title: Combining docking site and phosphosite predictions to find new substrates: identification of smoothelin-like-2 (SMTNL2) as a c-Jun N-terminal kinase (JNK) substrate.
abstract: Specific docking interactions between mitogen-activated protein kinases (MAPKs), their regulators, and their downstream substrates, are crucial for efficient and accurate signal transmission. To identify novel substrates of the c-Jun N-terminal kinase (JNK) family of MAPKs, we searched the human genome for proteins that contained (1), a predicted JNK-docking site (D-site); and (2), a cluster of putative JNK target phosphosites located close to the D-site. Here we describe a novel JNK substrate that emerged from this analysis, the functionally uncharacterized protein smoothelin-like 2 (SMTNL2). SMTNL2 protein bound with high-affinity to multiple MAPKs including JNK1-3 and ERK2; furthermore, the identity of conserved amino acids in the predicted docking site (residues 180-193) was necessary for this high-affinity binding. In addition, purified full-length SMTNL2 protein was phosphorylated by JNK1-3 in vitro, and this required the integrity of the D-site. Using mass spectrometry and mutagenesis, we identified four D-site-dependent phosphoacceptor sites in close proximity to the docking site, at S217, S241, T236 and T239. A short peptide comprised of the SMTNL2 D-site inhibited JNK-mediated phosphorylation of the ATF2 transcription factor, showing that SMTNL2 can compete with other substrates for JNK binding. Moreover, when transfected into HEK293 cells, SMTNL2 was phosphorylated by endogenous JNK in a D-site dependent manner, on the same residues identified in vitro. SMTNL2 protein was expressed in many mammalian tissues, with a notably high expression in skeletal muscle. Consistent with the hypothesis that SMTNL2 has a function in skeletal muscle, SMTNL2 protein expression was strongly induced during the transition from myoblasts to myotubes in differentiating C2C12 cells.
authors: Department of Developmental and Cell Biology, University of California Irvine, United States; Center for Complex Biological Systems, University of California Irvine, United States.
authors: Elizabeth A
authors: EA
authors: Gordon
authors: Thomas C
authors: TC
authors: Whisenant
authors: Michael
authors: M
authors: Zeller
authors: Robyn M
authors: RM
authors: Kaake
authors: William M
authors: WM
authors: Gordon
authors: Pascal
authors: P
authors: Krotee
authors: Vishal
authors: V
authors: Patel
authors: Lan
authors: L
authors: Huang
authors: Pierre
authors: P
authors: Baldi
authors: Lee
authors: L
authors: Bardwell
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D057809:HEK293 Cells; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D032446:Myoblasts / Q000166:cytology / Q000378:metabolism; D010750:Phosphoproteins / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D013379:Substrate Specificity
chemical_list: D010750:Phosphoproteins; C000593215:SMTNL2 protein, human; D048031:JNK Mitogen-Activated Protein Kinases
keywords: D-site; Docking; JNK; MAP kinase; Phosphorylation; SMTNL2
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