Expression of LINE-1 retrotransposons in human breast cancer

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Abstract
Background. Several diseases have been linked to the insertion of human LINE-1 retrotransposons (L1Hs) into structural genes. Recently, the element has been shown to be expressed in a variety of adult and pediatric germ cell cancers, leading to speculation that L1Hs-induced insertion mutations may play a role in the etiology of some neoplasias. Methods. An L1Hs-encoded protein (p40) was assayed in breast cancer cell lines by Western blotting and in solid tumors by immunohistochemical staining and Western blotting. Results. L1Hs retrotransposons are expressed in a significant number of human breast cancers: expression was detected in 7 of 8 malignant cell lines and in 9 of 12 primary infiltrating ductal carcinomas. No expression was detected in two nonmalignant breast epithelial cell lines, five malignant B- or T-cell lines, tissue from a normal breast, a primary breast sarcoma, or a primary medullary carcinoma of the breast. Conclusions. These results raise the possibility that L1Hs expression may contribute to the origin or progression of some breast cancers.