A novel RON splice variant lacking exon 2 activates the PI3K/AKT pathway via PTEN phosphorylation in colorectal carcinoma cells.

Abnormal expression of the Recepteur d'Origine Nantais (RON) receptor tyrosine kinase is accompanied by the generation of multiple splice or truncated variants, which mediate many critical cellular functions that contribute to tumor progression and metastasis. Here, we report a new RON splice variant in the human colorectal cancer (CRC) cell line HT29. This variant is a 165 kda protein generated by alternative pre-mRNA splicing that eliminates exon 2, causing an in-frame deletion of 63 amino acids in the extracellular domain of the RON ß chain. The deleted transcript was a single chain expressed in the intracellular compartment. Although it lacked tyrosine phosphorylation activity, the RONΔ165E2 variant could phosphorylate phosphatase and tensin homolog (PTEN), thereby activating the PI3K/AKT pathway. In addition, in vitro and in vivo experiments showed that the RONΔ165E2 promoted cell migration and tumor growth. Finally, in an investigation of 67 clinical CRC samples, the variant was highly expressed in about 58% of the samples, and was positively correlated with the invasive depth of the tumor (P < 0.05). These results demonstrate that the novel RONΔ165E2 variant promoted tumor progression while activating the PI3K/AKT pathway via PTEN phosphorylation.

A novel variant of the RON receptor tyrosine kinase derived from colorectal carcinoma cells which lacks tyrosine phosphorylation but induces cell migration.

Generation of splice variants in the RON receptor tyrosine kinase facilitates the invasive phenotype of colorectal cancers. Here, we report a new splice variant of RON in the human colorectal cancer cell line HCT116. This variant is encoded by a transcript differing from the full-length RON mRNA by an in-frame deletion of 106 amino acids in the extracellular domain of RON ß-chain. The deleted transcript originates by an alternative deletion of exon 2 and exon 3. The molecular weight of this variant is 160 kDa. Thus, we named this variant RONΔ160(E2E3). This variant is a single-chain protein and expressed in the intracellular compartment. We found that RONΔ160(E2E3) had no tyrosine phosphorylation ability, but it has constitutively activated Akt activity in transfected HEK293 epithelial cells. The expression of this variant in HEK293 cells resulted in an increased migratory activity in vitro mediated through the PI-3K/Akt pathway. Our data describes a new splice variant of RON and suggests a novel role for the RON receptor in the progression of metastasis in colorectal cancer.

Blocking tumorigenic activities of colorectal cancer cells by a splicing RON receptor variant defective in the tyrosine kinase domain.

Altered expression of the RON receptor tyrosine kinase, accompanied by generation of splicing variants, contributes to the pathogenesis of epithelial cancers such as invasive growth of colorectal caners. In this study, we have studied a novel RON variant (designated as RONdelta170) that regulates tumorigenic activities of colorectal cancer cells by blocking RON-mediated tumorigenic signals. RONdelta170 is a splicing variant with a deletion of exon 19 that encodes 46 amino acids in the catalytic kinase domain. This deletion also causes a reading-frame shift and creates a new stop codon, which effectively eliminates the multi-functional docking site and truncates the RON C-terminus. As a RON variant without kinase activities and the C-terminal docking domain, RONdelta170 acts as a variant receptor that negatively regulates biochemical and biological activities mediated by RON or its oncogenic variant RONdelta160. In NIH3T3 expressing RONdelta160, RONdelta170 formed a complex with RONdelta160 and prevented RONdelta160-mediated activation of signaling proteins such as Erk1/2 and AKT. These effects resulted in decreased cell proliferation, reduced colony formation, and diminished cell migration. These negative activities were also observed in colorectal cancer cells naturally expressing RON or RONdelta160 including HT-29, HCT116 and SW620. Introduction of RONdelta170 into HCT116 cells blocked MSP-induced Erkl/2 and AKT phosphorylation, reduced cytoplasmic beta-catenin accumulation, restored glycogen synthase kinase-beta activity, and attenuated various tumorigenic activities. Moreover, RONdelta170 expression significantly reduced SW620 cell-mediated tumor growth in vivo. Thus, RONdelta170 is a naturally occurring variant with dominant negative activities and has potential for inhibiting RON-mediated tumorigenic activities in colorectal cancer cells.

[Activity of the TNF-related apoptosis-inducing ligand gene expressed from the hTERT promoter on colon cancer cell line HT-29].

OBJECTIVE: To evaluate the expression and activity of TNF-related apoptosis-inducing ligand (TRAIL) gene expressed from the hTERT promoter on colon cancer cell line HT-29. METHODS: GFP/TRAIL gene expressed from the hTERT promoter was transfected into HT-29 with adenoviral vectors system, expression and apoptosis inducing ability of GFP/TRAIL protein were determined with fluorescence-activated cell sorting (FACS) method. RESULTS: The expression of GFP gene was 31.4 % and 67.0 % with either hTERT promoter or CMV promoter in DLD1 cells; GFP/TRAIL gene was able to inhibit cell growth (74.2%) and induce apoptosis (25.8%) of HT-29 cells. There was significant difference between Ad/hTERT-gTRAIL and the other two control groups (PBS and Ad/CMV-GFP, P<0.05). CONCLUSION: The GFP/TRAIL gene with hTERT promoter transfected by adenoviral vector was successfully expressed in HT-29 cell, which can both inhibit cell growth and induce apoptosis of colon cancer cell line HT-29.

Anti-liver cancer activity of TNF-related apoptosis-inducing ligand gene and its bystander effects.

AIM: To observe the anti-liver cancer activity of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) gene and its bystander effects on hepatocellular carcinoma (HCC) cell line SMMC7721. METHODS: Full-length cDNA of human TRAIL was transferred into SMMC7721 cells with a binary adenoviral vector system. Polymerase-chain reaction following reverse transcription (RT-PCR) was used to determine the expression of TRAIL gene. Effects of the transfected gene on proliferation of SMMC7721 cells were measured by MTT assay. Its influence on apoptosis was demonstrated by fluorescence-activated cell sorting (FACS). The bystander effect was observed by co-culturing the SMMC7721 cells with and without the transfected TRAIL gene at different ratios, and the culture medium supernatant from the transfected cells was also examined for its influence on SMMC7721 cells. RESULTS: The growth-inhibition rate and apoptotic cell fraction in the cells transfected with the TRAIL gene, Bax gene or only LacZ gene were 91.2%, 48.0%, 28.8% and 29.1%, 12.5%, 6.6%, respectively. The growth-inhibition rate of transfection with these three sequences in normal human fibroblasts was 6.1%, 45.5% and 7.6%, respectively, indicating a discriminative inhibition of TRAIL transfection on the cancer cells. In the co-culturing test, addition of the transfected TRAIL to SMMC7721 cells in proportions of 5%, 25%, 50%, 75% and 100%, resulted in a growth-inhibition of 15.9%, 67%, 80.2%, 86.4% and 87.7%, respectively. We failed to observe a significant growth-inhibition effect of the culture medium supernatant on SMMC7721 cells. CONCLUSION: TRAIL gene transferred by a binary adenoviral vector system can inhibit proliferation of SMMC7721 cells and induce their apoptosis. A bystander effect was observed, which seemed not to be mediated by soluble factors.

[Effects of sodium hyaluronate on growth and adhesion of two human colorectal cancer cell lines in vitro].

OBJECTIVE: To investigate the effects of sodium hyaluronate on the growth and adhesion of colorectal cancer cells. METHODS: Human colorectal cancer cell lines SW620 and Colo205 were treated with sodium hyaluronate (25 -2,500 microg/ml), and cancer cell proliferation was measured by MTT assay in vitro. Flow-cytometric analysis was applied to detect expression of CD44 on SW620 and Colo205 cells. RESULT: In vitro sodium hyaluronate enhanced proliferation of Colo205 cells, but it had no appreciable effect on SW620 growth under the same doses, Meantime, CD44 expression on cancer cells decreased compared with controls. CONCLUSION: In vitro sodium hyaluronate has different effects on growth of different colorectal cancer cell lines, but can inhibit CD44 expression of colorectal cancer cells and influence their ability of adhesion.