The observation that indirubin derivatives, potent inhibitors of GSK-3 beta [27], [28], stabilize the beta-catenin-TCF/LEF complex and promote melanogenesis in B16F10 melanoma cells suggests that Mitf expression, rather than the phosphorylation-dependent activation of MITF, is the rate-limiting step of the melanogenic program [29]. Here, CTNNB1 is linked to melanoma.