(A) Schematic illustration of the Id2-DBM-δHLH construct. In this construct, the HLH domain encoded by amino acid residues from 35 to 76 was deleted from Id2, and the key arginine and leucine residues within the D-box motif (RxxLxxxN) at residues 100 to 107 were changed to glycine and valine. (B) Western blot analysis of Id2 and its mutants in MCF-7 and SKOV-3 cells. Total proteins were extracted from cells transfected with the indicated plasmids, and then underwent SDS-PAGE electrophoresis and immunoblotting analysis using the indicated antibodies. β-actin was used as the loading control. (C) RT-PCR analysis of Id2 and its mutants in MCF-7 and SKOV-3 cells. Total RNA was extracted from cells transfected with the indicated plasmids and used for RT-PCR analysis of the mRNA expression of Id2 and its mutants. β-actin was the loading control. The results shown in B and C are representative of three independent experiments.