Mice lacking a transcriptional corepressor Tob are predisposed to cancer

A genome-wide CRISPR screening uncovers that TOB1 acts as a key host factor for FMDV infection via both IFN and EGFR mediated pathways

The interaction between foot-and-mouth disease virus (FMDV) and the host is extremely important for virus infection, but there are few researches on it, which is not conducive to vaccine development and FMD control. In this study, we designed a porcine genome-scale CRISPR/Cas9 knockout library containing 93,859 single guide RNAs targeting 16,886 protein-coding genes, 25 long ncRNAs, and 463 microRNAs. Using this library, several previously unreported genes required for FMDV infection are highly enriched post-FMDV selection in IBRS-2 cells. Follow-up studies confirmed the dependency of FMDV on these genes, and we identified a functional role for one of the FMDV-related host genes: TOB1 (Transducer of ERBB2.1). TOB1-knockout significantly inhibits FMDV infection by positively regulating the expression of RIG-I and MDA5. We further found that TOB1-knockout led to more accumulation of mRNA transcripts of transcription factor CEBPA, and thus its protein, which further enhanced transcription of RIG-I and MDA5 genes. In addition, TOB1-knockout was shown to inhibit FMDV adsorption and internalization mediated by EGFR/ERBB2 pathway. Finally, the FMDV lethal challenge on TOB1-knockout mice confirmed that the deletion of TOB1 inhibited FMDV infection in vivo. These results identify TOB1 as a key host factor involved in FMDV infection in pigs.

TOB1 and TOB2 mark distinct RNA processing granules in differentiating lens fiber cells

Differentiation of lens fiber cells involves a complex interplay of signals from growth factors together with tightly regulated gene expression via transcriptional and post-transcriptional regulators. Various studies have demonstrated that RNA-binding proteins, functioning in ribonucleoprotein granules, have important roles in regulating post-transcriptional expression during lens development. In this study, we examined the expression and localization of two members of the BTG/TOB family of RNA-binding proteins, TOB1 and TOB2, in the developing lens and examined the phenotype of mice that lack Tob1. By RT-PCR, both Tob1 and Tob2 mRNA were detected in epithelial and fiber cells of embryonic and postnatal murine lenses. In situ hybridization showed Tob1 and Tob2 mRNA were most intensely expressed in the early differentiating fibers, with weaker expression in anterior epithelial cells, and both appeared to be downregulated in the germinative zone of E15.5 lenses. TOB1 protein was detected from E11.5 to E16.5 and was predominantly detected in large cytoplasmic puncta in early differentiating fiber cells, often co-localizing with the P-body marker, DCP2. Occasional nuclear puncta were also observed. By contrast, TOB2 was detected in a series of interconnected peri-nuclear granules, in later differentiating fiber cells of the inner cortex. TOB2 did not appear to co-localize with DCP2 but did partially co-localize with an early stress granule marker (EIF3B). These data suggest that TOB1 and TOB2 are involved with different aspects of the mRNA processing cycle in lens fiber cells. In vitro experiments using rat lens epithelial explants treated with or without a fiber differentiating dose of FGF2 showed that both TOB1 and TOB2 were up-regulated during FGF-induced differentiation. In differentiating explants, TOB1 also co-localized with DCP2 in large cytoplasmic granules. Analyses of Tob1-/- mice revealed relatively normal lens morphology but a subtle defect in cell cycle arrest of some cells at the equator and in the lens fiber mass of E13.5 embryos. Overall, these findings suggest that TOB proteins play distinct regulatory roles in RNA processing during lens fiber differentiation.

Nonalcoholic steatohepatitis-associated hepatocarcinogenesis in mice fed a modified choline-deficient, methionine-lowered, L-amino acid-defined diet and the role of signal changes

Nonalcoholic steatohepatitis (NASH) can progress to cirrhosis and even hepatocellular carcinoma (HCC). The incidence of NASH-associated HCC is increasing, posing a serious public health threat. Unfortunately, the underlying pathological mechanisms, including the possible differences between neoplastic and non-neoplastic lesions, remain largely unknown. Previously, we reported a dietary mouse NASH model with a choline-deficient, methionine-lowered, L-amino-acid-defined, high-fat diet containing shortening without trans fatty acids (CDAA-HF-T[-]), which rapidly induces fibrosis and proliferative lesions in the liver. This study aimed to develop a mouse CDAA-HF-T(-) model capable of assessing NASH-associated hepatocarcinogenesis and identifying key signaling factors involved in its underlying mechanisms. Multiple large masses, histopathologically hepatocellular adenomas and carcinomas, and hemangiosarcomas were detected in the liver samples of mice fed CDAA-HF-T(-) for 52 or 63 weeks, along with highly advanced fibrosis and numerous foamy, phagocytic macrophages in the adjacent nontumoral area. Multiple metastatic nodules were found in the lungs of one of the animals, and lymphoid clusters were found in all CDAA-HF-T(-) group mice. In the Ingenuity Pathways Analysis of RNA expression data, the CDAA-HF-T(-) feeding revealed common signal changes in nontumoral and tumoral liver tissues, including increased IL-8 and RhoGTPases signaling and decreased lipid metabolism. Meanwhile, macrophage inflammatory protein 2 (MIP-2) expression levels were upregulated in nontumoral liver tissue from the end of Week 13 of CDAA-HF-T(-) feeding to the end of Week 63. On the other hand, MIP-2 was expressed on macrophages in non-tumor areas and hepatocytes in tumor areas. Therefore, the CDAA-HF-T(-) mouse model is useful for assessing NASH and NASH-associated hepatocarcinogenesis, and IL-8 signaling plays important roles in NASH-associated carcinogenesis and cirrhosis, but it may also play different roles in nontumoral liver tissue and tumorigenesis.

TOB1 attenuates IRF3-directed antiviral responses by recruiting HDAC8 to specifically suppress IFN-β expression

Interferon regulatory factor 3 (IRF3) is a key transcription factor required for the secretion of type I interferons (IFN-α/β) and initiation of antiviral immune response. However, the negative feedback regulator of IRF3-directed antiviral response remains unknown. In this study, we demonstrated that viral infection induced the interaction of the transducer of ERBB2.1 (TOB1) with IRF3, which bound to the promoter region of Ifnb1 in macrophages. TOB1 inhibited Ifnb1 transcription by disrupting IRF3 binding and recruiting histone deacetylase 8 (HDAC8) to the Ifnb1 promoter region. Consequently, TOB1 attenuated IRF3-directed IFN-β expression in virus-infected macrophages. Tob1 deficiency enhanced antiviral response and suppressed viral replication in vivo. Thus, we identified TOB1 as a feedback inhibitor of host antiviral innate immune response and revealed a mechanism underlying viral immune escape.

TOB1 is identified as an interferon regulatory factor 3 (IRF3) binding partner that operates as a negative feedback inhibitor of IFNβ in toll-like receptor and cytosolic nucleic acid receptor sensing pathways.

TOB is an effector of the hippocampus-mediated acute stress response

Stress affects behavior and involves critical dynamic changes at multiple levels ranging from molecular pathways to neural circuits and behavior. Abnormalities at any of these levels lead to decreased stress resilience and pathological behavior. However, temporal modulation of molecular pathways underlying stress response remains poorly understood. Transducer of ErbB2.1, known as TOB, is involved in different physiological functions, including cellular stress and immediate response to stimulation. In this study, we investigated the role of TOB in psychological stress machinery at molecular, neural circuit, and behavioral levels. Interestingly, TOB protein levels increased after mice were exposed to acute stress. At the neural circuit level, functional magnetic resonance imaging (fMRI) suggested that intra-hippocampal and hippocampal-prefrontal connectivity were dysregulated in Tob knockout (Tob-KO) mice. Electrophysiological recordings in hippocampal slices showed increased postsynaptic AMPAR-mediated neurotransmission, accompanied by decreased GABA neurotransmission and subsequently altered Excitatory/Inhibitory balance after Tob deletion. At the behavioral level, Tob-KO mice show abnormal, hippocampus-dependent, contextual fear conditioning and extinction, and depression-like behaviors. On the other hand, increased anxiety observed in Tob-KO mice is hippocampus-independent. At the molecular level, we observed changes in factors involved in stress response like decreased stress-induced LCN2 expression and ERK phosphorylation, as well as increased MKP-1 expression. This study introduces TOB as an important modulator in the hippocampal stress signaling machinery. In summary, we reveal a molecular pathway and neural circuit mechanism by which Tob deletion contributes to expression of pathological stress-related behavior.

TOB1 Blocks Intestinal Mucosal Inflammation Through Inducing ID2-Mediated Suppression of Th1/Th17 Cell Immune Responses in IBD

BACKGROUND & AIMS

TOB1 is an anti-proliferative protein of Tob/BTG family and typically involved in the tumorigenesis and T cell activation. Although TOB1 is associated with T helper 17 cell-related autoimmunity, its role in modulating T cell-mediated immune responses in IBD remains poorly understood. Here, we explored its expression and the underlying mechanisms involved in the pathogenesis of inflammatory bowel disease (IBD).

METHODS

TOB1 and ID2 expression in IBD patients was examined by quantitative real time polymerase chain reaction and immunohistochemistry. IBD CD4⁺ T cells were transfected with lentivirus expressing TOB1, ID2, TOB1 short hairpin RNA and ID2 short hairpin RNA, respectively, and Tob1^-/-CD4⁺ T cells were transfected with lentivirus expressing Id2. Experimental colitis was established in Tob1^-/- mice by trinitrobenzene sulfonic acid enema and in Rag1^-/- mice reconstituted with Tob1^-/-CD45RB^highCD4⁺ T cells to further explore the role of Tob1 in intestinal mucosal inflammation. Splenic CD4⁺ T cells of Tob1^-/- mice were sorted to determine transcriptome differences by RNA sequencing.

RESULTS

TOB1 expression was decreased in inflamed mucosa and peripheral blood CD4⁺ T cells of IBD patients compared with healthy subjects. Overexpression of TOB1 downregulated IBD CD4⁺ T cells to differentiate into Th1/Th17 cells compared with control subjects. Severe colitis was observed in Tob1^-/- mice through trinitrobenzene sulfonic acid enema or in Rag1^-/- mice reconstituted with Tob1^-/-CD45RB^highCD4⁺ T cells, compared with control animals. RNA sequencing analysis revealed ID2 as functional target of TOB1 to inhibit IBD CD4⁺ T cell differentiation into Th1/Th17 cells. Mechanistically, TOB1 was associated with Smad4/5 to induce ID2 expression and restrain Th1/Th17 cell differentiation.

CONCLUSIONS

TOB1 restrains intestinal mucosal inflammation through suppressing Th1/Th17 cell-mediated immune responses via the Smad4/5-ID2 pathway. It may serve as a novel therapeutic target for treatment of human IBD.

Transcription factor RFX7 governs a tumor suppressor network in response to p53 and stress

Despite its prominence, the mechanisms through which the tumor suppressor p53 regulates most genes remain unclear. Recently, the regulatory factor X 7 (RFX7) emerged as a suppressor of lymphoid neoplasms, but its regulation and target genes mediating tumor suppression remain unknown. Here, we identify a novel p53-RFX7 signaling axis. Integrative analysis of the RFX7 DNA binding landscape and the RFX7-regulated transcriptome in three distinct cell systems reveals that RFX7 directly controls multiple established tumor suppressors, including PDCD4, PIK3IP1, MXD4, and PNRC1, across cell types and is the missing link for their activation in response to p53 and stress. RFX7 target gene expression correlates with cell differentiation and better prognosis in numerous cancer types. Interestingly, we find that RFX7 sensitizes cells to Doxorubicin by promoting apoptosis. Together, our work establishes RFX7’s role as a ubiquitous regulator of cell growth and fate determination and a key node in the p53 transcriptional program.

Tob2 Inhibits TLR-Induced Inflammatory Responses by Association with TRAF6 and MyD88

Optimal activation of TLR pathways is crucial for the initiation of inflammatory responses and eliminating invading micro-organisms. However, excessive of TLR activation may lead to autoimmune and inflammatory diseases. Thus, TLR pathways should be tightly controlled. In this study, we identify Tob2, a Tob/BTG family member, as a suppressor of TLR pathways. Tob2 deficiency enhances TLR-induced NF-κB and MAPK activation and promotes the expression of proinflammatory cytokines in primary peritoneal macrophages of C57BL/6 mice. Furthermore, Tob2-defective C57BL/6 mice may be more susceptible to endotoxemic shock in vivo. Mechanistically, Tob2 interacts with TRAF6 and MyD88 and thus inhibits signaling from the MyD88-TRAF6 complex in primary peritoneal macrophages and HEK293T cells. Therefore, our results uncover a regulatory mechanism of TLR pathways and provide a potential target for the intervention of diseases with excessive TLR activation.

BTG4 is A Novel p53 Target Gene That Inhibits Cell Growth and Induces Apoptosis

BTG4 is the last cloned and poorly studied member of BTG/Tob family. Studies have suggested that BTG4 is critical for the degradation of maternal mRNAs in mice during the process of maternal-to-zygotic transition, and downregulated in cancers, such as gastric cancer. However, the regulatory mechanism of BTG4 and its function in cancers remain elusive. In this study, we have for the first time identified the promoter region of the human BTG4 gene. Serial luciferase reporter assay demonstrated that the core promoter of BTG4 is mainly located within the 388 bp region near its transcription initiation site. Transcription factor binding site analysis revealed that the BTG4 promoter contains binding sites for canonical transcription factors, such as Sp1, whereas its first intron contains two overlapped consensus p53 binding sites. However, overexpression of Sp1 has negligible effects on BTG4 promoter activity, and site-directed mutagenesis assay further suggested that Sp1 is not a critical transcription factor for the transcriptional regulation of BTG4. Of note, luciferase assay revealed that one of the intronic p53 binding sites is highly responsive to p53. Both exogenous p53 overexpression and adriamycin-mediated endogenous p53 activation result in the transcriptional upregulation of BTG4. In addition, BTG4 is downregulated in lung and colorectal cancers, and overexpression of BTG4 inhibits cell growth and induces apoptosis in cancer cells. Taken together, our results strongly suggest that BTG4 is a novel p53-regulated gene and probably functions as a tumor suppressor in lung and colorectal cancers.

TOB1 suppresses proliferation in K-Ras wild-type pancreatic cancer

TOB1 participates in various kinds of cancers. However, its role in pancreatic cancer has rarely been reported. In this study, we explored the expression and mechanisms of TOB1 in regulating the malignant phenotype of pancreatic cancer cells. TOB1 expression was determined by data mining and immunohistochemistry (IHC), and its localization was observed by immunofluorescence. CCK‐8 cell proliferation, colony formation, flow cytometric, transwell migration, and Western blot (WB) assays were used to examine how it impacts the malignant phenotype of pancreatic cancer. Furthermore, Foxa2 binding to TOB1 was tested by dual‐luciferase reporter assays, and RNA‐Seq was performed to identify signaling pathways. We found TOB1 was downregulated in pancreatic cancer tissues and was mainly located in the cytoplasm. TOB1 overexpression reduced the proliferation of K‐Ras wild‐type pancreatic cancer cells but made no difference to cell migration and invasion. Foxa2 overexpression significantly enhanced TOB1 promoter activity. Moreover, overexpressing TOB1 substantially enriched the calcium pathway in K‐Ras wild‐type pancreatic cancer cells. In conclusion, TOB1 may suppress the proliferation of K‐Ras wild‐type pancreatic cancer cells by regulating calcium pathway genes.

Decreased expression levels of DAL-1 and TOB1 are associated with clinicopathological features and poor prognosis in gastric cancer

PURPOSE

We previously demonstrated that the functional inactivation of DAL-1 and TOB1 promotes an aggressive phenotype in gastric cancer cells, but the links between both genes and the survival of patients with gastric cancer are unknown. Here, we investigated the correlations of the expression levels of DAL-1 and TOB1 with the progression of gastric cancer.

METHODS

A total of 270 patients who underwent resectable gastrectomy were included. The expression of DAL-1 and TOB1 was detected by immunohistochemistry.

RESULTS

Low expression of DAL-1 in cancer tissue was significantly associated with tumor site (p < 0.05), histological grade (p < 0.01), depth of invasion (p < 0.05), lymph node metastasis status (p < 0.05), Lauren classification (p < 0.001), and clinical stage (p < 0.01). A lower level of TOB1 was observed in gastric cancer patients with diffuse type disease compared to patients with either intestinal or mixed type disease (p < 0.001). Additionally, Spearman's correlation analysis revealed that decreased expression of DAL-1 was positively correlated with low TOB1 expression (r=0.304, p < 0.001). The survival analysis showed that low levels of DAL-1 and TOB1 were significantly associated with poor survival of gastric cancer patients (p <0.001 and p < 0.05, respectively).

CONCLUSION

The downregulation of DAL-1 and TOB1 expression is associated with shorter survival of gastric cancer patients. Hence, DAL-1 and TOB1 may be considered potential novel markers for predicting the outcomes of patients with gastric cancer.

Prognostic value of transducer of ErbB2.1 (TOB1) expression in patients with gastric cancer: tissue microarray analysis

BACKGROUND

Transducer of ErbB2.1 (TOB1) protein plays an important role in cell cycle regulation, apoptosis induction, and metastasis inhibition. However, the prognostic value of TOB1 in the survival of gastric cancer (GC) patients has not been examined.

METHODS

In the present study, western blot and real-time qPCR were used to detect the protein and mRNA level of TOB1 in fresh samples from GC patients. A tissue microarray comprising 90 pairs of primary GC and adjacent normal tissues was analysed using immunohistochemistry. Western blot analysis of 16 samples from GC patients showed that 81% (13/16) of patients exhibited decreased expression of TOB1, and real-time qPCR analysis showed that GC patients had decreased expression of TOB1 mRNA.

RESULTS

Tissue microarrays showed that 72.2% of gastric cancer tissues exhibited down-regulated expression of TOB1, and the expression level was significantly lower in cases with poor differentiation and positive lymph node metastasis, compared with normal tissues. Moreover, the Kaplan-Meier analysis indicated that patients with low TOB1 expression had shorter survival time than those with high TOB1 expression (5-year survival rate, 26.2% vs. 56.0%, P=0.002). In addition, multivariate analysis indicated that TOB1 was an independent prognostic factor for outcome in gastric cancer (HR, 0.256; 95% CI, 0.127-0.514; P=0.000).

CONCLUSIONS

Down-regulated TOB1 expression was found in gastric cancer. Furthermore, low TOB1 expression may be an independent indicator of poor prognosis in gastric cancer.

The BTG4 and CAF1 complex prevents the spontaneous activation of eggs by deadenylating maternal mRNAs

Once every menstrual cycle, eggs are ovulated into the oviduct where they await fertilization. The ovulated eggs are arrested in metaphase of the second meiotic division, and only complete meiosis upon fertilization. It is crucial that the maintenance of metaphase arrest is tightly controlled, because the spontaneous activation of the egg would preclude the development of a viable embryo (Zhang et al. 2015 J. Genet. Genomics 42, 477-485. (doi:10.1016/j.jgg.2015.07.004); Combelles et al. 2011 Hum. Reprod. 26, 545-552. (doi:10.1093/humrep/deq363); Escrich et al. 2011 J. Assist. Reprod. Genet. 28, 111-117. (doi:10.1007/s10815-010-9493-5)). However, the mechanisms that control the meiotic arrest in mammalian eggs are only poorly understood. Here, we report that a complex of BTG4 and CAF1 safeguards metaphase II arrest in mammalian eggs by deadenylating maternal mRNAs. As a follow-up of our recent high content RNAi screen for meiotic genes (Pfender et al. 2015 Nature 524, 239-242. (doi:10.1038/nature14568)), we identified Btg4 as an essential regulator of metaphase II arrest. Btg4-depleted eggs progress into anaphase II spontaneously before fertilization. BTG4 prevents the progression into anaphase by ensuring that the anaphase-promoting complex/cyclosome (APC/C) is completely inhibited during the arrest. The inhibition of the APC/C relies on EMI2 (Tang et al. 2010 Mol. Biol. Cell 21, 2589-2597. (doi:10.1091/mbc.E09-08-0708); Ohe et al. 2010 Mol. Biol. Cell 21, 905-913. (doi:10.1091/mbc.E09-11-0974)), whose expression is perturbed in the absence of BTG4. BTG4 controls protein expression during metaphase II arrest by forming a complex with the CAF1 deadenylase and we hypothesize that this complex is recruited to the mRNA via interactions between BTG4 and poly(A)-binding proteins. The BTG4-CAF1 complex drives the shortening of the poly(A) tails of a large number of transcripts at the MI-MII transition, and this wave of deadenylation is essential for the arrest in metaphase II. These findings establish a BTG4-dependent pathway for controlling poly(A) tail length during meiosis and identify an unexpected role for mRNA deadenylation in preventing the spontaneous activation of eggs.

HDAC1, HDAC4, and HDAC9 Bind to PC3/Tis21/Btg2 and Are Required for Its Inhibition of Cell Cycle Progression and Cyclin D1 Expression

PC3/Tis21 is a transcriptional cofactor that inhibits proliferation in several cell types, including neural progenitors. Here, we report that PC3/Tis21 associates with HDAC1, HDAC4, and HDAC9 in vivo, in fibroblast cells. Furthermore, when HDAC1, HDAC4, or HDAC9 are silenced in fibroblasts or in a line of cerebellar progenitor cells, the ability of PC3/Tis21 to inhibit proliferation is significantly reduced. Overexpression of HDAC1, HDAC4, or HDAC9 in fibroblasts and in cerebellar precursor cells synergizes with PC3/Tis21 in inhibiting the expression of cyclin D1, a cyclin selectively inhibited by PC3/Tis21. Conversely, the depletion of HDAC1 or HDAC4 (but not HDAC9) in fibroblasts and in cerebellar precursor cells significantly impairs the ability of PC3/Tis21 to inhibit cyclin D1 expression. An analysis of HDAC4 deletion mutants shows that both the amino-terminal moiety and the catalytic domain of HDAC4 associate to PC3/Tis21, but neither alone is sufficient to potentiate the inhibition of cyclin D1 by PC3/Tis21. As a whole, our findings indicate that PC3/Tis21 inhibits cell proliferation in a way dependent on the presence of HDACs, in fibroblasts as well as in neural cells. Considering that several reports have demonstrated that HDACs can act as transcriptional corepressors on the cyclin D1 promoter, our data suggest that the association of PC3/Tis21 to HDACs is functional to recruit them to target genes, such as cyclin D1, for repression of their expression. J. Cell. Physiol. 232: 1696-1707, 2017. © 2016 Wiley Periodicals, Inc.

Apoptosis during embryonic tissue remodeling is accompanied by cell senescence

This study re-examined the dying process in the interdigital tissue during the formation of free digits in the developing limbs. We demonstrated that the interdigital dying process was associated with cell senescence, as deduced by induction of β-gal activity, mitotic arrest, and transcriptional up-regulation of p21 together with many components of the senescence-associated secretory phenotype. We also found overlapping domains of expression of members of the Btg/Tob gene family of antiproliferative factors in the regressing interdigits. Notably, Btg2 was up-regulated during interdigit remodeling in species with free digits but not in the webbed foot of the duck. We also demonstrate that oxidative stress promoted the expression of Btg2, and that FGF2 and IGF1 which are survival signals for embryonic limb mesenchyme inhibited Btg2 expression. Btg2 overexpression in vivo and in vitro induced all the observed changes during interdigit regression, including oxidative stress, arrest of cell cycle progression, transcriptional regulation of senescence markers, and caspase-mediated apoptosis. Consistent with the central role of p21 on cell senescence, the transcriptional effects induced by overexpression of Btg2 are attenuated by silencing p21. Our findings indicate that cell senescence and apoptosis are complementary processes in the regression of embryonic tissues and share common regulatory signals.

Immune cell-specific transcriptional profiling highlights distinct molecular pathways controlled by Tob1 upon experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system characterized by focal lymphocytic infiltration, demyelination and neurodegeneration. Despite the recent advances in understanding MS molecular basis, no reliable biomarkers have been identified yet to monitor disease progression. Our group has previously reported that low levels of TOB1 in CD4(+) T cells are strongly associated with a higher risk of MS conversion in individuals experiencing an initial demyelinating event. Consistently, Tob1 ablation in mice exacerbates the clinical phenotype of the MS model experimental autoimmune encephalomyelitis (EAE). To shed light on Tob1 molecular functions in the immune system, we have conducted the first cell-based transcriptomic analysis in Tob1(-/-) and wildtype mice upon EAE. Next-generation sequencing was employed to characterize the changes in gene expression in T and B cells at pre- and post-symptomatic EAE stages. Remarkably, we found only modest overlap among the different genetic signatures, suggesting that Tob1 may control distinct genetic programs in the different cytotypes. This hypothesis was corroborated by gene ontology and global interactome analyses, which highlighted specific cellular pathways in each cellular subset before and after EAE induction. In summary, our work pinpoints a multifaceted activity of Tob1 in both homeostasis and disease progression.

HDACi Valproic Acid (VPA) and Suberoylanilide Hydroxamic Acid (SAHA) Delay but Fail to Protect against Warm Hepatic Ischemia-Reperfusion Injury

BACKGROUND

Histone deacetylases (HDAC) catalyze N-terminal deacetylation of lysine-residues on histones and multiple nuclear and cytoplasmic proteins. In various animal models, such as trauma/hemorrhagic shock, ischemic stroke or myocardial infarction, HDAC inhibitor (HDACi) application is cyto- and organoprotective and promotes survival. HDACi reduce stress signaling, cell death and inflammation. Hepatic ischemia-reperfusion (I/R) injury during major liver resection or transplantation increases morbidity and mortality. Assuming protective properties, the aim of this study was to investigate the effect of the HDACi VPA and SAHA on warm hepatic I/R.

MATERIAL AND METHODS

Male Wistar-Kyoto rats (age: 6-8 weeks) were randomized to VPA, SAHA, vehicle control (pre-) treatment or sham-groups and underwent partial no-flow liver ischemia for 90 minutes with subsequent reperfusion for 6, 12, 24 and 60 hours. Injury and regeneration was quantified by serum AST and ALT levels, by macroscopic aspect and (immuno-) histology. HDACi treatment efficiency, impact on MAPK/SAPK-activation and Hippo-YAP signaling was determined by Western blot.

RESULTS

Treatment with HDACi significantly enhanced hyperacetylation of Histone H3-K9 during I/R, indicative of adequate treatment efficiency. Liver injury, as measured by macroscopic aspect, serum transaminases and histology, was delayed, but not alleviated in VPA and SAHA treated animals. Importantly, tissue destruction was significantly more pronounced with VPA. SAPK-activation (p38 and JNK) was reduced by VPA and SAHA in the early (6h) reperfusion phase, but augmented later on (JNK, 24h). Regeneration appeared enhanced in SAHA and VPA treated animals and was dependent on Hippo-YAP signaling.

CONCLUSIONS

VPA and SAHA delay warm hepatic I/R injury at least in part through modulation of SAPK-activation. However, these HDACi fail to exert organoprotective effects, in this setting. For VPA, belated damage is even aggravated.

Genomic Analyses of Sperm Fate Regulator Targets Reveal a Common Set of Oogenic mRNAs in Caenorhabditis elegans

Germ cell specification as sperm or oocyte is an ancient cell fate decision, but its molecular regulation is poorly understood. In Caenorhabditis elegans, the FOG-1 and FOG-3 proteins behave genetically as terminal regulators of sperm fate specification. Both are homologous to well-established RNA regulators, suggesting that FOG-1 and FOG-3 specify the sperm fate post-transcriptionally. We predicted that FOG-1 and FOG-3, as terminal regulators of the sperm fate, might regulate a battery of gamete-specific differentiation genes. Here we test that prediction by exploring on a genomic scale the messenger RNAs (mRNAs) associated with FOG-1 and FOG-3. Immunoprecipitation of the proteins and their associated mRNAs from spermatogenic germlines identifies 81 FOG-1 and 722 FOG-3 putative targets. Importantly, almost all FOG-1 targets are also FOG-3 targets, and these common targets are strongly biased for oogenic mRNAs. The discovery of common target mRNAs suggested that FOG-1 and FOG-3 work together. Consistent with that idea, we find that FOG-1 and FOG-3 proteins co-immunoprecipitate from both intact nematodes and mammalian tissue culture cells and that they colocalize in germ cells. Taking our results together, we propose a model in which FOG-1 and FOG-3 work in a complex to repress oogenic transcripts and thereby promote the sperm fate.

Transducer of ERBB2.1 (TOB1) as a Tumor Suppressor: A Mechanistic Perspective

Transducer of ERBB2.1 (TOB1) is a tumor-suppressor protein, which functions as a negative regulator of the receptor tyrosine-kinase ERBB2. As most of the other tumor suppressor proteins, TOB1 is inactivated in many human cancers. Homozygous deletion of TOB1 in mice is reported to be responsible for cancer development in the lung, liver, and lymph node, whereas the ectopic overexpression of TOB1 shows anti-proliferation, and a decrease in the migration and invasion abilities on cancer cells. Biochemical studies revealed that the anti-proliferative activity of TOB1 involves mRNA deadenylation and is associated with the reduction of both cyclin D1 and cyclin-dependent kinase (CDK) expressions and the induction of CDK inhibitors. Moreover, TOB1 interacts with an oncogenic signaling mediator, β-catenin, and inhibits β-catenin-regulated gene transcription. TOB1 antagonizes the v-akt murine thymoma viral oncogene (AKT) signaling and induces cancer cell apoptosis by activating BCL2-associated X (BAX) protein and inhibiting the BCL-2 and BCL-XL expressions. The tumor-specific overexpression of TOB1 results in the activation of other tumor suppressor proteins, such as mothers against decapentaplegic homolog 4 (SMAD4) and phosphatase and tensin homolog-10 (PTEN), and blocks tumor progression. TOB1-overexpressing cancer cells have limited potential of growing as xenograft tumors in nude mice upon subcutaneous implantation. This review addresses the molecular basis of TOB1 tumor suppressor function with special emphasis on its regulation of intracellular signaling pathways.

Acquisition of estrogen independence induces TOB1-related mechanisms supporting breast cancer cell proliferation

Resistance to therapies targeting the estrogen pathway remains a challenge in the treatment of estrogen receptor-positive breast cancer. To address this challenge, a systems biology approach was used. A library of small interfering RNAs targeting an estrogen receptor (ER)- and aromatase-centered network identified 46 genes that are dispensable in estrogen-dependent MCF7 cells, but are selectively required for the survival of estrogen-independent MCF7-derived cells and multiple additional estrogen-independent breast cancer cell lines. Integration of this information identified a tumor suppressor gene TOB1 as a critical determinant of estrogen-independent ER-positive breast cell survival. Depletion of TOB1 selectively promoted G1 phase arrest and sensitivity to AKT and mammalian target of rapmycin (mTOR) inhibitors in estrogen-independent cells but not in estrogen-dependent cells. Phosphoproteomic profiles from reverse-phase protein array analysis supported by mRNA profiling identified a significant signaling network reprogramming by TOB1 that differed in estrogen-sensitive and estrogen-resistant cell lines. These data support a novel function for TOB1 in mediating survival of estrogen-independent breast cancers. These studies also provide evidence for combining TOB1 inhibition and AKT/mTOR inhibition as a therapeutic strategy, with potential translational significance for the management of patients with ER-positive breast cancers.

BTG/Tob family members Tob1 and Tob2 inhibit proliferation of mouse embryonic stem cells via Id3 mRNA degradation

The mammalian BTG/Tob family is a group of proteins with anti-proliferative ability, and there are six members including BTG1, BTG2/PC3/Tis21, BTG3/ANA, BTG4/PC3B, Tob1/Tob and Tob2. Among them, Tob subfamily members, specifically Tob1/Tob and Tob2, have the most extensive C-terminal regions. As previously reported, overexpression of BTG/Tob proteins is associated with the inhibition of G1 to S-phase cell cycle progression and decreased cell proliferation in a variety of cell types. Tob subfamily proteins have similar anti-proliferative effects on cell cycle progression in cultured tumor cells. An important unresolved question is whether or not they have function in rapidly proliferating cells, such as embryonic stem cells (ESCs). Tob1 and Tob2 were expressed ubiquitously in mouse ESCs (mESCs), suggesting a possible role in early embryonic development and mESCs. To address the above question and explore the possible functions of the Tob subfamily in ESCs, we established ESCs from different genotypic knockout inner cell mass (ICM). We found that Tob1(-/-), Tob2(-/-), and Tob1/2 double knockout (DKO, Tob1(-/-) & Tob2(-/-)) ESCs grew faster than wild type (WT) ESCs without losing pluripotency, and we provide a possible mechanistic explanation for these observations: Tob1 and Tob2 inhibit the cell cycle via degradation of Id3 mRNA, which is a set of directly targeted genes of BMP4 signaling in mESCs that play critical roles in the maintenance of ESC properties. Together, our data suggest that BTG/Tob family protein Tob1 and Tob2 regulation cell proliferation does not compromise the basic properties of mESCs.

Clinicopathological significance of cytoplasmic transducer of ErbB2. 1 expression in gastric cancer

The aim of the present study was to investigate the expression of transducer of ErbB2. 1 (TOB1) in gastric carcinoma and to clarify the association between TOB1 expression and the clinical significance of this expression in patients with gastric carcinoma. Western blot analysis was performed to confirm the expression of TOB1 in gastric cancer. Immunohistochemistry (IHC) was performed on a tissue microarray containing 90 pairs of primary gastric cancer and adjacent normal tissue samples. TOB1 expression was evaluated separately with cytoplasmic and nuclear staining. Western blot analysis revealed significantly lower expression levels of TOB1 in gastric cancer tissues than those in adjacent normal tissues in 91.7% of cases. This was confirmed by IHC, which revealed decreased cytoplasmic TOB1 expression in cancer tissues compared with those of normal tissue samples in 84.4% of cases. The IHC data also revealed low cytoplasmic expression of TOB1 in 67.8% of human gastric cancer samples. Nuclear TOB1 expression exhibited no significant association with specific pathological features. However, a significant association was identified between cytoplasmic expression levels of TOB1 and clinicopathological characteristics, including the depth of invasion (P=0.017), differentiation grade (P=0.034) and tumor-node-metastasis stage (P<0.000). In conclusion, cytoplasmic TOB1 expression was suggested to be significant in angiogenesis and cell differentiation in gastric cancer tissues and may be used as a potential prognostic marker.

Candidate tumor suppressor B-cell translocation gene 3 impedes neoplastic progression by suppression of AKT

BTG3 (B-cell translocation gene 3) is a p53 target that also binds and inhibits E2F1. Although it connects two major growth-regulatory pathways functionally and is downregulated in human cancers, whether and how BTG3 acts as a tumor suppressor remain largely uncharacterized. Here we present evidence that BTG3 binds and suppresses AKT, a kinase frequently deregulated in cancers. BTG3 ablation results in increased AKT activity that phosphorylates and inhibits glycogen synthase kinase 3β. Consequently, we also observed elevated β-catenin/T-cell factor activity, upregulation of mesenchymal markers, and enhanced cell migration. Consistent with these findings, BTG3 overexpression suppressed tumor growth in mouse xenografts, and was associated with diminished AKT phosphorylation and reduced β-catenin in tissue specimens. Significantly, a short BTG3-derived peptide was identified, which recapitulates these effects in vitro and in cells. Thus, our study provides mechanistic insights into a previously unreported AKT inhibitory pathway downstream of p53. The identification of an AKT inhibitory peptide also unveils a new avenue for cancer therapeutics development.

Accumulation of cytolytic CD8+ T cells in B16-melanoma and proliferation of mature T cells in TIS21-knockout mice after T cell receptor stimulation

In vivo and in vitro effects of TIS21 gene on the mature T cell activation and antitumor activities were explored by employing MO5 melanoma orthograft and splenocytes isolated from the TIS21-knockout (KO)(2) mice. Proliferation and survival of mature T cells were significantly increased in the KO than the wild type (WT3)e cells, indicating that TIS21 inhibits the rate of mature T cell proliferation and its survival. In MO5 melanoma orthograft model, the KO mice recruited much more CD8(+) T cells into the tumors at around day 14 after tumor cell injection along with reduced tumor volumes compared with the WT. The increased frequency of granzyme B+ CD8+ T cells in splenocytes of the KO mice compared with the WT may account for antitumor-immunity of TIS21 gene in the melanoma orthograft. In contrast, reduced frequencies of CD107a+ CD8+ T cells in the splenocytes of KO mice may affect the loss of CD8+ T cell infiltration in the orthograft at around day 19. These results indicate that TIS21 exhibits antiproliferative and proapoptotic effects in mature T cells, and differentially affects the frequencies of granzyme B+ CD8+ T-cells and CD107a+ CD8+ T-cells, thus transiently regulating in vivo anti-tumor immunity.

Tob1 plays a critical role in the activation of encephalitogenic T cells in CNS autoimmunity

Loss of antiproliferative gene TOB1 results in more severe EAE driven by augmented pathogenic T cell responses.

Reliable biomarkers corresponding to disease progression or therapeutic responsiveness in multiple sclerosis (MS) have not been yet identified. We previously reported that low expression of the antiproliferative gene TOB1 in CD4⁺ T cells of individuals presenting with an initial central nervous system (CNS) demyelinating event (a clinically isolated syndrome), correlated with high risk for progression to MS. We report that experimental autoimmune encephalomyelitis (EAE) in Tob1^−/− mice was associated with augmented CNS inflammation, increased infiltrating CD4⁺ and CD8⁺ T cell counts, and increased myelin-reactive Th1 and Th17 cells, with reduced numbers of regulatory T cells. Reconstitution of Rag1^−/− mice with Tob1^−/− CD4⁺ T cells recapitulated the aggressive EAE phenotype observed in Tob1^−/− mice. Furthermore, severe spontaneous EAE was observed when Tob1^−/− mice were crossed to myelin oligodendrocyte glycoprotein–specific T cell receptor transgenic (2D2) mice. Collectively, our results reveal a critical role for Tob1 in adaptive T cell immune responses that drive development of EAE, thus providing support for the development of Tob1 as a biomarker for demyelinating disease activity.

C. elegans FOG-3/Tob can either promote or inhibit germline proliferation, depending on gene dosage and genetic context

Vertebrate Tob/BTG proteins inhibit cell proliferation when overexpressed in tissue-culture cells, and they can function as tumor suppressors in mice. The single Caenorhabditis elegans Tob/BTG ortholog, FOG-3, by contrast, was identified from its loss-of-function phenotype as a regulator of sperm fate specification. Here we report that FOG-3 also regulates proliferation in the germline tissue. We first demonstrate that FOG-3 is a positive regulator of germline proliferation. Thus, fog-3 null mutants possess fewer germ cells than normal, a modest but reproducible decrease observed for each of two distinct fog-3 null alleles. A similar decrease also occurred in fog-3/+ heterozygotes, again for both fog-3 alleles, revealing a haplo-insufficient effect on proliferation. Therefore, FOG-3 normally promotes proliferation, and two copies of the fog-3 gene are required for this function. We next overexpressed FOG-3 by removal of FBF, the collective term for FBF-1 and FBF-2, two nearly identical PUF RNA-binding proteins. We find that overexpressed FOG-3 blocks proliferation in fbf-1 fbf-2 mutants; whereas germ cells stop dividing and instead differentiate in fbf-1 fbf-2 double mutants, they continue to proliferate in fog-3; fbf-1 fbf-2 triple mutants. Therefore, like its vertebrate Tob/BTG cousins, overexpressed FOG-3 is 'antiproliferative'. Indeed, some fog-3; fbf-1 fbf-2 mutants possess small tumors, suggesting that FOG-3 can act as a tumor suppressor. Finally, we show that FOG-3 and FBF work together to promote tumor formation in animals carrying oncogenic Notch mutations. A similar effect was not observed when germline tumors were induced by manipulation of other regulators; therefore, this FOG-3 tumor-promoting effect is context dependent. We conclude that FOG-3 can either promote or inhibit proliferation in a manner that is sensitive to both genetic context and gene dosage. The discovery of these FOG-3 effects on proliferation has implications for our understanding of vertebrate Tob/BTG proteins and their influence on normal development and tumorigenesis.

Flipping the switch from g1 to s phase with e3 ubiquitin ligases

The cell cycle ensures genome maintenance by coordinating the processes of DNA replication and chromosome segregation. Of particular importance is the irreversible transition from the G1 phase of the cell cycle to S phase. This transition marks the switch from preparing chromosomes for replication ("origin licensing") to active DNA synthesis ("origin firing"). Ubiquitin-mediated proteolysis is essential for restricting DNA replication to only once per cell cycle and is the major mechanism regulating the G1 to S phase transition. Although some changes in protein levels are attributable to regulated mRNA abundance, protein degradation elicits very rapid changes in protein abundance and is critical for the sharp and irreversible transition from one cell cycle stage to the next. Not surprisingly, regulation of the G1-to-S phase transition is perturbed in most cancer cells, and deregulation of key molecular events in G1 and S phase drives not only cell proliferation but also genome instability. In this review we focus on the mechanisms by which E3 ubiquitin ligases control the irreversible transition from G1 to S phase in mammalian cells.

Cross-Platform Microarray Data Integration Combining Meta-Analysis and Gene Set Enrichment Analysis

Integrative analysis of microarray data has been proven as a more reliable approach to deciphering molecular mechanisms underlying biological studies. Traditional integration such as meta-analysis is usually gene-centered. Recently, gene set enrichment analysis (GSEA) has been widely applied to bring gene-level interpretation to pathway-level. GSEA is an algorithm focusing on whether an a priori defined set of genes shows statistically significant differences between two biological states. However, GSEA does not support integrating multiple microarray datasets generated from different studies. To overcome this, the improved version of GSEA, ASSESS, is more applicable, after necessary modifications. By making proper combined use of meta-analysis, GSEA, and modified ASSESS, this chapter reports two workflow pipelines to extract consistent expression pattern change at pathway-level, from multiple microarray datasets generated by the same or different microarray production platforms, respectively. Such strategies amplify the advantage and overcome the disadvantage than if using each method individually, and may achieve a more comprehensive interpretation towards a biological theme based on an increased sample size. With further network analysis, it may also allow an overview of cross-talking pathways based on statistical integration of multiple gene expression studies. A web server where one of the pipelines is implemented is available at: http://lifecenter.sgst.cn/mgsea//home.htm.

Early origins of heart disease: low birth weight and determinants of cardiomyocyte endowment

1. World-wide epidemiological and experimental animal studies demonstrate that adversity in fetal life, resulting in intrauterine growth restriction, programmes the offspring for a greater susceptibility to ischaemic heart disease and heart failure in adult life. 2. After cardiogenesis, cardiomyocyte endowment is determined by a range of hormones and signalling pathways that regulate cardiomyocyte proliferation, apoptosis and the timing of multinucleation/terminal differentiation. 3. The small fetus may have reduced cardiomyocyte endowment owing to the impact of a suboptimal intrauterine environment on the signalling pathways that regulate cardiomyocyte proliferation, apoptosis and the timing of terminal differentiation.

RNA decay machines: deadenylation by the Ccr4-not and Pan2-Pan3 complexes

Shortening and removal of the 3' poly(A) tail of mature mRNA by poly(A)-specific 3' exonucleases (deadenylases) is the initial and often rate-limiting step in mRNA degradation. The majority of cytoplasmic deadenylase activity is associated with the Ccr4-Not and Pan2-Pan3 complexes. Two distinct catalytic subunits, Caf1/Pop2 and Ccr4, are associated with the Ccr4-Not complex, whereas the Pan2 enzymatic subunit forms a stable complex with Pan3. In this review, we discuss the composition and activity of these two deadenylases. In addition, we comment on generic and specific mechanisms of recruitment of Ccr4-Not and Pan2-Pan3 to mRNAs. Finally, we discuss specialised and redundant functions of the deadenylases and review the importance of Ccr4-Not subunits in the regulation of physiological processes. This article is part of a Special Issue entitled: RNA Decay mechanisms.

The anti-proliferative activity of BTG/TOB proteins is mediated via the Caf1a (CNOT7) and Caf1b (CNOT8) deadenylase subunits of the Ccr4-not complex

The human BTG/TOB protein family comprises six members (BTG1, BTG2/PC3/Tis21, BTG3/Ana, BTG4/PC3B, TOB1/Tob, and TOB2) that are characterised by a conserved BTG domain. This domain mediates interactions with the highly similar Caf1a (CNOT7) and Caf1b (CNOT8) catalytic subunits of the Ccr4-Not deadenylase complex. BTG/TOB proteins have anti-proliferative activity: knockdown of BTG/TOB can result in increased cell proliferation, whereas over-expression of BTG/TOB leads to inhibition of cell cycle progression. It was unclear whether the interaction between BTG/TOB proteins and the Caf1a/Caf1b deadenylases is necessary for the anti-proliferative activity of BTG/TOB. To address this question, we further characterised surface-exposed amino acid residues of BTG2 and TOB1 that mediate the interaction with the Caf1a and Caf1b deadenylase enzymes. We then analysed the role of BTG2 and TOB1 in the regulation of cell proliferation, translation and mRNA abundance using a mutant that is no longer able to interact with the Caf1a/Caf1b deadenylases. We conclude that the anti-proliferative activity of BTG/TOB proteins is mediated through interactions with the Caf1a and Caf1b deadenylase enzymes. Furthermore, we show that the activity of BTG/TOB proteins in the regulation of mRNA abundance and translation is dependent on Caf1a/Caf1b, and does not appear to require other Ccr4-Not components, including the Ccr4a (CNOT6)/Ccr4b (CNOT6L) deadenylases, or the non-catalytic subunits CNOT1 or CNOT3.

Tob2 inhibits peroxisome proliferator-activated receptor γ2 expression by sequestering Smads and C/EBPα during adipocyte differentiation

Adipogenesis is an important component of adipose tissue development and is critically related to obesity. A cascade of transcription factors is involved in adipogenesis, in which peroxisome proliferator-activated receptor gamma (PPARγ) and CCAAT/enhancer-binding proteins (C/EBPs) play pivotal roles. Bone morphogenetic proteins (BMPs) and Smad proteins are implicated in this cascade, although the precise regulatory mechanisms have yet to be elucidated. Here, we show that Tob2, a member of the Tob/BTG antiproliferative protein family, inhibits adipogenesis by interfering with Smad signaling. tob2 expression is downregulated in the white adipose tissue of high-fat diet-induced or genetically mutated obese mice. Consistent with this, tob2(-/-) mice exhibit increased adiposity with augmented expression of the genes encoding the type 1A BMP receptor (BMPR1A) and PPARγ2 as well as their target genes. We further show accelerated adipogenesis in primary tob2(-/-) preadipocytes. Furthermore, exogenously expressed Tob2 inhibits adipogenic differentiation of 3T3-L1 preadipocytes: the Tob2 protein suppresses PPARγ2 transcription by inhibiting BMP2-induced Smad1/5 phosphorylation through its interaction with Smad6 and by sequestering C/EBPα from the PPARγ2 promoter. Thus, Tob2 negatively regulates adipogenesis by inhibiting PPARγ2 expression.

Inhibition of DNA damage-induced apoptosis through Cdc7-mediated stabilization of Tob

BACKGROUND

Preventing unnecessary cell death is essential for DNA-damaged cells to carry out the DNA repair process.

RESULTS

Cdc7 inhibits the Cul4-DDB1(Cdt2)-dependent Tob degradation.

CONCLUSION

Cdc7 enables mild DNA-damaged cells to keep their viability by competing with the Tob degradation system.

SIGNIFICANCE

Cells deal with moderate DNA damage not only by cessation of the cell cycle but also through direct mediated pro-survival signaling. Cells respond to DNA damage by activating alternate signaling pathways that induce proliferation arrest or apoptosis. The correct balance between these two pathways is important for maintaining genomic integrity and preventing unnecessary cell death. The mechanism by which DNA-damaged cells escape from apoptosis during DNA repair is poorly understood. We show that the DNA replication-initiating kinase Cdc7 actively prevents unnecessary death in DNA-damaged cells. In response to mild DNA damage, Tob levels increase through both a transcriptional mechanism and protein stabilization, resulting in inhibition of pro-apoptotic signaling. Cells lacking Cdc7 expression undergo apoptosis after mild DNA damage, where Cul4-DDB1(Cdt2) induces Tob ubiquitination and subsequent degradation. Cdc7 phosphorylates and interacts with Tob to inhibit the Cul4-DDB1(Cdt2)-dependent Tob degradation. Thus, Cdc7 defines an essential pro-survival signaling pathway by contributing to stabilization of Tob, thereby the viability of DNA-damaged cells being maintained.

The role of the TOB1 gene in growth suppression of hepatocellular carcinoma

The TOB1 gene, mapped on 17q21, is a member of the BTG/Tob family. In breast cancer it has been identified as a candidate tumor suppressor gene. However, whether TOB1 is a bona fide tumor suppressor and downregulated in hepatocellular carcinoma (HCC) remains unclear. In addition, whether its expression is regulated through methylation requires investigation. In the present study, we therefore analyzed the expression of TOB1 in HCC and its methylation levels in human HCC and breast cancer. No significant difference in the expression levels of TOB1 was observed between tumor tissues and adjacent normal tissues in HCC. Quantitative methylation analysis by MassArray revealed no significant differences at single CpG sites or in the global promoter region, and all these CpG sites shared a similar methylation pattern in HCC and breast cancer. Moreover, 5-aza-2'-deoxycytidine treatment of three tumor cell lines did not cause elevation of TOB1 mRNA in HepG2 cell lines. Based on these data, we speculate that TOB1 may be a candidate non-tumor suppressor gene in HCC. Furthermore, the clinical outcome was not correlated with TOB1 expression or expression rate. In addition, TOB1 expression or expression rate was not correlated with the overall survival (OS) rates or cumulative recurrence rates. Taken together, we suggest that TOB1 does not act as a tumor suppressor in HCC.

Tob1 induces apoptosis and inhibits proliferation, migration and invasion of gastric cancer cells by activating Smad4 and inhibiting β‑catenin signaling

Transducer of ErbB-2.1 (Tob1), a tumor suppressor protein, is inactivated in a variety of cancers including stomach cancer. However, the role of Tob1 in gastric carcinogenesis remains elusive. The present study aimed to investigate whether Tob1 could inhibit gastric cancer progression in vitro, and to elucidate its underlying molecular mechanisms. We found differential expression of Tob1 in human gastric cancer (MKN28, AGS and MKN1) cells. The overexpression of Tob1 induced apoptosis in MKN28 and AGS cells, which was associated with sub-G1 arrest, activation of caspase-3, induction of Bax, inhibition of Bcl-2 and cleavage of poly (ADP-ribose) polymerase (PARP). In addition, Tob1 inhibited proliferation, migration and invasion, which were reversed in MKN1 and AGS cells transfected with Tob1 siRNA. Overexpression of Tob1 in MKN28 and AGS cells induced the expression of Smad4, leading to the increased expression and the promoter activity of p15, which was diminished by silencing of Tob1 using specific siRNA. Tob1 decreased the phosphorylation of Akt and glycogen synthase kinase-3β (GSK3β) in MKN28 and AGS cells, resulting in the reduced protein expression and the transcriptional activity of β‑catenin, which in turn decreased the expression of cyclin D1, cyclin-dependent kinase-4 (CDK4), urokinase plasminogen activator receptor (uPAR) and peroxisome proliferator and activator receptor-δ (PPARδ). Conversely, silencing of Tob1 induced the phosphorylation of Akt and GSK-3β, and increased the expression of β‑catenin and its target genes. Collectively, our study demonstrates that the overexpression of Tob1 inhibits gastric cancer progression by activating Smad4- and inhibiting β‑catenin-mediated signaling pathways.

Suppression of human lung cancer cell proliferation and metastasis in vitro by the transducer of ErbB-2.1 (TOB1)

AIM

To investigate the effects of the transducer of ErbB-2.1 (TOB1) on the proliferation, migration and invasion of human lung cancer cells in vitro.

METHODS

Human lung cancer cell lines (95-D, A549, NCI-H1299, NCI-H1975, NCI-H661, NCI-H446, NCI-H1395, and Calu-3) and the normal human bronchial epithelial (HBE) cell line were tested. The expression levels of TOB1 in the cells were determined with Western blot and RT-PCR analyses. TOB1-overexpressing cell line 95-D/TOB1 was constructed using lipofectamine-induced TOB1 recombinant plasmid transfection and selective G418 cell culture. The A549 cells were transcend-transfected with TOB1-siRNA. MTT assay, flow cytometry and Western blot analysis were used to examine the effects of TOB1 on cancer cell proliferation and wound healing. Transwell invasive assay was performed to evaluate the effects of TOB1 on cancer cell migration and invasion. The activity of MMP2 and MMP9 was measured using gelatin zymography assay.

RESULTS

The expression levels of TOB1 in the 8 human lung cancer cell lines were significantly lower than that in HBE cells. TOB1 overexpression inhibited the proliferation of 95-D cells, whereas TOB1 knockdown with TOB1-siRNA promoted the growth of A549 cells. Decreased cell migration and invasion were detected in 95-D/TOB1 cells, and the suppression of TOB1 enhanced the metastasis in A549 cells. TOB1 overexpression not only increased the expression of the phosphatase and tensin homolog (PTEN), an important tumor suppressor, but also regulated the downstream effectors in the PI3K/PTEN signaling pathway, including Akt, ERK1/2, etc. In contrast, decreased expression of TOB1 oppositely regulated the expression of these factors. TOB1 also regulates the gelatinase activity of MMP2 and MMP9 in lung cancer cells.

CONCLUSION

The results demonstrate that the PI3K/PTEN pathway, which is essential for carcinogenesis, angiogenesis, and metastasis, may be one of the possible signaling pathways for regulation of proliferation and metastasis of human lung cancer cells by TOB1 in vitro.

Evidence providing new insights into TOB-promoted deadenylation and supporting a link between TOB's deadenylation-enhancing and antiproliferative activities

The mammalian TOB1 and TOB2 proteins have emerged as key players in repressing cell proliferation. Accumulating evidence indicates that TOBs regulate mRNA deadenylation. A recruitment model was proposed in which TOBs promote deadenylation by recruiting CAF1-CCR4 deadenylase complex to the 3' end of mRNAs by simultaneously binding CAF1 and PABP. However, the exact molecular mechanism underlying TOB-promoted deadenylation remains unclear. It is also unclear whether TOBs' antiproliferative and deadenylation-promoting activities are connected. Here, we combine biochemical analyses with a functional assay directly monitoring deadenylation and mRNA decay to characterize the effects of tethering TOBs or their mutant derivatives to mRNAs. The results provide direct evidence supporting the recruitment model and reveal a link between TOBs' antiproliferative and deadenylation-promoting activities. We also find that TOBs' actions in deadenylation are independent of the phosphorylation state of three serines known to regulate antiproliferative actions, suggesting that TOBs arrest cell growth through at least two different mechanisms. TOB1 and TOB2 were interchangeable in the properties tested here, indicating considerable functional redundancy between the two proteins. We propose that their multiple modes of modulating mRNA turnover and arresting cell growth permit the TOB proteins to coordinate their diverse roles in controlling cell growth and differentiation.

Molecular characterization of Tob1 in muscle development in pigs

Cell proliferation is an important biological process during myogenesis. Tob1 encoded a member of the Tob/BTG family of anti-proliferative proteins. Our previous LongSAGE (Long Serial Analysis of Gene Expression) analysis suggested that Tob1 was differentially expressed during prenatal skeletal muscle development. In this study, we isolated and characterized the swine Tob1 gene. Subsequently, we examined Tob1 chromosome assignment, subcellular localization and dynamic expression profile in prenatal skeletal muscle (33, 65 and 90 days post-conception, dpc) from Landrace (lean-type) and Tongcheng pigs (obese-type). The Tob1 gene was mapped to pig chromosome 12 (SSC12). The Tob1 protein was distributed throughout the nucleus and cytoplasm of PK15 cells. During prenatal skeletal muscle development, Tob1 was up-regulated and highly expressed in skeletal muscle at 90 dpc in Tongcheng pigs but peaked at 65 dpc in Landrace pigs. This result suggested that there were different proliferation patterns during myogenesis between Tongcheng and Landrace pigs. During postnatal skeletal muscle development, the expression of Tob1 increased with aging, indicating that the proliferation potential of myoblasts decreased in postnatal muscle development. In tissues of adult wuzhishan miniature pigs, the Tob1 gene was highly expressed in skeletal muscle. The expression of Tob1 was significantly increased at day 6 during C2C12 differentiation time, suggesting a possible role in skeletal muscle development. Therefore, this study indicated that Tob1 perhaps played an important role in skeletal muscle development.

Identification of novel subregions of LOH in gastric cancer and analysis of the HIC1 and TOB1 tumor suppressor genes in these subregions

Previously, we identified 3 overlapping regions showing loss of heterozygosity (LOH, R(1)-R(3) from 11 to 30 cM) on chromosome 17 in 45 primary gastric cancers (GCs). The data indicated the presence of tumor suppressor genes (TSGs) on chromosome 17 involved in GC. Among the putative TSGs in these regions, HIC1 (in SR(1)) and TOB1 (in SR(3)) remain to be examined in GC. By immunohistochemistry (IHC), methylation-specific PCR (MSP) and western blot, we evaluated the expression and regulation status for HIC1 and TOB1 protein in GC. We narrowed down the deletion intervals on chromosome 17 and defined five smaller LOH subregions, SR(1)-SR(5) (0.54 to 3.42 cM), in GC. We found that HIC1 had downregulated expression in 86% (91/106) and was methylated in 87% (26/30) of primary GCs. Of the primary GCs showing downregulation of HIC1 protein, 75% (18/24) had methylated HIC1 gene. TOB1 was either absent or expressed at reduced levels in 75% (73/97) of the GC samples. In addition, a general reduction was found in total and the ratio of unphosphorylated to phosphorylated TOB1 protein levels in the differentiated GC cell lines. Further analysis revealed significant simultaneous downregulation of both HIC1 and TOB1 protein in GC tissue microarray samples (67%, 52/78) and in primary GCs (65%, 11/17). These results indicate that silencing of HIC1 and TOB1 expression is a common occurrence in GC and may contribute to the development and progression of the disease.

Monoubiquitination of Tob/BTG family proteins competes with degradation-targeting polyubiquitination

Tob belongs to the anti-proliferative Tob/BTG protein family. The expression level of Tob family proteins is strictly regulated both transcriptionally and through post-translational modification. Ubiquitin (Ub)/proteosome-dependent degradation of Tob family proteins is critical in controlling cell cycle progression and DNA damage responses. Various Ub ligases (E3s) are responsible for degradation of Tob protein. Here, we show that Tob family proteins undergo monoubiquitination even in the absence of E3s in vitro. Determination of the ubiquitination site(s) in Tob by mass spectrometric analysis revealed that two lysine residues (Lys48 and Lys63) located in Tob/BTG homology domain are ubiquitinated. A mutant Tob, in which both Lys48 and Lys63 are substituted with alanine, is more strongly polyubiquitinated than wild-type Tob in vivo. These data suggest that monoubiquitination of Tob family proteins confers resistance against polyubiquitination, which targets proteins for degradation. The strategy for regulating the stability of Tob family proteins suggests a novel role for monoubiquitination.

Epigenetic silencing of a proapoptotic cell adhesion molecule, the immunoglobulin superfamily member IGSF4, by promoter CpG methylation protects Hodgkin lymphoma cells from apoptosis

The malignant Hodgkin/Reed-Sternberg (HRS) cells of Hodgkin lymphoma (HL) are believed to derive from germinal center (GC) B cells, but lack expression of a functional B cell receptor. As apoptosis is the normal fate of B-cell receptor-negative GC B cells, mechanisms that abrogate apoptosis are thus critical in HL development, such as epigenetic disruption of certain pro-apoptotic cancer genes including tumor suppressor genes. Identifying methylated genes elucidates oncogenic mechanisms and provides valuable biomarkers; therefore, we performed a chemical epigenetic screening for methylated genes in HL through pharmacological demethylation and expression profiling. IGSF4/CADM1/TSLC1, a pro-apoptotic cell adhesion molecule of the immunoglobulin superfamily, was identified together with other methylated targets. In contrast to its expression in normal GC B cells, IGSF4 was down-regulated and methylated in HL cell lines, most primary HL, and microdissected HRS cells of 3/5 cases, but not in normal peripheral blood mononuclear cells and seldom in normal lymph nodes. We also detected IGSF4 methylation in sera of 14/18 (78%) HL patients but seldom in normal sera. Ectopic IGSF4 expression decreased HL cells survival and increased their sensitivity to apoptosis. IGSF4 induction that normally follows heat shock stress treatment was also abrogated in methylated lymphoma cells. Thus, our data demonstrate that IGSF4 silencing by CpG methylation provides an anti-apoptotic signal to HRS cells important in HL pathogenesis.

Tob1 is a constitutively expressed repressor of liver regeneration

How proliferative and inhibitory signals integrate to control liver regeneration remains poorly understood. A screen for antiproliferative factors repressed after liver injury identified transducer of ErbB2.1 (Tob1), a member of the PC3/BTG1 family of mito-inhibitory molecules as a target for further evaluation. Tob1 protein decreases after 2/3 hepatectomy in mice secondary to posttranscriptional mechanisms. Deletion of Tob1 increases hepatocyte proliferation and accelerates restoration of liver mass after hepatectomy. Down-regulation of Tob1 is required for normal liver regeneration, and Tob1 controls hepatocyte proliferation in a dose-dependent fashion. Tob1 associates directly with both Caf1 and cyclin-dependent kinase (Cdk) 1 and modulates Cdk1 kinase activity. In addition, Tob1 has significant effects on the transcription of critical cell cycle components, including E2F target genes and genes involved in p53 signaling. We provide direct evidence that levels of an inhibitory factor control the rate of liver regeneration, and we identify Tob1 as a crucial check point molecule that modulates the expression and activity of cell cycle proteins.

BTG/TOB factors impact deadenylases

BTG/TOB factors are a family of antiproliferative proteins whose expression is altered in numerous cancers. They have been implicated in cell differentiation, development and apoptosis. Although proposed to affect transcriptional regulation, these factors interact with CAF1, a subunit of the main eukaryotic deadenylase, and with poly(A)-binding-proteins, strongly suggesting a role in post-transcriptional regulation of gene expression. The recent determination of the structures of BTG2, TOB1 N-terminal domain (TOB1N138) and TOB1N138-CAF1 complexes support a role for BTG/TOB proteins in mRNA deadenylation, a function corroborated by recently published functional characterizations. We highlight molecular mechanisms by which BTG/TOB proteins influence deadenylation and discuss the need for a better understanding of BTG/TOB physiological functions.

TOB suppresses breast cancer tumorigenesis

Transducer of ErbB-2 (TOB) is a member of the TOB/Btg gene family. A role for TOB in the suppression of human tumorigenesis has been proposed, based on the observations that TOB-knockout mice spontaneously form tumors and TOB expression is lost in human lung and thyroid cancers. However, the role of TOB in human breast cancer remains unknown. To evaluate the this role, we screened a panel of breast cancer cell lines for TOB expression levels and found that they are inversely correlated with the tumorigenicity and metastatic potential of the cell lines. In addition, we demonstrated for the first time that TOB expression is inversely correlated with breast cancer progression in clinical specimens. These results strongly indicate that the loss of TOB expression plays a role in breast cancer progression. We have also provided the first evidence that TOB functions as a tumor suppressor in breast cancer MCF-7 cells, using gain-of-function and loss-of-function approaches to manipulate TOB expression. Cell-cycle analysis further revealed that TOB can prolong the G1-S phase transition by inducing arrest at G1-S phase. Moreover, upregulation of the cyclin-dependent kinase inhibitor p27 and downregulation of the antiapoptotic proteins Bcl-2 and Bcl-XL were observed in MCF7/TOB transfectants. Conversely, opposite results were observed in shRNA-TOB transfectants. Furthermore, decreased activity of Erk2, AKT, CrkL, PDK1, and Smads were observed in TOB-overexpressing cells. Taken together, these data provide evidence that TOB can function as a tumor suppressor in breast cancer through modulation and regulation of multiple signaling pathways.

The Ccr4-NOT deadenylase subunits CNOT7 and CNOT8 have overlapping roles and modulate cell proliferation

Accurate gene expression requires the precise control of mRNA levels, which are determined by the relative rates of nuclear (pre-)mRNA synthesis and processing, and cytoplasmic mRNA turnover. A key step in mRNA degradation is the removal of the poly(A) tail, which involves several deadenylases including components of the Ccr4-Not complex. Here, we focused on the role of the human paralogues CNOT7 (hCaf1/Caf1a) and CNOT8 (hPop2/Caf1b/Calif), which possess deadenylase activity mediated by DEDD nuclease domains. We show that efficient proliferation requires both subunits, although combined knockdown of CNOT7 and CNOT8 further reduces cell proliferation indicating partial redundancy between these proteins. Interestingly, the function of CNOT7 in cell proliferation partly depends on its catalytic activity. On the other hand, the interaction between CNOT7 and BTG2, a member of the antiproliferative BTG/Tob family involved in transcription and mRNA decay appears less important for proliferation of MCF7 cells, suggesting that CNOT7 does not function solely in conjunction with BTG2. Further analysis of gene expression profiles of CNOT7 and/or CNOT8 knockdown cells underscores the partial redundancy between these subunits and suggests that regulation of several genes, including repression of the antiproliferative genes MSMB and PMP22, by the Ccr4-Not complex contributes to cell proliferation.

TOB1 is regulated by EGF-dependent HER2 and EGFR signaling, is highly phosphorylated, and indicates poor prognosis in node-negative breast cancer

Clinical and animal studies have shown that coexpression of the receptor tyrosine kinases HER2 and epidermal growth factor (EGF) receptor (EGFR) indicates a highly metastatic phenotype of breast cancer. In a cellular model of this phenotype using differential gene expression analysis, we identified TOB1 to be up-regulated depending on EGF stimulation and transduction through phosphorylation of HER2 tyrosine 1248. mRNA expression analysis of breast cancers from a cohort of node-negative patients showed significantly shortened distant metastasis-free survival for patients with high TOB1 expression. In subsequent tissue microarray studies of 725 clinical samples, high HER2 and EGF protein levels were significantly correlated with TOB1 expression in breast cancer, whereas EGFR and EGF levels correlated with TOB1 phosphorylation. We did not observe a correlation between TOB1 expression and cyclin D1, which was previously suggested to mediate the antiproliferative effect of unphosphorylated TOB1. A positive correlation of TOB1 phosphorylation status with proliferation marker Ki67 suggests that elevated TOB1 phosphorylation might abrogate the antiproliferative effect of TOB1 in breast cancer. This suggests a new regulatory role for TOB1 in cancer progression with particular significance in HER2- and/or EGFR-positive breast cancers.