Interleukin-1β induction of mitogen-activated protein kinases in human mesangial cells: Role of oxidation

Abstract

Interleukin-1β (IL-1β) significantly influences renal cellular function through the induction of several gene products. The molecular mechanisms involved in gene regulation by IL-1β are poorly understood; however, the appearance of novel tyrosine phosphoproteins in IL-1β-treated cells suggests that IL-1β may function through tyrosine phosphoprotein intermediates. The mitogen-activated protein (MAP) kinases are tyrosine phosphoproteins that could potentially mediate the effects of IL-1β. Protein tyrosine phosphorylation following IL-1β treatment may be dependent on redox changes since the IL-1β receptor is not a protein-tyrosine kinase and oxidation has been shown to induce tyrosine phosphorylation. In this report we demonstrate that conditioning human glomerular mesangial cells with IL- 1β results in the tyrosine phosphorylation and activation of two members of the MAP kinase family, extracellular signal-regulated protein kinase 2 (ERK2) and p54 Jun-NH 2 terminal kinase (JNK). This effect of IL-1β is abrogated by pretreating cells with the antioxidants N-acetyl-L-cysteine or dithiothreitol. Furthermore, the effects of IL-1β on ERK and JNK activation are reproduced by treating mesangial cells with membrane-permeable oxidants. IL-1β and oxidants also cause phosphorylation and activation of the upstream ERK regulatory element MAP kinase kinase. Interestingly, IL-1β, but not exogenous oxidants, causes phosphorylation of the upstream JNK activator, JNK kinase. These data indicate that IL-1β activates ERK2 through an oxidation- dependent pathway. Exogenous oxidants and IL-1β activate JNK through different upstream mechanisms; however, antioxidant inhibition of JNK activation indicates that endogenous oxidants may play a role in IL-1β- induced JNK activation. Thus IL-1β may affect mesangial cell function by activating MAP kinases, which can then regulate gene transcription. Furthermore, reactive oxygen species released during inflammatory glomerular injury may also affect mesangial function through a MAP kinase signal.