GALECTIN-3 AND L1 RETROTRANSPOSONS IN HUMAN BREAST CARCINOMAS

Galectin-3 is a galactoside binding protein found at elevated levels i n a wide variety of neoplastic cells and thought to be involved in cog nitive cellular interactions during transformation and metastasis. Pre viously, we have shown that introduction of human galectin-3 (M-r 31,0 00) cDNA into the human breast cancer cells BT-549 which are galectin- 3 null and non-tumorigenic in nude mice resulted in the establishment of four galectin-3 expressing clones. Three of them acquired tumorigen icity when inoculated in the mammary fat pad of nude mice. Here, we qu estioned what is the molecular difference between the nude mouse tumor igenic and non-tumorigenic galectin-3 expressing BT-549 cell clones. D ifferential display analysis and Northern blotting revealed that, unli ke the tumorigenic clones, neither the parental cells nor the non-tumo rigenic clone expressed a 6.5 Kb transcript. A 607 bp PCR (polymerase chain reaction) product from the differentially displayed mRNA reveale d a 93% sequence homology with the human L1 retrotransposon previously suggested to play a role in the pathobiology of some breast cancers. In addition, we show that the two gene products, i.e., galectin-3 and L1, are co-expressed in breast carcinoma specimens and in other nude m ouse tumorigenic cell lines.