Despite numerous advances in systemic lupus erythematosis (SLE), the molecular pathogenesis of this disease remains poorly understood. This proposal takes advantage of recent findings we have uncovered that suggest defective regulation of translation initiation in SLE. It was previously known that T cells from patients with active SLE are refractory to mitogenic stimuli. An important T cell response to mitogenic stimuli is an increased rate of protein synthesis, regulated at translation initiation. It was previously known that T dells from patients with active SLE are refractory to mitogenic stimuli. An important T cell response to mitogenic stimuli is an increased rate of protein synthesis, regulated at translation control. We investigated the effect of activating signals on translation initiation factor activates, in T cells from SLE patients. Activation by mitogens resulting in a strong increase in protein synthesis in control T cells but not in T cells from SLE patients. This lack of response in SLE T cells was further associated with over-expression of the pr4oytein kinase PKR and with increased phosphorylation of its substrate, the initiation factor eIF2alpha. Interestingly, up-regulation of PKR impairs cell functions that are relevant to lupus, including: cell proliferation, Fas-dependent apoptosis, cytokine gene expression and signaling and release of Ca2+ from intracellular stores. Therefore we propose to test in this application the hypothesis that high expression of PKR and subsequent eIF2alpha phosphorylation contribute to the impaired responses to mitogens in T cells from SLE patients.
The specific aims are: (i) to determine the role of PKR in lupus pathogenesis. We will produce PKR-/- lupus-prone mice by backcrossing PKR knockout mice with MRL-lpr breeders. We will analyze in these mice different parameters of relevance to this lupus-like disease including serum immunoglobulin production, anti-nuclear auto-antibody response, end-organ disease and mortality. (ii) to identify specific mRNAs whose translation is highly dependent on PKR and eIOOF2alpha phosphorylation in T cells, and that may be affected in SLE. We will analyze gene products in TG cells from control mice and from transgenic mice with either a dominant negative mutant of eIF2alpha or with a targeted disruption of the PKR gene. Gene products will be identified using two-dimensional gel electrophoresis and mass spectrometry. (iii) PKR regulates cytokine signaling mediated by the transcription factor IRF-1 and we reported that IRF-1 trans-activates PKR expression. We will investigate the function of IRF-1 in lupus T cells. It is anticipated that these studiers will provide novel and important insights into mechanisms contributing to SLE.
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