Differential expression of SMAD3 transcripts is not regulated by cis-acting genetic elements but has a gender specificity

As a key component of the transforming growth factor-beta (TGF-beta) pathway, SMAD3 plays an essential role in development and maintenance of self-tolerance. Furthermore, a recent study based on gene-expression profiling in donors of allogeneic hematopoietic cell grafts revealed that the level of expression of several components of the TGF-beta pathway can predict the occurrence of graft-versus-host disease (GVHD) in recipients. The gene with the best GVHD predictive accuracy was SMAD3: no recipients suffered from GVHD when their donor cells expressed high levels of SMAD3 transcripts. The present study had two specific aims: to validate differential expression of SMAD3 transcripts in an independent and larger cohort of subjects and to determine whether interindividual differences were dictated by cis-acting genetic elements. In a cohort of 397 subjects, we found that SMAD3 transcript levels varied over a sixfold range. Analyses of SMAD3 single nucleotide polymorphisms and of SMAD3 promoter methylation patterns provide compelling evidence that interindividual differences in SMAD3 transcript levels do not result from in-cis genetic variations. Of note, part of the variance in SMAD3 expression was gender related as women expressed lower levels of SMAD3 transcripts than men.