Tumor-associated macrophages play an important role in tumor progression, but whether they exert a tumor-progressive effect remains controversial. Here, we demonstrated that activated macrophage-conditioned medium (AMCM) obtained from RAW macrophages (RAW/AMCM) induced epithelial-mesenchymal transition (EMT) and stimulated the migratory and invasive activities of HepG2 cells, whereas control conditioned media had no effect. Epithelial-cadherin (E-cadherin) and b-catenin staining patterns were altered at the adherens junctions by RAW/AMCM treatment, with an approximately 50% decrease in E-cadherin and b-catenin in the cell membrane. Importantly, levels of b-cateninassociated E-cadherin were also decreased. Following RAW/ AMCM treatment, enhanced activation of c-Src was seen prior to increased tyrosine phosphorylation of b-catenin, and this led to the destabilization of adherens junctions. Pretreatment of HepG2 cells with the Src kinase inhibitor, PP2, completely abolished the effects of RAW/AMCM on the EMT, migration, invasion, and expression and association of E-cadherin and bcatenin. AMCMs obtained from human THP-1 monocytes and mouse peritoneal macrophages also caused disassembly of the adherens junctions and migration of HepG2 cells. Furthermore, inhibition of the epidermal growth factor receptor (EGFR) with gefitinib partially prevented the downregulation of E-cadherin and b-catenin at the adherens junctions and migration behavior induced by RAW/AMCM. Our results suggest that activated macrophages have a tumor-progressive effect on HepG2 cells which involves the c-Src-and EGFR-dependent signaling cascades.
Extracellular matrix (ECM) is thought to participate significantly in guiding the differentiation process of mesenchymal stem cells (MSCs). In this study, we hypothesized that cartilage fragments from osteoarthritic knee could promote chondrogenesis of MSCs. Nonworn parts of cartilage tissues were obtained during total knee arthroplasty (TKA) surgery. Cartilage fragments and MSCs were wrapped into fibrin glue; and the constructs were implanted subcutaneously into nude mice. Histological analysis showed neocartilage-like structure with positive Alcian blue staining in the cartilage fragment-fibrin-MSC constructs. However, constructs with only MSCs in fibrin showed condensed appearance like MSCs in the pellet culture. Gene expression of type II collagen in the constructs with 60 mg cartilage fragments were significantly elevated after 4 weeks of implantation. Conversely, the constructs without cartilage fragments failed to express type II collagen, which indicated MSCs did not differentiate into a chondrogenic lineage. In conclusion, we demonstrated the effect of cartilage fragments from osteoarthritic knee in promoting chondrogenic differentiation of MSCs. This may be a favorable strategy for MSC chondrogenesis without exogenous growth factor induction. ß
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