Src-dependent impairment of autophagy by oxidative stress in a mouse model of Duchenne muscular dystrophy.

Duchenne muscular dystrophy (DMD) is a fatal degenerative muscle disease resulting from mutations in the dystrophin gene. Increased oxidative stress and altered Ca(2+) homeostasis are hallmarks of dystrophic muscle. While impaired autophagy has recently been implicated in the disease process, the mechanisms underlying the impairment have not been elucidated. Here we show that nicotinamide adenine dinucleotide phosphatase (Nox2)-induced oxidative stress impairs both autophagy and lysosome formation in mdx mice. Persistent activation of Src kinase leads to activation of the autophagy repressor mammalian target of rapamycin (mTOR) via PI3K/Akt phosphorylation. Inhibition of Nox2 or Src kinase reduces oxidative stress and partially rescues the defective autophagy and lysosome biogenesis. Genetic downregulation of Nox2 activity in the mdx mouse decreases reactive oxygen species (ROS) production, abrogates defective autophagy and rescues histological abnormalities and contractile impairment. Our data highlight mechanisms underlying the pathogenesis of DMD and identify NADPH oxidase and Src kinase as potential therapeutic targets.

Conserved C-terminal motifs required for avirulence and suppression of cell death by Phytophthora sojae effector Avr1b.

The sequenced genomes of oomycete plant pathogens contain large superfamilies of effector proteins containing the protein translocation motif RXLR-dEER. However, the contributions of these effectors to pathogenicity remain poorly understood. Here, we show that the Phytophthora sojae effector protein Avr1b can contribute positively to virulence and can suppress programmed cell death (PCD) triggered by the mouse BAX protein in yeast, soybean (Glycine max), and Nicotiana benthamiana cells. We identify three conserved motifs (K, W, and Y) in the C terminus of the Avr1b protein and show that mutations in the conserved residues of the W and Y motifs reduce or abolish the ability of Avr1b to suppress PCD and also abolish the avirulence interaction of Avr1b with the Rps1b resistance gene in soybean. W and Y motifs are present in at least half of the identified oomycete RXLR-dEER effector candidates, and we show that three of these candidates also suppress PCD in soybean. Together, these results indicate that the W and Y motifs are critical for the interaction of Avr1b with host plant target proteins and support the hypothesis that these motifs are critical for the functions of the very large number of predicted oomycete effectors that contain them.