Requirement of GTP binding for TIF-90-regulated ribosomal RNA synthesis and oncogenic activities in human colon cancer cells.

Abstract

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.

• Authors: Dang Quan Nguyen, Dinh Hoa Hoang, Michael Nelson, Lokesh Nigam, Vo Thanh Thao Nguyen, Lianjun Zhang, Tram Kim Thi Pham, Huu Duc Ho, Dai Dong Thi Nguyen, Trung Quoc Lam, Trinh To Tat, Yasmin Elhajmoussa, Quoc Trung Ly, Flavia Pichiorri, Vinod Pullarkat, Bin Zhang, Ya-Huei Kuo, Guido Marcucci, Le Xuan Truong Nguyen
• Journal: Journal of cellular physiology (J Cell Physiol) Vol. 235 Issue 10 Pg. 7567-7579 (10 2020) ISSN: 1097-4652 [Electronic] United States
• PMID: 32159236 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: © 2020 Wiley Periodicals, Inc.

Chemical References

• DNA, Ribosomal
• RNA, Ribosomal
• Transcription Factors
• Guanosine Triphosphate
• RNA Polymerase I

Topics

• Carcinogenesis (genetics)
• Cell Line, Tumor
• Cell Proliferation (genetics)
• Colonic Neoplasms (genetics)
• DNA, Ribosomal (genetics)
• Guanosine Triphosphate (genetics)
• HCT116 Cells
• Humans
• RNA Polymerase I (genetics)
• RNA, Ribosomal (genetics)
• Ribosomes (genetics)
• Signal Transduction (genetics)
• Transcription Factors (genetics)
• Transcription, Genetic (genetics)