1032 Although the high mobility group A1 ( HMGA1) is an oncogene that is widely overexpressed in aggressive human cancers, the molecular mechanisms that underlie transformation by HMGA1 have not been clearly elucidated. HMGA1 encodes the HMGA1a and HMG1b protein isoforms, which function in regulating gene expression. To better understand how HMGA1 overexpression leads to neoplastic transformation, we looked for genes regulated by HMGA1 using gene expression profile analysis. Ninety-seven genes were differentially regulated by > 2-fold in fibroblasts overexpressing HMGA1a and 103 genes were differentially regulated by > 2-fold in fibroblasts overexpressing HMGA1b. Fifty-five of these genes were common to both the HMGA1a and HMG1b fibroblasts. From the list of genes up-regulated in cells overexpressing HMGA1a or HMG1b, the gene encoding the signaling molecule, signal transducer and activator of transcription or STAT3, was studied further because of its prominent role in malignancy. Here, we demonstrate that STAT3 is a critical downstream target of HMGA1. We show that HMGA1 binds to a conserved region of the STAT3 promoter in vivo by chromatin immunoprecipitation experiments. STAT3 mRNA and activated protein (phosphorylated STAT3) levels are increased in leukemia cells from HMGA1a transgenic mice. Activated STAT3 also recapitulates the transforming activity of HMGA1a in fibroblasts. Blocking STAT3 function induces apoptosis preferentially in leukemia cells from HMGA1a transgenic mice, but not in nontransgenic control cells. Moreover, blocking STAT3 function in human erythroleukemia (HEL) cells overexpressing HMGA1a also blocks colony formation in soft agar and cell motility. STAT3 mRNA is also increased in human acute lymphoid leukemia samples that overexpress HMGA1a , suggesting that this pathway is important in human lymphoid leukemia. Our results demonstrate that STAT3 is a direct HMGA1 target gene involved in HMGA1-mediated transformation and a potential therapeutic target in human lymphoid leukemia.
Despite the success of genomics in identifying new essential oncogenic signaling pathways, there have been a limited number of sustainable leads in anticancer drug discovery to address increasing chemoresistance. To improve progress in this area, our lab synthesized several novel benzisoxazoloazinium tetrafluoroborates (1-3) with structural characteristics similar to clinically effective DNA binding drugs. From a series of eight tricyclic pyridinium compounds with various substituents, Compound 1a effectively inhibits proliferation in colon cancer cell lines (IC50 = 2.95 µM) and shows significant in silico and in vitro DNA binding affinity. Incorporation of a fourth ring generated quinolinium derivatives (2) that recapitulate DNA binding activity of ellipticine. Preliminary IC50 values range from 52 µM for 2b to 202 µM for 2a. To evaluate the impact of second nitrogen, we synthesized and evaluated a quinoxalinium analog (3); results for this compound (IC50 of 18 µM) show increased cytotoxicity compared to 2b. All compounds induce cell death via non-apoptotic pathways. Future work will involve the synthesis and evaluation of other quinoxalinium analogs, as well as evaluation of their activity against PC3 human prostate cancer cells.
<div>Abstract<p>Although <i>HMGA1</i> (<i>high-mobility group A1</i>; formerly <i>HMG-I/Y</i>) is an oncogene that is widely overexpressed in aggressive cancers, the molecular mechanisms underlying transformation by <i>HMGA1</i> are only beginning to emerge. <i>HMGA1</i> encodes the HMGA1a and HMGA1b protein isoforms, which function in regulating gene expression. To determine how <i>HMGA1</i> leads to neoplastic transformation, we looked for genes regulated by HMGA1 using gene expression profile analysis. Here, we show that the <i>STAT3</i> gene, which encodes the signaling molecule signal transducer and activator of transcription 3 (STAT3), is a critical downstream target of HMGA1a. <i>STAT3</i> mRNA and protein are up-regulated in fibroblasts overexpressing <i>HMGA1a</i> and activated STAT3 recapitulates the transforming activity of HMGA1a in fibroblasts. HMGA1a also binds directly to a conserved region of the <i>STAT3</i> promoter <i>in vivo</i> in human leukemia cells by chromatin immunoprecipitation and activates transcription of the <i>STAT3</i> promoter in transfection experiments. To determine if this pathway contributes to HMGA1-mediated transformation, we investigated <i>STAT3</i> expression in our <i>HMGA1a</i> transgenic mice, all of which developed aggressive lymphoid malignancy. <i>STAT3</i> expression was increased in the leukemia cells from our transgenics but not in control cells. Blocking STAT3 function induced apoptosis in the transgenic leukemia cells but not in controls. In primary human leukemia samples, there was a positive correlation between <i>HMGA1a</i> and <i>STAT3</i> mRNA. Moreover, blocking STAT3 function in human leukemia or lymphoma cells led to decreased cellular motility and foci formation. Our results show that the HMGA1a–STAT3 axis is a potential Achilles heel that could be exploited therapeutically in hematopoietic and other malignancies overexpressing <i>HMGA1a</i>. [Cancer Res 2008;68(24):10121–7]</p></div>
Abstract HMG-I/Y is overexpressed in human cancer, although a direct role for this gene in transformation has not been established. We generated transgenic mice with HMG-I targeted to lymphoid cells. All seven informative founder HMG-I mice developed aggressive lymphoma by a mean age of 4.8 months. Tumors express T-cell markers and are transplantable. We also demonstrate that HMG-I mRNA and protein are increased in human acute lymphocytic leukemia samples. Our results show that HMG-I functions as an oncogene and suggest that it contributes to the pathogenesis of leukemia and other cancers with increased HMG-I expression.
Supplementary Table 1 from The High-Mobility Group A1a/Signal Transducer and Activator of Transcription-3 Axis: An Achilles Heel for Hematopoietic Malignancies?
