Measurement of skin surface biomakers by Transdermal Analyses Patch following different in vivo models of irritation: a pilot study.

BACKGROUND/PURPOSE: FibroTx Transdermal Analyses Patch (TAP) is a novel technology for non-invasive measurements of protein biomarkers on the skin surface, in vivo. The aim of this study was to explore the potential of TAP in detecting skin surface biomarkers following mild perturbations, in vivo, using two experimental models: tape stripping, mimicking acute barrier disruption, and histamine iontophoresis, mimicking acute and local inflammation at minimal skin barrier insult. METHODS: Tape stripping and histamine iontophoresis were performed in two separate experiments on the volar forearm of healthy volunteers (n = 27 and n = 10, respectively). Biomarker levels were assessed with TAP at baseline and up to 72 h after stimulation. Functional (transepidermal water loss -TEWL- and a* value) and morphological (confocal reflectance microscopy -RCM) assessments were added in the tape stripping and histamine iontophoresis experiments, respectively. RESULTS: Cytokines IL-1α and IL-1RA and the antimicrobial peptide hBD-1 showed distinct dynamics, despite substantial inter-individual variation in levels, with an increase following tape stripping and a decrease following histamine iontophoresis. These dynamics could be related to the assessments made by TEWL and RCM. In the tape stripping experiment, additional biomarkers could be detected. CONCLUSION: TAP measurements, especially IL-1α, IL-1RA, and hBD-1, from the skin surface were sensitive enough for monitoring dynamic changes in the skin in the two models of skin perturbation. We conclude that TAP holds promise for non-invasively unraveling the dynamics of processes related to skin perturbation and repair.

Cross-presentation of glycoprotein 96-associated antigens on major histocompatibility complex class I molecules requires receptor-mediated endocytosis.

Heat shock proteins (HSPs) like glycoprotein (gp)96 (glucose-regulated protein 94 [grp94]) are able to induce specific cytotoxic T lymphocyte (CTL) responses against cells from which they originate. Here, we demonstrate that for CTL activation by gp96-chaperoned peptides, specific receptor-mediated uptake of gp96 by antigen-presenting cells (APCs) is required. Moreover, we show that in both humans and mice, only professional APCs like dendritic cells (DCs), macrophages, and B cells, but not T cells, are able to bind gp96. The binding is saturable and can be inhibited using unlabeled gp96 molecules. Receptor binding by APCs leads to a rapid internalization of gp96, which colocalizes with endocytosed major histocompatibility complex (MHC) class I and class II molecules in endosomal compartments. Incubation of gp96 molecules isolated from cells expressing an adenovirus type 5 E1B epitope with the DC line D1 results in the activation of E1B-specific CTLs. This CTL activation can be specifically inhibited by the addition of irrelevant gp96 molecules not associated with E1B peptides. Our results demonstrate that only receptor-mediated endocytosis of gp96 molecules leads to MHC class I-restricted re-presentation of gp96-associated peptides and CTL activation; non-receptor-mediated, nonspecific endocytosis is not able to do so. Thus, we provide evidence on the mechanisms by which gp96 is participating in the cross-presentation of antigens from cellular origin.

TAP-translocated peptides specifically bind proteins in the endoplasmic reticulum, including gp96, protein disulfide isomerase and calreticulin.

The endoplasmic reticulum (ER) membrane-embedded transporter associated with antigen processing (TAP) associates with peptides in the cytosol and translocates these into the ER lumen. Here, MHC class I molecules bind a subset of these peptides and the remainder is either removed or degraded, or may be retained in the ER in association with other proteins. We have visualized peptide-binding proteins in the ER using radioactive peptides with a photoreactive group. Besides TAP, two proteins were identified as gp96 and protein disulfide isomerase (PDI). Calreticulin, previously found in complex with TAP, only binds glycosylated peptides. In addition, two as yet unidentified, ER luminal glycoproteins (gp120 and gp170) were visualized. The effects of peptide size and sequence on binding to the ER-resident proteins were studied by using partially degenerated peptides with photoreactive side chains. All identified proteins were able to bind peptides within the size range of peptides translocated by TAP, from 8 to more than 20 amino acids. Whereas PDI associated with all peptides tested, gp96 and gp120 showed a clear sequence preference for non-charged amino acids at positions 2 and 9 in 9mer peptides. Thus various ER proteins, other than the MHC class I heterodimer and TAP, are able to interact with peptides albeit with a different substrate selectivity.

Identification of novel peptide binding proteins in the endoplasmic reticulum: ERp72, calnexin, and grp170.

Transient interactions between molecular chaperones and nascent polypeptide chains assist protein folding in the endoplasmic reticulum. In an experimental setting that resembles the ER, we have used peptides as model substrates to identify and compare substrate specificities of ER-resident chaperones. The ER-located peptide transporter TAP was used to introduce peptides into the lumen of microsomes. In addition to PDI and gp96, previously identified as peptide-binding chaperones in the ER, we show that ERp72, calnexin, and grp170 interact with TAP-translocated peptides. The chaperones that have been identified can all bind peptide substrates that range from 8 to 40 amino acids in a manner independent of ATP. In addition, these chaperones exhibit broad and largely overlapping, however not identical, substrate selectivities. Our data indicate that peptide translocation into microsomes via TAP can be used as a method to monitor substrate selectivities of ER-resident chaperones. The implications of the observed preferences for chaperone-substrate interactions and for chaperones applied as vehicles in peptide-based vaccination strategies will be discussed.

Membrane topology and dimerization of the two subunits of the transporter associated with antigen processing reveal a three-domain structure.

Presentation of peptides derived from cytosolic and nuclear proteins by MHC class I molecules requires their translocation across the membrane of the endoplasmic reticulum (ER) by a specialized ABC (ATP-binding cassette) transporter, TAP. To investigate the topology of the heterodimeric TAP complex, we constructed a set of C-terminal deletions for the TAP1 and TAP2 subunits. We identified eight and seven transmembrane (TM) segments for TAP1 and TAP2, respectively. TAP1 has both its N and C terminus in the cytoplasm, whereas TAP2 has its N terminus in the lumen of the ER. A putative TM pore consists of TM1-6 of TAP1 and, by analogy, TM1-5 of TAP2. Multiple ER-retention signals are present within this region, of which we positively identified TM1 of both TAP subunits. The N-terminal domain containing TM1-6 of TAP1 is sufficient for dimerization with TAP2. A second, independent dimerization domain, located between the putative pore and the nucleotide-binding cassette, lies within the cytoplasmic peptide-binding domains, which are anchored to the membrane via TM doublets 7/8 and 6/7 of TAP1 and TAP2, respectively. We present a model in which TAP is composed of three subdomains: a TM pore, a cytoplasmic peptide-binding pocket, and a nucleotide-binding domain.

Export of antigenic peptides from the endoplasmic reticulum intersects with retrograde protein translocation through the Sec61p channel.

Antigenic peptides are translocated by the TAP peptide transporter from the cytosol into the endoplasmic reticulum (ER) for loading onto MHC class I molecules. Peptides that fail to bind need to be removed from the ER. Here we provide evidence that peptide export utilizes the Sec61p translocon as demonstrated by blocking this channel with bacterial exotoxin. Peptide export interferes with the retrotranslocation of beta2-microglobulin from the ER to the cytosol, suggesting similar pathways for the disposal of proteins and oligopeptides. Peptide export requires ATP supply to the ER lumen but is independent of ATP hydrolysis.

The murine cytomegalovirus pp89 immunodominant H-2Ld epitope is generated and translocated into the endoplasmic reticulum as an 11-mer precursor peptide.

The 20S proteasome is involved in the processing of MHC class I-presented Ags. A number of epitopes is known to be generated as precursor peptides requiring trimming either before or after translocation into the endoplasmic reticulum (ER). In this study, we have followed the proteasomal processing and TAP-dependent ER translocation of the immunodominant epitope of the murine CMV immediate early protein pp89. For the first time, we experimentally linked peptide generation by the proteasome system and TAP-dependent ER translocation. Our experiments show that the proteasome generates both an N-terminally extended 11-mer precursor peptide as well as the correct H2-L(d) 9-mer epitope, a process that is accelerated in the presence of PA28. Our direct peptide translocation assays, however, demonstrate that only the 11-mer precursor peptide is transported into the ER by TAPs, whereas the epitope itself is not translocated. In consequence, our combined proteasome/TAP assays show that the 11-mer precursor is the immunorelevant peptide product that requires N-terminal trimming in the ER for MHC class I binding.