WWOX Induction Promotes Bcl-X_L and Mcl-1 Degradation Through a Lysosomal Pathway upon Stress Responses

The human WWOX gene resides on a common fragile site and is frequently deleted or altered during DNA replication. WWOX mutations are associated with various human diseases, including cancer, neurodegeneration, and developmental deficits. However, the regulation of WWOX expression remains largely unclear. We demonstrated that stress responses, including serum deprivation, oxidative stress, and anticancer drug treatment, increase WWOX expression in human SCC-15 cells and wild-type mouse embryonic fibroblasts (MEFs) through transcriptional activation. Serum deprivation induces higher levels of reactive oxygen species and cell death in Wwox^+/+ than Wwox^-/- MEFs. Anti-apoptotic Bcl-2 family proteins regulate mitochondrial homeostasis and prevent serum deprivation-induced oxidative stress and cell death. Our results showed that serum starvation decreases protein expression levels of Bcl-X_L and Mcl-1 in Wwox^+/+ but not in Wwox^-/- MEFs. Serum starvation also fails to downregulate Bcl-X_L and Mcl-1 protein expression in WWOX-knockdown SCC-15 cells. Replenishment of ectopic WWOX induces downregulation of Bcl-X_L and Mcl-1 protein levels in Wwox^-/- MEFs after serum starvation. We determined that WWOX-mediated downregulation of Bcl-XL and Mcl-1 is accomplished through a lysosome-dependent protein degradation pathway. Moreover, a decline in reactive oxygen species generation by pretreatment of Wwox^+/+ MEFs with an antioxidant N-acetyl-L-cysteine leads to decreased WWOX induction upon serum starvation. Taken together, our results suggest that stress stimuli trigger WWOX induction by elevating the production of reactive oxygen species in cells, which promotes the degradation of Bcl-XL and Mcl-1 proteins via a lysosome-mediated pathway, thereby further aggravating oxidative stress and cell death.