Syndecan-1 overexpression is regulated by an autocrine loop orchestrated by TGF-β through the activation of the Smad pathway and the transcription factor Sp1 and is further enhanced by the highly invasive human breast cancer cells MDA-MB-231, both in young and senescent fibroblasts, via a paracrine action of TGF-β [19]. The gene discussed is SP1; the disease is breast carcinoma.