School of Life Science and Medicine, Dalian University of Technology, Panjin, 122406, China.
School of Life Science and Biotechnology, Dalian University of Technology, Dalian, China.
J Physiol Biochem. 2019 Nov;75(4):549-559. doi: 10.1007/s13105-019-00703-6. Epub 2019 Sep 16.
Caveolin-1 (Cav-1) is a critical structural protein of caveolae and plays an oncogene-like role by participating in abnormal protein glycosylation in hepatocellular carcinoma (HCC). However, the mechanism by which Cav-1 regulates glycosylation and glycosyltransferase expression has not been completely defined. Here, we show that Cav-1 promotes the expression of Rfng, which is a β-1,3-N-acetylglucosaminyltransferase included in the Fringe family. In this study, we showed that the mouse HCC cell line, Hepa1-6, with low Rfng transcription and protein levels, lacked Cav-1 expression, whereas strong Rfng expression was found in the mouse HCC cell line Hca-F, with high transcription and protein levels for Cav-1. Subsequently Cav-1 overexpression in Hepa1-6 was found to activate mitogen-activated protein kinase (MAPK) signaling and induce phosphorylation of the transcription factors Hnf4a and Sp1, which bind to the Rfng promoter region to promote its transcription. On the contrary, when knocking down Cav-1 expression in Hca-F, the activity of the MAPK pathway was significantly inhibited, and phosphorylation of Hnf4a, Sp1 and the expression of Rfng were attenuated. These data reveal that Cav-1 promotes phosphorylation of transcription factors Hnf4a and Sp1, which bind to the Rfng promoter region, via the MAPK signaling pathway, to induce the transcription of Rfng. Our current findings provide molecular genetic evidence that Cav-1 plays an important role in regulating glycosyltransferase expression and may participate in the abnormal glycosylation that mediates the invasion and metastasis of HCC.
窖蛋白-1（Cav-1）是质膜微囊的重要结构蛋白，通过参与肝癌（HCC）中异常的蛋白质糖基化，发挥癌基因样作用。然而，Cav-1 调节糖基化和糖基转移酶表达的机制尚未完全确定。在这里，我们表明 Cav-1 促进了 Fringe 家族中包含的β-1,3-N-乙酰氨基葡萄糖基转移酶 Rfng 的表达。在这项研究中，我们表明转录和蛋白水平较低的小鼠肝癌细胞系 Hepa1-6 缺乏 Cav-1 表达，而转录和蛋白水平较高的小鼠肝癌细胞系 Hca-F 中则存在强烈的 Rfng 表达。随后发现，Cav-1 在 Hepa1-6 中的过表达激活了丝裂原活化蛋白激酶（MAPK）信号通路，并诱导转录因子 Hnf4a 和 Sp1 的磷酸化，这两种转录因子结合到 Rfng 启动子区域以促进其转录。相反，当在 Hca-F 中敲低 Cav-1 的表达时，MAPK 通路的活性显著受到抑制，Hnf4a、Sp1 的磷酸化和 Rfng 的表达减弱。这些数据表明，Cav-1 通过 MAPK 信号通路促进转录因子 Hnf4a 和 Sp1 的磷酸化，这些转录因子结合到 Rfng 启动子区域，从而诱导 Rfng 的转录。我们目前的研究结果提供了分子遗传证据，表明 Cav-1 在调节糖基转移酶表达方面发挥着重要作用，并且可能参与了介导 HCC 侵袭和转移的异常糖基化。
