Stimulation of pp60 Src activity limits nitric oxide signaling through increases in asymmetric dimethylarginine

We have shown that a decrease in dimethylaminohydrolase type 2 (DDAH2) activity and an increase in asymmetric dimethylarginine (ADMA) results in nitric oxide synthase derived oxidative/nitrative stress and that this contributes to acute lung injury (ALI) in mice exposed to lipopolysaccharide (LPS). The mechanism by which DDAH2 is regulated is unknown and was the focus of this study. pp60 Src is a member of the Src-family protein tyrosine kinases. In pulmonary arterial endothelial cells (PAEC) and the mouse lung, LPS increased ADMA-mediated NOS-derived superoxide and this correlated with an increase in pp60 Src activation and DDAH2 inhibition. LPS also increased the interaction of pp60 Src with DDAH2 resulting in increased DDAH2 tyrosine phosphorylation. In PAEC, the over-expression of a dominant negative mutant of pp60 Src (K295MSrc) prevented the LPS dependent decrease in DDAH2 activity and the resulting increase in ADMA levels and attenuated the ability of LPS to stimulate NOS-derived superoxide and peroxynitrite generation. Further, the over-expression of a constitutively active pp60 Src (Y527FSrc) either in PAEC or the mouse endothelium was sufficient to inhibit DDAH2 activity and increase ADMA levels. Y527FSrc over-expression also increased NOS-derived superoxide and peroxynitrite generation. Mutating the single tyrosine (Y) residue of DDAH II located at aa207 to phenylalanine (Y207FDDAH2) produced an enzyme that was resistant to pp60 Src dependent inhibition. Together our data suggest that in ALI, the effects of LPS on DDAH/ADMA signaling and downstream NOS-derived oxidative stress are dependent on the pp60 Src -mediated tyrosine phosphorylation of DDAH II at Y 207 .