PAQR3 expression is downregulated in human breast cancers and correlated with HER2 expression

Golgi apparatus targeted therapy in cancer: Are we there yet?

Membrane trafficking within the Golgi apparatus plays a pivotal role in the intracellular transportation of lipids and proteins. Dysregulation of this process can give rise to various pathological manifestations, including cancer. Exploiting Golgi defects, cancer cells capitalise on aberrant membrane trafficking to facilitate signal transduction, proliferation, invasion, immune modulation, angiogenesis, and metastasis. Despite the identification of several molecular signalling pathways associated with Golgi abnormalities, there remains a lack of approved drugs specifically targeting cancer cells through the manipulation of the Golgi apparatus. In the initial section of this comprehensive review, the focus is directed towards delineating the abnormal Golgi genes and proteins implicated in carcinogenesis. Subsequently, a thorough examination is conducted on the impact of these variations on Golgi function, encompassing aspects such as vesicular trafficking, glycosylation, autophagy, oxidative mechanisms, and pH alterations. Lastly, the review provides a current update on promising Golgi apparatus-targeted inhibitors undergoing preclinical and/or clinical trials, offering insights into their potential as therapeutic interventions. Significantly more effort is required to advance these potential inhibitors to benefit patients in clinical settings.

The Emerging Roles and Mechanisms of PAQR3 in Human Cancer: Pathophysiology and Therapeutic Implications

Cancer was one of the common causes of death in the world, and it was increasing year by year. At present, Progestin and AdipoQ receptor family member 3 (PAQR3) was widely studied in cancer. It has been found that PAQR3 was down regulated in various cancers, such as the gastric cancer, osteosarcoma, glioma, hepatocellular carcinoma, acute lymphoblastic leukemia, laryngeal squamous cell carcinoma, esophageal cancer, breast cancer, non-small cell lung cancer, and colorectal cancer. The decreased expression of PAQR3 was associated with short overall survival and disease-free survival in patients with gastric cancer, hepatocellular carcinoma, laryngeal squamous cell carcinoma, esophageal cancer, breast cancer, and non-small cell lung cancer. PAQR3 could inhibit cancer progression by using the Ras/Raf/MEK/ERK, PI3/AKT, EMT and other mechanisms, and was negatively regulated by the miR-543, miR-15b-5p and miR-15b. The roles and signaling mechanisms of PAQR3, and the relationship between the expression of PAQR3 and prognosis in cancer progression are reviewed in this article, and provides new tumor marker and idea to guide cancer treatment.

PAQR3 Inhibits Non-small Cell Lung Cancer Growth by Regulating the NF-κB/p53/Bax Axis

Background

The expression of progestin and adipoQ receptor 3 (PAQR3) is generally downregulated in multiple tumors, which is associated with tumor progression and poor prognosis.

Methods

The clinical value of PAQR3 was analyzed using various databases and in 60 patients with non-small cell lung cancer (NSCLC). In addition, cell counting kit-8 (CCK-8), colony formation, and flow cytometry assays were used to evaluate the effect of PAQR3 on the growth of NSCLC cells in vitro. Gene set enrichment analysis (GSEA) was performed to investigate the possible mechanism through which PAQR3 is involved in the progression of lung cancer. Furthermore, western blotting was employed to verify the relevant mechanism.

Results

The expression of PAQR3 was decreased in 60 NSCLC patients and was related to the histological subtype, lymph node metastasis, tumor size, and diagnosis of NSCLC. Patients with lung adenocarcinoma with increased PAQR3 expression tended to have a better prognosis. Besides, PAQR3 inhibited proliferation, clone formation, and cycle transition in NSCLC cells, but induced apoptosis. The results of GSEA showed that PAQR3 regulated the progression of lung cancer by affecting cell cycle, DNA replication, and the p53 signaling pathway. We confirmed that PAQR3 overexpression inhibited the expression of NF-κB, while it increased the expression of p53, phospho-p53, and Bax. On the contrary, PAQR3 inhibition played an opposite role in these proteins.

Conclusion

PAQR3 inhibited the growth of NSCLC cells through the NF-κB/P53/Bax signaling pathway and might be a new target for diagnosis and treatment.

PAQR3 suppresses the growth of non-small cell lung cancer cells via modulation of EGFR-mediated autophagy

Macroautophagy/autophagy is an evolutionarily conserved intracellular process that recycles and degrades intracellular components to sustain homeostasis in response to deficiency of nutrients or growth factors. PAQR3 is a newly discovered tumor suppressor that also regulates autophagy induced by nutrient starvation via AMPK and MTORC1 signaling pathways. In this study, we investigated whether PAQR3 modulates EGFR-mediated autophagy and whether such regulation is associated with the tumor suppressive activity of PAQR3. PAQR3 is able to inhibit the in vitro and in vivo growth of non-small cell lung cancer (NSCLC) cells. PAQR3 potentiates autophagy induced by EGFR inhibitor erlotinib. Knockdown of PAQR3 abrogates erlotinib-mediated reduction of BECN1 interaction with autophagy inhibitory proteins RUBCN/Rubicon and BCL2. PAQR3 blocks the interaction of BECN1 with the activated form of EGFR and inhibits tyrosine phosphorylation of BECN1. Furthermore, inhibition of autophagy by knocking down ATG7 abrogates the tumor suppressive activity of PAQR3 in NSCLC cells. Collectively, these data indicate that PAQR3 suppresses tumor progression of NSCLC cells through modulating EGFR-regulated autophagy.

ABBREVIATIONS

AKT: thymoma viral proto-oncogene; ATG5: autophagy related 5; ATG7: autophagy related 7; ATG14: autophagy related 14; BCL2: B cell leukemia/lymphoma 2; BECN1: beclin 1; CCK-8: cell counting kit-8; CQ: chloroquine diphosphate; DMEM: Dulbecco's modified Eagle's medium; EdU: 5-ethynyl-2'-deoxyuridine; EGFR: epidermal growth factor receptor; FBS: fetal bovine serum; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; IgG: Immunoglobulin G; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; MTOR: mechanistic target of rapamycin kinase; MTORC1: mechanistic target of rapamycin kinase complex 1; MTT: thiazolyl blue tetrazolium bromide; NSCLC: Non-small cell lung cancer; MAP2K/MEK: mitogen-activated protein kinase kinase; MAPK/ERK: mitogen-activated protein kinase; PAQR3: progestin and adipoQ receptor family member 3; PI3K: phosphatidylinositol-4,5-bisphosphate 3-kinase; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PIK3R4/VPS15: phosphoinositide-3-kinase regulatory subunit 4; PRKAA/AMPK: protein kinase, AMP-activated alpha catalytic; RUBCN: rubicon autophagy regulator; RPS6: ribosomal protein S6; RAS: Ras proto-oncogene; RAF: Raf proto-oncogene; TKI: tyrosine kinase inhibitor; TUBA4A: tubulin alpha 4a; UVRAG: UV radiation resistance associated.

PAQR4 promotes chemoresistance in non-small cell lung cancer through inhibiting Nrf2 protein degradation

Purpose: Lung cancer is the leading cause of cancer related deaths worldwide. We have previously identified many differentially expressed genes (DEGs) from large scale pan-cancer dataset using the Cross-Value Association Analysis (CVAA) method. Here we focus on Progestin and AdipoQ Receptor 4 (PAQR4), a member of the progestin and adipoQ receptor (PAQR) family localized in the Golgi apparatus, to determine their clinical role and mechanism in the development of non-small cell lung cancer (NSCLC). Methods: The protein expression profile of PAQR4 was examined by IHC using tissue microarrays, and the effects of PAQR4 on cell proliferation, colony formation and xenograft tumor formation were tested in NSCLC cells. Real-time RT-PCR, co-immunoprecipitation (co-IP) and GST-pulldown assays were used to explore the mechanism of action of PAQR4. Results: We provided evidence showing that PAQR4 is increased in NSCLC cancer cell lines (A549, H1299, H1650, H1975, H358, GLC-82 and SPC-A1), and identified many mutations in PAQR4 in non-small cell lung cancer (NSCLC) tissues. We demonstrated that PAQR4 high expression correlates with a worse clinical outcome, and that its knockdown suppresses cell proliferation by inducing apoptosis. Importantly, overexpressed PAQR4 physically interacts with Nrf2 in NSCLC cells, blocking the interaction between Nrf2 and Keap1. Conclusion: Our results suggest that PAQR4 depletion enhances the sensitivity of cancerous cell to chemotherapy both in vitro and xenograft tumor formation in vivo, by promoting Nrf2 protein degradation through a Keap1-mediated ubiquitination process.

Characterization of the Golgi scaffold protein PAQR3, and its role in tumor suppression and metabolic pathway compartmentalization

The Golgi apparatus is critical in the compartmentalization of signaling cascades originating from the cytoplasmic membrane and various organelles. Scaffold proteins, such as progestin and adipoQ receptor (PAQR)3, specifically regulate this process, and have recently been identified in the Golgi apparatus. PAQR3 belongs to the PAQR family, and was recently described as a tumor suppressor. Accumulating evidence demonstrates PAQR3 is downregulated in different cancers to suppress its inhibitory effects on malignant potential. PAQR3 functions biologically through the pathological regulation of altered signaling pathways. Significant cell proliferation networks, including Ras proto-oncogene (Ras)/mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt), insulin, and vascular endothelial growth factor, are closely controlled by PAQR3 for physiologically relevant effects. Meanwhile, genetic/epigenetic susceptibility and environmental factors, may have functions in the downregulation of PAQR3 in human cancers. This study aimed to assess the subcellular localization of PAQR3 and determine its topological features and functional domains, summarizing its effects on cell signaling compartmentalization. The pathophysiological functions of PAQR3 in cancer pathogenesis, metabolic diseases, and developmental ailments were also highlighted.

Selected Golgi-Localized Proteins and Carcinogenesis: What Do We Know?

The role of the Golgi apparatus in carcinogenesis still remains unclear. A number of structural and functional cis-, medial-, and trans-Golgi proteins as well as a complexity of metabolic pathways which they mediate may indicate a central role of the Golgi apparatus in the development and progression of cancer. Pleiotropy of cellular function of the Golgi apparatus makes it a "metabolic heart" or a relay station of a cell, which combines multiple signaling pathways involved in carcinogenesis. Therefore, any damage to or structural abnormality of the Golgi apparatus, causing its fragmentation and/or biochemical dysregulation, results in an up- or downregulation of signaling pathways and may in turn promote tumor progression, as well as local nodal and distant metastases. Three alternative or parallel models of spatial and functional Golgi organization within tumor cells were proposed: (1) compacted Golgi structure, (2) normal Golgi structure with its increased activity, and (3) the Golgi fragmentation with ministacks formation. Regardless of the assumed model, the increased activity of oncogenesis initiators and promoters with inhibition of suppressor proteins results in an increased cell motility and migration, increased angiogenesis, significantly activated trafficking kinetics, proliferation, EMT induction, decreased susceptibility to apoptosis-inducing factors, and modulating immune response to tumor cell antigens. Eventually, this will lead to the increased metastatic potential of cancer cells and an increased risk of lymph node and distant metastases. This chapter provided an overview of the current state of knowledge of selected Golgi proteins, their role in cytophysiology as well as potential involvement in tumorigenesis.

Suppressor PAQR3 associated with the clinical significance and prognosis in esophageal squamous cell carcinoma

Progestin and adipoQ receptor family member 3 (PAQR3) is a novel tumor suppressor; however, its function in esophageal cancer is not well understood. The present study explored the association between PAQR3, and the survival and clinical phenotype in patients with esophageal squamous cell carcinoma (ESCC). The expression of PAQR3 in 80 cases of ESCC and its corresponding adjacent tissues was detected by reverse transcription-quantitative polymerase chain reaction. The results demonstrated that PAQR3 expression in cancer tissues was significantly lower compared with that in adjacent tissues. Clinicopathological analysis indicated that PAQR3 expression was significantly correlated with ethnicity (P=0.032), tumor length (P=0.019), lymph node metastasis (P=0.011) and local recurrence (P=0.009). Notably, the Kaplan-Meier survival curve demonstrated that a decrease in PAQR3 expression was associated with poor prognosis in patients with ESCC. Multivariate analysis indicated that PAQR3 expression was an independent prognostic indicator for patients with ESCC. PAQR3 may serve an important role in the progress of ESCC and become a potential candidate for ESCC targeted therapy.

Aberrant promoter methylation of the PAQR3 gene is associated with prostate cancer

Methylation markers are promising tools for diagnosis, prognosis and targeted treatment of cancer. In prostate carcinoma, aberrant promoter hypermethylation occurs earlier in the disease course and more consistently than recurrent somatic mutations. PAQR3, a tumor suppressor gene, was recently found to be downregulated in prostate cancer cell lines. We hypothesized that promoter methylation could be responsible for PAQR3 silencing in prostate cancer tissues. We aimed to investigate PAQR3 promoter methylation in prostate cancer by comparing it to benign prostatic hyperplasia (BPH). A total of 154 human prostate tissue samples, including 92 cases with prostate cancer and 62 cases with BPH, were examined by methylation-specific PCR. Clinicopathological correlation between PAQR3 promoter methylation and prognostically relevant variables was studied by statistical analysis. Promoter methylation of PAQR3 was significantly more frequent in prostate carcinoma compared to BPH (73.9% vs. 25.8%, p<0.01). The high prevalence of PAQR3 methylation in cancer foci was also confirmed with microdissection technique in 12 samples of prostate adenocarcinoma. PAQR3 hypermethylation was associated with perineural invasion (p=0.03), an adverse clinicopathological feature of prostate cancer. We concluded that PAQR3 can be a promising methylation marker candidate for the detection and monitoring of prostate cancer.

PAQR3 suppresses the proliferation, migration and tumorigenicity of human prostate cancer cells

As a newly discovered tumor suppressor, the potential function of PAQR3 in human prostate cancer has not been demonstrated. In this study, we report that PAQR3 is able to inhibit the growth and migration of human prostate cancer cells both in vitro and in vivo. Overexpression of PAQR3 inhibits the proliferation of PC3 and DU145 cells by both MTT and colony formation assays. Consistently, knockdown of PAQR3 enhances the proliferation of these cells. In wound-healing and transwell assays, overexpression of PAQR3 reduces the migration of PC3 and DU145 cells, while PAQR3 knockdown increases it. In a tumor xenograft model, overexpression of PAQR3 suppresses tumor growth of PC3 cells in vivo, while PAQR3 knockdown promotes the tumor growth. PAQR3 is also able to inhibit serum-induced phosphorylation of AKT and ERK in both PC3 and DU145 cells. In addition, PAQR3 suppresses the expression of epithelial-mesenchymal transition (EMT) markers in PC3 cells. Collectively, these data indicate that PAQR3 has a tumor suppressive activity in human prostate cancer cells and may stand out as a potential therapeutic target for prostate cancers.

PAQR3 overexpression suppresses the aggressive phenotype of esophageal squamous cell carcinoma cells via inhibition of ERK signaling

Progestin and adipoQ receptor family member 3 (PAQR3) has exhibited anticancer activity in multiple malignancies. However, its expression and function in esophageal squamous cell carcinoma (ESCC) is still elusive. In this work, we examined the expression of PAQR3 in 40 surgically resected ESCC specimens and their adjacent normal tissues. The expression of PAQR3 in ESCC cell lines was measured after treatment with the demethylating agent 5-aza-2'-deoxycytidine (5-Aza-CdR). The effects of overexpression of PAQR3 on cell proliferation, colony formation, invasion, and tumorigenesis were investigated. It was found that the PAQR3 mRNA level was significantly lower in ESCC than that in adjacent normal tissues (P=0.0318). Low PAQR3 expression was significantly associated with more advanced TNM stage (P=0.0093) and absent lymph node involvement (P=0.0324). Compared to normal esophageal epithelial cells, ESCC cells had significantly lower levels of PAQR3. 5-Aza-CdR treatment led to an induction of PAQR3 in ESCC cells. Enforced expression of PAQR3 significantly inhibited ESCC cell proliferation, colony formation and invasion. Moreover, PAQR3 overexpression blocked cell cycle transition from G1 to S phase, which was associated with induction of p27 and p21 and reduction of cyclin D1, CDK4, and CDK2. Mechanistically, overexpression of PAQR3 suppressed the phosphorylation of ERK1/2 in ESCC cells. In vivo tumorigenic studies confirmed that PAQR3 overexpression retarded the growth of ECA-109 xenograft tumors and inhibited the activation of ERK signaling. Taken together, PAQR3 is epigenetically silenced in ESCC and restoration of PAQR3 suppresses the aggressive phenotype of ESCC cells. Therefore, PAQR3 may represent a potential target for the treatment of ESCC.

A synthetic peptide hijacks the catalytic subunit of class I PI3K to suppress the growth of cancer cells

Activation of class I Phosphoinositide 3-kinases (PI3Ks) by mutation or overexpression closely correlates with the development of various human cancers. Class I PI3Ks are heterodimers composed of p110 catalytic subunits and regulatory subunits represented by p85. PAQR3 has been found to inhibit p110α activity by blocking its interaction with p85. In this study, we identified the N-terminal 6-55 amino acid residues of PAQR3 being sufficient for its interaction with p110α. A synthetic peptide, P6-55, that contains the N-terminus of PAQR3 could disrupt the interactions of p110α with both PAQR3 and p85. The activity of PI3K was also inhibited by P6-55, accompanied by significant inhibition of cancer cell proliferation. In a xenograft mouse model, P6-55 was able to reduce tumor growth in vivo. Furthermore, P6-55 was capable of inhibiting the elevated basal PI3K activity of H1047R, a hotspot mutation found in many types of human cancers. The cell proliferation and migration of cancer cells bearing H1047R mutation were also reduced by P6-55. In conclusion, our study provides a proof of concept that blocking the interaction of p110α with p85 by a peptide can serve as a new strategy to inhibit the oncogenic activity of PI3K in cancer therapy.

Overexpression of miR-15b-5p promotes gastric cancer metastasis by regulating PAQR3

Gastric cancer (GC) is the fifth most common cancer in the world, with 952,000 new cases diagnosed in 2012. Tumor metastasis is the major cause of cancer recurrence and death. miR-15b-5p has been reported to be dysregulated in numerous types of cancers. However, the role of miR-15b-5p in GC metastasis remains unclear. An miRNA microarray was adopted to analyze the miRNA expression profile. By employing quantitative real-time polymerase chain reaction (qRT-PCR), miR-15b-5p expression levels were detected in GC cell lines, tissues and plasma samples. In addition, the effects of miR-15b-5p on cell proliferation, migration and invasion were studied by applying gain-of-function approaches. Moreover, the target of miR-15b-5p was assessed by dual-luciferase assay, and the mechanism underlying the regulation of GC metastasis by miR-15b-5p was assessed by rescue experiments. The results revealed that miR-15b-5p was upregulated in GC cell lines, tissues and plasma samples. A high plasma level of miR-15b-5p was correlated with distant tumor metastasis. In addition, overexpression of miR‑15b-5p in GC cells promoted cell proliferation, migration, invasion and epithelial-mesenchymal transition (EMT). Moreover, progestin and adipoQ receptor family member 3 (PAQR3) was found to be a direct target of miR-15b-5p and re-expression of PAQR3 in miR-15b-5p-overexpressing GC cells partly attenuated the proliferation, migration and invasion. These findings revealed that miR-15b-5p promotes the metastasis of GC cells through PAQR3 and may represent a potential biomarker of GC.

[Expression and Clinical Significance of Progesterone and Adiponectin Receptor Family Member 3 in Lung Cancer]

BACKGROUND

Progesterone and adiponectin receptor family member 3 (PAQR3) is a recently discovered tumor suppressor gene, which affects the development of a tumor by inhibiting cell proliferation, cell malignant transformation, angiogenesis, and tumor metastasis. This study investigates the expression of PAQR3 in lung cancer and its clinical significance.

METHODS

A total of 106 patients with lung cancer received surgical treatment in hospital, and adjacent normal tissues of these patients were utilized as control group. The diagnosis of all patients was confirmed through clinical pathology. The expression of PAQR3 protein was detected by immunohistochemistry in lung cancer and adjacent normal tissues. The clinical significance of its expression was also investigated.

RESULTS

The positive expression rate of PAQR3 protein in lung cancer was lower than that in adjacent normal tissues (P<0.01). The positive expression rate of PAQR3 protein was unrelated to age, tumor size, and gender, but it exhibited a significant relationship with the pathological type and differentiation, TNM staging, and lymph node metastasis (P<0.05). Kaplan-Meier survival analysis showed that the five-year survival rate of patients with PAQR3 protein positive expression was higher than that in patients with negative expression (P=0.026).

CONCLUSIONS

The expression of PAQR3 protein significantly decreased in lung cancer, indicating that PAQR3 protein plays an important role in the pathogenesis of PAQR3 in lung cancer.

Identification of an adaptor protein that facilitates Nrf2-Keap1 complex formation and modulates antioxidant response

Nrf2 plays a key role in the protection of the body against environmental stress via inducible expression of detoxification and antioxidant enzymes. Keap1 functions as a sensor for oxidative and electrophilic stresses and promotes Nrf2 degradation via its E3 ligase activity. Modulation of the Nrf2-Keap1 pathway has been extensively explored as a strategy to combat against drug toxicity and stress-induced diseases. Here we report a new player that modulates the Nrf2-Keap1 pathway. PAQR3, a membrane protein specifically localized in the Golgi apparatus, negatively regulates the expression of an array of Nrf2 target genes and alters cellular level of reactive oxygen species. PAQR3 tethers Nrf2 and Keap1, but not small MAF proteins to the Golgi apparatus. PAQR3 interacts with both Nrf2 and Keap1 and facilitates the interaction of Nrf2 with Keap1. PAQR3 promotes ubiquitination and degradation of Nrf2. Disruption of PAQR3 interaction with Nrf2 and Keap1 by a synthetic peptide reduces Nrf2 ubiquitination and elevates expression of Nrf2 target genes. At the animal level, deletion of PAQR3 increases Nrf2 protein level and the expression of Nrf2 target genes. In conclusion, our study pinpoints that PAQR3 functions as an adaptor protein to promote Nrf2-Keap1 complex formation, thereby modulating the Nrf2-Keap2 pathway and playing an important role in controlling antioxidant response of the cell.

PAQR3 regulates Golgi vesicle fission and transport via the Gβγ-PKD signaling pathway

Heterotrimeric G proteins function at diverse subcellular locations, in addition to canonical signaling at the plasma membrane (PM). Gβγ signals at the Golgi, via protein kinase D (PKD), to regulate fission of PM-destined vesicles. However, the mechanism by which Gβγ is regulated at the Golgi in this process remains elusive. Recent studies have revealed that PAQR3 (Progestin and AdipoQ Receptor 3), also called RKTG (Raf Kinase Trapping to the Golgi), interacts with the Gβ subunit and localizes Gβ to the Golgi thereby inhibiting Gβγ signaling at the PM. Herein we show that, in contrast to this inhibition of canonical Gβγ signaling at the PM, PAQR3 promotes Gβγ signaling at the Golgi. Expression of PAQR3 causes fragmentation of the Golgi, while a Gβ binding-deficient mutant of PAQR3 does not cause Golgi fragmentation. Also, a C-terminal fragment of GRK2 (GRK2ct), which interacts with Gβγ and inhibits Gβγ signaling, and gallein, a small molecule inhibitor of Gβγ, are both able to inhibit PAQR3-mediated Golgi fragmentation. Furthermore, a dominant negative form of PKD (PKD-DN) and a pharmacological inhibitor of PKD, Gö6976, also inhibit PAQR3-mediated fragmentation of the Golgi. Importantly, expression of the Gβ binding-deficient mutant of PAQR3 inhibits the constitutive transport of the model cargo protein VSV-G from the Golgi to the PM, indicating the involvement of PAQR3 in Golgi-to PM vesicle transport and a dominant negative role for this mutant. Collectively, these results reveal a novel role for the newly characterized, Golgi-localized PAQR3 in regulating Gβγ at the non-canonical subcellular location of the Golgi and thus for controlling Golgi-to-PM protein transport via the Gβγ-PKD signaling pathway.