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](i)) on tumor necrosis factor (TNF)-alpha -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) E-2 forskolin, or dibutyryl cAMP inhibited TNF-alpha -induced RANTES secretion but increased TN F-alpha -induced IL-6 secretion. Moreover, stimulation with PGE(2) forskolin, or dibutyryl cAMP alone increased basal IL-6 secretion in a concentration-dependent manner. SE 207499, a specific phosphodiesterase type 4 inhibitor, augmented the inhibitory effects of PGE(2) and forskolin on TNF-alpha -induced RANTES, Collectively, these data demonstrate that increasing [cAMP](i) in HASM effectively increases IL-6 secretion but reduces RANTES secretion promoted by TNF-alpha. Reverse transcriptase/polymerase chain reaction and ribonuclease protection assays suggested that these opposite effects of increased [cAMP](i) on TNF-alpha -induced IL-6 and RANTES secretion may occur at the transcriptional level, Accordingly, we examined the effects of TNF-alpha and cAMP on the regulation of nuclear factor (NF)-kappaB, a transcription factor known to modulate cytokine synthesis in numerous cell types. Stimulation of HASM cells with TNF-alpha increased NF-kappaB DNA-binding activity. However, increased [cAMP], in HASM neither activated NF-kappaB nor altered TNF-alpha -induced NF-kappaB DNA-binding activity. These results were confirmed using a NF-kappaB-luciferase reporter assay. Together, our data suggest that TNF-alpha -induced IL-6 and RANTES secretion may be associated with NF-kappaB activation, and that inhibition of TNF-alpha -stimulated RANTES secretion and augmentation of IL-6 secretion by increased [cAMP](i) in HASM cells occurs via an NF-kappaB-independent mechanism.