Recurrent Mutations in the MTOR Regulator RRAGC in Follicular Lymphoma.
OBJECTIVE
This study was performed to further our understanding of the biological and genetic basis of follicular lymphoma and to identify potential novel therapy targets.


METHODS
We analyzed previously generated whole exome sequencing data of 23 follicular lymphoma cases and one transformed follicular lymphoma case and expanded findings to a combined total of 125 follicular lymphoma/3 transformed follicular lymphoma. We modeled the three-dimensional location of RRAGC-associated hotspot mutations. We performed functional studies on novel RRAGC mutants in stable retrovirally transduced HEK293T cells, stable lentivirally transduced lymphoma cell lines, and in Saccharomyces cerevisiae RESULTS: We report recurrent mutations, including multiple amino acid hotspots, in the small G-protein RRAGC, which is part of a protein complex that signals intracellular amino acid concentrations to MTOR, in 9.4% of follicular lymphoma cases. Mutations in RRAGC distinctly clustered on one protein surface area surrounding the GTP/GDP-binding sites. Mutated RRAGC proteins demonstrated increased binding to RPTOR (raptor) and substantially decreased interactions with the product of the tumor suppressor gene FLCN (folliculin). In stable retrovirally transfected 293T cells, cultured in the presence or absence of leucine, multiple RRAGC mutations demonstrated elevated MTOR activation as evidenced by increased RPS6KB/S6-kinase phosphorylation. Similar activation phenotypes were uncovered in yeast engineered to express mutations in the RRAGC homolog Gtr2 and in multiple lymphoma cell lines expressing HA-tagged RRAGC-mutant proteins.


CONCLUSIONS
Our discovery of activating mutations in RRAGC in approximately 10% of follicular lymphoma provides the mechanistic rationale to study mutational MTOR activation and MTOR inhibition as a potential novel actionable therapeutic target in follicular lymphoma. Clin Cancer Res; 22(21); 5383-93. ©2016 AACR.
Division of Hematology and Oncology, Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan.
Zhang Xiao
ZX
Ying
Life Sciences Institute, University of Michigan, Ann Arbor, Michigan.
Meiyan
M
Jin
Division of Hematology and Oncology, Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan.
Luke F
LF
Peterson
Division of Hematology and Oncology, Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan.
Denzil
D
Bernard
Division of Hematology and Oncology, Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan.
Kamlai
K
Saiya-Cork
Division of Hematology and Oncology, Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan.
Mehmet
M
Yildiz
Division of Hematology and Oncology, Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan.
Shaomeng
S
Wang
Division of Hematology and Oncology, Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan.
Mark S
MS
Kaminski
Department of Surgery, University of Michigan, Ann Arbor, Michigan.
Alfred E
AE
Chang
Life Sciences Institute, University of Michigan, Ann Arbor, Michigan.
Daniel J
DJ
Klionsky
Division of Hematology and Oncology, Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan. smalek@med.umich.edu.
Sami N
SN
Malek
D000596:Amino Acids / Q000235:genetics; D001665:Binding Sites / Q000235:genetics; D002460:Cell Line; D016147:Genes, Tumor Suppressor / Q000502:physiology; D006153:Guanosine Diphosphate / Q000235:genetics; D006160:Guanosine Triphosphate / Q000235:genetics; D057809:HEK293 Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics; D008224:Lymphoma, Follicular / Q000235:genetics*; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics*; D009154:Mutation / Q000235:genetics*; D009364:Neoplasm Recurrence, Local / Q000235:genetics*; D010766:Phosphorylation / Q000235:genetics; D000076223:Regulatory-Associated Protein of mTOR / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics; D058570:TOR Serine-Threonine Kinases / Q000235:genetics*
D000596:Amino Acids; D047908:Intracellular Signaling Peptides and Proteins; C430722:RRAGC protein, human; D000076223:Regulatory-Associated Protein of mTOR; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases; D020559:Monomeric GTP-Binding Proteins