Heritable, Allele-Specific Chromosomal Looping between Tandem Promoters Specifies Promoter Usage of SHC1

One-half of the genes in the human genome contain alternative promoters, some of which generate products with opposing functions. Aberrant silencing or activation of such alternative promoters is associated with multiple diseases, including cancer, but little is known regarding the molecular mechanisms that control alternative promoter choice. TheSHC1 gene encodes p46Shc /p52Shc and p66Shc , proteins oppositely regulating anchorage-independent growth that are produced by transcription initiated from the upstream and downstream tandem promoters ofSHC1 , respectively. Here we demonstrate that activation of these promoters is mutually exclusive on separate alleles in single primary endothelial cells in a heritable fashion, ensuring expression of both transcripts by the cell. Peripheral blood lymphocytes that do not transcribe p66Shc transcribed p52Shc biallelically. This distinct monoallelic transcription pattern is established by allele-specific chromosomal looping between tandem promoters, which silences the upstream promoter. Our results reveal a new mechanism to control alternative promoter usage through higher-order chromatin structure.