Department of Nutrition and Health Sciences, University of Nebraska-Lincoln, Lincoln, NE, 68583, USA.
Department of Nutrition and Health Sciences, University of Nebraska-Lincoln, Lincoln, NE, 68583, USA.
Biochem Biophys Res Commun. 2021 Mar 19;545:183-188. doi: 10.1016/j.bbrc.2021.01.070. Epub 2021 Feb 6.
The mechanistic target of rapamycin complex 1 (mTORC1) signaling is the prototypical pathway regulating protein synthesis and cell proliferation. The level of mTORC1 activity is high in intestinal stem cells located at the base of the crypts and thought to gradually decrease as transit-amplifying cells migrate out of the crypts and differentiate into enterocytes, goblet cells or enteroendocrine cells along the epithelium. The unknown mechanism responsible for the silencing of intestinal epithelium mTORC1 during cell differentiation was investigated in Caco-2 cells, which spontaneously differentiate into enterocytes in standard growth medium. The results show that TSC2, an upstream negative regulator of mTORC1 was central to mTORC1 silencing in differentiated Caco-2 cells. AMPK-mediated activation of TSC2 (Ser1387) and repression of Raptor (Ser792), an essential component of mTORC1, were stimulated in differentiated Caco-2 cells. ERK1/2-mediated repression of TSC2 (Ser664) seen in undifferentiated Caco-2 cells was lifted in differentiated cells. IRS-1-mediated activation of AKT (Thr308) phosphorylation was stimulated in differentiated Caco-2 cells and may be involved in cross-pathway repression of ERK1/2. Additionally, PRAS40 (Thr246) phosphorylation was decreased in differentiated Caco-2 cells compared to undifferentiated cells allowing dephosphorylated PRAS40 to displace Raptor thereby repressing mTORC1 kinase activity.
雷帕霉素靶蛋白复合物 1（mTORC1）信号通路是调节蛋白质合成和细胞增殖的典型途径。mTORC1 的活性水平在位于隐窝底部的肠干细胞中较高，并且被认为随着过渡扩增细胞从隐窝中迁移出来并沿着上皮分化为肠细胞、杯状细胞或肠内分泌细胞而逐渐降低。在 Caco-2 细胞中研究了负责细胞分化过程中肠上皮细胞 mTORC1 沉默的未知机制，Caco-2 细胞在标准生长培养基中自发分化为肠细胞。结果表明，mTORC1 的上游负调节因子 TSC2 是分化的 Caco-2 细胞中 mTORC1 沉默的核心。AMPK 介导的 TSC2（Ser1387）激活和 Raptor（Ser792）抑制，mTORC1 的必需组成部分，在分化的 Caco-2 细胞中受到刺激。在未分化的 Caco-2 细胞中观察到的 ERK1/2 介导的 TSC2（Ser664）抑制在分化细胞中被解除。IRS-1 介导的 AKT（Thr308）磷酸化激活在分化的 Caco-2 细胞中受到刺激，并且可能涉及 ERK1/2 的交叉途径抑制。此外，与未分化细胞相比，分化的 Caco-2 细胞中 PRAS40（Thr246）磷酸化减少，从而允许去磷酸化的 PRAS40 取代 Raptor，从而抑制 mTORC1 激酶活性。
