Functional analysis of Nck-interacting kinase (NIK)-related kinase (NRK) in vivo.

NCK相互作用激酶（NIK）相关激酶（NRK）是一种蛋白激酶，属于生发中心激酶（GCK）家族，激活c-Jun N-末端激酶（JNK）信号通路。在这项研究中，我们研究了NRK对小鼠肌肉发育中肌动蛋白细胞骨架组织的影响。NRK在COS 7细胞中的过表达诱导聚合肌动蛋白在核周聚集。在表达NRK的HEK 293 T细胞中，肌动蛋白解聚因子cofilin的磷酸化增加。此外，在体外磷酸化发生在位置3的丝氨酸残基（Ser-3）。由于Ser-3的磷酸化使cofilin的肌动蛋白解聚活性失活，这些结果表明NRK通过cofilin激酶或通过激活JNK诱导肌动蛋白聚合。因此，cofilin可能是NRK的直接底物。NRK主要在小鼠胚胎发育后期的骨骼肌中表达。因此，NRK可能通过cofilin磷酸化参与骨骼肌细胞中肌动蛋白细胞骨架组织的调节。我们成功地构建了在myogenin启动子下游表达Nrk或显性负性Nrk（Nrk-K54 E）的转基因小鼠，其表达模式与Nrk重叠。NRK在哺乳动物胚胎发育过程中参与cofilin的活性和肌动蛋白组装的调节，这一点还有待进一步研究。

Nck-interacting kinase (NIK)-related kinase (NRK) is a protein kinase that belongs to the germinal center kinase (GCK) family, and active the c-Jun N-terminal kinase (JNK) signaling pathway. In this study, we examined the effect of NRK on actin cytoskeletal organization in mouse muscle development. Overexpression of NRK in COS7 cells induced accumulation of polymerized actin at the perinuclear. Phosphorylation of cofilin, an actin-depolymerized factor, was increased in NRK-expressing HEK 293T cells. In addition, in vitro phosphorylation occurred at the serine residue of position 3 (Ser-3). Since the phosphorylation at Ser-3 inactives the actin-depolymerizing activitiy of cofilin, these results suggest that NRK induces actin polymerization through cofilin kinase, or through the activation of JNK. Thus, cofilin is likely to be a direct substrate o NRK. NRK is predominantly expressed in skeletal muscle during late stage of mouse embryogenesis. Thus, NRK may be involved in the regulation of actin cytoskeletal organization in skeletal muscle cells through cofilin phosphorylation. We have made the transgenic mouse that constracted Nrk or dominant negative Nrk (Nrk-K54 E) at the downstream of myogenin promoter, which overlapped the expression pattern with Nrk. Further studies are needed to clarify the involvement of NRK in the activity of cofilin and the regulation of actin assembly in skeletal muscle cells during mammalian embryogenesis.