The HMGA1a-STAT3 axis: an “Achilles Heel” for Hematopoietic Malignancies Overexpressing HMGA1a?

Although the high mobility group A1 (HMGA1) oncogene is widely overexpressed in high-risk hematopoietic malignancies and other aggressive cancers, the molecular mechanisms underlying transformation by HMGA1 are only beginning to emerge. The HMGA1 gene encodes the HMGA1a and HMGA1b protein isoforms, which function in regulating gene expression. We showed that HMGA1 induces leukemic transformation in cultured human lymphoid cells. Inhibiting HMGA1 expression blocks the transformed phenotype in cultured human leukemia and lymphoma cells. We also engineered HMGA1a transgenic mice and all mice develop aggressive lymphoid malignancy which closely models human T-cell acute lymphoblastic leukemia. Because HMGA1 participates in transcriptional regulation, we hypothesize that it drives leukemic transformation by dysregulating specific molecular pathways. To discover genes targeted by HMGA1 in leukemic transformation, we performed gene expression profile analysis. The signaltransducer andactivator oftranscription 3 (STAT3) gene was identified as a critical downstream target of HMGA1. STAT3 mRNA and protein are up-regulated in leukemic cells overexpressing HMGA1a and activated STAT3 recapitulates the transforming activity of HMGA1a. HMGA1a binds directly to a conserved region of the STAT3 promoter in vivo and activates transcription of the STAT3 promoter in human leukemia cells. Blocking STAT3 function with a small molecule, platinum compound inhibitor (CPA-7) induces apoptosis in leukemic cells from HMGA1 transgenic mice, but not in control cells. In primary, human leukemia samples, there is a positive correlation between HMGA1a and STAT3 mRNA. Moreover, blocking STAT3 function with a dominant-negative construct in human leukemia or lymphoma cells leads to decreased cellular motility and colony formation. We also showed that treatment with a small molecule, oligonucleotide inhibitor decreases the leukemic burden in the HMGA1a transgenic mice. Our results demonstrate that the HMGA1a-STAT3 axis is a potential “Achilles heel” that could be exploited therapeutically in selected hematopoietic malignancies.