Airborne particulate matter induces mitotic slippage and chromosomal missegregation through disruption of the spindle assembly checkpoint (SAC)

Particulate matter pollution, polygenic risk score and mosaic loss of chromosome Y in middle-aged and older men from the Dongfeng-Tongji cohort study

Mosaic loss of chromosome Y (mLOY) is the most common somatic alteration as men aging and may reflect genome instability. PM exposure is a major health concern worldwide, but its effects with genetic factors on mLOY has never been investigated. Here we explored the associations of PM2.5 and PM10 exposure with mLOY of 10,158 males measured via signal intensity of 2186 probes in male-specific chromosome-Y region from Illumina array data. The interactive and joint effects of PM2.5 and PM10 with genetic factors and smoking on mLOY were further evaluated. Compared with the lowest tertiles of PM2.5 levels in each exposure window, the highest tertiles in the same day, 7-, 14-, 21-, and 28-day showed a 0.005, 0.006, 0.007, 0.007, and 0.006 decrease in mLRR-Y, respectively (all P < 0.05), with adjustment for age, BMI, smoking pack-years, alcohol drinking status, physical activity, education levels, season of blood draw, and experimental batch. Such adverse effects were also observed in PM10-mLOY associations. Moreover, the unweighted and weighted PRS presented significant negative associations with mLRR-Y (both P < 0.001). Participants with high PRS and high PM2.5 or PM10 exposure in the 28-day separately showed a 0.018 or 0.019 lower mLRR-Y level [β (95 %CI) = -0.018 (-0.023, -0.012) and - 0.019 (-0.025, -0.014), respectively, both P < 0.001], when compared to those with low PRS and low PM2.5 or PM10 exposure. We also observed joint effects of PM with smoking on exacerbated mLOY. This large study is the first to elucidate the impacts of PM2.5 exposure on mLOY, and provides key evidence regarding the interactive and joint effects of PM with genetic factors on mLOY, which may promote understanding of mLOY development, further modifying and increasing healthy aging in males.

Sampling, composition, and biological effects of Mexico City airborne particulate matter from multiple periods

Air pollution is a worldwide environmental problem with an impact on human health. Particulate matter of ten micrometers or less aerodynamic diameter (PM10) as well as its fine fraction (PM2.5) is related to multiple pulmonary diseases. The impact of air pollution in Mexico City, and importantly, particulate matter has been studied and considered as a risk factor for two decades ago. Previous studies have reported the composition of Mexico City particulate matter, as well as the biological effects induced by this material. However, material collected and used in previous studies is a limited resource, and sampling and particle recovery techniques have been improved. In this study, we describe the methods used in our laboratory for Mexico City airborne particulate matter PM10 and PM2.5 sampling, considering the years 2017, 2018 and 2019. We also analyzed the PM10 and PM2.5 samples obtained to determine their composition. Finally, we exposed lung cell line cultures to PM10 and PM2.5 to evaluate the biological effect of the material in terms of cell viability, cell death, inflammatory response, and cytogenetic alterations. Our results showed that PM10 composition includes inorganic, organic and biological compounds, while PM2.5 is a mixture of more enriched organic compounds. PM10 and PM2.5 treatment in lung cells does not significantly impact cell viability/cell death. However, PM10 and PM2.5 increase the secretion levels of IL-6. Moreover, PM10 as well as PM2.5 induce cytogenetic alterations, such as micronuclei, anaphase bridges, trinucleated cells and apoptotic cells in lung cells. Our results update the evidence of the composition and biological effects of Mexico City particulate matter and provide us a reliable basis for future approaches.

Targeting ST8SIA6-AS1 counteracts KRASG12C inhibitor resistance through abolishing the reciprocal activation of PLK1/c-Myc signaling

BACKGROUND

KRASG12C inhibitors (KRASG12Ci) AMG510 and MRTX849 have shown promising efficacy in clinical trials and been approved for the treatment of KRASG12C-mutant cancers. However, the emergence of therapy-related drug resistance limits their long-term potential. This study aimed to identify the critical mediators and develop overcoming strategies.

METHODS

By using RNA sequencing, RT-qPCR and immunoblotting, we identified and validated the upregulation of c-Myc activity and the amplification of the long noncoding RNA ST8SIA6-AS1 in KRASG12Ci-resistant cells. The regulatory axis ST8SIA6-AS1/Polo-like kinase 1 (PLK1)/c-Myc was investigated by bioinformatics, RNA fluorescence in situ hybridization, RNA immunoprecipitation, RNA pull-down and chromatin immunoprecipitation. Gain/loss-of-function assays, cell viability assay, xenograft models, and IHC staining were conducted to evaluate the anti-cancer effects of co-inhibition of ST8SIA6-AS1/PLK1 pathway and KRAS both in vitro and in vivo.

RESULTS

KRASG12Ci sustainably decreased c-Myc levels in responsive cell lines but not in cell lines with intrinsic or acquired resistance to KRASG12Ci. PLK1 activation contributed to this ERK-independent c-Myc stability, which in turn directly induced PLK1 transcription, forming a positive feedback loop and conferring resistance to KRASG12Ci. ST8SIA6-AS1 was found significantly upregulated in resistant cells and facilitated the proliferation of KRASG12C-mutant cancers. ST8SIA6-AS1 bound to Aurora kinase A (Aurora A)/PLK1 and promoted Aurora A-mediated PLK1 phosphorylation. Concurrent targeting of KRAS and ST8SIA6-AS1/PLK1 signaling suppressed both ERK-dependent and -independent c-Myc expression, synergistically led to cell death and tumor regression and overcame KRASG12Ci resistance.

CONCLUSIONS

Our study deciphers that the axis of ST8SIA6-AS1/PLK1/c-Myc confers both intrinsic and acquired resistance to KRASG12Ci and represents a promising therapeutic target for combination strategies with KRASG12Ci in the treatment of KRASG12C-mutant cancers.

Urban dust particles disrupt mitotic progression by dysregulating Aurora kinase B-related functions

Particulate matter (PM), a major component of outdoor air pollution, damages DNA and increases the risk of cancer. Although the harmful effects of PM at the genomic level are known, the detailed mechanism by which PM affects chromosomal stability remains unclear. In this study, we investigated the novel effects of PM on mitotic progression and identified the underlying mechanisms. Gene set enrichment analysis of lung cancer patients residing in countries with high PM concentrations revealed the downregulation of genes associated with mitosis and mitotic structures. We also showed that exposure of lung cancer cells in vitro to urban dust particles (UDPs) inhibits cell proliferation through a prolonged M phase. The mitotic spindles in UDP-treated cells were hyperstabilized, and the number of centrioles increased. The rate of ingression of the cleavage furrow and actin clearance from the polar cortex was reduced significantly. The defects in mitotic progression were attributed to inactivation of Aurora B at kinetochore during early mitosis, and spindle midzone and midbody during late mitosis. While previous studies demonstrated possible links between PM and mitosis, they did not specifically identify the dysregulation of spatiotemporal dynamics of mitotic proteins and structures (e.g., microtubules, centrosomes, cleavage furrow, and equatorial and polar cortex), which results in the accumulation of chromosomal instability, ultimately contributing to carcinogenicity. The data highlight the novel scientific problem of PM-induced mitotic disruption. Additionally, we introduce a practical visual method for assessing the genotoxic outcomes of airborne pollutants, which has implications for future environmental and public health research.

Oxidative stress and activation of H2A.X in lung alveolar epithelial cells (A549) by nanoparticulate carbon black

Fine airborne particulate matter enter the respiratory system, induce oxidative stress and initiate DNA damage. The aim of our study was the estimation of cell viability, oxidative stress, DNA damage, cell cycle alterations and activation of histone H2A.X. Experiments were done on lung alveolar epithelial (A549) cells grown for 24 h with 200 µg mL-1 coarse carbon black (CB), or nanoparticulate CB (NPCB). Neither CB nor glutathione depletion altered cell viability, growth rates, and H2A.X expression while NPCB decreased cell viability, increased oxidative stress and DNA damage. The cell cycle was blocked at G0/G1. NPCB but not CB increased expression and activation of H2A.X at mRNA and protein levels. Co-expression data point to γH2A.X as a major NPCB target, and show the interdependence of γH2A.X and oxidative stress. We conclude, that NPCB increases γ-H2A.X expression in A549 cells at mRNA and protein levels and stimulates H2A.X (Ser139), phosphorylation, associated with oxidative stress, the DNA damage response and G1 cell cycle arrest.

Airborne particulate matter (PM10) induces cell invasion through Aryl Hydrocarbon Receptor and Activator Protein 1 (AP-1) pathway deregulation in A549 lung epithelial cells

BACKGROUND

Particulate matter with an aerodynamic size ≤ 10 μm (PM₁₀) is a risk factor for lung cancer development, mainly because some components are highly toxic. Polycyclic aromatic hydrocarbons (PAHs) are present in PM₁₀, such as benzo[a]pyrene (BaP), which is a well-known genotoxic and carcinogenic compound to humans, capable of activating AP-1 transcription factor family genes through the Aryl Hydrocarbon Receptor (AhR). Because effects of BaP include metalloprotease 9 (MMP-9) activation, cell invasion, and other pathways related to carcinogenesis, we aimed to demonstrate that PM₁₀ (10 µg/cm²) exposure induces the activation of AP-1 family members as well as cell invasion in lung epithelial cells, through AhR pathway.

METHODS AND RESULTS

The role of the AhR gene in cells exposed to PM₁₀ (10 µg/cm²) and BaP (1µM) for 48 h was evaluated using AhR-targeted interference siRNA. Then, the AP-1 family members (c-Jun, Jun B, Jun D, Fos B, C-Fos, and Fra-1), the levels/activity of MMP-9, and cell invasion were analyzed. We found that PM₁₀ increased AhR levels and promoted its nuclear localization in A549 treated cells. Also, PM₁₀ and BaP deregulated the activity of AP-1 family members. Moreover, PM₁₀ upregulated the secretion and activity of MMP-9 through AhR, while BaP had no effect. Finally, we found that cell invasion in A549 cells exposed to PM₁₀ and BaP is modulated by AhR.

CONCLUSION

Our results demonstrated that PM₁₀ exposure induces upregulation of the c-Jun, Jun B, and Fra-1 activity, the expression/activity of MMP-9, and the cell invasion in lung epithelial cells, effects mediated through the AhR. Also, the Fos B and C-Fos activity were downregulated. In addition, the effects induced by PM₁₀ exposure were like those induced by BaP, which highlights the potentially toxic effects of the PM₁₀ mixture in lung epithelial cells.

The Roles of Histone Post-Translational Modifications in the Formation and Function of a Mitotic Chromosome

During mitosis, many cellular structures are organized to segregate the replicated genome to the daughter cells. Chromatin is condensed to shape a mitotic chromosome. A multiprotein complex known as kinetochore is organized on a specific region of each chromosome, the centromere, which is defined by the presence of a histone H3 variant called CENP-A. The cytoskeleton is re-arranged to give rise to the mitotic spindle that binds to kinetochores and leads to the movement of chromosomes. How chromatin regulates different activities during mitosis is not well known. The role of histone post-translational modifications (HPTMs) in mitosis has been recently revealed. Specific HPTMs participate in local compaction during chromosome condensation. On the other hand, HPTMs are involved in CENP-A incorporation in the centromere region, an essential activity to maintain centromere identity. HPTMs also participate in the formation of regulatory protein complexes, such as the chromosomal passenger complex (CPC) and the spindle assembly checkpoint (SAC). Finally, we discuss how HPTMs can be modified by environmental factors and the possible consequences on chromosome segregation and genome stability.

Particulate matter (PM10) destabilizes mitotic spindle through downregulation of SETD2 in A549 lung cancer cells

Air pollution represents an environmental problem, impacting negatively in human health. Particulate matter of 10 μm or less in diameter (PM₁₀) is related to pulmonary diseases, including lung cancer. Mitotic spindle is made up by chromosome-microtubule (MT) interactions, where SETD2 plays an important role in MT stability. SETD2 binds and activates α-TUBULIN sub-unit and promotes MT polymerization. Alongside this mechanism, the spindle assembly checkpoint (SAC) senses the adequate mitotic progression through proteins such as BUBR1, AURORA B and SURVIVIN. Alterations in MT dynamics as well as in SAC cause aneuploidy and chromosomal instability, a common phenotype in cancer cells. In this study, we evaluated the effect of PM₁₀ in the expression and protein levels of SETD2, as well as the effect in the expression and protein levels of SAC and mitotic components involved in chromosomal segregation/mitosis, using the A549 lung cancer cell line. A549 cell cultures were exposed to PM₁₀ (10 μg/cm²) for 24 h to evaluate the expression and protein levels of SETD2 (SETD2), TUBA1A (α-TUBULIN), CCNB1 (CYCLIN B1), BUB1B (BUBR1), AURKB (AURORA B) and BIRC5 (SURVIVIN). We observed that PM₁₀ decreases the expression and protein levels of SETD2, α-TUBULIN and BUBR1 and increases the levels of AURORA B and SURVIVIN in A549 cells, compared with non-treated cells. PM₁₀ also caused a decrease in mitotic index and in the percentage of cells in G2/M when compared with control group. Co-localization of SETD2/α -TUB was lower in PM₁₀-treated cells in comparison with non-treated cells. Finally, micronuclei (MN) frequency was higher in PM₁₀-treated cells in contrast with non-treated cells, being whole chromosomes more common in PM₁₀-treated MN than in non-treated MN. Our results suggest that PM₁₀ causes missegregation and aneuploidy through downregulation of SETD2 and SAC components, inducing aneuploidy and predisposing to the generation of chromosomal instability in transformed cells.

Airborne particulate matter induces oxidative damage, DNA adduct formation and alterations in DNA repair pathways

Air pollution, which includes particulate matter (PM), is classified in group 1 as a carcinogen to humans by the International Agency for Research in Cancer. Specifically, PM exposure has been associated with lung cancer in patients living in highly polluted cities. The precise mechanism by which PM is linked to cancer has not been completely described, and the genotoxicity induced by PM exposure plays a relevant role in cell damage. In this review, we aimed to analyze the types of DNA damage and alterations in DNA repair pathways induced by PM exposure, from both epidemiological and toxicological studies, to comprehend the contribution of PM exposure to carcinogenesis. Scientific evidence supports that PM exposure mainly causes oxidative stress by reactive oxygen species (ROS) and the formation of DNA adducts, specifically by polycyclic aromatic hydrocarbons (PAH). PM exposure also induces double-strand breaks (DSBs) and deregulates the expression of some proteins in DNA repair pathways, precisely, base and nucleotide excision repairs and homologous repair. Furthermore, specific polymorphisms of DNA repair genes could lead to an adverse response in subjects exposed to PM. Nevertheless, information about the effects of PM on DNA repair pathways is still limited, and it has not been possible to conclude which pathways are the most affected by exposure to PM or if DNA damage is repaired properly. Therefore, deepening the study of genotoxic damage and alterations of DNA repair pathways is needed for a more precise understanding of the carcinogenic mechanism of PM.

Long non-coding RNA NORAD upregulation induced by airborne particulate matter (PM10) exposure leads to aneuploidy in A549 lung cells

Air pollution is a worldwide problem that affects human health predominantly in the largest cities. Particulate matter of 10 μm or less in diameter (PM₁₀) is considered a risk factor for multiple diseases, including lung cancer. The long non-coding RNA NORAD and the components of the spindle assembly checkpoint (SAC) ensure proper chromosomal segregation. Alterations in the SAC cause aneuploidy, a feature associated with carcinogenesis. In this study, we demonstrated that PM₁₀ treatment increased the expression levels of NORAD as well as those of SAC components mitotic arrest deficient 1 (MAD1L1), mitotic arrest deficient 2 (MAD2L1), BubR1 (BUB1B), aurora B (AURKB), and survivin (BIRC5) in the lung A549 cell line. We also demonstrated that MAD1L1, MAD2L1, and BUB1B expression levels were reduced when cells were transfected with small interfering RNAs (siRNAs) against NORAD. Interestingly, the expression levels of AURKB and BIRC5 (survivin) were not affected by transfection with NORAD siRNAs. Cells treated with PM₁₀ exhibited a decrease in mitotic arrest and an increase in micronuclei frequency in synchronized A549 cells. PM₁₀ exposure induced aneuploidy events as a result of SAC deregulation. We also observed a reduction in the protein levels of Pumilio 1 after PM₁₀ treatment. Our results provide novel clues regarding the effect of PM₁₀ in the generation of chromosomal instability, a phenotype observed in lung cancer cells.

Insights on the biological role of ultrafine particles of size PM<0.25: A prospective study from New Delhi

When the total ambient PM_2.5 levels are several-fold higher than the recommended limit, it may be important to study the distributions of different sizes of particulate matter (PM). Here, we assess the distributions of various sizes of total PM_2.5 for 12 months (on a monthly basis) in New Delhi, India. Importantly, we found that ultrafine particles (i.e., particles <0.5 μm) contribute significantly to total PM_2.5. PM_<0.25 were the most cytotoxic particles to human lung epithelial cells in all the 12 months. In addition, PM_<0.25 were associated with significantly higher cytotoxicity per unit mass compared to other size fractions constituting PM_2.5. For any given size of PM, the amount of reactive oxygen species (ROS) generated per unit mass is higher for the month of March as compared to that for the rest of the months in the year. The higher ROS generations for all sizes of PM collected in the month of March was not explained by differences in their metal content values. Our data suggests the lack of correlation between total PM_2.5 levels and the highly cytotoxic PM_<0.25. In summary, this work establishes the need for policy changes to routinely monitor PM_<0.25 and the necessity to establish exposure limits for PM_<0.25, especially when the total PM_2.5 levels are breached.

Fifteen Years of Airborne Particulates in Vitro Toxicology in Milano: Lessons and Perspectives Learned

Air pollution is one of the world’s leading environmental causes of death. The epidemiological relationship between outdoor air pollution and the onset of health diseases associated with death is now well established. Relevant toxicological proofs are now dissecting the molecular processes that cause inflammation, reactive species generation, and DNA damage. In addition, new data are pointing out the role of airborne particulates in the modulation of genes and microRNAs potentially involved in the onset of human diseases. In the present review we collect the relevant findings on airborne particulates of one of the biggest hot spots of air pollution in Europe (i.e., the Po Valley), in the largest urban area of this region, Milan. The different aerodynamic fractions are discussed separately with a specific focus on fine and ultrafine particles that are now the main focus of several studies. Results are compared with more recent international findings. Possible future perspectives of research are proposed to create a new discussion among scientists working on the toxicological effects of airborne particles.

Airborne Particulate Matter (PM10) Inhibits Apoptosis through PI3K/AKT/FoxO3a Pathway in Lung Epithelial Cells: The Role of a Second Oxidant Stimulus

Outdoor particulate matter (PM₁₀) exposure is carcinogenic to humans. The cellular mechanism by which PM₁₀ is associated specifically with lung cancer includes oxidative stress and damage to proteins, lipids, and DNA in the absence of apoptosis, suggesting that PM₁₀ induces cellular survival. We aimed to evaluate the PI3K/AKT/FoxO3a pathway as a mechanism of cell survival in lung epithelial A549 cells exposed to PM₁₀ that were subsequently challenged with hydrogen peroxide (H₂O₂). Our results showed that pre-exposure to PM₁₀ followed by H₂O₂, as a second oxidant stimulus increased the phosphorylation rate of pAKT^Ser473, pAKT^Thr308, and pFoxO3a^Ser253 2.5-fold, 1.8-fold, and 1.2-fold, respectively. Levels of catalase and p27^kip1, which are targets of the PIK3/AKT/FoxO3a pathway, decreased 38.1% and 62.7%, respectively. None of these changes had an influence on apoptosis; however, the inhibition of PI3K using the LY294002 compound revealed that the PI3K/AKT/FoxO3a pathway was involved in apoptosis evasion. We conclude that nontoxic PM₁₀ exposure predisposes lung epithelial cell cultures to evade apoptosis through the PI3K/AKT/FoxO3a pathway when cells are treated with a second oxidant stimulus.