Quantitative ubiquitylome analysis and crosstalk with proteome/acetylome analysis identified novel pathways and targets of perifosine treatment in neuroblastoma

ALKB homolog 5 (ALKBH5)-induced circPUM1 upregulation facilitated the progression of neuroblastoma via miR-423-5p/PA2G4 axis

BACKGROUND

The oncogenic role of circPUM1 has been revealed in multiple cancers. Nevertheless, the specific role and molecular mechanism of circPUM1 in neuroblastoma (NB) have never been reported.

METHODS

The expression of genes was detected using RT-qPCR and Western Blot assay. The proliferation, migration, and invasion of NB cells were evaluated by CCK-8 and Transwell assays. Besides, mouse model was established to evaluate the effect of circPUM1 on the progression of NB. The interaction among genes was verified through RIP, MeRIP, or Luciferase reporter assay.

RESULTS

Through our investigation, it was discovered that circPUM1 expression was abnormally elevated in NB tissues and the abundance of circPUM1 was correlated with unfavorable clinical outcomes in NB patients. Besides, the viability and mobility of NB cells as well as NB tumor growth were suppressed by silencing circPUM1. Moreover, bioinformatics prediction and experimental verification demonstrated that circPUM1 was a sponge for miR-423-5p which further targeted proliferation-associated protein 2G4 (PA2G4). The oncogenic effect of circPUM1 on NB was exerted through suppressing miR-423-5p to elevate PA2G4 expression. Finally, we investigated the transcriptional factor causing the upregulation of circPUM1 in NB. The result was that ALKB homolog 5 (ALKBH5), an m6A demethylase, suppressed the m6A modification of circPUM1 and caused the elevation of circPUM1 expression in NB.

CONCLUSION

ALKBH5 induced the upregulation of circPUM1 to accelerate the development of NB through regulating miR-423-5p/PA2G4 axis.

Quantitative ubiquitylome crosstalk with proteome analysis revealed cytoskeleton proteins influence CLas pathogen infection in Diaphorina citri

Huanglongbing (HLB), also known as citrus greening disease, is caused by Candidatus Liberbacter asiaticus (CLas) and transmitted by Diaphorina citri. Previous studies reported that CLas infection significantly influences the structure of the D. citri cytoskeleton. However, the mechanisms through which CLas manipulates cytoskeleton-related proteins remain unclear. In this study, we performed quantitative ubiquitylome crosstalk with the proteome to reveal the roles of cytoskeleton-related proteins during the infection of D. citri by CLas. Western blotting revealed a significant difference in ubiquitination levels between the CLas-free and CLas-infected groups. According to ubiquitylome and 4D label-free proteome analysis, 343 quantified lysine ubiquitination (Kub) sites and 666 differentially expressed proteins (DEPs) were identified in CLas-infected groups compared with CLas-free groups. A total of 53 sites in 51 DEPs were upregulated, while 290 sites in 192 DEPs were downregulated. Furthermore, functional enrichment analysis indicated that 18 DEPs and 21 lysine ubiquitinated proteins were associated with the cytoskeleton, showing an obvious interaction. Ubiquitination of D. citri tropomyosin was confirmed by immunoprecipitation, Western blotting, and LC-MS/MS. RNAi-mediated knockdown of tropomyosin significantly increased CLas bacterial content in D. citri. In summary, we provided the most comprehensive lysine ubiquitinome analysis of the D. citri response to CLas infection, thus furthering our understanding of the role of the ubiquitination of cytoskeleton proteins in CLas infection.

Effects of dedifferentiated fat cells on neurogenic differentiation and cell proliferation in neuroblastoma cells

PURPOSE

Mesenchymal stem cells (MSCs) can induce differentiation of neuroblastoma (NB) cells. Properties of dedifferentiated fat cells (DFATs) are similar to those of MSCs. Here, we investigated whether DFATs can induce NB cell differentiation and suppress cell proliferation.

METHODS

DFATs were obtained from mature adipocytes isolated from adipose tissue from a ceiling culture. NB cells were cultured in a medium with or without DFATs and, subsequently, cultured in a DFAT-conditioned medium (CM) with or without phosphatidylinositol 3-kinase (PI3K) inhibitor. The neurite lengths were measured, and mRNA expression levels of the neurofilament (NF) and tubulin beta III (TUBβ3) were assessed using quantitative real-time RT-PCR. Cell viability was assessed using the WST-1 assay.

RESULTS

NB cells cultured with DFATs caused elongation of the neurites and upregulated the expression of NF and Tubβ3. NB cells cultured in DFAT-CM demonstrated increased cell viability. NB cells cultured with DFAT-CM and PI3K inhibitors suppressed cell viability. NB cells cultured with DFAT-CM and PI3K inhibitor demonstrated increased neurite length and expression, and upregulation of Tubβ3.

CONCLUSION

The combined use of DFAT-CM and PI3K inhibitors suppresses the proliferation of NB cells and induces their differentiation. Thus, DFAT may offer new insights into therapeutic approaches in neuroblastoma.

Quantitative Ubiquitylomic Analysis of the Dynamic Changes and Extensive Modulation of Ubiquitylation in Papaya During the Fruit Ripening Process

Lysine ubiquitination is a highly conserved post-translational modification with diverse biological functions. However, there is little available information on lysine ubiquitination of non-histone proteins in papaya (Carica papaya L.). In total, 3,090 ubiquitination sites on 1,249 proteins with diverse localizations and functions were identified. Five conserved ubiquitinated K motifs were identified. Enrichment analysis showed that many Hsps were differentially ubiquitinated proteins (DUPs), suggesting an essential role of ubiquitination in degradation of molecular chaperone. Furthermore, 12 sugar metabolism-related enzymes were identified as DUPs, including an involvement of ubiquitination in nutrimental changes during the papaya ripening process. The ubiquitination levels of five fruit ripening-related DUPs, including one ethylene-inducible protein, two 1-aminocyclopropane-1-carboxylic acid oxidases, one endochitinase, and one cell wall invertase, were significantly changed during the ripening process. Our study extends the understanding of diverse functions for lysine ubiquitination in regulation of the papaya fruit ripening process.

Protein lysine acetylation and its role in different human pathologies: a proteomic approach

INTRODUCTION

Lysine acetylation is a reversible post-translational modification (PTM) regulated through the action of specific types of enzymes: lysine acetyltransferases (KATs) and lysine deacetylases (HDACs), in addition to bromodomains, which are a group of conserved domains which identify acetylated lysine residues, several of the players in the process of protein acetylation, including enzymes and bromodomain-containing proteins, have been related to the progression of several diseases. The combination of high-resolution mass spectrometry-based proteomics, and immunoprecipitation to enrich acetylated peptides has contributed in recent years to expand the knowledge about this PTM described initially in histones and nuclear proteins, and is currently reported in more than 5000 human proteins, that are regulated by this PTM.

AREAS COVERED

This review presents an overview of the main participant elements, the scenario in the development of protein lysine acetylation, and its role in different human pathologies.

EXPERT OPINION

Acetylation targets are practically all cellular processes in eukaryotes and prokaryotes organisms. Consequently, this modification has been linked to many pathologies like cancer, viral infection, obesity, diabetes, cardiovascular, and nervous system-associated diseases, to mention a few relevant examples. Accordingly, some intermediate mediators in the acetylation process have been projected as therapeutic targets.

Global analysis of HBV-mediated host proteome and ubiquitylome change in HepG2.2.15 human hepatoblastoma cell line

Hepatitis B virus (HBV) infection remains a major health issue worldwide and the leading cause of cirrhosis and hepatocellular carcinoma (HCC). It has been reported previously that HBV invasion can extensively alter transcriptome, the proteome of exosomes and host cell lipid rafts. The impact of HBV on host proteins through regulating their global post-translational modifications (PTMs), however, is not well studied. Viruses have been reported to exploit cellular processes by enhancing or inhibiting the ubiquitination of specific substrates. Nevertheless, host cell physiology in terms of global proteome and ubiquitylome has not been addressed yet. Here by using HBV-integrated HepG2.2.15 model cell line we first report that HBV significantly modify the host global ubiquitylome. As currently the most widely used HBV cell culture model, HepG2.2.15 can be cultivated for multiple generations for protein labeling, and can replicate HBV, express HBV proteins and secrete complete HBV Dane particles, which makes it a suitable cell line for ubiquitylome analysis to study HBV replication, hepatocyte immune response and HBV-related HCC progression. Our previous experimental results showed that the total ubiquitination level of HepG2.2.15 cell line was significantly higher than that of the corresponding parental HepG2 cell line. By performing a Ubiscan quantification analysis based on stable isotope labeling of amino acids in cell culture (SILAC) of HepG2.2.15 and HepG2 cell lines, we identified a total of 7188 proteins and the protein levels of nearly 19% of them were changed over 2-folds. We further identified 3798 ubiquitinated Lys sites in 1476 host proteins with altered ubiquitination in response to HBV. Our results also showed that the global proteome and ubiquitylome were negatively correlated, indicating that ubiquitination might be involved in the degradation of host proteins upon HBV integration. We first demonstrated the ubiquitination change of VAMP3, VAMP8, DNAJB6, RAB8A, LYN, VDAC2, OTULIN, SLC1A4, SLC1A5, HGS and TOLLIP. In addition, we described 5 novel host factors SLC1A4, SLC1A5, EIF4A1, TOLLIP and BRCC36 that efficiently reduced the amounts of secreted HBsAg and HBeAg. Overall, the HBV-mediated host proteome and ubiquitylome change we reported will provide a valuable resource for further investigation of HBV pathogenesis and host-virus interaction networks.

PaACL silencing accelerates flower senescence and changes the proteome to maintain metabolic homeostasis in Petunia hybrida

Cytosolic acetyl-CoA is an intermediate of the synthesis of most secondary metabolites and the source of acetyl for protein acetylation. The formation of cytosolic acetyl-CoA from citrate is catalysed by ATP-citrate lyase (ACL). However, the function of ACL in global metabolite synthesis and global protein acetylation is not well known. Here, four genes, PaACLA1, PaACLA2, PaACLB1, and PaACLB2, which encode the ACLA and ACLB subunits of ACL in Petunia axillaris, were identified as the same sequences in Petunia hybrida 'Ultra'. Silencing of PaACLA1-A2 and PaACLB1-B2 led to abnormal leaf and flower development, reduced total anthocyanin content, and accelerated flower senescence in petunia 'Ultra'. Metabolome and acetylome analysis revealed that PaACLB1-B2 silencing increased the content of many downstream metabolites of acetyl-CoA metabolism and the levels of acetylation of many proteins in petunia corollas. Mechanistically, the metabolic stress induced by reduction of acetyl-CoA in PaACL-silenced petunia corollas caused global and specific changes in the transcriptome, the proteome, and the acetylome, with the effect of maintaining metabolic homeostasis. In addition, the global proteome and acetylome were negatively correlated under acetyl-CoA deficiency. Together, our results suggest that ACL acts as an important metabolic regulator that maintains metabolic homeostasis by promoting changes in the transcriptome, proteome. and acetylome.

Quantitative acetylome and phosphorylome analysis reveals Girdin affects pancreatic cancer progression through regulating Cortactin

The actin-binding protein Girdin is involved in a variety of cellular processes, including pancreatic cancer. The objective of this study is to explore the role and the mechanism of Girdin in pancreatic cancer by quantitative acetylome and phosphorylome analysis. We firstly found that Girdin was overexpressed in pancreatic cancer tissue and increased expression of Girdin was associated with tumor size and stage of patients with pancreatic cancer. We established the shRNA knockdown of Girdin in PANC-1 and Aspc-1 cells, and we found that shGirdin inhibited proliferation, migration and invasion, and promoted apoptosis. Subsequently, we identified and quantified 5,338 phosphorylated sites in 2,263 proteins that changed in response to Girdin knockdown, and identified a similar set of Girdin-responsive acetylome data as well. Additional data revealed that down-regulation of Girdin affected Cortactin phosphorylation and acetylation, suggesting Cortactin as an important regulatory target of Girdin. Moreover, we found that overexpression of Cortactin could rescue the effect of shGirdin on proliferation, apoptosism, migration and invasion of pancreatic cancer cells. In general, our results provided new insights into the mechanisms of Girdin function including cell proliferation, migration and invasion, and offer biomarker candidates for clinical evaluation of Girdin.

Ubiquitylomes Analysis of the Whole blood in Postmenopausal Osteoporosis Patients and healthy Postmenopausal Women

Objectives

To determine the mechanisms of ubiquitination in postmenopausal osteoporosis and investigate the ubiquitinated spectrum of novel targets between healthy postmenopausal women and postmenopausal osteoporosis patients, we performed ubiquitylome analysis of the whole blood of postmenopausal women and postmenopausal osteoporosis patients.

Methods

To obtain a more comprehensive understanding of the postmenopausal osteoporosis mechanism, we performed a quantitative assessment of the ubiquitylome in whole blood from seven healthy postmenopausal women and seven postmenopausal osteoporosis patients using high‐performance liquid chromatography fractionation, affinity enrichment, and liquid chromatography coupled to tandem mass spectrometry (LC‐MS/MS). To examine the ubiquitylome data, we performed enrichment analysis using an ubiquitylated amino acid motif, Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway.

Results

Altogether, 133 ubiquitinated sites and 102 proteins were quantified. A difference of more than 1.2 times is considered significant upregulation and less than 0.83 significant downregulation; 32 ubiquitinated sites on 25 proteins were upregulated and 101 ubiquitinated sites on 77 proteins were downregulated. These quantified proteins, both with differently ubiquitinated sites, participated in various cellular processes, such as cellular processes, biological regulation processes, response to stimulus processes, single‐organism and metabolic processes. Ubiquitin conjugating enzyme activity and ubiquitin‐like protein conjugating enzyme activity were the most highly enriched in molecular function of upregulated sites with corresponding proteins, but they were not enriched in downregulated in sites with corresponding proteins. The KEGG pathways analysis of quantified proteins with differentiated ubiquitinated sites found 13 kinds of molecular interactions and functional pathways, such as glyoxylate and decarboxylate metabolism, dopaminergic synapse, ubiquitin‐mediated proteolysis, salivary secretion, coagulation and complement cascades, Parkinson's disease, and hippo signaling pathway. In addition, hsa04120 ubiquitin‐mediated proteolysis was the most highly enriched in proteins with upregulated sites, hsa04610 complement and coagulation cascades was the most highly enriched in proteins with downregulated ubiquitinated sites, and hsa04114 Oocyte meiosis was the most highly enriched among all differential proteins.

Conclusion

Our study expands the understanding of the spectrum of novel targets that are differentially ubiquitinated in whole blood from healthy postmenopausal women and postmenopausal osteoporosis patients. The findings will contribute toward our understanding of the underlying proteostasis pathways in postmenopausal osteoporosis and the potential identification of diagnostic biomarkers in whole blood.