Scientists at the National Cancer Institute (NCI) have uncovered a new function for BRCA1, a gene most commonly associated with hereditary breast and ovarian cancer. Working on mouse cells in the lab, they discovered that BRCA1 suppresses the expression of another gene that codes for a microRNA called miR-155, which is known to be cancer causing. These findings, published online Sept. 25, 2011, in Nature Medicine suggest that BRCA1 functions as a tumor suppressor not only by playing a role in DNA repair, as known previously, but also by silencing a gene that can cause cancer when over-expressed. When the scientists inactivated miR-155 in tumor cells in mice, it slowed down the growth of tumors. If the BRCA1-associated tumors are confirmed to be dependent upon miR-155, it may be possible to treat hereditary cancers by challenging them with agents that can inactivate mir-155.
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