Activation of AKT signaling promotes epithelial-mesenchymal transition and tumor growth in colorectal cancer cells.

Activation of the serine-threonine protein kinase AKT has emerged as a central feature of epithelial-mesenchymal transition (EMT), which is the initial step for metastasis in many cancer models, including colorectal cancer. The focus of our study was to dissect the role of AKT and its molecular regulation of EMT in colorectal cancer. HCT-116 colorectal cancer cells stably overexpressing AKT (AKT/HCT-116) showed significantly higher cell proliferation compared with vector-transfected cells (pCMV/HCT-116). Elevated expression of important EMT-related transcription factors and genes such as Snail, Slug, β-catenin, vimentin, and MMP-9 correlated with increased migration and invasion by AKT/HCT-116 cells. Further, in vivo studies confirmed that AKT/HCT-116 xenografts were highly aggressive and angiogenic in nature compared with pCMV/HCT-116 xenografts. Molecular analysis of tumor samples revealed transcriptional regulation of Snail, Slug, β-catenin, MMP-2, and MMP-9 in AKT/HCT-116 tumors. These results were supported by immunohistochemistry analysis. Low levels of E-cadherin expression with a concomitant increase in and nuclear localization of β-catenin were evident in AKT/HCT-116 tumors compared with control tumors. Increased microvessel formation coincident with high expression of Factor VIII and increased numbers of reticulocytes confirmed the angiogenic property of AKT/HCT-116 tumors. Our results confirm the potential role of AKT signaling in regulating EMT and angiogenesis in colorectal cancer and suggest that inhibition of AKT can serve as an important therapeutic strategy in modulating EMT in colorectal cancer growth and metastasis.

Suman S ，Kurisetty V ，Das TP ，Vadodkar A ，Ramos G ，Lakshmanaswamy R ，Damodaran C ... -  《-》

Consumption of high-fat diet induces tumor progression and epithelial-mesenchymal transition of colorectal cancer in a mouse xenograft model.

Epidemiologic studies suggest that intake of high-fat diet (HFD) promotes colon carcinogenesis. Epithelial-mesenchymal transition (EMT) and inflammation play important roles during tumor progression of colorectal cancer (CRC). Oncogenic pathways such as phosphatidylinositol-3-kinase (PI3K)/Akt/mTOR and mitogen-activated protein kinase (MAPK)/ERK signaling cascades induce EMT and inflammation in cancer. No experimental evidence has been demonstrated regarding HFD-mediated tumor progression including EMT in CRC so far. Our results demonstrated that HFD consumption could induce tumor growth and progression, including EMT and inflammation, in a mouse xenograft tumor model. The molecular mechanisms were through activation of MAPK/ERK and PI3K/Akt/mTOR signaling pathways. HFD induced up-regulation of cyclooxygenase-2, cyclin D1 and proliferating cell nuclear antigen proteins concomitant with increases in expression of nuclear factor-κB p65 (RelA) and β-catenin proteins. Surprisingly, HFD consumption could suppress p21(CIP1/WAF1) expression through increases in nuclear histone deacetylase complex (HDAC). Moreover, HFD could mediate the disassembly of E-cadherin adherent complex and the up-regulation of Vimentin and N-cadherin proteins in tumor tissues. Taken together, our novel findings support evidence for HFD-mediated modulation of HDAC activity and activation of oncogenic cascades, which involve EMT and inflammation in CRC, playing important roles in tumor growth and progression in a mouse xenograft model.

Tang FY ，Pai MH ，Chiang EP 《-》

The molecular chaperone Cosmc enhances malignant behaviors of colon cancer cells via activation of Akt and ERK.

Expression of T antigen (Galbeta1, 3GalNAc) is associated with enhanced metastatic potential and poor prognosis in colorectal cancer. Cosmc is a molecular chaperone required for the formation of an active T-synthase, which catalyzes the synthesis of T antigen. However, the expression and role of Cosmc in colorectal cancer are still unclear. Here, real-time PCR showed that overexpression of Cosmc mRNA in colorectal tumors compared with paired non-tumorous tissues was associated with increased American Joint Committee on Cancer (AJCC) tumor stage. Forced expression of Cosmc in HCT116 cells significantly increased T antigen expression and enhanced cell growth, migration, and invasion, which was associated with increased phosphorylation of focal adhesion kinase (FAK), ERK, and Akt. These Cosmc-enhanced malignant phenotypes were significantly suppressed by specific inhibitor of MEK or PI3K. We also found that Cosmc overexpression increased tumor growth and decreased survival of tumor-bearing SCID mice. Conversely, knockdown of Cosmc with siRNA in SW480 cells decreased malignant behaviors and the signaling pathways, which were substantially reversed by constitutively active Akt or MEK. Taken together, these results suggest that Cosmc promotes malignant phenotypes of colon cancer cells mainly via activation of MEK/ERK and PI3K/Akt signaling pathways, and that Cosmc may serve as a potential target for colorectal cancer treatment.

Huang J ，Che MI ，Lin NY ，Hung JS ，Huang YT ，Lin WC ，Huang HC ，Lee PH ，Liang JT ，Huang MC ... -  《-》

c-Kit is suppressed in human colon cancer tissue and contributes to L1-mediated metastasis.

The transmembrane neural cell adhesion receptor L1 is a Wnt/β-catenin target gene expressed in many tumor types. In human colorectal cancer, L1 localizes preferentially to the invasive front of tumors and when overexpressed in colorectal cancer cells, it facilitates their metastasis to the liver. In this study, we investigated genes that are regulated in human colorectal cancer and by the L1-NF-κB pathway that has been implicated in liver metastasis. c-Kit was the most highly suppressed gene in both colorectal cancer tissue and the L1-NF-κB pathway. c-Kit suppression that resulted from L1-mediated signaling relied upon NF-κB, which directly inhibited the transcription of SP1, a major activator of the c-Kit gene promoter. Reconstituting c-Kit expression in L1-transfected cells blocked the biological effects conferred by L1 overexpression in driving motility and liver metastasis. We found that c-Kit expression in colorectal cancer cells is associated with a more pronounced epithelial morphology, along with increased expression of E-cadherin and decreased expression of Slug. Although c-Kit overexpression inhibited the motility and metastasis of L1-expressing colorectal cancer cells, it enhanced colorectal cancer cell proliferation and tumorigenesis, arguing that separate pathways mediate tumorigenicity and metastasis by c-Kit. Our findings provide insights into how colorectal cancer metastasizes to the liver, the most common site of dissemination in this cancer.

Gavert N ，Shvab A ，Sheffer M ，Ben-Shmuel A ，Haase G ，Bakos E ，Domany E ，Ben-Ze'ev A ... -  《-》

3,5,4'-Trimethoxystilbene, a natural methoxylated analog of resveratrol, inhibits breast cancer cell invasiveness by downregulation of PI3K/Akt and Wnt/β-catenin signaling cascades and reversal of epithelial-mesenchymal transition.

The molecular basis of epithelial-mesenchymal transition (EMT) functions as a potential therapeutic target for breast cancer because EMT may endow breast tumor-initiating cells with stem-like characteristics and enable the dissemination of breast cancer cells. We have recently verified the antitumor activity of 3,5,4'-trimethoxystilbene (MR-3), a naturally methoxylated derivative of resveratrol, in colorectal cancer xenografts via an induction of apoptosis. The effect of MR-3 on EMT and the invasiveness of human MCF-7 breast adenocarcinoma cell line were also explored. We found that MR-3 significantly increased epithelial marker E-cadherin expression and triggered a cobblestone-like morphology of MCF-7 cells, while reciprocally decreasing the expression of mesenchymal markers, such as snail, slug, and vimentin. In parallel with EMT reversal, MR-3 downregulated the invasion and migration of MCF-7 cells. Exploring the action mechanism of MR-3 on the suppression of EMT and invasion indicates that MR-3 markedly reduced the expression and nuclear translocation of β-catenin, accompanied with the downregulation of β-catenin target genes and the increment of membrane-bound β-catenin. These results suggest the involvement of Wnt/β-catenin signaling in the MR-3-induced EMT reversion of MCF-7 cells. Notably, MR-3 restored glycogen synthase kinase-3β activity by inhibiting the phosphorylation of Akt, the event required for β-catenin destruction via a proteasome-mediated system. Overall, these findings indicate that the anti-invasive activity of MR-3 on MCF-7 cells may result from the suppression of EMT via down-regulating phosphatidylinositol 3-kinase (PI3K)/AKT signaling, and consequently, β-catenin nuclear translocation. These occurrences ultimately lead to the blockage of EMT and the invasion of breast cancer cells.

Tsai JH ，Hsu LS ，Lin CL ，Hong HM ，Pan MH ，Way TD ，Chen WJ ... -  《-》