Biomedical subjects

Yiping Liu

Publications and source records attributed to Yiping Liu.

8 recordsLinked to original sources

PubMed2006

Epstein-Barr virus latent membrane protein 1 mediates phosphorylation and nuclear translocation of annexin A2 by activating PKC pathway.

We have previously combined phosphorylation enrichment with proteomics technology to elucidate the novel phosphoproteins in the signaling pathways triggered by Epstein-Barr virus (EBV)-encoded latent membrane protein 1 (LMP1) and shown that LMP1 can increase the phosphorylation level of annexin A2. Here, we further showed that LMP1 increased the serine, but not tyrosine, phosphorylation of annexin A2 by activating a novel signaling pathway, the protein kinase C (PKC) signaling pathway. However, LMP1 did not affect the level of annexin A2 expression. In addition, we found that LMP1 induced the nuclear entry of annexin A2 in an energy- and temperature-dependent manner, suggesting that the nuclear entry of annexin A2 is an active process. Treatment of LMP1-expressing cells with the PKC inhibitor myr-psiPKC resulted in annexin A2 being present almost exclusively at cell surface, instead of within the nucleus, suggesting that the nuclear entry of annexin A2 was associated with serine phosphorylation mediated by PKC.

Active Transport, Cell Nucleus↗

PubMed2006

Identification of novel phosphoproteins in signaling pathways triggered by latent membrane protein 1 using functional proteomics technology.

Previous studies have shown that the Epstein-Barr virus-encoded latent membrane protein1 (LMP1) could activate nuclear factor kappa B, activator protein-1, and Janus kinases/signal transducer and activation of transcription factors pathways. However, many signaling molecules and downstream target proteins triggered by LMP1 have not been identified. To determine the functional components in signaling pathways triggered by LMP1, we combined the novel strategy of phosphoprotein enrichment with proteomics technology to elucidate the signaling cascade activated by LMP1. We found that LMP1 could increase the quantity of total phosphoproteins by 18.03%, and 43 proteins showed significant changes in the degree of phosphorylation when LMP1 was expressed. Twenty-five signaling molecules or downstream targets of signaling pathways triggered by LMP1 were identified, several of which had previously been implicated in LMP1 signal pathways. The other proteins, including annexin A2, heat shock protein 27, stathmin, annexin I, basic transcription factor 3, and porin, were novel signaling molecules or targets with no previously known function in LMP1 signal transduction. The method used here has proven to be suitable for the identification of molecules involved in various signaling pathways.

Blotting, Western↗

PubMed2005

Thermomechanics of the shape memory effect in polymers for biomedical applications.

We examine the shape memory effect in polymer networks intended for biomedical, and specifically cardiovascular, applications. The polymers were synthesized by photopolymerization from a tert-butyl acrylate monomer with a diethyleneglycol diacrylate crosslinker. Three-point flexural tests were used to systematically investigate the thermomechanics of shape storage (predeformation) and shape recovery. The glass transition temperature, T(g), of the polymers was determined to be approximately 65 degrees C. The polymers show 100% strain recovery, at low and high predeformation temperatures, up to maximum strains of approximately 80%. The polymers show a sigmoidal free strain recovery response as a function of increasing temperature at a constant heating rate. Free strain recovery was determined to depend on the temperature during predeformation; lower predeformation temperatures (T < T(g)) decreased the temperature required for free strain recovery. Constrained stress recovery shows a complex evolution as a function of temperature and also depends on the temperature during predeformation. Stress recovery after low-temperature predeformation (T < T(g)) shows a peak in the generated recovery stress, whereas stress recovery after high-temperature predeformation (T > T(g)) is sigmoidal. The isothermal free strain recovery rate was found to increase with increasing temperature or decreasing predeformation temperature. The thermomechanical results are discussed in light of potential biomedical applications, and a prototype device is presented.

Biocompatible Materials↗

PubMed2004

Nuclear accumulation of epidermal growth factor receptor and acceleration of G1/S stage by Epstein-Barr-encoded oncoprotein latent membrane protein 1.

Epstein-Barr virus (EBV)-encoded latent membrane protein 1 (LMP1) is considered to be the major oncogenic protein of EBV-encoded proteins and has always been the core of the oncogenic mechanism of EBV. Advanced studies on nuclear translocation of the epidermal growth factor receptor (EGFR) family have greatly improved our knowledge of the biological function of cell surface receptors. In this study, we used the Tet-on LMP1 HNE2 cell line as a cell model, which is a dual-stable LMP1-integrated nasopharyngeal carcinoma (NPC) cell line and the expression of LMP1 which could be regulated by the Tet system. We found that LMP1 could regulate the nuclear accumulation of EGFR in a dose-dependent manner quantitatively and qualitatively. We also demonstrated that the nuclear localization sequence of EGFR played some roles in the location of the protein within the nucleus under LMP1 regulation and EGFR in the nucleus could bind to the promoters of cyclinD1 and cyclinE, respectively. We further demonstrated that EGFR is involved in the acceleration of the G1/S phase transition by LMP1 through binding to cyclinD1 and cyclinE directly. These findings provided a novel view that the acceleration of LMP1 on the G1/S transition via the nuclear accumulation of EGFR was critical in the process of nasopharyngeal carcinoma.

Base Sequence↗

PubMed2003

Intracellular protein tyrosine phosphorylation of adherent human macrophages on adsorbed fibronectin.

Fibronectin (FN) was pre-adsorbed onto physicochemically distinct substrates: polyethyleneglycol-based networks or tissue culture polystyrene (TCPS). The role of these substrates in modulating FN-mediated intracellular protein tyrosine phosphorylation and cell adhesion was analyzed with human primary blood derived macrophages. Although macrophage adhesion on both FN-pre-adsorbed TCPS and networks was similarly dependent on protein tyrosine kinase (PTK) and protein serine/threonine kinase (PSK), the compensation between PTK and PSK, and the involvement of signaling molecules (such as protein kinase C (PKC) isoforms) were distinct between the substrates. The pattern and the extent of tyrosine phosphorylation of several proteins (i.e. approximately 70, approximately 44, approximately 30kDa) were differentially regulated by PKCs. FN-derived peptides were employed to probe this material-dependency in macrophage adhesion and tyrosine phosphorylation. The PHSRN domain in the peptide sequence was predominant in mediating this substrate-dependent FN signaling event. We conclude that the tyrosine phosphorylation and the cross talk between PTK and PSK are modulated by FN and the substrate onto which the protein is adsorbed.

Adsorption↗

PubMed2002

Intracellular signaling involved in macrophage adhesion and FBGC formation as mediated by ligand-substrate interaction.

Fibronectin and RGD- and/or PHSRN-containing oligopeptides were preadsorbed onto physicochemically distinct substrata: polyethyleneglycol-based networks or tissue culture polystyrene (TCPS). The role of selected signaling kinases (namely protein tyrosine kinases, protein serine/threonine kinases, PI3-kinase, Src, and MAPK) in the adhesion of human primary blood-derived macrophages and the formation of foreign-body giant cells (FBGC) on these modified substrata was investigated. The involvement of individual intracellular signaling molecules in mediating macrophage adhesion dynamically varied with the culture time, substrate, and ligand. For example, fibronectin on TCPS or networks involved similar signaling events for macrophage adhesion; however, fibronectin and G(3)RGDG(6)PHSRNG, but not peptides with other RGD and/or PHSRN orientations, mediated similar signaling events for macrophage adhesion on TCPS but mediated different signaling events on networks. Depending on the substrate, a specific molecule (i.e., Src, protein kinase C) within the protein tyrosine kinase or protein serine/threonine kinase family was either an antagonist or agonist in mediating FBGC formation.

Adsorption↗

PubMed2002

Engineering endogenous inflammatory cells as delivery vehicles.

Leukocytes are central in directing host inflammatory and immune processes; therefore, leukocyte response to biomaterials is extremely important. Although several leukocyte-derived molecules are used clinically, the long-term efficacy of treatments involving the systemic administration of these bioactive agents has yet to be demonstrated. Hence, the localized delivery of selected cytokines and growth factors produced by endogenous leukocytes is desirable and may have potential therapeutic values in the fundamental processes of tissue healing, growth regulation, and biocompatibility. The specificity and diversity of ligand-receptor interactions offer an attractive method in manipulating cellular behavior. Therefore, a more detailed understanding of the interplay between ligands and cell membrane receptors must be obtained. We designed interleukin-1-derived biomimetic agonists and antagonists to study and modulate leukocyte function in vitro. Selected agonists increased GM-CSF release by adherent human blood-derived macrophages in the presence of the natural IL1beta antagonist, namely IL1ra. Furthermore, IL1-derived biomimetic antagonists neutralized the ability of IL1beta in increasing the release of GM-CSF by adherent macrophages. We employed similar methodologies to elucidate the molecular mechanisms of integrin and extracellular matrix interaction in regulating leukocyte function. Oligopeptides were designed based on the functional structure of fibronectin and grafted on to a polymer network containing polyethyleneglycols. Macrophage adhesion was independent of the peptide identity that contained sequence RGD, PHSRN, PRRARV, or combinations thereof in an integrin-dependent fashion in vitro. However, integrin-dependent FBGC formation in vitro was highly dependent on both RGD and PHSRN in a single peptide formulation and with a specific orientation. From our intracellular signaling studies in vitro, protein tyrosine and serine/threonine kinases were found important in integrin signaling leading to macrophage adhesion mediated by fibronectin-integrin association. Furthermore, RGD and PHSRN appear to be significant in mediating this receptor-ligand association resulting in the necessary signaling characteristic for macrophage adhesion and the subsequent development. Our in vivo results showed that peptide identity played a minimal role in modulating the host inflammatory response and adherent macrophage density. RGD-containing peptides mediated rapid FBGC formation by 4 days of implantation by significantly increasing both the number of macrophages that participate in the cell fusion process and the rate of cell fusion. Both RGD and PHSRN domains were important in mediating FBGC formation at later implantation periods. These findings represent a mechanistic correlation between the role of protein functional architectures in ligand-receptor recognition and the post-ligation signaling events that control cellular behavior in vitro and in vivo.

Amino Acid Sequence↗

PubMed2002

Human macrophage adhesion on fibronectin: the role of substratum and intracellular signalling kinases.

Fibronectin and Arg-Gly-Asp (RGD)- and/or Pro-His-Ser-Arg-Asn (PHSRN)-containing oligopeptides were immobilized onto physicochemically distinct substrata: polyethyleneglycol-based networks or tissue culture polystyrene (TCPS). The role of selected signalling kinases in the adhesion of human primary blood-derived macrophages on these modified substrata was investigated. We demonstrated that the protein tyrosine kinase (PTK) or protein serine/threonine kinase (PSK) dependency and the PTK-PSK cross-talk compensation for macrophage adhesion varied dynamically with the substratum modification and the culture time. The inhibition of MAPK kinase (MAPKK) decreased macrophage adhesion on TCPS, whereas the inhibition of phosphoinositide-3 kinase (PI3 kinase) decreased macrophage adhesion on networks at 24 h. The PI3 kinase-protein kinase C (PKC)-MAPK cascade was involved in macrophage adhesion on fibronectin-preadsorbed TCPS or networks but not on fibronectin-grafted networks. This fibronectin-mediated adhesion signalling involved both RGD and PHSRN sequences in a form of G(3)RGDG(6)PHSRNG on TCPS but not on networks. Furthermore, G(3)RGDG(6)PHSRNG grafted onto networks evoked unique signalling in macrophage adhesion from that preadsorbed onto networks. Thus, macrophage adhesion and the role of selected signalling kinases were modulated by the substratum and the ligand conjugation method.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗