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Akt phosphorylates both Tsc1 and Tsc2 in Drosophila, but neither phosphorylation is required for normal animal growth

Sibylle Schleich1, Aurelio A Teleman

  • 1German Cancer Research Center (DKFZ), Heidelberg, Germany.

Plos One
|July 18, 2009
PubMed

Insights

The Akt kinase does not require phosphorylation of the Tsc1/2 complex to promote tissue growth. This study found that flies lacking Akt phosphorylation sites on Tsc1 and Tsc2 are viable and grow normally.

Area of Science:

  • Molecular Biology
  • Cell Signaling
  • Developmental Biology

Background:

  • Akt is a key regulator of cell growth and metabolism, downstream of insulin signaling.
  • Akt phosphorylates Tsc2, an inhibitor of the mechanistic target of rapamycin (TOR) kinase, suggesting a role in growth promotion.
  • The functional significance of Akt-mediated Tsc2 phosphorylation is unclear, as Tsc2 mutants lacking these sites are viable in Drosophila.

Purpose of the Study:

  • To investigate whether Akt redundantly phosphorylates the Tsc1/2 complex in Drosophila.
  • To determine the functional significance of Akt phosphorylation of Tsc1 and Tsc2 in tissue growth.

Main Methods:

  • Generated Drosophila mutants lacking Akt phosphorylation sites on Tsc1 and Tsc2.
  • Assessed the viability, size, and growth rates of these mutant flies.
  • Examined the role of Akt phosphorylation of the Tsc1/2 complex in TORC1 activation and tissue growth.

Main Results:

  • Akt phosphorylates Tsc1 at Ser533 in Drosophila.
  • Flies lacking Akt phosphorylation sites on Tsc1 alone, or on both Tsc1 and Tsc2, are viable and exhibit normal growth.
  • These findings indicate that Akt phosphorylation of the Tsc1/2 complex is not essential for Akt to activate TORC1 and promote tissue growth.

Conclusions:

  • Akt-mediated phosphorylation of the Tsc1/2 complex is dispensable for promoting tissue growth in Drosophila.
  • The study clarifies the non-essential role of Tsc1/2 phosphorylation by Akt in the context of insulin signaling and growth regulation.

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