Greasing the gears that drive the interferon signal

Interferon -- a critical protein that mediates the body's defense against a wide variety of infectious agents and tumors -- may soon have greater therapeutic value as the result of a new study by researchers at Washington University School of Medicine in St. Louis.

"Essentially, we found a way to grease the gears that drive the interferon signal," says Michael J. Holtzman, M.D., the Selma and Herman Seldin Professor of Medicine and director of the Division of Pulmonary and Critical Care Medicine.

The researchers modified the structure of a protein called Stat1, which relays signals from interferon at the cell surface to genes in the cell nucleus. The modification up shifted Stat1's response to interferon.

The study will appear in the October 7, 2005 issue of the Journal of Biological Chemistry and was selected as the journal's Paper of the Week, which recognizes the top one percent of the journal's papers in significance and overall importance.

The development of a mechanism to tweak Stat1's responsiveness may prove particularly useful for patients with such disorders as hepatitis C, multiple sclerosis and many types of systemic cancer, who currently benefit from interferon treatment, but sometimes find it difficult to tolerate the side effects of the high doses required.

"We reasoned that if we could enhance the way interferon produces its beneficial defensive effects, the body could respond to its normal level of interferon and receive enhanced benefit without side effects," Holtzman says.

The group engineered a mutant Stat1 protein in which the identities of two amino acids were switched. Investigations conducted on cells growing in culture showed that the altered Stat1 proteins reacted more efficiently to the presence of both type I and type II interferons. Further tests revealed that the souped-up Stat1 recruited more of a specific protein it needs to pass on the interferon signal, essentially raising the speed limit on signal transmission.

"Ordinarily, the interferon signaling system's rate may be slowed because this helper protein interacts with Stat1 at less than the maximum amount," Holtzman says. "It's possible that the maximal setting would be harmful in the long term, because too much interferon could lead to inflammatory diseases. But we may find advantages to increasing Stat1 action in the short term using drug treatments."

Such therapies could allow physicians to turn up the effect of interferon temporarily to treat infections or other disorders and then to turn it back down to normal levels when the patient is cured.

"The potential for this 'rheo-Stat' strategy is exciting," Holtzman says. "As an example, one could improve Stat1 efficiency during the winter months in patients at risk of developing serious viral infections, including children with asthma, heart disease or compromised immune systems."

It may be possible, as well, to screen patients for levels of Stat1 responsiveness and use the same treatment strategy to correct low levels of response, according to Holtzman. The researchers are currently screening newborn infants for levels of Stat1 action and tracking their susceptibility to viral infection.

In addition, the group is studying transgenic mice engineered to carry the same Stat1 mutations that were examined in cells. In this way, the researchers can investigate the benefits of hyper-responsive Stat1 for infection control and cancer treatment in a living organism. These studies lay the foundation for the development of human treatments that use drugs that increase Stat1 responsiveness and consequently enhance the benefits of interferon produced naturally in the body or given as treatment.