The bacterial redox protein azurin induces apoptosis in J774 macrophages through complex formation and stabilization of the tumor suppressor protein p53

Exploring roles of the chitinase ChiC in modulating Pseudomonas aeruginosa virulence phenotypes

Chitinases are ubiquitous enzymes involved in biomass degradation and chitin turnover in nature. Pseudomonas aeruginosa (PA), an opportunistic human pathogen, expresses ChiC, a secreted glycoside hydrolase 18 family chitinase. Despite speculation about ChiC's role in PA disease pathogenesis, there is scant evidence supporting this hypothesis. Since PA cannot catabolize chitin, we investigated the potential function(s) of ChiC in PA pathophysiology. Our findings show that ChiC exhibits activity against both insoluble (α- and β-chitin) and soluble chitooligosaccharides. Enzyme kinetics toward (GlcNAc)4 revealed a kcat of 6.50 s-1 and a KM of 1.38 mM, the latter remarkably high for a canonical chitinase. In our label-free proteomics investigation, ChiC was among the most abundant proteins in the Pel biofilm, suggesting a potential contribution to PA biofilm formation. Using an intratracheal challenge model of PA pneumonia, the chiC::ISphoA/hah transposon insertion mutant paradoxically showed slightly increased virulence compared to the wild-type parent strain. Our results indicate that ChiC is a genuine chitinase that contributes to a PA pathoadaptive pathway.IMPORTANCEIn addition to performing chitin degradation, chitinases from the glycoside hydrolase 18 family have been found to play important roles during pathogenic bacterial infection. Pseudomonas aeruginosa is an opportunistic pathogen capable of causing pneumonia in immunocompromised individuals. Despite not being able to grow on chitin, the bacterium produces a chitinase (ChiC) with hitherto unknown function. This study describes an in-depth characterization of ChiC, focusing on its potential contribution to the bacterium's disease-causing ability. We demonstrate that ChiC can degrade both polymeric chitin and chitooligosaccharides, and proteomic analysis of Pseudomonas aeruginosa biofilm revealed an abundance of ChiC, hinting at a potential role in biofilm formation. Surprisingly, a mutant strain incapable of ChiC production showed higher virulence than the wild-type strain. While ChiC appears to be a genuine chitinase, further investigation is required to fully elucidate its contribution to Pseudomonas aeruginosa virulence, an important task given the evident health risk posed by this bacterium.

Peptide-Based Agents for Cancer Treatment: Current Applications and Future Directions

Peptide-based strategies have received an enormous amount of attention because of their specificity and applicability. Their specificity and tumor-targeting ability are applied to diagnosis and treatment for cancer patients. In this review, we will summarize recent advancements and future perspectives on peptide-based strategies for cancer treatment. The literature search was conducted to identify relevant articles for peptide-based strategies for cancer treatment. It was performed using PubMed for articles in English until June 2023. Information on clinical trials was also obtained from ClinicalTrial.gov. Given that peptide-based strategies have several advantages such as targeted delivery to the diseased area, personalized designs, relatively small sizes, and simple production process, bioactive peptides having anti-cancer activities (anti-cancer peptides or ACPs) have been tested in pre-clinical settings and clinical trials. The capability of peptides for tumor targeting is essentially useful for peptide-drug conjugates (PDCs), diagnosis, and image-guided surgery. Immunomodulation with peptide vaccines has been extensively tested in clinical trials. Despite such advantages, FDA-approved peptide agents for solid cancer are still limited. This review will provide a detailed overview of current approaches, design strategies, routes of administration, and new technological advancements. We will highlight the success and limitations of peptide-based therapies for cancer treatment.

Computational Modeling, High-Level Soluble Expression and In Vitro Cytotoxicity Assessment of Recombinant Pseudomonas aeruginosa Azurin: A Promising Anti-Cancer Therapeutic Candidate

Azurin is a natural protein produced by Pseudomonas aeruginosa that exhibits potential anti-tumor, anti-HIV, and anti-parasitic properties. The current study aimed to investigate the potential of azurin protein against breast cancer using both in silico and in vitro analyses. The amino acid sequence of Azurin was used to predict its secondary and tertiary structures, along with its physicochemical properties, using online software. The resulting structure was validated and confirmed using Ramachandran plots and ERRAT2. The mature azurin protein comprises 128 amino acids, and the top-ranked structure obtained from I-TASSER was shown to have a molecular weight of 14 kDa and a quality factor of 100% by ERRAT2, with 87.4% of residues in the favored region of the Ramachandran plot. Docking and simulation studies of azurin protein were conducted using HDOCK and Desmond servers, respectively. The resulting analysis revealed that Azurin docked against p53 and EphB2 receptors demonstrated maximum binding affinity, indicating its potential to cause apoptosis. The recombinant azurin gene was successfully cloned and expressed in a BL21 (DE3) strain using a pET20b expression vector under the control of the pelB ladder, followed by IPTG induction. The azurin protein was purified to high levels using affinity chromatography, yielding 70 mg/L. In vitro cytotoxicity assay was performed using MCF-7 cells, revealing the significant cytotoxicity of the azurin protein to be 105 µg/mL. These findings highlight the potential of azurin protein as an anticancer drug candidate.

Cross-talk between cancer and Pseudomonas aeruginosa mediates tumor suppression

Microorganisms living at many sites in the human body compose a complex and dynamic community. Accumulating evidence suggests a significant role for microorganisms in cancer, and therapies that incorporate bacteria have been tried in various types of cancer. We previously demonstrated that cupredoxin azurin secreted by the opportunistic pathogen Pseudomonas aeruginosa, enters human cancer cells and induces apoptotic death^1-4. However, the physiological interactions between P. aeruginosa and humans and their role in tumor homeostasis are largely unknown. Here, we show that P. aeruginosa upregulated azurin secretion in response to increasing numbers of and proximity to cancer cells. Conversely, cancer cells upregulated aldolase A secretion in response to increasing proximity to P. aeruginosa, which also correlated with enhanced P. aeruginosa adherence to cancer cells. Additionally, we show that cancer patients had detectable P. aeruginosa and azurin in their tumors and exhibited increased overall survival when they did, and that azurin administration reduced tumor growth in transgenic mice. Our results suggest host-bacterial symbiotic mutualism acting as a diverse adjunct to the host defense system via inter-kingdom communication mediated by the evolutionarily conserved proteins azurin and human aldolase A. This improved understanding of the symbiotic relationship of bacteria with humans indicates the potential contribution to tumor homeostasis.

Pseudomonas aeruginosa Cytotoxins: Mechanisms of Cytotoxicity and Impact on Inflammatory Responses

Pseudomonas aeruginosa is one of the most virulent opportunistic Gram-negative bacterial pathogens in humans. It causes many acute and chronic infections with morbidity and mortality rates as high as 40%. P. aeruginosa owes its pathogenic versatility to a large arsenal of cell-associated and secreted virulence factors which enable this pathogen to colonize various niches within hosts and protect it from host innate immune defenses. Induction of cytotoxicity in target host cells is a major virulence strategy for P. aeruginosa during the course of infection. P. aeruginosa has invested heavily in this strategy, as manifested by a plethora of cytotoxins that can induce various forms of cell death in target host cells. In this review, we provide an in-depth review of P. aeruginosa cytotoxins based on their mechanisms of cytotoxicity and the possible consequences of their cytotoxicity on host immune responses.

Anticancer activity of Pseudomonas aeruginosa derived peptide with iRGD in colon cancer therapy

Objectives

Colon cancer is well-known as a life-threatening disease. Since the current treatment modalities for this type of cancer are powerful yet face some limitations, finding novel treatments is required to achieve better outcomes with fewer side effects. Here we investigated the therapeutic potential of Azurin-p28 alone or along with iRGD (Ac-CRGDKGPDC-amide) as a tumor-penetrating peptide and 5-fluorouracil (5-FU) for colon cancer.

Materials and Methods

Inhibitory effect of p28 with or without iRGD/5-FU was studied in CT26 and HT29, as well as the xenograft animal model of cancer. The effect of p28 alone or along with iRGD/5-FU on cell migration, apoptotic activity, and cell cycle of the cell lines was assessed. Level of the BAX and BCL2 genes, tumor suppressor genes [(p53 and collagen type-Iα1 (COL1A1), collagen type-Iα2 (COL1A2)] were assessed by quantitative RT-PCR.

Results

These findings show that using p28 with or without iRGD and 5-FU raised the level of p53 and BAX but decreased BCL2, compared with control and 5-FU groups in tissues of the tumor, which result in raising the apoptosis.

Conclusion

It seems that p28 may be used as a new therapeutic approach in colon cancer therapy that can enhance the anti-tumor effect of 5-FU.

Cell-Penetrating Peptides (CPPs) as Therapeutic and Diagnostic Agents for Cancer

Cell-Penetrating Peptides (CPPs) are short peptides consisting of <30 amino acids. Their ability to translocate through the cell membrane while carrying large cargo biomolecules has been the topic of pre-clinical and clinical trials. The ability to deliver cargo complexes through membranes yields potential for therapeutics and diagnostics for diseases such as cancer. Upon cellular entry, some CPPs have the ability to target specific organelles. CPP-based intracellular targeting strategies hold tremendous potential as they can improve efficacy and reduce toxicities and side effects. Further, recent clinical trials show a significant potential for future CPP-based cancer treatment. In this review, we summarize recent advances in CPPs based on systematic searches in PubMed, Embase, Web of Science, and Scopus databases until 30 September 2022. We highlight targeted delivery and explore the potential uses for CPPs as diagnostics, drug delivery, and intrinsic anti-cancer agents.

Microbial cancer therapeutics: A promising approach

The success of conventional cancer therapeutics is hindered by associated dreadful side-effects of antibiotic resistance and the dearth of antitumor drugs' selectivity and specificity. Hence, the conceptual evolution of anti-cancerous therapeutic agents that selectively target cancer cells without impacting the healthy cells or tissues, has led to a new wave of scientific interest in microbial-derived bioactive molecules. Such strategic solutions may pave the way to surmount the shortcomings of conventional therapies and raise the potential and hope for the cure of wide range of cancer in a selective manner. This review aims to provide a comprehensive summary of anti-carcinogenic properties and underlying mechanisms of bioactive molecules of microbial origin, and discuss the current challenges and effective therapeutic application of combinatorial strategies to attain minimal systemic side-effects.

Tumor-targeting cell-penetrating peptide, p28, for glioblastoma imaging and therapy

Despite recent advances in cancer research, glioblastoma multiforme (GBM) remains a highly aggressive brain tumor as its treatment options are limited. The current standard treatment includes surgery followed by radiotherapy and adjuvant chemotherapy. However, surgery without image guidance is often challenging to achieve maximal safe resection as it is difficult to precisely discern the lesion to be removed from surrounding brain tissue. In addition, the efficacy of adjuvant chemotherapy is limited by poor penetration of therapeutics through the blood-brain barrier (BBB) into brain tissues, and the lack of tumor targeting. In this regard, we utilized a tumor-targeting cell-penetration peptide, p28, as a therapeutic agent to improve the efficacy of a current chemotherapeutic agent for GBM, and as a carrier for a fluorescence imaging agent for a clear identification of GBM. Here, we show that a near-infrared (NIR) imaging agent, ICG-p28 (a chemical conjugate of an FDA-approved NIR dye, indocyanine green ICG, and tumor-targeting p28 peptide) can preferentially localize tumors in multiple GBM animal models. Moreover, xenograft studies show that p28, as a therapeutic agent, can enhance the cytotoxic activity of temozolomide (TMZ), one of the few effective drugs for brain tumors. Collectively, our findings highlight the important role of the tumor-targeting peptide, which has great potential for intraoperative image-guided surgery and the development of new therapeutic strategies for GBM.

Solution structure of the anticancer p28 peptide in biomimetic medium

The p28 peptide derived from Pseudomonas aeruginosa azurin shows an anticancer activity after binding to p53 protein and is currently in Phase I of clinical trials. We have studied its structure in water and in a biomimetic media and show that the peptide is unstructured in water but when studied in a biomimetic medium assumes a structure very similar to the one observed in azurin, suggesting a high propensity of this peptide to maintain this secondary structure. Analysis of p28 sequences from different bacterial species indicates conservation of the secondary structure despite amino acid replacement in different positions, suggesting that others, similar peptides could be tested for binding to p53.

Anticancer and antimicrobial potential of enterocin 12a from Enterococcus faecium

BACKGROUND

Increase in the number of infections caused by Gram-negative bacteria in neutropenic cancer patients has prompted the search for novel therapeutic agents having dual anticancer and antimicrobial properties. Bacteriocins are cationic proteins of prokaryotic origin that have emerged as one of the most promising alternative antimicrobial agents with applications as food preservatives and therapeutic agents. Apart from their antimicrobial activities, bacteriocins are also being explored for their anticancer potential.

RESULTS

In this study, a broad-spectrum, cell membrane-permeabilizing enterocin with a molecular weight of 65 kDa was purified and characterized from the culture supernatant of vaginal Enterococcus faecium 12a. Enterocin 12a inhibited multidrug-resistant strains of various Gram-negative pathogens such as Salmonella enterica, Shigella flexneri, Vibrio cholerae, Escherichia coli and Gram-positive, Listeria monocytogenes, but had no activities against different strains of gut lactobacilli. The mass spectrometric analysis showed that the enterocin 12a shared partial homology with 4Fe-4S domain-containing redox protein of E. faecalis R712. Further, enterocin 12a selectively inhibited the proliferation of various human cancer cell lines in a dose-dependent manner but not that of normal human peripheral blood mononuclear cells. Enterocin 12a-treated cancer cells showed apoptosis-like morphological changes.

CONCLUSION

Enterocin 12a is a novel bacteriocin that has anticancer properties against human cell lines and negligible activity towards non-malignant cells. Therefore, it should be further evaluated for its anticancer potential in animal models.

Echinococcus granulosus protoscoleces promotes proliferation and invasion of hepatocellular carcinoma cells

There may exist a connection between Echinococcus granulosus infection and cancer development. Here, it is aimed to investigate specific effects of E. granulosus protoscoleces (PSCs) on the proliferation and invasion capacities of hepatocellular carcinoma (HCC) cells in vitro and ex vitro. HepG2 cells were cultured with different quantities of E. granulosus PSCs in vitro. MTT analysis was used to evaluate effects of E. granulosus PSCs on the proliferation of HepG2 cells. Besides, scratch and transwell assays were respectively used for the detection of HepG2 cells migration and invasion capacities after co-culture with E. granulosus PSCs. Then, HepG2 cells were subcutaneously transplanted into nude mice with or without E. granulosus PSCs. From the 25th day of transplantation, the volume of subcutaneous lesions was measured every four days. At the 37th day, subcutaneous lesions were removed and their weight was evaluated. H&E staining was used for detecting basic pathological changes. HepG2 cells grew well without obvious morphological changes. Proliferation rate and migration capacity of HepG2 cells were higher in the co-culture group than the control group, which was closely associated with quantities of E. granulosus PSCs and co-culture time length. Moreover, HepG2 cells co-cultured with E. granulosus PSCs had stronger invasion ability than the control HepG2 cells. Importantly, there existed significant differences in the volume and weight of subcutaneous lesions after transplanting HepG2 cells with E. granulosus PSCs than the control group. HepG2 cells were also more pathologically heterogeneous in morphology after transplantation with E. granulosus PSCs. Thus, E. granulosus PSCs may promote proliferation and invasion of HCC cells.

Anticancer Actions of Azurin and Its Derived Peptide p28

Cancers are a great threat to humans. In cancer therapy, surgical removal of the tumor combined with radiotherapy and chemotherapy is the most routine treatment procedure and usually the most effective. However, radiotherapy and chemotherapy drugs that kill cancer cells efficiently also kill normal cells, thus exhibiting large side effects. Cancer-targeted drugs, which aim to specifically recognize proteins or signaling pathways associated with tumor proliferation and migration, have achieved marked progress in recent years. Azurin is a copper-containing redox protein secreted by Pseudomonas aeruginosa. Azurin and its derived peptide p28 preferentially enter a variety of cancer cells and induce apoptosis or cell cycle arrest. Mechanistic studies revealed that azurin and p28 target the p53 and receptor tyrosine kinase signaling pathways as well as other pathways. Two phase I trials of p28 have been carried out, with findings that p28 is safe and exhibits anticancer activity in both adult and pediatric patients. In this review paper, we provide an up-to-date summary of progress on the anticancer mechanisms and therapeutic strategies for azurin and p28.

Bacteria and bacterial anticancer agents as a promising alternative for cancer therapeutics

Cancer is the leading cause of deaths worldwide, though significant advances have occurred in its diagnosis and treatment. The development of resistance against chemotherapeutic agents, their side effects, and non-specific toxicity urge to screen for the novel anticancer agent. Hence, the development of novel anticancer agents with a new mechanism of action has become a major scientific challenge. Bacteria and bacterially produced bioactive compounds have recently emerged as a promising alternative for cancer therapeutics. Bacterial anticancer agents such as antibiotics, bacteriocins, non-ribosomal peptides, polyketides, toxins, etc. These are adopted different mechanisms of actions such as apoptosis, necrosis, reduced angiogenesis, inhibition of translation and splicing, and obstructing essential signaling pathways to kill cancer cells. Also, live tumor-targeting bacteria provided a unique therapeutic alternative for cancer treatment. This review summarizes the anticancer properties and mechanism of actions of the anticancer agents of bacterial origin and antitumor bacteria along with their possible future applications in cancer therapeutics.

p28 Bacterial Peptide, as an Anticancer Agent

Cancer remains a major cause of morbidity and mortality irrespective of the type of conventional chemotherapy. Therefore, there is an urgent need for new and effective anticancer therapeutic agents. Bacterial proteins and their derivative peptides appear as a promising approach for cancer treatment. Several, including an amphipathic, α-helical, 28-amino acid peptide derived from azurin, a 128-amino acid copper-containing redox protein secreted from Pseudomonas aeruginosa, show clinical promise in the treatment of adult and pediatric solid tumors. The peptide, p28, is a post-translational, multi-target anticancer agent that preferentially enters a wide variety of solid tumor cells. Mechanistically, after entry, p28 has two major avenues of action. It binds to both wild-type and mutant p53 protein, inhibiting constitutional morphogenic protein 1 (Cop1)-mediated ubiquitination and proteasomal degradation of p53. This results in increased levels of p53, which induce cell-cycle arrest at G2/M and an eventual apoptosis that results in tumor cell shrinkage and death. In addition, p28 also preferentially enters nascent endothelial cells and decreases the phosphorylation of FAK and Akt inhibiting endothelial cell motility and migration. Here, we review the current basic and clinical evidence suggesting the potential of p28 as a cancer therapeutic peptide.

Global Sequence Analysis and Expression of Azurin Gene in Different Clinical Specimens of Burn Patients with Pseudomonas aeruginosa Infection

Aim

The purpose of this study was to analyze the sequence of azurin gene in relation to its expression in Pseudomanas aeruginosa strains isolated from different clinical specimens of burn patients. Moreover, in silico sequence analysis of azurin gene using globally reported sequences was intended.

Materials and Methods

Fifty-nine multidrug-resistant P. aeruginosa isolates were selected from different clinical specimens of patients suffering from burn wound infections in two university hospitals and subjected to antibacterial susceptibility testing. The frequency and genetic diversity of the azurin gene was determined by polymerase chain reaction (PCR) and Sanger sequencing. The azurin gene sequences were compared with the sequence data from other countries. The expression level of azurin gene in P. aeruginosa isolates with different azurin sequences from different clinical specimens was evaluated by real-time PCR.

Results and Conclusion

About 98%-100% of the isolates were resistant to gentamicin, tobramycin, cefoxitin, ciprofloxacin, amikacin, and imipenem, while 100% and 23.9% of the isolates were susceptible to colistin and ceftazidime, respectively. Only eight point mutations were detected with amino acid substitutions in only two positions (81 and 102). In global analysis, 93% of strains showed missense mutation at positions 81 (alanine to threonine). The majority (81%) of Iranian strains were allocated to two major clusters distinct from the rest of world, which may suggest that strains from Iran have made a distinct genetic stockpile through point mutations which has established them separate from the other counties. However, 19% were distributed in different clusters together with the strains from different countries of North and South America, Europe, South and East Asia. The expression level of the azurin gene was statistically higher in the isolates collected from the blood of burns patients with systemic infection compared to the isolates collected from other specimens (wound, catheter and tissue), which shows a positive correlation between azurin gene expression and increased pathogenicity and capability for dissemination. This study may open new insight about azurin genetic variation and significance in P. aeruginosa pathogenesis.

Bacterial delivery of the anti-tumor azurin-like protein Laz to glioblastoma cells

Salmonella typhimurium VNP-20009 (VNP) is a non-pathogenic attenuated strain, which, as a facultative anaerobe, preferentially accumulates in hypoxic regions of solid tumors. Here, VNP was utilized as a delivery vehicle of the anti-tumor protein Lipidated azurin, Laz, which is produced by the meningitis-causing bacterium Neisseria meningitides. In brain cancer cells, Laz has been demonstrated to induce apoptosis through an interaction with the tumor suppressor protein p53. In this study, the laz gene, including its signal sequence, was cloned downstream of a hypoxia inducible promoter (HIP-1), before being electroporated into VNP. Successful ectopic expression and export of the Laz protein by VNP under hypoxic conditions were confirmed by Western blot analysis of the cell-free culture medium. Effective expression of Laz by VNP was investigated in two glioblastoma cell lines: LN-229 and U-373, with the latter line carrying a mutated version of p53; as well as in the breast cancer line MCF-7. Cytotoxicity of the VNP-Laz was assessed by determining the fluorescence of the apoptotic marker caspases 3/7. Compared to the purified Laz, VNP-Laz, significantly induced apoptosis in MCF-7, LN-229 and, to a much lower extent in U-373 cells, suggesting a p53-linked mechanism. Our results might represent a new approach of targeted gene delivery and suggest a potential application in brain tumor therapy.

Perturbing the Dynamics and Organization of Cell Membrane Components: A New Paradigm for Cancer-Targeted Therapies

Cancer is a multi-process disease where different mechanisms exist in parallel to ensure cell survival and constant adaptation to the extracellular environment. To adapt rapidly, cancer cells re-arrange their plasma membranes to sustain proliferation, avoid apoptosis and resist anticancer drugs. In this review, we discuss novel approaches based on the modifications and manipulations that new classes of molecules can exert in the plasma membrane lateral organization and order of cancer cells, affecting growth factor signaling, invasiveness, and drug resistance. Furthermore, we present azurin, an anticancer protein from bacterial origin, as a new approach in the development of therapeutic strategies that target the cell membrane to improve the existing standard therapies.

Bacteriocins: perspective for the development of novel anticancer drugs

Antimicrobial peptides (AMPs) from prokaryotic source also known as bacteriocins are ribosomally synthesized by bacteria belonging to different eubacterial taxonomic branches. Most of these AMPs are low molecular weight cationic membrane active peptides that disrupt membrane by forming pores in target cell membranes resulting in cell death. While these peptides known to exhibit broad-spectrum antimicrobial activity, including antibacterial and antifungal, they displayed minimal cytotoxicity to the host cells. Their antimicrobial efficacy has been demonstrated in vivo using diverse animal infection models. Therefore, we have discussed some of the promising peptides for their ability towards potential therapeutic applications. Further, some of these bacteriocins have also been reported to exhibit significant biological activity against various types of cancer cells in different experimental studies. In fact, differential cytotoxicity towards cancer cells as compared to normal cells by certain bacteriocins directs for a much focused research to utilize these compounds as novel therapeutic agents. In this review, bacteriocins that demonstrated antitumor activity against diverse cancer cell lines have been discussed emphasizing their biochemical features, selectivity against extra targets and molecular mechanisms of action.

Pseudomonas aeruginosa ExoS Induces Intrinsic Apoptosis in Target Host Cells in a Manner That is Dependent on its GAP Domain Activity

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen that causes serious infections in immunocompromised individuals and cystic fibrosis patients. ExoS and ExoT are two homologous bifunctional Type III Secretion System (T3SS) virulence factors that induce apoptosis in target host cells. They possess a GTPase Activating Protein (GAP) domain at their N-termini, which share ~76% homology, and an ADP-ribosyltransferase (ADPRT) domain at their C-termini, which target non-overlapping substrates. Both the GAP and the ADPRT domains contribute to ExoT's cytotoxicity in target epithelial cells, whereas, ExoS-induced apoptosis is reported to be primarily due to its ADPRT domain. In this report, we demonstrate that ExoS/GAP domain is both necessary and sufficient to induce mitochondrial apoptosis. Our data demonstrate that intoxication with ExoS/GAP domain leads to enrichment of Bax and Bim into the mitochondrial outer-membrane, disruption of mitochondrial membrane and release of and cytochrome c into the cytosol, which activates initiator caspase-9 and effector caspase-3, that executes cellular death. We posit that the contribution of the GAP domain in ExoS-induced apoptosis was overlooked in prior studies due to its slower kinetics of cytotoxicity as compared to ADPRT. Our data clarify the field and reveal a novel virulence function for ExoS/GAP as an inducer of apoptosis.

Bacterial cupredoxin azurin hijacks cellular signaling networks: Protein-protein interactions and cancer therapy

Azurin secreted by Pseudomonas aeruginosa is an anticancer bacteriocin, which preferentially enters human cancer cells and induces apoptosis or growth inhibition. It turns out that azurin is a multi-target anticancer agent interfering in the p53 signaling pathway and the non-receptor tyrosine kinases signaling pathway. This suggests that azurin exerts its anticancer activity by interacting with multiple targets and interfering in multiple steps in disease progression. Therefore, azurin could overcome resistance to therapy. Besides azurin, putative bacteriocins that possess functional properties similar to those of azurin have been identified in more bacteria species. A systematic investigation on the anticancer mechanisms of azurin and the azurin-like bacteriocins will provide more and better options in cancer therapy. In this review, we summarize how azurin and the derived peptides hijack key cellular regulators or cell surface receptors to remodel the cellular signaling networks. In particular, we highlight the necessity of determining the structure of azurin/p53 complex and investigating the influence of post-translational modifications on interactions between azurin and p53. Therapeutic applications of azurin and derived peptides are also discussed.

Structure, Dynamics, and Electron Transfer of Azurin Bound to a Gold Electrode

Blue copper redox protein azurin (AZ) constitutes an ideal active element for building bionano-optoelectronic devices based on the intriguing interplay among its electron transfer (ET), vibrational, and optical properties. A full comprehension of its dynamical and functional behavior is required for efficient applications. Here, AZ bound to gold electrode via its disulfide bridge was investigated by a molecular dynamics simulation approach taking into account for gold electron polarization which provides a more realistic description of the protein-gold interaction. Upon binding to gold, AZ undergoes slight changes in its secondary structure with the preservation of the copper-containing active site structure. Binding of AZ to gold promotes new collective motions, with respect to free AZ, as evidenced by essential dynamics. Analysis of the ET from the AZ copper ion to the gold substrate, performed by the Pathways model, put into evidence the main residues and structural motifs of AZ involved in the ET paths. During the dynamical evolution of the bionanosystem, transient contacts between some lateral protein atoms and the gold substrate occurred; concomitantly, the opening of additional ET channels with much higher rates was registered. These results provide new and detailed insights on the dynamics and ET properties of the AZ-gold system, by also helping to rationalize some imaging and conductive experimental evidences and also to design new bionanodevices with tailored features.

Pseudomonas Quinolone Signal Induces Oxidative Stress and Inhibits Heme Oxygenase-1 Expression in Lung Epithelial Cells

Pseudomonasaeruginosa causes lung infections in patients with cystic fibrosis (CF). The Pseudomonas quinolone signal (PQS) compound is a secreted P. aeruginosa virulence factor that contributes to the pathogenicity of P. aeruginosa We were able to detect PQS in sputum samples from CF patients infected with P. aeruginosa but not in samples from uninfected patients. We then tested the hypothesis that PQS induces oxidative stress in host cells by determining the ability of PQS to induce the production of reactive oxygen species (ROS) in lung epithelial cells (A549 and primary normal human bronchial epithelial [NHBE]) cells and macrophages (J774A.1 and THP-1). ROS production induced by PQS was detected with fluorescent probes (dichlorodihydrofluorescein diacetate, dihydroethidium, and MitoSOX Red) in conjunction with confocal microscopy and flow cytometry. PQS induced ROS production in lung epithelial (A549 and NHBE) cells and macrophages (J774A.1 and THP-1 cells). NHBE cells were sensitive to PQS concentrations as low as 500 ng/ml. PQS significantly induced early apoptosis (P < 0.05, n = 6) in lung epithelial cells, as measured by annexin/propidium iodide detection by flow cytometry. However, no change in apoptosis upon PQS treatment was seen in J774A.1 cells. Heme oxygenase-1 (HO-1) protein is an antioxidant enzyme usually induced by oxidative stress. Interestingly, incubation with PQS significantly reduced HO-1 and NrF2 expression in A549 and NHBE cells but increased HO-1 expression in J774A.1 cells (P < 0.05, n = 3), as determined by immunoblotting and densitometry. These PQS effects on host cells could play an important role in the pathogenicity of P. aeruginosa infections.

Quantitative proteomics unravels that the post-transcriptional regulator Crc modulates the generation of vesicles and secreted virulence determinants of Pseudomonas aeruginosa

Recent research indicates that the post-transcriptional regulator Crc modulates susceptibility to antibiotics and virulence in Pseudomonas aeruginosa. Several P. aeruginosa virulence factors are secreted or engulfed in vesicles. To decipher the Crc modulation of P. aeruginosa virulence, we constructed a crc deficient mutant and measure the proteome associated extracellular vesicles and the vesicle-free secretome using iTRAQ. Fifty vesicle-associated proteins were more abundant and 14 less abundant in the crc-defective strain, whereas 37 were more abundant and 17 less abundant in the vesicle-free secretome. Among them, virulence determinants, such as ToxA, protease IV, azurin, chitin-binding protein, PlcB and Hcp1, were less abundant in the crc-defective mutant. Transcriptomic analysis revealed that some of the observed changes were post-transcriptional and, thus, could be attributed to a direct Crc regulatory role; whereas, for other differentially secreted proteins, the regulatory role was likely indirect. We also observed that the crc mutant presented an impaired vesicle-associated secretion of quorum sensing signal molecules and less cytotoxicity than its wild-type strain. Our results offer new insights into the mechanisms by which Crc regulates P. aeruginosa virulence, through the modulation of vesicle formation and secretion of both virulence determinants and quorum sensing signals. This article is part of a Special Issue entitled: HUPO 2014.

Structural studies on Laz, a promiscuous anticancer Neisserial protein

Azurin and Laz (lipidated azurin) are 2 bacterial proteins with anticancer, anti-viral and anti-parasitic activities. Azurin, isolated from the bacterium Pseudomonas aeruginosa, termed Paz, demonstrates anticancer activity against a range of cancers but not against brain tumors. In contrast, Laz is produced by members of Gonococci/Meningococci, including Neisseria meningitides which can cross the blood-brain barrier to infect brain meninges. It has been previously reported that Laz has an additional 39 amino acid moiety, called an H.8 epitope, in the N-terminal part of the azurin moiety that allows Laz to cross the entry barrier to brain tumors such as glioblastomas. Exactly, how the H.8 epitope helps the azurin moiety of Laz to cross the entry barriers to attack glioblastoma cells is unknown. In this paper, we describe the structural features of the H.8 moiety in Laz using X-ray crystallography and demonstrate that while the azurin moiety of Laz adopts a β-sandwich fold with 2 β-sheets arranged in the Greek key motif, the H.8 epitope was present as a disordered structure outside the Greek key motif. Structures of Paz and H.8 epitope-deficient Laz are well superimposed. The structural flexibility of the H.8 motif in Laz explains the extracellular location of Laz in Neisseria where it can bind the key components of brain tumor cells to disrupt their tight junctions and allow entry of Laz inside the tumors to exert cytotoxicity.

Role of bacteria in oral carcinogenesis

Oral cancer is the most common cancer diagnosed in Indian men and is the leading cause of cancer deaths. It is considered as a multistep and multifactorial disease. Besides accumulation of genetic mutations, numerous other carcinogens are involved. In this category, viral and chemical carcinogens are well studied and documented. However, in the oral cavity, the role of microbiota in carcinogenesis is not known. Microbial populations on mouth mucosa differ between healthy and malignant sites, and certain oral bacterial species have been linked with malignancies, but the evidence is still weak in this respect. Nevertheless, oral microorganisms inevitably up-regulate cytokines and other inflammatory mediators that affect the complex metabolic pathways, and may thus be involved in carcinogenesis. Poor oral health associates statistically with prevalence of many types of cancer such as pancreatic and gastrointestinal cancer. This review presents possible carcinogenesis pathway involved in bacterial carcinogenesis, commonly implicated bacteria in oral carcinogenesis, and their role in cancer therapeutics as well.

Antileishmanial activity of a series of N²,N⁴-disubstituted quinazoline-2,4-diamines

A series of N(2),N(4)-disubstituted quinazoline-2,4-diamines has been synthesized and tested against Leishmania donovani and L. amazonensis intracellular amastigotes. A structure-activity and structure-property relationship study was conducted in part using the Topliss operational scheme to identify new lead compounds. This study led to the identification of quinazolines with EC50 values in the single digit micromolar or high nanomolar range in addition to favorable physicochemical properties. Quinazoline 23 also displayed efficacy in a murine model of visceral leishmaniasis, reducing liver parasitemia by 37% when given by the intraperitoneal route at 15 mg kg(-1) day(-1) for 5 consecutive days. Their antileishmanial efficacy, ease of synthesis, and favorable physicochemical properties make the N(2),N(4)-disubstituted quinazoline-2,4-diamine compound series a suitable platform for future development of antileishmanial agents.

Cell death paradigms in the pathogenesis of Mycobacterium tuberculosis infection

Cell death or senescence is a fundamental event that helps maintain cellular homeostasis, shapes the growth of organism, and provides protective immunity against invading pathogens. Decreased or increased cell death is detrimental both in infectious and non-infectious diseases. Cell death is executed both by regulated enzymic reactions and non-enzymic sudden collapse. In this brief review we have tried to summarize various cell death modalities and their impact on the pathogenesis of Mycobacterium tuberculosis.

Transcriptome profiling reveals links between ParS/ParR, MexEF-OprN, and quorum sensing in the regulation of adaptation and virulence in Pseudomonas aeruginosa

Background

The ParS/ParR two component regulatory system plays critical roles for multidrug resistance in Pseudomonas aeruginosa. It was demonstrated that in the presence of antimicrobials, ParR enhances bacterial survival by distinct mechanisms including activation of the mexXY efflux genes, enhancement of lipopolysaccharide modification through the arn operon, and reduction of the expression of oprD porin.

Results

In this study, we report on transcriptomic analyses of P. aeruginosa PAO1 wild type and parS and parR mutants growing in a defined minimal medium. Our transcriptomic analysis provides the first estimates of transcript abundance for the 5570 coding genes in P. aeruginosa PAO1. Comparative transcriptomics of P. aeruginosa PAO1 and par mutants identified a total of 464 genes regulated by ParS and ParR. Results also showed that mutations in the parS/parR system abolished expression of the mexEF-oprN operon by down-regulating the regulatory gene mexS. In addition to the known effects on drug resistance genes, transcript abundances of the quorum sensing genes (rhlIR and pqsABCDE-phnAB) were higher in both parS and parR mutants. In accordance with these results, a significant portion of the ParS/ParR regulated genes belonged to the MexEF-OprN and quorum sensing regulons. Deletion of the par genes also led to increased phenazine production and swarming motility, consistent with the up-regulation of the phenazine and rhamnolipid biosynthetic genes, respectively.

Conclusion

Our results link the ParS/ParR two component signal transduction system to MexEF-OprN and quorum sensing systems in P. aeruginosa. These results expand our understanding of the roles of the ParS/ParR system in the regulation of gene expression in P. aeruginosa, especially in the absence of antimicrobials.

Antimalarial activity of cupredoxins: the interaction of Plasmodium merozoite surface protein 119 (MSP119) and rusticyanin

The discovery of effective new antimalarial agents is urgently needed. One of the most frequently studied molecules anchored to the parasite surface is the merozoite surface protein-1 (MSP1). At red blood cell invasion MSP1 is proteolytically processed, and the 19-kDa C-terminal fragment (MSP119) remains on the surface and is taken into the red blood cell, where it is transferred to the food vacuole and persists until the end of the intracellular cycle. Because a number of specific antibodies inhibit erythrocyte invasion and parasite growth, MSP119 is therefore a promising target against malaria. Given the structural homology of cupredoxins with the Fab domain of monoclonal antibodies, an approach combining NMR and isothermal titration calorimetry (ITC) measurements with docking calculations based on BiGGER is employed on MSP119-cupredoxin complexes. Among the cupredoxins tested, rusticyanin forms a well defined complex with MSP119 at a site that overlaps with the surface recognized by the inhibitory antibodies. The addition of holo-rusticyanin to infected cells results in parasitemia inhibition, but negligible effects on parasite growth can be observed for apo-rusticyanin and other proteins of the cupredoxin family. These findings point to rusticyanin as an excellent therapeutic tool for malaria treatment and provide valuable information for drug design.

Interaction of an anticancer peptide fragment of azurin with p53 and its isolated domains studied by atomic force spectroscopy

p28 is a 28-amino acid peptide fragment of the cupredoxin azurin derived from Pseudomonas aeruginosa that preferentially penetrates cancerous cells and arrests their proliferation in vitro and in vivo. Its antitumor activity reportedly arises from post-translational stabilization of the tumor suppressor p53 normally downregulated by the binding of several ubiquitin ligases. This would require p28 to specifically bind to p53 to inhibit specific ligases from initiating proteosome-mediated degradation. In this study, atomic force spectroscopy, a nanotechnological approach, was used to investigate the interaction of p28 with full-length p53 and its isolated domains at the single molecule level. Analysis of the unbinding forces and the dissociation rate constant suggest that p28 forms a stable complex with the DNA-binding domain of p53, inhibiting the binding of ubiquitin ligases other than Mdm2 to reduce proteasomal degradation of p53.

The bacterial protein azurin enhances sensitivity of oral squamous carcinoma cells to anticancer drugs

PURPOSE

Surgical therapy is the primary treatment for oral cancer, but it can cause facial distortion. Therefore, if anticancer drugs are effective against oral cancer, they may be used preferentially. However, oral squamous carcinoma cells (OSCCs) are resistant to these drugs, so finding a way to enhance the sensitivity of these cells to anticancer drugs is important. The bacterial protein azurin is known to selectively enter cancer cells and induce apoptosis. In this study, we show the anticancer effect of azurin in OSCC.

MATERIALS AND METHODS

OSCC cell line (YD-9) was subjected to azurin treatment. Cell viability, morphology and protein expression levels were monitored after treatment of azurin. Cells were also subjected to combination treatment of azurin with either 5-fluorouracil or etopside.

RESULTS

Azurin-treated cells showed decreased cell viability accompanied by apoptotic phenotypes including morphological change, DNA breakage, and increases in p53 and cyclin B1 protein levels. Combination treatment of azurin with other anti-tumor agents caused an increase in sensitivity to anticancer drugs in azurin-treated YD-9 cells.

CONCLUSION

Azurin has a strong synergistic anticancer effect on oral cancer cells when it is used along with anticancer drugs.

The global regulator Crc modulates metabolism, susceptibility to antibiotics and virulence in Pseudomonas aeruginosa

The capacity of a bacterial pathogen to produce a disease in a treated host depends on the former's virulence and resistance to antibiotics. Several scattered pieces of evidence suggest that these two characteristics can be influenced by bacterial metabolism. This potential relationship is particularly important upon infection of a host, a situation that demands bacteria adapt their physiology to their new environment, making use of newly available nutrients. To explore the potential cross-talk between bacterial metabolism, antibiotic resistance and virulence, a Pseudomonas aeruginosa model was used. This species is an important opportunistic pathogen intrinsically resistant to many antibiotics. The role of Crc, a global regulator that controls the metabolism of carbon sources and catabolite repression in Pseudomonas, was analysed to determine its contribution to the intrinsic antibiotic resistance and virulence of P. aeruginosa. Using proteomic analyses, high-throughput metabolic tests and functional assays, the present work shows the virulence and antibiotic resistance of this pathogen to be linked to its physiology, and to be under the control (directly or indirectly) of Crc. A P. aeruginosa strain lacking the Crc regulator showed defects in type III secretion, motility, expression of quorum sensing-regulated virulence factors, and was less virulent in a Dictyostelium discoideum model. In addition, this mutant strain was more susceptible to beta-lactams, aminoglycosides, fosfomycin and rifampin. Crc might therefore be a good target in the search for new antibiotics.

Structural characteristics of the hydrophobic patch of azurin and its interaction with p53: a site-directed spin labeling study

Site-directed spin labeling (SDSL) is a powerful tool for monitoring protein structure, dynamics and conformational changes. In this study, the domain-specific properties of azurin and its interaction with p53 were studied using this technique. Mutations of six residues, that are located in the hydrophobic patch of azurin, were prepared and spin labeled. Spectra of the six azurin mutants in solution showed that spin labeled residues 45 and 63 are in a very restricted environment, residues 59 and 65 are in a spacious environment and have free movement, and residues 49 and 51 are located in a relatively closed pocket. Polarity experiments confirmed these results. The changes observed in the spectra of spin labeled azurin upon interaction with p53 indicate that the hydrophobic patch is involved in this interaction. Our results provide valuable insight into the topographic structure of the hydrophobic domain of azurin, as well as direct evidence of its interaction with p53 in solution via the hydrophobic patch. Cytotoxicity studies of azurin mutants showed that residues along the hydrophobic patch are important for its cytotoxicity.

Microbial-based therapy of cancer: current progress and future prospects

The use of bacteria in the regression of certain forms of cancer has been recognized for more than a century. Much effort, therefore, has been spent over the years in developing wild-type or modified bacterial strains to treat cancer. However, their use at the dose required for therapeutic efficacy has always been associated with toxicity problems and other deleterious effects. Recently, the old idea of using bacteria in the treatment of cancer has attracted considerable interest and new genetically engineered attenuated strains as well as microbial compounds that might have specific anticancer activity without side effects are being evaluated for their ability to act as new anticancer agents. This involves the use of attenuated bacterial strains and expressing foreign genes that encode the ability to convert non-toxic prodrugs to cytotoxic drugs. Novel strategies also include the use of bacterial products such as proteins, enzymes, immunotoxins and secondary metabolites, which specifically target cancer cells and cause tumor regression through growth inhibition, cell cycle arrest or apoptosis induction. In this review we describe the current knowledge and discuss the future directions regarding the use of bacteria or their products, in cancer therapy.

A peptide fragment of azurin induces a p53-mediated cell cycle arrest in human breast cancer cells

We report that amino acids 50 to 77 of azurin (p28) preferentially enter the human breast cancer cell lines MCF-7, ZR-75-1, and T47D through a caveolin-mediated pathway. Although p28 enters p53 wild-type MCF-7 and the isogenic p53 dominant-negative MDD2 breast cancer cell lines, p28 only induces a G(2)-M-phase cell cycle arrest and apoptosis in MCF-7 cells. p28 exerts its antiproliferative activity by reducing proteasomal degradation of p53 through formation of a p28:p53 complex within a hydrophobic DNA-binding domain (amino acids 80-276), increasing p53 levels and DNA-binding activity. Subsequent elevation of the cyclin-dependent kinase inhibitors p21 and p27 reduces cyclin-dependent kinase 2 and cyclin A levels in a time-dependent manner in MCF-7 cells but not in MDD2 cells. These results suggest that p28 and similar peptides that significantly reduce proteasomal degradation of p53 by a MDM2-independent pathway(s) may provide a unique series of cytostatic and cytotoxic (apoptotic) chemotherapeutic agents.

The construction of the eukaryotic expression plasmid pcDNA3.1/azurin and the increased apoptosis of U2OS cells transfected with it

In our previous study, we demonstrated that azurin could selectively trigger apoptosis in human osteosarcoma cell line U2OS cells. However, the rate of apoptosis (35.8 ± 3.2%) is not very high, and azurin is too expensive to obtain readily. To solve these problems, we constructed a eukaryotic expression plasmid containing the azurin gene with an influenza virus haemagglutinin 9 peptide HA epitope tag, and transfected the recombinant plasmid pcDNA3.1(+)/azurin into U2OS cells. RT-PCR and Western blot analysis validated the successful transfection and the expression of the azurin-HA protein. Conspicuous apoptosis of the transfected cells was detected by flow cytometry (FCM) and the DNA ladder test. The apoptosis rate reached 64.3 ± 13.1%. The transcriptional levels of the Bax and p53 genes increased significantly in U2OS cells transfected with pcDNA3.1(+)/azurin, but the Bcl-2 mRNA level decreased. There was no difference in the levels of Bcl-xl mRNA and Survivin mRNA. We propose that the transfection of the recombinant plasmid pcDNA3.1(+)/azurin can significantly induce apoptosis in U2OS cells. This is closely associated with the up-regulation of the transcriptional level of the Bax and p53 genes, and the down-regulation of that of the Bcl-2 gene.

Expression of Pseudomonas aeruginosa toxin ExoS effectively induces apoptosis in host cells

Pseudomonas aeruginosa is an opportunistic bacterial pathogen that primarily infects immunocompromised individuals and patients with cystic fibrosis. Invasive strains of P. aeruginosa are known to induce apoptosis at a high frequency in HeLa cells and in many other cell lines, a process that is dependent on the ADP-ribosylation (ADPRT) activity of a type III secreted protein ExoS. In our previous report, it was proposed that P. aeruginosa secreting ExoS, upon infection, shuts down host cell survival signal pathways by inhibiting ERK1/2 and p38 activation, and it activates proapoptotic pathways through activation of JNK1/2, leading ultimately to cytochrome c release and activation of caspases. In this study, we demonstrate that the expression of ExoS in HeLa cells by eukaryotic expression vector effectively caused apoptosis in an ADPRT activity-dependent manner, indicating that ExoS alone is sufficient to trigger apoptotic death of host cells independent of any other bacterial factors. By expressing an EGFP-ExoS fusion protein, we were able to directly correlate the death of HeLa cells with the presence of intracellular ExoS and further proved the dependence of this process on both JNK activation and mitochondrial proapoptotic event. The cellular pathway responsible for the ExoS-induced cytotoxicity appears to be well conserved, since the expression of the ADPRT-competent ExoS also induced rapid cell death in the Drosophila melanogaster S2 cell lines. The presented study not only highlights the ability of ExoS ADPRT to modulate host cell signaling, eventually leading to apoptosis, but also establishes ExoS as a valuable tool, in principle, for the elucidation of apoptosis mechanisms.

Two GacA-dependent small RNAs modulate the quorum-sensing response in Pseudomonas aeruginosa

In Pseudomonas aeruginosa, the GacS/GacA two-component system positively controls the quorum-sensing machinery and the expression of extracellular products via two small regulatory RNAs, RsmY and RsmZ. An rsmY rsmZ double mutant and a gacA mutant were similarly impaired in the synthesis of the quorum-sensing signal N-butanoyl-homoserine lactone, the disulfide bond-forming enzyme DsbA, and the exoproducts hydrogen cyanide, pyocyanin, elastase, chitinase (ChiC), and chitin-binding protein (CbpD). Both mutants showed increased swarming ability, azurin release, and early biofilm development.

Oxidative stress by biphenyl metabolites induces inhibition of bacterial cell separation

Cell-cell separation of a polychlorinated biphenyl (PCB)-degrading bacterium Comamonas testosteroni TK102 was monitored by flow cytometry. When monohydroxy metabolites of biphenyl (BP) (2-hydroxybiphenyl and 3-hydroxybiphenyl) were added to the culture, cell-cell separation of strain TK102 was inhibited at stationary phase. This inhibition was reproduced on non-PCB degrading bacteria such as Pseudomonas putida PpY101 and Escherichia coli MV1184, but was not observed on Pseudomonas aeruginosa PAO1. An opportunistic pathogen, P. aeruginosa PAO1, produces exopolysaccharide, which is known to scavenge damaging chemicals such as reactive oxygen species (ROS). The higher level of ROS and lipid peroxidants were detected in the cells treated by monohydroxybiphenyls. Fat-soluble vitamin E, which is a lipid radical scavenger, maintained bacterial cell separation during monohydroxybiphenyls treatment. Our results demonstrated that intracellular oxidative stress played an important role in the inhibition of bacterial cell separation during BP metabolism. This study shows that metabolites of environmental pollutants, such as monohydroxylated BP, inhibit bacterial cell separation by oxidative stress.

Azurin of pathogenic Neisseria spp. is involved in defense against hydrogen peroxide and survival within cervical epithelial cells

Laz, a lipid-modified azurin of the human pathogens Neisseria gonorrhoeae and Neisseria meningitidis, is involved in defense against oxidative stress and copper toxicity; laz mutant strains are hypersensitive to hydrogen peroxide and copper. The N. gonorrhoeae laz mutant also has decreased survival in an ex vivo primary human ectocervical epithelial assay.

Human cytochrome c enters murine J774 cells and causes G1 and G2/M cell cycle arrest and induction of apoptosis

Cytochrome c is well known as a carrier of electrons during respiration. Current evidence indicates that cytochrome c also functions as a major component of apoptosomes to induce apoptosis in eukaryotic cells as well as an antioxidant. More recently, a prokaryotic cytochrome c, cytochrome c(551) from Pseudomonas aeruginosa, has been shown to enter in mammalian cells such as the murine macrophage-like J774 cells and causes inhibition of cell cycle progression. Much less is known about such functions by mammalian cytochromes c, particularly the human cytochrome c. We now report that similar to P. aeruginosa cytochrome c(551), the purified human cytochrome c protein can enter J774 cells and induce cell cycle arrest at the G(1) to S phase, as well as at the G(2)/M phase at higher concentrations. Unlike P. aeruginosa cytochrome c(551) which had no effect on the induction of apoptosis, human cytochrome c induces significant apoptosis and cell death in J774 cells, presumably through inhibition of the cell cycle at the G(2)/M phase. When incubated with human breast cancer MCF-7 and normal mammary epithelial cell line MCF-10A1 cells, human cytochrome c entered in both types of cells but induced cell death only in the normal MCF-10A1 cells. The ability of human cytochrome c to enter J774 cells was greatly reduced at 4 degrees C, suggesting energy requirement in the entry process.