Controversy over the function of the BRCA1 gene and its link tobreast and ovarian cancer has erupted into a scientific feud, withnationally recognized combatants publicly trading blows in anunusual flurry of letters to the July Nature Genetics.
The seeds of the controversy go back to March when researchers atthe University of Washington, in Seattle, and Vanderbilt University,in Nashville, reported in the journal that adding a working copy ofthe gene to tumor cells stops them from dividing and limits tumorgrowth. The research was regarded by many as a promisingindication that research into BRCA1 may yield new ways of treatingcancer.
But in the same article the investigators reported a particularlycontroversial finding _ that the BRCA1 protein is secreted by breastcells and may belong to the family known as granins, which operateat the surface of cells. This suggests that the BRCA1 proteinsomehow suppresses cancer by binding to molecules on the surfacesof breast and ovarian cells.
If so, reported Roy Jensen of Vanderbilt and his coworkers, it mightbe possible to design anticancer drugs that supplant the protein at thebinding site. The notion that the BRCA1 protein is similar to thegranins touched off an immediate dispute.
"It's about something that's pretty important so it has gotten moreattention than other skirmishes," Jensen said.
The debate quickly grew to such proportions that the director of theNational Cancer Institute, in Bethesda, Md., Richard Klausner,invited all of the participants to a May 13, 1996, meeting to discussthe differences in their data and perhaps arrive at a mutuallyacceptable explanation of their conflicting results.
Instead, the researchers agreed to disagree, and to air out theirdispute in the genetics journal. Jensen said the participants alsotraded reagents and protocols so that they could try to duplicate oneanother's experiments.
Other researchers, however, including a team at the Institute ofMolecular Genetics, at Baylor College of Medicine in Houston, andanother at the National Center for Biotechnology Information at theNational Institutes of Health (NIH), also in Bethesda, reject thisview, arguing that the BRCA1 protein isn't pumped out of the cell atall, it remains in the nucleus.
Allan Bradley, of Baylor, and his coworkers contend that it would bedifficult for the BRCA1 protein to function as a true tumorsuppressor if it were pumped outside the nucleus, because it wouldlose its ability to shut down a deranged cell that had begun the wildcell divisions that lead to the devastating accumulation of cancercells.
Frank Calzone, of Amgen Inc., in Thousand Oaks, Calif., reportedthat one of the antibodies commonly used to detect the BRCA1protein also recognizes human epidermal growth factor and severalother related proteins, raising the possibility that research using thisantibody may mistake one of these for BRCA1.
"Nobody has been able to develop a perfect antibody that willrecognize BRCA1 and only BRCA1," Jensen said. "But you can tagBRCA1 protein by altering the gene so that it expresses taggedproteins."
His team has developed a monoclonal antibody that recognizes thehemagglutinin tag, Jensen said. "There's no controversy about this _and we've also showed that the tag did not disrupt the function ofBRCA1."
Using this method, Jensen and his colleagues have demonstrated thepresence of BRCA1 protein in the cell cytoplasm and nucleus. Hesaid he and his colleagues also said BRCA1 can be found outside thecell, and they are looking for proof strong enough to satisfy theircritics. "We're now using tagged proteins to try to replicate thoseexperiments," he said.
E.P. Diamandis, a pathologist at Mount Sinai Hospital, in Toronto,offered support for the Vanderbilt-Washington team. He noted in aletter to the journal that prostate specific antigen (PSA) _ which alsois thought to play a role in breast cancer _ also is secreted.
"PSA is found in the milk of lactating women, and its presence inbreast discharge fluid is associated with a low risk of breast cancer,"Diamandis argued. "In women with a family history of breast canceror with sporadic breast cancer, PSA levels in breast discharge fluidare dramatically reduced."
Stephen Altschul, one of the NIH experts, argues against the graninand secretion theories on statistical grounds. He said Jensen and hiscolleagues failed to convincingly demonstrate that the match betweenthe BRCA1 protein sequence and the granin sequence could not haveoccurred by chance. "They made an error in their probabilitycalculation," Altschul said.
When Altschul and colleague Eugene V. Koonin searched a protein-sequence data base they found that BRCA1 also resembled anotherprotein, p53-binding protein, and that the association was statisticallymuch stronger.
Making Good Biological Sense
"This would make sense," Altschul said. "Virtually any cancer youfind has mutations in p53. One of its functions is telling the cell notto divide when there is some damage to cell the cell's DNA. Findinga similarity to a protein that has some interaction with p53 suggeststhat BRCA1 is interacting with p53, which would make very goodbiological sense on its face."
The BRCA1-p53 protein match has another parallel, this one theRAD9 protein found in yeast. Researchers have speculated on arelationship between RAD9 and p53 because they act in similar ways."If you damage DNA in yeast, RAD9 will shut down the cell andprohibit cell division," Altschul said. "If you knock out RAD9, thecell can go on happily dividing, passing on its damaged DNA."
Unfortunately, neither Altschul nor Koonin are experimentalists, theyare expert sequence analysts who can offer no laboratory evidence tosupport their argument.
Jensen doesn't dispute the possibility that BRCA1 contains anothermotif besides the granin configuration. He said, however, that hisgroup stands behind their own probability calculation, which suggeststhat the granin-BRCA1 match is more than mere chance, and therelationship serves an as-yet-unknown purpose.
As matters stand, the debate is likely to continue until someoneproduces evidence that is impervious to challenge. But, as Altschulsaid, that hasn't happened yet. "The experimental evidence is still upin the air," he said, "with everyone maintaining that they are doingtheir experiments correctly." n
-- Steve Sternberg Special To BioWorld Today
(c) 1997 American Health Consultants. All rights reserved.