YNO1 (YGL160w) is the only known S. cerevisiae NADPH oxidase. As we have shown in a previous publication (1), overexpression of this enzyme leads to superoxide production and apoptotic death of the cells. Deletion of the gene presents with hypersensitivity to drugs inhibiting the actin cytoskeleton like wiskostatin and latrunculin B. The growth defect in the presence of these drugs can be mitigated by adding a small non-toxic concentration of hydrogen peroxide, a natural metabolite of superoxide. The mating pheromone, alpha factor, in otherwise wild type cells leads to a large increase in superoxide production which is absent in the yno1 deletion mutants. Isoamyl alcohol, an inducer of pseudohyphae, leads to increased expression of a chromosomally integrated reporter construct consisting of the complete upstream sequence of YNO1 and green fluorescent protein. We hypothesize that Yno1-produced hydrogen peroxide is a natural signaling substance needed to trigger re-organization of the actin cytoskeleton in situations like transition to the stationary phase, reaction to the mating pheromone, alpha factor, and induction of pseudohyphal growth which all need re-structuring of the actin cytoskeleton. Because the standard BY4741 genetic background does not allow pseudohyphae formation, experiments are now under way to test pseudohyphae development in a suitable genetic background by nitrogen starvation, but without isoamyl alcohol.

Among the seven human NADPH oxidases, Nox4 is the one with the highest sequence similarity to the yeast YNO1 gene, is also located in the ER membrane, and produces hydrogen peroxide as a signaling substance. Nox4 is expressed in most human somatic cells. We are showing here (2) that similar to Yno1 of yeast cells, Nox4 in human cells is needed for restructuring of the actin cytoskeleton. Nox4 is strongly expressed in many human tumors. Inhibition of Nox4 in the SH-SY5Y neuronal tumor cell line leads to loss of actin stress fibers and prevents cell migration, which is needed for metastasis. The human Nox4 enzyme is therefore a possible target for cancer therapy.  

References: 

(1) Rinnerthaler, M, et al. PNAS 109, 8658 – 8663 (2012)

(2) Auer, S., et al. Frontiers in Oncology (2017), accepted with minor revisions