Cancer-associated fibroblasts nurture LGR5 marked liver tumor-initiating cells and promote their tumor formation, growth, and metastasis

BACKGROUND & AIMS

In liver cancer, leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5) compartment represents an important tumor-initiating cell (TIC) population and served as a potential therapeutic target. Cancer-associated fibroblasts (CAFs) is a critical part of the tumor microenvironment, heavily influenced TIC function and fate. However, deeply investigations have been hindered by the lack of accurate preclinical models to investigate the interaction between CAFs and TIC. Organoids model have achieved major advancements as a precious research model for recapitulating the morphological aspects of organs, and thus also serving as a candidate model to investigate the mutual interaction between different cell types. Consequently, this study aimed to construct a three-dimensional (3D) co-culture organoid model of primary LGR5-expressing tumor stem cells from primary murine liver tumors with CAFs to investigate the impact of CAFs on LGR5 marked TICs in liver cancer.

MATERIALS AND METHODS

First, both of the transgenic LGR5-diphtheria toxin receptor (DTR)-GFP knock-in mice and transgenic Rosa26-mT mice developed primary liver tumors by diethylnitrosamine (DEN) administration. Tumor organoids and CAFs were generated from those primary liver cancer separately. Second, LGR5-expressing TICs organoid with CAFs were established ex vivo based on cell-cell contact or trans-well co-culture system, and the mutual influence between those two types of cells was further investigated. Subsequently, immunodeficient mouse-based xenograft model was further adopted to evaluate the influence of CAFs to LGR5 tumor stem cell, tumor formation, and metastasis.

RESULTS

The co-culture organoid model composed of murine liver tumor LGR5+ tumor-initiating cells and CAFs in 3D co-culture was successfully established, with the intention to investigate their mutual interaction. The existence of CAFs upon engrafting tumor organoids resulted in dramatic higher number of LGR5+ cells in the neoplasia when compared with engrafting tumor organoids alone. Furthermore, ex vivo culture of isolated LGR5+ cells from tumors of co-engrafted mice formed significantly larger size of organoids than mono-engrafted. Our results also indicated significantly larger size and number of formed organoids, when LGR5+ cells co-cultured with CAF in both cell-cell contact and paracrine signaling in vitro, comparing to LGR5+ cells alone. Furthermore, we found that specific knockout of LGR5 expressing cells suppressed CAF-mediated promotion of tumor formation, growth, and metastasis in the experimental mice model.

CONCLUSIONS

Altogether, in a 3D co-culture type of murine liver LGR5+ cells and cancer-associated fibroblasts, we have demonstrated robust effects of CAFs in the promotion of LGR5 marked liver TICs. We also further revealed the influence of tumor microenvironment on stem cell-related therapy, suggesting the possibility of combing CAF-targeted and tumor stem cell targeted therapy in treating liver cancer.

Honokiol Affects Stem Cell Viability by Suppressing Oncogenic YAP1 Function to Inhibit Colon Tumorigenesis

Honokiol (HNK) is a biphenolic compound that has been used in traditional medicine for treating various ailments, including cancers. In this study, we determined the effect of HNK on colon cancer cells in culture and in a colitis-associated cancer model. HNK treatment inhibited proliferation and colony formation while inducing apoptosis. In addition, HNK suppressed colonosphere formation. Molecular docking suggests that HNK interacts with reserve stem cell marker protein DCLK1, with a binding energy of -7.0 Kcal/mol. In vitro kinase assays demonstrated that HNK suppressed the DCLK1 kinase activity. HNK also suppressed the expression of additional cancer stem cell marker proteins LGR5 and CD44. The Hippo signaling pathway is active in intestinal stem cells. In the canonical pathway, YAP1 is phosphorylated at Ser127 by upstream Mst1/2 and Lats1/2. This results in the sequestration of YAP1 in the cytoplasm, thereby not allowing YAP1 to translocate to the nucleus and interact with TEAD1-4 transcription factors to induce gene expression. However, HNK suppressed Ser127 phosphorylation in YAP1, but the protein remains sequestered in the cytoplasm. We further determined that this occurs by YAP1 interacting with PUMA. To determine if this also occurs in vivo, we performed studies in an AOM/DSS induced colitis-associated cancer model. HNK administered by oral gavage at a dose of 5mg/kg bw for 24 weeks demonstrated a significant reduction in the expression of YAP1 and TEAD1 and in the stem marker proteins. Together, these data suggest that HNK prevents colon tumorigenesis in part by inducing PUMA-YAP1 interaction and cytoplasmic sequestration, thereby suppressing the oncogenic YAP1 activity.

LGR5 enhances the osteoblastic differentiation of MC3T3-E1 cells through the Wnt/β-catenin pathway

Leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5) is a Wnt-associated gene that contributes to cell proliferation and self-renewal in various organs. LGR5 is expressed in Ewing sarcoma, and LGR5-overexpressing mesenchymal stem cells promote fracture healing. However, the effects of LGR5 on osteoblastic differentiation remain unclear. The aim of the present study was to explore the function of LGR5 in osteoblastic differentiation. LGR5 was overexpressed or knocked down in the MC3T3-E1 pre-osteoblastic cell line via lentiviral transfection and its function in osteoblastic differentiation was investigated. The mRNA expression levels of the osteoblast differentiation markers alkaline phosphatase (ALP), osteocalcin and collagen type I a1 were determined, and ALP and Alizarin red staining were performed. In addition, the effects of LGR5 modulation on β-catenin and the expression of target genes in the Wnt pathway were investigated. The results revealed that the overexpression of LGR5 promoted osteoblastic differentiation. This was associated with enhancement of the stability of β-catenin and its levels in the cell nucleus, which enabled it to activate Wnt signaling. By contrast, the inhibition of LGR5 decreased the osteogenic capacity of MC3T3-E1 cells. These results indicate that LGR5 is a positive regulator of osteoblastic differentiation, whose effects are mediated through the Wnt/β-catenin signaling pathway. This suggests suggesting that the regulation of LGR5/Wnt/β-catenin signaling has potential as a therapy for osteoporosis.

LGR5 promotes hepatocellular carcinoma metastasis through inducting epithelial-mesenchymal transition

The purpose of the present study was to investigate the prognostic value of Leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5) in hepatocellular carcinoma (HCC) and its role in promoting HCC metastasis. The expression level of LGR5 in liver tumor tissues and adjacent non-tumor tissues were detected adopting immunohistochemistry (IHC), real-time PCR (RT-PCR) and western blot assays. Chi-square test was used to evaluate the correlation between LGR5 expression and clinicopathological characteristics. In addition, we assessed the relationship between LGR5 and two epithelial-mesenchymal transition (EMT) markers (E-cadherin and N-cadherin) in HCC tissues and cell lines. Our results showed that the expression of LGR5 was significantly higher in liver tumor tissues than in adjacent non-tumor tissues. Moreover, up-regulated LGR5 was associated with larger tumor diameter (>5cm, P=0.001), higher TNM stage (P=0.021), increased recurrence (P=0.023) and growing metastasis (P=0.030). Besides, we found that the expression level of LGR5 was correlated with E-cadherin and N-cadherin. In conclusion, up-regulated LGR5 in HCC patients is associated with malignant clinicopathological characteristics. LGR5 may promote HCC metastasis through inducting EMT process, and thus can be regarded as a candidate biomarker for prognosis and as a target in therapy.

LGR5 promotes the proliferation of colorectal cancer cells via the Wnt/β-catenin signaling pathway

Leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5) is an established cancer stem cell marker and is a target gene of the Wnt/β-catenin signaling pathway, a critical pathway in the process of tumor initiation and growth. In the present study, the mRNA expression levels of LGR5, adenomatous polyposis coli (APC) and β-catenin were detected in 20 colorectal cancer (CRC) tissues and matched healthy mucosa samples using reverse transcription-quantitative polymerase chain reaction. HT-29 CRC cell line was treated with siRNA-Lgr5; the APC, β-catenin and LGR5 RNA expressions were detected and cell viability was measured using a CCK8 assay. The results revealed that LGR5 was significantly overexpressed in CRC tissue compared with healthy mucosa (P<0.05). Furthermore, knockdown of LGR5 by small interfering RNA decreased the expression of APC and β-catenin in HT29 colon cancer cells as well as inhibited the proliferation of HT29 cells. These findings demonstrated that LGR5 expression is critical for the promotion of neoplastic CRC cell proliferation, indicating that LGR5 may be a novel therapeutic target for CRC.