Interleukin-8 binds to syndecan-2 on human endothelial cells.

Application of reverse transcription-PCR to total RNA prepared from TNF-alpha (tumour necrosis factor-alpha)-stimulated HUVECs (human umbilical vein endothelial cells) revealed that the syndecan-2 mRNA was up-regulated by this inflammatory stimulus. By immunoprecipitation using an anti-syndecan-2 antibody on TNF-alpha-stimulated HUVEC lysates, inflammation-induced interleukin-8 was found to be an interaction partner of this HS (heparan sulphate) proteoglycan, but not of any other syndecan on these cells. The glycosylated [Syn2(ect)(+HS)] and non-glycosylated [Syn2(ect)(-HS)] forms of Syn2(ect) (the syndecan-2 ectodomain) were purified from a stably transfected human cell line and from a bacterial expression system respectively. By CD spectroscopy, Syn2(ect) was found to adopt an all-beta secondary structure. The dissociation constant of Syn2(ect)(+HS) with respect to interleukin-8 binding was determined by isothermal fluorescence titrations to be 23 nM. Despite its lack of HS chains, Syn2(ect)(-HS) exhibited significant binding to the chemokine, with a K (d) of >1 microM. Thus, in addition to glycosaminoglycan binding, protein-protein contacts might also contribute to the chemokine-proteoglycan interaction.