Elevated level of SUMOylated IRF-1 in tumor cells interferes with IRF-1-mediated apoptosis

Molecular Therapy Research Center, Sungkyunkwan University, Seoul 135-710, Korea.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 11/2007; 104(43):17028-33. DOI: 10.1073/pnas.0609852104
Source: PubMed

ABSTRACT SUMOylation of transcription factors often attenuates transcription activity. This regulation of protein activity allows more diversity in the control of gene expression. Interferon regulatory factor-1 (IRF-1) was originally identified as a regulator of IFN-alpha/beta, and its expression is induced by viral infection or IFN stimulation. Accumulating evidence supports the theory that IRF-1 functions as a tumor suppressor and represses the transformed phenotype. Here we report that the level of SUMOylated IRF-1 is elevated in tumors. Site-directed mutagenesis experiments disclose that the SUMOylation sites of IRF-1 are identical to the major ubiquitination sites. Consequently, SUMOylated IRF-1 displays enhanced resistance to degradation. SUMOylation of IRF-1 attenuates its transcription activity, and SUMOylated IRF-1 inhibits apoptosis by repression of its transcriptional activity. These data support a mechanism whereby SUMOylation of IRF-1 inactivates its tumor suppressor function, which facilitates resistance to the immune response.

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Available from: Seung-Hoon Lee, Mar 04, 2014
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    • "IRFs control expression of cytokines, growth factors, cell adhesion molecules, chemokines and regulate a large number of genes in a variety of cells and tissues under diverse conditions (Ozato et al. 2007). Dysregulation of IRFs by gene mutation (Nishio et al. 2001), differential expression (Choo et al. 2006), alternative splicing of the mRNAs (Maratheftis et al. 2006), post-translational modifi cation and proteolytic processing (Park et al. 2007) during various pathological conditions and diseases have been reported. IRF-1 and IRF-2, the two founding members of IRF family, provide examples of both positive and negative regulators of transcription of genes during immune response (Colonna 2007), cell growth (Masumi et al. 2003), differentiation (Chung and Kawamoto 2004) and cancer (Wang et al. 2007). "
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    ABSTRACT: Interferon regulatory factor-2 (IRF-2) is an important transcription factor involved in cell growth regulation, immune response and cancer. IRF-2 can function as a transcriptional repressor and activator depending on its DNA-binding activity and protein-protein interactions. We compared the amino acid sequences of IRF-2 and found a C-terminal tetrapeptide (314PAPV317) of mouse IRF-2 to be different (314SSSM317) from human IRF-2. Recombinant GST-IRF-2 with 314PAPV317 (wild type) and 314SSSM317 (mutant) expressed in Escherichia coli were assessed for DNA-binding activity with 32P-(GAAAGT) 4 by electrophoretic mobility shift assay (EMSA). Wild type- and mutant GST-IRF-2 showed similar expression patterns and immunoreactivities but different DNA-binding activities. Mutant (mt) IRF-2 formed higher-molecular-mass, more and stronger DNA-protein complexes in comparison to wild type (wt) IRF-2. Anti-IRF-2 antibody stabilized the DNA-protein complexes formed by both wt IRF-2 and mt IRF-2, resolving the differences. This suggests that PAPV and SSSM sequences at 314-317 in the C-terminal region of mouse and human IRF-2 contribute to conformation of IRF-2 and influence DNA-binding activity of the N-terminal region, indicating intramolecular interactions. Thus, evolution of IRF-2 from murine to human genome has resulted in subtle differences in C-terminal amino acid motifs, which may contribute to qualitative changes in IRF-2-dependent DNA-binding activity and gene expression.
    Journal of Biosciences 12/2010; 35(4):547-56. DOI:10.1007/s12038-010-0063-x · 1.94 Impact Factor
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    • "In human tumors, IRF-1 is inactivated to prevent cell cycle arrest and apoptosis by genetic alteration, such as gene and exon deletion [10,14–16]. IRF-1 also has been shown to play roles in regulating both ubiquitination and SUMOylation in cancer [5] [17] [18]. "
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    ABSTRACT: Interferon regulatory factor-1 (IRF-1) is a tumor suppressor and transcriptional modulator that can regulate gene expression involved in cell growth control, induction of apoptosis, and post-translation modification. In this study, we found that IRF-1 inhibits endothelial cell angiogenesis using human umbilical vein endothelial cell (HUVECs) culture system. In addition, IRF-1 directly inhibited the tube formation of endothelial cells on Matrigel and reduced the expression of p-Akt, and p-eNOS, which play a significant role in angiogenesis when stimulated by VEGF. We also demonstrate that C-terminal region including transactivation domain (TA) of IRF-1 functions as a signal for its angiostatic activity, and is spliced in human tumor tissues. These findings indicate that splicing variant involving exons 7 of IRF-1 could potentially modulate anti-angiogenic effect of IRF-1. In overall, this study provides the first evidence for anti-angiogenic role of IRF-1, which may have therapeutic values for cancer and angiogenesis-associated diseases.
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    ABSTRACT: The destiny and activity of sterol regulatory element-binding proteins (SREBPs) in the nucleus are regulated by modification with ubiquitin, small ubiquitin-like modifier (SUMO), or phosphorus. ERK-dependent phosphorylation causes an increase in their transcriptional activity, whereas SUMO modification halts it. We hypothesized a causal linkage between phosphorylation and sumoylation because their sites are very closely located in SREBP-1 and -2 molecules. When Ser(455), a phosphorylation site in SREBP-2, was substituted with Ala, this SREBP-2 mutant was more efficiently modified by SUMO-1. On the other hand, substitution of Asp inhibited SUMO conjugation, mimicking phosphoserine. When cells were cultured with insulin-like growth factor-1, sumoylation of SREBP-2 was decreased with an increase in its phosphorylation, but SREBP-2(S455A) was continuously sumoylated. An ERK cascade inhibitor, U0126, inversely augmented SUMO modification of SREBP-2. Insulin-like growth factor-1 treatment stimulated the expression of SREBP target genes such as the low density lipoprotein (LDL) receptor, squalene synthase, and hydroxymethylglutaryl-CoA synthase genes. These results indicate that growth factor-induced phosphorylation of SREBP-2 inhibits sumoylation, thereby facilitating SREBP transcriptional activity. Glutathione S-transferase pulldown assays revealed that wild-type SREBP-2, but not a mutant lacking Lys(464), interacts with HDAC3 preferentially among the histone deacetylase family members. HDAC3 small interfering RNA induced gene expression of the LDL receptor and thereby augmented fluorescently labeled LDL uptake in HepG2 cells. In summary, growth factors inhibit sumoylation of SREBPs through their phosphorylation, thus avoiding the recruitment of an HDAC3 corepressor complex and stimulating the lipid uptake and synthesis required for cell growth.
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