FIG. 6.

Model depicting the function and regulation of IRF6 protein expression and phosphorylation. Nonphosphorylated IRF6 promotes differentiation and entry into the G₀ stage. During this stage, the unknown IRF6 kinase is targeted for degradation by the proteasome. Upon receipt of a proliferation signal, degradation of the IRF6 kinase is ablated and expression of the kinase increases, leading to IRF6 phosphorylation (P). Phosphorylated IRF6 is either targeted for proteasomal degradation or is sequestered by maspin, which may regulate IRF6 function and preserve IRF6 expression. Arrows depicting differentiation signals are shown in red, while those depicting cell proliferation signals are shown in green. Ub, ubiquitin.