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Scientists Identify Protein that Ties Disruption of a Critical Cellular Pathway to Birt-Hogg-Dube Syndrome

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Researchers at the National Cancer Institute (NCI), part of the National Institutes of Health, have linked specific genetic mutations to defects in cells that lead to a rare disease known as Birt-Hogg-Dubé syndrome.

Building on previous clinical and genetic work spanning several years, the researchers discovered a protein that binds to the normal version, but not the mutant version, of the protein implicated in Birt-Hogg-Dubé syndrome.

This protein, which they named folliculin interacting protein 1 (or FNIP1), links Birt-Hogg-Dubé syndrome to disruptions in critical energy- and nutrient-sensing cellular pathways.

The findings appear online October 2, 2006, in "The Proceedings of the National Academy of Sciences." The research was led by Masaya Baba, M.D., Ph.D., and a team of scientists from NCI's Center for Cancer Research.

"These findings open new avenues of further research and therapeutic development for Birt-Hogg-Dubé syndrome, as well as other diseases and cancers related to the same pathways," said NCI Director John Niederhuber, M.D. 

"Although Birt-Hogg-Dubé syndrome is relatively rare, it is an important disease to study not only for the sake of these patients, but also for the further understanding we will gain about the basic cellular defects of both Birt-Hogg-Dubé and related diseases."

In 2001, researchers in the Urologic Oncology Branch of NCI's Center for Cancer Research, working in partnership with Birt-Hogg-Dubé patients and their families, mapped the genetic location of the responsible gene to chromosome 17.

In 2002, they discovered multiple mutations in a previously unidentified gene on chromosome 17, which they named "BHD." Folliculin, or FLCN, is the protein product of the BHD gene.

According to Laura S. Schmidt, Ph.D., corresponding author of the "Proceedings" paper and staff scientist at the Urologic Oncology Branch of NCI's Center for Cancer Research, "Focusing on how alterations in protein interactions actually result in disease symptoms is critical to the development of truly effective therapies."

Recent findings from other studies of noncancerous growths, including birthmarks, suggest that mutations in genes that code for proteins that are involved in critical energy/nutrient-sensing molecular pathways underlie the pathologic conditions seen in these diseases. 

These molecular pathways converge on the protein product of a key regulatory gene known as mammalian target of rapamycin (mTOR), leading researchers to question whether FCLN was an element in an mTOR-related pathway.

To accomplish this, they first sought to identify the proteins that interact with FCLN in normal living cells.

By isolating groups of interacting proteins, they found that one protein in particular, FNIP1, tightly binds to FLCN.

They also determined that the binding of FNIP1 to FLCN in normal cells occurs in the section of the protein that is missing in mutated forms of FLCN identified in Birt-Hogg-Dubé patients.

The results of these studies give direction to understanding Birt-Hogg-Dubé syndrome as well as additional diseases and cancers that are linked to defects in mTOR and other pathways.

In addition, previous work suggests that FLCN acts as a tumor suppressor, although the mechanism for that activity is still being studied.

"I am encouraged by our progress in understanding how these genes contribute to cancer, and I am hopeful that this type of work will lead more quickly to effective forms of treatment," said W. Marston Linehan, M.D., chief of the NCI's Urologic Oncology Branch and an author of the "Proceedings" paper.

"The support of NCI for this kind of long-term, focused study is absolutely necessary as we seek to understand and treat the many different cellular mechanisms that can contribute to the formation of cancer."