Regulation of NDR Protein Kinase by Hydrophobic Motif Phosphorylation Mediated by the Mammalian Ste20-Like Kinase MST3

Abstract

NDR protein kinases are involved in the regulation of cell cycle progression and morphology. NDR1/NDR2 protein kinase is activated by phosphorylation on the activation loop phosphorylation site Ser281/Ser282 and the hydrophobic motif phosphorylation site Thr444/Thr442. Autophosphorylation of NDR is responsible for phosphorylation on Ser281/Ser282, whereas Thr444/Thr442 is targeted by an upstream kinase. Here we show that MST3, a mammalian Ste20-like protein kinase, is able to phosphorylate NDR protein kinase at Thr444/ Thr442. In vitro, MST3 selectively phosphorylated Thr442 of NDR2, resulting in a 10-fold stimulation of NDR activity. MOB1A (Mps one binder 1A) protein further increased the activity, leading to a fully active kinase. In vivo, Thr442 phosphorylation after okadaic acid stimulation was potently inhibited by MST3KR, a kinasedead mutant of MST3. Knockdown of MST3 using short hairpin constructs abolished Thr442 hydrophobic motif phosphorylation of NDR in HEK293F cells. We conclude that activation of NDR is a multistep process involving phosphorylation of the hydrophobic motif site Thr444/2 by MST3, autophosphorylation of Ser281/2, and binding of MOB1A.The NDR and LATS family of serine/threonine protein kinases participates in the regulation of cell cycle progression and cell morphology (14,43,53). These kinases share a conserved N-terminal regulatory domain that interacts with MOB (3, 6, 18, 33, 50) and S100B (31) proteins. The conserved catalytic (kinase) domain has an insertion of 30 amino acids between subdomains VII and VIII containing the activation segment phosphorylation site Ser281/Ser282 and, in the case of mammalian NDR1 and NDR2, an autoinhibitory sequence (3). The C-terminal regulatory domain encompasses the regulatory hydrophobic motif phosphorylation site Thr444 (32). Recent data show that NDR1 and NDR2 protein kinase activities are stimulated by Ca 2ϩ /S100B-and MOB1-binding-induced autophosphorylation on S281/S282 in vitro and in vivo (3, 31). Phosphorylation of the hydrophobic motif phosphorylation site T444/T442 is required for maximal activation and involves an upstream kinase (42,44).Genetic evidence suggests that Ste20 (Sterile)-like protein kinases function as upstream kinases of the NDR family. For example, one of the Saccharomyces cerevisiae Ste20-like kinases, Cdc15p, phosphorylates Dbf2p (28), and the Schizosaccharomyces pombe Ste20-like kinase Pak1p/Shk1p genetically interacts with Orb6p (49). Furthermore, the Ste20-like kinase Kic1p functionally interacts with Cbk1p, the closest relative of NDR from Saccharomyces cerevisiae (33), and the Drosophila melanogaster Ste20-like kinase HIPPO phosphorylates WARTS/LATS kinase (16,20,34,45,51). The closest mammalian homologues of Kic1p and Hippo are the mammalian Ste20-like protein kinases MST1/KRS1, MST2/KRS2, MST3, MST4/MASK, and SOK/YSK (29), which are involved in the regulation of cell morphology, proliferation, and apoptosis (7,9,22,25,38). This group of kinases contains an N-terminal kinase domain as well as an autoinhibitory C-...

Mutations in the Saccharomyces cerevisiae Kinase Cbk1p Lead to a Fertility Defect That Can Be Suppressed by the Absence of Brr1p or Mpt5p (Puf5p), Proteins Involved in RNA Metabolism

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Rapid detection, discovery, and identification of post‐translationally myristoylated proteins during apoptosis using a bio‐orthogonal azidomyristate analog

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Hippo signalling in the G2/M cell cycle phase: Lessons learned from the yeast MEN and SIN pathways

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