TY - JOUR
T1 - Requirement of GTP binding for TIF-90-regulated ribosomal RNA synthesis and oncogenic activities in human colon cancer cells
AU - Nguyen, Dang Quan
AU - Hoang, Dinh Hoa
AU - Nelson, Michael
AU - Nigam, Lokesh
AU - Nguyen, Vo Thanh Thao
AU - Zhang, Lianjun
AU - Pham, Tram Kim Thi
AU - Ho, Huu Duc
AU - Nguyen, Dai Dong Thi
AU - Lam, Trung Quoc
AU - Tat, Trinh To
AU - Elhajmoussa, Yasmin
AU - Ly, Quoc Trung
AU - Pichiorri, Flavia
AU - Pullarkat, Vinod
AU - Zhang, Bin
AU - Kuo, Ya Huei
AU - Marcucci, Guido
AU - Nguyen, Le Xuan Truong
N1 - Funding Information:
This study is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number (106‐YS.02–2015.60).
Publisher Copyright:
© 2020 Wiley Periodicals, Inc.
PY - 2020/10/1
Y1 - 2020/10/1
N2 - Transcription initiation factor 90 (TIF-90), an alternatively spliced variant of TIF-IA, differs by a 90 base pair deletion of exon 6. TIF-90 has been shown to regulate ribosomal RNA (rRNA) synthesis by interacting with polymerase I (Pol I) during the initiation of ribosomal DNA (rDNA) transcription in the nucleolus. Recently, we showed that TIF-90-mediated rRNA synthesis can play an important role in driving tumorigenesis in human colon cancer cells. Here we show that TIF-90 binds GTP at threonine 310, and that GTP binding is required for TIF-90-enhanced rRNA synthesis. Overexpression of activated AKT induces TIF-90 T310, but not a GTP-binding site (TIF-90 T310N) mutant, to translocate into the nucleolus and increase rRNA synthesis. Complementing this result, treatment with mycophenolic acid (MPA), an inhibitor of GTP production, dissociates TIF-90 from Pol I and hence abolishes AKT-increased rRNA synthesis by way of TIF-90 activation. Thus, TIF-90 requires bound GTP to fulfill its function as an enhancer of rRNA synthesis. Both TIF variants are highly expressed in colon cancer cells, and depletion of TIF-IA expression in these cells results in significant sensitivity to MPA-inhibited rRNA synthesis and reduced cell proliferation. Finally, a combination of MPA and AZD8055 (an inhibitor of both AKT and mTOR) synergistically inhibits rRNA synthesis, in vivo tumor growth, and other oncogenic activities of primary human colon cancer cells, suggesting a potential avenue for the development of therapeutic treatments by targeting the regulation of rRNA synthesis by TIF proteins.
AB - Transcription initiation factor 90 (TIF-90), an alternatively spliced variant of TIF-IA, differs by a 90 base pair deletion of exon 6. TIF-90 has been shown to regulate ribosomal RNA (rRNA) synthesis by interacting with polymerase I (Pol I) during the initiation of ribosomal DNA (rDNA) transcription in the nucleolus. Recently, we showed that TIF-90-mediated rRNA synthesis can play an important role in driving tumorigenesis in human colon cancer cells. Here we show that TIF-90 binds GTP at threonine 310, and that GTP binding is required for TIF-90-enhanced rRNA synthesis. Overexpression of activated AKT induces TIF-90 T310, but not a GTP-binding site (TIF-90 T310N) mutant, to translocate into the nucleolus and increase rRNA synthesis. Complementing this result, treatment with mycophenolic acid (MPA), an inhibitor of GTP production, dissociates TIF-90 from Pol I and hence abolishes AKT-increased rRNA synthesis by way of TIF-90 activation. Thus, TIF-90 requires bound GTP to fulfill its function as an enhancer of rRNA synthesis. Both TIF variants are highly expressed in colon cancer cells, and depletion of TIF-IA expression in these cells results in significant sensitivity to MPA-inhibited rRNA synthesis and reduced cell proliferation. Finally, a combination of MPA and AZD8055 (an inhibitor of both AKT and mTOR) synergistically inhibits rRNA synthesis, in vivo tumor growth, and other oncogenic activities of primary human colon cancer cells, suggesting a potential avenue for the development of therapeutic treatments by targeting the regulation of rRNA synthesis by TIF proteins.
KW - GTP
KW - MPA
KW - TIF-90
KW - TIF-IA
KW - rRNA synthesis
KW - RNA Polymerase I/genetics
KW - Colonic Neoplasms/genetics
KW - HCT116 Cells
KW - Humans
KW - Signal Transduction/genetics
KW - Ribosomes/genetics
KW - Transcription Factors/genetics
KW - DNA, Ribosomal/genetics
KW - RNA, Ribosomal/genetics
KW - Transcription, Genetic/genetics
KW - Cell Line, Tumor
KW - Cell Proliferation/genetics
KW - Guanosine Triphosphate/genetics
KW - Carcinogenesis/genetics
UR - http://www.scopus.com/inward/record.url?scp=85081301949&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85081301949&partnerID=8YFLogxK
U2 - 10.1002/jcp.29661
DO - 10.1002/jcp.29661
M3 - Article
C2 - 32159236
AN - SCOPUS:85081301949
SN - 0021-9541
VL - 235
SP - 7567
EP - 7579
JO - Journal of Cellular Physiology
JF - Journal of Cellular Physiology
IS - 10
ER -