FIGURE 5.

XIAP is required for the degradation of ERα by SNIPER(ER)-87. A, depletion of XIAP suppresses the SNIPER(ER)-87-induced degradation of ERα. MCF-7 and T47D cells were transfected with the indicated siRNA for 42 h and treated with 10 nm SNIPER(ER)-87 for 3 h. Whole-cell lysates were analyzed by Western blotting with the indicated antibodies. Numbers below the ERα panel represent ERα/actin ratio normalized by vehicle control as 100. Three different siRNAs against XIAP and cIAP1 were used. B, depletion of XIAP does not inhibit the ERα degradation by fulvestrant and β-estradiol. MCF-7 cells were transfected with the indicated siRNA for 42 h and treated with 10 nm of the indicated compounds for 3 h. Whole-cell lysates were analyzed by Western blotting with the indicated antibodies. Numbers below the ERα panel represent the ERα/actin ratio normalized by the vehicle control as 100. C, essential role of XIAP RING domain in the SNIPER(ER)-induced ERα degradation. MCF-7 cells were transfected with the indicated siRNA for 24 h. Then cells were infected with the indicated lentiviral vectors for 45 h and treated with 10 nm SNIPER(ER)-87 for 3 h. Whole-cell lysates were analyzed by Western blotting. D, XIAP ΔRing suppresses the SNIPER(ER)-87-induced degradation of ERα. Cells were infected with indicated lentiviral vectors for 45 h and then treated with 10 nm SNIPER(ER)-87 for 3 h. Whole-cell lysates were analyzed by Western blotting. D, DMSO; SN, SNIPER(ER)-87.