SMAD3 and melanoma: To monitor Activin-A signaling, we incubated the melanoma cell SNs on HepG2 reporter cells that were stably transduced with the SMAD3 luciferase reporter CAGA-Luc and with Renilla for signal normalization.30 Treatment with iBIP2 2891L SN stimulated CAGA-Luc expression more than 100-fold, and this effect was blocked on addition of the Activin-A antagonist Follistatin (FST).