Diagnostic and prognostic impact of serum-soluble UL16-binding protein 2 in lung cancer patients

A potential mechanism of tumor immune escape: Regulation and application of soluble natural killer group 2 member D ligands (Review)

The immune system is integral to the surveillance and eradication of tumor cells. Interactions between the natural killer group 2 member D (NKG2D) receptor and its ligands (NKG2DLs) are vital for activating NKG2D receptor‑positive immune cells, such as natural killer cells. This activation enables these cells to identify and destroy tumor cells presenting with NKG2DLs, which is an essential aspect of tumor immunity. However, tumor immune escape is facilitated by soluble NKG2DL (sNKG2DL) shed from the surface of tumor cells. The production of sNKG2DL is predominantly regulated by metalloproteinases [a disintegrin and metalloproteinases (ADAM) and matrix metalloproteinase (MMP) families] and exosomes. sNKG2DL not only diminish immune recognition on the tumor cell surface but also suppress the function of immune cells, such as NK cells, and reduce the expression of the NKG2D receptor. This process promotes immune evasion, progression, and metastasis of tumors. In this review, an in‑depth summary of the mechanisms and factors that influence sNKG2DL production and their contribution to immune suppression within the tumor microenvironment are provided. Furthermore, due to the significant link between sNKG2DLs and tumor progression and metastasis, they have great potential as novel biomarkers. Detectable via liquid biopsies, sNKG2DLs could assess tumor malignancy and prognosis, and act as pivotal targets for immunotherapy. This could lead to the discovery of new drugs or the enhancement of existing treatments. Thus, the application of sNKG2DLs in clinical oncology was explored, offering substantial theoretical support for the development of innovative immunotherapeutic strategies for sNKG2DLs.

Molecular and immune characterization of Chinese early-stage non-squamous non-small cell lung cancer: a multi-omics cohort study

Background

Albeit considered with superior survival, around 30% of the early-stage non-squamous non-small cell lung cancer (Ns-NSCLC) patients relapse within 5 years, suggesting unique biology. However, the biological characteristics of early-stage Ns-NSCLC, especially in the Chinese population, are still unclear.

Methods

Multi-omics interrogation of early-stage Ns-NSCLC (stage I-III), paired blood samples and normal lung tissues (n=76) by whole-exome sequencing (WES), RNA sequencing, and T-cell receptor (TCR) sequencing were conducted.

Results

An average of 128 exonic mutations were identified, and the most frequently mutant gene was EGFR (55%), followed by TP53 (37%) and TTN (26%). Mutations in MUC17, ABCA2, PDE4DIP, and MYO18B predicted significantly unfavorable disease-free survival (DFS). Moreover, cytobands amplifications in 8q24.3, 14q13.1, 14q11.2, and deletion in 3p21.1 were highlighted in recurrent cases. Higher incidence of human leukocyte antigen loss of heterozygosity (HLA-LOH), higher tumor mutational burden (TMB) and tumor neoantigen burden (TNB) were identified in ever-smokers than never-smokers. HLA-LOH also correlated with higher TMB, TNB, intratumoral heterogeneity (ITH), and whole chromosomal instability (wCIN) scores. Interestingly, higher ITH was an independent predictor of better DFS in early-stage Ns-NSCLC. Up-regulation of immune-related genes, including CRABP2, ULBP2, IL31RA, and IL1A, independently portended a dismal prognosis. Enhanced TCR diversity of peripheral blood mononuclear cells (PBMCs) predicted better prognosis, indicative of a noninvasive method for relapse surveillance. Eventually, seven machine-learning (ML) algorithms were employed to evaluate the predictive accuracy of clinical, genomic, transcriptomic, and TCR repertoire data on DFS, showing that clinical and RNA features combination in the random forest (RF) algorithm, with area under the curve (AUC) of 97.5% and 83.3% in the training and testing cohort, respectively, significantly outperformed other methods.

Conclusions

This study comprehensively profiled the genomic, transcriptomic, and TCR repertoire spectrums of Chinese early-stage Ns-NSCLC, shedding light on biological underpinnings and candidate biomarkers for prognosis development.

The Function of NK Cells in Tumor Metastasis and NK Cell-Based Immunotherapy

Metastatic tumors cause the most deaths in cancer patients. Treating metastasis remains the primary goal of current cancer research. Although the immune system prevents and kills the tumor cells, the function of the immune system in metastatic cancer has been unappreciated for decades because tumors are able to develop complex signaling pathways to suppress immune responses, leading them to escape detection and elimination. Studies showed NK cell-based therapies have many advantages and promise for fighting metastatic cancers. We here review the function of the immune system in tumor progression, specifically focusing on the ability of NK cells in antimetastasis, how metastatic tumors escape the NK cell attack, as well as the recent development of effective antimetastatic immunotherapies.

Immune-related pan-cancer gene expression signatures of patient survival revealed by NanoString-based analyses

The immune system plays a central role in the onset and progression of cancer. A better understanding of transcriptional changes in immune cell-related genes associated with cancer progression, and their significance in disease prognosis, is therefore needed. NanoString-based targeted gene expression profiling has advantages for deployment in a clinical setting over RNA-seq technologies. We analysed NanoString PanCancer Immune Profiling panel gene expression data encompassing 770 genes, and overall survival data, from multiple previous studies covering 10 different cancer types, including solid and blood malignancies, across 515 patients. This analysis revealed an immune gene signature comprising 39 genes that were upregulated in those patients with shorter overall survival; of these 39 genes, three (MAGEC2, SSX1 and ULBP2) were common to both solid and blood malignancies. Most of the genes identified have previously been reported as relevant in one or more cancer types. Using Cibersort, we investigated immune cell levels within individual cancer types and across groups of cancers, as well as in shorter and longer overall survival groups. Patients with shorter survival had a higher proportion of M2 macrophages and γδ T cells. Patients with longer overall survival had a higher proportion of CD8+ T cells, CD4+ T memory cells, NK cells and, unexpectedly, T regulatory cells. Using a transcriptomics platform with certain advantages for deployment in a clinical setting, our multi-cancer meta-analysis of immune gene expression and overall survival data has identified a specific transcriptional profile associated with poor overall survival.

8-Gene signature related to CD8+ T cell infiltration by integrating single-cell and bulk RNA-sequencing in head and neck squamous cell carcinoma

Background: CD8⁺ T cells, a critical component of the tumor immune microenvironment, have become a key target of cancer immunotherapy. Considering the deficiency of robust biomarkers for head and neck squamous cell carcinoma (HNSCC), this study aimed at establishing a molecular signature associated with CD8+T cells infiltration.

Methods: Single-cell RNA sequencing data retrieved from the Gene Expression Omnibus (GEO) database was analyzed to obtain the different cell types. Next, the cell proportions were investigated through deconvolution of RNA sequencing in the Cancer Genome Atlas (TCGA) database, and then the immune-related genes (IRGs) were identified by weighted gene co-expression network analysis (WGCNA). LASSO-Cox analysis was employed to establish a gene signature, followed by validation using a GEO dataset. Finally, the molecular and immunological properties, and drug responses between two subgroups were explored by applying “CIBERSORT”, “ESTIMATE”, and single sample gene set enrichment analysis (ssGSEA) methods.

Results: A total of 215 differentially expressed IRGs were identified, of which 45 were associated with the overall survival of HNSCC. A risk model was then established based on eight genes, including DEFB1, AICDA, TYK2, CCR7, SCARB1, ULBP2, STC2, and LGR5. The low-risk group presented higher infiltration of memory activated CD4⁺ T cells, CD8⁺ T cells, and plasma cells, as well as a higher immune score, suggesting that they could benefit more from immunotherapy. On the other hand, the high-risk group showed higher abundance of activated mast cells and M2 macrophages, as well as a lower immune score.

Conclusion: It was evident that the 8-gene signature could accurately predict HNSCC prognosis and thus it may serve as an index for clinical treatment.

Recruited and Tissue-Resident Natural Killer Cells in the Lung During Infection and Cancer

Natural killer (NK) cells are an important component of the innate immune system, and have a key role in host defense against infection and in tumor surveillance. Tumors and viruses employ remarkably similar strategies to avoid recognition and killing by NK cells and so much can be learnt by comparing NK cells in these disparate diseases. The lung is a unique tissue environment and immune cells in this organ, including NK cells, exist in a hypofunctional state to prevent activation against innocuous stimuli. Upon infection, rapid NK cell infiltration into the lung occurs, the amplitude of which is determined by the extent of inflammation and damage. Activated NK cells kill infected cells and produce pro-inflammatory cytokines and chemokines to recruit cells of the adaptive immune system. More recent evidence has shown that NK cells also play an additional role in resolution of inflammation. In lung cancer however, NK cell recruitment is impaired and those that are present have reduced functionality. The majority of lung NK cells are circulatory, however recently a small population of tissue-resident lung NK cells has been described. The specific role of this subset is yet to be determined, but they show similarity to resident memory T cell subsets. Whether resident or recruited, NK cells are important in the control of pulmonary infections, but equally, can drive excessive inflammation if not regulated. In this review we discuss how NK cells are recruited, controlled and retained in the specific environment of the lung in health and disease. Understanding these mechanisms in the context of infection may provide opportunities to promote NK cell recruitment and function in the lung tumor setting.

Expressional regulation of NKG2DLs is associated with the tumor development and shortened overall survival in lung adenocarcinoma

Natural killer group 2D ligands (NKG2DLs) are expressed on tumor cells as a ligand for Natural killer group 2D (NKG2D) receptors. NKG2DLs interact with NKG2D to induce immune cell-mediated cytotoxicity for eliminating tumors. Studies demonstrated that tumor cells can reduce NKG2DLs' expression to escape from anti-tumor immunity, leading to an aggressive cancer phenotype and poor prognosis in some cancers. However, these studies are limited and there is no comprehensive work on the regulation of NKG2DLs in lung adenocarcinoma (LUAD) which is one of the deadliest cancers worldwide. Here, we conducted an in silico analysis to evaluate the changes in NKG2DLs in LUAD by analyzing The Cancer Genome Atlas and the Gene Expression Omnibus datasets including tumor vs. normal comparisons, TNM stages, survival and infiltrating immune estimation profile. Results indicated that some members of NKG2DL were downregulated in LUAD as compared to normal samples. We determined that MICA (MHC class I polypeptide-related sequence A) was the most and significantly downregulated ligand among others and the results were nearly consistent with the different datasets which we used. Furthermore, survival analysis revealed that down-regulated MICA transcript expression might be one of the prognostic indicators of LUAD. Interestingly, according to the immune cell infiltrating analysis, there wasn't a direct correlation between the MICA transcript expression and immune cell infiltration, while for MICB there was. In addition, in genetic alteration, DNA methylation and miRNA analyses, we did not observe critical outcomes that would clarify the down-regulated MICA expression in detail. Regardless, this study is highly comprehensive and contributes valuable suggestions to further functional studies about the regulation of NKG2DLs and promising immunotherapeutic approaches in LUAD.

Exosomal circDNER enhances paclitaxel resistance and tumorigenicity of lung cancer via targeting miR-139-5p/ITGB8

BACKGROUND

Circular RNAs (circRNAs) are regarded as vital regulatory factors in various cancers. However, the biological functions of circDNER in the paclitaxel (PTX) resistance of lung cancer remain largely unexplored.

METHODS

Quantitative reverse transcription polymerase chain reaction (qRT-PCR) was used to analyze circDNER, miR-139-5p, and ITGB8. Cell proliferation was assessed via colony formation and MTT assays. Cell apoptosis was evaluated by flow cytometry. Western blot was performed to assess protein expression. The targeted interaction among circDNER, miR-139-5p, and ITGB8 were validated using dual-luciferase reporter or RNA immunoprecipitation assays.

RESULTS

Inhibition of circDNER reduced IC50 of PTX, inhibited cell proliferation, invasion and migration, as well as promoted cell apoptosis in PTX-resistant lung cancer cells. Mechanistically, circDNER sponged miR-139-5p to upregulate ITGB8 expression. Overexpression of miR-139-5p reversed the biological functions mediated by circDNER in PTX-resistant lung cancer cells. MiR-139-5p overexpression suppressed PTX resistance and malignant behaviors of PTX-resistant lung cancer cells, with ITGB8 elevation rescued the impacts. Moreover, we demonstrated that circDNER was upregulated in plasma exosomes from lung cancer patients. The plasma exosomes derived from these patients are the key factors enhancing the migration and invasion potential of lung cancer cells.

CONCLUSION

The circDNER mediated miR-139-5p/ITGB8 axis suppresses lung cancer progression. Our findings suggest that circDNER might act as a potential prognostic biomarker and therapeutic target for lung cancer treatment.

NKG2D Natural Killer Cell Receptor-A Short Description and Potential Clinical Applications

Natural Killer (NK) cells are natural cytotoxic, effector cells of the innate immune system. They can recognize transformed or infected cells. NK cells are armed with a set of activating and inhibitory receptors which are able to bind to their ligands on target cells. The right balance between expression and activation of those receptors is fundamental for the proper functionality of NK cells. One of the best known activating receptors is NKG2D, a member of the CD94/NKG2 family. Due to a specific NKG2D binding with its eight different ligands, which are overexpressed in transformed, infected and stressed cells, NK cells are able to recognize and attack their targets. The NKG2D receptor has an enormous significance in various, autoimmune diseases, viral and bacterial infections as well as for transplantation outcomes and complications. This review focuses on the NKG2D receptor, the mechanism of its action, clinical relevance of its gene polymorphisms and a potential application in various clinical settings.

High-throughput proteomics of breast cancer interstitial fluid: identification of tumor subtype-specific serologically relevant biomarkers

Despite significant advancements in breast cancer (BC) research, clinicians lack robust serological protein markers for accurate diagnostics and tumor stratification. Tumor interstitial fluid (TIF) accumulates aberrantly externalized proteins within the local tumor space, which can potentially gain access to the circulatory system. As such, TIF may represent a valuable starting point for identifying relevant tumor-specific serological biomarkers. The aim of the study was to perform comprehensive proteomic profiling of TIF to identify proteins associated with BC tumor status and subtype. A liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis of 35 TIFs of three main subtypes: luminal (19), Her2 (4), and triple-negative (TNBC) (12) resulted in the identification of > 8800 proteins. Unsupervised hierarchical clustering segregated the TIF proteome into two major clusters, luminal and TNBC/Her2 subgroups. High-grade tumors enriched with tumor infiltrating lymphocytes (TILs) were also stratified from low-grade tumors. A consensus analysis approach, including differential abundance analysis, selection operator regression, and random forest returned a minimal set of 24 proteins associated with BC subtypes, receptor status, and TIL scoring. Among them, a panel of 10 proteins, AGR3, BCAM, CELSR1, MIEN1, NAT1, PIP4K2B, SEC23B, THTPA, TMEM51, and ULBP2, was found to stratify the tumor subtype-specific TIFs. In particular, upregulation of BCAM and CELSR1 differentiates luminal subtypes, while upregulation of MIEN1 differentiates Her2 subtypes. Immunohistochemistry analysis showed a direct correlation between protein abundance in TIFs and intratumor expression levels for all 10 proteins. Sensitivity and specificity were estimated for this protein panel by using an independent, comprehensive breast tumor proteome dataset. The results of this analysis strongly support our data, with eight of the proteins potentially representing biomarkers for stratification of BC subtypes. Five of the most representative proteomics databases currently available were also used to estimate the potential for these selected proteins to serve as putative serological markers.

The Immune Microenvironment and Cancer Metastasis

The dynamic interplay between neoplastic cells and the immune microenvironment regulates every step of the metastatic process. Immune cells contribute to invasion by secreting a cornucopia of inflammatory factors that promote epithelial-to-mesenchymal transition and remodeling of the stroma. Cancer cells then intravasate to the circulatory system assisted by macrophages and use several pathways to avoid recognition by cytotoxtic lymphocytes and phagocytes. Circulating tumor cells that manage to adhere to the vasculature and encounter premetastic niches are able to use the associated myeloid cells to extravasate into ectopic organs and establish a dormant microscopic colony. If successful at avoiding repetitive immune attack, dormant cells can subsequently grow into overt, clinically detectable metastatic lesions, which ultimately account to most cancer-related deaths. Understanding how disseminated tumor cells evade and corrupt the immune system during the final stages of metastasis will be pivotal in developing new therapeutic modalities that combat metastasis.

Clinicopathological relevance of tumor expression of NK group 2 member D ligands in resected non-small cell lung cancer

UL16-binding protein (ULBP) 1-6 and MHC class I chain-related molecule A and B (MICA/B) are NK group 2, member D (NKG2D) ligands, which are specifically expressed in infected or transformed cells and are recognized by NK cells via NKG2D-NKG2D ligand interactions. We previously reported that MICA/B overexpression predicted improved clinical outcomes in patients with resected non-small cell lung cancer (NSCLC). However, the clinicopathological features and prognostic significance of ULBPs in NSCLC remain unclear. Here,ULBP1-6 expression was evaluated based on immunohistochemistry of 91 NSCLC samples from patients following radical surgery. ULBPs were expressed by the majority of NSCLC. Either ULBP1 or ULBP2/5/6 overexpression was associated with squamous-cell carcinoma histology, whereas ULBP4 overexpression was associated with younger age and adenocarcinoma histology. Although overexpression of ULBP1-6 did not impact clinical outcomes in NSCLC patients, integrative profiling with cluster analysis classified patients into 3 subgroups based on the expression pattern of NKG2D ligands. The subgroup characterized by ULBP1 or ULBP2/5/6 high expressing but ULBP4 low expressing tumors showed poor overall survival. Taken together with previous results, NSCLC histological subtype strongly correlates with NKG2D ligands expression pattern. NKG2D ligands expression levels assessed by multiple immune parameters could predict clinical outcomes of patients with NSCLC.

A six-mRNA prognostic model to predict survival in head and neck squamous cell carcinoma

BACKGROUND

Transcriptional dysregulation is one of the most important features of cancer genesis and progression. Applying gene expression dysregulation information to predict the development of cancers is useful for cancer diagnosis. However, previous studies mainly focused on the relationship between a single gene and cancer. Prognostic prediction using combined gene models remains limited.

MATERIALS AND METHODS

Gene expression profiles were downloaded from The Cancer Genome Atlas and the data sets were randomly divided into training data sets and test data sets. A six-gene signature associated with head and neck squamous cell carcinoma (HNSCC) and overall survival (OS) was identified according to a training cohort by using weighted gene correlation network analysis and least absolute shrinkage and selection operator Cox regression. The test data set and gene expression omnibus (GEO) data set were used to validate this signature.

RESULTS

We identified six candidate genes, namely, FOXL2NB, PCOLCE2, SPINK6, ULBP2, KCNJ18, and RFPL1, and, using a six-gene model, predicted the risk of death of head and neck squamous cell carcinoma in The Cancer Genome Atlas. At a selected cutoff, patients were clustered into low- and high-risk groups. The OS curves of the two groups of patients had significant differences, and the time-dependent receiver operating characteristics of OS, disease-specific survival (DSS), and progression-free survival (PFS) were as high as 0.766, 0.731, and 0.623, respectively. Then, the test data set and the GEO data set were used to evaluate our model, and we found that the OS time in the high-risk group was significantly shorter than in the low-risk group in both data sets, and the receiver operating characteristics of test data set were 0.669, 0.675, and 0.614, respectively. Furthermore, univariate and multivariate Cox regression analyses showed that the risk score was independent of clinicopathological features.

CONCLUSION

The six-gene model could predict the OS of HNSCC patients and improve therapeutic decision-making.

NKG2D and its ligands in cancer

NKG2D is an activating immune receptor expressed by NK and effector T cells. Induced expression of NKG2D ligand on tumor cell surface during oncogenic insults renders cancer cells susceptible to immune destruction. In advanced human cancers, tumor cells shed NKG2D ligand to produce an immune soluble form as a means of immune evasion. Soluble NKG2D ligands have been associated with poor clinical prognosis in cancer patients. Harnessing NKG2D pathway is considered a viable avenue in cancer immunotherapy over recent years. In this review, we will discuss the progress and perspectives.

Natural killer cells unleashed: Checkpoint receptor blockade and BiKE/TriKE utilization in NK-mediated anti-tumor immunotherapy

Natural killer (NK) cells have long been known to mediate anti-tumor responses without prior sensitization or recognition of specific tumor antigens. However, the tumor microenvironment can suppress NK cell function resulting in tumor escape and disease progression. Despite recent advances in cytokine therapy and NK cell adoptive transfer, tumor expression of ligands to NK - expressed checkpoint receptors can still suppress NK mediated tumor lysis. This review will explore many of the checkpoint receptors tumors utilize to manipulate the NK cell response as well as some of the current and upcoming pharmacological solutions to limit tumor suppression of NK cell function. Furthermore, we will discuss the potential to use these drugs in combinational therapies with novel antibody reagents such as bi- and tri-specific killer engagers (BiKEs and TriKEs) against tumor-specific antigens to enhance NK cell-mediated tumor rejection.

Control of Metastasis by NK Cells

The metastatic spread of malignant cells to distant anatomical locations is a prominent cause of cancer-related death. Metastasis is governed by cancer-cell-intrinsic mechanisms that enable neoplastic cells to invade the local microenvironment, reach the circulation, and colonize distant sites, including the so-called epithelial-to-mesenchymal transition. Moreover, metastasis is regulated by microenvironmental and systemic processes, such as immunosurveillance. Here, we outline the cancer-cell-intrinsic and -extrinsic factors that regulate metastasis, discuss the key role of natural killer (NK) cells in the control of metastatic dissemination, and present potential therapeutic approaches to prevent or target metastatic disease by harnessing NK cells.

Soluble NKG2D ligands are biomarkers associated with the clinical outcome to immune checkpoint blockade therapy of metastatic melanoma patients

The introduction of immune checkpoint blockade into the clinical practice resulted in improvement of survival of a significant portion of melanoma patients. Consequently, predictive biomarkers of response are needed to optimize patient's stratification and the development of combination therapies. The aim of this study was to determine whether levels of soluble NKG2D ligands (MICA, MICB, ULBP1, 2 and 3; sNKG2DLs) in the serum of melanoma patients can serve as useful predictors of response to the treatment with immune checkpoint blockade. sNKG2DLs were measured by ELISA in baseline and post-treatment serum and these results were correlated with the clinical outcome of melanoma patients (N = 194). The same determinations were performed also in a cohort of patients (N = 65) treated with either chemotherapy, radiotherapy, or mutated BRAF inhibitors (BRAFi). Absence of soluble MICB and ULBP-1 in baseline serum correlated with improved survival (OS = 21.6 and 25.3 mo and p = 0.02 and 0.01, respectively) of patients treated with immunological therapies while detectable levels of these molecules were found in poor survivors (OS = 8.8 and 12.1 mo, respectively). Multivariate analysis showed that LDH (p <0.0001), sULBP-1 (p = 0.02), and sULBP-2 (p = 0.02) were independent predictors of clinical outcome for the cohort of melanoma patients treated with immune checkpoint blockade. Only LDH but not sNKG2DLs was significantly associated with the clinical outcome of patients treated with standard or BRAFi regimens. These findings highlight the relevance of sNKG2DLs in the serum of melanoma patients as biomarkers for patients' stratification and optimization of immune checkpoint inhibition regimens.

A Combined ULBP2 and SEMA5A Expression Signature as a Prognostic and Predictive Biomarker for Colon Cancer

Background: Prognostic biomarkers for cancer have the power to change the course of disease if they add value beyond known prognostic factors, if they can help shape treatment protocols, and if they are reliable. The aim of this study was to identify such biomarkers for colon cancer and to understand the molecular mechanisms leading to prognostic stratifications based on these biomarkers. Methods and Findings: We used an in house R based script (SSAT) for the in silico discovery of stage-independent prognostic biomarkers using two cohorts, GSE17536 and GSE17537, that include 177 and 55 colon cancer patients, respectively. This identified 2 genes, ULBP2 and SEMA5A, which when used jointly, could distinguish patients with distinct prognosis. We validated our findings using a third cohort of 48 patients ex vivo. We find that in all cohorts, a combined ULBP2/SEMA5A classification (SU-GIB) can stratify distinct prognostic sub-groups with hazard ratios that range from 2.4 to 4.5 (p≤0.01) when overall- or cancer-specific survival is used as an end-measure, independent of confounding prognostic parameters. In addition, our preliminary analyses suggest SU-GIB is comparable to Oncotype DX colon(®) in predicting recurrence in two different cohorts (HR: 1.5-2; p≤0.02). SU-GIB has potential as a companion diagnostic for several drugs including the PI3K/mTOR inhibitor BEZ235, which are suitable for the treatment of patients within the bad prognosis group. We show that tumors from patients with worse prognosis have low EGFR autophosphorylation rates, but high caspase 7 activity, and show upregulation of pro-inflammatory cytokines that relate to a relatively mesenchymal phenotype. Conclusions: We describe two novel genes that can be used to prognosticate colon cancer and suggest approaches by which such tumors can be treated. We also describe molecular characteristics of tumors stratified by the SU-GIB signature.

Expression and prognostic significance of unique ULBPs in pancreatic cancer

Background

Pancreatic cancer is one of the most lethal cancers worldwide, due to the lack of efficient therapy and difficulty in early diagnosis. ULBPs have been shown to behave as important protectors with prognostic significance in various cancers.

Materials and methods

Immunohistochemistry and enzyme-linked immunosorbent assays were used to explore the expression of ULBPs in cancer tissue and in serum, while survival analysis was used to evaluate the subsequent clinical value of ULBPs.

Results

Statistics showed that high expression of membrane ULBP1 was a good biomarker of overall survival (18 months vs 13 months), and a high level of soluble ULBP2 was deemed an independent poor indicator for both overall survival (P<0.001) and disease-free survival (P<0.001).

Conclusion

ULBP1 provides additional information for early diagnosis, and soluble ULBP2 can be used as a novel tumor marker to evaluate the risk of pancreatic cancer patients.

Genetics, genomics, and evolutionary biology of NKG2D ligands

Human and mouse NKG2D ligands (NKG2DLs) are absent or only poorly expressed by most normal cells but are upregulated by cell stress, hence, alerting the immune system in case of malignancy or infection. Although these ligands are numerous and highly variable (at genetic, genomic, structural, and biochemical levels), they all belong to the major histocompatibility complex class I gene superfamily and bind to a single, invariant, receptor: NKG2D. NKG2D (CD314) is an activating receptor expressed on NK cells and subsets of T cells that have a key role in the recognition and lysis of infected and tumor cells. Here, we review the molecular diversity of NKG2DLs, discuss the increasing appreciation of their roles in a variety of medical conditions, and propose several explanations for the evolutionary force(s) that seem to drive the multiplicity and diversity of NKG2DLs while maintaining their interaction with a single invariant receptor.

MHC class I chain-related molecule A and B expression is upregulated by cisplatin and associated with good prognosis in patients with non-small cell lung cancer

MHC class I chain-related molecule A and B (MICA/B) are NK group 2 member D (NKG2D) ligands, which are broadly expressed in transformed cells. Both DNA damage-induced ataxia-telangiectasia-mutated (ATM)- and ATM and Rad3-related protein kinases (ATM-ATR) signaling and oncogene-induced PI3K-AKT signaling regulate the expression of NKG2D ligands, which promote NK cell-mediated cytotoxicity via NKG2D-NKG2D ligand interactions. NKG2D ligand overexpression was recently reported to be correlated with good prognosis in several types of cancer. However, the prognostic significance of NKG2D ligands in non-small cell lung cancer (NSCLC) remains unclear. Here, MICA/B expression was evaluated based on immunohistochemistry of 91 NSCLC samples from patients following radical surgery. In addition, expression of MICA/B was assessed in NSCLC cell lines treated with cisplatin in order to evaluate the regulatory mechanisms of MICA/B expression. Overall, 28 out of 91 (30.8%) specimens showed high expression level of MICA/B, which was associated with low (18)F-fluorodeoxyglucose uptake and manifestation of adenocarcinoma. After a median follow-up of 48.2 months, high MICA/B expression was associated with good recurrence-free survival (p = 0.037). In vitro assays using cell lines revealed that MICA/B expression was upregulated by cisplatin via ATM-ATR signaling, resulting in enhanced NK cell-mediated cytotoxicity. Upregulated MICA/B expressions in patients with radically resected NSCLC are predictive of good disease prognosis. Cisplatin-induced MICA/B upregulation is possibly an indirect mechanism by which the innate immune system eliminates tumor cells. NKG2D-NKG2D ligand-targeting therapy is a promising avenue for future immune-chemotherapy development.

Effect of Clarithromycin on the Expression of UL16-Binding Protein 2 in Human Cells

BACKGROUND

Clarithromycin is a macrolide antibiotic that possesses anti-inflammatory and immunomodulatory properties. Although recent data suggests that macrolide antibiotics enhance Pseudomonas aeruginosa clearance from the lung, involving natural killer (NK) T cells in this process by activating the NKG2D-NKG2D ligand system, the precise underlying mechanism is still unclear. In this study, we examined the effect of clarithromycin on a potent NKG2D ligand, UL16-binding protein 2 (ULBP2), in the lung and its shedding mechanism.

METHODS

The gene expressions of ULBP2 and the shredder proteinases of ULBP2, a disintegrin and metalloproteinase domain 10 (ADAM10) and ADAM17, were measured using real-time PCR. The cell surface ULBP2 expression was measured by flow cytometry. The amount of solubilized ULBP2 (sULBP2) was measured using an ELISA. The activity of ADAM17 was examined by measurement of fluorescence intensity from the fluorescence resonance energy transfer peptide substrate cleaved by ADAM17.

RESULTS

Clarithromycin significantly induced transcription of ULBP2 and ADAM17 in both A549 and LCSC #2 cells, which endogenously express minimal and abundant levels of ULBP2, respectively. However, there was no significant change on transcription of ADAM10. The same tendency was observed when LCSC #2 cells were treated with tumor necrosis factoralpha processing inhibitor-2 to inhibit ADAM17 activity. The amount of sULBP2 was significantly decreased in both A549 and LCSC #2 cells by treatment with clarithromycin. Finally, clarithromycin significantly inhibited the activity of ADAM17 in LCSC #2 cells.

CONCLUSION

These findings suggest that clarithromycin induces ULBP2 expression and reduces the amount of sULBP2, by possibly inhibiting the activity of the potent ULBP2-shedding enzyme ADAM17. Because these changes in ULBP2 and sULBP2 levels could activate NKT cells, this finding might indicate a novel mechanism by which clarithromycin improves the clearance of P. aeruginosa in chronic respiratory diseases.

PRL-3 mediates the protein maturation of ULBP2 by regulating the tyrosine phosphorylation of HSP60

Many malignant cells release the NKG2D ligand ULBP2 from their cell surface to evade immunosurveillance by NK cells and CD8 T cells. Although the shedding mechanism remains unclear, various inhibitors of matrix metalloproteinases have been shown to efficiently block the release of soluble ULBP2. The clinical use of these inhibitors, however, is limited because of adverse side effects. Using high-throughput screening technique, we identified a specific inhibitor of phosphatase of regenerating liver 3 (PRL-3) that could reduce the level of soluble ULBP2 in the culture supernatant of various cancer cell lines. Inhibition or gene knockdown of PRL-3 did not reduce ULBP2 shedding, but rather suppressed posttranslational maturation of ULBP2, resulting in intracellular retention of immature ULBP2. We then found that ULBP2 was constitutively associated with heat shock protein HSP60. Complete maturation of ULBP2 required tyrosine phosphorylation of HSP60 which was mediated by PRL-3.

Combined detection of serum UL16-binding protein 2 and macrophage inhibitory cytokine-1 improves early diagnosis and prognostic prediction of pancreatic cancer

Pancreatic cancer (PC) is the fourth leading cause of cancer-related mortality in the United States. There is no effective serum biomarker for the early diagnosis of PC at present. Although serum UL16-binding protein 2 (ULBP2) and macrophage inhibitory cytokine-1 (MIC-1) levels are reported to be elevated in PC patients, the diagnostic and prognostic value of ULBP2 and MIC-1 alone or in combination remains unknown. The aim of the present case-control study was to compare the diagnostic value of ULBP2, MIC-1 and carbohydrate antigen 19-9 (CA19-9) in 359 serum samples, consisting of 152 cases of PC, 20 cases of pre-pancreatic cancer, 91 cases of chronic pancreatitis (CP) and 96 normal controls (NC). All patients were followed up for a median of 2 years. It was found that the serum levels of ULBP2, MIC-1 and CA19-9 were significantly higher in the PC patients compared with those in the NC group. In distinguishing PC from the CP, the highest sensitivity and specificity were ULBP2 (0.878) and CA19-9 (0.816), respectively. The area under the receiver operating characteristic curve of ULBP2 was 0.923, which was the highest of the three biomarkers. MIC-1 was the optimal choice for the diagnosis of early-stage PC (area under the curve, 0.831). Overall, MIC-1 in combination with ULBP2 improved the diagnostic accuracy in differentiating PC from CP and NC. In addition, a higher level of MIC-1 was correlated with a poorer prognosis, as calculated by the Kaplan-Meier test (P=0.039). Patients with serum MIC-1 levels of ≥1,932 ng/ml had a median survival time of 15.62±2.44 months (mean ± standard deviation) vs. 18.66±2.43 months in patients with a lower level of MIC-1. Overall, combined detection of serum MIC-1 and ULBP2 improved the diagnostic accuracy in differentiating PC from CP and NC, and serum MIC-1 level alone was a predictor of survival in the patients with PC.

Secretory pathways generating immunosuppressive NKG2D ligands: New targets for therapeutic intervention

Natural Killer Group 2 member D (NKG2D) activating receptor, present on the surface of various immune cells, plays an important role in activating the anticancer immune response by their interaction with stress-inducible NKG2D ligands (NKG2DL) on transformed cells. However, cancer cells have developed numerous mechanisms to evade the immune system via the downregulation of NKG2DL from the cell surface, including the release of NKG2DL from the cell surface in a soluble form. Here, we review the mechanisms involved in the production of soluble NKG2DL (sNKG2DL) and the potential therapeutic strategies aiming to block the release of these immunosuppressive ligands. Therapeutically enabling the NKG2D-NKG2DL interaction would promote immunorecognition of malignant cells, thus abrogating disease progression.

Molecular Bases for the Regulation of NKG2D Ligands in Cancer

NKG2D is an activating receptor expressed by NK and T cells primarily involved in the elimination of transformed and infected cells. NKG2D ligands are self-proteins restrictedly expressed in healthy tissues, but induced in response to signaling pathways commonly associated with transformation. Proliferative, tumor suppressor, and stress signaling pathways linked to the tumorigenic process induce the expression of NKG2D ligands, initiating an immune response against the incipient tumor. Nevertheless, the activity of NKG2D ligands is counter-regulated in vivo by the immunoediting of cancer cells, resulting in the expression of multiple mechanisms of immune evasion in advanced tumors. The redundancy of NKG2D ligands, besides increasing the complexity of their regulation, may impair the generation of these immune evasion mechanisms. In this review, we attempt to integrate the mechanisms and pathways involved in the regulation of NKG2D ligand expression in cancer.

Natural killer cell-mediated shedding of ULBP2

UL16 binding proteins (ULBPs) are a family of cell surface proteins that are present in transformed and stressed cells and ligands for NKG2D. Soluble NKG2D ligands have been found in sera from cancer patients with their protein concentrations correlated with poor cancer prognosis. Here we show, for the first time, that human tumor cells lost their surface expression of ULBP2, but not ULBP1 and ULBP3, during NK cell-mediated cytolysis. In contrast to spontaneous shedding of NKG2D ligands, NK cytolysis-mediated shedding of ULBP2 was linked to target cell apoptosis, although both resulted from metalloproteinase cleavages. Inhibition of ULBP2 shedding by a metalloproteinase inhibitor BB-94 lead to reduced NK cell-mediated cytotoxicity and cytokine production. These results illustrate a regulation of NK cell effector functions through cytolysis-induced NKG2D ligand shedding. Consequently, compounds inhibiting NKG2D ligand shedding may offer therapeutic means to reduce excessive pathogenic NK cell activities.

Generation of soluble NKG2D ligands: proteolytic cleavage, exosome secretion and functional implications

The activating natural killer group 2 member D (NKG2D) receptor is expressed on NK cells, cytotoxic T cells and additional T cell subsets. Ligands for human NKG2D comprise two groups of MHC class I-related molecules, the MHC class I chain-related proteins A and B (MICA/B) and 6 UL16-binding proteins (ULBP1-6). While NKG2D ligands are absent from most normal cells, expression is induced upon stress and malignant transformation. In fact, most solid tumours and leukaemia/lymphomas constitutively express at least one NKG2D ligand and thereby are susceptible to NKG2D-dependent immunosurveillance. However, soluble NKG2D ligands are released from tumour cells and can down-modulate NKG2D activation as a means of tumour immune escape. In some tumour entities, levels of soluble NKG2D ligands in the serum correlate with tumour progression. NKG2D ligands can be proteolytically shed from the cell surface or liberated from the membrane by phospholipase C in the case of glycosylphosphatidylinositol (GPI)-anchored molecules. Moreover, NKG2D ligands can be secreted in exosomal microvesicles together with other tumour-derived molecules. Depending on the specific tumour/immune cell setting, these various forms of soluble and/or exosome-bound NKG2D ligands can exert multiple effects on NKG2D/NKG2D ligand interactions. In this review, we focus on the role of various proteases in the shedding of human NKG2D ligands from tumour cells and discuss the not completely unanimous reported functional implications of soluble and exosome-secreted NKG2D ligands for immunosurveillance.