SUMOylation in Drosophila Development

SUMOylation of Warts kinase promotes neural stem cell reactivation

A delicate balance between neural stem cell (NSC) quiescence and proliferation is important for adult neurogenesis and homeostasis. Small ubiquitin-related modifier (SUMO)-dependent post-translational modifications cause rapid and reversible changes in protein functions. However, the role of the SUMO pathway during NSC reactivation and brain development is not established. Here, we show that the key components of the SUMO pathway play an important role in NSC reactivation and brain development in Drosophila. Depletion of SUMO/Smt3 or SUMO conjugating enzyme Ubc9 results in notable defects in NSC reactivation and brain development, while their overexpression leads to premature NSC reactivation. Smt3 protein levels increase with NSC reactivation, which is promoted by the Ser/Thr kinase Akt. Warts/Lats, the core protein kinase of the Hippo pathway, can undergo SUMO- and Ubc9-dependent SUMOylation at Lys766. This modification attenuates Wts phosphorylation by Hippo, leading to the inhibition of the Hippo pathway, and consequently, initiation of NSC reactivation. Moreover, inhibiting Hippo pathway effectively restores the NSC reactivation defects induced by SUMO pathway inhibition. Overall, our study uncovered an important role for the SUMO-Hippo pathway during Drosophila NSC reactivation and brain development.

Developmental stage-specific proteome analysis of the legume pod borer Maruca vitrata provides insights on relevant proteins

The spotted pod borer, Maruca vitrata (Lepidoptera: Crambidae) is a destructive insect pest that inflicts significant productivity losses on important leguminous crops. Unravelling insect proteomes is vital to comprehend their fundamental molecular mechanisms. This research delved into the proteome profiles of four distinct stages -three larval and pupa of M. vitrata, utilizing LC-MS/MS label-free quantification-based methods. Employing comprehensive proteome analysis with fractionated datasets, we mapped 75 % of 3459 Drosophila protein orthologues out of which 2695 were identified across all developmental stages while, 137 and 94 were exclusive to larval and pupal stages respectively. Cluster analysis of 2248 protein orthologues derived from MaxQuant quantitative dataset depicted six clusters based on expression pattern similarity across stages. Consequently, gene ontology and protein-protein interaction network analyses using STRING database identified cluster 1 (58 proteins) and cluster 6 (25 proteins) associated with insect immune system and lipid metabolism. Furthermore, qRT-PCR-based expression analyses of ten selected proteins-coding genes authenticated the proteome data. Subsequently, functional validation of these chosen genes through gene silencing reduced their transcript abundance accompanied by a marked increase in mortality among dsRNA-injected larvae. Overall, this is a pioneering study to effectively develop a proteome atlas of M. vitrata as a potential resource for crop protection programs.

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

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

Construction, expression, and in vitro assembly of virus-like particles of L1 protein of human papillomavirus type 52 in Escherichia coli BL21 DE3

Background

A major discovery in human etiology recognized that cervical cancer is a consequence of an infection caused by some mucosatropic types of human papillomavirus (HPV). Since L1 protein of HPV is able to induce the formation of neutralizing antibodies, it becomes a protein target to develop HPV vaccines. Therefore, this study aims to obtain and analyze the expression of HPV subunit recombinant protein, namely L1 HPV 52 in E. coli BL21 DE3. The raw material used was L1 HPV 52 protein, while the synthetic gene, which is measured at 1473 bp in pD451-MR plasmid, was codon-optimized (ATUM) and successfully integrated into 5643 base pairs (bps) of pETSUMO. Bioinformatic studies were also conducted to analyze B cell epitope, T cell epitope, and immunogenicity prediction for L1HPV52 protein.

Results

The pETSUMO-L1HPV52 construct was successfully obtained in a correct ligation size when it was cut with EcoRI. Digestion by EcoRI revealed a size of 5953 and 1160 bps for both TA cloning petSUMO vector and gene of interest, respectively. Furthermore, the right direction of construct pETSUMO-L1HPV52 was proven by PCR techniques using specific primer pairs then followed by sequencing, which shows 147 base pairs. Characterization of L1 HPV 52 by SDS-PAGE analysis confirms the presence of a protein band at a size of ~55 kDa with 6.12 mg/L of total protein concentration. Observation under by transmission electron microscope demonstrates the formation of VLP-L1 at a size between 30 and 40 nm in assembly buffer under the condition of pH 5.4. Based on bioinformatics studies, we found that there are three B cell epitopes (GFPDTSFYNPET, DYLQMASEPY, KEKFSADLDQFP) and four T cell epitopes (YLQMASEPY, PYGDSLFFF, DSLFFFLRR, MFVRHFFNR). Moreover, an immunogenicity study shows that among all the T cell epitopes, the one that has the highest affinity value is DSLFFFLRR for Indonesian HLAs.

Conclusion

Regarding the achievement on successful formation of L1 HPV52-VLPs, followed by some possibilities found from bioinformatics studies, this study suggests promising results for future development of L1 HPV type 52 vaccine in Indonesia.

Drosophila H2Av negatively regulates the activity of the IMD pathway via facilitating Relish SUMOylation

Insects depend on the innate immune response for defense against a wide array of pathogens. Central to Drosophila immunity are antimicrobial peptides (AMPs), released into circulation when pathogens trigger either of the two widely studied signal pathways, Toll or IMD. The Toll pathway responds to infection by Gram-positive bacteria and fungi while the IMD pathway is activated by Gram-negative bacteria. During activation of the IMD pathway, the NF-κB-like transcription factor Relish is phosphorylated and then cleaved, which is crucial for IMD-dependent AMP gene induction. Here we show that loss-of-function mutants of the unconventional histone variant H2Av upregulate IMD-dependent AMP gene induction in germ-free Drosophila larvae and adults. After careful dissection of the IMD pathway, we found that Relish has an epistatic relationship with H2Av. In the H2Av mutant larvae, SUMOylation is down-regulated, suggesting a possible role of SUMOylation in the immune phenotype. Eventually we demonstrated that Relish is mostly SUMOylated on amino acid K823. Loss of the potential SUMOylation site leads to significant auto-activation of Relish in vivo. Further work indicated that H2Av regulates Relish SUMOylation after physically interacting with Su(var)2-10, the E3 component of the SUMOylation pathway. Biochemical analysis suggested that SUMOylation of Relish prevents its cleavage and activation. Our findings suggest a new mechanism by which H2Av can negatively regulate, and thus prevent spontaneous activation of IMD-dependent AMP production, through facilitating SUMOylation of the NF-κB like transcription factor Relish.

Toll and IMD signaling pathways should be involved in the production of antimicrobial peptides in animals upon infection. Immunity responses are energy consuming. Thus, these two pathways are fine-tuned. Animal H2A variant histones are involved in many physiological functions. In Drosophila, the production of antibacterial peptides is out of control in the mutant of H2A variant (H2Av⁸¹⁰). After careful examination, we found that Relish, the transcription factor of the IMD pathway, was activated in this mutant. Eventually we demonstrate that Relish can be SUMOylated with the involvement of H2Av. Loss of the main SUMOylation site in Relish induces it to auto-activate following over-expression. Therefore, H2Av is a negative regulator of the IMD signaling pathway by maintaining the normal level of Relish SUMOylation in Drosophila.

Intrinsically Disordered Proteins as Regulators of Transient Biological Processes and as Untapped Drug Targets

Intrinsically disordered proteins (IDPs) are critical players in the dynamic control of diverse cellular processes, and provide potential new drug targets because their dysregulation is closely related to many diseases. This review focuses on several medicinal studies that have identified low-molecular-weight inhibitors of IDPs. In addition, clinically relevant liquid-liquid phase separations-which critically involve both intermolecular interactions between IDPs and their posttranslational modification-are analyzed to understand the potential of IDPs as new drug targets.

SON protects nascent transcripts from unproductive degradation by counteracting DIP1

Gene expression involves the transcription and splicing of nascent transcripts through the removal of introns. In Drosophila, a double-stranded RNA binding protein Disco-interacting protein 1 (DIP1) targets INE-1 stable intronic sequence RNAs (sisRNAs) for degradation after splicing. How nascent transcripts that also contain INE-1 sequences escape degradation remains unknown. Here we observe that these nascent transcripts can also be bound by DIP1 but the Drosophila homolog of SON (Dsn) protects them from unproductive degradation in ovaries. Dsn localizes to the satellite body where active decay of INE-1 sisRNAs by DIP1 occurs. Dsn is a repressor of DIP1 posttranslational modifications (primarily sumoylation) that are assumed to be required for efficient DIP1 activity. Moreover, the pre-mRNA destabilization caused by Dsn depletion is rescued in DIP1 or Sumo heterozygous mutants, suggesting that Dsn is a negative regulator of DIP1. Our results reveal that under normal circumstances nascent transcripts are susceptible to DIP1-mediated degradation, however intronic sequences are protected by Dsn until intron excision has taken place.

Screening and verification for proteins that interact with leucine aminopeptidase of Taenia pisiformis using a yeast two-hybrid system

Leucine aminopeptidase of Taenia pisiformis (TpLAP) belonging to the M17 peptidase family has been implicated as a stage-differentially expressed protein in the adult stage of T. pisiformis. In order to further dissect the biological functions of TpLAP in the growth and development of adult worms, TpLAP-interacting partners were investigated. In this study, a yeast two-hybrid (Y2H) cDNA library from adult T. pisiformis was constructed. Using pGBKT7-TpLAP as bait, proteins interacting with TpLAP were screened by Y2H system and positive preys were sequenced and analyzed using the Basic Local Alignment Search Tool (BLAST). Our results showed that six genuine TpLAP-interacting proteins, including LAP, dynein light chain (DLC), SUMO-conjugating enzyme (UBC9), histone-lysine n-methyltransferase, trans-acting transcriptional, and one unknown protein, were identified via Y2H assay. Furthermore, the interaction between TpLAP and UBC9 of T. pisiformis (TpUBC9), an important protein involved in SUMOylation pathway, was further validated by one-to-one Y2H assay, co-immunoprecipitation, and confocal analysis. These findings provide a deeper understanding of the biological functions of TpLAP and offer the first clue that TpLAP may act as a novel SUMOylated substrate, suggesting that the SUMO modification pathway plays an important role in regulation of adult worm growth and development.

Ubc9 deficiency selectively impairs the functionality of common lymphoid progenitors (CLPs) during bone marrow hematopoiesis

Hematopoietic development occurs in the bone marrow, and this process begins with hematopoietic stem cells (HSCs). Ubc9 is a unique E2-conjugating enzyme required for SUMOylation, an evolutionarily conserved post-translational modification system. We herein show that a conditional Ubc9 deletion in the hematopoietic system caused decreased thymus weight and reduced lymphocyte to myeloid cell ratio. Importantly, Ubc9 deletion in the hematopoietic system only selectively impaired the development of common lymphoid progenitors (CLPs) in the bone marrow and perturbed their potential to differentiate into lymphocytes, thereby decreasing the number of T/B cells in the periphery. Ubc9 was found to be required for CLP viability, and therefore, Ubc9 deficiency rendered CLPs to undergo apoptosis and attenuated their proliferation. Thus, Ubc9 plays a critical role in the regulation of CLP function during hematopoietic development in the bone marrow.

NMR characterization of conformational fluctuations and noncovalent interactions of SUMO protein from Drosophila melanogaster (dSmt3)

Structural heterogeneity in the native-state ensemble of dSmt3, the only small ubiquitin-like modifier (SUMO) in Drosophila melanogaster, was investigated and compared with its human homologue SUMO1. Temperature dependence of amide proton's chemical shift was studied to identify amino acids possessing alternative structural conformations in the native state. Effect of small concentration of denaturant (1M urea) on this population was also monitored to assess the ruggedness of near-native energy landscape. Owing to presence of many such amino acids, especially in the β₂ -loop-α region, the native state of dSmt3 seems more flexible in comparison to SUMO1. Information about backbone dynamics in ns-ps timescale was quantified from the measurement of ¹⁵ N-relaxation experiments. Furthermore, the noncovalent interaction of dSmt3 and SUMO1 with Daxx12 (Daxx⁷²⁹ DPEEIIVLSDSD⁷⁴⁰ ), a [V/I]-X-[V/I]-[V/I]-based SUMO interaction motif, was characterized using Bio-layer Interferometery and NMR spectroscopy. Daxx12 fits itself in the groove formed by β₂ -loop-α structural region in both dSmt3 and SUMO1, but the binding is stronger with the former. Flexibility of β₂ -loop-α region in dSmt3 is suspected to assist its interaction with Daxx12. Our results highlight the role of native-state flexibility in assisting noncovalent interactions of SUMO proteins especially in organisms where a single SUMO isoform has to tackle multiple substrates single handedly.

The Biology of SUMO-Targeted Ubiquitin Ligases in Drosophila Development, Immunity, and Cancer

The ubiquitin and SUMO (small ubiquitin-like modifier) pathways modify proteins that in turn regulate diverse cellular processes, embryonic development, and adult tissue physiology. These pathways were originally discovered biochemically in vitro, leading to a long-standing challenge of elucidating both the molecular cross-talk between these pathways and their biological importance. Recent discoveries in Drosophila established that ubiquitin and SUMO pathways are interconnected via evolutionally conserved SUMO-targeted ubiquitin ligase (STUbL) proteins. STUbL are RING ubiquitin ligases that recognize SUMOylated substrates and catalyze their ubiquitination, and include Degringolade (Dgrn) in Drosophila and RNF4 and RNF111 in humans. STUbL are essential for early development of both the fly and mouse embryos. In the fly embryo, Dgrn regulates early cell cycle progression, sex determination, zygotic gene transcription, segmentation, and neurogenesis, among other processes. In the fly adult, Dgrn is required for systemic immune response to pathogens and intestinal stem cell regeneration upon infection. These functions of Dgrn are highly conserved in humans, where RNF4-dependent ubiquitination potentiates key oncoproteins, thereby accelerating tumorigenesis. Here, we review the lessons learned to date in Drosophila and highlight their relevance to cancer biology.

Structural and functional analysis of SMO-1, the SUMO homolog in Caenorhabditis elegans

SUMO proteins are important post-translational modifiers involved in multiple cellular pathways in eukaryotes, especially during the different developmental stages in multicellular organisms. The nematode C. elegans is a well known model system for studying metazoan development and has a single SUMO homolog, SMO-1. Interestingly, SMO-1 modification is linked to embryogenesis and development in the nematode. However, high-resolution information about SMO-1 and the mechanism of its conjugation is lacking. In this work, we report the high-resolution three dimensional structure of SMO-1 solved by NMR spectroscopy. SMO-1 has flexible N-terminal and C-terminal tails on either side of a rigid beta-grasp folded core. While the sequence of SMO-1 is more similar to SUMO1, the electrostatic surface features of SMO-1 resemble more with SUMO2/3. SMO-1 can bind to typical SUMO Interacting Motifs (SIMs). SMO-1 can also conjugate to a typical SUMOylation consensus site as well as to its natural substrate HMR-1. Poly-SMO-1 chains were observed in-vitro even though SMO-1 lacks any consensus SUMOylation site. Typical deSUMOylation enzymes like Senp2 can cleave the poly-SMO-1 chains. Despite being a single gene, the SMO-1 structure allows it to function in a large repertoire of signaling pathways involving SUMO in C. elegans. Structural and functional features of SMO-1 studies described here will be useful to understand its role in development.

SUMO regulates the activity of Smoothened and Costal-2 in Drosophila Hedgehog signaling

In Hedgehog (Hh) signaling, the GPCR-family protein Smoothened (Smo) acts as a signal transducer that is regulated by phosphorylation and ubiquitination, which ultimately change the cell surface accumulation of Smo. However, it is not clear whether Smo is regulated by other post-translational modifications, such as sumoylation. Here, we demonstrate that knockdown of the small ubiquitin-related modifier (SUMO) pathway components Ubc9 (a SUMO-conjugating enzyme E2), PIAS (a SUMO-protein ligase E3), and Smt3 (the SUMO isoform in Drosophila) by RNAi prevents Smo accumulation and alters Smo activity in the wing. We further show that Hh-induced-sumoylation stabilizes Smo, whereas desumoylation by Ulp1 destabilizes Smo in a phosphorylation independent manner. Mechanistically, we discover that excessive Krz, the Drosophila β-arrestin 2, inhibits Smo sumoylation and prevents Smo accumulation through Krz regulatory domain. Krz likely facilitates the interaction between Smo and Ulp1 because knockdown of Krz by RNAi attenuates Smo-Ulp1 interaction. Finally, we provide evidence that Cos2 is also sumoylated, which counteracts its inhibitory role on Smo accumulation in the wing. Taken together, we have uncovered a novel mechanism for Smo activation by sumoylation that is regulated by Hh and Smo interacting proteins.

SUMO in Drosophila Development

The ubiquitin -like protein SUMO is conjugated covalently to hundreds of target proteins in organisms throughout the eukaryotic domain. Genetic and biochemical studies using the model organism Drosophila melanogaster are beginning to reveal many essential functions for SUMO in cell biology and development. For example, SUMO regulates multiple signaling pathways such as the Ras/MAPK, Dpp, and JNK pathways. In addition, SUMO regulates transcription through conjugation to many transcriptional regulatory proteins, including Bicoid, Spalt , Scm, and Groucho. In some cases, conjugation of SUMO to a target protein inhibits its normal activity, while in other cases SUMO conjugation stimulates target protein activity. SUMO often modulates a biological process by altering the subcellular localization of a target protein. The ability of SUMO and other ubiquitin-like proteins to diversify protein function may be critical to the evolution of developmental complexity.

Characterisation and expression analysis of UBC9 and UBS27 genes in developing gonads of cicindelids (Coleoptera: Cicindelidae)

Ubiquitin and small ubiquitin-like modifiers (SUMO) are post-translational modifiers essential in a variety of cellular processes, including gametogenesis. SUMO-conjugating enzyme (UBC9) and the ubiquitin ribosomal fusion protein UBS27 have been characterised in several model species. However, their expression in coleopteran remains unstudied. In this study, UBC9 and UBS27 genes have been characterised in the tiger beetle Cicindela campestris for the first time. Bioinformatic analysis showed that the Cc-UBC9 gene encoded a 159 amino acid protein with a predicted molecular weight of 18.18kDa, and the Cc-UBS27 gene encoded a 156 amino acid protein with a predicted molecular weight of 17.71kDa. Selection analyses carried out in several cicindelid species revealed that both genes were affected by purifying selection. Real time quantitative PCR analysis demonstrated that Cc-UBC9 and Cc-UBS27 were expressed in different tissues. The highest expression on both genes was found in the ovary and testis, and there were differential expression levels between immature and mature stages of testis development. The expression patterns of Cc-UBC9 and Cc-UBS27 suggest that these genes play important roles in gametogenesis in C. campestris. This information is relevant to better understand the reproductive process in cicindelids and the function of ubiquitin and small ubiquitin-related modifier genes in the Coleoptera.

UHRF1 regulation of Dnmt1 is required for pre-gastrula zebrafish development

Landmark epigenetic events underlie early embryonic development, yet how epigenetic modifiers are regulated to achieve rapid epigenome re-patterning is not known. Uhrf1 and DNA methyltransferase 1 (Dnmt1) are known to largely mediate maintenance DNA methylation and Uhrf1 is also required for both Dnmt1 localization and stability. Here, we investigate how these two key epigenetic modifiers regulate early zebrafish development and characterize the developmental consequences of disrupting their homeostatic relationship. Unlike Uhrf1 knockdown, which causes developmental arrest and death prior to gastrulation, overexpression of human UHRF1 (WT-UHRF1) caused asymmetric epiboly, inefficient gastrulation and multi-systemic defects. UHRF1 phosphorylation was previously demonstrated as essential for zebrafish embryogenesis, and we found that penetrance of the asymmetric epiboly phenotype was significantly increased in embryos injected with mRNA encoding non-phosphorylatable UHRF1 (UHRF1(S661A)). Surprisingly, both WT-UHRF1 and UHRF1(S661A) overexpression caused DNA hypomethylation. However, since other approaches that caused an equivalent degree of DNA hypomethylation did not cause the asymmetric epiboly phenotype, we conclude that bulk DNA methylation is not the primary mechanism. Instead, UHRF1(S661A) overexpression resulted in accumulation of Dnmt1 protein and the overexpression of both WT and a catalytically inactive Dnmt1 phenocopied the assymetric epiboly phenotype. Dnmt1 knockdown suppressed the phenotype caused by UHRF1(S661A) overexpression, and Uhrf1 knockdown suppressed the effect of Dnmt1 overexpression. Therefore, we conclude that the interaction between these two proteins is the mechanism underlying the gastrulation defects. This indicates that Dnmt1 stability requires UHRF1 phosphorylation and that crosstalk between the proteins is essential for the function of these two important epigenetic regulators during gastrulation.

SUMO regulates somatic cyst stem cells maintenance and directly targets hedgehog pathway in adult Drosophila testis

SUMO (Small ubiquitin-related modifier) modification (SUMOylation) is a highly dynamic post-translational modification (PTM) playing important roles in tissue development and disease progression. However, its function in adult stem cell maintenance is largely unknown. Here we report the function of SUMOylation in somatic cyst stem cells (CySCs) self-renewal in adult Drosophila testis. The SUMO pathway cell-autonomously regulates CySCs maintenance. Reduction of SUMOylation promotes premature differentiation of CySCs and impedes the proliferation of CySCs, which finally reduce the number of CySCs. Consistently, CySC clones carrying mutation of the SUMO conjugating enzyme are rapidly lost. Furthermore, inhibition of SUMO pathway phenocopies the disruption of Hedgehog (Hh) pathway, and can block the promoted proliferation of CySCs by Hh activation. Importantly, SUMO pathway directly regulates the SUMOylation of Hh pathway transcriptional factor, Cubitus interruptus (Ci), which is required for promoting CySCs proliferation. Thus, we conclude that SUMO directly targets Hh pathway and regulates CySCs maintenance in adult Drosophila testis.

A conserved SUMOylation signaling for cell cycle control in a holocentric species Bombyx mori

SUMOylation is an essential post-translational modification that regulates a variety of cellular processes including cell cycle progression. Although the SUMOylation pathway has been identified and investigated in many eukaryotes, the mechanisms of SUMOylation in regulating the functions of various substrates are still poorly understood. Here, we utilized a model species, the silkworm Bombyx mori that possesses holocentric chromosomes, to exploit the role of the SUMOylation system in cell cycle regulation. We identified all the components that are involved in the SUMOylation pathway in the silkworm genome. Our data revealed a cell cycle-dependent transcription of the SUMOylation genes, localization of the SUMOylation proteins, and abundance of the SUMOylation substrates in cultured silkworm cells. Importantly, the proliferation of the silkworm cells was strikingly inhibited by interference with SUMOylation genes expression, possibly due to an arrest of the SUMOylation-deficient cells at the G2/M phase. Furthermore, disruption of the SUMOylation genes induced the defects of holocentric chromosome congression and segregation during mitosis, which was consistent with high expressions of the SUMOylation genes and high enrichments of global SUMOylation at this stage, suggesting that the SUMOylation system in silkworm is essential for cell cycle regulation, with one particular role in mitosis.

SUMO as a solubility tag and in vivo cleavage of SUMO fusion proteins with Ulp1

Expression of proteins in E. coli is often plagued by insolubility of the protein of interest. A solution to this problem is the expression of proteins as fusions to solubility tags such as the SUMO protein. SUMO fusion proteins can be cleaved to remove the SUMO moiety using SUMO-specific proteases such as Ulp1. Here, we describe the use of vectors for the expression of recombinant proteins in E. coli as fusions to the Drosophila SUMO protein. This includes a vector that encodes not only the SUMO tagged protein of interest but also SUMO-tagged Ulp1. Coexpression of these two proteins results in the in vivo cleavage of the protein of interest from the SUMO tag, while still leaving the protein of interest in a form that can be purified from a soluble cell lysate by nickel affinity chromatography.

Regulation of Toll signaling and inflammation by β-arrestin and the SUMO protease Ulp1

The Toll signaling pathway has a highly conserved function in innate immunity and is regulated by multiple factors that fine tune its activity. One such factor is β-arrestin Kurtz (Krz), which we previously implicated in the inhibition of developmental Toll signaling in the Drosophila melanogaster embryo. Another level of controlling Toll activity and immune system homeostasis is by protein sumoylation. In this study, we have uncovered a link between these two modes of regulation and show that Krz affects sumoylation via a conserved protein interaction with a SUMO protease, Ulp1. Loss of function of krz or Ulp1 in Drosophila larvae results in a similar inflammatory phenotype, which is manifested as increased lamellocyte production; melanotic mass formation; nuclear accumulation of Toll pathway transcriptional effectors, Dorsal and Dif; and expression of immunity genes, such as Drosomycin. Moreover, mutations in krz and Ulp1 show dosage-sensitive synergistic genetic interactions, suggesting that these two proteins are involved in the same pathway. Using Dorsal sumoylation as a readout, we found that altering Krz levels can affect the efficiency of SUMO deconjugation mediated by Ulp1. Our results demonstrate that β-arrestin controls Toll signaling and systemic inflammation at the level of sumoylation.