Cellular retinoic acid binding protein I mediates rapid non-canonical activation of ERK1/2 by all-trans retinoic acid

► AtRA activates ERK1/2 in a biphasic manner. ► CRABPI mediates phase 1, non-canonical activation of ERK1/2 by atRA. ► Phase 1 ERK1/2 activation by atRA is independent of RAR and membrane signaling events. ► Non-canonical activity of atRA/CRABPI negatively modulates G1 progression.