Morinville Anne, Martin Stéphane, Lavallée Mariette, Vincent Jean-Pierre, Beaudet Alain, Mazella Jean
Montreal Neurological Institute, McGill University, 3801 University Street, Montreal, Que., Canada H3A 2B4.
Int J Biochem Cell Biol. 2004 Nov;36(11):2153-68. doi: 10.1016/j.biocel.2004.04.013.
The neurotensin receptor-3, originally identified as sortilin, is unique among neuropeptide receptors in that it is a single trans-membrane domain, type I receptor. To gain insight into the functionality of neurotensin receptor-3, we examined the neurotensin-induced intracellular trafficking of this receptor in the human carcinoma cell line HT29, which expresses both neurotensin receptor-1 and -3 sub-types. At steady state, neurotensin receptor-3 was found by sub-cellular fractionation and electron microscopic techniques to be predominantly associated with intracellular elements. A small proportion (approximately 10%) was associated with the plasma membrane, but a significant amount (approximately 25%) was observed inside the nucleus. Following stimulation with neurotensin (NT), neurotensin/neurotensin receptor-3 complexes were internalized via the endosomal pathway. This internalization entailed no detectable loss of cell surface receptors, suggesting compensation through either recycling or intracellular receptor recruitment mechanisms. Internalized ligand and receptors were both sorted to the pericentriolar recycling endosome/Trans-Golgi Network (TGN), indicating that internalized neurotensin is sorted to this compartment via neurotensin receptor-3. Furthermore, within the Trans-Golgi Network, neurotensin was bound to a lower molecular form of the receptor than at the cell surface or in early endosomes, suggesting that signaling and transport functions of neurotensin receptor-3 may be mediated through different molecular forms of the protein. In conclusion, the present work suggests that the neurotensin receptor-3 exists in two distinct forms in HT29 cells: a high molecular weight, membrane-associated form responsible for neurotensin endocytosis from the cell surface and a lower molecular weight, intracellular form responsible for the sorting of internalized neurotensin to the Trans-Golgi Network.
神经降压素受体3最初被鉴定为sortilin，在神经肽受体中是独特的，因为它是一种单跨膜结构域的I型受体。为了深入了解神经降压素受体3的功能，我们研究了神经降压素诱导的该受体在人癌细胞系HT29中的细胞内运输，该细胞系表达神经降压素受体1和3亚型。在稳态下，通过亚细胞分级分离和电子显微镜技术发现神经降压素受体3主要与细胞内成分相关。一小部分（约10%）与质膜相关，但在细胞核内观察到相当数量（约25%）。用神经降压素（NT）刺激后，神经降压素/神经降压素受体3复合物通过内体途径内化。这种内化不会导致细胞表面受体的可检测损失，表明通过再循环或细胞内受体招募机制进行补偿。内化的配体和受体都被分选到中心粒周围再循环内体/反式高尔基体网络（TGN），表明内化的神经降压素通过神经降压素受体3被分选到这个区室。此外，在反式高尔基体网络中，与细胞表面或早期内体相比，神经降压素与受体的较低分子量形式结合，这表明神经降压素受体3的信号传导和运输功能可能通过该蛋白的不同分子形式介导。总之，目前的研究表明，神经降压素受体3在HT29细胞中以两种不同形式存在：一种高分子量的膜相关形式，负责从细胞表面进行神经降压素内吞作用；另一种低分子量的细胞内形式，负责将内化的神经降压素分选到反式高尔基体网络。
