Recently, it has been reported that long non-coding RNA (lncRNA) cancer susceptibility candidate 2 (CASC2), a novel tumor suppressor, participates in regulating the carcinogenesis and suppresses tumor progression by sponging microRNAs (miRNAs). However, the expression and function of CASC2 in hepatocellular carcinoma (HCC) remain unclear. The expression of CASC2 and miR-367 in HCC specimens and cell lines were detected by real-time PCR. Western blotting and immunohistochemistry were carried out for detection of epithelial-to-mesenchymal transition (EMT) markers in HCC. Transwell assays were used to determine migration and invasion of HCC cells. A mouse model for lung metastasis was established to evaluated HCC metastasis in vivo. The correlation among CASC2, miR-367 and F-box and WD repeat domain containing 7 (FBXW7) were disclosed by a dual-luciferase reporter assay, RIP assay and biotin pull-down assay. Here, CASC2 expression was significantly downregulated in HCC tissues, especially in aggressive and recurrent cases. In accordance, CASC2 underexpression was observed in HCC cell lines compared to LO2. In vitro and in vivo experiments revealed that CASC2 inhibited migration and invasion of HCC cells. Additionally, CASC2 repressed EMT process of HCC cells. Further studies demonstrated that CASC2 could function as a competing endogenous RNA (ceRNA) by sponging miR-367 in HCC cells. Functionally, gain- and loss-of-function studies showed that miR-367 promoted migration, invasion and EMT progression of HCC cells. Moreover, further investigations disclosed that FBXW7 was a downstream target of miR-367 and CASC2 prohibited EMT progression and subsequently exerted its anti-metastatic effects via CASC2/miR-367/FBXW7 axis in HCC cells. Clinically, CASC2 underexpression and miR-367 overexpression were closely correlated with the metastasis-associated clinicopathologic features. Notably, CASC2 low-expressing and miR-367 high-expressing HCC patients showed the poorest clinical outcome. Overall, we conclude that the CASC2/miR-367/FBXW7 axis may be a ponderable and promising therapeutic target for HCC.

The E3 ubiquitin ligase Fbxw7 functions as a general tumor suppressor by targeting several well-known oncoproteins for ubiquitination and proteasomal degradation. However, the clinical significance of Fbxw7 and the mechanisms involved in the anti-cancer effect of Fbxw7 in HCC are not clear. The Fbxw7 and YAP expression in 60 samples of surgical resected HCC and matched normal tumor-adjacent tissues were assessed using IHC or immunoblotting. Flow cytometry, caspase 3/7 activity assay, BrdU cell proliferation assay and MTT assay were used to detect proliferation and apoptosis of HCC cells. The regulatory effect of Fbxw7 on YAP in HCC cells was confirmed by qRT-PCR, immunoblotting and immunofluorescence. Co-immunoprecipitation was used to analyze interaction between YAP and Fbxw7. Nude mice subcutaneous injection, Ki-67 staining and TUNEL assay were used to evaluate tumor growth and apoptosis in vivo. In this study, we found that Fbxw7 expression was impaired in HCC tissues and loss of Fbxw7 expression was correlated with poor clinicopathological features including large tumor size, venous infiltration, high pathological grading and advanced TNM stage. Additionally, we demonstrated that patients with positive Fbxw7 expression had a better 5-year survival and Fbxw7 was an independent factor for predicting the prognosis of HCC patients. We confirmed that Fbxw7 inhibited HCC by inducing both apoptosis and growth arrest. Elevated YAP expression was observed in the same cohort of HCC tissues. Pearson's correlation coefficient analysis indicated that Fbxw7 was inversely associated with YAP protein expression in HCC tissues. We also found that Fbxw7 regulated YAP protein abundance by targeting YAP for ubiquitination and proteasomal degradation in HCC. Furthermore, restoring YAP expression partially abrogated Fbxw7 induced HCC cell apoptosis and growth arrest in vitro and in vivo. These results indicate that Fbxw7 may serve as a prognostic marker and that YAP may be a potential target of Fbxw7 in HCC.

Sterol regulatory element-binding protein 1 (SREBP-1) is a well-known nuclear transcription factor involved in lipid synthesis. Recent studies have focused on its functions in tumor cell proliferation and apoptosis, but its role in cell migration and invasion, especially in hepatocellular carcinoma (HCC), is still unclear. In this study, we found that the expression of SREBP-1 in HCC tissues was significantly higher than those in matched tumor-adjacent tissues (p < 0.05). SREBP-1 was expressed at significantly higher levels in patients with large tumor size, high histological grade and advanced tumor-node-metastasis (TNM) stage (p < 0.05). The positive expression of SREBP-1 correlated with a worse 3-year overall and disease-free survival of HCC patients (p < 0.05). Additionally, SREBP-1 was an independent factor for predicting both 3-year overall and disease-free survival of HCC patients (p < 0.05). In vitro studies revealed that downregulation of SREBP-1 inhibited cell proliferation and induced apoptosis in both HepG2 and MHCC97L cells (p < 0.05). Furthermore, wound healing and transwell assays showed that SREBP-1 knockdown prominently inhibited cell migration and invasion in both HepG2 and MHCC97L cells (p < 0.05). These results suggest that SREBP-1 may serve as a prognostic marker in HCC and may promote tumor progression by promoting cell growth and metastasis.

Cartilage oligomeric matrix protein (COMP) is known to promote fibrosis in skin, lung and liver. Emerging evidence shows that COMP plays critical roles in tumor development, including breast cancer, colon cancer and hepatocellular carcinoma (HCC). Nevertheless, the role of COMP in HCC proliferation and metastasis and its underlying mechanisms remain fully unclear. Serum COMP was determined by ELISA. Cell Counting Kit-8 and plate colony formation were performed to evaluate cell proliferation. Wound healing and transwell assays were used to determine migration and invasion of HCC cells. Western blotting and immunofluorescence were carried out for detection of epithelial-to-mesenchymal transition (EMT) markers and MMPs in HCC cells. The in vivo role of COMP was evaluated using mouse models. We also measured effects of hepatic stellate cells (HSCs)-conditioned medium (CM) on HCC progression using transwell coculture system. Here, we found that serum COMP levels in HCC patients were significantly higher than those in healthy controls. Accordingly, high serum COMP levels in HCC patients significantly correlated with malignant clinical characteristics and poor clinical outcomes. Next, we investigated that recombinant human COMP protein (rCOMP) treatment resulted in increased abilities of proliferation, invasion and migration of HCC cells. Furthermore, rCOMP treatment enhanced proliferative and metastatic colonization of HCC cells in vivo. Mechanistically, CD36 receptor played an essential role in COMP-mediated HCC cell proliferation and metastasis. Functionally, COMP/CD36 signaling caused phosphorylation of ERK and AKT, resulting in the upregulation of tumor-progressive genes such as EMT markers, MMP-2/9, Slug and Twist in HCC cells. Interestingly, we revealed that COMP was secreted by HSCs. CM of LX2 cells with COMP knockdown showed weaker effects on the activation of MEK/ERK and PI3K/AKT signaling pathways in HCC cells compared to control CM. Our findings indicated that HSCs-derived COMP collaborated with CD36 and subsequently played an essential role in MEK/ERK and PI3K/AKT-mediated HCC progression. COMP might act as a promising target for the diagnosis and treatment of aggressive HCC.

Cancer stem cells (CSCs) require stromal signals for maintaining pluripotency and self-renewal capacities to confer tumor metastasis. Resolvin D1 (RvD1), an endogenous anti-inflammatory lipid mediator, has recently been identified to display anti-cancer effects by acting on stroma cells. Our previous study reveals that hepatic stellate cells (HSCs)-derived cartilage oligomeric matrix protein (COMP) contributes to hepatocellular carcinoma (HCC) progression. However, whether RvD1 inhibits paracrine of cancer-associated fibroblasts (CAFs)-derived COMP to prevent epithelial-mesenchymal transition (EMT) and cancer stemness in HCC remains to be elucidated. CAFs were isolated from HCC tissues. Direct and indirect co-culture models were established to analyze the interactions between HCC cells and CAFs in the presence of RvD1 in vitro. The transwell and tumor sphere formation assays were used to determine invasion and stemness of HCC cells. The subcutaneous tumor formation and orthotopic liver tumor models were established by co-implantation of CAFs and HCC cells to evaluate the role of RvD1 in vivo. To characterize the mechanism of RvD1 inhibited paracrine of COMP in CAFs, various signaling molecules were analyzed by ELISA, western blotting, reactive oxygen species (ROS) detection, immunofluorescence staining, dual luciferase reporter assay and chromatin immunoprecipitation assay. Our data revealed that RvD1 treatment can impede the CAFs-induced cancer stem-like properties and the EMT of HCC cells under co-culture conditions. In vivo studies indicated that RvD1 intervention repressed the promoting effects of CAFs on tumor growth and metastasis of HCC. Furthermore, RvD1 inhibited CAF-induced EMT and stemness features of HCC cells by suppressing the secretion of COMP. Mechanistically, formyl peptide receptor 2 (FPR2) receptor mediated the suppressive effects of RvD1 on COMP and forkhead box M1 (FOXM1) expression in CAFs. Notably, RvD1 impaired CAF-derived COMP in a paracrine manner by targeting FPR2/ROS/FOXM1 signaling to ultimately abrogate FOXM1 recruitment to the COMP promoter. Our results indicated that RvD1 impaired paracrine of CAFs-derived COMP by targeting FPR2/ROS/FOXM1 signaling to repress EMT and cancer stemness in HCC. Thus, RvD1 may be a potential agent to promote treatment outcomes in HCC.