HLA class I is most tightly linked to levels of tapasin compared with other antigen-processing proteins in glioblastoma

Background:

Tumour cells can evade the immune system by dysregulation of human leukocyte antigens (HLA-I). Low quantity and/or altered quality of HLA-I cell surface expression is the result of either HLA-I alterations or dysregulations of proteins of the antigen-processing machinery (APM). Tapasin is an APM protein dedicated to the maturation of HLA-I and dysregulation of tapasin has been linked to higher malignancy in several different tumours.

Methods:

We studied the expression of APM components and HLA-I, as well as HLA-I tapasin-dependency profiles in glioblastoma tissues and corresponding cell lines.

Results:

Tapasin displayed the strongest correlation to HLA-I heavy chain but also clustered with β₂-microglobulin, transporter associated with antigen processing (TAP) and LMP. Moreover, tapasin also correlated to survival of glioblastoma patients. Some APM components, for example, TAP1/TAP2 and LMP2/LMP7, showed variable but coordinated expression, whereas ERAP1/ERAP2 displayed an imbalanced expression pattern. Furthermore, analysis of HLA-I profiles revealed variable tapasin dependence of HLA-I allomorphs in glioblastoma patients.

Conclusions:

Expression of APM proteins is highly variable between glioblastomas. Tapasin stands out as the APM component strongest correlated to HLA-I expression and we proved that HLA-I profiles in glioblastoma patients include tapasin-dependent allomorphs. The level of tapasin was also correlated with patient survival time. Our results support the need for individualisation of immunotherapy protocols.

Tapasin and human leukocyte antigen class I dysregulation correlates with survival in glioblastoma multiforme

Human leukocyte antigen class I (HLA-I) molecules present antigenic peptides to cytotoxic CD8(+) T cells. Downregulation of peptide:HLA-I complexes is common in tumors and results in tumor immune escape variants. Also molecules involved in the maturation of HLA-I have been demonstrated to be dysregulated in malignant neoplasms. We here set out to investigate the antigen presentation capabilities of a set of 12 glioblastoma multiforme (GBM) tumors based on the expression of HLA-I. Moreover, we analyzed the expression of tapasin, a protein dedicated and essential to HLA-I maturation, as well as the infiltration of CD8+ cells using immunohistochemistry on paraffin-embedded sections. Comparison of different GBMs showed a variation in expression of both HLA-I heavy chain (HC) and tapasin. Interestingly, the expression of tapasin and HLA-I HC correlated significantly (p=0.0002) suggesting tapasin to be a key factor for efficient HLA-I antigen presentation in GBMs. Although no statistically significant correlation between CD8(+) cells and survival was found, probably due to a very low number of infiltrating CD8(+) cells at the time of surgical resection, both tapasin and HLA-I HC levels significantly correlated with survival. We suggest that analysis of expression of tapasin and/or HLA-I may be of value as prognostic tool for GBM patients, especially when considering immunotherapy.

Tapasin facilitation of natural HLA-A and -B allomorphs is strongly influenced by peptide length, depends on stability, and separates closely related allomorphs

Despite an abundance of peptides inside a cell, only a small fraction is ultimately presented by HLA-I on the cell surface. The presented peptides have HLA-I allomorph-specific motifs and are restricted in length. So far, detailed length studies have been limited to few allomorphs. Peptide-HLA-I (pHLA-I) complexes of different allomorphs are qualitatively and quantitatively influenced by tapasin to different degrees, but again, its effect has only been investigated for a small number of HLA-I allomorphs. Although both peptide length and tapasin dependence are known to be important for HLA-I peptide presentation, the relationship between them has never been studied. In this study, we used random peptide libraries from 7- to 13-mers and studied binding in the presence and absence of a recombinant truncated form of tapasin. The data show that HLA-I allomorphs are differentially affected by tapasin, different lengths of peptides generated different amounts of pHLA-I complexes, and HLA-A allomorphs are generally less restricted than HLA-B allomorphs to peptides of the classical length of 8-10 aa. We also demonstrate that tapasin facilitation varies for different peptide lengths, and that the correlation between high degree of tapasin facilitation and low stability is valid for different random peptide mixes of specific lengths. In conclusion, these data show that tapasin has specificity for the combination of peptide length and HLA-I allomorph, and suggest that tapasin promotes formation of pHLA-I complexes with high on and off rates, an important intermediary step in the HLA-I maturation process.

Tapasin discriminates peptide-human leukocyte antigen-A*02:01 complexes formed with natural ligands

A plethora of peptides are generated intracellularly, and most peptide-human leukocyte antigen (HLA)-I interactions are of a transient, unproductive nature. Without a quality control mechanism, the HLA-I system would be stressed by futile attempts to present peptides not sufficient for the stable peptide-HLA-I complex formation required for long term presentation. Tapasin is thought to be central to this essential quality control, but the underlying mechanisms remain unknown. Here, we report that the N-terminal region of tapasin, Tpn(1-87), assisted folding of peptide-HLA-A*02:01 complexes according to the identity of the peptide. The facilitation was also specific for the identity of the HLA-I heavy chain, where it correlated to established tapasin dependence hierarchies. Two large sets of HLA-A*02:01 binding peptides, one extracted from natural HLA-I ligands from the SYFPEITHI database and one consisting of medium to high affinity non-SYFPEITHI ligands, were studied in the context of HLA-A*02:01 binding and stability. We show that the SYFPEITHI peptides induced more stable HLA-A*02:01 molecules than the other ligands, although affinities were similar. Remarkably, Tpn(1-87) could functionally discriminate the selected SYFPEITHI peptides from the other peptide binders with high sensitivity and specificity. We suggest that this HLA-I- and peptide-specific function, together with the functions exerted by the more C-terminal parts of tapasin, are major features of tapasin-mediated HLA-I quality control. These findings are important for understanding the biogenesis of HLA-I molecules, the selection of presented T-cell epitopes, and the identification of immunogenic targets in both basic research and vaccine design.

Expression of matrix metalloprotease-2, -7 and -9 on human colon, liver and bile duct cell lines by enteric and gastricHelicobacterspecies

Gastric and enteric Helicobacter species have been associated with malignant and inflammatory diseases of the stomach, liver, gall bladder and intestine. Matrix metalloproteinases (MMPs) participate in degradation of extracellular matrix, which allows bacteria to come in contact with and interact with the cells. Enhanced level of MMPs facilitates metastasis and cell invasion of tumor cells by removal of physical barriers, as well as modulation of biologic activities of the proteins residing in the extracellular matrix. The aim of this study was to evaluate the effect of gastric and enteric Helicobacter on induction of MMPs in hepatocytes and epithelial cells of gall bladder and colon. Human hepatocytes HepG2, gall bladder epithelial cells TFK-1, and colon epithelial cells HT29 were infected with strains of H. pylori cagA+, cagE+, H. pylori cagA-, cagE-, H. pullorum, H. cholecystus, H. bilis and H. hepaticus. Protein levels of MMPs were analyzed by enzyme-linked immunosorbent assay and immunohistochemistry. Reverse transcription-quantitative polymerase chain reaction was used to study mRNA levels. Increased expression of MMP-2 and MMP-9 was observed on HepG2, TFK-1 and HT29 infected with H. pylori cagA+, cagE+ and H. cholecystus strains. H. pylori cagA+, cagE+, H. cholecystus, H. pullorum, H. bilis and H. hepaticus strains increased expression of MMP-7 on HT29, compared to uninfected control cells. The effect of MMP upregulation on HepG2, TFK-1 and HT29 was bacterial dose dependent. H. pylori cagA-, cagE- strain did not increase expression of MMPs. Inducible MMPs on colon and bile duct epithelial cells as well as hepatocytes may play an important role in facilitating invasion and progression of cancer by Helicobacter species colonizing the hepatobiliary and gastrointestinal tract.