Signal transducer and activator of transcription 3 (STAT3) is a recently characterized transcription factor which is essential to liver regeneration. We have previously reported that hepatic stimulator substance (HSS)...Signal transducer and activator of transcription 3 (STAT3) is a recently characterized transcription factor which is essential to liver regeneration. We have previously reported that hepatic stimulator substance (HSS), a novel growthpromoting substance, phosphorylated the epidermal growth factor (EGF) receptors and activated downstream RasMAP kinase (extracellular signal-regulated kinases, ERK1/2) cascade. However, whether HSS signal is related to STAT3pathway remains unclear. The present study is aiming to explore the regulatory effect of activation of ERK1/2 evoked by HSS on STAT3 phosphorylation and STAT3 signaling. Human hepatoma cell line HepG2 was stably transfected with HSS cDNA and HSS expression was measured by Northern blot. The results showed that the transfection of HSS into HepG2 resulted in remarkable increase in cellular proliferation as compared with the non-transfected cells, and it was further proved that the cellular proliferation in the HSS-transfected cells was related to ERK1/2 activation. Treatment of the cells with 50 μM of PD98059, an ERK1/2 specific upstream inhibitor, resulted in ERK1/2 inactivation completely.Inhibition of ERK1/2 allowed the tyrosine of STAT3 to be phosphorylated in a dose-dependent manner to PD98059.Furthermore, transient transfection of STAT3 mutant (STAT3S727A) into HSS-bearing cells could remarkably reverse the inhibitory effect of ERK1/2 on STAT3 phosphorylation. Based upon these results, it is concluded that ERK1/2negatively modulates STAT3 phosphorylation and this function is dependent on residual serine-727 (S727) of STAT3.展开更多
Interleukin-2 （IL）-2 signaling plays a pivotal role in the activation of immune responses, and drugs that block this pathway have been shown to be effective for the immunosuppression in patients with organ transplan...Interleukin-2 （IL）-2 signaling plays a pivotal role in the activation of immune responses, and drugs that block this pathway have been shown to be effective for the immunosuppression in patients with organ transplantation to alleviate/eliminate allograft rejection. The first humanized monoclonal antibody （mAb） daclizumab falls into this category and shows high specificity and affinity against a key component of the IL-2 receptor complex, namely IL-2Ra. To reveal the molecular mechanism of the inhibition of the IL-2 signaling pathway by dacllzumab, we determined the crystal structures of the daclizumab Fab in free form and in complex with the IL-2Ra ectodomain at 2.6 and 2.8 A resolution, respectively. The daclizumab Fab adopts a similar conformation in the presence or absence of the IL- 2Ra ectodomain. The antigen-binding site of daclizumab is mainly composed of live complementarity determining regions （CDRs） that form a large positively charged surface depression and two flanking patches that are generally hydrophobic. The conformational epitope consists of several discontinuous segments of the IL-2Ru ectodomain, a large portion of which overlaps with the regions that interact with IL-2, suggesting that the binding of daclizumab to IL-2Ra would prevent the IL-2 binding to IL-2Ra and the subsequent formation of the IL-2fIL-2Ra[~/c complex, and therefore block the IL-2 signaling pathway. These results also have implications for the design and development of improved mAb drugs targeting IL-2Ra.展开更多
The covalent attachment of O-linked β-N- acetylglucosamine （O-GIcNAc） to Ser/Thr residues of proteins acts as not only a posttranslational modification but also a nutritional sensor in nucleus and cytoplasm, which ...The covalent attachment of O-linked β-N- acetylglucosamine （O-GIcNAc） to Ser/Thr residues of proteins acts as not only a posttranslational modification but also a nutritional sensor in nucleus and cytoplasm, which directly regulates the expression of genes and multiple crucial signal transduction pathways. Dynamic O- GlcNAcylation at Ser/Thr residues is catalyzed by two key enzymes, O-GIcNAc transferase （OGT） and O-GlcNAcase, which are responsible for addition and removal of the O- GlcNAc modification, respectively. O-GlcNAc modifica- tion plays important roles in cellular signaling in animals, especially in human diseases. Two orthologs of OGT in plants, SECRET AGENT and SPINDLY, have been reported to be involved in diverse plant processes. However, compared with the functional mechanisms revealed in animals, the consequences of protein O-GlcNAc modifi- cation in plants is largely unknown, and the relationship between O-GlcNAcylation and cellular processes needs to be explored. In this review, we summarized the recent advances on O-GlcNAc modification and its biological functions in animals and plants, and prospect of more special functions of O-GlcNAc will be revealed in plants.展开更多
基金This work was supported by the National Natural Science Foundation of China(No.39870285,No.0070342).
文摘Signal transducer and activator of transcription 3 (STAT3) is a recently characterized transcription factor which is essential to liver regeneration. We have previously reported that hepatic stimulator substance (HSS), a novel growthpromoting substance, phosphorylated the epidermal growth factor (EGF) receptors and activated downstream RasMAP kinase (extracellular signal-regulated kinases, ERK1/2) cascade. However, whether HSS signal is related to STAT3pathway remains unclear. The present study is aiming to explore the regulatory effect of activation of ERK1/2 evoked by HSS on STAT3 phosphorylation and STAT3 signaling. Human hepatoma cell line HepG2 was stably transfected with HSS cDNA and HSS expression was measured by Northern blot. The results showed that the transfection of HSS into HepG2 resulted in remarkable increase in cellular proliferation as compared with the non-transfected cells, and it was further proved that the cellular proliferation in the HSS-transfected cells was related to ERK1/2 activation. Treatment of the cells with 50 μM of PD98059, an ERK1/2 specific upstream inhibitor, resulted in ERK1/2 inactivation completely.Inhibition of ERK1/2 allowed the tyrosine of STAT3 to be phosphorylated in a dose-dependent manner to PD98059.Furthermore, transient transfection of STAT3 mutant (STAT3S727A) into HSS-bearing cells could remarkably reverse the inhibitory effect of ERK1/2 on STAT3 phosphorylation. Based upon these results, it is concluded that ERK1/2negatively modulates STAT3 phosphorylation and this function is dependent on residual serine-727 (S727) of STAT3.
基金Acknowledgments We are grateful to the staff members at Shanghai Synchrotron Radiation Facility for support in diffraction data collection and other members of our group for helpful discussion. This work was supported by grants from the Ministry of Science and Technology of China （2010CB833601, 2006AA02A313, and 2009ZX09503- 009）, the National Natural Science Foundation of China （30730028 and 90713046）, and the Chinese Academy of Sciences （KSCX2-YW-R- 107 and SIBS2008002）.
文摘Interleukin-2 （IL）-2 signaling plays a pivotal role in the activation of immune responses, and drugs that block this pathway have been shown to be effective for the immunosuppression in patients with organ transplantation to alleviate/eliminate allograft rejection. The first humanized monoclonal antibody （mAb） daclizumab falls into this category and shows high specificity and affinity against a key component of the IL-2 receptor complex, namely IL-2Ra. To reveal the molecular mechanism of the inhibition of the IL-2 signaling pathway by dacllzumab, we determined the crystal structures of the daclizumab Fab in free form and in complex with the IL-2Ra ectodomain at 2.6 and 2.8 A resolution, respectively. The daclizumab Fab adopts a similar conformation in the presence or absence of the IL- 2Ra ectodomain. The antigen-binding site of daclizumab is mainly composed of live complementarity determining regions （CDRs） that form a large positively charged surface depression and two flanking patches that are generally hydrophobic. The conformational epitope consists of several discontinuous segments of the IL-2Ru ectodomain, a large portion of which overlaps with the regions that interact with IL-2, suggesting that the binding of daclizumab to IL-2Ra would prevent the IL-2 binding to IL-2Ra and the subsequent formation of the IL-2fIL-2Ra[~/c complex, and therefore block the IL-2 signaling pathway. These results also have implications for the design and development of improved mAb drugs targeting IL-2Ra.
基金This work was supported by the National Basic Research Program of China （2011CB915404） the National Natural Science Foundation of China （No.31270310） and the Fundamental Research Funds for the Central Universities （2572014EA04）.
文摘The covalent attachment of O-linked β-N- acetylglucosamine （O-GIcNAc） to Ser/Thr residues of proteins acts as not only a posttranslational modification but also a nutritional sensor in nucleus and cytoplasm, which directly regulates the expression of genes and multiple crucial signal transduction pathways. Dynamic O- GlcNAcylation at Ser/Thr residues is catalyzed by two key enzymes, O-GIcNAc transferase （OGT） and O-GlcNAcase, which are responsible for addition and removal of the O- GlcNAc modification, respectively. O-GlcNAc modifica- tion plays important roles in cellular signaling in animals, especially in human diseases. Two orthologs of OGT in plants, SECRET AGENT and SPINDLY, have been reported to be involved in diverse plant processes. However, compared with the functional mechanisms revealed in animals, the consequences of protein O-GlcNAc modifi- cation in plants is largely unknown, and the relationship between O-GlcNAcylation and cellular processes needs to be explored. In this review, we summarized the recent advances on O-GlcNAc modification and its biological functions in animals and plants, and prospect of more special functions of O-GlcNAc will be revealed in plants.
