Our laboratory studies the the EGF-CFC family and their role in the development of the mouse mammary gland and in the initiation and progression of mouse and human breast cancer. The EGF-CFC family has been identified in all chordate species and consists of Cripto-1 (CR-1) and Cryptic that perform an obligatory role as co-receptors for the TGF beta subfamily of proteins, Nodal/GDF1/GDF3 and that regulate gastrulation, germ layer formation and left-right axis determination. In addition, Nodal and Cripto-1 are essential in the maintenance of embryonic stem cell (ES) self renewal and pluripotency. Nodal binding to cripto-1 functions through the ALK4 and Act-R-IIB Activin/TGF beta class of serine-threonine kinase receptors to activate a canonical Smad2 and Smad3 intracellular signaling pathway through dimerization with Smad4. We have shown that human CR-1 is overexpressed in approximately 40-90% of a variety of human carcinomas including breast tumors. We have also found that overexpression of either Cr-1 or CR-1 in mouse mammary epithelial cells in vitro and in vivo as a transgene results in their transformation and in their enhanced ability to migrate and invade as a result of epithelial-mesenchymal transition (EMT). We were able to demonstrate that CR-1 can also activate Nodal and ALK4-independent signaling pathways by binding to glypican-1 and by subsequently activating c-src, MAPK, PI-3 kinase and Akt which are critical for CR-1 in stimulating EMT. We have also recently found that Cripto-1 can enhance canonical Wnt/beta-catenin signaling at limiting concentrations of Wnt by facilitating the binding of Wnt to the Lrp5 or Lrp6 co-receptors on the cell surface. Finally, we have found that two transcription factors, LRH-1 and GCNF, can positively and negatively regulate CR-1 expression, respectively, in human breast cancer cell lines. Expression of CR-1 was found to correlate with LRH-1 expression in a tissue microarray of human breast tumors and this correlation in LRH-1 and CR-1 expression occurs more frequently in HER+ and in triple negative breast tumors ( HER-, ER- and PR-) as compared to more differentiated Luminal A and Luminal B breast tumors.
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