Enhanced Binding of Polypolymerase-1 and Ku80/70 to the ITGA2 Promoter via an Extended Cytosine-Adenosine Repeat

Background We have identified a cytosine-adenosine (CA) repeat length polymorphism in the 5'-regulatory region of the human integrin [alpha]2 gene ITGA2 that begins at -605. Our objective was to establish the contribution of this polymorphism to the regulation of integrin [alpha]2[beta]1 expression, which is known to vary several-fold among normal individuals, and to investigate the underlying mechanism(s). Methodology/Principal Findings In combination with the SNP C-52T, previously identified by us as a binding site for the transcription factor Sp1, four ITGA2 haplotypes can be distinguished, in the order in which they enhance ITGA2 transcription: (CA).sub.12 /-52C>(CA).sub.11 /-52C>(CA).sub.11 /-52T>(CA).sub.10 /-52T. By DNA affinity chromatography and chromatin immunoprecipitation (ChIP) assays, we show that poly (ADP-ribose)polymerase-1 (PARP-1) and Ku80/70 bind specifically and with enhanced affinity to the longer (CA).sub.12 repeat alleles. Conclusions/Significance The increased binding of PARP-1 and Ku80/70, known components of transcription co-activator complexes, to the longer (CA).sub.12 alleles of ITGA2 coincides with enhanced [alpha]2[beta]1 expression. The most likely explanation for these findings is that PARP-1 and Ku80/70 contribute to the transcriptional regulation of ITGA2. These observations provide new insight into the mechanisms(s) underlying haplotype-dependent variability in integrin [alpha]2[beta]1 expression in human platelets and other cells.