ULK1/2 Restricts the Formation of Inducible SINT-Speckles, Membraneless Organelles Controlling the Threshold of TBK1 Activation

Vera Vivian Saul; Markus Seibert; Marcus Krüger; Sylvia Jeratsch; Michael Kracht; Michael Lienhard Schmitz

doi:10.1016/j.isci.2019.08.001

ULK1/2 Restricts the Formation of Inducible SINT-Speckles, Membraneless Organelles Controlling the Threshold of TBK1 Activation

iScience. 2019 Sep 27:19:527-544. doi: 10.1016/j.isci.2019.08.001. Epub 2019 Aug 6.

Authors

Vera Vivian Saul¹, Markus Seibert¹, Marcus Krüger², Sylvia Jeratsch³, Michael Kracht⁴, Michael Lienhard Schmitz⁵

Affiliations

¹ Institute of Biochemistry, Medical Faculty, Friedrichstrasse 24, Justus-Liebig-University, D-35392 Giessen, Germany, Member of the German Center for Lung Research.
² Institute for Genetics, Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD), 50931 Cologne, Germany; Center for Molecular Medicine (CMMC), University of Cologne, 50931 Cologne, Germany.
³ Max Planck Institute for Heart and Lung Research, 61231 Bad Nauheim, Germany.
⁴ Rudolf-Buchheim-Institute of Pharmacology, Justus-Liebig-University, D-35392 Giessen, Germany, Member of the German Center for Lung Research.
⁵ Institute of Biochemistry, Medical Faculty, Friedrichstrasse 24, Justus-Liebig-University, D-35392 Giessen, Germany, Member of the German Center for Lung Research. Electronic address: lienhard.schmitz@biochemie.med.uni-giessen.de.

Abstract

Membraneless organelles (MLOs) are liquid-like subcellular compartments providing spatiotemporal control to biological processes. This study reveals that cellular stress leads to the incorporation of the adaptor protein SINTBAD (TBKBP1) into membraneless, cytosolic speckles. Determination of the interactome identified >100 proteins forming constitutive and stress-inducible members of an MLO that we termed SINT-speckles. SINT-speckles partially colocalize with activated TBK1, and deletion of SINTBAD and the SINT-speckle component AZI2 leads to impaired TBK1 phosphorylation. Dynamic formation of SINT-speckles is positively controlled by the acetyltransferase KAT2A (GCN5) and antagonized by heat shock protein-mediated chaperone activity. SINT-speckle formation is also inhibited by the autophagy-initiating kinases ULK1/2, and knockdown of these kinases prevented focal TBK1 phosphorylation in a pathway-specific manner. The phlebovirus-encoded non-structural protein S enhances ULK1-mediated TBK1 phosphorylation and shows a stress-induced translocation to SINT-speckles, raising the possibility that viruses can also target this signaling hub to manipulate host cell functions.

Keywords: Biochemistry; Biological Sciences; Cell Biology; Molecular Biology.