OBJECTIVE: A key event in the pathways leading to preterm labor may be the activation of nuclear factor-kappaB (NF-kappaB) in the fetal membranes and the cervix. Anti-inflammatory agents, such as the corticosteroids, inhibit the activation of NF-kappaB. We proposed to investigate the effects of progesterone pretreatment on cytokine-stimulated activation of NF-kappaB in HeLa cells, a human cervical epithelial cell line. METHODS: HeLa cells were pretreated with 10(-7) M progesterone for 24 hours and exposed to 1 ng/mL interleukin-1beta (IL-1beta) for 1 hour. Nuclear and cytosolic extracts were subjected to Western blot analysis using anti-p65 and anti-inhibitory protein-kappaBalpha (anti-IkappaBalpha) antibodies. Densitometric data (n=5) were compared using Kruskal-Wallis test. RESULTS: Pretreatment with progesterone interfered with IL-1beta-induced IkappaBalpha degradation. However, progesterone pretreatment resulted in a significant decrease in NF-kappaB protein subunit p65 in the cytoplasm. Pretreatment with progesterone did not reduce the amount of nuclear p65 and did not interfere with nuclear translocation of p65. CONCLUSION: Our observations suggest that any possible role played by progesterone in preterm labor prevention is not exerted through anti-inflammatory mechanisms of NF-kappaB down-regulation.