16K prolactin induces NF-κB activation in pulmonary fibroblasts

The amino-terminal 16 kDa fragment of prolactin (16K PRL) promotes the expression of the inducible isoform of nitric oxide synthase (iNOS) accompanied by the production of nitric oxide (NO) by rat pulmonary fibroblasts. The present study was designed to elucidate whether the mechanism by which 16K PRL promotes iNOS expression involves the activation of nuclear factor-kappa B (NF-κB), a key transcription factor for iNOS induction. 16K PRL stimulated DNA-binding activity of NF-κB in pulmonary fibroblasts as demonstrated by gel shift assays. Likewise, fluorescence immunocytochemistry showed that 16K PRL promotes nuclear translocation of the p65 subunit of NF-κB. Finally, treatment with 16K PRL induced the degradation of the NF-κB inhibitor κB-beta (IκB-β), and such degradation was prevented by blocking IκB-β phosphorylation. Altogether, these results show that 16K PRL activates NF-κB nuclear translocation via the phosphorylation and degradation of IκB-β. These findings are consistent with NF-κB being part of the signal transduction pathway activated by 16K PRL to induce iNOS expression.