Effect of Dioxin (TCDD) on Gene Transcription of Human CD34+ Hematopoietic Cells.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) binds to aryl hydrocarbon receptor (AhR), a member of the erb-A family, allowing, after DNA binding, gene expression regulation. TCDD has a large number of biological effects, as skin and cardiovascular disease, diabetes and cancer. An increase in myeloid leukemia, Hodgkin’s and non-Hodgkin’s lymphomas, was observed after 15 years in the population exposed to TCDD after the 1976 accident in Seveso, Italy. In the present study, we analyzed the in vitro effect of TCDD exposure on human CD34⁺ progenitor cells from G-CSF stimulated leukapheresis of 4 normal donors. Gene expression modulation induced by TCDD was analysed on highly purified (>96%) CD34⁺ cells, after exposure to 10 nM of TCDD for 12 hrs. Gene expression profiles have been generated by high-density oligonucleotide arrays (Affymetrix GeneChip U133A) and subsequently analyzed with a supervised approach (DNA-Chip Analyzer, dChip 2006). The differential expression of 257 transcripts (150 up regulated and 106 down-regulated) distinguished the 4 TCDD treated from the 4 untreated control samples. Interestingly, a number of the differentially expressed genes were involved in skin and cardiovascular diseases, diabetes, and different cancers, all of which have been associated with TCDD exposure. Among skin diseases, defects in laminin beta 3, ALOX12B and keratin 2a, all downregulated in TCDD exposed CD34+ cells, are associated with development of epidermolysis bullosa, erythroderma ichthyosiform, and Siemens ichthyosis bullosa, respectively. As far as diabetes and cardiovascular disease pathogenesis are concerned, defects of SLC2A4 gene, dowregulated by TCDD, is associated with the development of non insulin dependent diabetes, while epoxide hydrolase 2 and EGR2 are associated with cardiovascular disease. Among cancer related genes, ARHGAP26 and ABL2 are associated with juvenile myelomonocytic leukemia and acute myeloid leukemia with eosinophilia, respectively. Nevertheless, the expression of numerous other genes potentially involved in hemopoiesis/leukemogenesis, was modulated by TCDD exposure. Among these examples are c-kit ligand, LIF receptor, pre B lymphocyte gene 1, piwi-like 2, FLT3 ligand, chemokine ligands 14 and 15, and cdk2, that were all up regulated, while MLL4, wnt inhibitory factor 1, chemokine ligand 7, and lymphoid blast crisis oncogene, were down regulated. In conclusion, the gene expression pattern induced by TCDD exposure on the CD34⁺ normal progenitor cells is consistent with the spectrum of TCDD induced toxicities/diseases. In particular, it provides the basis for a possible role of TCDD in the neoplastic transformation of hemopoietic stem cells and support the epidemiologic data of increased hematologic cancer risk in the population exposed accidentally to the substance.