LAFEM: A Scoring Model to Evaluate Functional Landscape of Lysine Acetylome.

Protein lysine acetylation is a critical post-translational modification involved in a wide range of biological processes. To date, about 20,000 acetylation sites of Homo sapiens were identified through mass spectrometry-based proteomic technology, but more than 95% of them have unclear functional annotations because of the lack of existing prioritization strategy to assess the functional importance of the acetylation sites on large scale. Hence, we established a lysine acetylation functional evaluating model (LAFEM) by considering eight critical features surrounding lysine acetylation site to high-throughput estimate the functional importance of given acetylation sites. This was achieved by selecting one of the random forest models with the best performance in 10-fold cross-validation on undersampled training dataset. The global analysis demonstrated that the molecular environment of acetylation sites with high acetylation functional scores (AFSs) mainly had the features of larger solvent-accessible surface area, stronger hydrogen bonding-donating abilities, near motif and domain, higher homology, and disordered degree. Importantly, LAFEM performed well in validation dataset and acetylome, showing good accuracy to screen out fitness directly relevant acetylation sites and assisting to explain the core reason for the difference between biological models from the perspective of acetylome. We further used cellular experiments to confirm that, in nuclear casein kinase and cyclin-dependent kinase substrate 1, acetyl-K35 with higher AFS was more important than acetyl-K9 with lower AFS in the proliferation of A549 cells. LAFEM provides a prioritization strategy to large scale discover the fitness directly relevant acetylation sites, which constitutes an unprecedented resource for better understanding of functional acetylome.

LINC00493-encoded microprotein SMIM26 exerts anti-metastatic activity in renal cell carcinoma.

Human microproteins encoded by long non-coding RNAs (lncRNA) have been increasingly discovered, however, complete functional characterization of these emerging proteins is scattered. Here, we show that LINC00493-encoded SMIM26, an understudied microprotein localized in mitochondria, is tendentiously downregulated in clear cell renal cell carcinoma (ccRCC) and correlated with poor overall survival. LINC00493 is recognized by RNA-binding protein PABPC4 and transferred to ribosomes for translation of a 95-amino-acid protein SMIM26. SMIM26, but not LINC00493, suppresses ccRCC growth and metastatic lung colonization by interacting with acylglycerol kinase (AGK) and glutathione transport regulator SLC25A11 via its N-terminus. This interaction increases the mitochondrial localization of AGK and subsequently inhibits AGK-mediated AKT phosphorylation. Moreover, the formation of the SMIM26-AGK-SCL25A11 complex maintains mitochondrial glutathione import and respiratory efficiency, which is abrogated by AGK overexpression or SLC25A11 knockdown. This study functionally characterizes the LINC00493-encoded microprotein SMIM26 and establishes its anti-metastatic role in ccRCC, and therefore illuminates the importance of hidden proteins in human cancers.

Identifying PE2 and PE5 Proteins from Existing Mass Spectrometry Data Using pFind.

The Chromosome-Centric Human Proteome Project (C-HPP) aims to identify all proteins encoded by the human genome. Currently, the human proteome still contains approximately 2000 PE2-PE5 proteins, referring to annotated coding genes that lack sufficient protein-level evidence. During the past 10 years, it has been increasingly difficult to identify PE2-PE5 proteins in C-HPP approaches due to the limited occurrence. Therefore, we proposed that reanalyzing massive MS data sets in repository with newly developed algorithms may increase the occurrence of the peptides of these proteins. In this study, we downloaded 1000 MS data sets via the ProteomeXchange database. Using pFind software, we identified peptides referring to 1788 PE2-PE5 proteins. Among them, 11 PE2 and 16 PE5 proteins were identified with at least 2 peptides, and 12 of them were identified using 2 peptides in a single data set, following the criteria of the HPP guidelines. We found translation evidence for 16 of the 11 PE2 and 16 PE5 proteins in our RNC-seq data, supporting their existence. The properties of the PE2 and PE5 proteins were similar to those of the PE1 proteins. Our approach demonstrated that mining PE2 and PE5 proteins in massive data repository is still worthy, and multidata set peptide identifications may support the presence of PE2 and PE5 proteins or at least prompt additional studies for validation. Extremely high throughput could be a solution to finding more PE2 and PE5 proteins.

Pan-Cancer Proteomics Analysis Reveals Wiskott-Aldrich Syndrome Protein as a Potential Regulator of Programmed Death-Ligand 1.

The programmed death-ligand 1 (PD-L1) is a key mediator of immunosuppression in the tumor microenvironment. The expression of PD-L1 in cancer cells is useful for the clinical determination of an immune checkpoint blockade (ICB). However, the regulatory mechanism of the PD-L1 abundance remains incompletely understood. Here, we integrated the proteomics of 52 patients with solid tumors and examined immune cell infiltration to reveal PD-L1-related regulatory modules. Wiskott-Aldrich syndrome protein (WASP) was identified as a potential regulator of PD-L1 transcription. In two independent cohorts containing 164 cancer patients, WASP expression was significantly associated with PD-L1. High WASP expression contributed to immunosuppressive cell composition, including cells positive for immune checkpoints (PD1, CTLA4, TIGIT, and TIM3), FoxP3+ Treg cells, and CD163+ tumor-associated macrophages. Overexpression of WASP increased, whereas knockdown of WASP decreased the protein level of PD-L1 in cancer cells without alteration of PD-L1 protein stability. The WASP-mediated cell migration and invasion were markedly attenuated by the silence of PD-L1. Collectively, our data suggest that WASP is a potential regulator of PD-L1 and the WASP/PD-L1 axis is responsible for cell migration and an immunosuppressive microenvironment.

Repurposing cinacalcet suppresses multidrug-resistant Staphylococcus aureus by disruption of cell membrane and inhibits biofilm by targeting IcaR.

BACKGROUND: MDR Staphylococcus aureus infections, along with the severity of biofilm-associated infections, continue to threaten human health to a great extent. It necessitates the urgent development of novel antimicrobial and antibiofilm agents. OBJECTIVES: To reveal the mechanism and target of cinacalcet as an antibacterial and antimicrobial agent for S. aureus. METHODS: Screening of non-antibiotic drugs for antibacterial and antibiofilm properties was conducted using a small-molecule drug library. In vivo efficacy was assessed through animal models, and the antibacterial mechanism was studied using quantitative proteomics, biochemical assays, LiP-SMap, BLI detection and gene knockout techniques. RESULTS: Cinacalcet, an FDA-approved drug, demonstrated antibacterial and antibiofilm activity against S. aureus, with less observed development of bacterial resistance. Importantly, cinacalcet significantly improved survival in a pneumonia model and bacterial clearance in a biofilm infection model. Moreover, the antibacterial mechanism of cinacalcet mainly involves the destruction of membrane-targeted structures, alteration of energy metabolism, and production of reactive oxygen species (ROS). Cinacalcet was found to target IcaR, inhibiting biofilm formation through the negative regulation of IcaADBC. CONCLUSIONS: The findings suggest that cinacalcet has potential for repurposing as a therapeutic agent for MDR S. aureus infections and associated biofilms, warranting further investigation.

Polyphyllin D punctures hypertrophic lysosomes to reverse drug resistance of hepatocellular carcinoma by targeting acid sphingomyelinase.

Hypertrophic lysosomes are critical for tumor progression and drug resistance; however, effective and specific lysosome-targeting compounds for cancer therapy are lacking. Here we conducted a lysosomotropic pharmacophore-based in silico screen in a natural product library (2,212 compounds), and identified polyphyllin D (PD) as a novel lysosome-targeted compound. PD treatment was found to cause lysosomal damage, as evidenced by the blockade of autophagic flux, loss of lysophagy, and the release of lysosomal contents, thus exhibiting anticancer effects on hepatocellular carcinoma (HCC) cell both in vitro and in vivo. Closer mechanistic examination revealed that PD suppressed the activity of acid sphingomyelinase (SMPD1), a lysosomal phosphodieserase that catalyzes the hydrolysis of sphingomyelin to produce ceramide and phosphocholine, by directly occupying its surface groove, with Trp148 in SMPD1 acting as a major binding residue; this suppression of SMPD1 activity irreversibly triggers lysosomal injury and initiates lysosome-dependent cell death. Furthermore, PD-enhanced lysosomal membrane permeabilization to release sorafenib, augmenting the anticancer effect of sorafenib both in vivo and in vitro. Overall, our study suggests that PD can potentially be further developed as a novel autophagy inhibitor, and a combination of PD with classical chemotherapeutic anticancer drugs could represent a novel therapeutic strategy for HCC intervention.

ZSWIM1 Promotes the Proliferation and Metastasis of Lung Adenocarcinoma Cells through the STK38/MEKK2/ERK1/2 Axis.

Investigating the functions of the proteins with no or less functional annotations is an important goal of the HPP (Human Proteome Project) Grand Project. In this study, we investigated the function of such a protein, ZSWIM1 (C20orf162), its gene located on chromosome 20. Its expression is upregulated in lung adenocarcinoma compared with the adjacent normal tissues and negatively correlated with the overall survival. Overexpressing ZSWIM1 markedly promotes the proliferation, migration, invasion as well as epithelial-to-mesenchymal transition in lung adenocarcinoma cells, while knocking down ZSWIM1 functions oppositely. The interactome of ZSWIM1 was identified by immunoprecipitation-mass spectrometry, and we verified the interaction of ZSWIM1 with the potential partner, STK38. ZSWIM1 antagonized the function of STK38. Mechanically, ZSWIM1 promoted the activation of MEKK2/ERK1/2 pathway through interacting with STK38, leading to the release of MEKK2. Taken together, ZSWIM1 can be annotated as an oncogene in lung adenocarcinoma, and the STK38/MEKK2/ERK1/2 axis mediates its promoting role in lung adenocarcinoma.

EFHD1, a novel mitochondrial regulator of tumor metastasis in clear cell renal cell carcinoma.

The biological function of many mitochondrial proteins in mechanistic detail has not been well investigated in clear cell renal cell carcinoma (ccRCC). A seven-mitochondrial-gene signature was generated by Lasso regression analysis to improve the prediction of prognosis of patients with ccRCC, using The Cancer Genome Atlas and Clinical Proteomic Tumor Analysis Consortium cohort. Among those seven genes, EFHD1 is less studied and its role in the progression of ccRCC remains unknown. The decreased expression of EFHD1 was validated in clinical samples and was correlated with unfavorable outcome. Overexpression of EFHD1 in ccRCC cells resulted in the reduction of mitochondrial Ca2+ , and the inhibition of cell migration and invasion in vitro and tumor metastasis in vivo. Mechanistically, EFHD1 physically bound to the core mitochondrial calcium transporter (mitochondrial calcium uniporter, MCU) through its N-terminal domain. The interaction between EFHD1 and MCU suppressed the uptake of Ca2+ into mitochondria, and deactivated the Hippo/YAP signaling pathway. Further data revealed that the ectopic expression of EFHD1 upregulated STARD13 to enhance the phosphorylation of YAP protein at Ser-127. The knockdown of STARD13 or the overexpression of MCU partly abrogated the EFHD1-mediated induction of phosphorylation of YAP at Ser-127 and suppression of cell migration. Taken together, the newly identified EFHD1-MCU-STARD13 axis participates in the modulation of the Hippo/YAP pathway and serves as a novel regulator in the progression of ccRCC.

Residue Lys219 of CpxR is critical in the regulation of the antibiotic resistance of Escherichia coli.

BACKGROUND: CpxR is a critical regulator in bacterial adaptation to various harmful stresses, and is known to regulate bacterial resistance to commonly used antibiotics, such as aminoglycosides, ß-lactams and polypeptides. However, the detailed study of functional residues of CpxR remains insufficient. OBJECTIVES: To investigate the contribution of Lys219 to CpxR's function in regulating antibiotic resistance of Escherichia coli. METHODS: We performed sequence alignment and conservative analysis of the CpxR protein and constructed mutant strains. We then performed electrophoretic mobility shift assay, real-time quantitative PCR assay, determination of reactive oxygen species (ROS) levels, molecular dynamics simulation, conformational analysis and circular dichroism. RESULTS: All mutant proteins (K219Q, K219A and K219R) lost the cpxP DNA-binding ability. Additionally, the three complemented strains eK219A, eK219Q, and eK219R exhibited lower resistance to copper toxicity and alkaline pH toxicity than eWT. Molecular dynamics analysis revealed that mutation of Lys219 leads to looser and more unstable conformation of CpxR, leading to its decreased binding affinity with downstream genes. Moreover, the Lys219 mutation resulted in the down-regulation of efflux pump genes (acrD, tolC, mdtB and mdtA), leading to the accumulation of antibiotics inside the cells and an increase in ROS production, which significantly reduces antibiotic resistance. CONCLUSIONS: The mutation of the key residue Lys219 causes a conformational change that results in the loss of regulatory ability of CpxR, which may potentially reduce to antibiotic resistance. Therefore, this study suggests that targeting the highly conserved sequence of CpxR could be a promising strategy for the development of new antibacterial drugs.

Proteomic Study of the Adaptive Mechanism of Ciprofloxacin-Resistant Staphylococcus aureus to the Host Environment.

Antibiotic-resistant bacteria can escape host immune killing and settle in the host to form persistent infections. In this study we investigated the adaptive mechanism of resistant Staphylococcus aureus to the host environment by data-independent acquisition-based quantitative proteomics and functional validation. The growth curve and minimum inhibitory concentration (MIC) indicated that ciprofloxacin-resistant (Cip-R) S. aureus showed a survival advantage over sensitive strains. Cip-R also exhibited a stronger invasion and biofilm formation ability than sensitive bacteria. Cip-R stimulation resulted in the improved production of inflammatory factors of the host cells. Proteomics study combined with biochemical validations showed that Cip-R obtained adaptability to the host via upregulation of the tricarboxylic acid cycle (TCA cycle) and downregulation of ribosome metabolism and protein folding to maintain energy to support Cip-R's survival. Thus, this study will help us to further explain the growth strategy of resistant bacteria to adapt to the host environment, and provide important information for the development of new antibacterial drugs.

Highly Robust de Novo Full-Length Protein Sequencing.

Accurate full-length sequencing of a purified unknown protein is still challenging nowadays due to the error-prone mass-spectrometry (MS)-based methods. De novo identified peptide sequence largely contain errors, undermining the accuracy of assembly. Bias on the detectability of the peptides also makes low-coverage regions, resulting in gaps. Although recent advances on multi-enzyme hydrolysis and algorithms showed complete assembly of full-length protein sequences in a few examples, the robustness in practical application is still to be improved. Here, inspired by genome assembly strategies, we demonstrate a contig-scaffolding strategy to assemble protein sequences with high robustness and accuracy. This strategy integrates multiple unspecific hydrolysis methods to minimize the bias in the hydrolysis process. After de novo identification of the peptides, our assembly algorithm, named Multiple Contigs & Scaffolding (MuCS), assembles the peptide sequences in a multistep, i.e., contig-scaffold manner, with error correction in each step. MS data from different hydrolysis experiments complement each other for robust contig extension and error correction. We demonstrated that our strategy on three proteins and three replications all reached 100% coverage (except one with 98.85%) and 98.69-100% accuracy. It can also efficiently deal with the membrane protein, although the transmembrane region was missing due to the limitation of the MS. The three replicates reached 88.85-92.57% coverage and 97.57-100% accuracy. In sum, we provided a practical, robust, and accurate solution for full-length protein sequencing. The MuCS software is available at http://chi-biotech.com/mucs/.

Ciprofloxacin-Resistant Staphylococcus aureus Displays Enhanced Resistance and Virulence in Iron-Restricted Conditions.

The unreasonable misuse of antibiotics has led to the emergence of large-scale drug-resistant bacteria, seriously threatening human health. Compared with drug-sensitive bacteria, resistant bacteria are difficult to clear by host immunity. To fully explore the adaptive mechanism of resistant bacteria to the iron-restricted environment, we performed data-independent acquisition-based quantitative proteomics on ciprofloxacin (CIP)-resistant (CIP-R) Staphylococcus aureus in the presence or absence of iron. On bioinformatics analysis, CIP-R bacteria showed stronger amino acid synthesis and energy storage ability. Notably, CIP-R bacteria increased virulence by upregulating the expression of many virulence-related proteins and enhancing the synthesis of virulence-related amino acids under iron-restricted stress. This study will help us to further explain the adaptive mechanisms that lead to bacterial resistance to antibiotics depending on the host environment and provide insights into the development of novel drugs for the treatment of drug-resistant bacterial infections.

Proteomic Investigation of the Antibacterial Mechanism of trans-Cinnamaldehyde against Escherichia coli.

Trans-Cinnamaldehyde (TC) is a widely used food additive, known for its sterilization, disinfection, and antiseptic properties. However, its antibacterial mechanism is not completely understood. In this study, quantitative proteomics was performed to investigate differentially expressed proteins (DEPs) in Escherichia coli in response to TC treatment. Bioinformatics analysis suggested aldehyde toxicity, acid stress, oxidative stress, interference of carbohydrate metabolism, energy metabolism, and protein translation as the bactericidal mechanism. E. coli BW25113ΔyqhD, ΔgldA, ΔbetB, ΔtktB, ΔgadA, ΔgadB, ΔgadC, and Δrmf were used to investigate the functions of DEPs through biochemical methods. The present study revealed that TC exerts its antibacterial effects by inducing the toxicity of its aldehyde group producing acid stress. These findings will contribute to the application of TC in the antibacterial field.

Autoactivation of Translation Causes the Bloom of Prorocentrum donghaiense in Harmful Algal Blooms.

Harmful algal blooms (HABs) are symptomatic of ecosystem imbalance, leading to major worldwide marine natural disasters, and seriously threaten the human health. Some HAB algae's exceptional genome size prohibited the genomic investigations on molecular mechanisms, for example, Prorocentrum. This study performed translatome sequencing (RNC-seq) for Prorocentrum donghaiense to assemble the translatome reference sequences on appropriate cost to enable the global molecular study at translatome and proteome levels. By analyzing the translatome and proteome of P. donghaiense in phosphor-rich, phosphor-deficient, and phosphor-restored media, we found massive up-regulation of energy and material production pathways in phosphor-rich conditions that enables autoactivation of translation, which is the key to its exponential growth in HABs. To break down the autoactivation, we demonstrated that mild translation delay using very low concentrations of cycloheximide efficiently controls the blooming without harming other aquatic organisms and humans. Our result provides a novel hint for controlling HABs and demonstrated the RNC-seq as an economic strategy on investigating functions of organisms with large and unknown genomes.

Phosphoproteome and Biological Evidence Revealed Abnormal Calcium Homeostasis in Keloid Fibroblasts and Induction of Aberrant Platelet Aggregation.

Keloid is a benign tumor characterized by persistent inflammation, increased fibroblast proliferation, and abnormal deposition of collagen in the wound. The etiology of keloid is unclear. Here, we explored the phospho-signaling changes in human keloid fibroblasts via phosphoproteome mass spectrometry analysis. We found that comparative phosphoproteomics could statistically distinguish keloid from control fibroblasts. Differentially expressed phosphoproteins could predict the activation of known keloid-relevant upstream regulators including transforming growth factor-ß1, interleukin (IL)-4, and IL-5. With multiple bioinformatics analyses, phosphorylated FLNA, TLN1, and VCL were significantly enriched in terms of calcium homeostasis and platelet aggregation. We biologically verified that keloid fibroblasts had a higher level of Ca2+ influx than the control fibroblasts upon ionomycin stimulation. Via co-cultivation analysis, we found that human keloid fibroblasts could directly promote platelet aggregation. As suggested by PhosphoPath and gene set enrichment analysis, pFLNA was centered as the top phosphoproteins associated with keloid phenotypes. We validated that pFLNA was upregulated both in keloid fibroblasts and keloid tissue section, implicating its biomarker potential. In conclusion, we reported the first phosphoproteome on keloid fibroblasts, based on which we revealed that keloid fibroblasts had aberrant calcium homeostasis and could directly induce platelet aggregation.

A hidden human proteome encoded by 'non-coding' genes.

It has been a long debate whether the 98% 'non-coding' fraction of human genome can encode functional proteins besides short peptides. With full-length translating mRNA sequencing and ribosome profiling, we found that up to 3330 long non-coding RNAs (lncRNAs) were bound to ribosomes with active translation elongation. With shotgun proteomics, 308 lncRNA-encoded new proteins were detected. A total of 207 unique peptides of these new proteins were verified by multiple reaction monitoring (MRM) and/or parallel reaction monitoring (PRM); and 10 new proteins were verified by immunoblotting. We found that these new proteins deviated from the canonical proteins with various physical and chemical properties, and emerged mostly in primates during evolution. We further deduced the protein functions by the assays of translation efficiency, RNA folding and intracellular localizations. As the new protein UBAP1-AST6 is localized in the nucleoli and is preferentially expressed by lung cancer cell lines, we biologically verified that it has a function associated with cell proliferation. In sum, we experimentally evidenced a hidden human functional proteome encoded by purported lncRNAs, suggesting a resource for annotating new human proteins.

Quantitative Mitochondrial Proteomics Reveals ANXA7 as a Crucial Factor in Mitophagy.

Mitochondria are involved in many crucial cellular processes. Maintaining healthy mitochondria is essential for cellular homeostasis. Parkin-dependent mitophagy plays an important role in selectively eliminating damaged mitochondria in mammalian cells. However, mechanisms of Parkin-dependent mitophagy remain elusive. In this research, we performed data-independent acquisition-based quantitative mitochondrial proteomics to study the proteomic alterations of carbonyl cyanide m-chlorophenylhydrazone (CCCP)-induced Parkin-mediated mitophagy. We identified 222 differentially expressed proteins, with 76 upregulations and 146 downregulations, which were potentially involved in mitophagy. We then demonstrated that annexin A7 (ANXA7), a calcium-dependent phospholipid-binding protein, can translocate to impaired mitochondria upon CCCP treatment, where it played a pivotal part in the process of Parkin-dependent mitophagy via interacting with BASP1. As a mitochondrial uncoupling agent, CCCP indirectly regulated ANXA7 and BASP1 to induce Parkin-dependent mitophagy.

Quantitative secretome analysis of polymyxin B resistance in Escherichia coli.

Bacterial resistance has become a serious threat to human health. In particular, the gradual development of resistance to polymyxins, the last line of defense for human infections, is a major issue. Secreted proteins contribute to the interactions between bacteria and the environment. In this study, we compared the secretomes of polymyxin B-sensitive and -resistant Escherichia coli strains by data-independent acquisition mass spectrometry. In total, 87 differentially expressed secreted proteins were identified in polymyxin B-resistant E. coli compared to the sensitive strain. A GO enrichment analysis indicated that the differentially expressed proteins were involved in biological processes, including bacterial-type flagellum-dependent cell motility, ion transport, carbohydrate derivative biosynthetic process, cellular response to stimulus, organelle organization, and cell wall organization or biogenesis. The differentially expressed secreted proteins in polymyxin B-resistant bacteria were enriched for multiple pathways, suggesting that the resistance phenotype depends on complex regulatory mechanisms. A potential biomarker or drug target (YebV) was found in polymyxin B-resistant E. coli. This work clarifies the secretome changes associated with the acquisition of polymyxin resistance and may contribute to drug development.

Deep Coverage Tissue and Cellular Proteomics Revealed IL-1ß Can Independently Induce the Secretion of TNF-Associated Proteins from Human Synoviocytes.

Synovitis is a key contributor to the inflammatory environment in osteoarthritis (OA) joints. Currently, the biological therapy of OA is not satisfactory in multiple single-target trials on anti-TNF agents, or IL-1 antagonists. Systems biological understanding of the phosphorylation state in OA synovium is warranted to direct further therapeutic strategies. Therefore, in this study, we compared the human synovial phosphoproteome of the OA with the acute joint fracture subjects. We found that OA synovium had significantly more phosphoproteins, and 82 phosphoproteins could only be specifically found in all the OA samples. Differentially expressed proteins of the OA synovium were focusing on endoplasmic reticulum-/Golgi-associated secretion and negative regulation of cell proliferation, which was verified through an IL-1ß-treated human synoviocyte (HS) in vitro model. With data-independent acquisition-based mass spectrometry, we found that IL-1ß could induce HS to secrete proteins that were significantly associated with the endosomal/vacuolar pathway, endoplasmic reticulum/Golgi secretion, complement activation, and collagen degradation. Especially, we found that while specifically suppressing HS endocytosis, IL-1ß could activate the secretion of 25 TNF-associated proteins, and the change of SERPINE2 and COL3A1 secretion was verified by immunoblotting. In conclusion, our results suggest that OA synovium has a polarized phosphoproteome to inhibit proliferation and maintain active secretion of HS, whereas IL-1ß alone can transform HS to produce a synovitis-associated secretome, containing numerous TNF-associated secretory proteins in a TNF-independent mode.

Proteomic Analysis Reveals that Odoroside A Triggers G2/M Arrest and Apoptosis in Colorectal Carcinoma Through ROS-p53 Pathway.

Odoroside A (OA) is an active ingredient extracted from the leaves of Nerium oleander Linn. (Apocynaceae). This study aims to examine the anticancer bioactivity of OA against CRC cells and to investigate the action mechanisms involved. As a result, OA can significantly inhibit cellular ability and induce apoptosis of CRC cells in a concentration-dependent manner without any obvious cytotoxicity in normal colorectal epithelial cells. Then, quantitative proteomics combined with bioinformatics is adopted to investigate the alterations of proteins and signaling pathways in response to OA treatment. As suggested by the proteomic analysis, flow cytometry and Western blotting analyses validate that exposure of CRC cells to OA causes cell cycle arrest and apoptosis, accompanied with the activation of the ROS/p53 signaling pathway. This observation demonstrates that OA, as a natural product, can induce oxidative stress to suppress tumor cell growth, implicating a novel therapeutic agent against CRC without obvious side effects.