Serum AGR2 as a useful biomarker for pituitary adenomas

Modulation of Protein Disulfide Isomerase Functions by Localization: The Example of the Anterior Gradient Family

Significance: Oxidative folding within the endoplasmic reticulum (ER) introduces disulfide bonds into nascent polypeptides, ensuring proteins' stability and proper functioning. Consequently, this process is critical for maintaining proteome integrity and overall health. The productive folding of thousands of secretory proteins requires stringent quality control measures, such as the unfolded protein response (UPR) and ER-Associated Degradation (ERAD), which contribute significantly to maintaining ER homeostasis. ER-localized protein disulfide isomerases (PDIs) play an essential role in each of these processes, thereby contributing to various aspects of ER homeostasis, including maintaining redox balance, proper protein folding, and signaling from the ER to the nucleus. Recent Advances: Over the years, there have been increasing reports of the (re)localization of PDI family members and other ER-localized proteins to various compartments. A prime example is the anterior gradient (AGR) family of PDI proteins, which have been reported to relocate to the cytosol or the extracellular environment, acquiring gain of functions that intersect with various cellular signaling pathways. Critical Issues: Here, we summarize the functions of PDIs and their gain or loss of functions in non-ER locations. We will focus on the activity, localization, and function of the AGR proteins: AGR1, AGR2, and AGR3. Future Directions: Targeting PDIs in general and AGRs in particular is a promising strategy in different human diseases. Thus, there is a need for innovative strategies and tools aimed at targeting PDIs; those strategies should integrate the specific localization and newly acquired functions of these PDIs rather than solely focusing on their canonical roles.

Serum exosomal circCCDC66 as a potential diagnostic and prognostic biomarker for pituitary adenomas

Purpose

Circular RNAs (circRNAs) play an important role in tumorigenesis, and exosomal circRNAs have the potential to be novel biomarkers for cancer diagnosis. Here, we are committed to reveal serum exosomal circCCDC66 as a noninvasive biomarker to diagnose and predict recurrence in pituitary adenoma (PA).

Methods

A total of 90 PA patients and 50 healthy subjects were enrolled for clinical validation. Exosomes were extracted from the serum and validated by transmission electron microscopy, nanoparticle tracking analysis, and Western blot assay. The expression of circCCDC66 in serum exosomes was assessed using quantitative real-time PCR (qRT-PCR), and correlations between circCCDC66 expression and clinicopathological factors were analyzed. The reliability of serum exosomal circCCDC66 to diagnose PA was evaluated using receiver operating characteristic (ROC) analysis.

Results

Initially, an obviously significantly increasing level of serum exosomal circCCDC66 was verified in the PA specimens compared with healthy controls. Importantly, serum exosomal circCCDC66, which was secreted and released by PA cells, could monitor tumor dynamics and serve as a potentially prognostic biomarker during treatment. Additionally, ROC curve analysis was performed and the corresponding area under the curve (AUC) values were used to confirm the ability of serum exosomal circCCDC66 as a potentially diagnostic and prognostic biomarker for PA patients. Importantly, the progression-free survival was much longer in the low serum exosomal circCCDC66 group than in the high serum exosomal circCCDC66 group.

Conclusion

Serum exosomal circCCDC66 is abnormally elevated and may serve as a promising factor for the diagnosis of and predicting prognosis in PA patients.

Inhibitory Effect of Etravirine, a Non-Nucleoside Reverse Transcriptase Inhibitor, via Anterior Gradient Protein 2 Homolog Degradation against Ovarian Cancer Metastasis

Anterior gradient protein 2 homolog (AGR2), an endoplasmic reticulum protein, is secreted in the tumor microenvironment. AGR2 is a member of the disulfide isomerase family, is highly expressed in multiple cancers, and promotes cancer metastasis. In this study, we found that etravirine, which is a non-nucleoside reverse transcriptase inhibitor, could induce AGR2 degradation via autophagy. Moreover, etravirine diminished proliferation, migration, and invasion in vitro. Moreover, in an orthotopic xenograft mouse model, the combination of etravirine and paclitaxel significantly suppressed cancer progression and metastasis. This drug may be a promising therapeutic agent for the treatment of ovarian cancer.

Identification of key genes in benign prostatic hyperplasia using bioinformatics analysis

PURPOSE

This study aimed to identify differentially expressed genes (DEGs) and pathways in benign prostatic hyperplasia (BPH) by comprehensive bioinformatics analysis.

METHODS

Data of the gene expression microarray (GSE6099) were downloaded from GEO database. DEGs were obtained by GEO2R. Functional and enrichment analyses of selected genes were performed using DAVID database. Protein-protein interaction network was constructed through STRING. Anterior gradient 2 (ARG2) and lumican (LUM) staining in paraffin-embedded specimens from BPH and normal prostate (NP) were detected by immunohistochemistry (IHC). Differences between groups were analyzed by the Student's t test.

RESULTS

A total of 24 epithelial DEGs and 39 stromal DEGs were determined. The GO analysis results showed that epithelial DEGs between BPH and NP were enriched in biological processes of glucose metabolic process, glucose homeostasis and negative regulation of Rho protein signal transduction. For DEGs in stroma, enriched biological processes included response to ischemia, antigen processing and presentation, cartilage development, T cell costimulation and energy reserve metabolic process. ARG2, as one of the epithelial DEGs, was mainly located in epithelial cells of prostate. In addition, LUM is primarily expressed in the stroma. We further confirmed that compared with NP, the BPH have the lower ARG2 protein level (p = 0.029) and higher LUM protein level (p = 0.003) using IHC.

CONCLUSIONS

Our study indicated that there are possible differentially expressed genes in epithelial and stromal cells, such as ARG2 and LUM, which may provide a novel insight for the pathogenesis of BPH.

Effects of ER-resident and secreted AGR2 on cell proliferation, migration, invasion, and survival in PANC-1 pancreatic cancer cells

Background

Anterior gradient-2 (AGR2) is a proto-oncogene involved in tumorigenesis and cancer progression. AGR2, predominantly localized in the endoplasmic reticulum (ER), is also a secreted protein detected in the extracellular compartment in multiple cancers. However, the biological functions of intracellular and extracellular AGR2 remain to be elucidated.

Methods

Based on the biochemical structure of AGR2 protein, PANC-1 pancreatic cancer cells stably expressing ER-resident or secreted AGR2 were generated by a lentivirus-mediated stable overexpression system. The capacities of cell proliferation, migration, invasion and survival were assessed in PANC-1 stable cells. Moreover, EGFR expression and activation were determined to explore the possible mechanism of AGR2 roles in pancreatic cancer tumorigenesis.

Results

It was discovered that secreted AGR2, but not ER-resident AGR2, promotes cell proliferation, migration and invasion of PANC-1 cells. Moreover, the data indicated that both the ER-resident and the secreted AGR2 enhance the survival capacity of PANC-1 cells after tunicamycin-induced ER stress and gemcitabine treatment. However, EGFR expression and activation were not found to be involved in AGR2-dependent oncogenic phenotypes in PANC-1 cells.

Conclusions

Secreted AGR2 is predominantly involved in cell proliferation, migration and invasion in PANC-1 pancreatic cancer cells. Both secreted and ER-resident AGR2 contribute to the survival of PANC-1 cells under the challenging conditions. These findings provide insight into how different localizations of AGR2 have contributed to pancreatic cancer growth, metastasis, and drug sensitivity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-020-07743-y.

Secretion of pro-oncogenic AGR2 protein in cancer

Anterior gradient-2 (AGR2) protein mediates the formation, breakage and isomerization of disulphide bonds during protein maturation in the endoplasmic reticulum (ER) and contributes to the homoeostasis of the secretory pathway. AGR2 promotes tumour development and metastasis and its elevated expression is almost completely restricted to malignant tumours. Interestingly, this supposedly ER-resident protein can be localised to other compartments of cancer cells and can also be secreted into the extracellular milieu. There are emerging evidences that describe the gain-of-function activities of the extracellular AGR2, particularly in cancer development. Here, we reviewed studies detailing the expression, pathological and physiological roles associated with AGR2 and compared the duality of localization, intracellular and extracellular, with special emphasis on the later. We also discussed the possible mechanisms of AGR2 secretion as well as deliberating the functional impacts of AGR2 in cancer settings. Last, we deliberate the current therapeutic strategies and posit the potential use AGR2, as a prognosis and diagnosis marker in cancer.

The anterior gradient-2 interactome

The anterior gradient-2 (AGR2) is an endoplasmic reticulum (ER)-resident protein belonging to the protein disulfide isomerase family that mediates the formation of disulfide bonds and assists the protein quality control in the ER. In addition to its role in proteostasis, extracellular AGR2 is responsible for various cellular effects in many types of cancer, including cell proliferation, survival, and metastasis. Various OMICs approaches have been used to identify AGR2 binding partners and to investigate the functions of AGR2 in the ER and outside the cell. Emerging data showed that AGR2 exists not only as monomer, but it can also form homodimeric structure and thus interact with different partners, yielding different biological outcomes. In this review, we summarize the AGR2 “interactome” and discuss the pathological and physiological role of such AGR2 interactions.

LINC02273 drives breast cancer metastasis by epigenetically increasing AGR2 transcription

BACKGROUND

The majority of breast cancer patients die of metastasis rather than primary tumors, whereas the molecular mechanisms orchestrating cancer metastasis remains poorly understood. Long noncoding RNAs (lncRNA) have been shown to regulate cancer occurrence and progression. However, the lncRNAs that drive metastasis in cancer patients and their underlying mechanisms are still largely unknown.

METHODS

lncRNAs highly expressed in metastatic lymph nodes were identified by microarray. Survival analysis were made by Kaplan-Meier method. Cell proliferation, migration, and invasion assay was performed to confirm the phenotype of LINC02273. Tail vein model and mammary fat pad model were used for in vivo study. RNA pull-down and RIP assay were used to confirm the interaction of hnRNPL and LINC02273. Chromatin isolation by RNA purification followed by sequencing (ChIRP-seq), RNA-seq, ChIP-seq, and luciferase reporter assay reveal hnRNPL-LINC02273 regulates AGR2. Antisense oligonucleotides were used for in vivo treatment.

RESULTS

We identified a novel long noncoding RNA LINC02273, whose expression was significantly elevated in metastatic lesions compared to the primary tumors, by genetic screen of matched tumor samples. Increased LINC02273 promoted breast cancer metastasis in vitro and in vivo. We further showed that LINC02273 was stabilized by hnRNPL, a protein increased in metastatic lesions, in breast cancer cells. Mechanistically, hnRNPL-LINC02273 formed a complex which activated AGR2 transcription and promoted cancer metastasis. The recruitment of hnRNPL-LINC02273 complex to AGR2 promoter region epigenetically upregulated AGR2 by augmenting local H3K4me3 and H3K27ac levels. Combination of AGR2 and LINC02273 was an independent prognostic factor for predicting breast cancer patient survival. Moreover, our data revealed that LINC02273-targeting antisense oligonucleotides (ASO) substantially inhibited breast cancer metastasis in vivo.

CONCLUSIONS

Our findings uncover a key role of LINC02273-hnRNPL-AGR2 axis in breast cancer metastasis and provide potential novel therapeutic targets for metastatic breast cancer intervention.

RAD9A promotes metastatic phenotypes through transcriptional regulation of anterior gradient 2 (AGR2)

RAD9A plays an important role in prostate tumorigenesis and metastasis-related phenotypes. The protein classically functions as part of the RAD9A-HUS1-RAD1 complex but can also act independently. RAD9A can selectively transactivate multiple genes, including CDKN1A and NEIL1 by binding p53-consensus sequences in or near promoters. RAD9A is overexpressed in human prostate cancer specimens and cell lines; its expression correlates with tumor progression. Silencing RAD9A in prostate cancer cells impairs their ability to form tumors in vivo and migrate as well as grow anchorage independently in vitro. We demonstrate herein that RAD9A transcriptionally controls AGR2, a gene aberrantly overexpressed in patients with metastatic prostate cancer. Transient or stable knockdown of RAD9A in PC-3 cells caused downregulation of AGR2 protein abundance. Reduced AGR2 protein levels were due to lower abundance of AGR2 mRNA. The AGR2 genomic region upstream of the coding initiation site contains several p53 consensus sequences. RAD9A bound specifically to the 5'-untranslated region of AGR2 in PC-3 cells at a partial p53 consensus sequence at position +3136 downstream from the transcription start site, determined by chromatin immunoprecipitation, followed by PCR amplification. Binding of RAD9A to the p53 consensus sequence was sufficient to drive AGR2 gene transcription, shown by a luciferase reporter assay. In contrast, when the RAD9A-binding sequence on the AGR2 was mutated, no luciferase activity was detected. Knockdown of RAD9A in PC-3 cells impaired cell migration and anchorage-independent growth. However, ectopically expressed AGR2 in RAD9A-depleted PC-3 cells restored these phenotypes. Our results suggest RAD9A drives metastasis by controlling AGR2 abundance.

Leveraging the Role of the Metastatic Associated Protein Anterior Gradient Homologue 2 in Unfolded Protein Degradation: A Novel Therapeutic Biomarker for Cancer

Effective diagnostic, prognostic and therapeutic biomarkers can help in tracking disease progress, predict patients’ survival, and considerably affect the drive for successful clinical management. The present review aims to determine how the metastatic-linked protein anterior gradient homologue 2 (AGR2) operates to affect cancer progression, and to identify associated potential diagnostic, prognostic and therapeutic biomarkers, particularly in central nervous system (CNS) tumors. Studies that show a high expression level of AGR2, and associate the protein expression with the resilience to chemotherapeutic treatments or with poor cancer survival, are reported. The primary protein structures of the seven variants of AGR2, including their functional domains, are summarized. Based on experiments in various biological models, this review shows an orchestra of multiple molecules that regulate AGR2 expression, including a feedback loop with p53. The AGR2-associated molecular functions and pathways including genomic integrity, proliferation, apoptosis, angiogenesis, adhesion, migration, stemness, and inflammation, are detailed. In addition, the mechanisms that can enable the rampant oncogenic effects of AGR2 are clarified. The different strategies used to therapeutically target AGR2-positive cancer cells are evaluated in light of the current evidence. Moreover, novel associated pathways and clinically relevant deregulated genes in AGR2 high CNS tumors are identified using a meta-analysis approach.

Biomarker Discovery for Immunotherapy of Pituitary Adenomas: Enhanced Robustness and Prediction Ability by Modern Computational Tools

Pituitary adenoma (PA) is prevalent in the general population. Due to its severe complications and aggressive infiltration into the surrounding brain structure, the effective management of PA is required. Till now, no drug has been approved for treating non-functional PA, and the removal of cancerous cells from the pituitary is still under experimental investigation. Due to its superior specificity and safety profile, immunotherapy stands as one of the most promising strategies for dealing with PA refractory to the standard treatment, and various studies have been carried out to discover immune-related gene markers as target candidates. However, the lists of gene markers identified among different studies are reported to be highly inconsistent because of the greatly limited number of samples analyzed in each study. It is thus essential to substantially enlarge the sample size and comprehensively assess the robustness of the identified immune-related gene markers. Herein, a novel strategy of direct data integration (DDI) was proposed to combine available PA microarray datasets, which significantly enlarged the sample size. First, the robustness of the gene markers identified by DDI strategy was found to be substantially enhanced compared with that of previous studies. Then, the DDI of all reported PA-related microarray datasets were conducted to achieve a comprehensive identification of PA gene markers, and 66 immune-related genes were discovered as target candidates for PA immunotherapy. Finally, based on the analysis of human protein⁻protein interaction network, some promising target candidates (GAL, LMO4, STAT3, PD-L1, TGFB and TGFBR3) were proposed for PA immunotherapy. The strategy proposed together with the immune-related markers identified in this study provided a useful guidance for the development of novel immunotherapy for PA.

Loss of ER retention motif of AGR2 can impact mTORC signaling and promote cancer metastasis

Anterior gradient 2 (AGR2) is a member of the protein disulfide isomerase (PDI) family, which plays a role in the regulation of protein homeostasis and the unfolded protein response pathway (UPR). AGR2 has also been characterized as a proto-oncogene and a potential cancer biomarker. Cellular localization of AGR2 is emerging as a key component for understanding the role of AGR2 as a proto-oncogene. Here, we provide evidence that extracellular AGR2 (eAGR2) promotes tumor metastasis in various in vivo models. To further characterize the role of the intracellular-resident versus extracellular protein, we performed a comprehensive protein-protein interaction screen. Based on these results, we identify AGR2 as an interacting partner of the mTORC2 pathway. Importantly, our data indicates that eAGR2 promotes increased phosphorylation of RICTOR (T1135), while intracellular AGR2 (iAGR2) antagonizes its levels and phosphorylation. Localization of AGR2 also has opposing effects on the Hippo pathway, spheroid formation, and response to chemotherapy in vitro. Collectively, our results identify disparate phenotypes predicated on AGR2 localization. Our findings also provide credence for screening of eAGR2 to guide therapeutic decisions.

Anterior gradient 2 as a supervisory marker for tumor vessel normalization induced by anti-angiogenic treatment

Anti-angiogenic therapy provides transient tumor vascular normalization, which results in a window of opportunity for improvement of radio- or chemotherapy. Biomarkers indicating this window are required for rationalizing anti-angiogenesis. Anterior gradient 2 (AGR2), the majority of which is secreted from tumor cells, is an easily detected plasma protein. In the present study, it was demonstrated that AGR2 could be applied as a biomarker for the supervision of vascular normalization during anti-angiogenic treatment with gold nanoparticles (AuNPs). Nude mice inoculated with SW620 human colorectal cancer cells were treated with AuNPs. Vessel density, pericyte coverage, vessel permeability, tumor hypoxia, tumor growth and AGR2 secretion were detected following treatment with AuNPs at days 0, 4, 6, 9 and 14. Tumor volume and vessel density were reduced, whereas pericyte coverage was increased, and hypoxia and vessel permeability were improved between days 6–9; however, these improvements decreased by day 14, revealing a time frame for tumor vascular normalization, namely days 4–9, during treatment with AuNPs in mice. AGR2 levels in tumor tissues and plasma were significantly low at day 9, along with vascular normalization; therefore, AGR2 can be used as a potential marker for monitoring tumor vascular normalization during anti-angiogenic treatment.

AGR2 diagnostic value in nasopharyngeal carcinoma prognosis

BACKGROUND

Anterior Gradient (AGR) 2 concentration increases in the serum of tumor patients, and their diagnostic and prognostic significances were evaluated in some tumors. The previous works showed that AGR2 high express in nasopharyngeal carcinoma (NPC) biopsy tissues. However, whether AGR2 serves as a diagnostic and prognostic marker for NPC remains unclear.

METHODS

42 healthy volunteers, 34 breast cancer patients and 124 NPC patients were enrolled into this study, and the serum samples were collected from these healthy volunteers, breast cancer patients and NPC patients. Concomitantly, 79 frozen nasopharyngeal specimens consisted of 65 NPC tissues and 14 normal nasopharyngeal tissues were enrolled in the observation. The enzyme linked immunosorbent assay (ELISA) was used to estimate AGR2 concentration in the serum samples, and AGR2 mRNA expressions in the frozen tissue samples were detected by real time RT-PCR.

RESULTS

The real time RT-PCR results showed that AGR2 mRNA level was increased in NPC tissues compared with the normal nasopharyngeal tissues (p<0.05). The ELISA data showed that AGR2 concentration in NPC serum was significantly higher in NPC patient serums than that in the health population (p<0.05). And, AGR2 expression showed a correlation with tumor node metastasis (TNM) grade (p<0.05) and Recurrence (p<0.05). Moreover, the cumulative survival rate of patients with high concentration of AGR2 was significantly lower than that of patients with low concentration of AGR2 (p<0.05), and the cumulative hazard rate of patients with high concentration of AGR2 was significantly higher than that with low concentration of AGR2 (p<0.05).

CONCLUSION

Serum AGR2 can be used as a serum marker for clinical prognosis of nasopharyngeal carcinoma. However, serum AGR2 levels could not provide advantages in clinical practice for the differential diagnosis of cancer.