The proteosome inhibitor, MG132, quells RAR trans-activation a potentiates RAR trans-repression of NFκB. (A) at-RA induces a dose dependent decrease in RAR protein levels while increasing concentrations of AGN193109 have a restorative effect. The expression of RelA and β-actin is however not affected by at-RA +/- AGN193109. (B) at-RA (1 μM) induced degradation of RAR is blocked by the proteosome inhibitor MG132 (5 μM). Correspondingly, induction of RAR reporter activity by at-RA (1 μM) is quelled by MG132 (5 μM). (C) Basal NFκB reporter activity in mIκB-Line 1 cells is further repressed by MG132 (5 μM) by mechanism independent of the IκB-NFκB signaling axis (* P value < 0.05).