Overexpression of semaphorin 4D (SEMA4D), an immune semaphorin, is found in various human malignancies, including colorectal cancer (CRC). In this study, we explored the relationship between silencing SEMA4D expression and 5-fluorouracil (5-FU) response in the colorectal cancer cell line. SW48 cells were transfected with a short interfering RNA (siRNA) in order to silence SEMA4D gene expression and then exposed to 5-FU for 48 h. The down-regulation of SEMA4D expression was confirmed by qRT-PCR and the particular concentration of 5-FU was acquired using MTT assay. Flow cytometry and western blot were used to evaluate apoptosis rate and pro- and anti-apoptotic expression levels of proteins involved in apoptosis including Bax, Bcl-2, P53, and caspase-3. Other oncogenic activities including epithelial-mesenchymal transition (EMT) process, cancer stem cell (CSC) markers, and β-catenin pathway were investigated using qRT-PCR, and western blot. The proliferation was analyzed via colony formation test and cell invasion was assessed by transwell assay. Our data demonstrate that SEMA4D silencing results in strikingly elevated apoptosis in response to 5-FU treatment and leads to down-regulation of Bcl-2 and overexpression of Bax, P53, and caspase-3 in protein levels. Furthermore, the mRNA and protein expression levels of β-catenin, as well as transcript expressions of CSCs and EMT markers, were remarkably diminished. However, mRNA expression of E-cadherin as an epithelial marker was significantly increased in 5-FU treatment combined with siRNA SEMA4D. This study implicates that the silencing of SEMA4D by siRNA promotes the chemosensitivity of SW48 cells to 5-FU and it may be a potential therapeutic agent for colon cancer therapy.

semaphorin 4D（SEMA4D）（一种免疫信号量）的过度表达在包括结肠直肠癌（CRC）在内的各种人类恶性肿瘤中被发现。在这项研究中，我们探讨了沉默SEMA4D表达与大肠癌细胞株中5-氟尿嘧啶（5-FU）反应之间的关系。为了使SEMA4D基因表达沉默，将SW48细胞用短干扰RNA（siRNA）转染，然后暴露于5-FU 48小时。通过qRT-PCR证实了SEMA4D表达的下调，并且使用MTT测定法获得了5-FU的特定浓度。流式细胞仪和蛋白质印迹用于评估细胞凋亡率以及凋亡相关蛋白（包括Bax，Bcl-2，P53和caspase-3）的凋亡前后表达水平。其他致癌活动包括上皮-间质转化（EMT）过程，使用qRT-PCR和Western blot研究了癌症干细胞（CSC）标记和β-catenin途径。通过集落形成测试分析增殖，并通过transwell测定评估细胞侵袭。我们的数据表明，SEMA4D沉默导致响应5-FU处理的细胞凋亡显着增加，并导致Bcl-2的下调和蛋白水平中Bax，P53和caspase-3的过表达。此外，β-catenin的mRNA和蛋白质表达水平以及CSCs和EMT标记的转录物表达显着降低。然而，E-钙粘蛋白作为上皮标志物的mRNA表达在5-FU与siRNA SEMA4D联合治疗中显着增加。