The relationship between increased ifi202 expression and SLE was first suggested by Rozzo et al in 2001. It was discovered due to the over-expression of p202 in splenic B cells of mice showing similar symptoms as lupus. Currently the prototypical mouse model for SLE is (NZWxNZB)F1, which is short for the first generation offspring of New Zealand Black and New Zealand White mice. The overproduction of p202 seems to lead to the suppression of p53 protein, which is a regulatory protein in the process of apoptosis. This is hypothesized to contribute to some of the symptoms of SLE.
The p202 protein has the following structure
Humans have an ifi202 and ifi204 similar gene known as ifi16. They share some similarities in the amino acid sequence. (Trapani, 1992).
Ifi202 is known to be regulated by IL-6. The binding of IL-6 to its receptors leads to the activation STAT3 (Signal Transducer and Transcription 3), which seems to be a transcription factor in the expression of Ifi202. (Pramanik, 2004) P202 expression is known to retard cell proliferation and increases cell survival.
Gene 200 cluster is located on Chromosome 1 of murine genome. (Choubey 1995) Nba2 locus is suspected to be a major contributor to the susceptibility of mice to SLE. Ifi202 and ifi203, both of which seem to be linked to SLE susceptibility, are within Nba2 interval. (Rozzo, 2001) Using QPCR, it was shown that splenic B cells and non-B/non-T cell have increased ifi202 expression in SLE susceptible mice. (Rozzo, 2001) Based on the knowledge that ifi202 gene is a regulator of apoptosis and cell proliferation, ifi202 was implicated in the autoimmunie disease SLE.
Using in B6.Nba2 lupus susceptible mice as the animal model, researchers were able to show increased expression of Ifi202, an IFN-activatable gene, inhibits p53-mediated apoptosis of splenic B cells. (Xin, 2006) They also inhibit UV induced apoptosis of embryonic fibroblasts of mice. Since it is known that p53 mediates the expression of proapoptotic proteins, the increased p202 correlates with increased p53 levels. p202 seems to bind to p53 protein at the N-terminal region, and important to inhibits p53 function. (Xin, 2006) Interestingly, p53 expression appears to inhibit the expression of ifi202. Levels of p202 decrease after exposure of cells to UV light, while p53 levels increased. The overexpression of p202 in cells decreased the p53 mediated apoptosis. (D'Souza et al, 2001).