Plunc

Abstract: The upper respiratory tract, including the nasal and oral cavities, is the major route of entry of pathogens into the body, and early recognition of bacterial products in this region is critical for host defence. A well-established family of four proteins involved in this process are bactericidal/permeability-increasing protein (BPI) and lipopolysaccharide-binding protein (LBP), which are central to the host defence against bacteria, and cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP), which have also been implicated in this response. In this paper, we demonstrate the existence of a related family of seven human proteins, which we designate PLUNC proteins. The PLUNC proteins are encoded by adjacent genes found within a 300 kb region of chromosome 20, suggesting that they may be under transcriptional control of shared genomic elements, and expression data shows that these proteins are found in overlapping regions of the pulmonary, nasopharyngeal and oral epithelium, sites where the previously described BPI family members are not expressed. Whereas the BPI family are predicted to share very closely similar three-dimensional structures, the PLUNC family is predicted to have much greater variability in the N-terminal domain, corresponding to the active domain of BPI, thus creating the notion of a BPI/PLUNC structural superfamily. We suggest that members of the PLUNC family may function in the innate immune response in regions of the mouth, nose and lungs, which are sites of significant bacterial exposure.

Abstract: There is now significant interest in identifying, quantifying and characterizing the human proteome, and new powerful techniques (proteomics) have evolved to deal with this giant task. In the present study, proteomics have been applied for the first time to map the proteins of the upper airways. The protein contents of human nasal fluid (NLF) and saliva were analysed using two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) and the proteins were identified by peptide mass fingerprinting using matrix assisted laser desorptioniionization time of night mass spectrometry (MALDI-TOF MS) or by amino acid sequencing using electrospray ionization tandem mass spectrometry (ESI- MS/MS). More than 100 proteins were identified and protein maps of nasal fluid and saliva were thus established. Of particular interest was the identification of a new lipopolysaccharide (LPS)-binding protein, PLUNC (palate lung and nasal epithelial clone), which was shown to be the only protein in NLF that binds to LPS. PLUNC was characterized as multiple isoforms (Mr/p1: 27/5.1, 26/5.2, 25/5.3, 27.5/5.1, 27/5.2, 26/5.3, 25.1/5.5 and 24.8/5.4), and several of these isoforms were demonstrated to be sialylated. Notably, decreased levels of PLUNC were found in NLF of (i) smokers, (ii) epoxy workers with airway irritation, and (iii) patients with seasonal allergic rhinitis (SAR) during allergy season. In addition, the levels of von Ebner's gland protein, α1-antitrypsin, cystatin S, Clara cell protein 16 and lipocortin-1 were altered, either in smokers or SAR patients or both. One previously unidentified NLF protein was found in SAR patients during allergy season but not before season: this protein was identified as eosinophil lysophospholipase. Many of these proteins were post-translationally modified by glycosylation (PLUNC, α1-antitrypsin, von Ebner's gland protein), phosphorylation (cystatin S), acetylation (eosinophil lysophospholipase), or truncation (lipocortin-1). Altogether, these findings illustrate the potential use of proteomics for identifying new markers of upper airway inflammation and for revealing structural details of such markers. The findings also indicate that allergic inflammation in the nasal mucosa is associated with decreased nasal fluid levels of the endogenous proteinase inhibitors, cystatin S and von Ebner's gland protein, and of the new irritation marker, PLUNC. Further studies are required to explore the possibility that PLUNC plays an important part in microbial recognition and that this function is impaired after exposure to airway irritants and during upper airway inflammation.

Abstract: Background The PLUNC (“Palate, lung, nasal epithelium clone”) protein is an abundant secretory product of epithelia present throughout the conducting airways of humans and other mammals, which is evolutionarily related to the lipid transfer/lipopolysaccharide binding protein (LT/LBP) family. Two members of this family - the bactericidal/permeability increasing protein (BPI) and the lipopolysaccharide binding protein (LBP) - are innate immune molecules with recognized roles in sensing and responding to Gram negative bacteria, leading many to propose that PLUNC may play a host defense role in the human airways.