Haploinsufficiency of the c-myc transcriptional repressor FIR, as a dominant negative-alternative splicing model, promoted p53-dependent T-cell acute lymphoblastic leukemia progression by activating Notch1.

Abstract

FUSE-binding protein (FBP)-interacting repressor (FIR) is a c-myc transcriptional suppressor. A splice variant of FIR that lacks exon 2 in the transcriptional repressor domain (FIRΔexon2) upregulates c-myc transcription by inactivating wild-type FIR. The ratio of FIRΔexon2/FIR mRNA was increased in human colorectal cancer and hepatocellular carcinoma tissues. Because FIRΔexon2 is considered to be a dominant negative regulator of FIR, FIR heterozygous knockout (FIR⁺/⁻) C57BL6 mice were generated. FIR complete knockout (FIR⁻/⁻) was embryonic lethal before E9.5; therefore, it is essential for embryogenesis. This strongly suggests that insufficiency of FIR is crucial for carcinogenesis. FIR⁺/⁻ mice exhibited prominent c-myc mRNA upregulation, particularly in the peripheral blood (PB), without any significant pathogenic phenotype. Furthermore, elevated FIRΔexon2/FIR mRNA expression was detected in human leukemia samples and cell lines. Because the single knockout of TP53 generates thymic lymphoma, FIR⁺/⁻TP53⁻/⁻ generated T-cell type acute lymphocytic/lymphoblastic leukemia (T-ALL) with increased organ or bone marrow invasion with poor prognosis. RNA-sequencing analysis of sorted thymic lymphoma cells revealed that the Notch signaling pathway was activated significantly in FIR⁺/⁻TP53⁻/⁻ compared with that in FIR⁺/⁺TP53⁻/⁻ mice. Notch1 mRNA expression in sorted thymic lymphoma cells was confirmed using qRT-PCR. In addition, flow cytometry revealed that c-myc mRNA was negatively correlated with FIR but positively correlated with Notch1 in sorted T-ALL/thymic lymphoma cells. Moreover, the knockdown of TP53 or c-myc using siRNA decreased Notch1 expression in cancer cells. In addition, an adenovirus vector encoding FIRΔexon2 cDNA increased bleomycin-induced DNA damage. Taken together, these data suggest that the altered expression of FIRΔexon2 increased Notch1 at least partially by activating c-Myc via a TP53-independent pathway. In conclusion, the alternative splicing of FIR, which generates FIRΔexon2, may contribute to both colorectal carcinogenesis and leukemogenesis.

• Authors: Kazuyuki Matsushita, Kouichi Kitamura, Bahityar Rahmutulla, Nobuko Tanaka, Takayuki Ishige, Mamoru Satoh, Tyuji Hoshino, Satoru Miyagi, Takeshi Mori, Sakae Itoga, Hideaki Shimada, Takeshi Tomonaga, Minoru Kito, Yaeko Nakajima-Takagi, Shuji Kubo, Chiaki Nakaseko, Masahiko Hatano, Takashi Miki, Masafumi Matsuo, Masaki Fukuyo, Atsushi Kaneda, Atsushi Iwama, Fumio Nomura
• Journal: Oncotarget (Oncotarget) Vol. 6 Issue 7 Pg. 5102-17 (Mar 10 2015) ISSN: 1949-2553 [Electronic] United States
• PMID: 25671302 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• NOTCH1 protein, human
• Notch1 protein, mouse
• Proto-Oncogene Proteins c-myc
• RNA Splicing Factors
• RNA-Binding Proteins
• Receptor, Notch1
• Repressor Proteins
• Tumor Suppressor Protein p53
• poly-U binding splicing factor 60KDa

Topics

• Adult
• Alternative Splicing
• Animals
• Disease Progression
• Female
• Haploinsufficiency
• Humans
• Male
• Mice
• Mice, Inbred C57BL
• Mice, Knockout
• Precursor T-Cell Lymphoblastic Leukemia-Lymphoma (genetics, metabolism, pathology)
• Proto-Oncogene Proteins c-myc (genetics, metabolism)
• RNA Splicing Factors
• RNA-Binding Proteins (genetics, metabolism)
• Receptor, Notch1 (genetics, metabolism)
• Repressor Proteins (genetics, metabolism)
• Tumor Suppressor Protein p53 (genetics, metabolism)