To activate <scp>NAD</scp> (P)H oxidase with a brief pulse of photodynamic action

Reduced nicotinamide adenine dinucleotide phosphate [NAD(P)H] oxidases (NOX) are a major cellular source of reactive oxygen species, regulating vital physiological functions, whose dys-regulation leads to a plethora of major diseases. Much effort has been made to develop varied types of NOX inhibitors, but biotechnologies for spatially and temporally controlled NOX activation, however, are not readily available. We previously found that ultraviolet A (UVA) irradiation activates NOX2 in rodent mast cells, to elicit persistent calcium spikes. NOX2 is composed of multiple subunits, making studies of its activation rather complicated. Here we show that the single-subunit nonrodent-expressing NOX5, when expressed ectopically in CHO-K1 cells, is activated by UVA irradiation (380 nm, 0.1-12 mW/cm², 1.5 min) inducing repetitive calcium spikes, as monitored by Fura-2 fluorescent calcium imaging. UVA-elicited calcium oscillations are inhibited by NOX inhibitor diphenyleneiodonium chloride (DPI) and blocked by singlet oxygen (¹O₂) quencher Trolox-C (300 μM). A brief pulse of photodynamic action (1.5 min) with photosensitizer sulfonated aluminum phthalocyanine (SALPC 2 μM, 675 nm, 85 mW/cm²) in NOX5-CHO-K1 cells, or with genetically encoded protein photosensitizer miniSOG fused to N-terminus of NOX5 (450 nm, 85 mW/cm²) in miniSOG-NOX5-CHO-K1 cells, induces persistent calcium oscillations, which are blocked by DPI. In the presence of Trolox-C, miniSOG photodynamic action no longer induces any calcium increases in miniSOG-NOX5-CHO-K1 cells. DUOX2 in human thyroid follicular cells SW579 and in DUOX2-CHO-K1 cells is similarly activated by UVA irradiation and SALPC photodynamic action. These data together suggest that NOX is activated with a brief pulse of photodynamic action.