Midkine and Pleiotrophin Have Bactericidal Properties

Abstract

Antibacterial peptides of the innate immune system combat pathogenic microbes, but often have additional roles in promoting inflammation and as growth factors during tissue repair. Midkine (MK) and pleiotrophin (PTN) are the only two members of a family of heparin-binding growth factors. They show restricted expression during embryogenesis and are up-regulated in neoplasia. In addition, MK shows constitutive and inflammation-dependent expression in some non-transformed tissues of the adult. In the present study, we show that both MK and PTN display strong antibacterial activity, present at physiological salt concentrations. Electron microscopy of bacteria and experiments using artificial lipid bilayers suggest that MK and PTN exert their antibacterial action via a membrane disruption mechanism. The predicted structure of PTN, employing the previously solved MK structure as a template, indicates that both molecules consist of two domains, each containing three antiparallel ␤-sheets. The antibacterial activity was mapped to the unordered C-terminal tails of both molecules and the last ␤-sheets of the N-terminals. Analysis of the highly conserved MK and PTN orthologues from the amphibian Xenopus laevis and the fish Danio rerio suggests that they also harbor antibacterial activity in the corresponding domains. In support of an evolutionary conserved function it was found that the more distant orthologue, insect Miple2 from Drosophila melanogaster, also displays strong antibacterial activity. Taken together, the findings suggest that MK and PTN, in addition to their earlier described activities, may have previously unrealized important roles as innate antibiotics.

The Drosophila Midkine/Pleiotrophin Homologues Miple1 and Miple2 Affect Adult Lifespan but Are Dispensable for Alk Signaling during Embryonic Gut Formation

“…This is suggested by recent studies reporting bactericidal [78] and fungicidal [79] activities of MDK and PTN in vitro, that are conserved for Miple2 in vitro [78]. Thus increased levels of Miple proteins would not necessarily be harmful for the fly, but may exert a positive effect.…”

Identification of Novel Predictor Classifiers for Inflammatory Bowel Disease by Gene Expression Profiling

“…The best predictor from our study was able to distinguish IBD from healthy subjects with 97% accuracy with only 5 probes (sensitivity and specificity of 100% and 86% respectively), 2 of them representing the gene PTN (pleiotrophin) which has already been described to be down-regulated in CD patients [20]. Pleiotrophin controls several processes such as angiogenesis or cell proliferation but it also exerts strong antibacterial activity [21], suggesting another innate immune mechanism deregulated in IBD. The same accounts for the glycoprotein olfactomedin 4 (OLFM4), up-regulated in both forms of IBD according to our data, that is secreted into mucus [22] and acts by inhibiting immune responses against Helicobacter pylori , hence contributing to the persistence of infection by a mechanism involving NOD1 and NOD2 [23].…”

Midkine Is Part of the Antibacterial Activity Released at the Surface of Differentiated Bronchial Epithelial Cells

“…3d, e). Thus, membrane-destabilizing properties of MK are likely of importance for the bactericidal activity [17]. …”

“…According to the manufacturer, the purity of MK was >98%, as determined by SDS-PAGE and HPLC analyses. Confirmation of the correct tertiary conformation and insertion of disulfide bonds was previously described [17,18,19]. The folded C-domain (amino acids 84-126) and C-terminal half domain (amino acids 82-143) of MK, synthesized as described, were generously supplied by Dr. Tatsuya Inui, Peptide Institute, Osaka, Japan [20,21].…”

“…More recently, vitamin A (retinol R 2 and its esters), the precursor of retinoic acid (RA), has been demonstrated to be crucial for, among other things, differentiation and maintaining the phenotypic characteristics of the ciliated columnar epithelium of the bronchi, mucus production and the production of surfactant proteins [15]. Recently, we showed that midkine (MK) and pleiotrophin, the two members of a family of heparin-binding growth factors with RA-responsive elements in their promoter region, have strong antibacterial activity in vitro [16,17]. The present study was set out to investigate whether MK is produced by airway epithelial cells in vivo and in vitro and whether it may play a role as a host defense molecule in this context.…”