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for directed subcellular targeting of synthetic transcriptional activators or repressors that might not<br />

otherwise be directed to the nucleus.<br />

Page 453<br />

Finally, the C-terminal region of IFN-γ offers another possibility. With respect to the induction of an<br />

antiviral state, or the upregulation of MHC class II molecule expression, synthetic peptides<br />

corresponding to the C-terminal 39 amino acids of either human or murine IFN-γ function as potent<br />

agonists. This activity is due to the interaction of these peptides with the cytoplasmic domain of the IFNγ<br />

receptor and the associated protein tyrosine kinases. Furthermore, in contrast to the stringent species<br />

specificity of intact IFN-γ, the action of the C-terminal peptides agonists is not limited <strong>by</strong> species<br />

constraints. This property therefore renders the C-terminal portion of the IFN-γ molecule an attractive<br />

model for the development of IFN-γ agonists and antagonists. The identification of the C-terminus of<br />

IFN-γ as that part of the molecule that contacts the cytoplasmic portion of the receptor implies that in<br />

developing IFN-γ agonists, the primary focus should be on this region of the protein. Corresponding<br />

antagonists may be developed <strong>based</strong> upon the portion of the receptor to which the IFN-γ C-terminus<br />

binds.<br />

IV. Conclusion<br />

The interest in IFNs as therapeutics has existed from their initial discovery in 1957. Since then scientists<br />

have been trying to understand the mechanism of their action and apply that knowledge to the treatment<br />

of many different diseases, meeting with some success. The effort now is to understand how IFNs work<br />

at the molecular level, with the goal being to design better, more specific therapeutics. Through<br />

structure/function studies, we now know where the functional sites lie on many of the IFNs. We also<br />

know the sites of interaction with their receptors and second messenger systems. From these studies,<br />

initial candidates for structure-<strong>based</strong> drug design have been identified. Although more work is needed to<br />

further characterize the IFNs and their receptor systems, the challenge now is to apply our existing<br />

knowledge and create second generation molecules that can modulate the many activities of these<br />

fascinating proteins.<br />

References<br />

1a. Isaacs A and Lindenmann J. Virus Interference. I. The interferon. Proc R Soc London Ser B 1957;<br />

147:258.<br />

1b. Johnson HM, Bazer FW, Szente BE, Jarpe MA. How interferons fight disease. Scientific American<br />

1994; 270:40–47.<br />

2. Senda T, Shimazu T, Matsuda S, Kawano G, Shimizu H, Nakamura KT, Mitsui Y. Three-dimensional<br />

crystal structure of recombinant murine interferon-β. EMBO J 1992; 11:3193–3201.<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_453.html (1 of 2) [4/9/2004 12:12:07 AM]

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