The collagen receptor endo180 (CD280) is expressed on basal-like breast tumor cells and promotes tumor growth in vivo

Tumor cell invasion into the surrounding stroma requires increased cell motility and extensive remodeling of the extracellular matrix. Endo180 (CD280, MRC2, urokinase-type plasminogen activator receptor-associated protein) is a recycling endocytic receptor that functions in both these cellular activities by promoting cell migration and uptake of collagens for intracellular degradation. In the normal breast, Endo180 is predominantly expressed by stromal fibroblasts. The contrary observation that Endo180 is expressed on epithelial tumor cell lines that display a high invasive capacity suggested that up-regulation of this receptor may be an associated and functional component in the acquisition of a more aggressive phenotype by tumor cells in vivo. Here, we show that high levels of Endo180 are found in a subset of basal-like breast cancers and that this expression is an independent prognostic marker for shorter disease-free survival. Two potential mechanisms for Endo180 up-regulation were uncovered. First, it was shown that Endo180 can be transcriptionally up-regulated in vitro following transforming growth factor-beta treatment of breast cancer cells. Second, a proportion of Endo180(+) tumors were shown to have Endo180 gene copy number gains and amplifications. To investigate the functional consequence of Endo180 up-regulation, MCF7 cells transfected with Endo180 were inoculated into immunocompromised mice. Expression of wild-type Endo180, but not an internalization-defective Endo180 mutant, resulted in enhanced tumor growth together with a reduction in tumor collagen content. Together, these data argue that elevated expression of this receptor in tumor cells could have important consequences in subsets of basal-like carcinomas for which there is a current lack of effective treatment.