The effect of CAG repeat length polymorphism in the murine glucocorticoid receptor on transactivation potential

Abstract

Severe sepsis remains an important cause of death, particularly among trauma and burn patients. The severity of the systemic inflammatory response after trauma or burns and susceptibility to sepsis vary among individuals. One possible mechanism is through differential effects on glucocorticoid receptor (GR) expression by pro-inflammatory mediators (e.g. lipopolysaccharide signaling). In a mouse burn model, we demonstrated differential GR levels, size, and transcriptional activity in CD14 knockout (KO) mice when compared to wild-type (C57BL/6J) after injury. Sequence analysis revealed only 8 CAG repeats in the GR transactivation domain in the CD14 KO; the wild-type contained seventeen. A survey of genomic DNA from 51 mouse strains demonstrated CAG repeat length range from 7 - 17. We then studied the effect of polymorphism in CAG repeat length on GR activity. Fragments with CAG repeats varying from 8-40 (8, 17, 30, 38, and 40) were engineered and shuttled into the wild-type GR expression vector. The resulting plasmids were then co-transfected with a glucocorticoid response element linked to a luciferase in order to compare their transactivation potentials. Transactivation potential was highest in the 17-CAG GR. The effect of GR polymorphisms on GR activity warrants more research as this data suggests a mechanism for the individual differences in response to steroid treatment and the response to injury.