Stromal Cells Expressing Hedgehog-Interacting Protein Are One of the Main Regulators of the Hedgehog Signaling System in Myeloid Neoplasms

Abstract 3840

Aberrant reactivation of Hedgehog (Hh) signaling has been described in a wide variety of human cancers including cancer stem cells. However, involvement of the Hh signaling system in the bone marrow (BM) microenvironment during the development of myeloid neoplasm is unclear. In this study we assessed the expression of Hh-related proteins in normal human CD34⁺ cells, CD34⁺ leukemic/dysplastic cells and BM stromal cells. Both Indian hedgehog (Ihh) and its signal transducer, SMO, were expressed in CD34⁺ acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) derived cells, suggesting that Ihh could be affected in an autocrine manner. Remarkably, expression of the endogenous Hh signaling inhibitor, human hedgehog-interacting protein (HHIP), in AML/MDS-associated stromal cells was significantly lower than in healthy donor-derived stromal cells. Moreover, HHIP expression level in BM stromal cells highly correlated with their tumor-supporting activity of SMO⁺ leukemic cells. Demethylating agent 5-aza-dC rescued HHIP expression via demethylation of HHIP gene and reduced the leukemia-supporting activity of AML/MDS-associated stromal cells. This effect of 5-aza-dC was negated by HHIP shRNA transfer into stromal cells. These results indicate that suppression of stromal HHIP expression could be involved in the progression of AML/MDS and 5-aza-dC may improve the protective function of BM stromal cells for AML/MDS.

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