Evidence Towards a Dual Phosphatase Mechanism that Restricts Aurora A(T295) Phosphorylation During the Early Embryonic Cell Cycle [Signal Transduction]

May 13th, 2014 by Kang, Q., Srividhya, J., Ipe, J., Pomerening, J. R.

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: S51; Xenopus: S53) destabilizes the protein, while mitotic dephosphorylation of its T-loop (human: T288; Xenopus: T295) by PP6 represses AurA activity. But AurA(T295) phosphorylation is restricted throughout the early embryonic cell cycle, not just during M-phase, and how T295 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(T295) 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(T295) phosphorylation late during interphase that corresponded with delayed CDK1 activation. AurA(T295) phosphorylation indeed influenced this timing, as AurA isoforms retaining an intact T295 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 T295 of AurA to prevent premature AurA activation during interphase, and that phosphorylated AurA(T295) 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.
  • Posted in Journal of Biological Chemistry, Publications
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