Mol. Cell. Biol., Jun 1997, 3459-3467, Vol 17, No. 6
H Melander Gradin, U Marklund, N Larsson, TA Chatila and M Gullberg
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+.
Copyright © 1997, American Society for Microbiology
Regulation of microtubule dynamics by Ca2+/calmodulin-dependent kinase IV/Gr-dependent phosphorylation of oncoprotein 18
Department for Cell and Molecular Biology, University of Umea, Sweden.
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