α-Melanocyte-related tripeptide, Lys-D-Pro-Val, ameliorates endotoxin-induced nuclear factor κB translocation and activation:: evidence for involvement of an interleukin-1β193-195 receptor antagonism in the alveolar epithelium

The potential anti-inflammatory role of alpha -melanocyte-stimulating hormone (alpha -MSH)-related tripeptide, lysine(11)-D-proline-valine(13) (KDPV), an analogue of interleukin (IL)-1 beta (193-195) and an antagonist of IL-1 beta /prostaglandin E-2, is not well characterized in the alveolar epithelium. In a model of foetal alveolar type II epithelial cells in vitro, we showed that lipopolysaccharide endotoxin (LPS) differentially, but selectively, induced the nuclear subunit composition of nuclear factor kappaB(1) (NF-kappaB(1)) (p50), RelA (p65) and c-Rel (p75), in parallel to up-regulating the DNA-binding activity (supershift indicating the presence of the p50-p65 complex), LPS accelerated the degradation of inhibitory kappaB-alpha (I kappaB-alpha), accompanied by enhancing its phosphorylation in the cytosolic compartment but not in the nucleus. KDPV suppressed, in a dose-dependent manner, the nuclear localization of p50, p65 and p75, an effect that led to the subsequent inhibition of NF-kappaB activation. Interleukin-1 receptor antagonist (IL-1ra) decreased the nuclear abundance of p50, p65 and p75, and subsequently depressed the DNA-binding activity induced by LPS. Analysis of the mechanism involved in the KDPV- and IL-1ra-mediated inhibition of NF-kappaB nuclear localization revealed a reversal in I kappaB-alpha phosphorylation and degradation, followed by cytosolic accumulation. LPS induced endogenous IL-1 beta biosynthesis in a time-dependent manner; the administration of exogenous recombinant human interleukin 1 (rhIL-1) resulted in a dose-dependent activation of NF-kappaB. KDPV and IL-1ra abrogated the effect of rhIL-1. Pretreatment with the non-steroidal anti-inflammatory drug (NSAID) indomethacin, an inhibitor of cyclo-oxygenase, blocked the LPS-induced activation of NF-kappaB, These results indicate the involvement of prostanoid-dependent (NSAID-sensitive) and IL-1-dependent (IL-1ra-sensitive) mechanisms mediating LPS-induced NF-kappaB translocation and activation, a pathway that is regulated, in part, by a negative feedback mechanism transduced through I kappaB-alpha, the major cytosolic inhibitor of NF-kappaB.