SENP1 and SENP2 affect spatial and temporal control of sumoylation in mitosis

Sumoylation of centromere, kinetochore, and other mitotic chromosome-associated proteins is essential for chromosome segregation. The mechanisms regulating spatial and temporal sumoylation of proteins in mitosis, however, are not well understood. Here we show that the small ubiquitin-related modifier (SUMO)–specific isopeptidases SENP1 and SENP2 are targeted to kinetochores in mitosis. SENP2 targeting occurs through a mechanism dependent on the Nup107-160 subcomplex of the nuclear pore complex and is modulated through interactions with karyopherin α. Overexpression of SENP2, but not other SUMO-specific isopeptidases, causes a defect in chromosome congression that depends on its precise kinetochore targeting. By altering SENP1 kinetochore associations, however, this effect on chromosome congression could be phenocopied. In contrast, RNA interference–mediated knockdown of SENP1 delays sister chromatid separation at metaphase, whereas SENP2 knockdown produces no detectable phenotypes. Our findings indicate that chromosome segregation depends on precise spatial and temporal control of sumoylation in mitosis and that SENP1 and SENP2 are important mediators of this control.     

Structure of the human SENP7 catalytic domain and poly-SUMO deconjugation activities for SENP6 and SENP7

Small ubiquitin-like modifier (SUMO) proteases regulate the abundance and lifetime of SUMO-conjugated substrates by antagonizing reactions catalyzed by SUMO-conjugating enzymes. Six SUMO proteases constitute the human SENP/ULP protease family (SENP1-3 and SENP5-7). SENP6 and SENP7 include the most divergent class of SUMO proteases, which also includes the yeast enzyme ULP2. We present the crystal structure of the SENP7 catalytic domain at a resolution of 2.4 angstroms. Comparison with structures of human SENP1 and SENP2 reveals unique elements that differ from previously characterized structures of SUMO-deconjugating enzymes. Biochemical assays show that SENP6 and SENP7 prefer SUMO2 or SUMO3 in deconjugation reactions with rates comparable with those catalyzed by SENP2, particularly during cleavage of di-SUMO2, di-SUMO3, and poly-SUMO chains composed of SUMO2 or SUMO3. In contrast, SENP6 and SENP7 exhibit lower rates for processing pre-SUMO1, pre-SUMO2, or pre-SUMO3 in comparison with SENP2. Structure-guided mutational analysis reveals elements unique to the SENP6 and SENP7 subclass of SENP/ULP proteases that contribute to protease function during deconjugation of poly-SUMO chains.     

The SUMO proteases SENP1 and SENP2 play a critical role in nucleoporin homeostasis and nuclear pore complex function

Nuclear pore complexes are composed of ∼30 different proteins, each present at the pore in multiple copies. Together these proteins create specialized channels that convey cargo between the cytoplasm and the nuclear interior. With the building blocks of nuclear pores identified, one challenge is to decipher how these proteins are coordinately produced and assembled into macromolecular pore structures with each cell division. Specific individual pore proteins and protein cofactors have been probed for their role in the assembly process, as well as certain kinases that add a layer of regulation via the phosphorylation status of nucleoporins. Other posttranslational modifications are candidates for coordinating events of pore assembly as well. In this study of two pore-associated small ubiquitin-like modifier (SUMO) proteases, sentrin/SUMO-specific protease 1 (SENP1) and SENP2, we observe that many nucleoporins are mislocalized and, in some cases, reduced in level when SENP1 and SENP2 are codepleted. The pore complexes present under these conditions are still capable of transport, although the kinetics of specific cargo is altered. These results reveal a new role for the pore-associated SENPs in nucleoporin homeostasis and in achieving proper configuration of the nuclear pore complex.     

Lessons from the clinical trials of interleukin-2

The initial results of interleukin-2 (IL-2) therapy in man are reviewed from the perspective of how they conform to predictions from preclinical studies. These preclinical models predict that tumors will vary in their susceptibility to IL-2 therapy and will be most successfully treated at lower tumor burdens. In addition, the dose and schedule of IL-2 are important for successful therapy. Host-related factors, including the presence of suppressor activities, may also be important. In these models, the addition of other cytokines, including interferon-alpha or tumor necrosis factor, to IL-2 can enhance antitumor activity. The concomitant administration of ex vivo IL-2-activated lymphokine-activated killer cells or tumor-infiltrating lymphocytes also enhances the IL-2 antitumor effect. Clinical trials addressing all of these issues have been completed or are underway; the results suggest overall that the preclinical models are predictive, with both host- and tumor-related factors as well as such IL-2-therapy-related factors as dose, schedule, route and the use of additional agents all playing a role in the success of therapy. A more complete understanding of the mechanisms of response and resistance involved in this therapy will facilitate the rational development of more effective and less toxic IL-2-based therapy of human malignancy.     

Mitochondrial SENP2 regulates the assembly of SDH complex under metabolic stress

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SENP1与前列腺癌

SUMO (small ubiquitin-related modifier)是一种小泛素相关修饰物,能共价结合许多调控基因转录的重要蛋白,包括转录因子、转录辅助因子等．SUMO化修饰对蛋白-蛋白之间的相互作用、亚细胞定位、基因转录的活性以及靶蛋白的稳定性等具有重要的调节作用． SUMO化修饰是一个动态可逆的过程,将SUMO从靶蛋白上去除,称为去SUMO化（desumoylation）,去SUMO化是SUMO特异蛋白酶（SUMO-specific proteases,SENPｓ）的主要功能．由于SUMO化是近几年才发现的一种新的蛋白质翻译后修饰系统,对其生物学功能还不十分清楚．前列腺癌是男性最常见的恶性肿瘤,最近的研究发现,SENP1在前列腺癌细胞中高表达,而且雄激素能诱导SENP1的表达,表明SENP1与前列腺癌的发生、发展密切相关．在本篇综述中,我们将就SENP1作一介绍．     

RanBP2 and SENP3 function in a mitotic SUMO2/3 conjugation-deconjugation cycle on Borealin

The ubiquitin-like SUMO system controls cellular key functions, and several lines of evidence point to a critical role of SUMO for mitotic progression. However, in mammalian cells mitotic substrates of sumoylation and the regulatory components involved are not well defined. Here, we identify Borealin, a component of the chromosomal passenger complex (CPC), as a mitotic target of SUMO. The CPC, which additionally comprises INCENP, Survivin, and Aurora B, regulates key mitotic events, including chromosome congression, the spindle assembly checkpoint, and cytokinesis. We show that Borealin is preferentially modified by SUMO2/3 and demonstrate that the modification is dynamically regulated during mitotic progression, peaking in early mitosis. Intriguingly, the SUMO ligase RanBP2 interacts with the CPC, stimulates SUMO modification of Borealin in vitro, and is required for its modification in vivo. Moreover, the SUMO isopeptidase SENP3 is a specific interaction partner of Borealin and catalyzes the removal of SUMO2/3 from Borealin. These data thus delineate a mitotic SUMO2/3 conjugation–deconjugation cycle of Borealin and further assign a regulatory function of RanBP2 and SENP3 in the mitotic SUMO pathway.     

Structural Basis for the SUMO2 Isoform Specificity of SENP7

SUMO proteases or deSUMOylases regulate the lifetime of SUMO-conjugated targets in the cell by cleaving off the isopetidic bond between the substrate and the SUMO modifier, thus reversing the conjugation activity of the SUMO E3 ligases. In humans the deSUMOylating activity is mainly conducted by the SENP/ULP protease family, which is constituted of six members sharing a homologous catalytic globular domain. SENP6 and SENP7 are the most divergent members of the family and they show a unique SUMO2/3 isoform preference and a particular activity for dismantling polySUMO2 chains. Here, we present the crystal structure of the catalytic domain of human SENP7 bound to SUMO2, revealing structural key elements for the SUMO2 isoform specificity of SENP7. In particular, we describe the specific contacts between SUMO2 and a unique insertion in SENP7 (named Loop1) that is responsible for the SUMO2 isoform specificity. All the other interface contacts between SENP7 and SUMO2, including the SUMO2 C-terminal tail interaction, are conserved among members of the SENP/ULP family. Our data give insight into an evolutionary adaptation to restrict the deSUMOylating activity in SENP6 and SENP7 for the SUMO2/3 isoforms.     

SENP3 Suppresses Osteoclastogenesis by De-conjugating SUMO2/3 from IRF8 in Bone Marrow-Derived Monocytes

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Lessons from 1950

Second-trimester maternal serum screening is a noninvasive means of identifying pregnant women at an increased risk for various conditions including a fetus with open spina bifida, fetal Down syndrome, trisomy 18, multiple gestation, and adverse pregnancy outcome. Combinations of several different markers are available for screening. These include alpha-fetoprotein, human chorionic gonadotropin, and unconjugated estriol. In this review, we discuss the benefits and limitations of the screening tests and the suggested protocols for the care of patients.     

Swapping small ubiquitin-like modifier (SUMO) isoform specificity of SUMO proteases SENP6 and SENP7

SUMO proteases can regulate the amounts of SUMO-conjugated proteins in the cell by cleaving off the isopeptidic bond between SUMO and the target protein. Of the six members that constitute the human SENP/ULP protease family, SENP6 and SENP7 are the most divergent members in their conserved catalytic domain. The SENP6 and SENP7 subclass displays a clear proteolytic cleavage preference for SUMO2/3 isoforms. To investigate the structural determinants for such isoform specificity, we have identified a unique sequence insertion in the SENP6 and SENP7 subclass that is essential for their proteolytic activity and that forms a more extensive interface with SUMO during the proteolytic reaction. Furthermore, we have identified a region in the SUMO surface determinant for the SUMO2/3 isoform specificity of SENP6 and SENP7. Double point amino acid mutagenesis on the SUMO surface allows us to swap the specificity of SENP6 and SENP7 between the two SUMO isoforms. Structure-based comparisons combined with biochemical and mutagenesis analysis have revealed Loop 1 insertion in SENP6 and SENP7 as a platform to discriminate between SUMO1 and SUMO2/3 isoforms in this subclass of the SUMO protease family.     

Structural basis for SENP2 protease interactions with SUMO precursors and conjugated substrates

SUMO processing and deconjugation are essential proteolytic activities for nuclear metabolism and cell-cycle progression in yeast and higher eukaryotes. To elucidate the mechanisms used during substrate lysine deconjugation, SUMO isoform processing and SUMO isoform interactions, X-ray structures were determined for a catalytically inert SENP2 protease domain in complex with conjugated RanGAP1-SUMO-1 or RanGAP1-SUMO-2, or in complex with SUMO-2 or SUMO-3 precursors. Common features within the active site include a 90 degrees kink proximal to the scissile bond that forces C-terminal amino acid residues or the lysine side chain toward a protease surface that appears optimized for lysine deconjugation. Analysis of this surface reveals SENP2 residues, particularly Met497, that mediate, and in some instances reverse, in vitro substrate specificity. Mutational analysis and biochemistry provide a mechanism for SENP2 substrate preferences that explains why SENP2 catalyzes SUMO deconjugation more efficiently than processing.     

Lessons on pattern formation from planet WATOR

It is well known that if reacting species experience unequal diffusion rates, then dynamics that lead to a constant steady state in a "well-mixed" environment can in a spatial setting lead to interesting patterns. In this paper, we focus on complementary pattern formation mechanisms that operate even when the diffusion rates are equal. In particular, we can say that when the mean-field ODE has an attracting periodic orbit then the stochastic spatial model will have large-scale spatial structures in equilibrium. We explore this mechanism in depth through the dynamics of the simulator WATOR.     

Association of the human SUMO-1 protease SENP2 with the nuclear pore

SUMO-1 is a small ubiquitin-like protein that can be covalently conjugated to other proteins. A family of proteases catalyzes deconjugation of SUMO-1-containing species. Members of this family also process newly synthesized SUMO-1 into its conjugatable form. To understand these enzymes better, we have examined the localization and behavior of the human SUMO-1 protease SENP2. Here we have shown that SENP2 associates with the nuclear face of nuclear pores and that this association requires protein sequences near the N terminus of SENP2. We have also shown that SENP2 binds to Nup153, a nucleoporin that is localized to the nucleoplasmic face of the pore. Nup153 binding requires the same domain of SENP2 that mediates its targeting in vivo. Removal of the Nup153-interacting region of SENP2 results in a significant change in the spectrum of SUMO-1 conjugates within the cell. Our results suggest that association with the pore plays an important negative role in the regulation of SENP2, perhaps by restricting its activity to a subset of the conjugated proteins within the nucleus.