Extracellular signal-regulated kinase (ERK), also known as classical mitogen-activated protein kinase, plays critical roles in cell regulation. ERK is activated through phosphorylation by a cascade of protein kinases including MEK. Various ligands activate the MEK/ERK pathway through receptor-dependent cell signaling. In cultured cells, many ligands such as growth factors, hormones, cytokines and vasoactive peptides elicit transient activation of MEK/ERK, often peaking at ~10 min after the cell treatment. Here, we describe a novel biological event, in which ligand-mediated cell signaling results in the dephosphorylation of MEK/ERK. Neuromedin N and neurotensin, peptides derived from the same precursor polypeptide, elicit cell signaling through the neurotensin receptors. In cultured human pulmonary artery smooth muscle cells (PASMCs), but not in human pulmonary artery endothelial cells (PAECs), we found that both neuromedin N and neurotensin promoted the dephosphorylation of ERK and MEK. Human PASMCs were found to express neurotensin receptor (NTR)-1, −2 and −3, while human PAECs only express NTR3. Neuromedin N-mediated dephosphorylation was suppressed by small chemical inhibitors of protein phosphatase 1/2A and peptidyl-prolyl isomerase. Transmission electron microscopy showed the formation of endocytic vesicles in response to neuromedin N treatment, and dephosphorylation did not occur when sorting nexin 9, a critical regulator of the endocytic vesicle formation, was knocked down. We conclude that neuromedin N and neurotensin elicit a unique dephosphorylation signaling in the MEK/ERK pathway that is regulated by endocytosis. Considering the pathophysiological importance of the MEK/ERK pathway, this discovery of the dephosphorylation mechanism should advance the field of cell signaling.

细胞外信号调节激酶（ERK），也称为经典的促分裂原活化蛋白激酶，在细胞调节中起关键作用。ERK通过包括MEK在内的一系列蛋白激酶的磷酸化作用被激活。各种配体通过受体依赖性细胞信号传导激活MEK / ERK途径。在培养的细胞中，许多配体（例如生长因子，激素，细胞因子和血管活性肽）会引起MEK / ERK的瞬时激活，通常在细胞处理后约10分钟达到峰值。在这里，我们描述了一种新型的生物事件，其中配体介导的细胞信号传导导致MEK / ERK的去磷酸化。来自同一前体多肽的肽Neuromedin N和Neurotensin通过神经降压素受体引发细胞信号转导。在培养的人肺动脉平滑肌细胞（PASMC）中，但是在人肺动脉内皮细胞（PAEC）中却没有，我们发现神经调节素N和神经降压素都能促进ERK和MEK的去磷酸化。发现人PASMC表达神经降压素受体（NTR）-1，-2和-3，而人PAEC仅表达NTR3。Neuromedin N介导的去磷酸化被蛋白质磷酸酶1 / 2A和肽基脯氨酰异构酶的小型化学抑制剂所抑制。透射电子显微镜显示响应神经调节素N的处理，内吞小泡的形成，当分选内毒素9（一种内吞小泡形成的关键调节剂）时，未发生去磷酸化作用。我们得出的结论是，神经调节素N和神经降压素在由内吞作用调节的MEK / ERK途径中引起独特的去磷酸化信号传导。