Utility of siRNA against Keap1 as a strategy to stimulate a cancer chemopreventive phenotype

A duplex 21 nucleotide small interfering RNA (siRNA) against human Keap1 is described that represents a unique class of cancer chemopreventive agent. This siRNA can knockdown Keap1 mRNA and thereby relieve negative regulation of nuclear factor erythroid 2 p45-related factor 2 (Nrf2)-mediated gene expression. The siRNA lowered endogenous Keap1 mRNA to <30% of control levels between 24 and 72 h after transfection in human HaCaT keratinocyte cells and was capable of blocking ectopic expression of FLAG-tagged human Keap1 protein but not that of ectopic V5-tagged mouse Keap1 protein. Transfection of human HaCaT cells with Keap1 siRNA markedly enhanced endogenous levels of nuclear factor erythroid 2 p45-related factor 2 (Nrf2) protein and increased transcription of an antioxidant response element-driven reporter gene by 2.3-fold. Furthermore, 48 h after transfection of these cells with Keap1 siRNA, expression of aldo-keto reductase 1C1/2 and the glutamate cysteine ligase catalytic and modifier subunits was elevated between 5- and 14-fold. A modest increase of 3-fold in NAD(P)H:quinone oxidoreductase 1 was also observed. The Keap1 siRNA produced a 1.75-fold increase in intracellular glutathione 48 h after transfection. Thus, antagonism of Keap1 by siRNA can be used to preadapt human cells to oxidative stress without the need to expose them to redox stressors.