RIG-G inhibits the proliferation of NB4 cells and propels ATRA-induced differentiation of APL cells.

RIG-G (retinoic acid-induced gene G) was originally identified in ATRA (all-trans retinoic acid)-treated NB4 acute promyelocytic leukemia (APL) cells. It was induced to expression by ATRA along with the differentiation of the cells. However, little is known about its role(s). Here, we established a RIG-G stably expression transformant of NB4 cells. By using the transformant, we showed that expression of RIG-G in NB4 cells not only arrested the cells at G1/G0 transition phase and inhibited their proliferation, but also markedly drive the maturation of NB4 cells in the presence of very low concentration of ATRA (10(-9)mol/L). What's more, by detecting the expression of RIG-G in fresh primary bone marrow mononuclear cells of APL patients in different morbid states, we found high RIG-G expression level in complete remission patients, while low level in untreated or relapsed patients. These results indicated that RIG-G level was high in maturated cells and low in blast cells, and suggested that RIG-G might play a role in the differentiation of bone marrow hemocytes in vivo.

Impact of Chemotherapy Delay on Overall Survival for AML with IDH1/2 Mutations: A Study in Adult Chinese Patients.

The effect of time from diagnosis to treatment (TDT) on overall survival of patients with acute myeloid leukemia (AML) remains obscure. Furthermore, whether chemotherapy delay impacts overall survival (OS) of patients with a special molecular subtype has not been investigated. Here, we enrolled 364 cases of AML to assess the effect of TDT on OS by fractional polynomial regression in the context of clinical parameters and genes of FLT3ITD, NPM1, CEBPA, DNMT3a, and IDH1/2 mutations. Results of the current study show IDH1/2 mutations are associated with older age, M0 morphology, an intermediate cytogenetic risk group, and NPM1 mutations. TDT associates with OS for AML patients in a nonlinear pattern with a J shape. Moreover, adverse effect of delayed treatment on OS was observed in patients with IDH1/2 mutations, but not in those with IDH1/2 wildtype. Therefore, initiating chemotherapy as soon as possible after diagnosis might be a potential strategy to improve OS in AML patients with IDH1/2 mutations.

[Role of auto-secreted interferon α in all-trans retinoic acid-induced expression of RIG-G gene].

OBJECTIVE: To explore the relationship between interferon (IFN) α and all-trans retinoic acid (ATRA)-induced signaling pathways in the expression of retinoic acid-induced gene G (RIG-G). METHODS: Acute promyelocytic leukemia cell line NB4 and signal transducer and activator of transcription (STAT)1-deficient U3A cells were used. The protein levels of tyrosine-phosphorylated STAT2 in ATRA-treated NB4 cells were detected by Western blot. The culture supernatants of NB4 cells treated with ATRA for different time or U3A cells transfected with interferon regulatory factor (IRF)-1 were respectively collected. And the concentration of IFN-α was determined by enzyme-linked immunosorbent assay (ELISA). The effects of NB4 cell culture supernatants on the phosphorylation of STAT2 and the expression of RIG-G were detected by Western blot. RESULTS: The level of phosphorylated-STAT2 was obviously up-regulated in NB4 cells treated with ATRA for 72 hours, as well as the concentration of IFN-α in culture supernatants. The concentration of IFN-α increased from (1.5 ± 0.5) pg/ml in the untreated group to (7.6 ± 0.3) pg/ml (P < 0.05). After a 96-hour treatment, the concentration of IFN-α was up to (63.8 ± 5.8) pg/ml. And these culture supernatants could induce the tyrosine phosphorylation of STAT2 and up-regulate the protein level of RIG-G. As for U3A cells transfected with IRF-1, the concentration of IFN-α from the culture supernatant also increased 3-fold versus the control group transfected with empty vectors [(8.8 ± 1.4) pg/ml vs (3.4 ± 0.4) pg/ml, P < 0.05]. CONCLUSIONS: RIG-G gene expression is closely correlated with the cross-talk between ATRA and IFN-α-induced signaling pathways. ATRA increases the secretion of IFN-α by up-regulating the protein level of IRF-1. Then the secreted IFN-α may induce the phosphorylation of STAT2 and reinforce the expression of RIG-G.

Intact JAK-STAT signaling pathway is a prerequisite for STAT1 to reinforce the expression of RIG-G gene.

We previously reported that IRF-9/STAT2 functional interaction could drive the expression of retinoic acid-induced gene G (RIG-G), independently of STAT1 and the classical JAK-STAT pathway, providing a novel alternative pathway for interferons (IFN) to mediate their multiple biological properties. In addition, we also found that IRF-1 could regulate RIG-G induction as well as the expression of IRF-9 and STAT2 in some cases. But the mechanisms by which IRF-1 exerted its action remained to be elucidated. Here, we showed that STAT1 could significantly enhance the effects of the IRF-9/STAT2 complex or IRF-1 on RIG-G induction through an activated JAK-STAT pathway, though it was not essential for RIG-G expression. In STAT1-deficient U3A cells, IRF-1 could induce RIG-G expression via the IFN-stimulated response elements in the RIG-G gene promoter, but it failed to upregulate IRF-9 and STAT2 unless the U3A cells were reconstituted by exogenous STAT1. In STAT1-expressing cells, IRF-1 indirectly activated RIG-G expression through an IRF-9/STAT2-dependent manner. Taken together, we concluded that the expression of RIG-G was independent on the classical JAK-STAT pathway, but could be greatly increased by it. This work will be of great benefit to us for a better understanding of the mechanisms on RIG-G gene expression regulation.

[Role of the interferon-stimulated response elements I/II in expression regulation of the retinoic acid induced gene G].

OBJECTIVE: To study the regulatory role of interferon-stimulated response elements (ISREs) located on the retinoic acid-induced gene G (RIG-G) promoter in RIG-G expression. METHODS: By using point mutation technique, the authors constructed the wide type and site mutant reporter gene plasmids according to the ISRE sequence on RIG-G promoter, and detected the functional activities by luciferase reporter assay. RESULTS: Mutation in ISRE II alone had no obvious effect on the expression of the reporter gene, whereas mutation in ISRE I dramatically inhibited the transactivity of RIG-G promoter. Mutation in both ISRE I and ISRE II resulted in complete loss of its response to the transcription factors for the reporter gene. CONCLUSION: Both ISRE I and ISRE II on the RIG-G promoter are the binding sites for the complex of transcription factors. They are required for RIG-G expression, and ISRE I has a preferential role over ISRE II.

[A novel molecular mechanism of interferon alpha-regulated expression of retinoic acid-induced gene G].

OBJECTIVE: To investigate the molecular mechanisms by which IFN-alpha regulated retinoic acid-induced gene G (RIG-G) expression. METHODS: The expression of STAT1, p-STAT1 and RIG-G in IFN-alpha-treated NB4 cells was detected by Western blot. The roles of STAT1, STAT2 and IRF-9 in IFN-alpha-induced RIG-G expression were analyzed in STAT1-null U3A cells by cell transfection, reporter gene assay, co-immunoprecipitation and chromatin immunoprecipitaion. RESULTS: In U3A cells, only when STAT2 and IRF-9 were co-transfected, the luciferase activities of RIG-G promoter-containing reporter gene could be highly increased about 8-fold compared with that in the control group. Moreover, in the absence of IFN-alpha, similar effects were observed in either IRF-9 co-transfected with wild type or mutant form of STAT2, whereas IFN-alpha could increase the transactivation activity of wild type STAT2 and IRF-9 by 6-fold compared with that without IFN-alpha, but had no effect on mutant STAT2. In addition, STAT2 could interact with IRF-9 and bind to the RIG-G promoter. CONCLUSION: STAT2 may interact with IRF-9 in a STAT1-independent manner. The complex STAT2/IRF-9 is the key factor mediating the expression of RIG-G gene regulated by IFN-alpha. This is a novel signal transduction cascade for IFN which is different from the classical JAK-STAT pathway.

[Regulation mechanism for rig-g gene expression induced by all-trans retinoic acid].

To investigate the molecular mechanisms of all-trans retinoic acid (ATRA)-induced rig-g gene expression and to better understand the signal transduction of ATRA during acute promyelocytic leukemia (APL) cell differentiation, the luciferase reporter assay, co-immunoprecipitation and chromatin immunoprecipitation were used to clarify the basic transcriptional factors, which directly initiated the expression of rig-g gene. The results showed that the expression of STAT2, IRF-9 and IRF-1 could be upregulated by ATRA with different kinetics in NB4 cells. IRF-9 was able to interact with STAT2 to form a complex, which could bind the rig-g gene promoter and trigger the rig-g expression. IRF-1 alone could also activate the reporter gene containing rig-g gene promoter, but C/EBPalpha could strongly inhibit this transcription activity of IRF-1. It is concluded that during ATRA-induced APL cell differentiation, IRF-1 is first upregulated by ATRA, and then IRF-1 increases the protein levels of IRF-9 and STAT2 with the downregulation of C/EBPalpha. The complex of IRF-9 and STAT2 is the primary transcriptional factor for rig-g gene induction. This study will be helpful for better understanding the signal transduction networks of ATRA during the course of APL cell differentiation.

IRF-9/STAT2 [corrected] functional interaction drives retinoic acid-induced gene G expression independently of STAT1.

Retinoic acid-induced gene G (RIG-G), a gene originally identified in all-trans retinoic acid-treated NB4 acute promyelocytic leukemia cells, is also induced by IFNalpha in various hematopoietic and solid tumor cells. Our previous work showed that RIG-G possessed a potent antiproliferative activity. However, the mechanism for the transcriptional regulation of RIG-G gene remains unknown. Here, we report that signal transducer and activator of transcription (STAT) 2 together with IFN regulatory factor (IRF)-9 can effectively drive the transcription of RIG-G gene by their functional interaction through a STAT1-independent manner, even without the tyrosine phosphorylation of STAT2. The complex IRF-9/STAT2 is both necessary and sufficient for RIG-G gene expression. In addition, IRF-1 is also able to induce RIG-G gene expression through an IRF-9/STAT2-dependent or IRF-9/STAT2-independent mechanism. Moreover, the induction of RIG-G by retinoic acid in NB4 cells resulted, to some extent, from an IFNalpha autocrine pathway, a finding that suggests a novel mechanism for the signal cross-talk between IFNalpha and retinoic acid. Taken together, our results provide for the first time the evidence of the biological significance of IRF-9/STAT2 complex, and furnish an alternative pathway modulating the expression of IFN-stimulated genes, contributing to the diversity of IFN signaling to mediate their multiple biological properties in normal and tumor cells.

[Effects of PML-RARalpha on cAMP-induced AML cell differentiation].

To explore the molecular mechanisms of acute promyelocytic leukemia cell differentiation induced by cAMP combined with low-dose As2O3, the PR9 cell line, which was stably transfected by PML-RARa fusion gene, was used as in vitro model. The effects of PML-RARa on cAMP-induced AML cell differentiation were evaluated according to cell growth, cell morphology, cell surface antigen as well as luciferase reporter gene assay, in the cells before and after the treatment with cAMP and/or As2O3. The results showed that cAMP alone could slightly increase the expression of CD11b in the PR9 cells expressing the PML-RARa fusion protein, but could not induce these cells to differentiate. The cells presented the terminal differentiation morphology and significantly increased CD11b expression only under the treatment of cAMP combined with As2O3. In addition, PML-RARa had strong inhibitory activity on the transcription of the reporter gene containing cAMP response elements. In conclusions, the PML-RARa fusion protein could dramatically block the signaling pathway of cAMP during the AML cell differentiation.

[Molecular mechanism of the inhibitory effect of retinoic acid-induced gene G protein on tumor cell proliferation].

OBJECTIVE: To investigate the molecular mechanisms of anti-proliferative effect of retinoic acid-induced gene G (RIG-G) protein on tumor cells. METHODS: HA-RIG-G expression plasmid and FLAG-Jun activating binding protein 1 (JAB1) expression plasmid were construction and transfected into the African green monkey kidney cells of the line CDS-7 and mouse fibroblast cells of the line NIH3T3. Western blotting was used to detect the p27 expression in the cells. Analysis, and Immunofluorescence staining was used to examine the distribution of JAB1 protein. Coimmunoprecipitation was used to analyze the interference of RIG-G on the function of JAB1 protein. RESULTS: Coimmunoprecipitation showed that when HA-RIG-G and FLAG-JAB1 were co-expressed, the RIG-G protein and JAB1 protein could be co-precipitated by the antibodies of the other side. RIG-G was able to interact with JAB1 and alter its intracellular localization and distribution. When JAB1 was transfected alone into the NIH3T3 cells, it dispersed in both nucleus and cytoplasm; however, when RIG-G and JAB1 were cotransfected, the nuclear JAB1 was markedly diminished and exhibited a partly co-localization with RIG-G in the cytoplasm. Western blotting showed that along with the increase of the dose of transfected JAB1 the amount of p27 in the cell; and along with the increase of co-transfected RIG-G gene expression plasmid the amount of p27 in the cells re-increased. CONCLUSION: RIG-G interacts with JAB1, thus resulting in JAB1 sequestration in the cytoplasm, disturbing the JAB1 normal function, interfering the JAB1-mediated p27 degradation, maintaining p27 protein stability so as to prevent cells from entering the cycle and inhibiting cell proliferation.

[Study on mechanisms of the expression regulation of interferon-induced gene RIG-G].

OBJECTIVE: To investigate the molecular mechanisms of the expression regulation of retinoic acidinduced gene G (RIG-G) by interferon alpha (IFNalpha). METHODS: RIG-G promoter region was analyzed by bioinformatics. The functional activities of RIG-G promoter with or without IFNalpha were detected by luciferase reporter assay and electrophoretic mobility shift assay (EMSA). RESULTS: RIG-G promoter region contained two well-conserved IFN-stimulated response elements (ISREs). Both ISRE I and ISRE II showed their effective binding abilities with signal transducer and activator of transcription 1 (STAT1). In HT1080 cells, in contrast with the empty plasmid pXP2, pXP2-A reporter construct containing intact ISRE I and ISRE II showed a significant higher baseline expression (1741.2 +/- 517.5) which could be further enhanced up to three-four folds by IFNalpha (5338.7 +/- 1226.9, P < 0.05). However, the luciferase activity of pXP2-A as well as its IFNalpha inducibility could be abrogated in STAT1-deficient U3A cells (from 1741.2 +/- 517.5 to 406.1 +/- 103.2, P < 0.05), indicating that the STAT1 protein was a prerequisite for the activities of ISRE I and ISRE II. CONCLUSION: ISREs present in RIG-G promoter region are molecular basis of IFNalpha induced RIG-G expression. RIG-G is a target gene directly regulated by STAT1 protein and should play a key role in IFNalpha signaling pathways.