Tumor necrosis factor-α-induced secretion of RANTES and interleukin-6 from human airway smooth-muscle cells modulation by cyclic adenosine monophosphate

Although 3′:5′ cyclic adenosine monophosphate (cAMP) is known to modulate cytokine production in a number of cell types, little information exists regarding cAMP-mediated effects on this synthetic function of human airway smooth-muscle (HASM) cells. We examined the effect of increasing intracellular cAMP concentration ([cAMP];) on tumor necrosis factor (TNF)-α-induced regulated on activation, normal T cells expressed and secreted (RANTES) and interleukin (IL)-6 secretion from cultured HASM cells. Pretreatment of HASM with prostaglandin (PG) E₂, forskolin, or dibutyryl cAMP inhibited TNF-α-induced RANTES secretion but increased TNF-α-induced IL-6 secretion. Moreover, stimulation with PGE₂, forskolin, or dibutyryl cAMP alone increased basal IL-6 secretion in a concentration-dependent manner. SB 207499, a specific phosphodiesterase type 4 inhibitor, augmented the inhibitory effects of PGE₂ and forskolin on TNF-α-induced RANTES. Collectively, these data demonstrate that increasing [cAMP]/in HASM effectively increases IL-6 secretion but reduces RANTES secretion promoted by TNF-α. Reverse transcriptase/polymerase chain reaction and ribonuclease protection assays suggested that these opposite effects of increased [cAMP]; on TNF-α-induced IL-6 and RANTES secretion may occur at the transcriptional level. Accordingly, we examined the effects of TNF-α and cAMP on the regulation of nuclear factor (NF)-κB, a transcription factor known to modulate cytokine synthesis in numerous cell types. Stimulation of HASM cells with TNF-α increased NF-κB DNA-binding activity. However, increased [cAMP], in HASM neither activated NF-κB nor altered TNF-α-induced NF-κB DNA-binding activity. These results were confirmed using a NF-κB-luciferase reporter assay. Together, our data suggest that TNF-α-induced IL-6 and RANTES secretion may be associated with NF-κB activation, and that inhibition of TNF-α-stimulated RANTES secretion and augmentation of IL-6 secretion by increased [cAMP], in HASM cells occurs via an NF-κB-independent mechanism.