High lib mRNA expression in breast carcinomas.

Lib, first identified as a novel beta-amyloid responsive gene in rat astrocytes, has an extracellular domain of 15 leucine-rich repeats (LRRs) followed by a transmembrane domain and a short cytoplasmic region. It is a distinctly inducible gene and is thought to play a key role in inflammatory states via the LRR extracellular motif, an ideal structural framework for protein-protein and protein-matrix interactions. To evaluate potential roles of Lib, we screened various tumors for Lib expression. Lib mRNA expression was high and uniquely expressed in breast tumor tissues, compared to paired normal breast tissues. Lib mRNA was localized in the ductal carcinoma cells and Lib protein displayed a homophilic association on the surface of cultured cells. These data suggest that Lib may play a role in the progression of breast carcinomas and may be a diagnostic marker for breast tumors.