Ras homolog enriched in brain (Rheb) enhances apoptotic signaling.
Rheb is a homolog of Ras GTPase that regulates cell growth, proliferation, and regeneration via mammalian target of rapamycin (mTOR). Because of the well established potential of activated Ras to promote survival, we sought to investigate the ability of Rheb signaling to phenocopy Ras. We found that overexpression of lipid-anchored Rheb enhanced the apoptotic effects induced by UV light, TNFα, or tunicamycin in an mTOR complex 1 (mTORC1)-dependent manner. Knocking down endogenous Rheb or applying rapamycin led to partial protection, identifying Rheb as a mediator of cell death. Ras and c-Raf kinase opposed the apoptotic effects induced by UV light or TNFα but did not prevent Rheb-mediated apoptosis. To gain structural insight into the signaling mechanisms, we determined the structure of Rheb-GDP by NMR. The complex adopts the typical canonical fold of RasGTPases and displays the characteristic GDP-dependent picosecond to nanosecond backbone dynamics of the switch I and switch II regions. NMR revealed Ras effector-like binding of activated Rheb to the c-Raf-Ras-binding domain (RBD), but the affinity was 1000-fold lower than the Ras/RBD interaction, suggesting a lack of functional interaction. shRNA-mediated knockdown of apoptosis signal-regulating kinase 1 (ASK-1) strongly reduced UV or TNFα-induced apoptosis and suppressed enhancement by Rheb overexpression. In conclusion, Rheb-mTOR activation not only promotes normal cell growth but also enhances apoptosis in response to diverse toxic stimuli via an ASK-1-mediated mechanism. Pharmacological regulation of the Rheb/mTORC1 pathway using rapamycin should take the presence of cellular stress into consideration, as this may have clinical implications.
Karassek
Sascha
S
Department of Molecular Neurobiochemistry, Faculty of Chemistry and Biochemistry, Ruhr University of Bochum, 44780 Bochum, Germany.
Berghaus
Carsten
C
Schwarten
Melanie
M
Goemans
Christoph G
CG
Ohse
Nadine
N
Kock
Gerd
G
Jockers
Katharina
K
Neumann
Sebastian
S
Gottfried
Sebastian
S
Herrmann
Christian
C
Heumann
Rolf
R
Stoll
Raphael
R
D000595:Amino Acid Sequence; D017209:Apoptosis; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D000076222:Mechanistic Target of Rapamycin Complex 1; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism*; D046912:Multiprotein Complexes; D009474:Neurons / Q000378:metabolism; D009479:Neuropeptides / Q000378:metabolism*; D018384:Oxidative Stress; D011506:Proteins; D000076205:Ras Homolog Enriched in Brain Protein; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000378:metabolism
D046912:Multiprotein Complexes; D009479:Neuropeptides; D011506:Proteins; C490211:RHEB protein, human; D000076205:Ras Homolog Enriched in Brain Protein; D014157:Transcription Factors; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; D020559:Monomeric GTP-Binding Proteins; D020123:Sirolimus