SHP-1 Inhibition by 4-Hydroxynonenal Activates Jun N-Terminal Kinase and Glutamate Cysteine Ligase

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Abstract
4-Hydroxy-2-nonenal (HNE), a major lipid peroxidation product, is toxic at high concentrations, but at near-physiological concentrations it induces detoxifying enzymes. Previous data established that in human bronchial epithelial (HBE1) cells, both genes for glutamate cysteine ligase (GCL) are induced by HNE through the c-Jun N-terminal kinase (JNK) pathway. The protein-tyrosine phosphatase SH2 domain containing phosphatase-1 (SHP-1) is thought to play a role as a negative regulator of cell signaling, and has been implicated as such in the JNK pathway. In the present study, SHP-1 was demonstrated to contribute to HNE-induced-gclc expression via regulation of the JNK pathway in HBE1 cells. Treatment of HBE1 cells with HNE induced phosphorylation of mitogen-activated protein kinase kinase 4 (MKK4), JNK, and c-Jun. HNE was able to inhibit protein tyrosine phosphatase activity of SHP-1 through increased degradation of the protein. Furthermore, transfection with small interference RNA SHP-1 showed an enhancement of JNK and c-Jun phosphorylation, but not of MKK4, leading to increased gclc expression. These results demonstrate that SHP-1 plays a role as a negative regulator of the JNK pathway and that HNE activated the JNK pathway by inhibiting SHP-1. Thus, SHP-1 acts as a sensor for HNE and is responsible for an important adaptive response to oxidative stress.