Regulation of CD40 Ligand Gene Expression: Implications in Asthma
Type of Culminating Activity
Master of Science in Biology
CD40 ligand (CD40L) is an important immunoregulatory protein expressed predominantly on activated CD4+ T cell. Our previous studies have shown that CD40L expression is increased in asthmatics following treatment with β-adrenergic agonists, a class of medications that largely exerts its actions by increasing intracellular cAMP levels and, importantly, is associated with asthma related deaths. The actions of β-agonists to increase CD40L may be of clinical interest and account for the molecular mechanisms underlying the adverse effects of this class of medications. In addition to the cAMP pathway, CD40L is also regulated by changes in intracellular calcium. In this study, we examined how the calcium and cAMP signaling pathways interact to coordinately regulate CD40L gene expression. Using a reporter assay where the proximal CD40L promoter (494 bp) was linked to a green fluorescent protein (GFP) reporter, we demonstrated that this promoter region was sufficient to drive GFP expression in a calcium and cyclic AMP dependent manner. We also demonstrated, that the first 200 base pairs of the promoter contain critical calcium and cAMP responsive elements. Furthermore, site-directed mutagenesis experiments showed that transcription factor NFAT plays a significant role in the calcium dependent regulation of CD40L. Additional experiments showed that the transcription factors CREB and MEF-2 contribute to CD40L gene expression while the GATA-3 binding site at nucleotide position -146 is not involved. Given the dysregulated expression of CD40L in asthma, a better understanding of its molecular regulation may help elucidate the mechanisms of asthma pathogenesis as well as the molecular basis for adverse drug response to long acting β- adrenergic agonists.
Hodzic, Alma, "Regulation of CD40 Ligand Gene Expression: Implications in Asthma" (2007). Boise State University Theses and Dissertations. 1181.