Co-expression of Hsp70 Protein and Autophagy Marker Protein LC3 in A549 Cells and THP1 Cells Exposed to Nanoparticles of Air Pollution

Abstract

The ability of air particulate matter (PM) to cause reactive oxygen species-driven protein damage is associated with both COPD and lung cancer, but the mechanisms are unsettled. In this study, we investigated the co-expression of Hsp70 and the autophagy marker protein LC3 in A549 cells (alveolar epithelial cell line) and THP-1 cells (monocyte/macrophage cells) grown in media supplemented with 100 μg/mL of four types of PM: carbon black (CB), urban dust (UD), nanoparticulate CB (NPCB), and nanoparticulate CB coated with benzo(a)pyrene (NPCB-BaP). Fluorescent monoclonal antibodies and flow cytometry were used to assess the expression and co-expression of HSP70 and LC3 proteins. Hsp70 expression was significantly increased by all PM, while LC3 was decreased by CB in A549 cells, unchanged by CB and UD in THP-1 cells and increased by NPCB and NPCB-BaP in both cell types. All PMs increased the Hsp70/LC3 ratio in binary scatterplots; the relationship was positive and linear, which may reflect chaperone-dependent autophagy. The UD was the only PM type that affected the slopes of the spatial trend lines and altered binary patterns of Hsp70/LC3 distribution in THP1 cells. These findings provide an insight into the molecular mechanisms regulating proteostasis in PM-exposed cells through the chaperone-autophagy system in the cytoplasm.