Na Song

Down-regulation of Cbl-b by bufalin results in up-regulation of DR4/DR5 and sensitization of TRAIL-induced apoptosis in breast cancer cells.

PurposeTNF-related apoptosis-inducing ligand (TRAIL) is a potential cancer therapeutic agent that preferentially induces apoptosis in cancer cells. However, breast cancer cells are generally resistant to TRAIL. Bufalin is a major active ingredient of the traditional Chinese medicine ChanSu. The present study aimed to assess the synergistic effect of bufalin and TRAIL and elucidate the underlying mechanisms in breast cancer cells.MethodsCell proliferation and apoptosis were measured by MTT assay and flow cytometry, respectively. The expression of proteins was assayed by flow cytometry and/or Western blotting. Transfection studies were used to determine the involvement of DR4, DR5 and Cbl-b in the synergistic effect of bufalin and TRAIL.ResultsMCF-7 and MDA-MB-231 cells were resistant to TRAIL. Both cell lines were dramatically sensitized to TRAIL-induced apoptosis by bufalin. Further experiments indicated that bufalin up-regulated DR4 and DR5, activated ERK, JNK and p38 MAPK and down-regulated Cbl-b. Blocking the up-regulation of DR4 and DR5 by siRNA rendered cells less sensitive to apoptosis induced by the combination of bufalin and TRAIL. Inhibition of the activation of ERK, JNK and p38 MAPK by specific inhibitors attenuated DR4 and DR5 up-regulation. Moreover, down-regulation of Cbl-b by shRNA led to stronger activation of ERK, JNK and p38 MAPK, more up-regulation of DR4 and DR5, and a stronger synergistic effect of bufalin and TRAIL.ConclusionsBufalin enhanced TRAIL-induced apoptosis by up-regulating the expression of DR4 and DR5. Bufalin-induced down-regulation of Cbl-b contributed to the up-regulation of DR4 and DR5, which might be partially mediated by the activation of ERK, JNK and p38 MAPK.

Cetuximab-Induced MET Activation Acts as a Novel Resistance Mechanism in Colon Cancer Cells

Aberrant MET expression and hepatocyte growth factor (HGF) signaling are implicated in promoting resistance to targeted agents; however, the induced MET activation by epidermal growth factor receptor (EGFR) inhibitors mediating resistance to targeted therapy remains elusive. In this study, we identified that cetuximab-induced MET activation contributed to cetuximab resistance in Caco-2 colon cancer cells. MET inhibition or knockdown sensitized Caco-2 cells to cetuximab-mediated growth inhibition. Additionally, SRC activation promoted cetuximab resistance by interacting with MET. Pretreatment with SRC inhibitors abolished cetuximab-mediated MET activation and rendered Caco-2 cells sensitive to cetuximab. Notably, cetuximab induced MET/SRC/EGFR complex formation. MET inhibitor or SRC inhibitor suppressed phosphorylation of MET and SRC in the complex, and MET inhibitor singly led to disruption of complex formation. These results implicate alternative targeting of MET or SRC as rational strategies for reversing cetuximab resistance in colon cancer.

IGF-IR signaling in epithelial to mesenchymal transition and targeting IGF-IR therapy: overview and new insights.

The insulin-like growth factor-I (IGF-I) signaling induces epithelial to mesenchymal transition (EMT) program and contributes to metastasis and drug resistance in several subtypes of tumors. In preclinical studies, targeting of the insulin-like growth factor-I receptor (IGF-IR) showed promising anti-tumor effects. Unfortunately, high expectations for anti-IGF-IR therapy encountered challenge and disappointment in numerous clinical trials. This review summarizes the regulation of EMT by IGF-I/IGF-IR signaling pathway and drug resistance mechanisms of targeting IGF-IR therapy. Most importantly, we address several factors in the regulation of IGF-I/IGF-IR-associated EMT progression that may be potential predictive biomarkers in targeted therapy.

The Role of E3 Ubiquitin Ligase Cbl Proteins in β-Elemene Reversing Multi-Drug Resistance of Human Gastric Adenocarcinoma Cells

Recent studies indicate that β-elemene, a compound isolated from the Chinese herbal medicine Curcuma wenyujin, is capable of reversing tumor MDR, although the mechanism remains elusive. In this study, β-Elemene treatment markedly increased the intracellular accumulation of doxorubicin (DOX) and rhodamine 123 in both K562/DNR and SGC7901/ADR cells and significantly inhibited the expression of P-gp. Treatment of SGC7901/ADR cells with β-elemene led to downregulation of Akt phosphorylation and significant upregulation of the E3 ubiquitin ligases, c-Cbl and Cbl-b. Importantly, β-elemene significantly enhanced the anti-tumor activity of DOX in nude mice bearing SGC7901/ADR xenografts. Taken together, our results suggest that β-elemene may target P-gp-overexpressing leukemia and gastric cancer cells to enhance the efficacy of DOX treatment.

Lipid raft-regulated IGF-1R activation antagonizes TRAIL-induced apoptosis in gastric cancer cells

Gastric cancer cells are resistant to tumor necrosis factor‐related apoptosis‐inducing ligand (TRAIL) and the resistance mechanism is not fully understood. In human gastric cancer MGC803 and BGC823 cells, TRAIL induces insulin‐like growth factor‐1 receptor (IGF‐1R) pathway activation. Treatment with IGF‐1R inhibitor OSI‐906 or small interfering RNAs against IGF‐1R, prevents IGF‐1R pathway activation and increases TRAIL‐induced apoptosis. The TRAIL‐induced IGF‐1R pathway activation is promoted by IGF‐1R translocation into lipid rafts. Moreover, the translocation of IGF‐1R into lipid rafts is regulated by Casitas B‐lineage lymphoma b (Cbl‐b). Taken together, TRAIL‐induced IGF‐1R activation antagonizes TRAIL‐induced apoptosis by Cbl‐b‐regulated distribution of IGF‐1R in lipid rafts.

CXCL12/SDF‑1α induces migration via SRC‑mediated CXCR4‑EGFR cross‑talk in gastric cancer cells

Metastasis is the primary cause of mortality in patients with advanced gastric carcinoma, and multiple signaling pathways promote the development of this condition. Stromal cell-derived factor-1 (SDF-1α/CXCL12), the main ligand for CXC chemokine receptor-4 (CXCR4), serves an important role in gastric cancer cell migration. Previous studies have demonstrated that CXCL12 could also stimulate the secretion of epidermal growth factor receptor (EGFR) ligands, including amphiregulin and heparin-binding epidermal growth factor-like growth factor, from gastric cancer cells, resulting in an increase in the ability of migration. However, it remains to be elucidated whether CXCL12 activates EGFR intracellular signaling and therefore stimulates migration in gastric cancer. The present study demonstrated that three gastric cancer cell lines, SGC-7901, MGC-803 and BGC-823, all expressed CXCR4. The increased chemotactic migratory ability stimulated by CXCL12 was effectively abrogated by the CXCR4 antagonist, AMD3100. Furthermore, a rapid phosphorylation of Akt/extracellular signal-regulated kinase (ERK)/EGFR was demonstrated to be involved in CXCL12/CXCR4-induced gastric cancer cell migration. Knockdown of EGFR gene or the use of a monoclonal antibody against EGFR (C225) blocked the activation of ERK/Akt and partially prevented the ability of migration induced by CXCL12, which indicated that EGFR signaling is located downstream of CXCL12. In addition, it was also revealed that the activation of non-receptor tyrosine kinase c-steroid receptor co-activator (SRC) and the formation of the SRC/EGFR heterodimer are promoted by CXCL12, whereas the SRC inhibitor, PP2, blocks the SRC/EGFR heterodimer and the activation of EGFR, as well as CXCR4-meditated migration induced by CXCL12. The present results indicated that SRC mediates a potential CXCR4-EGFR cross-talk, and thereby utilizes the EGFR-Akt/ERK axis to promote cellular migration. The present study provided a novel insight into the underlying regulatory mechanisms of the CXCL12/CXCR4 pathway in gastric cancer cell migration.

A novel function of hepatocyte growth factor in the activation of checkpoint kinase 1 phosphorylation in colon cancer cells

The ATR/checkpoint kinase 1 (Chk1) pathway plays an essential role in modulating the DNA damage response and homologous recombination. Particularly, Chk1 phosphorylation is related to cancer prognosis and therapeutic resistance. Some receptor tyrosine kinases participate in the regulation of Chk1 phosphorylation; however, the effect of hepatocyte growth factor (HGF) on Chk1 phosphorylation is unknown. In the present study, we demonstrated that HGF moderately activated Chk1 phosphorylation in colon cancer cells by upregulating TopBP1 and RAD51, and promoting TopBP1–ATR complex formation. Furthermore, AKT activity, which was promoted by HGF, served as an important mediator linking HGF/MET signaling and Chk1 phosphorylation. Depleting AKT activity attenuated basal expression of p-Chk1 and HGF-induced Chk1 activation. Moreover, AKT activity directly regulated TopBP1 and RAD51 expression. AKT inhibition suppressed HGF-induced upregulation of TopBP1 and RAD51, and enhanced TopBP1/ATR complex formation. Our results show that HGF was involved in regulating Chk1 phosphorylation, and further demonstrate that AKT activity was responsible for this HGF-induced Chk1 phosphorylation. These findings might potentially result in management of prognosis and therapeutic sensitivity in cancer therapy.

Thalidomide improves prevention of chemotherapy-induced gastrointestinal side effects following a modified FOLFOX7 regimen: results of a prospective randomized crossover study.

Aims and Background Thalidomide was firstly evaluated for the control of chemotherapy-induced gastrointestinal side effects following a modified FOLFOX7 (mFOLFOX7) regimen. Methods and Study Design Chemotherapy-naive patients with malignant tumors were randomized into two groups: A-B group (A, 0.3 mg of ramosetron plus 10 mg of dexamethasone on day 1, was given intravenously in the first cycle, and B, 0.3 mg of ramosetron plus 10 mg of dexamethasone on day 1 intravenously plus 150 mg orally twice daily of thalidomide on days 2 through 5, in the second cycle) and B-A group (those drugs were given in the reverse sequence). The primary end point was the efficacy of thalidomide in controlling delayed (days 2 through 5) chemotherapy-induced nausea and vomiting (CINV). The secondary end point was the safety of thalidomide. Results Of 52 patients enrolled, 50 patients (96%) were assessable. Complete response rates of delayed nausea (no nausea) were higher with group B than group A (52% vs 24%, P = 0.004 on day 2; 58% vs 24%, P =0.001 on day 3; and 60% vs 36%, P = 0.016 on day 4). Complete response rates of delayed emesis (no emetic episodes, no rescue therapy) for group B and A also showed significance (86% vs 66%, P = 0.019 on day 2 and 76% vs 56%, P = 0.035 on day 3). Complete response rates on anorexia for group B were higher than those for group A on days 2 through 5. More patients in group B reported sedation or dizziness than in group A (42% vs 9.6%; P = 0.000). Conclusions Thalidomide improves prevention of chemotherapy-induced gastrointestinal side effects following the mFOLFOX7 regimen. It is a safe, effective antiemetic.

The Chemokine Receptor CXCR4 and c-MET Cooperatively Promote Epithelial-Mesenchymal Transition in Gastric Cancer Cells

The C-X-C motif chemokine receptor 4 (CXCR4) pathway can promote tumor metastasis but is dependent on cross talk with other signaling pathways. The MET proto-oncogene (c-MET) participates in metastasis and is highly expressed in gastric cancer. However, the relationship between CXCR4 and c-MET signaling and their mechanisms of action in gastric cancer metastasis remain unclear. In this study, in vitro experiments demonstrated that C-X-C motif chemokine ligand 12 (CXCL12)/CXCR4 induces epithelial-mesenchymal transition (EMT) and promotes migration in gastric cancer cells, which is accompanied by c-MET activation. These phenomena were reversed by c-MET inhibition. Further investigation revealed that c-MET activation correlated with its interaction with caveolin 1 in lipid rafts, induced by CXCL12. In clinical samples, we observed a significant positive association between CXCR4 expression and c-MET phosphorylation (r = 0.259, P = .005). Moreover, samples expressing both receptors were found to indicate significantly poorer patient prognosis (P < .001). These results suggest that CXCL12 induces EMT at least partially through cross talk between CXCR4 and c-MET signaling. In addition, changes in these pathways could have clinical importance for the treatment of gastric cancer.

Src promotes EGF-induced epithelial-to-mesenchymal transition and migration in gastric cancer cells by upregulating ZEB1 and ZEB2 through AKT: Src in EGF-induced EMT and migration

Epithelial‐to‐mesenchymal transition (EMT) plays important roles in the migration, invasion, and metastasis of cancer cells. However, the role of Src in epidermal growth factor (EGF)‐induced EMT and migration in gastric cancer cells remains to be clarified. In the current study, the effect of Src on EGF‐stimulated EMT and migration was explored in gastric cancer cells. EGF induced EMT in gastric cancer cells and increased their migratory ability, which was accompanied by the phosphorylation of Src. PP2, the Src inhibitor, markedly suppressed EGF‐mediated EMT and migration in gastric cancer cells. Additionally, EGF‐stimulated upregulation of zinc finger E‐box binding homeobox 1 (ZEB1) and zinc finger E‐box binding homeobox 2 (ZEB2) was significantly repressed by PP2. Further analysis showed that EGF‐stimulated phosphorylation of protein kinase B (AKT) was almost completely abolished by PP2, whereas that of extracellular signal‐regulated kinase (ERK), signal transducer and activator of transcription 3 (STAT3) was only mildly suppressed. Moreover, LY294002, the AKT inhibitor, significantly inhibited EGF‐induced upregulation of ZEB1 and ZEB2 as well as EMT and migration stimulated by EGF in gastric cancer cells. However, neither ERK inhibitor nor STAT3 inhibitor repressed EGF‐induced EMT‐related changes. Taken together, these results suggest that Src promotes EGF‐stimulated EMT and migration by upregulation of ZEB1 and ZEB2 through AKT signaling pathway in gastric cancer cells.