Millward T A, Hess D, Hemmings B A
Friedrich Miescher-Institut, Maulbeerstrasse 66, CH-4058 Basel, Switzerland.
J Biol Chem. 1999 Nov 26;274(48):33847-50. doi: 10.1074/jbc.274.48.33847.
Ndr is a nuclear serine/threonine protein kinase that belongs to a subfamily of kinases implicated in the regulation of cell division and cell morphology. This subfamily includes the kinases LATS, Orb6, Cot-1, and Dbf2. We show here that Ndr is potently activated when intact cells are treated with okadaic acid, suggesting that Ndr is normally held in a state of low activity by protein phosphatase 2A. We mapped the regulatory phosphorylation sites of Ndr protein kinase and found that active Ndr is phosphorylated on Ser-281 and Thr-444. Mutation of either site to alanine strongly reduced both basal and okadaic acid-stimulated Ndr activity, while combined mutation abolished Ndr activity completely. Importantly, each of these sites (and also the surrounding sequences) are conserved in the kinase relatives of Ndr, suggesting a general mechanism of activation for kinases of this subfamily. Ser-281 and Thr-444 are also similar to the regulatory phosphorylation sites in several targets of the phosphoinositide-dependent protein kinase PDK1.(1) However, PDK1 does not appear to function as an upstream kinase for Ndr. Thus, Ndr and its close relatives may operate in a novel signaling pathway downstream of an as-yet-unidentified kinase with specificity similar to, but distinct from, PDK1.
Ndr是一种核丝氨酸/苏氨酸蛋白激酶，属于与细胞分裂和细胞形态调控相关的激酶亚家族。该亚家族包括激酶LATS、Orb6、Cot-1和Dbf2。我们在此表明，当完整细胞用冈田酸处理时，Ndr会被有效激活，这表明Ndr通常通过蛋白磷酸酶2A保持在低活性状态。我们绘制了Ndr蛋白激酶的调节磷酸化位点图谱，发现活性Ndr在Ser-281和Thr-444处被磷酸化。将这两个位点中的任何一个突变为丙氨酸都会强烈降低基础和冈田酸刺激的Ndr活性，而双重突变则会完全消除Ndr活性。重要的是，这些位点（以及周围序列）在Ndr的激酶亲属中都是保守的，这表明该亚家族激酶的激活存在一种普遍机制。Ser-281和Thr-444也与磷酸肌醇依赖性蛋白激酶PDK1的几个靶标的调节磷酸化位点相似。(1)然而，PDK1似乎并不作为Ndr的上游激酶发挥作用。因此，Ndr及其近亲可能在一条尚未确定的激酶下游的新信号通路中发挥作用，该激酶具有与PDK1相似但又不同的特异性。
