to pulsatile GnRH stimulation in LβT2 gonadotrope cells as well as in vivo in prepubertal female mice supporting its physiological relevance. In conclusion, this study highlights a regulation of SET protein by the neurohormone GnRH and identifies some of the mechanisms involved.

SET de novo frameshift variants associated with developmental delay and intellectual disabilities

Trio based whole exome sequencing via the Deciphering Developmental Disorders (DDD) study has identified three individuals with de novo frameshift variants in the Suppressor of Variegation, Enhancer of Zeste, and Trithorax (SET) gene. Variants in the SET gene have not previously been recognised to be associated with human developmental disorders. Here we report detailed phenotypic information and propose that SET is a new Intellectual Disability/Developmental Delay (ID/DD) gene.

A comprehensive and perspective view of oncoprotein SET in cancer

SET is a multifunctional oncoprotein which is ubiquitously expressed in all kinds of cells. The SET protein participates in many cellular processes including cell cycle, cell migration, apoptosis, transcription, and DNA repair. Accumulating evidence demonstrates that the expression and activity of SET correlate with cancer occurrence, metastasis, and prognosis. Therefore, the SET protein is regarded as a potential target for cancer therapy and several inhibitors are being developed for clinical use. Herein, we comprehensively review the physiological and pathological functions of SET as well as its structure-function relationship. Additionally, the regulatory mechanisms of SET at both transcriptional and posttranslational levels are also discussed.

The SET protein promotes androgen production in testicular Leydig cells

Approximately 40% of middle‐aged men exhibit symptoms of late‐onset hypogonadism (LOH). However, the mechanism of androgen deficiency is still currently unclear. As shown in our previous studies, the SET protein is expressed in testicular Leydig cells and ovarian granule cells. This study was designed to investigate the effect of the SET protein on androgen production in Leydig cells. The AdCMV/SET and AdH1siRNA/SET adenoviruses were individually transduced into a cultured mouse Leydig cell line (mLTC‐1) with or without human chorionic gonadotropin (HCG) stimulation in vitro. The primary mouse Leydig cells were used to confirm the main data from mLTC‐1 cells. The SET protein was expressed in the cytoplasm and nucleus of mLTC‐1 cells. Testosterone production was significantly increased in mLTC‐1 cells overexpressing the SET protein compared with the control group (p < 0.05), whereas testosterone production was significantly decreased in the SET knockdown mLTC‐1 cells (p < 0.05). Consistent with the testosterone levels, the expression levels of the steroidogenic acute regulatory (StAR) and cytochrome P450c17α‐hydroxylase (CYP17a1) mRNAs and proteins synchronously changed according to the expression level of the SET protein. Interestingly, the expression of the SET protein was significantly increased in the mLTC‐1 cells stimulated with 0.04 and 0.1 U/mL hCG. In the mLTC‐1 cells transfected with AdH1siRNA/SET and concurrently stimulated with 0.1 U/mL hCG, both testosterone production and StAR expression were significantly lower than in the cells without SET knockdown (p < 0.05). In conclusion, the SET protein participates in regulating testosterone production by increasing the expression of StAR and CYP17a1, and it may be a downstream factor of the classic luteinizing hormone (LH)/luteinizing hormone receptor (LHR) signaling pathway. This study improves our understanding of the intracellular mechanism of testicular steroidogenesis and the pathophysiological mechanism of LOH in the aging male.

Involvement of Activation of Asparaginyl Endopeptidase in Tau Hyperphosphorylation in Repetitive Mild Traumatic Brain Injury

Traumatic brain injury (TBI) is an established risk factor for the development of neurodegeneration and dementia late in life. Repetitive mild TBI (r-mTBI) is directly associated with chronic traumatic encephalopathy (CTE), a progressive neurodegenerative disorder characterized by focal perivascular to widespread Alzheimer-type neurofibrillary pathology of hyperphosphorylated tau. Studies in animal models have shown hyperphosphorylation of tau after TBI. However, the molecular mechanisms by which TBI leads to tau pathology are not understood. In this study, we employed western blots and immunohistochemistry to test, in triple-transgenic mouse model of Alzheimer's disease (3xTg-AD), the effect of r-mTBI on tau hyperphosphorylation and activation of asparaginyl endopeptidase (AEP), a cysteine proteinase which is known to be involved in tau hyperphosphorylation. We found that the level of active AEP was increased and correlated with the level of tau hyperphosphorylation following r-mTBI, and that fimbria showed increased immunoreactivity to phospho-tau. In addition, inhibitor 2 of protein phosphatase 2A (I2PP2A) was translocated from neuronal nucleus to the cytoplasm and colocalized with hyperphosphorylated tau. These data suggest the involvement of AEP-I2PP2A-PP2A-ptau pathway in tau pathology in TBI.

Prognostic significance of Cytokeratin 20-positive lymph node vascular endothelial growth factor A mRNA and chromodomain helicase DNA binding protein 4 in pN0 colorectal cancer patients

BACKGROUND

Cytokeratin 20-positive cells in lymph nodes from pN0 colorectal cancer (CRC) patients were detected previously by us. The aims of this study were to investigate which tumor metastasis-related genes were involved and their potential clinical significance.

RESULTS

Fourteen of 84 (17%) genes were differentially expressed by at least 2-fold. Among them, 10 genes were up-regulated whereas 4 genes were down-regulated. Those differential expressed genes were validated in the second cohort of specimens. Follow-up analysis for 60 months showed that patients with lymph node vascular endothelial growth factor A (VEGF-A) mRNA and chromodomain helicase DNA binding protein 4 (CHD4) mRNA expression higher than the median copies had significantly shorter time to recurrence than those with lower than the median copies. Multivariate analysis showed that VEGF-A mRNA, CHD4 mRNA and lymphatic vessel involvement were independent prognostic factors for disease recurrence.

CONCLUSIONS

VEGF-A mRNA and CHD4 mRNA were up-regulated in CK20-positive pN0 lymph nodes and they may have prognostic significance in pN0 CRC patients.

METHODS

Two cohorts of lymph node specimens from pN0 CRC patients of each with and without CK20-positive cells were recruited. In the first cohort, tumor metastasis genes were profiled using gene expression arrays. Differential expressed genes were validated in the second cohort. Moreover, their prognostic significance was examined by following-up the second cohort of patients with CK20-positive cells for 60 months and all histopathological findings were correlated to recurrence.

Development and identification of Set transgenic mice

As a multifunctional protein involved in numerous biological processes, Set is expressed in several embryonic and adult organs. Furthermore, Set is overexpressed in numerous types of human cancers, including acute myeloid leukemia, breast cancer and pancreatic cancer. The expression of Set in germ cells is involved in gonad development, and the overexpression of Set has been observed in polycystic ovaries. In order to elucidate the physiological and pathological roles of Set, a Set transgenic mouse model was developed, in which the global overexpression of Set in adult tissues could be induced via the Cre/loxP system with the precise deletion of the Stop fragment in double-transgenic hybrids. This result was then confirmed by genotypical and protein analysis using polymerase chain reaction and bioluminescence imaging. In conclusion, the conditional Set transgenic mice carrying a reporter system were successfully generated. The transgenic mice open a new window for the further investigation of the function of Set using tissue-specific Cre mice and inducible Cre systems.

Assembly and remodeling of viral DNA and RNA replicons regulated by cellular molecular chaperones

A variety of cellular reactions mediated by interactions among proteins and nucleic acids requires a series of proteins called molecular chaperones. The viral genome encodes relatively few kinds of viral proteins and, therefore, host-derived cellular factors are required for virus proliferation. Here we discuss those cellular proteins known as molecular chaperones, which are essential for the assembly of functional viral DNA/RNA replicons. The function of these molecular chaperones in the cellular context is also discussed.

Therapeutic targeting of PP2A

Protein phosphatase 2A (PP2A) is a major serine/threonine phosphatase that regulates many cellular processes. Given the central role of PP2A in regulating diverse biological functions and its dysregulation in many diseases, including cancer, PP2A directed therapeutics have become of great interest. The main approaches leveraged thus far can be categorized as follows: 1) inhibiting endogenous inhibitors of PP2A, 2) targeted disruption of post translational modifications on PP2A subunits, or 3) direct targeting of PP2A. Additional insight into the structural, molecular, and biological framework driving the efficacy of these therapeutic strategies will provide a foundation for the refinement and development of novel and clinically tractable PP2A targeted therapies.

OP449 inhibits breast cancer growth without adverse metabolic effects

Hyperinsulinemia is associated with a decrease in breast cancer recurrence-free survival and overall survival. Inhibition of insulin receptor signaling is associated with glycemic dysregulation. SET is a direct modulator of PP2A, which negatively regulates the PI3K/AKT/mTOR pathway. OP449, a SET inhibitor, decreases AKT/mTOR activation. The effects of OP449 treatment on breast cancer growth in the setting of pre-diabetes, and its metabolic implications are currently unknown. We found that the volumes and weights of human MDA-MB-231 breast cancer xenografts were greater in hyperinsulinemic mice compared with controls (P < 0.05), and IR phosphorylation was 4.5-fold higher in these mice (P < 0.05). Human and murine breast cancer tumors treated with OP449 were 47% and 39% smaller than controls (P < 0.05, for both, respectively). AKT and S6RP phosphorylation were 82% and 34% lower in OP449-treated tumors compared with controls (P < 0.05, P = 0.06, respectively). AKT and S6RP phosphorylation in response to insulin was 30% and 12% lower in cells, pre-treated with OP449, compared with control cells (P < 0.01, P < 0.05, respectively). However, even with decreased AKT/mTOR activation, body weights and composition, blood glucose and plasma insulin, glucose tolerance, serum triglyceride and cholesterol levels were similar between OP449-treated mice and controls. Xenografts and liver tissue from OP449-treated mice showed a 64% and 70% reduction in STAT5 activation, compared with controls (P < 0.01 and P = 0.06, respectively). Our data support an anti-neoplastic effect of OP449 on human breast cancer cells in vitro and in xenografts in the setting of hyperinsulinemia. OP449 led to the inhibition of AKT/mTOR signaling, albeit, not leading to metabolic derangements.

Phorbol esters in seed oil of Jatropha curcas L. (saboodam in Thai) and their association with cancer prevention: from the initial investigation to the present topics

PURPOSE

In 1988, we first reported the complete chemical structure of a new type of phorbol ester, abbreviated to DHPB, found in seed oil of Jatropha curcas L. (Saboodam in Thai) and its tumor-promoting activity on mouse skin. Although this seed oil contains toxic phorbol ester, it was planned to use it as a feasible renewable oil and the extracted seed cake as fertilizer. This utilization value opened a new science of Jatropha curcas.

METHODS

The main experimental results are cited from our publications, and the relevant literature screened from journals and PubMed.

RESULTS AND DISCUSSION

This paper begins with our original work on the structural elucidation of a new phorbol ester, 12-deoxy-16-hydroxyphorbol (DHPB): its tumor-promoting activity was compared with that of TPA. We think that it is timely to review the following research advances with Jatropha curcas, so numerous topics are classified as follows: (1) historical development of phorbol esters in seed oil; (2) toxicity of phorbol ester based on various bioassays; (3) degradation of phorbol ester; (4) a new pharmaceutical compound in seed; and (5) tumor promotion and progression with endogeneous tumor promoters in human carcinogenesis. The discovery of phorbol ester in seed oil raised awareness of the danger of public use of seed oil and seed cake in Thailand, and also indicated the necessity of discussing the concept of primary and tertiary cancer preventions.

CONCLUSION

It is worthwhile to study the future benefits and cancer risks of globally distributed Jatropha curcas L.

The role of SET/I2PP2A in canine mammary tumors

Canine mammary tumor is the most common neoplasm in female dogs, and it has generated considerable attention as a translational model for human breast cancer. Ser/Thr protein phosphatase 2A (PP2A) plays a critical role as a tumor suppressor, and SET/I2PP2A, the endogenous inhibitory protein of PP2A, binds directly to PP2A and suppresses its phosphatase activity. Here, we investigated the role of SET in the tumorigenic growth in canine mammary tumor as well as in the sensitivity of tumors to existing therapeutics. Elevated protein levels of SET were observed in advanced-stage of canine mammary tumor tissues of dogs compared with paired normal tissues. Knockdown of SET expression in a canine mammary tumor cell line CIP-m led to increased PP2A activity and decreased cell proliferation, colony formation, and in vivo tumor growth. We observed suppression of mTOR, β-catenin, and NFκB signaling by SET knockdown. The sensitivity of CIP-m cells to doxorubicin was decreased by SET knockdown, while SET knockdown in CIP-m cells did not affect sensitivity to 4-OH-tamoxifen, carboplatin, bortezomib, and X-ray radiation. These data suggest that SET plays important roles in the tumor progression of a subset of canine mammary tumor by suppressing PP2A activity and enhancing mTOR, β-catenin, and NFκB signaling.

Genomics of chronic neutrophilic leukemia

Chronic neutrophilic leukemia (CNL) is a distinct myeloproliferative neoplasm with a high prevalence (>80%) of mutations in the colony-stimulating factor 3 receptor (CSF3R). These mutations activate the receptor, leading to the proliferation of neutrophils that are a hallmark of CNL. Recently, the World Health Organization guidelines have been updated to include CSF3R mutations as part of the diagnostic criteria for CNL. Because of the high prevalence of CSF3R mutations in CNL, it is tempting to think of this disease as being solely driven by this genetic lesion. However, recent additional genomic characterization demonstrates that CNL has much in common with other chronic myeloid malignancies at the genetic level, such as the clinically related diagnosis atypical chronic myeloid leukemia. These commonalities include mutations in SETBP1, spliceosome proteins (SRSF2, U2AF1), and epigenetic modifiers (TET2, ASXL1). Some of these same mutations also have been characterized as frequent events in clonal hematopoiesis of indeterminate potential, suggesting a more complex disease evolution than was previously understood and raising the possibility that an age-related clonal process of preleukemic cells could precede the development of CNL. The order of acquisition of CSF3R mutations relative to mutations in SETBP1, epigenetic modifiers, or the spliceosome has been determined only in isolated case reports; thus, further work is needed to understand the impact of mutation chronology on the clonal evolution and progression of CNL. Understanding the complete landscape and chronology of genomic events in CNL will help in the development of improved therapeutic strategies for this patient population.

Complete response of extramedullary relapse in breast of acute T lymphoblastic leukemia after bone marrow transplantation to chemoradiotherapy: a case report and literature review

BACKGROUND

Relapse of acute lymphoblastic leukemia (ALL) occurring in the breast after allografting is extremely rare, with only 22 reported cases in the literature thus far. Further, the lack of a systemic analysis provides little information about this entity. We present a case of isolated extramedullary relapse from acute T lymphoblastic leukemia (ATLL) after allogeneic hematopoietic stem cell transplantation (HSCT).

CASE PRESENTATION

A 32-year-old Chinese woman diagnosed with ATLL with myeloid antigen expression received HSCT from her human leukocyte antigen (HLA)-matched sister and presented with two lesions in her right breast 6 months later. Pathology investigation revealed breast relapse, with complete remission on the basis of bone marrow findings. Combined modality treatment including chemotherapy and local radiotherapy helped achieve complete remission with mild side effects.

CONCLUSION

The findings from this case indicate that the breast is a potentially involved extramedullary site of relapse for ALL patients after HSCT. In the case of a newly developed breast lump in such patients, clinicians consider local relapse even if the bone marrow findings indicate remission. Combined modality treatment will contribute to better local control and improve prognosis.

The Oncogenic Fusion Proteins SET-Nup214 and Sequestosome-1 (SQSTM1)-Nup214 Form Dynamic Nuclear Bodies and Differentially Affect Nuclear Protein and Poly(A)+ RNA Export

Genetic rearrangements are a hallmark of several forms of leukemia and can lead to oncogenic fusion proteins. One example of an affected chromosomal region is the gene coding for Nup214, a nucleoporin that localizes to the cytoplasmic side of the nuclear pore complex (NPC). We investigated two such fusion proteins, SET-Nup214 and SQSTM1 (sequestosome)-Nup214, both containing C-terminal portions of Nup214. SET-Nup214 nuclear bodies containing the nuclear export receptor CRM1 were observed in the leukemia cell lines LOUCY and MEGAL. Overexpression of SET-Nup214 in HeLa cells leads to the formation of similar nuclear bodies that recruit CRM1, export cargo proteins, and certain nucleoporins and concomitantly affect nuclear protein and poly(A)+ RNA export. SQSTM1-Nup214, although mostly cytoplasmic, also forms nuclear bodies and inhibits nuclear protein but not poly(A)+ RNA export. The interaction of the fusion proteins with CRM1 is RanGTP-dependent, as shown in co-immunoprecipitation experiments and binding assays. Further analysis revealed that the Nup214 parts mediate the inhibition of nuclear export, whereas the SET or SQSTM1 part determines the localization of the fusion protein and therefore the extent of the effect. SET-Nup214 nuclear bodies are highly mobile structures, which are in equilibrium with the nucleoplasm in interphase and disassemble during mitosis or upon treatment of cells with the CRM1-inhibitor leptomycin B. Strikingly, we found that nucleoporins can be released from nuclear bodies and reintegrated into existing NPC. Our results point to nuclear bodies as a means of preventing the formation of potentially insoluble and harmful protein aggregates that also may serve as storage compartments for nuclear transport factors.

Zinc Finger and X-Linked Factor (ZFX) Binds to Human SET Transcript 2 Promoter and Transactivates SET Expression

SET (SE Translocation) protein carries out multiple functions including those for protein phosphatase 2A (PP2A) inhibition, histone modification, DNA repair, and gene regulation. SET overexpression has been detected in brain neurons of patients suffering Alzheimer's disease, follicle theca cells of Polycystic Ovary Syndrome (PCOS) patients, and ovarian cancer cells, indicating that SET may play a pathological role for these disorders. SET transcript 2, produced by a specific promoter, represents a major transcript variant in different cell types. In this study, we characterized the transcriptional activation of human SET transcript 2 promoter in HeLa cells. Promoter deletion experiments and co-transfection assays indicated that ZFX, the Zinc finger and X-linked transcription factor, was able to transactivate the SET promoter. A proximal promoter region containing four ZFX-binding sites was found to be critical for the ZFX-mediated transactivation. Mutagenesis study indicated that the ZFX-binding site located the closest to the transcription start site accounted for most of the ZFX-mediated transactivity. Manipulation of ZFX levels by overexpression or siRNA knockdown confirmed the significance and specificity of the ZFX-mediated SET promoter activation. Chromatin immunoprecipitation results verified the binding of ZFX to its cognate sites in the SET promoter. These findings have led to identification of ZFX as an upstream factor regulating SET gene expression. More studies are required to define the in vivo significance of this mechanism, and specifically, its implication for several benign and malignant diseases related to SET dysregulation.

Acetylation-regulated interaction between p53 and SET reveals a widespread regulatory mode

Although lysine acetylation is now recognized as a general protein modification for both histones and non-histone proteins^1-3, the mechanisms of acetylation mediated actions are not completely understood. Acetylation of the C-terminal domain (CTD) of p53 was the first example for non-histone protein acetylation⁴. Yet the precise role of the CTD acetylation remains elusive. Lysine acetylation often creates binding sites for bromodomain-containing “reader” proteins^5,6; surprisingly, in a proteomic screen, we identified SET as a major cellular factor whose binding with p53 is totally dependent on the CTD acetylation status. SET profoundly inhibits p53 transcriptional activity in unstressed cells but SET-mediated repression is completely abolished by stress-induced p53 CTD acetylation. Moreover, loss of the interaction with SET activates p53, resulting in tumor regression in mouse xenograft models. Notably, the acidic domain of SET acts as a “reader” for unacetylated CTD of p53 and this mechanism of acetylation-dependent regulation is widespread in nature. For example, p53 acetylation also modulates its interactions with similar acidic domains found in other p53 regulators including VPRBP, DAXX and PELP1 (refs. 7-9), and computational analysis of the proteome identified numerous proteins with the potential to serve as the acidic domain readers and lysine-rich ligands. Unlike bromodomain readers, which preferentially bind the acetylated forms of their cognate ligands, the acidic domain readers specifically recognize the unacetylated forms of their ligands. Finally, the acetylation-dependent regulation of p53 was further validated in vivo by using a knockin mouse model expressing an acetylation-mimicking form of p53. These results reveal that the acidic domain-containing factors act as a new class of acetylation-dependent regulators by targeting p53 and potentially, beyond.

Regulation of SET Gene Expression by NFkB

SET is elevated and mislocalized in the neuronal cytoplasm in brains of Alzheimer's disease (AD) and Down syndrome (DS) patients. Cytoplasm SET leads to inhibition of protein phosphatase 2A and is involved in the tau pathology. However, the regulation of SET gene expression remains elusive. In the present study, we cloned a 1399-bp segment of the 5' flanking region of the human SET gene and identified that the transcription start site (TSS) of SET transcript 1 is located at 123 bp upstream of the translation start site ATG in exon 1. Sequence analysis reveals several putative regulatory elements including NFkB, Sp1, and HSE. Luciferase assay and electrophoretic mobility shift assay (EMSA) identified a functional cis-acting NFkB-responsive element in the SET gene promoter. Overexpression and activation of NFkB upregulate transcription of SET isoform 1 but not isoform 2, indicating that the expression of these two isoforms is differentially regulated. The results demonstrate that NFkB plays an important role in regulation of the human SET gene expression. Our findings suggest that oxidative stress and inflammatory responses could result in abnormal SET gene expression, contributing to the tauopathy in AD pathogenesis.

Leukemia-Associated Nup214 Fusion Proteins Disturb the XPO1-Mediated Nuclear-Cytoplasmic Transport Pathway and Thereby the NF-κB Signaling Pathway

Nuclear-cytoplasmic transport through nuclear pore complexes is mediated by nuclear transport receptors. Previous reports have suggested that aberrant nuclear-cytoplasmic transport due to mutations or overexpression of nuclear pore complexes and nuclear transport receptors is closely linked to diseases. Nup214, a component of nuclear pore complexes, has been found as chimeric fusion proteins in leukemia. Among various Nup214 fusion proteins, SET-Nup214 and DEK-Nup214 have been shown to be engaged in tumorigenesis, but their oncogenic mechanisms remain unclear. In this study, we examined the functions of the Nup214 fusion proteins by focusing on their effects on nuclear-cytoplasmic transport. We found that SET-Nup214 and DEK-Nup214 interact with exportin-1 (XPO1)/CRM1 and nuclear RNA export factor 1 (NXF1)/TAP, which mediate leucine-rich nuclear export signal (NES)-dependent protein export and mRNA export, respectively. SET-Nup214 and DEK-Nup214 decreased the XPO1-mediated nuclear export of NES proteins such as cyclin B and proteins involved in the NF-κB signaling pathway by tethering XPO1 onto nuclear dots where Nup214 fusion proteins are localized. We also demonstrated that SET-Nup214 and DEK-Nup214 expression inhibited NF-κB-mediated transcription by abnormal tethering of the complex containing p65 and its inhibitor, IκB, in the nucleus. These results suggest that SET-Nup214 and DEK-Nup214 perturb the regulation of gene expression through alteration of the nuclear-cytoplasmic transport system.

Critical role of DEK and its regulation in tumorigenesis and metastasis of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related mortality globally. Therefore, it is quite essential to identify novel HCC-related molecules for the discovery of new prognostic markers and therapeutic targets. As an oncogene, DEK plays an important role in cell processes and participates in a variety of cellular metabolic functions, and its altered expression is associated with several human malignancies. However, the functional significance of DEK and the involved complex biological events in HCC development and progression are poorly understood. Here, combing the results from clinical specimens and cultured cell lines, we uncover a critical oncogenic role of DEK, which is highly expressed in HCC cells. DEK protein encompasses two isoforms (isoforms 1 and 2) and isoform 1 is the most frequently expressed DEK isoform in HCC cells. DEK depletion by using shRNA inhibited the cell proliferation and migration in vitro and suppressed tumorigenesis and metastasis in mouse models. Consistently, DEK overexpression regardless of which isoform produced the opposite effects. Further studies showed that DEK induced cell proliferation through upregulating cell cycle related CDK signaling, and promoted cell migration and EMT, at least in part, through the repression of β-catenin/E-cadherin axis. Interestingly, isoform 1 induced cell proliferation more efficiently than isoform 2, however, no functional differences existed between these two isoforms in cell migration. Together, our study indicates that DEK expression is required for tumorigenesis and metastasis of HCC, providing molecular insights for DEK-related pathogenesis and a basis for developing new strategies against HCC.

All roads lead to PP2A: exploiting the therapeutic potential of this phosphatase

Protein phosphatase 2A (PP2A) is a serine/threonine phosphatase involved in the regulation of many cellular processes. A confirmed tumor suppressor protein, PP2A is genetically altered or functionally inactivated in many cancers highlighting a need for its therapeutic reactivation. In this review we discuss recent literature on PP2A: the elucidation of its structure and the functions of its subunits, and the identification of molecular lesions and post-translational modifications leading to its dysregulation in cancer. A final section will discuss the proteins and small molecules that modulate PP2A and how these might be used to target dysregulated forms of PP2A to treat cancers and other diseases.

Inhibition of Pten deficient Castration Resistant Prostate Cancer by Targeting of the SET - PP2A Signaling axis

The PP2A signaling axis regulates multiple oncogenic drivers of castration resistant prostate cancer (CRPC). We show that targeting the endogenous PP2A regulator, SET (I2PP2A), is a viable strategy to inhibit prostate cancers that are resistant to androgen deprivation therapy. Our data is corroborated by analysis of prostate cancer patient cohorts showing significant elevation of SET transcripts. Tissue microarray analysis reveals that elevated SET expression correlates with clinical cancer grading, duration of neoadjuvant hormone therapy (NHT) and time to biochemical recurrence. Using prostate regeneration assays, we show that in vivo SET overexpression is sufficient to induce hyperplasia and prostatic intraepithelial neoplasia. Knockdown of SET induced significant reductions in tumorgenesis both in murine and human xenograft models. To further validate SET as a therapeutic target, we conducted in vitro and in vivo treatments using OP449 - a recently characterized PP2A-activating drug (PAD). OP449 elicits robust anti-cancer effects inhibiting growth in a panel of enzalutamide resistant prostate cancer cell lines. Using the Pten conditional deletion mouse model of prostate cancer, OP449 potently inhibited PI3K-Akt signaling and impeded CRPC progression. Collectively, our data supports a critical role for the SET-PP2A signaling axis in CRPC progression and hormone resistant disease.

Eviction of linker histone H1 by NAP-family histone chaperones enhances activated transcription

Background

In the Metazoan nucleus, core histones assemble the genomic DNA to form nucleosome arrays, which are further compacted into dense chromatin structures by the linker histone H1. The extraordinary density of chromatin creates an obstacle for accessing the genetic information. Regulation of chromatin dynamics is therefore critical to cellular homeostasis, and histone chaperones serve as prominent players in these processes. In the current study, we examined the role of specific histone chaperones in negotiating the inherently repressive chromatin structure during transcriptional activation.

Results

Using a model promoter, we demonstrate that the human nucleosome assembly protein family members hNap1 and SET/Taf1β stimulate transcription in vitro during pre-initiation complex formation, prior to elongation. This stimulatory effect is dependent upon the presence of activators, p300, and Acetyl-CoA. We show that transcription from our chromatin template is strongly repressed by H1, and that both histone chaperones enhance RNA synthesis by overcoming H1-induced repression. Importantly, both hNap1 and SET/Taf1β directly bind H1, and function to enhance transcription by evicting the linker histone from chromatin reconstituted with H1. In vivo studies demonstrate that SET/Taf1β, but not hNap1, strongly stimulates activated transcription from the chromosomally-integrated model promoter, consistent with the observation that SET/Taf1β is nuclear, whereas hNap1 is primarily cytoplasmic. Together, these observations indicate that SET/Taf1β may serve as a critical regulator of H1 dynamics and gene activation in vivo.

Conclusions

These studies uncover a novel function for SET that mechanistically couples transcriptional derepression with H1 dynamics. Furthermore, they underscore the significance of chaperone-dependent H1 displacement as an essential early step in the transition of a promoter from a dense chromatin state into one that is permissive to transcription factor binding and robust activation.

Expression of the SET protein in testes of mice at different developmental stages

SET is a multifunctional protein involved in regulating many biological processes of the cell cycle. It is also a regulator of steroidogenesis in the ovary. However, the expression of SET protein in testis, and its function, still remains ambiguous. In this study, we observed the expression of SET in the testes of mice at different developmental stages, and have discussed its potential function in regulating spermatogenesis and androgen production. Forty-eight male mice at different developmental stages (1 week old as the infancy group; 4 weeks old as the prepubertal group; 12 weeks old as the adult group; over 12 months old as the ageing group) were used. Cellular location of SET protein in the testes was observed by immuno-histochemistry. Expression levels of Set mRNA and SET protein were analyzed by quantitative polymerase chain reaction and Western blotting. SET protein was expressed in spermatogonial cells and spermatocytes; the highest level was mainly in haploid and tetraploid cells of the prepubertal and adult groups, and Leydig cells of the adult and ageing groups. There was a low expression in Sertoli cells. Expression of Set mRNA in the prepubertal group was significantly higher than that in the adult group (P < 0.05), while expression of SET protein was at the highest level in the adult group (P < 0.05). SET protein is mainly expressed in spermatogonial cells and spermatocytes, and poorly expressed in Sertoli cells, suggesting that it is involved in spermatogenesis. Expression of SET protein in Leydig cells suggests a possible role in steroidogenesis.

The N-terminal Set-β Protein Isoform Induces Neuronal Death

Set-β protein plays different roles in neurons, but the diversity of Set-β neuronal isoforms and their functions have not been characterized. The expression and subcellular localization of Set-β are altered in Alzheimer disease, cleavage of Set-β leads to neuronal death after stroke, and the full-length Set-β regulates retinal ganglion cell (RGC) and hippocampal neuron axon growth and regeneration in a subcellular localization-dependent manner. Here we used various biochemical approaches to investigate Set-β isoforms and their role in the CNS, using the same type of neurons, RGCs, across studies. We found multiple alternatively spliced isoforms expressed from the Set locus in purified RGCs. Set transcripts containing the Set-β-specific exon were the most highly expressed isoforms. We also identified a novel, alternatively spliced Set-β transcript lacking the nuclear localization signal and demonstrated that the full-length (∼39-kDa) Set-β is localized predominantly in the nucleus, whereas a shorter (∼25-kDa) Set-β isoform is localized predominantly in the cytoplasm. Finally, we show that an N-terminal Set-β cleavage product can induce neuronal death.

Structural basis for assembly and function of the Nup82 complex in the nuclear pore scaffold

The yeast Nup82 complex forms an unusual asymmetric structure with a dimeric array of subunits that mediate its anchorage to the NPC scaffold and its concomitant interaction with the soluble nucleocytoplasmic transport machinery.

Nuclear pore complexes (NPCs) are huge assemblies formed from ∼30 different nucleoporins, typically organized in subcomplexes. One module, the conserved Nup82 complex at the cytoplasmic face of NPCs, is crucial to terminate mRNA export. To gain insight into the structure, assembly, and function of the cytoplasmic pore filaments, we reconstituted in yeast the Nup82–Nup159–Nsp1–Dyn2 complex, which was suitable for biochemical, biophysical, and electron microscopy analyses. Our integrative approach revealed that the yeast Nup82 complex forms an unusual asymmetric structure with a dimeric array of subunits. Based on all these data, we developed a three-dimensional structural model of the Nup82 complex that depicts how this module might be anchored to the NPC scaffold and concomitantly can interact with the soluble nucleocytoplasmic transport machinery.

Regulation of PP2A by Sphingolipid Metabolism and Signaling

Protein phosphatase 2A (PP2A) is a serine/threonine phosphatase that is a primary regulator of cellular proliferation through targeting of proliferative kinases, cell cycle regulators, and apoptosis inhibitors. It is through the regulation of these regulatory elements that gives PP2A tumor suppressor functions. In addition to mutations on the regulatory subunits, the phosphatase/tumor suppressing activity of PP2A is also inhibited in several cancer types due to overexpression or modification of the endogenous PP2A inhibitors such as SET/I2PP2A. This review focuses on the current literature regarding the interactions between the lipid signaling molecules, selectively sphingolipids, and the PP2A inhibitor SET for the regulation of PP2A, and the therapeutic potential of sphingolipids as PP2A activators for tumor suppression via targeting SET oncoprotein.

The Basic Biology of PP2A in Hematologic Cells and Malignancies

Reversible protein phosphorylation plays a crucial role in regulating cell signaling. In normal cells, phosphoregulation is tightly controlled by a network of protein kinases counterbalanced by several protein phosphatases. Deregulation of this delicate balance is widely recognized as a central mechanism by which cells escape external and internal self-limiting signals, eventually resulting in malignant transformation. A large fraction of hematologic malignancies is characterized by constitutive or unrestrained activation of oncogenic kinases. This is in part achieved by activating mutations, chromosomal rearrangements, or constitutive activation of upstream kinase regulators, in part by inactivation of their anti-oncogenic phosphatase counterparts. Protein phosphatase 2A (PP2A) represents a large family of cellular serine/threonine phosphatases with suspected tumor suppressive functions. In this review, we highlight our current knowledge about the complex structure and biology of these phosphatases in hematologic cells, thereby providing the rationale behind their diverse signaling functions. Eventually, this basic knowledge is a key to truly understand the tumor suppressive role of PP2A in leukemogenesis and to allow further rational development of therapeutic strategies targeting PP2A.