Abstract 5224: MicroRNA mediated regulation of TGF-β signaling leads to stem cell alterations in myelodysplastic syndromes

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Myelodysplastic syndromes (MDS) are hematologic malignancies characterized by hematopoietic stem cell dysfunction that leads to ineffective hematopoiesis and cytopenias. Even though a third of MDS cases transform to leukemia, most of the mortality in MDS is due to low blood counts that occur because of failure of hematopoiesis. Development of effective treatments for MDS have been impeded by a limited understanding of the molecular pathways that suppress hematopoietic stem cells. We previously demonstrated that the myelosuppressive cytokine TGF-β mediated SMAD2 activation can inhibit stem and progenitor cells in MDS. We demonstrated that SMAD7, a negative regulator of TGF-β receptor-I kinase, is markedly reduced in MDS, and can lead to ineffective hematopoiesis by overactivation of Smad2/3 mediated TGF-β signaling. To determine the cause of SMAD7 reduction in MDS, we analyzed the 3′UTR of the gene and found a highly conserved binding site for microRNA-21. Strikingly, we observed significantly elevated levels of miR-21 in MDS marrow samples when compared with age matched controls. miR-21 was shown to directly bind to the 3′UTR of SMAD7 and reduce its expression in hematopoietic cells. Next, we tested the role of miR-21 in regulating TGF-β signaling in a TGF-β overexpressing transgenic mouse model that develops progressive anemia and dysplasia and thus serves as a model of human bone marrow failure. Treatment with a chemically modified miR-21 inhibitor led to significant increases in hematocrit and an increase in SMAD7 expression in vivo. Inhibition of miR-21 also led to increase in erythroid colony formation from primary MDS bone marrow progenitors, demonstrating its ability in stimulating hematopoiesis in vitro. Even though miR-21 was found to be elevated in MDS, the mechanisms of its elevation in MDS as well as in other cancers are not well elucidated. The miR-21 gene locus has been shown to contain upstream STAT3 binding sites. Furthermore, STAT3 has also been shown to directly lead to miR-21 upregulation in myeloma and other immune cells. Genomic profiling of highly purified hematopoietic stem cells in MDS by us demonstrated that STAT3 is selectively upregulated in these cells. STAT3 overexpression was validated in an expanded set of 183 MDS CD34+ cells as well. These results suggest that a STAT3-miR-21 pathway leads to enhancement of TGF-β signaling, thus leading to ineffective hematopoiesis in MDS. Citation Format: Tushar D. Bhagat, Li Zhou, Lubomir Sokol, Ioannis Mantzaris, Sanchari Bhattacharyya, Shanisha A.K. Gordon, Yiting Yu, Krishna Gundabolu, Sangeeta Nischal, Rahul Polineni, Carolina Schinke, Grigorios Chrysofakis, Amittha Wickrema, Andrea Pellagatti, Jacqueline Boultwood, Ulrich Steidl, Gang Liu, Alan F. List, Markus Bitzer, Amit Verma. MicroRNA mediated regulation of TGF-β signaling leads to stem cell alterations in myelodysplastic syndromes. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5224. doi:10.1158/1538-7445.AM2014-5224