IGFBP1 and breast carcinoma: To further investigate whether the transcriptional activation of IGFBP1 by HBP1 is dependent on the DNA-binding domain of HBP1, we utilized two kinds of HBP1 mutants [8]: pmHMG, which has three amino acid mutations in the HMG domain that eliminate its DNA-binding ability, and delEx7, which was isolated from a breast cancer and lacks the entire DNA-binding domain and part of the repression domain (Figure 4D, left panel).