Abell Amy N, Rivera-Perez Jaime A, Cuevas Bruce D, Uhlik Mark T, Sather Susan, Johnson Nancy L, Minton Suzanne K, Lauder Jean M, Winter-Vann Ann M, Nakamura Kazuhiro, Magnuson Terry, Vaillancourt Richard R, Heasley Lynn E, Johnson Gary L
Department of Pharmacology, University of North Carolina, Chapel Hill, 27599-7365, USA.
Mol Cell Biol. 2005 Oct;25(20):8948-59. doi: 10.1128/MCB.25.20.8948-8959.2005.
Skeletal disorders and neural tube closure defects represent clinically significant human malformations. The signaling networks regulating normal skeletal patterning and neurulation are largely unknown. Targeted mutation of the active site lysine of MEK kinase 4 (MEKK4) produces a kinase-inactive MEKK4 protein (MEKK4(K1361R)). Embryos homozygous for this mutation die at birth as a result of skeletal malformations and neural tube defects. Hindbrains of exencephalic MEKK4(K1361R) embryos show a striking increase in neuroepithelial cell apoptosis and a dramatic loss of phosphorylation of MKK3 and -6, mitogen-activated protein kinase kinases (MKKs) regulated by MEKK4 in the p38 pathway. Phosphorylation of MAPK-activated protein kinase 2, a p38 substrate, is also inhibited, demonstrating a loss of p38 activity in MEKK4(K1361R) embryos. In contrast, the MEK1/2-extracellular signal-regulated kinase 1 (ERK1)/ERK2 and MKK4-Jun N-terminal protein kinase pathways were unaffected. The p38 pathway has been shown to regulate the phosphorylation and expression of the small heat shock protein HSP27. Compared to the wild type, MEKK4(K1361R) fibroblasts showed significantly reduced phosphorylation of p38 and HSP27, with a corresponding heat shock-induced instability of the actin cytoskeleton. Together, these data demonstrate MEKK4 regulation of p38 and that substrates downstream of p38 control cellular homeostasis. The findings are the first demonstration that MEKK4-regulated p38 activity is critical for neurulation.
骨骼疾病和神经管闭合缺陷是具有临床意义的人类畸形。调节正常骨骼模式形成和神经胚形成的信号网络在很大程度上尚不清楚。MEK激酶4（MEKK4）活性位点赖氨酸的靶向突变产生了一种激酶失活的MEKK4蛋白（MEKK4(K1361R)）。该突变的纯合胚胎因骨骼畸形和神经管缺陷在出生时死亡。无脑畸形的MEKK4(K1361R)胚胎的后脑显示神经上皮细胞凋亡显著增加，以及p38途径中受MEKK4调节的丝裂原活化蛋白激酶激酶（MKK）MKK3和MKK6的磷酸化显著丧失。p38底物MAPK活化蛋白激酶2的磷酸化也受到抑制，表明MEKK4(K1361R)胚胎中p38活性丧失。相比之下，MEK1/2-细胞外信号调节激酶1（ERK1）/ERK2和MKK4- Jun N端蛋白激酶途径未受影响。已证明p38途径调节小热休克蛋白HSP27的磷酸化和表达。与野生型相比，MEKK4(K1361R)成纤维细胞显示p38和HSP27的磷酸化显著降低，同时热休克诱导的肌动蛋白细胞骨架稳定性相应降低。总之，这些数据证明了MEKK4对p38的调节作用，以及p38下游底物对细胞稳态的控制。这些发现首次证明MEKK4调节的p38活性对神经胚形成至关重要。
