α1-Adrenergic Receptor Stimulates Interleukin-6 Expression and Secretion through Both mRNA Stability and Transcriptional Regulation: Involvement of p38 Mitogen-Activated Protein Kinase and Nuclear Factor-κB

Abstract

Our previous studies have demonstrated that activation of alpha(1)-adrenergic receptors (ARs) increased interleukin-6 (IL-6) mRNA expression and protein secretion, which is probably an important yet unknown mechanism contributing to the regulation of cardiac function. Using Rat-1 fibroblasts stably transfected with the alpha(1A)-AR subtype and primary mouse neonatal cardiomyocytes, we elucidated the basic molecular mechanisms responsible for the alpha(1)-AR modulation of IL-6 expression. IL-6 mRNA production mediated by alpha(1)-AR peaked at 1 to 2 h. Studies of the mRNA decay rate indicated that alpha(1)-AR activation enhanced IL-6 mRNA stability. Analysis of IL-6 promoter activity using a series of deletion constructs indicated that alpha(1)-ARs enhanced IL-6 transcription through several transcriptional elements, including nuclear factor kappaB (NF-kappaB). Inhibition of alpha(1)-AR mediated IL-6 production and secretion by actinomycin D and the increase of intracellular IL-6 levels by alpha(1)-AR activation suggest that alpha(1)-AR mediated IL-6 secretion through de novo synthesis. Both IL-6 transcription and protein secretion mediated by alpha(1)-ARs were significantly reduced by chemical inhibitors for p38 mitogen-activated protein kinase (MAPK) and NF-kappaB and by a dominant-negative construct of p38 MAPK. Serum level of IL-6 was elevated in transgenic mice expressing a constitutively active mutant of the alpha(1A)-AR subtype but not in a similar mouse model expressing the alpha(1B)-AR subtype. Our results indicate that alpha(1)-ARs stimulated IL-6 expression and secretion through regulating both mRNA transcription and stability, involving p38 MAPK and NF-kappaB pathways.