Expression analysis of the human adducin gene family and evidence of ADD2 β 4 multiple splicing variants

Adducin is a cytoskeleton heterodimeric protein. Its subunits are encoded by three related genes (ADD1, ADD2, and ADD3) which show alternative spliced variants. Adducin polymorphisms are involved in blood pressure regulation in humans and rats. We have analyzed mRNA distribution of ADD gene family in human tissues and cells with Real-Time TaqMan RT-PCR. Whereas ADD1 is ubiquitously distributed, ADD3 is more expressed in kidney medulla and cortex than in fetal kidney, while in adult liver it is less abundant than in fetal liver. ADD2 β1 and β4 variants show the same pattern of distribution with the highest expression in brain, fetal liver, and kidney. Conventional RT-PCR identified new β4 variants. β4a is characterized by an in-frame insertion of 21 nucleotides upstream exon 15 predicting a 7 amino acids longer protein with a similar C-terminus region. It is coexpressed with β1 and β4 in several tissues. Fetal kidney shows further β4b, β4c and β4d variants containing internal exon deletions that enormously modify the predicted NH₂ and central regions. Our findings could help one to understand the functional role of adducin variants in specific tissues and cells.