Nickel nanoparticle-induced cell transformation: involvement of DNA damage and DNA repair defect through HIF-1α/miR-210/Rad52 pathway

Background Nickel nanoparticles (Nano-Ni) are increasingly used in industry and biomedicine with the development of nanotechnology. However, the genotoxic and carcinogenic effects of Nano-Ni and the underlying mechanisms are still unclear. Methods At first, dose–response (0, 10, 20, and 30 μg/mL) and time-response (0, 3, 6, 12, and 24 h) studies were performed in immortalized normal human bronchial epithelial cells BEAS-2B to observe the effects of Nano-Ni on DNA damage response (DDR)-associated proteins and the HIF-1α/miR-210/Rad52 pathway by real-time PCR or Western blot. Then, a Hsp90 inhibitor (1 µM of 17-AAG, an indirect HIF-1α inhibitor), HIF-1α knock-out (KO) cells, and a miR-210 inhibitor (20 nM) were used to determine whether Nano-Ni-induced Rad52 down-regulation was through HIF-1α nuclear accumulation and miR-210 up-regulation. In the long-term experiments, cells were treated with 0.25 and 0.5 µg/mL of Nano-Ni for 21 cycles (~ 150 days), and the level of anchorage-independent growth was determined by plating the cells in soft agar. Transduction of lentiviral particles containing human Rad52 ORF into BEAS-2B cells was used to observe the role of Rad52 in Nano-Ni-induced cell transformation. Nano-Ni-induced DNA damage and dysregulation of HIF-1α/miR-210/Rad52 pathway were also investigated in vivo by intratracheal instillation of 50 µg per mouse of Nano-Ni. gpt delta transgenic mice were used to analyze mutant frequency and mutation spectrum in mouse lungs after Nano-Ni exposure. Results Nano-Ni exposure caused DNA damage at both in vitro and in vivo settings, which was reflected by increased phosphorylation of DDR-associated proteins such as ATM at Ser1981, p53 at Ser15, and H2AX. Nano-Ni exposure also induced HIF-1α nuclear accumulation, miR-210 up-regulation, and down-regulation of homologous recombination repair (HRR) gene Rad52. Inhibition of or knocking-out HIF-1α or miR-210 ameliorated Nano-Ni-induced Rad52 down-regulation. Long-term low-dose Nano-Ni exposure led to cell malignant transformation, and augmentation of Rad52 expression significantly reduced Nano-Ni-induced cell transformation. In addition, increased immunostaining of cell proliferation markers, Ki-67 and PCNA, was observed in bronchiolar epithelial cells and hyperplastic pneumocytes in mouse lungs at day 7 and day 42 after Nano-Ni exposure. Finally, using gpt delta transgenic mice revealed that Nano-Ni exposure did not cause increased gpt mutant frequency and certain DNA mutations, such as base substitution and small base insertions/deletions, are not the main types of Nano-Ni-induced DNA damage. Conclusions This study unraveled the mechanisms underlying Nano-Ni-induced cell malignant transformation; the combined effects of Nano-Ni-induced DNA damage and DNA repair defects through HIF-1α/miR-210/Rad52 pathway likely contribute to Nano-Ni-induced genomic instability and ultimately cell transformation. Our findings will provide information to further elucidate the molecular mechanisms of Nano-Ni-induced genotoxicity and carcinogenicity. Graphical Abstract

Interplay between IncF plasmids and topoisomerase mutations conferring quinolone resistance in the Escherichia coli ST131 clone: stability and resistance evolution

The Escherichia coli ST131 H30-Rx subclone vehicles CTX-M-15 plasmids and mutations in gyrA and parC conferring multidrug resistance successfully in the clinical setting. The aim of this study was (1) to investigate the relationship of specific topoisomerase mutations on the stability of IncF (CTX-M producing) plasmids using isogenic E. coli mutants and (2) to investigate the impact of the IncF-type plasmids present in the E. coli clone ST131 on the evolution of quinolone resistance. E. coli ATCC 25922 (background strain) and derived mutants encoding specific QRDR substitutions were used. Also, NGS-characterized IncFIA and IncFIB plasmids (encoding CTX-M genes) were included. Plasmid stability was evaluated by sequential dilutions into Luria broth medium without antibiotics for 7 days. Mutant frequency to ciprofloxacin was also evaluated. Moderate differences in the IncF plasmids stability were observed among E. coli ATCC 25922 and isogenic mutants. Under our experimental conditions, the fluctuation of bacteria harboring plasmids was less than 0.5-log(10) in all cases. In the mutant frequency tests, it was observed that the presence of these IncF plasmids increased this value significantly (10–1000-fold). Quinolone resistance substitutions in gyrA or parC genes, frequently found associated with E. coli clone ST131, do not modify the stability of ST131-associated IncFIA and IncFIB plasmids under in vitro conditions. IncF-type plasmids present in E. coli clone ST131 facilitate the selection of resistance to quinolones. These results are consistent with the clinical scenario in which the combination of resistance to quinolones and beta-lactams is highly frequent in the E. coli clone ST131.

Characteristic mutations induced in the small intestine of Msh2-knockout gpt delta mice

Background Base pair mismatches in genomic DNA can result in mutagenesis, and consequently in tumorigenesis. To investigate how mismatch repair deficiency increases mutagenicity under oxidative stress, we examined the type and frequency of mutations arising in the mucosa of the small intestine of mice carrying a reporter gene encoding guanine phosphoribosyltransferase (gpt) and in which the Msh2 gene, which encodes a component of the mismatch repair system, was either intact (Msh2+/+::gpt/0; Msh2-bearing) or homozygously knockout (KO) (Msh2−/−::gpt/0; Msh2-KO). Results Gpt mutant frequency in the small intestine of Msh2-KO mice was about 10 times that in Msh2-bearing mice. Mutant frequency in the Msh2-KO mice was not further enhanced by administration of potassium bromate, an oxidative stress inducer, in the drinking water at a dose of 1.5 g/L for 28 days. Mutation analysis showed that the characteristic mutation in the small intestine of the Msh2-KO mice was G-to-A transition, irrespective of whether potassium bromate was administered. Furthermore, administration of potassium bromate induced mutations at specific sites in gpt in the Msh2-KO mice: G-to-A transition was frequently induced at two known sites of spontaneous mutation (nucleotides 110 and 115, CpG sites) and at nucleotides 92 and 113 (3′-side of 5′-GpG-3′), and these sites were confirmed to be mutation hotspots in potassium bromate-administered Msh2-KO mice. Administration of potassium bromate also induced characteristic mutations, mainly single-base deletion and insertion of an adenine residue, in sequences of three to five adenine nucleotides (A-runs) in Msh2-KO mice, and elevated the overall proportion of single-base deletions plus insertions in Msh2-KO mice. Conclusions Our previous study revealed that administration of potassium bromate enhanced tumorigenesis in the small intestine of Msh2-KO mice and induced G-to-A transition in the Ctnnb1 gene. Based on our present and previous observations, we propose that oxidative stress under conditions of mismatch repair deficiency accelerates the induction of single-adenine deletions at specific sites in oncogenes, which enhances tumorigenesis in a synergistic manner with G-to-A transition in other oncogenes (e.g., Ctnnb1).

A platform for deep sequence-activity mapping and engineering antimicrobial peptides

Developing potent antimicrobials, and platforms for their study and engineering, is critical as antibiotic resistance grows. A high-throughput method to quantify antimicrobial peptide and protein (AMP) activity across a broad continuum can elucidate sequence-activity landscapes and identify potent mutants. We developed a platform to perform sequence-activity mapping of AMPs via depletion (SAMP-Dep): a bacterial host culture is transformed with an AMP mutant library, induced to express AMPs, grown, and deep sequenced to quantify mutant frequency. The slope of mutant growth rate versus induction level indicates potency. Using SAMP-Dep, we screened 170,000 mutants of oncocin, a proline-rich AMP, for intracellular activity against Escherichia coli. Clonal validation of 36 mutants supported SAMP-Dep sensitivity and accuracy. The efficiency and accuracy of SAMP-Dep enabled mapping the oncocin sequence-activity space with remarkable detail and scale and guided focused, successful synthetic peptide library design, yielding a mutant with two-fold enhancement in both intracellular and extracellular activity.

Competition for nutritional resources masks the true frequency of bacterial mutants

Background It is widely assumed that all mutant microorganisms present in a culture are able to grow and form colonies, provided that they express the features required for selection. Unlike wild-type Escherichia coli, PHO-constitutive mutants overexpress alkaline phosphatase and hence can hydrolyze glycerol-2-phosphate (G2P) to glycerol and form colonies on plates having G2P as the sole carbon source. These mutations mostly occur in the pst operon. However, the frequency of PHO-constitutive colonies on the G2P selective plate is exceptionally low. Results We show that the rate in which spontaneous PHO-constitutive mutations emerge is about 8.0 × 10−6/generation, a relatively high rate, but the growth of most existing mutants is inhibited by their neighboring wild-type cells. This inhibition is elicited only by non-mutant viable bacteria that can take up and metabolize glycerol formed by the mutants. Evidence indicates that the few mutants that do form colonies derive from microclusters of mutants on the selective plate. A mathematical model that describes the fate of the wild-type and mutant populations under these circumstances supports these results. Conclusion This scenario in which neither the wild-type nor the majority of the mutants are able to grow resembles an unavoidable “tragedy of the commons” case which results in the collapse of the majority of the population. Cooperation between rare adjacent mutants enables them to overcome the competition and eventually form mutant colonies. The inhibition of PHO-constitutive mutants provides an example of mutant frequency masked by orders of magnitude due to a competition between mutants and their ancestral wild-type cells. Similar “tragedy of the commons-like” cases may occur in other settings and should be taken into consideration while estimating true mutant frequencies and mutation rates.

Effect of RecA inactivation on quinolone susceptibility and the evolution of resistance in clinical isolates of Escherichia coli

Background SOS response suppression (by RecA inactivation) has been postulated as a therapeutic strategy for potentiating antimicrobials against Enterobacterales. Objectives To evaluate the impact of RecA inactivation on the reversion and evolution of quinolone resistance using a collection of Escherichia coli clinical isolates. Methods Twenty-three E. coli clinical isolates, including isolates belonging to the high-risk clone ST131, were included. SOS response was suppressed by recA inactivation. Susceptibility to fluoroquinolones was determined by broth microdilution, growth curves and killing curves. Evolution of quinolone resistance was evaluated by mutant frequency and mutant prevention concentration (MPC). Results RecA inactivation resulted in 2–16-fold reductions in fluoroquinolone MICs and modified EUCAST clinical category for several isolates, including ST131 clone isolates. Growth curves and time–kill curves showed a clear disadvantage (up to 10 log10 cfu/mL after 24 h) for survival in strains with an inactivated SOS system. For recA-deficient mutants, MPC values decreased 4–8-fold, with values below the maximum serum concentration of ciprofloxacin. RecA inactivation led to a decrease in mutant frequency (≥103-fold) compared with isolates with unmodified SOS responses at ciprofloxacin concentrations of 4×MIC and 1 mg/L. These effects were also observed in ST131 clone isolates. Conclusions While RecA inactivation does not reverse existing resistance, it is a promising strategy for increasing the effectiveness of fluoroquinolones against susceptible clinical isolates, including high-risk clone isolates.

A bacterial tragedy of the commons that masks the actual frequency of mutants

The frequency of mutants in a population is central to the understanding of evolution. Mutant frequency is usually assessed by plating a bacterial culture on selective medium in which only specific rare mutants can grow, assuming that all mutant cells present on the plate are able to form colonies. Here we show an exception to this rule. Wild-type Escherichia coli cells are unable to grow with glycerol-2-phosphate (G2P) as a carbon source. In contrast, PHO-constitutive mutants can hydrolyse G2P to glycerol and form colonies on plates having G2P as their sole carbon source. However, the frequency of PHO-constitutive colonies on the selective plate is exceptionally low. Here we show that such mutations occur at a relatively high rate, but the growth of the existing mutants is inhibited due to a competition with the surrounding wild-type cells for the limited amounts of glycerol produced by the mutants. This scenario in which neither the wild-type nor the majority of the mutants are able to grow constitutes an unavoidable case of the ‘tragedy of the commons’. Evidence shows that the few mutants that do form colonies derive from micro-clusters of mutants on the selective plate. In addition, a mathematical model describes the fate of the wild-type and mutant populations on the selective plate.

Association of SLCO1B1 and ABCB1 Genetic Variants with Atorvastatin-induced Myopathy in Patients with Acute Ischemic Stroke

Background:Certain patients experience muscle-related adverse effects after taking atorvastatin. Genetic factors play an important role in the occurrence of statin-induced myopathy.Aim:We aimed to identify genetic variants associated with statin-induced myotoxicity.Methods:We prospectively enrolled 1,102 acute ischemic stroke patients who underwent atorvastatin treatment for the first time after admission. Patients were separated into case and control groups after a follow-up of 3 months. We used a biochemical definition of myopathy consisting of serum creatine kinase values more than ten times the upper limit of normal for the reference laboratory (150 U/L). Fifty single nucleotide polymorphisms (SNPs) from seven genes of ABCB1, CoQ2, HTR3B, RYR2, CYP3A5, HTR7 and SLCO1B1 were selected and genotyped. The effects of genetic polymorphisms on myopathy were observed.Results:61 cases and 110 controls were recruited in the study. Compared with the controls, the cases had a significant higher mutant frequency of the allele A (ABCB1, rs2373588) (OR = 2.01, 95%CI = 1.10-3.67, P = 0.001) and a significant lower mutant frequency of the allele A (SLCO1B1, rs976754) (OR = 1.85, 95%CI = 1.12-3.03, P = 0.042). Genotypes or alleles of the other SNPs had no significant difference between the two groups (P > 0.05).Conclusion:Our findings reveal that SLCO1B1 and ABCB1 genetic variants are associated with statin-induced myopathy. These are valuable biomarkers for the evaluation of atorvastatin safety.

Associations between Bacteriophage Resistance and Antibiotic Resistance Phenotypes in Laboratory and Clinical strains of Salmonella Typhimurium

Background Bacteriophages have received great attention as alternative over antibiotics due to the host specificity. Therefore, this study was designed to evaluate the associations between bacteriophage-insensitive (BI) and antibiotic-resistant mutants of Salmonella Typhimurium strains. Bacteriophage-sensitive Salmonella Typhimurium ATCC 19585 (BSSTWT), ciprofloxacin-induced S. Typhimurium ATCC 19585 (BSSTCIP), S. Typhimurium KCCM 40253 (BSSTLAB), and clinically isolated multidrug-resistant S. Typhimurium CCARM 8009 (BSSTMDR) were used to induce the bacteriophage-insensitive mutants (BISTWT, BISTCIP, BISTLAB, and BISTMDR) against bacteriophage P22. Results The numbers of BSSTWT, BSSTCIP, and BSSTLAB were reduced by P22 (>3 log), while the least lytic activity was observed for BSSTMDR. BSSTWT treated with P22 showed the large variation in the cell state (CV>40%) and highest mutant frequency (62%), followed by 25% for STCIP. The least similarities between BSSTWT and BISTWT were observed at P22 and PBST-13 (<12%). The antibiotic susceptibilities were not significantly changed or slightly increased against BISTWT, BISTCIP, BISTLAB, and BISTMDR. The relative expression levels of bacteriophage-binding receptor-related genes (btuB, fhuA, fliK, fljB, ompC, ompF, rfaL, and tolC) were decreased in BISTCIP and BSSTMDR. Conclusion The results could pave the way for the application of bacteriophages as an alternative to control antibiotic-resistant bacteria.