SENP1-mediated GATA1 deSUMOylation is critical for definitive erythropoiesis

Interferon controls SUMO availability via the Lin28 and let-7 axis to impede virus replication

Small ubiquitin-related modifier (SUMO) protein conjugation onto target proteins regulates multiple cellular functions, including defence against pathogens, stemness and senescence. SUMO1 peptides are limiting in quantity and are thus mainly conjugated to high-affinity targets. Conjugation of SUMO2/3 paralogues is primarily stress inducible and may initiate target degradation. Here we demonstrate that the expression of SUMO1/2/3 is dramatically enhanced by interferons through an miRNA-based mechanism involving the Lin28/let-7 axis, a master regulator of stemness. Normal haematopoietic progenitors indeed display much higher SUMO contents than their differentiated progeny. Critically, SUMOs contribute to the antiviral effects of interferons against HSV1 or HIV. Promyelocytic leukemia (PML) nuclear bodies are interferon-induced domains, which facilitate sumoylation of a subset of targets. Our findings thus identify an integrated interferon-responsive PML/SUMO pathway that impedes viral replication by enhancing SUMO conjugation and possibly also modifying the repertoire of targets. Interferon-enhanced post-translational modifications may be essential for senescence or stem cell self-renewal, and initiate SUMO-dependent proteolysis.

The BTB-containing protein Kctd15 is SUMOylated in vivo

Potassium Channel Tetramerization Domain containing 15 (Kctd15) has a role in regulating the neural crest (NC) domain in the embryo. Kctd15 inhibits NC induction by antagonizing Wnt signaling and by interaction with the transcription factor AP-2α activation domain blocking its activity. Here we demonstrate that Kctd15 is SUMOylated by SUMO1 and SUMO2/3. Kctd15 contains a classical SUMO interacting motif, ψKxE, at the C-terminal end, and variants of the motif within the molecule. Kctd15 SUMOylation occurs exclusively in the C-terminal motif. Inability to be SUMOylated did not affect Kctd15's subcellular localization, or its ability to repress AP-2 transcriptional activity and to inhibit NC formation in zebrafish embryos. In contrast, a fusion of Kctd15 and SUMO had little effectiveness in AP-2 inhibition and in blocking of NC formation. These data suggest that the non-SUMOylated form of Kctd15 functions in NC development.

Whole-genome sequencing uncovers the genetic basis of chronic mountain sickness in Andean highlanders

The hypoxic conditions at high altitudes present a challenge for survival, causing pressure for adaptation. Interestingly, many high-altitude denizens (particularly in the Andes) are maladapted, with a condition known as chronic mountain sickness (CMS) or Monge disease. To decode the genetic basis of this disease, we sequenced and compared the whole genomes of 20 Andean subjects (10 with CMS and 10 without). We discovered 11 regions genome-wide with significant differences in haplotype frequencies consistent with selective sweeps. In these regions, two genes (an erythropoiesis regulator, SENP1, and an oncogene, ANP32D) had a higher transcriptional response to hypoxia in individuals with CMS relative to those without. We further found that downregulating the orthologs of these genes in flies dramatically enhanced survival rates under hypoxia, demonstrating that suppression of SENP1 and ANP32D plays an essential role in hypoxia tolerance. Our study provides an unbiased framework to identify and validate the genetic basis of adaptation to high altitudes and identifies potentially targetable mechanisms for CMS treatment.

Exploring the desumoylation process of SENP1: a study combined MD simulations with QM/MM calculations on SENP1-SUMO1-RanGAP1

The small ubiquitin-related modifier (SUMO)-specific protease (SENP) processes SUMOs to mature forms and deconjugates them from various modified substrates. Loss of the equilibrium from desumoylation catalyzed by abnormal SENP1 is associated with cancers and transcription factor activity. In spite of the significant role of SENP1, the molecular basis of its desumoylation remains unclear. Here, MD simulations and QM/MM methods are combined to investigate the catalytic mechanism of desumoylation. The results showed that substrate SUMO1-RanGAP1 fitted into the catalytic pocket of SENP1 by the break of internal hydrophobic interactions and the isomerization of isopeptide from trans to cis. After that, the nucleophilic sulfur anion of Cys603 in SENP1 attacked the carbonyl carbon of Gly97 of SUMO1 to trigger the reaction, and then a tetrahedral intermediate and an acyl-enzyme intermediate were generated in turn, leading to the final release of enzyme SENP1 and two products, free SUMO1 and RanGAP1. In the process, nucleophilic attack was identified as the rate-determining step with a potential energy barrier of 20.2 kcal/mol. These results are in agreement with experimental data from mutagenesis and other experiments. Our findings elucidate the catalytic mechanism of SENP1 with its substrate and may provide a better understanding of SENP desumoylation. In particular, we have identified key residues in SENP1 needed for desumoylation that might be beneficial for the design of novel inhibitors of SENP1-related diseases.

Inhibition of SENP1 induces radiosensitization in lung cancer cells

Lung cancer is one of the most common and lethal types of malignancy. To date, radiotherapy and chemotherapy have been used as the two major treatment methods. However, radioresistance of lung cancer remains a therapeutic hindrance. The aim of this study was to identify whether small ubiquitin-related modifier (SUMO)-specific protease 1 (SENP1) is a marker of radioresistance that may serve as a target for enhancing the efficacy of lung carcinoma radiotherapy. SENP1 was observed to be overexpressed in lung cancer tissues, and the modulation of SENP1 expression was demonstrated to significantly affect the proliferation of lung cancer cells. Moreover, silencing the expression of SENP1 using small interfering RNA (siRNA) significantly sensitized lung cancer cells to radiation. Mechanically, it was demonstrated that SENP1 depletion significantly enhanced ionizing radiation (IR)-induced cell cycle arrest, γ-H2AX expression and apoptosis. Thus, these data suggest that SENP1 may be a desirable drug target for lung carcinoma radiotherapy.

Protein sumoylation in brain development, neuronal morphology and spinogenesis

Small ubiquitin-like modifiers (SUMOs) are polypeptides resembling ubiquitin that are covalently attached to specific lysine residue of target proteins through a specific enzymatic pathway. Sumoylation is now seen as a key posttranslational modification involved in many biological processes, but little is known about how this highly dynamic protein modification is regulated in the brain. Disruption of the sumoylation enzymatic pathway during the embryonic development leads to lethality revealing a pivotal role for this protein modification during development. The main aim of this review is to briefly describe the SUMO pathway and give an overview of the sumoylation regulations occurring in brain development, neuronal morphology and synapse formation.

Sumoylation regulates nuclear localization and function of zinc finger transcription factor ZIC3

ZIC3, an X-linked zinc finger transcription factor, was the first identified gene involved in establishing normal left-right patterning in humans. Mutations in the Zic3 gene in patients cause heterotaxy, which includes congenital heart defects. However, very little is known about how the function of the ZIC3 protein is regulated. Sumoylation is a posttranslational modification process in which a group of small ubiquitin-like modifier (SUMO) proteins is covalently attached to targets via a series of enzymatic reactions. Here, we report for the first time that sumoylation targets human ZIC3 primarily on the consensus lysine residue K248, which is critical for the nuclear retention of ZIC3. Consequently, SUMO modification potentiates the repressive activity of ZIC3 on the promoter of its target gene cardiac α-actin, and the mutation of lysine 248 to arginine (K248R) abolishes its repressive function. We further revealed that ZIC3 variants with mutations found in human patients with congenital anomalies exhibit aberrant sumoylation activity, which at least partially accounts for their cytoplasmic diffusion. Improved sumoylation of human disease-associated ZIC3 variants reestablishes their nuclear occupancy in the presence of SUMO E3 ligase and SUMO-1. Thus, the altered sumoylation status of ZIC3 underpins the developmental abnormalities associated with these ZIC3 mutants. The SUMO targeting consensus sequence in ZIC3 is highly conserved in its paralogs and orthologs, pointing to sumoylation as a general mechanism underlying the functional control of ZIC proteins. This study provides a potential therapeutic strategy to regain the normal subcellular distribution and function of ZIC3 mutants by restoring SUMO conjugation.

AIP1 suppresses atherosclerosis by limiting hyperlipidemia-induced inflammation and vascular endothelial dysfunction

OBJECTIVE

Apoptosis signal-regulating kinase 1-interacting protein-1 (AIP1) is a signaling adaptor molecule implicated in stress and apoptotic signaling induced by proinflammatory mediators. However, its function in atherosclerosis has not been established. In the present study, we use AIP1-null (AIP1(-/-)) mice to examine its effect on atherosclerotic lesions in an apolipoprotein E-null (ApoE(-/-)) mouse model of atherosclerosis.

APPROACH AND RESULTS

ApoE(-/-) control mice developed atherosclerosis in the aortic roots and descending aortas on Western-type diet for 10 weeks, whereas the atherosclerotic lesions are significantly augmented in ApoE(-/-)AIP1(-/-) double knockout (DKO) mice. DKO mice show increases in plasma inflammatory cytokines with no significant alterations in body weight, total cholesterol levels, or lipoprotein profiles. Aortas in DKO mice show increased inflammation and endothelial cell (EC) dysfunction with nuclear factor-κB activity, correlating with increased accumulation of macrophages in the lesion area. Importantly, macrophages from DKO donors are not sufficient to augment inflammatory responses and atherogenesis when transferred to ApoE-KO recipients. Mechanistic studies suggest that AIP1 is highly expressed in aortic EC, but not in macrophages, and AIP1 deletion in EC significantly enhance oxidized low-density lipoprotein-induced nuclear factor-κB signaling, gene expression of inflammatory molecules, and monocyte adhesion, suggesting that vascular EC are responsible for the increased inflammatory responses observed in DKO mice.

CONCLUSIONS

Our data demonstrate that loss of AIP1 in aortic EC primarily contributes to the exacerbated lesion expansion in the ApoE(-/-)AIP1(-/-) mice, revealing an important role of AIP1 in limiting inflammation, EC dysfunction, and atherosclerosis.

The small ubiquitin-like modifier-deconjugating enzyme sentrin-specific peptidase 1 switches IFN regulatory factor 8 from a repressor to an activator during macrophage activation

Macrophages, when activated by IFN-γ and TLR signaling, elicit innate immune responses. IFN regulatory factor 8 (IRF8) is a transcription factor that facilitates macrophage activation and innate immunity. We show that, in resting macrophages, some IRF8 is conjugated to small ubiquitin-like modifiers (SUMO) 2/3 through the lysine residue 310. SUMO3-conjugated IRF8 failed to induce IL12p40 and other IRF8 target genes, consistent with SUMO-mediated transcriptional repression reported for other transcription factors. SUMO3-conjugated IRF8 showed reduced mobility in live nuclei and bound poorly to the IL12p40 gene. However, macrophage activation caused a sharp reduction in the amount of SUMOylated IRF8. This reduction coincided with the induction of a deSUMOylating enzyme, sentrin-specific peptidase 1 (SENP1), in activated macrophages. In transfection analysis, SENP1 removed SUMO3 from IRF8 and enhanced expression of IL12p40 and other target genes. Conversely, SENP1 knockdown repressed IRF8 target gene expression. In parallel with IRF8 deSUMOylation, macrophage activation led to the induction of proteins active in the SUMO pathway and caused a global shift in nuclear protein SUMOylation patterns. Together, the IRF8 SUMO conjugation/deconjugation switch is part of a larger transition in SUMO modifications that takes place upon macrophage activation, serving as a mechanism to trigger innate immune responses.

Lens epithelium-derived growth factor deSumoylation by Sumo-specific protease-1 regulates its transcriptional activation of small heat shock protein and the cellular response

Lens epithelium-derived growth factor (LEDGF), a ubiquitously expressed nuclear protein, acts by interacting with DNA and protein and is involved in widely varying cellular functions. Despite its importance, the mechanism(s) that regulate naturally occurring LEDGF activity are unidentified. In the present study, we report that LEDGF is constitutively Sumoylated, and that the dynamical regulatory mechanism(s) (i.e. Sumoylation and deSumoylation) act as a molecular switch in modulating the DNA-binding and transcriptional activity of LEDGF with the functional consequences. Using bioinformatics analysis coupled with in vitro and in vivo Sumoylation assays, we found that lysine (K) 364 of LEDGF was Sumoylated, repressing its transcriptional activity. Conversely, mutation of K364 to arginine (R) or deSumoylation by small ubiquitin-like modifier (Sumo)-specific protease-1, a nuclear deSumoylase, enhanced the transactivation capacity of LEDGF and its cellular abundance. The enhancements were directly correlated with an increase in the DNA-binding activity and small heat shock protein transcription of LEDGF, whereas the process was reversed in cells overexpressing Sumo1. Interestingly, cells expressing Sumoylation-deficient pEGFP-K364R protein showed increased cellular survival compared to wild-type LEDGF protein. The findings provide insights into the regulation and regulatory functions of LEDGF in Sumoylation-dependent transcriptional control that may be essential for modifying the physiology of cells to maintain cellular homeostasis. These studies also provide new evidence of the important role of post-translational modification in controlling LEDGF function.

SUMO-specific protease 1 promotes prostate cancer progression and metastasis

SUMO-specific protease 1 (SENP1) is a member of de-SUMOylation protease family and has an important role in the regulation of androgen receptor-dependent transcription and hypoxia signaling. This activity profile of SENP1 prompted us to investigate whether SENP1 is involved in the pathogenesis of prostate cancer. In previous studies, we have detected the overexpression of SENP1 in both precancerous prostate intraepithelial neoplasia (PIN) lesions and prostate cancer tissue samples from patients. Whereas our whole-animal model has demonstrated that SENP1 induction is critical for prostate cell transformation, the role of SENP1 in prostate cancer progression is still unknown. In this study, we show that SENP1 expression directly correlates with prostate cancer aggressiveness and reccurrence, by analyzing more than 150 prostate cancer specimens. Modulating SENP1 level dictates colony formation of prostate cancer cell lines, tumor growth in nude mice and also prostate cancer cell migration and invasion. Silencing SENP1 level in highly metastatic prostate cancer cells perturbs their ability to metastasize to the bone and initiates secondary tumors. Mechanistically, the expression of two critical bone remodeling proteins, matrix metalloproteinase 2 (MMP2) and MMP9, is regulated by SENP1 through the HIF1α signaling pathway. All these results show the contribution of SENP1 to the progression of prostate cancer, and suggest that SENP1 may be a prognostic marker and a therapeutic target for metastasis in prostate cancer patients.

SUMO-specific protease 1 is critical for early lymphoid development through regulation of STAT5 activation

Small ubiquitin-like modifier (SUMO) modification has emerged as an important regulatory mechanism during embryonic development. However, it is not known whether SUMOylation plays a role in the development of the immune system. Here, we show that SUMO-specific protease 1 (SENP1) is essential for the development of early T and B cells. STAT5, a key regulator of lymphoid development, is modified by SUMO-2 and is specifically regulated by SENP1. In the absence of SENP1, SUMO-2 modified STAT5 accumulates in early lymphoid precursors, resulting in a block in its acetylation and subsequent signaling. These results demonstrate a crucial role of SENP1 in the regulation of STAT5 activation during early lymphoid development.

Master regulatory GATA transcription factors: mechanistic principles and emerging links to hematologic malignancies

Numerous examples exist of how disrupting the actions of physiological regulators of blood cell development yields hematologic malignancies. The master regulator of hematopoietic stem/progenitor cells GATA-2 was cloned almost 20 years ago, and elegant genetic analyses demonstrated its essential function to promote hematopoiesis. While certain GATA-2 target genes are implicated in leukemogenesis, only recently have definitive insights emerged linking GATA-2 to human hematologic pathophysiologies. These pathophysiologies include myelodysplastic syndrome, acute myeloid leukemia and an immunodeficiency syndrome with complex phenotypes including leukemia. As GATA-2 has a pivotal role in the etiology of human cancer, it is instructive to consider mechanisms underlying normal GATA factor function/regulation and how dissecting such mechanisms may reveal unique opportunities for thwarting GATA-2-dependent processes in a therapeutic context. This article highlights GATA factor mechanistic principles, with a heavy emphasis on GATA-1 and GATA-2 functions in the hematopoietic system, and new links between GATA-2 dysregulation and human pathophysiologies.

Sumoylation of CCAAT/enhancer–binding protein α promotes the biased primitive hematopoiesis of zebrafish

Hematopoiesis is evolutionarily conserved from zebrafish to mammals, and this includes both primitive and definitive waves during embryogenesis. Primitive hematopoiesis is dominated by erythropoiesis with limited myelopoiesis. Protein sumoylation, a ubiquitination-like posttranslational protein modification, is implicated in a variety of biochemical processes, most notably in transcriptional repression. We show here that the loss of 6 small ubiquitin-related modifier (SUMO) paralogs triggers a sharp up-regulation of the myeloid-specific marker mpo and down-regulation of the erythroid-specific marker gata1 in myelo-erythroid progenitor cells (MPCs) in the intermediate cell mass (ICM) during primitive hematopoiesis. Accordingly, in transgenic zebrafish lines, hyposumoylation expands myelopoiesis at the expense of erythropoiesis. A SUMO–CCAAT/enhancer–binding protein α (SUMO-C/ebpα) fusion restores the normal myelopoiesis/erythropoiesis balance, suggesting that sumoylation status of C/ebpα contributes to myelo-erythroid lineage determination. Our results therefore implicate sumoylation in early lineage determination and reveal the possible molecular mechanism underlying the puzzling biased primitive hematopoiesis in vertebrates.

Networking erythropoiesis

A relatively small cadre of lineage-restricted transcription factors largely orchestrates erythropoiesis, but how these nuclear factors interact to regulate this complex biology is still largely unknown. However, recent technological advances, such as chromatin immunoprecipitation (ChIP) paired with massively parallel sequencing (ChIP-seq), gene expression profiling, and comprehensive bioinformatic analyses, offer new insights into the intricacies of red cell molecular circuits.