Insulin-like growth factor I (IGF-I) can induce epithelial mesenchymal transition (EMT) in many epithelial tumors; however, the molecular mechanism by which this occurs is not clearly understood. Additionally, little is known about the involvement of IGF-I in gastric cancer. Two gastric cancer cell lines were treated with IGF-I to induce EMT and levels of transcription factor ZEB2 and microRNA-200c (miR-200c) were measured. Cells were treated with Akt/ERK inhibitors to investigate the role of these pathways in IGF-I-mediated EMT. Transfection of shRNA plasmids was used to silence the ubiquitin ligase Cbl-b to assess its involvement in this process. The relationship between IGF-IR and Cbl-b expression, and the effect of IGF-IR and Cbl-b on metastasis were analyzed in primary gastric adenocarcinoma patients. IGF-I-induced gastric cancer cell EMT was accompanied by ZEB2 up-regulation. Furthermore, both Akt/ERK inhibitors and knockdown of Akt/ERK gene reversed IGF-I-induced ZEB2 up-regulation and EMT through up-regulation of miR-200c, suggesting the involvement of an Akt/ERK-miR-200c-ZEB2 axis in IGF-I-induced EMT. The ubiquitin ligase Cbl-b also ubiquitinated and degraded IGF-IR and inhibited the Akt/ERK-miR-200c-ZEB2 axis, leading to the repression of IGF-I-induced EMT. There was a significant negative correlation between the expression of IGF-IR and Cbl-b in gastric cancer patient tissues (r = -0.265, p < 0.05). More of patients with IGF-IR-positive expression and Cbl-b-negative expression were with lymph node metastasis (p < 0.001). Together, these findings demonstrate that the ubiquitin ligase Cbl-b represses IGF-I-induced EMT, likely through targeting IGF-IR for degradation and further inhibiting the Akt/ERK-miR-200c-ZEB2 axis in gastric cancer cells.

Multiple drug resistance (MDR) and metastasis are two major factors that contribute to the failure of cancer treatment. However, the relationship between MDR and metastasis has not been characterized. Additionally, the role of the E3 ubiquitin ligase Cbl-b in metastasis of MDR gastric and breast cancer is not well known. In the present study, we found that MDR gastric and breast cancer cells possess a typical mesenchymal phenotype and enhanced cell migration capacity. Additionally, Cbl-b is poorly expressed in MDR gastric and breast cancer cells. In MDR gastric adenocarcinoma tissues, gastric cancer patients with low Cbl-b expression were more likely to have tumor invasion (P=.016) and lymph node metastasis (P=.007). Moreover, overexpression of Cbl-b reduced cell migration in MDR cell cultures both in vitro and in vivo. Cbl-b overexpression also prevented EMT by inducing ubiquitination and degradation of EGFR, leading to inhibition of the EGFR-ERK/Akt-miR-200c-ZEB1 axis. However, further overexpression of EGFR on a background of Cbl-b overexpression restored both the mesenchymal phenotype and cell migration capacity of MDR gastric and breast cancer cells. These results suggest that Cbl-b is an important factor for maintenance of the epithelial phenotype and inhibition of cell migration in MDR gastric and breast cancer cells.

The epithelial-to-mesenchymal transition (EMT) is a well-known prerequisite for cancer cells to acquire the migratory and invasive capacity, and to subsequently metastasize. Bufalin is one of the major active components of the traditional Chinese medicine Chan Su, and accumulating evidence has shown its anticancer effect in multipe types of cancer. However, the role of bufalin in transforming growth factor‑β (TGF‑β)‑induced EMT and migration remains unclear. In the present study, the effect of bufalin on TGF‑β‑induced EMT and migration was investigated in human lung cancer A549 cells. TGF‑β induced EMT in A549 cells and increased their migratory ability, which were markedly suppressed by bufalin. Additionally, TGF‑β‑induced upregulation of Twist2 and zinc finger E‑box binding homeobox 2 (ZEB2), as well as the phosphorylation of Smad2 and Smad3 were also inhibited by bufalin. However, the Smad‑independent signaling pathways were not affected. Further analysis showed that the TGF‑β receptor I (TβRI) and TGF‑β receptor II (TβRII) were downregulated in the presence of bufalin. Pretreatment with SB431542, a potent inhibitor of the phosphorylation of TβRI, significantly attenuated TGF‑β‑induced EMT, mimicking the effect of bufalin on A549 cells. Taken together, these results suggest that bufalin suppresses TGF-β-induced EMT and migration by downregulating TβRI and TβRII in A549 cells.

Metastasis is the most common cause of mortality in patients with gastric cancer. Epithelial-to-mesenchymal transition (EMT), which may be stimulated by insulin-like growth factor-I (IGF-I) is involved in the metastasis of numerous tumors; however, the molecular mechanism by which IGF‑I may induce tumor cell EMT remains to be elucidated in gastric cancer. The present study aimed to investigate the induction of EMT in BGC‑823 gastric cancer cells. It was identified that IGF‑I induced EMT by upregulating the levels of ZEB2 transcription factor, and this was dependent on the phosphoinositide 3‑kinase (PI3K)/Akt signaling pathway in these cells. In addition, glycogen synthase kinase 3β (GSK‑3β), an intracellular downstream effector of PI3K/Akt, sustained the epithelial phenotype by repressing ZEB2 expression and the subsequent inhibition of EMT induced by IGF‑I, suggesting the involvement of a potential PI3K/Akt‑GSK‑3β‑ZEB2 signaling pathway in IGF‑I‑induced EMT in gastric cancer BGC‑823 cells. Overall, the results of the present study suggest that IGF‑I induced EMT by the activation of a PI3K/Akt‑GSK‑3β‑ZEB2 signaling pathway in gastric cancer BGC‑823 cells. Therefore, this study may provide more useful information regarding the mechanism of gastric cancer metastasis.

Although the efficacy of tamoxifen (TAM) for breast cancer has been attributed to inducing cell cycle arrest and apoptosis by inhibiting estrogen receptor (ER) signaling, recent evidence indicates that TAM also possesses ER-independent antitumor activity through an unclear mechanism. The present study investigated the anti-tumor mechanism of TAM on mesenchymal triple-negative breast cancer (TNBC). The inhibitory effect of TAM on tumor migration and metastasis was analyzed by transwell chamber in vitro and by murine xenograft model in vivo. The promoter sequence of miR-200c was predicted by an online CpG island predictor. Relative expression of miR-200c was measured by quantitative real-time PCR. After treatment with TAM, mesenchymal TNBC cells (MCF-7/ADR and MDA-MB-231) morphologically changed from mesenchymal to epithelial types. Meanwhile, cell migration ability was also significantly decreased in ER-positive breast cancer cells after exposure to TAM. Consistent with these in-vitro results, TAM significantly suppressed lung metastasis rate of mesenchymal TNBC cells in murine xenograft tumors. miRNA array analysis of two types of breast cancer cells showed that miR-200c expression was inhibited in mesenchymal TNBC cells, but increased after TAM treatment due to demethylation of miR-200c promoters. Our results indicate that TAM inhibits cell migration and enhances chemosensitivity of mesenchymal TNBC cells by reversing their EMT-like property; and that this EMT-reversal effect results from upregulation of miR-200c through demethylating its promoter. To our knowledge, this is the first explanation of a non-ER-related mechanism for the effect of TAM on mesenchymal TNBC cells.