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Transforming growth factor β1 (TGFβ1) controls proliferation, differentiation, and other cellular processes in a number of cell types. Not surprisingly, pathological deregulation of the TGFβ pathway has been implicated in the development of several major disease groups, including cancers. In keeping with this paradigm, we proposed that sequence variation in the promoter region of TGFβ1 could potentially lead to abnormal expression and variation in gene dosage, thereby predisposing carriers of such susceptibility variants to disease. Here we screened the proximal promoter region of TGFβ1 for single nucleotide polymorphisms (pSNPs) and performed in silico analysis and in vitro functional assays in conjunction with genetic association studies, in order to assess the functional impact of regulatory polymorphisms in TGFβ1 on the development of leukemia in children. Using denaturing high performance liquid chromatography we identified 4 pSNPs that were common in Europeans and that all lead to either a predicted gain and/or loss of putative transcription factor binding sites. When tested for differential binding by electrophoretic mobility shift assays, two of these pSNPs, -1886A>G and -1550DelAGG, showed differential allelic DNA-protein binding in at least one of the cell lines tested. From these common pSNPs we were able to construct 8 promoter haplotypes and following subcloning into a gene reporter system, we demonstrated that the two major promoter haplotypes significantly influenced transcriptional activity in an allele-specific manner. Moreover, a case-control study conducted in 258 acute lymphoblastic leukemia (ALL) patients and 277 healthy controls combined with a family-based analysis using 147 parental trios, all of European descent, was used to evaluate single site genotypic as well as multilocus haplotypic associations. Interestingly, the family-based association test revealed that the TGFβ1 low-expressing promoter haplotype was associated with an increased risk of ALL and was shown to be significantly over-transmitted to affected offspring (P= 0.032). Although the biological significance of these observations remains to be elucidated, these findings suggest that the expected variability of TGFβ1 expression levels due to regulatory polymorphisms could indeed influence the risk of childhood leukemia and contribute to carcinogenesis.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA