Clinical significance of Gremlin 1 in cervical cancer and its effects on cancer stem cell maintenance

GREM1 knockdown regulates the proliferation, apoptosis and EMT of benign prostatic hyperplasia by suppressing the STAT3/c-Myc signaling

BACKGROUND

Gremlin 1 (GREM1) has been reported to be highly expressed in prostate hyperplasia tissues. However, the role and molecular mechanism of GREM1 in benign prostatic hyperplasia (BPH) is still unclear.

METHODS

In this study, expression of GREM1 in BPH-1 cells was detected by western blot assay. Cell counting kit-8 assay was performed to assess cell proliferation. Flow cytometry and western blot were used to assess cell apoptosis and cell cycle. The EMT process was detected by western blot assay and immunofluorescence staining. In addition, colivelin was used as a STAT3 activator and the expressions of STAT3/c-Myc signaling were assessed by western blot assay.

RESULTS

The data showed that GREM1 silencing inhibited BPH-1 cell proliferation and promoted cell apoptosis. Moreover, GREM1 silencing repressed the cell cycle progression and the development of EMT. In addition, knockdown of GREM1 suppressed the expression of the STAT3/c-Myc signaling in BPH-1 cells and colivelin treatment rehabilitated this signaling. Moreover, c-Myc overexpression or colivelin reversed the effects of GREM1 silencing on BPH-1 cell proliferation, cell apoptosis, cell cycle, as well as EMT.

CONCLUSION

To sum up, GREM1 silencing may alleviate the BPH progress by inhibiting the STAT3/c-Myc signaling.

Regulation of Cervical Cancer Development by a Novel Circ_0000212/miR-1236-3p/GREM1 ceRNA Crosstalk

Circular RNAs (circRNAs) possess important functions in cervical carcinogenesis by operating as competing endogenous RNAs (ceRNAs). Our preliminary bioinformatics predicted the potential circ_0000212/microRNA (miR)-1236-3p/gremlin 1 (GREM1) ceRNA crosstalk. Thus, we further elucidated whether the novel ceRNA crosstalk can participate in cervical cancer development. Circ_0000212, miR-1236-3p and GREM1 were quantified by real-time quantitative polymerase chain reaction (qPCR) and immunoblotting. 5-ethynyl-2'-deoxyuridine (EdU) assay, flow cytometry, and tube formation assay were performed to assess cell proliferation, apoptosis and tube formation, respectively. Transwell assay was used to detect cell migration and invasion. Mouse xenografts were established to evaluate the role of circ_0000212 in vivo. Dual-luciferase reporter assay was performed to verify the direct relationship between miR-1236-3p and circ_0000212 or GREM1. Circ_0000212 expression was elevated in human cervical cancer. Silencing of endogenous circ_0000212 hindered cancer cell proliferation, motility and invasion and induced apoptosis, as well as diminished the tube formation of human umbilical vein endothelial cells (HUVECs) in vitro. Circ_0000212 silencing also weakened tumor growth in vivo. Mechanistically, circ_0000212 directly bound to miR-1236-3p, and downregulation of miR-1236-3p reversed these effects of circ_0000212 silencing on cell malignant phenotypes and HUVEC tube formation. GREM1 was a direct miR-1236-3p target, and its expression was regulated by circ_0000212 through miR-1236-3p. Moreover, miR-1236-3p upregulation impeded cancer cell malignant phenotypes and HUVEC tube formation by targeting GREM1. Our findings identify a novel ceRNA regulatory network, circ_0000212/miR-1236-3p/GREM1 axis, in cervical carcinogenesis, and provide potential targets that can be explored for therapeutic interventions.

Profiling and targeting cancer stem cell signaling pathways for cancer therapeutics

Tumorigenic cancer stem cells (CSCs) represent a subpopulation of cells within the tumor that express genetic and phenotypic profiles and signaling pathways distinct from the other tumor cells. CSCs have eluded many conventional anti-oncogenic treatments, resulting in metastases and relapses of cancers. Effectively targeting CSCs' unique self-renewal and differentiation properties would be a breakthrough in cancer therapy. A better characterization of the CSCs' unique signaling mechanisms will improve our understanding of the pathology and treatment of cancer. In this paper, we will discuss CSC origin, followed by an in-depth review of CSC-associated signaling pathways. Particular emphasis is given on CSC signaling pathways' ligand-receptor engagement, upstream and downstream mechanisms, and associated genes, and molecules. Signaling pathways associated with regulation of CSC development stand as potential targets of CSC therapy, which include Wnt, TGFβ (transforming growth factor-β)/SMAD, Notch, JAK-STAT (Janus kinase-signal transducers and activators of transcription), Hedgehog (Hh), and vascular endothelial growth factor (VEGF). Lastly, we will also discuss milestone discoveries in CSC-based therapies, including pre-clinical and clinical studies featuring novel CSC signaling pathway cancer therapeutics. This review aims at generating innovative views on CSCs toward a better understanding of cancer pathology and treatment.

Bone morphogenetic protein signaling is a possible therapeutic target in gynecologic cancer

Bone morphogenetic proteins (BMPs) belong to the transforming growth factor β (TGFβ) superfamily. BMPs play crucial roles in embryogenesis and bone remodeling. Recently, BMP signaling has been found to have diverse effects on different types of tumors. In this review, we summarized the effects of BMP signaling on gynecologic cancer. BMP signaling has tumor-promoting effects on ovarian cancer (OC) and endometrial cancer (EC), whereas it has tumor-suppressing effects on uterine cervical cancer (UCC). Interestingly, EC has frequent gain-of-function mutations in ACVR1, encoding one of the type I BMP receptors, which are also observed in fibrodysplasia ossificans progressiva and diffuse intrinsic pontine glioma. Little is known about the relationship between BMP signaling and other gynecologic cancers. Tumor-promoting effects of BMP signaling in OC and EC are dependent on the promotion of cancer stemness and epithelial-mesenchymal transition (EMT). In accordance, BMP receptor kinase inhibitors suppress the cell growth and migration of OC and EC. Since both cancer stemness and EMT are associated with chemoresistance, BMP signaling activation might also be an important mechanism by which OC and EC patients acquire chemoresistance. Therefore, BMP inhibitors are promising for OC and EC patients even if they become resistant to standard chemotherapy. In contrast, BMP signaling inhibits UCC growth in vitro. However, the in vivo effects of BMP signaling have not been elucidated in UCC. In conclusion, BMP signaling has a variety of functions, depending on the types of gynecologic cancer. Therefore, targeting BMP signaling should improve the treatment of patients with gynecologic cancer.

Discovery of ginisortamab, a potent and novel anti-gremlin-1 antibody in clinical development for the treatment of cancer

Gremlin-1, a high-affinity antagonist of bone morphogenetic proteins (BMP)-2, -4, and -7, is implicated in tumor initiation and progression. Increased gremlin-1 expression, and therefore suppressed BMP signaling, correlates with poor prognosis in a range of cancer types. A lack of published work using therapeutic modalities has precluded the testing of the hypothesis that blocking the gremlin-1/BMP interaction will provide benefits to patients. To address this shortfall, we developed ginisortamab (UCB6114), a first-in-class clinical anti-human gremlin-1 antibody, currently in clinical development for the treatment of cancer, along with its murine analog antibody Ab7326 mouse immunoglobulin G1 (mIgG1). Surface plasmon resonance assays revealed that ginisortamab and Ab7326 mIgG1 had similar affinities for human and mouse gremlin-1, with mean equilibrium dissociation constants of 87 pM and 61 pM, respectively. The gremlin-1/Ab7326 antigen-binding fragment (Fab) crystal structure revealed a gremlin-1 dimer with a Fab molecule bound to each monomer that blocked BMP binding. In cell culture experiments, ginisortamab fully blocked the activity of recombinant human gremlin-1, and restored BMP signaling pathways in human colorectal cancer (CRC) cell lines. Furthermore, in a human CRC - fibroblast co-culture system where gremlin-1 is produced by the fibroblasts, ginisortamab restored BMP signaling in both the CRC cells and fibroblasts, demonstrating its activity in a relevant human tumor microenvironment model. The safety and efficacy of ginisortamab are currently being evaluated in a Phase 1/2 clinical trial in patients with advanced solid tumors (NCT04393298).

Long noncoding RNA long intergenic non-protein-coding RNA 173 contributes to nasopharyngeal carcinoma progression by regulating microRNA-765/Gremlin 1 pathway

BACKGROUND

Long intergenic non-protein-coding RNA 173 (LINC00173) executes vital functions in various cancers. Nevertheless, its role and expression in nasopharyngeal carcinoma (NPC) have yet to be investigated. Here, we investigated its effects on the malignancy characteristics of NPC and elucidated the potential molecular mechanism of LINC00173 in NPC progression.

METHODS

Quantitative real-time reverse transcription-PCR (qRT-PCR) and immunoblotting were conducted to estimate the LINC00173, microRNA-765 (miR-765), and Gremlin 1 (GREM1) expressions in NPC cells and tissues. Cell counting kit-8 (CCK8), colony formation, and wound healing experiments were done to evaluate the proliferation, growth, and migration of NPC cells, respectively. The tumorous growth of NPC cells in vivo was assessed through the xenograft tumor experiment. Furthermore, the interactions among miR-765, LINC00173, and GREM1 were investigated through bioinformatics analyses, luciferase reporter and RNA immunoprecipitation chip assays.

RESULTS

An upregulated LINC00173 expression was found in NPC cell lines and tissues. The functional experiments uncovered that its downregulation repressed NPC cell proliferation, growth, and migration. In addition, LINC00173 knockdown hampered the NPC cells' tumorous growth in vivo. These effects could partially be reversed by downregulating miR-765. GREM1 is a downstream target of miR-765. GREM1 knockdown could repress the proliferation, growth, and migration of NPC cells. Nonetheless, these anti-tumor effects could be abolished by miR-765 downregulation. Mechanistically, LINC00173 increased the expression of GREM1 by binding with miR-765.

CONCLUSIONS

LINC00173 functions as an oncogenic factor by binding with miR-765 to promote the progression of NPC via GREM1 upregulation. This study provides a novel insight into the molecular mechanisms involved in NPC progression.

Timosaponin AIII Inhibits Migration and Invasion Abilities in Human Cervical Cancer Cells through Inactivation of p38 MAPK-Mediated uPA Expression In Vitro and In Vivo

Cervical cancer is one of the most common gynecologic cancers globally that require novel approaches. Timosaponin AIII (TSAIII) is a steroidal saponin that displays beneficial effects in antitumor activities. However, the effect of TSAIII on human cervical cancer remains unknown. In this study, we found that TSAIII showed no influence on cell viability, cytotoxicity, cell cycle distribution and apoptosis induction in human cervical cancer cells. TSAIII was revealed to have a significant inhibitory effect on cell migration and invasion through the downregulation of invasion-related uPA expression and p38 MAPK activation in both human cervical cancer cells and cervical cancer stem cells (CCSCs), indicating that the p38 MAPK-uPA axis mediated the TSAIII-inhibited capacity of cellular migration and invasion. In a synergistic inhibition assay, a TSAIII plus p38 siRNA cotreatment revealed a greater inhibition of uPA expression, migration and invasion in human cervical cancer cells. In an immunodeficient mouse model, TSAIII significantly inhibited lung metastases from human cervical cancer SiHa cells without TSAIII-induced toxicity. These findings first revealed the inhibitory effects of TSAIII on the progression of human cervical cancer through its downregulation of p38 MAPK-uPA axis activation. Therefore, TSAIII might provide a potential strategy for auxiliary therapy in human cervical cancer.

Cervical cancer heterogeneity: a constant battle against viruses and drugs

Cervical cancer is the first identified human papillomavirus (HPV) associated cancer and the most promising malignancy to be eliminated. However, the ever-changing virus subtypes and acquired multiple drug resistance continue to induce failure of tumor prevention and treatment. The exploration of cervical cancer heterogeneity is the crucial way to achieve effective prevention and precise treatment. Tumor heterogeneity exists in various aspects including the immune clearance of viruses, tumorigenesis, neoplasm recurrence, metastasis and drug resistance. Tumor development and drug resistance are often driven by potential gene amplification and deletion, not only somatic genomic alterations, but also copy number amplifications, histone modification and DNA methylation. Genomic rearrangements may occur by selection effects from chemotherapy or radiotherapy which exhibits genetic intra-tumor heterogeneity in advanced cervical cancers. The combined application of cervical cancer therapeutic vaccine and immune checkpoint inhibitors has become an effective strategy to address the heterogeneity of treatment. In this review, we will integrate classic and recently updated epidemiological data on vaccination rates, screening rates, incidence and mortality of cervical cancer patients worldwide aiming to understand the current situation of disease prevention and control and identify the direction of urgent efforts. Additionally, we will focus on the tumor environment to summarize the conditions of immune clearance and gene integration after different HPV infections and to explore the genomic factors of tumor heterogeneity. Finally, we will make a thorough inquiry into completed and ongoing phase III clinical trials in cervical cancer and summarize molecular mechanisms of drug resistance among chemotherapy, radiotherapy, biotherapy, and immunotherapy.

Gremlin-1 Promotes Colorectal Cancer Cell Metastasis by Activating ATF6 and Inhibiting ATF4 Pathways

Cancer cell survival, function and fate strongly depend on endoplasmic reticulum (ER) proteostasis. Although previous studies have implicated the ER stress signaling network in all stages of cancer development, its role in cancer metastasis remains to be elucidated. In this study, we investigated the role of Gremlin-1 (GREM1), a secreted protein, in the invasion and metastasis of colorectal cancer (CRC) cells in vitro and in vivo. Firstly, public datasets showed a positive correlation between high expression of GREM1 and a poor prognosis for CRC. Secondly, GREM1 enhanced motility and invasion of CRC cells by epithelial–mesenchymal transition (EMT). Thirdly, GREM1 upregulated expression of activating transcription factor 6 (ATF6) and downregulated that of ATF4, and modulation of the two key players of the unfolded protein response (UPR) was possibly through activation of PI3K/AKT/mTOR and antagonization of BMP2 signaling pathways, respectively. Taken together, our results demonstrate that GREM1 is an invasion-promoting factor via regulation of ATF6 and ATF4 expression in CRC cells, suggesting GREM1 may be a potential pharmacological target for colorectal cancer treatment.

Insights into the Role of Gremlin-1, a Bone Morphogenic Protein Antagonist, in Cancer Initiation and Progression

The bone morphogenic protein (BMP) antagonist Gremlin-1 is a biologically significant regulator known for its crucial role in tissue differentiation and embryonic development. Nevertheless, it has been reported that Gremlin-1 can exhibit its function through BMP dependent and independent pathways. Gremlin-1 has also been reported to be involved in organ fibrosis, which has been correlated to the development of other diseases, such as renal inflammation and diabetic nephropathy. Based on growing evidence, Gremlin-1 has recently been implicated in the initiation and progression of different types of cancers. Further, it contributes to the stemness state of cancer cells. Herein, we explore the recent findings on the role of Gremlin-1 in various cancer types, including breast, cervical, colorectal, and gastric cancers, as well as glioblastomas. Additionally, we highlighted the impact of Gremlin-1 on cellular processes and signaling pathways involved in carcinogenesis. Therefore, it was suggested that Gremlin-1 might be a promising prognostic biomarker and therapeutic target in cancers.

Gremlin-1 Promotes Metastasis of Breast Cancer Cells by Activating STAT3-MMP13 Signaling Pathway

Gremlin-1 (GREM1), one of the bone morphogenetic protein (BMP) antagonists, can directly bind to BMPs. GREM1 is involved in organogenesis, tissue differentiation, and organ fibrosis. Recently, numerous studies have reported the oncogenic role of GREM1 in cancer. However, the role of GREM1 in metastasis of breast cancer cells and its underlying mechanisms remain poorly understood. The role of GREM1 in breast cancer progression was assessed by measuring growth, migration, and invasion of breast cancer cells. An orthotopic breast cancer mouse model was used to investigate the role of GREM1 in lung metastasis of breast cancer cells. GREM1 knockdown suppressed the proliferation of breast cancer cells, while its overexpression increased their growth, migration, and invasion. Cells with Grem1-knockdown showed much lower tumor growth rates and lung metastasis than control cells. GREM1 enhanced the expression of matrix metalloproteinase 13 (MMP13). A positive correlation between GREM1 and MMP13 expression was observed in breast cancer patients. GREM1 activated signal transducer and activator of transcription 3 (STAT3) transcription factor involved in the expression of MMP13. Our study suggests that GREM1 can promote lung metastasis of breast cancer cells through the STAT3-MMP13 pathway. In addition, GREM1 might be a promising therapeutic target for breast cancer metastasis.

Targeted Disruption of Bone Marrow Stromal Cell-Derived Gremlin1 Limits Multiple Myeloma Disease Progression In Vivo

In most instances, multiple myeloma (MM) plasma cells (PCs) are reliant on factors made by cells of the bone marrow (BM) stroma for their survival and growth. To date, the nature and cellular composition of the BM tumor microenvironment and the critical factors which drive tumor progression remain imprecisely defined. Our studies show that Gremlin1 (Grem1), a highly conserved protein, which is abundantly secreted by a subset of BM mesenchymal stromal cells, plays a critical role in MM disease development. Analysis of human and mouse BM stromal samples by quantitative PCR showed that GREM1/Grem1 expression was significantly higher in the MM tumor-bearing cohorts compared to healthy controls (p < 0.05, Mann–Whitney test). Additionally, BM-stromal cells cultured with 5TGM1 MM PC line expressed significantly higher levels of Grem1, compared to stromal cells alone (p < 0.01, t-test), suggesting that MM PCs promote increased Grem1 expression in stromal cells. Furthermore, the proliferation of 5TGM1 MM PCs was found to be significantly increased when co-cultured with Grem1-overexpressing stromal cells (p < 0.01, t-test). To examine the role of Grem1 in MM disease in vivo, we utilized the 5TGM1/KaLwRij mouse model of MM. Our studies showed that, compared to immunoglobulin G (IgG) control antibody-treated mice, mice treated with an anti-Grem1 neutralizing antibody had a decrease in MM tumor burden of up to 81.2% (p < 0.05, two-way ANOVA). The studies presented here demonstrate, for the first time, a novel positive feedback loop between MM PCs and BM stroma, and that inhibiting this vicious cycle with a neutralizing antibody can dramatically reduce tumor burden in a preclinical mouse model of MM.

Secreted BMP antagonists and their role in cancer and bone metastases

Bone morphogenetic proteins (BMPs) are multifunctional secreted cytokines that act in a highly context-dependent manner. BMP action extends beyond the induction of cartilage and bone formation, to encompass pivotal roles in controlling tissue and organ homeostasis during development and adulthood. BMPs signal via plasma membrane type I and type II serine/threonine kinase receptors and intracellular SMAD transcriptional effectors. Exquisite temporospatial control of BMP/SMAD signalling and crosstalk with other cellular cues is achieved by a series of positive and negative regulators at each step in the BMP/SMAD pathway. The interaction of BMP ligand with its receptors is carefully controlled by a diverse set of secreted antagonists that bind BMPs and block their interaction with their cognate BMP receptors. Perturbations in this BMP/BMP antagonist balance are implicated in a range of developmental disorders and diseases, including cancer. Here, we provide an overview of the structure and function of secreted BMP antagonists, and summarize recent novel insights into their role in cancer progression and bone metastasis. Gremlin1 (GREM1) is a highly studied BMP antagonist, and we will focus on this molecule in particular and its role in cancer. The therapeutic potential of pharmacological inhibitors for secreted BMP antagonists for cancer and other human diseases will also be discussed.

Prognostic and clinicopathological significance of Hapto and Gremlin1 expression in extrahepatic cholangiocarcinoma

Background: Some studies have demonstrated that Hapto and Gremlin1 play an important biological role in many neoplasms. However, the role of Hapto and Gremlin1 in extrahepatic cholangiocarcinoma (ECC) remains to be revealed. Thus, this study investigated the prognostic and clinicopathological significance of Hapto and Gremlin1 expression in ECC.

Methods: We examined Hapto and Gremlin1 expression in 100 ECC, 30 peritumoral tissues, 10 adenoma and 15 normal biliary tract tissues using EnVision immunohistochemistry. The relationship between Hapto and Gremlin 1 expression and clinicopathological parameters was evaluated using the χ² test or Fisher's exact test. The overall survival of patients was analyzed using Kaplan-Meier univariate survival analysis and log-rank tests.

Results: Hapto and Gremlin1 proteins were overexpressed in ECC compared to peritumoral tissues, adenoma, and normal biliary tract (P<0.05 or P<0.01). The positive rate of Hapto and Gremlin1 expression was significantly higher in cases with poor differentiation, lymph node metastasis, invasion of surrounding tissues and organs, a tumor-node-metastasis (TNM) stage of III or IV and no resection. Kaplan-Meier survival analysis showed that ECC patients with positive Hapto and/or Gremlin1 expression survived significantly shorter than patients with negative Hapto and/or Gremlin1 expression. Cox multivariate analysis revealed that positive Hapto and Gremlin1 expression were independent poor prognostic factors in ECC patients.

Conclusion: The present study indicated that positive Hapto and/or Gremlin1 expression are closely associated with the pathogenesis, clinical, pathological and biological behaviors, and poor prognosis in ECC.

Cancer-associated fibroblast-derived Gremlin 1 promotes breast cancer progression

Background

Bone morphogenetic proteins (BMPs) have been reported to maintain epithelial integrity and to antagonize the transforming growth factor β (TGFβ)-induced epithelial to mesenchymal transition. The expression of soluble BMP antagonists is dysregulated in cancers and interrupts proper BMP signaling in breast cancer.

Methods

In this study, we mined the prognostic role of BMP antagonists GREMLIN 1 (GREM1) in primary breast cancer tissues using in-house and publicly available datasets. We determined which cells express GREM1 RNA using in situ hybridization (ISH) on a breast cancer tissue microarray. The effects of Grem1 on the properties of breast cancer cells were assessed by measuring the mesenchymal/stem cell marker expression and functional cell-based assays for stemness and invasion. The role of Grem1 in breast cancer-associated fibroblast (CAF) activation was measured by analyzing the expression of fibroblast markers, phalloidin staining, and collagen contraction assays. The role of Grem1 in CAF-induced breast cancer cell intravasation and extravasation was studied by utilizing xenograft zebrafish breast cancer (co-) injection models.

Results

Expression analysis of clinical breast cancer datasets revealed that high expression of GREM1 in breast cancer stroma is correlated with a poor prognosis regardless of the molecular subtype. The large majority of human breast cancer cell lines did not express GREM1 in vitro, but breast CAFs did express GREM1 both in vitro and in vivo. Transforming growth factor β (TGFβ) secreted by breast cancer cells, and also inflammatory cytokines, stimulated GREM1 expression in CAFs. Grem1 abrogated bone morphogenetic protein (BMP)/SMAD signaling in breast cancer cells and promoted their mesenchymal phenotype, stemness, and invasion. Moreover, Grem1 production by CAFs strongly promoted the fibrogenic activation of CAFs and promoted breast cancer cell intravasation and extravasation in co-injection xenograft zebrafish models.

Conclusions

Our results demonstrated that Grem1 is a pivotal factor in the reciprocal interplay between breast cancer cells and CAFs, which promotes cancer cell invasion. Targeting Grem1 could be beneficial in the treatment of breast cancer patients with high Grem1 expression.

Electronic supplementary material

The online version of this article (10.1186/s13058-019-1194-0) contains supplementary material, which is available to authorized users.

GREM1 overexpression inhibits proliferation, migration and angiogenesis of osteosarcoma

Osteosarcoma is the most common malignancy of bone that occurs in young adults and children, with a five-year survival rate of 60-70%. Metastasis of osteosarcoma maintains an even poorer prognosis. GREM1 plays an important role in regulating organogenesis, body patterning, and tissue differentiation. However, there are limited studies on GREM1 in osteosarcomas. This study was carried out to characterize the expression and function of GREM1 in osteosarcoma cells, thus extending our understanding of osteosarcoma metastasis. GREM1 expression was detected in hBMSC, hFOB1.19, Saos-2, MG63 and U2OS cell lines using quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot analysis. Gain- and loss-of-function approaches were used to assess the biological function of GREM1 in U2OS cells. The effects of GREM1 on U2OS cell proliferation were examined using the CCK-8 and colony formation assay. Migration and invasion ability were confirmed by the wound healing and Transwell assay, respectively. Flow cytometry was used to analyse the effect of GREM1 on the cell cycle and apoptosis. The expression of GREM1 targets was evaluated by qRT-PCR and western blotting. The expression of GREM1 was significantly downregulated in osteosarcoma. GREM1 overexpression inhibited the proliferation, migration and invasion of U2OS cells. GREM1 overexpression suppressed tumour cell-induced endothelial cell migration and invasion ability. The effect of GREM1 may be transduced through regulation of the BMP target transcription factor inhibitor of MMP-2 and -9 as well as Id1. GREM1 overexpression and knockdown regulates the tumorigenesis of osteosarcoma in vivo. In conclusion, GREM1 is downregulated in osteosarcoma cells, and overexpression of GREM1 inhibits the proliferation, migration, invasion and angiogenesis abilities of osteosarcoma cells in vitro and in vivo.

Fibroblast-derived Gremlin1 localises to epithelial cells at the base of the intestinal crypt

Gremlin1 (GREM1) is a secreted glycoprotein member of the differential screening-selected gene in aberrant neuroblastoma (DAN) family of bone morphogenetic protein (BMP) antagonists, which binds to BMPs preventing their receptor engagement. Previous studies have identified that stage II colorectal cancer (CRC) patients with high levels of GREM1 gene expression in their tumour tissue have a poorer prognosis. Using a series of in silico and in situ methodologies, we demonstrate that GREM1 gene expression is significantly higher (p < 0.0001) in CRC consensus molecular subtype 4 (CMS4), compared to the other CMS subtypes and correlates (p < 0.0001) with levels of cancer-associated fibroblasts (CAFs) within the CRC tumour microenvironment (TME). Our optimised immunohistochemistry protocol identified endogenous GREM1 protein expression in both the muscularis mucosa and adjacent colonic crypt bases in mouse intestine, in contrast to RNA expression which was shown to localise specifically to the muscularis mucosa, as determined by in situ hybridisation. Importantly, we demonstrate that cells with high levels of GREM1 expression display low levels of phospho-Smad1/5, consistent with reduced BMP signalling. Taken together, these data highlight a novel paracrine signalling circuit, which involves uptake of mature GREM1 protein by colonic crypt cells following secretion from neighbouring fibroblasts in the TME.

Knockdown GREM1 suppresses cell growth, angiogenesis, and epithelial-mesenchymal transition in colon cancer

Gremlin 1 (GREM1), as a bone morphogenetic protein (BMP) antagonist and vascular endothelial growth factor receptor-2 (VEGFR2) novel agonist, has been confirmed as overexpressed in colorectal cancer (CRC) tissues but its role in carcinogenesis remains unclear. Here we reported that the GREM1 expression in mesenchymal-like colon cancer cells (SW620 and SW480) was significantly higher than that of epithelial-like colon cancer cells (Caco-2, HTC116, and HT29) and normal colon cell. Simultaneously, we analyzed two series of CRC transcriptomes from Gene Expression Omnibus (GEO) databases and found the great majority of primary CRC tissues expressed high level of GREM1 messenger RNA (mRNA) compared with adjacent normal tissues, and that the GREM1 mRNA expression is correlated with low histological grade development and stage 2 to 3 metastatic recurrence in CRC based on a data analysis of 104 different stage CRC tissue from the GEO databases. Functional studies showed that GREM1 silencing by short hairpin RNA (shRNA) significantly inhibited CRC cells proliferation, migration, the formation of vascular endothelial growth factor (VEGF)-induced capillary structure of human umbilical vein endothelial cells (HUVECs), and epithelial-mesenchymal transition in colon cancer cells by repressing phosphorylation levels of BMP downstream signal Smad1, vascular endothelial growth factor (VEGF) downstream signal matrix metallopeptidase 2 (MMP2), and metastasis-related factor C-X-C motif chemokine ligand 12 (CXCL12) expression. In addition, shGREM1 combined with VEGF inhibitor BAW2881 displayed more effective antiangiogenesis to inhibit the tube formation of HUVEC. Hence, these experiments demonstrated that GREM1 is involved in CRC development and procession and provide a new idea for CRC diagnosis, resistance therapy, and prognosis.

LncRNA PVT1 Facilitates Tumorigenesis and Progression of Glioma via Regulation of MiR-128-3p/GREM1 Axis and BMP Signaling Pathway

The current research was aimed at probing into the role of long noncoding RNA (lncRNA) PVT1 in the pathogenesis of glioma and the regulatory mechanism of PVT1/miR-128-3p/GREM1 network in glioma via regulation of the bone morphogenetic protein (BMP) signaling pathway. Microarray analysis was used for preliminary screening for candidate lncRNAs and mRNAs in glioma tissues. Real-time quantitative polymerase chain reaction, Western blot, MTT assay, flow cytometry, migration and invasion assays, and xenograft tumor model were utilized to examine the influence of the lncRNA PVT1/miR-128-3p/GREM1 network on the biological functions of glioma cells. Luciferase assay and RNA-binding protein immunoprecipitation assay were used to validate the miR-128-3p-target relationships with lncRNA PVT1 or GREM1. In addition, the impact of GREM1 on BMP signaling pathway downstream proteins BMP2 and BMP4 was detected via Western blot. LncRNA PVT1 was highly expressed in human glioma tissues and significantly associated with WHO grade (I-II vs III-IV; p < 0.05). There existed a regulatory relationship between lncRNA PVT1 and miR-128-3p as well as that between miR-128-3p and GREM1. MiR-128-3p was downregulated, whereas GREM1 was upregulated in glioma tissues in comparison with para-carcinoma tissues. Overexpression of GREM1 promoted the proliferation and metastatic potential of glioma cells, whereas miR-128-3p mimics inhibited the glioma cell activity through targeting GREM1. Furthermore, lncRNA PVT1 acted as a sponge of miR-128-3p and, thus, influenced the BMP signaling pathway downstream proteins BMP2 and BMP4 through regulating GREM1. LncRNA PVT1 modulated GREM1 and BMP downstream signaling proteins through sponging miR-128-3p, thereby promoting tumorigenesis and progression of glioma.

Prognostic significance of stromal GREM1 expression in colorectal cancer

Cancer-associated fibroblasts are the dominant cell population in the cancer stroma. Gremlin 1 (GREM1), an antagonist of the bone morphogenetic protein pathway, is expressed by cancer-associated fibroblasts in a variety of human cancers. However, its biological significance for cancer patients is largely unknown. We applied RNA in situ hybridization to evaluate the prognostic value of stromal GREM1 expression in a large cohort of 670 colorectal cancers (CRCs). Overall, GREM1 expression in CRCs was lower than that of the matched normal mucosa, and GREM1 expression had a strong positive correlation with BMI1 and inverse correlations with EPHB2 and OLFM4. RNA in situ hybridization localized the GREM expression to smooth muscle cells of the muscularis mucosa and fibroblasts around crypt bases and in the submucosal space of a normal colon. In various colon polyps, epithelial GREM1 expression was exclusively observed in traditional serrated adenomas. In total, 44% of CRCs were positive for stromal GREM1, which was associated with decreased lymphovascular invasion, a lower cancer stage, and nuclear β-catenin staining. Stromal GREM1 was significantly associated with improved recurrence-free and overall survival, although it was not found to be an independent prognostic marker in multivariate analyses. In addition, for locally advanced stage II and III CRC, it was associated with better, stage-independent clinical outcomes. In summary, CRCs are frequently accompanied by GERM1-expressing fibroblasts, which are closely associated with low lymphovascular invasion and a better prognosis, suggesting stromal GREM1 as a potential biomarker and possible candidate for targeted therapy in the treatment of CRCs.