SOCS3 regulates p21 expression and cell cycle arrest in response to DNA damage

Genotoxic agents such as ionizing radiation trigger cell cycle arrest at the G1/S and G2/M checkpoints, allowing cells to repair damaged DNA before entry into mitosis. DNA damage-induced G1 arrest involves p53-dependent expression of p21 (Cip1/Waf-1), which inhibits cyclin-dependent kinases and blocks S phase entry. While much of the core DNA damage response has been well-studied, other signaling proteins that intersect with and modulate this response remain uncharacterized. In this study, we identify Suppressor of Cytokine Signaling (SOCS)-3 as an important regulator of radiation-induced G1 arrest. SOCS3-deficient fibroblasts fail to undergo G1 arrest and accumulate in the G2/M phase of the cell cycle. SOCS3 knockout cells phosphorylate p53 and H2AX normally in response to radiation, but fail to upregulate p21 expression. In addition, STAT3 phosphorylation is elevated in SOCS3-deficient cells compared to WT cells. Normal G1 arrest can be restored in SOCS3 KO cells by retroviral transduction of WT SOCS3 or a dominant-negative mutant of STAT3. Our results suggest a novel function for SOCS3 in the control of genome stability by negatively regulating STAT3-dependent radioresistant DNA synthesis, and promoting p53-dependent p21 expression.     

MicroRNA-21 accelerates hepatocyte proliferation in vitro via PI3K/Akt signaling by targeting PTEN

MicroRNAs (miRNAs) are involved in controlling hepatocyte proliferation during liver regeneration. In this study, we established the miRNAs-expression patterns of primary hepatocytes in vitro under stimulation of epidermal growth factor (EGF), and found that microRNA-21 (miR-21) was appreciably up-regulated and peaked at 12 h. In addition, we further presented evidences indicating that miR-21 promotes primary hepatocyte proliferation through in vitro transfecting with miR-21 mimics or inhibitor. We further demonstrated that phosphatidylinositol 3′-OH kinase (PI3K)/Akt signaling was altered accordingly, it is, by targeting phosphatase and tensin homologue deleted on chromosome 10, PI3K/Akt signaling is activated by miR-21 to accelerate hepatocyte rapid S-phase entry and proliferation in vitro.     

SOCS3/CIS3 negative regulation of STAT3 in HGF-induced keratinocyte migration

Hepatocyte growth factor (HGF) is a potent mitogen for mature hepatocytes. Because HGF has strong effects on the motility of keratinocytes and is produced by fibroblasts, HGF is thought to regulate keratinocyte migration during wound healing. However, the intracellular signaling mechanism of HGF-induced keratinocyte migration is poorly understood. In this report, we clarify the roles of STAT3 and SOCS/CIS family in HGF-induced keratinocyte migration. HGF activated STAT3 and strongly induced keratinocyte migration. Transfection with the dominant-negative mutant of STAT3 almost completely abolished HGF-induced keratinocyte migration and STAT3 phosphorylation. Next, we studied the mechanisms that regulate STAT3 phosphorylation. HGF enhanced the expression of SOCS3/CIS3 by sixfold within 1h, but had minimum effect on SOCS1/JAB expression. Transfection with SOCS3/CIS3 almost completely abolished HGF-induced STAT3 phosphorylation and keratinocyte migration, indicating that SOCS3/CIS3 acts as a negative regulator of HGF-induced keratinocyte migration. In conclusion, SOCS3/CIS3 regulates HGF-induced keratinocyte migration by inhibiting STAT3 phosphorylation.     

MicroRNA-19a-3p promotes rheumatoid arthritis fibroblast-like synoviocytes via targeting SOCS3

Rheumatoid arthritis (RA) is a common chronic autoimmune disease and effective treatment for RA is still lacking. In this study, the regulatory role of miR-19a-3p in RA was investigated. Quantitative polymerase chain reaction analysis of human blood samples showed that the level of miR-19a-3p was significantly lower in the RA patients compared with that in healthy patients (P < 0.05). In RA fibroblast-like synoviocytes (RAFLS), miR-19a-3p and suppressor of cytokine signaling 3 (SOCS3) were also downregulated and upregulated, respectively, compared with those of normal FLS. Transfection of miR-19a-3p mimic in RAFLS inhibited cell proliferation and promoted cell apoptosis. TargetScan identified SOCS3 as a target of miR-19a-3p, which was confirmed by dual-luciferase assay. Western blot indicated that SOCS3 protein level was significantly decreased after miR-19a-3p overexpression. Moreover, SOCS3 silencing through siRNA transfection also enhanced cell proliferation, meanwhile inhibiting RAFLS apoptosis. In addition, SOCS3 overexpression abrogated the effects of miR-19a-3p overexpression on cell proliferation and apoptosis, corroborating that SOCS3 acts as a downstream effector in the miR-19a-3p-mediated function of RAFLS. These findings suggest that miR-19a-3p plays an important role in RA, and the miR-19a-3p/SOCS3 axis may become a potential therapeutic target for RA.     

The IL-6 family of cytokines modulates STAT3 activation by desumoylation of PML through SENP1 induction

Post-translational modification by small ubiquitin-like modifier (SUMO) plays an important role in the regulation of different signaling pathways and is involved in the formation of promyelocytic leukemia (PML) protein nuclear bodies following sumoylation of PML. In the present study, we found that IL-6 induces desumoylation of PML and dissociation between PML and SUMO1 in hepatoma cells. We also found that IL-6 induces mRNA expression of SENP1, a member of the SUMO-specific protease family. Furthermore, wild-type SENP1 but not an inactive SENP1 mutant restored the PML-mediated suppression of STAT3 activation. These results indicate that the IL-6 family of cytokines modulates STAT3 activation by desumoylation and inactivation PML through SENP1 induction.     

Interaction of SOCS3 with NonO attenuates IL-1beta-dependent MUC8 gene expression

The intracellular negatively regulatory mechanism which affects IL-1β-induced MUC8 gene expression remains unclear. We found that SOCS3 overexpression suppressed IL-1β-induced MUC8 gene expression in NCI-H292 cells, whereas silencing of SOCS3 restored IL-1β-induced MUC8 gene expression. Sequentially activated ERK1/2, RSK1, and CREB by IL-1β were not affected by SOCS3, indicating that SOCS3 has an independent mechanism of action. Using immunoprecipitaion and nano LC mass analysis, we found that SOCS3 bound NonO (non-POU-domain containing, octamer-binding domain protein) in the absence of IL-1β, whereas IL-1β treatment dissociated the direct binding of SOCS3 and NonO. A dominant-negative SOCS3 mutant (Y204F/Y221F) did not bind to NonO. Interestingly, SOCS3 overexpression dramatically suppressed MUC8 gene expression in cells transfected with wild-type or siRNA of NonO. Moreover, silencing of SOCS3 dramatically increased NonO-mediated MUC8 gene expression caused by IL-1β compared to NonO overexpression alone, suggesting that SOCS3 acts as a suppressor by regulating the action of NonO.     

IL-6-induced Bcl6 variant 2 supports IL-6-dependent myeloma cell proliferation and survival through STAT3

IL-6 is a growth and survival factor for myeloma cells, although the mechanism by which it induces myeloma cell proliferation through gene expression is largely unknown. Microarray analysis showed that some B-cell lymphoma-associated oncogenes such as Bcl6, which is absent in normal plasma cells, were upregulated by IL-6 in IL-6-dependent myeloma cell lines. We found that Bcl6 variant 2 was upregulated by STAT3. ChIP assay and EMSA showed that STAT3 bound to the upstream region of variant 2 DNA. Expression of p53, a direct target gene of Bcl6, was downregulated in the IL-6-stimulated cells, and this process was impaired by an HDAC inhibitor. Bcl6 was knocked down by introducing small hairpin RNA, resulting in decreased proliferation and increased sensitivity to a DNA damaging agent. Thus, STAT3-inducible Bcl6 variant 2 appears to generate an important IL-6 signal that supports proliferation and survival of IL-6-dependent myeloma cells.     

miR-17-5p promotes proliferation by targeting SOCS6 in gastric cancer cells

This study aimed to test the exact functions and potential mechanisms of miR-17-5p in gastric cancer. Using real-time PCR, miR-17-5p was found to be expressed more highly in gastric cancer compared with-normal tissues. Gain- and loss-of-function assays demonstrated that miR-17-5p increased the proliferation and growth of gastric cancer cells in vitro and in vivo. Through reporter gene and western blot assays, SOCS6 was shown to be a direct target of miR-17-5p, and proliferative assays confirmed that SOCS6 exerted opposing function to that of miR-17-5p in gastric cancer. In short, miR-17-5p might function as a pro-proliferative factor by repressing SOCS6 in gastric cancer.     

Up-regulation of p21CIP1 expression mediated by ERK-dependent and -independent pathways contributes to hepatocyte growth factor-induced inhibition of HepG2 hepatoma cell proliferation

Strong activation of the ERK signal is required for hepatocyte growth factor (HGF) to inhibit proliferation of the human hepatocellular carcinoma cell line HepG2. However, it is still to be elucidated whether the activation alone is sufficient to induce the inhibitory effect. In this study, we constructed HepG2 cell clones expressing a high level of epidermal growth factor receptor (EGFR), and examined the effect of the strong activation of ERK on the proliferation of the cell clones. EGF treatment of the cell clones induced strong activation of ERK similar to HGF treatment, but did not inhibit cell proliferation. HGF treatment of the cell clones up-regulated the expression of a Cdk inhibitor p16(INK4a), which has previously been shown to be required to inhibit the proliferation of HepG2 cells, but EGF treatment did not. Furthermore, EGF treatment of the cell clones did not induce the up-regulation of another Cdk inhibitor p21(CIP1), whereas HGF treatment did. Knockdown of p21 by siRNA restored the proliferation of HepG2 cells inhibited by HGF, and restored Cdk2 activity suppressed in HGF-treated HepG2 cells. These results suggest that strong activation of ERK alone is not sufficient, and some other pathway(s), which is activated through the HGF receptor but not through EGFR, is also required to induce the up-regulation of p16 and p21 expression, and also suggest that in addition to the up-regulated expression of p16, that of p21 contributes to the suppression of Cdk2 activity leading to the inhibition of proliferation of HGF-treated HepG2 cells.     

Identification of the nuclear localization signal of p21(cip1) and consequences of its mutation on cell proliferation

Overexpression of p21(cip1) induces cell cycle arrest. Although this ability has been correlated with its nuclear localization, the evidence is not conclusive. The mutants that were used to inhibit its nuclear translocation could no longer bind to several proteins known to interact with the last 25 amino acids of p21(cip1). Here we used point mutation analysis and fusion of the proteins to DsRed to identify which amino acids are essential for the nuclear localization of p21(cip1). We conclude that amino acids RKR(140-142) are essential for nuclear translocation of p21(cip1). While wild-type DsRed-p21 induces cell cycle arrest in 95% of transfected cells, overexpression of cytoplasmatic p21AAA(140-142) arrested only 20% of transfected cells. We conclude that cytoplasmatic p21, with no deletion in the C-terminal region, had a much lower capacity to arrest the cell cycle.     

IL-1-induced ERK1/2 activation up-regulates p21 protein by inhibition of degradation via ubiquitin-independent pathway in human melanoma cells A375

IL-1 inhibits the proliferation of human melanoma cells A375 by arresting the cell cycle at G0/G1 phase, which accompanies the increase of p21^Waf1/Cip1 (p21) protein. Here, we demonstrate that IL-1 induces the stabilization of p21 protein via ERK1/2 pathway. The degradation of p21 was inhibited by IL-1, however the ubiquitination level of p21 was not affected. In addition, the degradation of non-ubiquitinated form of lysine less mutant p21-K6R was also inhibited by IL-1, suggesting that IL-1 stabilized p21 protein via ubiquitin-independent pathway. Furthermore, the inhibition of p21 protein degradation was prevented by a selective inhibitor of ERK1/2 pathway, PD98059. These results suggest that IL-1-induced ERK1/2 activation leads to the up-regulation of p21 by inhibiting degradation via ubiquitin-independent pathway in human melanoma cells A375.     

MiR‐485‐3p modulates neural stem cell differentiation and proliferation via regulating TRIP6 expression

Recent references have showed crucial roles of several miRNAs in neural stem cell differentiation and proliferation. However, the expression and role of miR‐485‐3p remains unknown. In our reference, we indicated that miR‐485‐3p expression was down‐regulated during NSCs differentiation to neural and astrocytes cell. In addition, the TRIP6 expression was up‐regulated during NSCs differentiation to neural and astrocytes cell. We carried out the dual‐luciferase reporter and found that overexpression of miR‐485‐3p decreased the luciferase activity of pmirGLO‐TRIP6‐wt but not the pmirGLO‐TRIP6‐mut. Ectopic expression of miR‐485‐3p decreased the expression of TRIP6 in NSC. Ectopic miR‐485‐3p expression suppressed the cell growth of NSCs and inhibited nestin expression of NSCs. Moreover, elevated expression of miR‐485‐3p decreased the ki‐67 and cyclin D1 expression in NSCs. Furthermore, we indicated that miR‐485‐3p reduced proliferation and induced differentiation of NSCs via targeting TRIP6 expression. These data suggested that a crucial role of miR‐485‐3p in self‐proliferation and differentiation of NSCs. Thus, altering miR‐485‐3p and TRIP6 modulation may be one promising therapy for treating with neurodegenerative and neurogenesis diseases.     

AICAR stimulates IL-6 production via p38 MAPK in cardiac fibroblasts in adult mice: a possible role for AMPK

Though known as a sensor of energy balance, AMP-activated protein kinase (AMPK) was recently shown to limit damage and apoptotic activity and contribute to the late preconditioning in heart. Interleukin-6 was also reported to involve in anti-apoptosis and cardio-protection in myocardium. Interestingly, both AMPK activity and IL-6 level were increased in response to ischemia, hypertrophy and oxidative stress. To determine whether AMPK activation will promote IL-6 production, cardiac fibroblasts (CFs) from mice were incubated with AMPK activator, 5-aminoimidazole-4-carboxamide-1-4-ribofuranoside (AICAR). The results demonstrated that AICAR time and dose-dependently stimulated IL-6 production by ELISA and immunofluorescence. Pretreatment with p38 mitogen-activated protein kinase (MAPK) inhibitor blocked AICAR-induced IL-6 production; furthermore, AICAR-activated p38 MAPK phosphorylation by Western blot. To confirm that the increase in IL-6 production is ascribed to AMPK activation, we used another known AMPK activator, metformin. It also dose-dependently potentiated IL-6 production in CFs, and this potentiation could be reversed by p38 MAPK inhibitor. In conclusion, AMPK activation promoted IL-6 production in CFs via p38 MAPK-dependent pathway.