Effect of DNA methylation and chromatin structure on ITGAL expression

LFA-1 (CD11a/CD18, alphaLbeta2) is an integrin expressed in a tissue-specific fashion and is important in inflammatory and immune responses. Promoter analysis has identified transcription factors that may be involved in CD11a expression, but the mechanisms contributing to its tissue specific expression are incompletely characterized. In this report we have asked if DNA methylation and/or chromatin structure could contribute to tissue-specific CD11a expression. Bisulfite sequencing was used to compare methylation patterns in the promoter and 5' flanking regions of the ITGAL gene, encoding CD11a, in normal human T cells, which express LFA-1, and fibroblasts, which do not. The region was found to be heavily methylated in fibroblasts but not T cells, and methylation correlated with an inactive chromatin configuration as analyzed by deoxyribonuclease 1 sensitivity. Patch methylation of the promoter region revealed that promoter activity was methylation-sensitive but that methylation of the 5' flanking regions more than 500 base pairs 5' to the transcription start site could also suppress promoter function. Treating fibroblasts with a DNA methylation inhibitor decreased ITGAL promoter methylation and increased CD11a messenger RNA. The results thus indicate that methylation and chromatin structure may contribute to the tissue-specific expression of CD11a.