COMPARATIVE EXPRESSION OF THE LINE-1 P40 PROTEIN IN HUMAN BREAST CARCINOMAS AND NORMAL BREAST TISSUES

Human LINE-1 (L1Hs) retrotransposons can act as insertional mutagens a nd are expressed in a variety of tumors, including breast cancer. The purpose of the present study was to examine expression of the p40 prot ein encoded by the first open reading frame of a L1Hs element in norma l human breast tissue of patients without malignant breast disease and in nontumor breast tissue adjacent to cancer and to compare it to exp ression in breast carcinomas. An antiserum specific for the L1Hs p40 p rotein was used to analyze its expression in 5 reduction mammoplasties , 16 primary breast cancers, 1 lymph node metastasis and 13 nonmaligna nt breast tissues adjacent to matched primaries by western blotting an d/or immunocytochemistry. The immunoreactive band observed on westerns consistently had a M, of approximate to 46 kDa. Westerns detected som e p40 protein expression in all malignant and nonmalignant tissues exa mined, although 4 of 5 reduction mammoplasties had very low or trace l evels as compared with tumors. Nonmalignant breast tissues adjacent to cancers showed significant western band reactivity, and all 15 tumors were positive. Immunocytochemistry revealed staining specificity of t he antibody for epithelial cells. Of 12 invasive carcinomas examined, 100% were positive for the p40 protein, whereas one reduction with ben ign proliferative disease was very weakly reactive, two histologically normal reductions were negative, and 4 of 6 nonmalignant tissues adja cent to cancers were negative. Our data indicated that expression of t he L1Hs p40 protein was often elevated in tumor cells of human breast cancers compared to epithelium of normal mammary gland. Copyright (C) 1996 Elsevier Science Inc.