Allelic diversity in the TGFB1 regulatory region: characterization of novel functional single nucleotide polymorphisms

Abstract

Altered TGF-beta1 expression due to polymorphisms affects a wide variety of normal cellular and disease processes such as T cell activation and proliferation, tumor progression, and asthma. In this study, a comprehensive examination of function and diversity was undertaken for the TGFB1 promoter region and exon 1 (-2,665 to +423). The known TGF-beta1 promoter was extended to encompass 463 bases by the identification of a strong enhancer activity for a distal segment (-2,665 to -2,204). Ten novel polymorphisms and 14 novel alleles were identified. Most single nucleotide polymorphisms (SNPs) appear to be randomly associated except c.-768_-769insC and c.+74G > C and a set of five novel polymorphisms present in a single allele in persons of African descent. The TGFB1 alleles clustered into three phylogenetic groups based on the common functional SNPs c.-1347C > T (commonly known as -509C-T) and c.+29T > C (commonly known as +869T-C) suggesting three phenotypic groups. Two SNPs unique to African-Americans affect the TGFB1 regulatory region. The c.-1287G > A SNP in the promoter alters the binding affinity of two unidentified transcription factor complexes which translates into a significant difference in reporter gene expression and the c.-387C > T SNP in the 5' UTR alters the binding of Stimulating protein 1 and 3. Thus, TGFB1 possesses a highly polymorphic, extensive regulatory region that likely impacts the pathogenesis of numerous TGF-beta1 related diseases.