Air pollution presents a major environmental problem, inducing harmful effects on human health. Particulate matter of 10 μm or less in diameter (PM₁₀) is considered an important risk factor in lung carcinogenesis. Epithelial–mesenchymal transition (EMT) is a regulatory program capable of inducing invasion and metastasis in cancer. In this study, we demonstrated that PM₁₀ treatment induced phosphorylation of SMAD2/3 and upregulation of SMAD4. We also reported that PM₁₀ increased the expression and protein levels of TGFB1 (TGF-β), as well as EMT markers SNAI1 (Snail), SNAI2 (Slug), ZEB1 (ZEB1), CDH2 (N-cadherin), ACTA2 (α-SMA), and VIM (vimentin) in the lung A549 cell line. Cell exposed to PM₁₀ also showed a decrease in the expression of CDH1 (E-cadherin). We also demonstrated that expression levels of these EMT markers were reduced when cells are transfected with small interfering RNAs (siRNAs) against TGFB1. Interestingly, phosphorylation of SMAD2/3 and upregulation of SMAD induced by PM₁₀ were not affected by transfection of TGFB1 siRNAs. Finally, cells treated with PM₁₀ exhibited an increase in the capacity of invasiveness because of EMT induction. Our results provide new evidence regarding the effect of PM₁₀ in EMT and the acquisition of an invasive phenotype, a hallmark necessary for lung cancer progression.

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.

Airborne particulate matter with a diameter size of ≤10 µm (PM₁₀) is a carcinogen that contains polycyclic aromatic hydrocarbons (PAH), which form PAH–DNA adducts. However, the way in which these adducts are managed by DNA repair pathways in cells exposed to PM₁₀ has been partially described. We evaluated the effect of PM₁₀ on nucleotide excision repair (NER) activity and on the levels of different proteins of this pathway that eliminate bulky DNA adducts. Our results showed that human lung epithelial cells (A549) exposed to 10 µg/cm² of PM₁₀ exhibited PAH–DNA adducts as well as an increase in RAD23 and XPD protein levels (first responders in NER). In addition, PM₁₀ increased the levels of H4K20me2, a recruitment signal for XPA. However, we observed a decrease in total and phosphorylated XPA (Ser196) and an increase in phosphatase WIP1, aside from the absence of XPA–RPA complex, which participates in DNA-damage removal. Additionally, an NER activity assay demonstrated inhibition of the NER functionality in cells exposed to PM₁₀, indicating that XPA alterations led to deficiencies in DNA repair. These results demonstrate that PM₁₀ exposure induces an accumulation of DNA damage that is associated with NER inhibition, highlighting the role of PM₁₀ as an important contributor to lung cancer.