Fig. 12.
PPARβ/δ- and RAR/RXR-dependent modulation of keratinocyte cell growth. In response to ligand activation, PPARβ/δ heterodimerizes with RXR, leading to up-regulation of target genes that cause terminal differentiation and apoptotic signaling culminating in the inhibition of cell growth. 9-cis RA may also interact with this signaling by enhancing this effect. atRA or 9-cis RA activate RAR and RXR, respectively, and lead to either heterodimerization or homodimerization with RXR, respectively, and up-regulation of target genes that cause an increase in apoptotic signaling and inhibition of cell growth.