EXPRESSION OF LINE-1 RETROTRANSPOSONS IN HUMAN BREAST-CANCER

Background. Several diseases have been linked to the insertion of huma n LINE-1 retrotransposons (L1Hs) into structural genes. Recently, the element has been shown to be expressed in a variety of adult and pedia tric germ cell cancers, leading to speculation that L1Hs-induced inser tion mutations may play a role in the etiology of some neoplasias. Met hods. An L1Hs-encoded protein (p40) was assayed in breast cancer cell lines by Western blotting and in solid tumors by immunohistochemical s taining and Western blotting. Results. L1Hs retrotransposons are expre ssed in a significant number of human breast cancers: expression was d etected in 7 of 8 malignant cell lines and in 9 of 12 primary infiltra ting ductal carcinomas. No expression was detected in two nonmalignant breast epithelial cell lines, five malignant B- or T-cell lines, tiss ue from a normal breast, a primary breast sarcoma, or a primary medull ary carcinoma of the breast. Conclusions. These results raise the poss ibility that L1Hs expression may contribute to the origin or progressi on of some breast cancers.