St. Louis, Oct. 1, 1999 -- A paper in today’s Science identifies an enzyme essential for the body’s daily battle against bacteria in the intestine and possibly in other organs such as the lung and bladder. This work might one day help drug companies design more effective drugs to combat a myriad of diseases, including gingivitis, bladder infections and cystic fibrosis.
"This enzyme activates molecules called defensins, which people always thought were a key line of defense against bacteria. But no one has proven it until this paper," said senior author William C. Parks, Ph.D., associate professor of pediatrics and of cell biology and physiology at Washington University School of Medicine in St. Louis.
The enzyme, called matrilysin, belongs to a large family of enzymes called matrix metalloproteinases, or MMPs. Implicated in a surprising number of diseases, MMPs chew up proteins in the extracellular matrix, a supportive network surrounding cells.
When matrix-degrading metalloproteinases go overboard, they can cause disease. In osteoarthritis, for example, they are thought to break down cartilage in joints, making it painful and difficult for people to use their hands or walk. In cancer, tumor cells use the enzymes to tear down extracellular matrix, gaining passage into the bloodstream and spreading through the body.
MMPs also play important roles in healthy tissue. They often spur normal growth and healing, shaping embryos and remodeling skin in healing wounds.
The Science paper showed that matrilysin protects the epithelial lining of the intestine by regulating the activity of defensins. This might be a common role for this metalloproteinase in the many places where it is made.
Parks and lead author Carole L. Wilson, Ph.D., research assistant professor of pediatrics at Washington University School of Medicine, began studying matrilysin, which shows up in normal, uninjured epithelium, to find out its normal function. In the laboratory of Lynn M. Matrisian, Ph.D., professor of cell biology at Vanderbilt University, Wilson had developed a strain of knockout mice lacking this enzyme. The researchers focused on the small intestine, which in normal mice produces high levels of matrilysin. The cells at the base of the small intestinal crypts — called Paneth cells — are believed to be defense cells in the intestines.
"That’s what made us think that matrilysin could be associated with host defense against bacteria," Wilson said. Wilson started collaborating with Andre J. Ouellette, Ph.D., professor of pathology and of microbiology and molecular genetics at the University of California, Irvine, who studies a class of antimicrobial peptides made by Paneth cells. These peptides are called cryptdins, a term derived from crypt defensins.
Cutting off a short segment activates cryptdins. Parks and Wilson wanted to determine whether matrilysin could be responsible for the cleavage reaction.
Using purified proteins, they found that matrilysin can cleave cryptdin exactly at the site that is used to make an active defensin. And when they analyzed tissue from the small intestine of the mice tissue that lacked matrilysin, they found no evidence of activated cryptdins.
The researchers also discovered that this tissue couldn’t kill bacteria. "We found a decrease in antimicrobial activity in the absence of matrilysin," Wilson said. "Therefore, we concluded that the enzyme is needed to activate these defensins." Depending on the assay the researchers used, there was between a 10-fold and 100-fold difference in the tissue’s ability to kill bacteria.
The researchers were surprised by their findings. "This was an enzyme considered to be one of the most vigorous of those that can degrade connective tissue in the body," Parks said. "We determined it’s going in a completely opposite direction, being released away from the connective tissue and toward surfaces where bacteria are first encountered."
A number of drug companies are developing inhibitors for MMPs for treatment of cancer and arthritis, with the idea that these drugs will block the ability of cells to metastasize or to erode cartilage in the leg. But these broad-acting compounds would inhibit matrilysin as well. Therefore, Parks thinks the companies should try a different approach. "An important thing about this work is that it tells drug companies that you might not want to inhibit this enzyme. Apparently, it’s a good guy," Parks said. "For example, in arthritis you want to target the metalloproteinase that’s causing a problem and leave matrilysin alone."
This research was funded by grants from the Barnes-Jewish Hospital Foundation and the National Institutes of Health.
Wilson CL, Ouellette AJ, Satchell DP, Tokiyoshi A, Yolanda SL, Stratman JL, Hultgren SJ, Matrisian LM, Parks WC. Regulation of Intestinal a -Defensin Activation by the Metalloproteinase Matrilysin in Innate Host Defense. Science, 286, 113--17, Oct. 1, 1999.
The full-time and volunteer faculty of Washington University School of Medicine are the physicians and surgeons of Barnes-Jewish and St. Louis Children's hospitals. The School of Medicine is one of the leading medical research, teaching and patient care institutions in the nation. Through its affiliations with Barnes-Jewish and St. Louis Children's hospitals, the School of Medicine is linked to BJC Health System.
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