LRP6 and breast cancer: Since Syndecan-1-deficient mice were proposed to be resistant to mammary tumor formation due to reduced Wnt-1 responsive progenitor cell pools, we investigated the influence of Syndecan-1 siRNA knockdown on the expresssion of Wnt-1, its coreceptor LRP-6, and the target of canonical Wnt-signaling, ß-catenin, in the triple negative MDA-MB-231 cell line.