Although men inherit the same mutant genes that women, regarding the hereditary breast cancer, men just do not get it. New research suggests why maybe. A mutation that leads to breast cancer and ovarian cancer in women can unlock problems in the second X chromosome, which is lacking in men.
About 5% to 10% of hereditary breast and ovarian cancers are due to mutations in the BRCA1 gene, whose protein product normally repairs damaged DNA . Although men also carry these mutations, breast cancer in men is extremely rare. Previously, researchers have noticed that dividing cells in mouse testes produce a lot of BRCA1 RNA messenger. Sometimes the chromosomes in the cells are tightened, similar to one of the X chromosomes in female cells. It packed chromosome in females is inactivated to prevent women from obtaining double the dose of the genes encoded on the X chromosome; one man X is never stopped.
To determine whether BRCA1 helps to inactivate the X chromosome in women, a team led by David Livingston cancer biologist at Dana-Farber Cancer Institute in Boston examined the cells of non-cancerous breast, cultured, using antibodies to mark BRCA1 and an RNA molecule known under the name XIST which coats the X and inactivating chromosomes. Livingston and his colleagues found that the two molecules linked together and rested on stopping X chromosome. In tumor cells of breast and five patients with ovarian cancer who lack BRCA1 , however, they found no coating XIST either chromosome, suggesting that the loss of BRCA1 could fuel the second X. the researchers turned to breast cancer cells lacking Culture BRCA1 to determine the effect the restoration of BRCA1 . When they added BRCA1 in these cells, once inlaid XIST inactivated X, they report in the November 1st issue of cell .
cells without BRCA1 may be unable to inactivate the second X chromosome, speculates molecular biologist Robert Weinberg of the Massachusetts Institute of Technology in Cambridge. This could enable some gene products to be overproduced and perhaps contribute to cancer in women. "The finding was totally unexpected and surprising," he said.
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David Livingston at the Cancer Institute Dana-Farber
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