Atg13 and FIP200 act independently of Ulk1 and Ulk2 in autophagy induction

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Sebastian Alers1, Antje S Löffler, Florian Paasch

  • 1Department of Internal Medicine I; University Clinic of Tübingen; Tübingen, Germany.

Autophagy
|October 26, 2011
PubMed

Insights

Autophagy induction requires Atg13, which binds to FIP200. This study shows Atg13 is essential for autophagy, independent of Ulk1/2 kinases, highlighting a novel FIP200-Atg13 partnership in this vital cellular process.

Area of Science:

  • Cellular Biology
  • Molecular Biology
  • Biochemistry

Background:

  • The mammalian target of rapamycin complex 1 (mTORC1) normally inhibits autophagy by repressing the Unc-51-like kinases 1/2 (Ulk1/2), focal adhesion kinase family-interacting protein of 200 kDa (FIP200), and Atg13 complex.
  • Starvation releases this inhibition, activating Ulk1/2 and initiating autophagy.
  • Atg13 has been hypothesized to bridge Ulk1/2 and FIP200, boosting Ulk1/2 kinase activity.

Purpose of the Study:

  • To investigate the essential role of Atg13 in autophagy induction.
  • To determine the dependency of Atg13 function on FIP200 binding and Ulk1/2 kinases.
  • To elucidate the specific mechanisms by which Atg13 regulates autophagy.

Main Methods:

  • Utilized Atg13-deficient cells to assess autophagy.
  • Performed FIP200 binding assays.
  • Generated Ulk1 and Ulk2 double knockout cells.
  • Identified and analyzed Ulk1-dependent phosphorylation sites on Atg13.

Main Results:

  • Atg13-deficient cells exhibited a complete failure in autophagy induction, confirming Atg13's indispensability.
  • Atg13's function in autophagy was strictly dependent on its interaction with FIP200.
  • Simultaneous knockout of Ulk1 and Ulk2 did not impair autophagy induction, indicating an Ulk1/2-independent role for Atg13.
  • Ulk1-dependent phosphorylation sites on Atg13 were found to be dispensable for autophagy.

Conclusions:

  • Atg13 is a critical and indispensable component for autophagy induction.
  • Atg13's essential role in autophagy is mediated through its interaction with FIP200, independent of Ulk1/2 kinase activity.
  • Atg13 and FIP200 function in a coordinated manner to drive autophagy induction, suggesting a previously unrecognized regulatory mechanism.

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