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2014 ; 289
(25
): 17480-96
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Evidence toward a dual phosphatase mechanism that restricts Aurora A (Thr-295)
phosphorylation during the early embryonic cell cycle
#MMPMID24825897
Kang Q
; Srividhya J
; Ipe J
; Pomerening JR
J Biol Chem
2014[Jun]; 289
(25
): 17480-96
PMID24825897
show ga
The mitotic kinase Aurora A (AurA) is regulated by a complex network of factors
that includes co-activator binding, autophosphorylation, and dephosphorylation.
Dephosphorylation of AurA by PP2A (human, Ser-51; Xenopus, Ser-53) destabilizes
the protein, whereas mitotic dephosphorylation of its T-loop (human, Thr-288;
Xenopus, Thr-295) by PP6 represses AurA activity. However, AurA(Thr-295)
phosphorylation is restricted throughout the early embryonic cell cycle, not just
during M-phase, and how Thr-295 is kept dephosphorylated during interphase and
whether or not this mechanism impacts the cell cycle oscillator were unknown.
Titration of okadaic acid (OA) or fostriecin into Xenopus early embryonic extract
revealed that phosphatase activity other than PP1 continuously suppresses
AurA(Thr-295) phosphorylation during the early embryonic cell cycle.
Unexpectedly, we observed that inhibiting a phosphatase activity highly sensitive
to OA caused an abnormal increase in AurA(Thr-295) phosphorylation late during
interphase that corresponded with delayed cyclin-dependent kinase 1 (CDK1)
activation. AurA(Thr-295) phosphorylation indeed influenced this timing, because
AurA isoforms retaining an intact Thr-295 residue further delayed M-phase entry.
Using mathematical modeling, we determined that one phosphatase would be
insufficient to restrict AurA phosphorylation and regulate CDK1 activation,
whereas a dual phosphatase topology best recapitulated our experimental
observations. We propose that two phosphatases target Thr-295 of AurA to prevent
premature AurA activation during interphase and that phosphorylated AurA(Thr-295)
acts as a competitor substrate with a CDK1-activating phosphatase in late
interphase. These results suggest a novel relationship between AurA and protein
phosphatases during progression throughout the early embryonic cell cycle and
shed new light on potential defects caused by AurA overexpression.