The deubiquitylase USP33 discriminates between RALB functions in autophagy and innate immune response.
The RAS-like GTPase RALB mediates cellular responses to nutrient availability or viral infection by respectively engaging two components of the exocyst complex, EXO84 and SEC5. RALB employs SEC5 to trigger innate immunity signalling, whereas RALB-EXO84 interaction induces autophagocytosis. How this differential interaction is achieved molecularly by the RAL GTPase remains unknown. We found that whereas GTP binding turns on RALB activity, ubiquitylation of RALB at Lys 47 tunes its activity towards a particular effector. Specifically, ubiquitylation at Lys 47 sterically inhibits RALB binding to EXO84, while facilitating its interaction with SEC5. Double-stranded RNA promotes RALB ubiquitylation and SEC5-TBK1 complex formation. In contrast, nutrient starvation induces RALB deubiquitylation by accumulation and relocalization of the deubiquitylase USP33 to RALB-positive vesicles. Deubiquitylated RALB promotes the assembly of the RALB-EXO84-beclin-1 complexes driving autophagosome formation. Thus, ubiquitylation within the effector-binding domain provides the switch for the dual functions of RALB in autophagy and innate immune responses.
1] VIB Center for the Biology of Disease, VIB, 3000 Leuven, Belgium [2] Department of Human Genetics, KU Leuven, Herestraat 49, 3000 Leuven, Belgium.
Michal
M
Simicek
Sam
S
Lievens
Mathias
M
Laga
Dmytro
D
Guzenko
Vasily N
VN
Aushev
Peter
P
Kalev
Maria Francesca
MF
Baietti
Sergei V
SV
Strelkov
Kris
K
Gevaert
Jan
J
Tavernier
Anna A
AA
Sablina
D001343:Autophagy / Q000235:genetics / Q000502:physiology*; D002478:Cells, Cultured; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D007113:Immunity, Innate / Q000235:genetics / Q000502:physiology*; D008958:Models, Molecular; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D015398:Signal Transduction; D043222:Ubiquitin Thiolesterase / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination; D020725:ral GTP-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
C483163:Ralb protein, human; C449799:USP33 protein, human; D043222:Ubiquitin Thiolesterase; D020725:ral GTP-Binding Proteins