Jie An Huang

The present study investigated the sensitization of 5‑fluorouracil (5‑FU)‑resistant colon cancer cells in vitro, using oxymatrine, a Chinese herb, and a quinolizidine alkaloid compound extracted from the root of Sophora flavescens. The HCT‑8 colon cancer cell line and its 5‑FU‑resistant subline HCT‑8/5‑FU were treated with 5‑FU and oxymatrine, alone or in combination, at various doses. The cells were subsequently assessed for changes in cell viability, apoptosis and morphology and analyzed by fluorescence microscopy and western blotting. The data demonstrated that HCT‑8/5‑FU markedly increased the dose of 5‑FU required for the suppression of tumor cell viability (78.77±1.90 µg/ml vs. 9.20±0.96 µg/ml in parental HCT‑8 cells), whereas HCT‑8/5‑FU induced the tumor cell epithelial‑mesenchymal transition (EMT). By contrast, oxymatrine alone and in combination with 5‑FU altered HCT‑8/5‑FU cell morphology, apoptosis and EMT phenotypes. The combination of oxymatrine and 5‑FU reduced the protein expression of snail family transcriptional repressor 2 and vimentin, phosphorylated p65 and induced the expression of E‑cadherin, by inhibiting the nuclear factor κB (NF‑κB) signaling pathway. In conclusion, the data from the present study demonstrated that EMT was associated with 5‑FU chemoresistance in HCT‑8/5‑FU colon cancer cells, and that oxymatrine treatment was able to reverse such resistance. Oxymatrine may regulate tumor cell EMT and inactivate the NF‑κB signaling pathway, and may therefore serve as a potential therapeutic drug to reverse 5‑FU resistance in colon cancer cells.

Sphingosine kinase 1 (SphK1) is a master kinase that catalyzes the synthesis of sphingosine 1 phosphate and participates in the regulation of cell proliferation and autophagy. The present study aimed to assess the effects of the activation of the SphK1/extracellular signal‑regulated kinase (ERK)/phosphorylated (p‑)ERK pathway in the regulation of autophagy in colon cancer (HT‑29) cells. Inverted fluorescence microscopy was used to detect the expression of green fluorescent protein (GFP) in the SphK1‑overexpressing HT‑29 cells [SphK1(+)‑HT‑29] and the negative control HT‑29 cells (NC‑HT‑29). Western blotting was used to detect the protein expression levels of SphK1, ERK1/2, p‑ERK1/2, as well as those of the autophagy‑associated markers LC3A, ATG5, and ULK1. Protein localization and expression of the LC3A antibody were detected by immunofluorescence. The results demonstrated that GFP was similarly expressed in SphK1(+)‑HT‑29 and NC‑HT‑29 cells. However, significantly increased SphK1 mRNA and protein expression levels were detected in SphK1(+)‑HT‑29 cells compared with in NC‑HT‑29 cells, which resulted in upregulated ERK/p‑ERK. Furthermore, the protein expression levels of the three autophagy‑associated markers increased. LC3A protein was localized in the cytoplasm of SphK1(+)‑HT‑29 cells, indicating autophagy. In summary, the findings of the present study suggested that activation of the SphK1/ERK/p‑ERK pathway promotes autophagy in colon cancer HT‑29 cells.

Sphingosine kinase 1 (SphK1) plays an important role in colorectal carcinoma metastasis. However, whether SphK1 modulates epithelial-mesenchymal transition (EMT)-related marker expression and the underlying mechanisms remain unclear. In this study, in order to clarify this issue, we used various colorectal cancer (CRC) cell lines, Caco2, HT29, RKO and HCT116. Each of the cell lines was divided into 3 groups as follows: the control group, SKI-Ⅱ (SphK1 inhibitor) group and PF-562271 [focal adhesion kinase (FAK) inhibitor] group. The migratory ability of the cells was examined by Transwell chamber assay. The mRNA and protein expression levels of SphK1, FAK (p-FAK), Slug, vimentin, N-cadherin and E-cadherin were detected by PCR and western blot analysis, respectively. The results revealed that the suppression of SphK1 reduced the cell migratory ability, and decreased the expression of Slug, vimentin and N-cadherin; however, the expression of E-cadherin was increased. Moreover, the inhibition of SphK1 reduced the expression of p-FAK. The inhibition of FAK (p-FAK) also decreased the cell migratory ability, and decreased the expression of Slug, vimentin and N-cadherin, whereas the expression of E-cadherin was increased. Thus, our data suggest that SphK1 modulates the expression of EMT-related markers and cell migration by regulating the expression of p-FAK in CRC cells. Thus, SphK1 may play a functional role in mediating the EMT process in CRC.