Nicholas Ktistakis

Research Summary

Autophagy (from the Greek self-eating) is a cellular mechanism which generates nutrients for the cell, primarily during times of starvation. Autophagy is also used to eliminate cell material that becomes damaged, leading to a periodic clean-up of the cell interior. Although it is a response by single cells, it is also very important for the health of an organism.

When autophagy is suppressed cells exhibit signs of oxidative damage because their dysfunctional mitochondria cannot be removed and continue to produce reactive oxygen species. Similarly, suppression of autophagy causes the build-up of mutant proteins that cause neurodegenerative disorders.

Autophagy is also critical for the neonatal period: animals which lack autophagy die soon after birth because they cannot generate nutrients during that time. Finally, autophagy is critical for the extension of lifespan in all organisms studied, and is therefore a significant factor that affects healthy ageing. The pathway of autophagy starts when a novel double membrane vesicle called an autophagosome is formed in the cell interior.

We have shown that one of the signals for formation of autophagosomes is the synthesis of a lipid called PI3P which leads to formation of omegasomes. These are membrane extensions of the endoplasmic reticulum, from which some autophagosomes emerge. We are studying exactly how this happens, both in terms of signals and of how the intermediate structures eventually lead to an autophagosome.

Latest Publications

Who plays the ferryman: ATG2 channels lipids into the forming autophagosome.
Ktistakis NT

Expansion of the autophagosomal membrane requires a mechanism to supply lipids while excluding most membrane proteins. In this issue, Valverde et al. (2019. https://doi.org/10.1083/jcb.201811139) identify ATG2, a member of the autophagy-related protein family, as a lipid transfer protein and provide important novel insights on how autophagosomes grow.

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The Journal of cell biology, , 1540-8140, , 2019

PMID: 31076453

ER platforms mediating autophagosome generation.
Ktistakis NT

The origin of the autophagosomal membrane started to be debated by scientists working in the field within one year of the modern definition of autophagy in 1963. There is now converging evidence from older and newer studies that the endoplasmic reticulum is involved in formation of autophagosomes. Thus, it is possible to trace from early morphological work - done without the benefit of molecular descriptions - to recent studies - dissecting how specific proteins nucleate autophagosome biogenesis - a long series of experimental findings that are beginning to answer the 55-year old question with some confidence. The view that has emerged is that specialised regions of the endoplasmic reticulum, in dynamic cross talk with most intracellular organelles via membrane contact sites, provide a platform for autophagosome biogenesis.

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Biochimica et biophysica acta. Molecular and cell biology of lipids, , 1879-2618, , 2019

PMID: 30890442

Phosphorylation of Syntaxin 17 by TBK1 Controls Autophagy Initiation.
Kumar S, Gu Y, Abudu YP, Bruun JA, Jain A, Farzam F, Mudd M, Anonsen JH, Rusten TE, Kasof G, Ktistakis N, Lidke KA, Johansen T, Deretic V

Syntaxin 17 (Stx17) has been implicated in autophagosome-lysosome fusion. Here, we report that Stx17 functions in assembly of protein complexes during autophagy initiation. Stx17 is phosphorylated by TBK1 whereby phospho-Stx17 controls the formation of the ATG13FIP200 mammalian pre-autophagosomal structure (mPAS) in response to induction of autophagy. TBK1 phosphorylates Stx17 at S202. During autophagy induction, Stx17 transfers from the Golgi, where its steady-state pools localize, to the ATG13FIP200 mPAS. Stx17 was in complexes with ATG13 and FIP200, whereas its non-phosphorylatable mutant Stx17 was not. Stx17 or TBK1 knockouts blocked ATG13 and FIP200 puncta formation. Stx17 or TBK1 knockouts reduced the formation of ATG13 protein complexes with FIP200 and ULK1. Endogenous Stx17 colocalized with LC3B following induction of autophagy. Stx17 knockout diminished LC3 response and reduced sequestration of the prototypical bulk autophagy cargo lactate dehydrogenase. We conclude that Stx17 is a TBK1 substrate and that together they orchestrate assembly of mPAS.

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Developmental cell, , 1878-1551, , 2019

PMID: 30827897