title: Regulation of microtubule dynamics by Ca2+/calmodulin-dependent kinase IV/Gr-dependent phosphorylation of oncoprotein 18.
abstract: Oncoprotein 18 (Op18; also termed p19, 19K, p18, prosolin, and stathmin) is a regulator of microtubule (MT) dynamics and is phosphorylated by multiple kinase systems on four Ser residues. In addition to cell cycle-regulated phosphorylation, external signals induce phosphorylation of Op18 on Ser-25 by the mitogen-activated protein kinase and on Ser-16 by the Ca2+/calmodulin-dependent kinase IV/Gr (CaMK IV/Gr). Here we show that induced expression of a constitutively active mutant of CaMK IV/Gr results in phosphorylation of Op18 on Ser-16. In parallel, we also observed partial degradation of Op18 and a rapid increase of total cellular MTs. These results suggest a link between CaMK IV/Gr, Op18, and MT dynamics. To explore such a putative link, we optimized a genetic system that allowed conditional coexpression of a series of CaMK IV/Gr and Op18 derivatives. The result shows that CaMK IV/Gr can suppress the MT-regulating activity of Op18 by phosphorylation on Ser-16. In line with these results, by employing a chemical cross-linking protocol, it was shown that phosphorylation of Ser-16 is involved in weakening of the interactions between Op18 and tubulin. Taken together, these data suggest that the mechanism of CaMK IV/Gr-mediated suppression of Op18 activity involves both partial degradation of Op18 and direct modulation of the MT-destabilizing activity of this protein. These results show that Op18 phosphorylation by CaMK IV/Gr may couple alterations of MT dynamics in response to external signals that involve Ca2+.
authors.affiliation: Department for Cell and Molecular Biology, University of Umeå, Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Melander Gradin
authors.forename: U
authors.initials: U
authors.lastname: Marklund
authors.forename: N
authors.initials: N
authors.lastname: Larsson
authors.forename: T A
authors.initials: TA
authors.lastname: Chatila
authors.forename: M
authors.initials: M
authors.lastname: Gullberg
mesh_terms: D054734:Calcium-Calmodulin-Dependent Protein Kinase Type 4; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D005822:Genetic Vectors; D004854:Herpesvirus 4, Human; D006801:Humans; D008868:Microtubule Proteins; D008870:Microtubules / Q000378:metabolism; D008970:Molecular Weight; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011108:Polymers / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D050777:Stathmin
chemical_list: D008868:Microtubule Proteins; D010750:Phosphoproteins; D011108:Polymers; C493995:STMN1 protein, human; D050777:Stathmin; D012694:Serine; C517683:CAMK4 protein, human; D054734:Calcium-Calmodulin-Dependent Protein Kinase Type 4; D017871:Calcium-Calmodulin-Dependent Protein Kinases