Fig. 2

Mcl-1 is an upstream regulator of Her2 under hypoxic conditions. a Genetic depletion of Mcl-1 in Her2-positive BC cells promotes downregulation of Her2 and Hif-1α followed by inhibition of BC cell survival. b Mcl-1 protein levels do not decrease after genetically downregulating Her2. a, b BC cells were transfected with siMCL1 a or siHER2 b for 2 days and then exposed to hypoxia for 6 hours. c, d CoCl₂-mediated stabilization of Hif-1α does not alter Mcl-1 or Her2 levels. BT-474 cells were exposed to CoCl₂with indicated doses for 24 hours c and 100 μM CoCl₂ for the indicated time periods d. e, f Pharmacologically targeting Her2 decreases Hif-1α but not Mcl-1 protein levels. BC cells were treated with the indicated doses of trastuzumab e or lapatinib f for 2 days and then exposed to hypoxia for 6 hours. g siMCL1-induced downregulation of Her2 and Hif-1α is not triggered by caspase-mediated off-target effects of MCL1 siRNA. Her2-positive BC cells were transfected with siMCL1 for 2 days and then exposed to hypoxia for 6 hours. ZVAD (50 μM) was added 24 hours before collecting samples. a–g Whole-cell extracts were analyzed by immunoblotting with indicated antibodies. Immunoblotting for Erk2 confirmed equal protein loading. Erk2 extracellular signal-regulated kinase 2, Her2 human epidermal growth factor receptor 2, Hif hypoxia-inducible factor, kD kilodalton, Mcl-1 myeloid cell leukemia-1, PARP Poly (ADP-ribose) polymerase