Figure 8. Schematic diagram illustrating the proposed signaling pathway involved in particulate matter (PM)-induced cyclooxygenase 2 (COX-2) expression in HaCaT cells.

PMs activate the aryl hydrocarbon receptor (AhR)/Nox2/p47^phox pathway, which increases generation of reactive oxygen species (ROS), and in turn activates two separate signaling cascades; one involving ERK/p38-dependent activation of NF-κB and another involving JNK-dependent activation of activator protein 1 (AP-1) transcription factors in HaCaT cells. Impairment of skin barrier function by down-regulation of filaggrin via COX2/PGE2 expression in HaCaT cells.