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Biomedical subjects

D Yin

Publications and source records attributed to D Yin.

At least 19 recordsLinked to original sources
PubMed2001

Gene therapy for streptozotocin-induced diabetic mice by electroporational transfer of naked human insulin precursor DNA into skeletal muscle in vivo.

Transfer of naked plasmid with insulin precursor DNA into skeletal muscle of streptozotocin (STZ)-induced diabetic mice through electroporation and detection of gene expression is described. Four different human insulin precursor DNA fragments were inserted into pcDNA3.1(-), downstream of a CMV promoter. Three of them, with a secretion signal sequence, succeeded in lowering blood glucose at a range of 30-50% in STZ diabetic mice. The other, with a synthetic DNA fragment encoding human proinsulin, failed. The mortality rate of very seriously STZ diabetic mice was reduced significantly by the treatment. The circulating insulin-like protein (mouse insulin, human proinsulin, or intermediates during conversion of proinsulin to insulin) level in the blood of less seriously STZ diabetic mice treated with the human preproinsulin gene with an intron was about 15-23 microU/ml, while that of STZ diabetic mice treated with empty vector was only about 6 microU/ml and that of normal mice was about 18 microU/ml. Transcription of the three human insulin precursor DNAs in mouse skeletal muscle was also detected by RT-PCR. The human preproinsulin gene with the intron showed a slightly higher potency in reducing blood glucose of mildly diabetic mice. These studies indicate that the skeletal muscle transferred with appropriate preproinsulin DNA by electroporation in vivo can secrete insulin-like protein resulting in reduction of blood glucose, and a basal blood insulin level can be achieved for at least 1 month.

Animals↗
PubMed2001

Analysis of the signal pathways involved in the regulation of fatty acid synthase gene expression by insulin and somatotropin.

Our previous studies have shown that somatotropin (ST) antagonizes insulin stimulation of fatty acid synthase (FAS) enzyme activity and gene transcription in adipocytes. In the present study, inhibitors of insulin and ST signaling pathways were used to dissect the mechanisms by which these hormones regulate FAS gene expression in 3T3-F442A adipocytes. Treating 3T3-F442A adipocytes with 10 microM PD98059, an inhibitor of mitogen-activated protein (MAP) kinase, did not affect the induction of FAS mRNA by insulin. When cells were cultured with H-89 (10 microM), GF109203X (10 microM), or staurosporine (100 nM), inhibitors of protein kinase A, protein kinase C, and Janus kinase (JAK) 2, respectively, the inhibitory effect of ST on FAS mRNA levels was not altered. However, H-89 significantly decreased the stimulatory effect of insulin on FAS mRNA abundance. Moreover, treatment with okadaic acid (1 microM), a serine/threonine phosphatase inhibitor, abolished the induction of FAS mRNA by insulin. These results suggest that serine/threonine dephosphorylation and protein kinase A-dependent pathways are involved in the regulation of FAS gene expression by insulin, but MAP kinase is probably not involved. Furthermore, our data indicate that protein kinase A, protein kinase C, and JAK2 do not mediate the effect of ST on regulation of FAS mRNA abundance.

3T3 Cells↗
PubMed2000

Mechanisms of inactivation of human S-adenosylhomocysteine hydrolase by 5',5',6',6'-tetradehydro-6'-deoxy-6'-halohomoadenosines.

In an effort to design more specific and potent inhibitors of S-adenosylhomocysteine (AdoHcy) hydrolase, we investigated the mechanisms by which 5',5',6', 6'-tetradehydro-6'-deoxy-6'-halohomoadenosines (X = Cl, Br, I) inactivated this enzyme. The 6'-chloro (a) and 6'-bromo (b) acetylenic nucleoside analogues produced partial ( approximately 50%) loss of enzyme activity with a concomitant ( approximately 50%) reduction of E-NAD(+) to E-NADH. In addition, Ade and halide ions were released from the inhibitors in amounts suggestive of a process involving enzyme catalysis. AdoHcy hydrolase, which was inactivated with compound a, was shown to contain 2 mol of the inhibitor covalently bound to Lys318 of two subunits of the homotetramer. These data suggest that the enzyme-mediated water addition at the 5' position of compound a or b produces an alpha-halomethyl ketone intermediate, which is then attacked by a proximal nucleophile (i.e., Lys318) to form the enzyme-inhibitor covalent adduct (lethal event); in a parallel pathway (nonlethal event), addition of water at the 6' position produces an acyl halide, which is released into solution and chemically degrades into Ade, halide ion, and sugar-derived products. In contrast, compound c completely inactivated AdoHcy hydrolase by converting 2 equiv of E-NAD(+) to E-NADH and causing the release of 2 equiv of E-NAD(+) into solution. Four moles of the inhibitor was shown to be tightly bound to the tetrameric enzyme. These data suggest that compound c inactivates AdoHcy hydrolase by a mechanism similar to the acetylenic analogue of Ado described previously by Parry et al. [(1991) Biochemistry 30, 9988-9997].

Adenine↗
PubMed2000

Closer proximity between opposing domains of vertebrate calmodulin following deletion of Met(145)-Lys(148).

To investigate the structural linkage between the opposing globular domains in vertebrate calmodulin (CaM), we have constructed a CaM mutant (CaMX(145)) deficient in the last four amino acids between Met(145) and Lys(148) at the carboxyl terminal. Circular dichroism and fluorescence spectroscopic measurements were used to detect changes in the average secondary and tertiary structure of CaMX(145) in comparison to full-length CaM. Complementary measurements of the maximal calcium-binding stoichiometry and ability to activate the plasma membrane (PM) Ca-ATPase permit an assessment of the functional significance of observed structural changes. In comparison with native CaM, we find that CaMX(145) exhibits (i) a large reduction in alpha-helical content, (ii) a dramatic decrease in the average spatial separation between the opposing globular domains, (iii) the loss of one high-affinity calcium-binding site, and (iv) a diminished binding affinity for the PM-Ca-ATPase. Thus, the sequence near the carboxyl terminus functions to stabilize high-affinity calcium binding at one site and facilitates important intramolecular interactions that maintain CaM in an extended conformation. However, despite the large conformational changes resulting from deletion of the last four amino acids at the carboxyl terminal, CaMX(145) can fully activate the PM-Ca-ATPase. These results indicate that target protein binding can restore the nativelike structure critical to function, emphasizing that the structure of the central helix is not critical to CaM function under equilibrium conditions. Rather, the central helix functions to maintain the spatial separation between the opposing domains in CaM that may be critical to high-affinity binding and the rapid activation of the PM-Ca-ATPase, which are necessary for optimal calcium signaling. Thus, following initial association between CaM and target proteins, structural changes involving the carboxyl-terminal sequence have the potential to play an important role in triggering the structural collapse of CaM that facilitates the rapid and cooperative binding of the opposing globular domains with target proteins, which is important to high-affinity binding and rapid enzyme activation.

Allosteric Regulation↗
PubMed2000

Substrate binding stabilizes S-adenosylhomocysteine hydrolase in a closed conformation.

Comparison of crystal structures of S-adenosylhomocysteine (AdoHcy) hydrolase in the substrate-free, NAD(+) form [Hu, Y., Komoto, J., Huang, Y., Gomi, T., Ogawa, H., Takata, Y., Fujioka, M., and Takusagawa, F. (1999) Biochemistry 38, 8323-8333] and a substrate-bound, NADH form [Turner, M. A., Yuan, C.-S., Borchardt, R. T., Hershfield, M. S., Smith, G. D., and Howell, P. L. (1998) Nat. Struct. Biol. 5, 369-376] indicates large differences in the spatial arrangement of the catalytic and NAD(+) binding domains. The substrate-free, NAD(+) form exists in an "open" form with respect to catalytic and NAD(+) binding domains, whereas the substrate-bound, NADH form exists in a closed form with respect to those domains. To address whether domain closure is induced by substrate binding or its subsequent oxidation, we have measured the rotational dynamics of spectroscopic probes covalently bound to Cys(113) and Cys(421) within the catalytic and carboxyl-terminal domains. An independent domain motion is associated with the catalytic domain prior to substrate binding, suggesting the presence of a flexible hinge element between the catalytic and NAD(+) binding domains. Following binding of substrates (i.e., adenosine or neplanocin A) or a nonsubstrate (i.e., 3'-deoxyadenosine), the independent domain motion associated with the catalytic domain is essentially abolished. Likewise, there is a substantial decrease in the average hydrodynamic volume of the protein that is consistent with a reduction in the overall dimensions of the homotetrameric enzyme following substrate binding and oxidation observed in earlier crystallographic studies. Thus, the catalytic and NAD(+) binding domains are stabilized to form a closed active site through interactions with the substrate prior to substrate oxidation.

Adenosylhomocysteinase↗
PubMed2000

Chronic restraint stress promotes lymphocyte apoptosis by modulating CD95 expression.

Depending on the duration and severity, psychological tension and physical stress can enhance or suppress the immune system in both humans and animals. Although it is well established that stress alters the release of various hormones and neurotransmitters, the mechanisms by which stress affects immune responses remain elusive. We report here that mice subjected to chronic 12-hour daily physical restraint for two days exhibited a significant reduction in splenocytes, a process likely mediated by apoptosis as demonstrated by the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling assay. CD95 (Fas/APO-1) expression in splenic lymphocytes of stressed mice was substantially increased. Interestingly, Fas-immunoglobulin fusion protein and blocking antibodies against CD95 ligand inhibit stress-induced reduction in lymphocytes. The stress-induced changes in CD95 expression and lymphocyte number could be blocked by naltrexone or naloxone, specific opioid receptor antagonists, indicating a pivotal role of endogenous opioids in this process. In addition, the reduction of splenocytes in this model system seems to be independent of the hypothalamo-pituitary-adrenal axis, as both adrenalectomized and sham-operated mice exhibited similar responses to chronic stress. Moreover, chronic physical restraint failed to induce a decrease in lymphocyte numbers in CD95-deficient (Fas(lpr/lpr)) mice. Therefore, stress modulates the immune system through CD95-mediated apoptosis dependent on endogenous opioids.

Animals↗
PubMed2000

Chiral nonsteroidal affinity ligands for the androgen receptor. 1. Bicalutamide analogues bearing electrophilic groups in the B aromatic ring.

A series of chiral analogues of bicalutamide bearing electrophilic groups (isothiocyanate, N-chloroacetyl, and N-bromoacetyl) on aromatic ring B of the parent molecule were synthesized. These compounds were designed as affinity ligands for the androgen receptor (AR). We prepared the (R)- and (S)-optical isomers of these compounds as pure enantiomers. The AR binding affinities of these compounds were measured in a competitive binding assay with the radiolabeled high-affinity AR ligand, [(3)H]mibolerone. In accordance with our previous results for the enantiomers of bicalutamide, we found that all (R)-isomers demonstrated much higher binding affinity to the AR as compared to their corresponding (S)-isomers. The para-substituted affinity ligands in ring B bound the AR with higher affinities than the corresponding meta-substituted analogues. Oxidation of thioester affinity ligands to their sulfonyl analogues for the para-substituted compounds decreased AR binding affinities and similar modification increased binding affinities for corresponding meta-analogues. The least potent para-substituted sulfonyl compounds had higher AR binding affinities than the most potent meta-substituted sulfonyl compounds. Overall, the para-substituted unoxidized molecules demonstrated the highest AR binding affinity. Subsequent research using AR exchange assays and Scatchard analyses showed that the isothiocyanate affinity ligands (R)-7, (R)-9, and (R)-10 reported herein are the first specific chemoaffinity ligands for the AR.

Androgen Antagonists↗
PubMed2000

Glutamyl hydrolase. pharmacological role and enzymatic characterization.

gamma-Glutamyl hydrolase (GH, EC 3.4.19.9) is a lysosomal and secreted glycoprotein that hydrolyzes the gamma-glutamyl tail of antifolate and folate polyglutamates. Tumor cells that have high levels of GH are inherently resistant to classical antifolates, and further resistance can be acquired by elevations in GH following exposure to this class of antitumor agents. The highest level of expression in normal tissues occurs in the liver and kidney in humans. When panels of tumors are compared with normal tissues, GH expression is elevated in cancerous hepatic and breast tissue. A second poly-gamma-glutamate hydrolyzing enzyme, glutamate carboxypeptidase II, is a transmembrane protein whose active site is on the outside of the cell, occurring in the prostate gland, small intestine, brain, kidney, and tumor neovasculature. It is a high-affinity (nanomolar), low-turnover, zinc co-catalytic enzyme. In contrast, GH is a low-affinity (micromolar), high-turnover enzyme that has a cysteine at the active site. Data are presented suggesting that Cys110 is the nucleophile that attacks the gamma-amide linkage and causes hydrolysis. GH is being evaluated as an intracellular target for inhibition in order to enhance the therapeutic activity of antifolates and fluorouracil.

Animals↗
PubMed2000

Anti-galactose-alpha(1,3) galactose antibody production in alpha1,3-galactosyltransferase gene knockout mice after xeno and allo transplantation.

Antibodies (Abs) that mediate the hyperacute rejection and acute vascular rejection/delayed xenograft rejection of pig organs in humans and Old World primates are predominantly directed at a single carbohydrate epitope, galactose-alpha1,3-galactose (alpha1,3Gal). The T-cell dependence of elicited anti-alpha1,3Gal Ab responses in humans and Old World primates is controversial. In this study we have characterized anti-alpha1,3Gal Ab production in mice with disrupted alpha1,3-galactosyltransferase genes (GT-Ko mice) and determined the T-cell dependence of anti-alpha1,3Gal Ab responses, following xenograft and allograft transplantation. GT-Ko mice produce natural anti-alpha1,3Gal IgM and IgG in an age-dependent manner, however, these Abs could not elicit hyperacute rejection nor affect the rate of cardiac xenograft (3-5 days) or allograft rejection (7-9 days). Transplantation of xenogeneic Lewis rats hearts elicited modest anti-alpha1,3Gal Ab, but vigorous xenoAb responses. The anti-alpha1,3Gal Ab response was restricted to the IgM and IgG3 subclass while the xenoAb response comprised IgM and all four IgG subclasses. Transplantation of allogeneic C3H hearts elicited weak anti-alpha1,3Gal Ab responses that were primarily IgM, but vigorous alloAb responses. Despite the restriction of elicited anti-alpha 1,3Gal Ab responses to the IgM and IgG3 isotypes, these responses are T-cell dependent. The ability of allografts to elicit weak anti-alpha1,3Gal but strong allo-Ab responses, can be explained by the dependence of alpha1,3Gal-specific B cells on cognate help from T cells.

Age Factors↗
PubMed2000

The sensitivity of carboxyl-terminal methionines in calmodulin isoforms to oxidation by H(2)O(2) modulates the ability to activate the plasma membrane Ca-ATPase.

The oxidative modification of methionines within the primary sequence of calmodulin (CaM) results in an inability to activate the PM-Ca-ATPase fully, and may contribute to alterations in calcium homeostasis under conditions of oxidative stress. To identify differences in the sensitivities of CaM isoforms to oxidative modification, we have compared the function and patterns of oxidative modification resulting from the exposure of CaM isolated from bovine testes and wheat germ to H(2)O(2). In comparison to CaM isolated from wheat germ, vertebrate CaM is functionally resistant to oxidant-induced loss of function. The decreased functional sensitivity of vertebrate CaM correlates with a 75 +/- 3% reduction in the rate of oxidative modification of a methionine near the carboxyl terminus (i.e., Met(144) or Met(145)). The extent of oxidative modification to other methionines in these CaM isoforms is similar. These results suggest that the sensitivity of Met(144) or Met(145) to oxidation modulates the ability of CaM to activate the PM-Ca-ATPase. Consistent with this interpretation, a CaM mutant in which glutamines were substituted for Met(144) and Met(145) fully activates the PM-Ca-ATPase irrespective of the oxidative modification of the other seven methionines to their corresponding methionine sulfoxides. The extent of oxidative modification to individual methionines in vertebrate CaM by H(2)O(2) correlates with the time-averaged surface accessibility of individual sulfurs calculated from molecular dynamics simulations. Thus, the sensitivity of individual methionines to oxidative modification is directly related to the solvent accessibility. These results indicate that sequence differences between vertebrate and plant CaM alter the sensitivity of methionines near the carboxyl terminus to oxidative modification because of alterations in their solvent accessibility. We suggest that these sequence differences between CaM isoforms have a regulatory role in modulating the functional sensitivity of CaM to conditions of oxidative stress.

Amino Acid Sequence↗
PubMed2000

Tolerance of T-independent xeno-antibody responses in the hamster-to-rat xenotransplantation model is species-restricted but not tissue-specific.

Control of early acute xenograft rejection xenoreactions in the hamster-to-Lewis rat xenotransplantation model with cyclosporine (CsA) and leflunomide subdues early T-independent xenoreactivity and uncovers a late immune response that can be controlled by CsA alone. We had attributed this acquired responsiveness to CsA to the induction of tolerance of T-independent xeno-antibody responses in the recipient and recently reported that this tolerance is species-specific. Here we have further characterized the specificity and nature of this tolerant state. Lewis rats transplanted with either hearts, skin, kidney or spleen/pancreas from Golden Syrian hamsters were treated with leflunomide (5 mg/kg/day by gavage) for 14-21 days and CsA (20 mg/kg/day by gavage) continuously from the day of transplant. Some Lewis rats received a second graft of hearts or skin from Golden Syrian hamsters (day 21-30 after first transplant), and a third heart graft from Balb/c mice (day 60 after the first transplant). Serum was harvested and the titers of xenoreactive antibodies were quantified by flow cytometry. All grafts were harvested at the end of each experiment and examined by histological and immunohistochemical methods. The combination of CsA and leflunomide was able to completely inhibit the rejection of kidney, spleen and pancreas xenografts in this hamster-to-rat xenotransplantation model. In addition, only a transient treatment with leflunomide was necessary, and long-term graft survival could subsequently be maintained by CsA alone. Histological examination of these grafts at > 80 days post-transplantation indicated minimal signs of rejection. These immediately vascularized organs induced T-independent B-cell tolerance, so that second grafts of hamster hearts and skin could be maintained with CsA alone. Under the same immunosuppressive regimen, only four out of nine Lewis rats exhibited long-term hamster skin survival, probably reflecting the increased immunogenicity of the skin compared with other vascularized grafts. Nonetheless, all rats that did not reject the hamster skin graft also did not reject the hamster heart while on CsA alone. Finally, we demonstrate that the tolerant state could be maintained for up to 30 days in the absence of xenograft. The vigorous T-independent antibody response that mediates acute xenograft rejection in the hamster-to-rat model can be tolerized by the immunosuppressive regimen of CsA and leflunomide. The lack of organ specificity for the induction of this tolerance suggests that the xenoantigens inducing tolerance may be common endothelial cell antigens. Finally, the presence of the xenograft has been previously shown to be critical for the induction of T-independent B-cell tolerance, however, the tolerant state is relatively stable and persists after the removal of the xenograft.

Animals↗
PubMed2000

Non-depleting anti-CD4, but not anti-CD8, antibody induces long-term survival of xenogeneic and allogeneic hearts in alpha1,3-galactosyltransferase knockout (GT-Ko) mice.

The anti-galactose-alpha1,3-galactose (Gal) antibody (Ab) response following pig-to-human transplantation is vigorous and largely resistant to currently available immunosuppression. The recent generation of GT-Ko mice provides a unique opportunity to study the immunological basis of xenograft-elicited anti-Gal Ab response in vivo, and to test the efficacy of various strategies at controlling this Ab response [1]. In this study, we compared the ability of non-depleting anti-CD4 and anti-CD8 to control rejection and antibody production in GT-Ko mice following xenograft and allograft transplantation. Hearts from baby Lewis rat or C3H mice were transplanted heterotopically into GT-Ko. Non-depleting anti-CD4 (YTS177) and anti-CD8 (YTS105) Abs were used at 1 mg/mouse, and given as four doses daily from day -2 to 1 then q.o.d. till day 21. Xenograft rejection occurred at 3 to 5 days post-transplantation in untreated GT-Ko recipients, and was histologically characterized as vascular rejection. Anti-CD4, but not anti-CD8, Ab treatment prolonged xenograft survival to 68 to 74 days and inhibited anti-Gal Ab as well as xeno-Ab production. In four of the five hearts from anti-CD4 mAbs-treated GT-Ko mice, we observed classic signs of chronic rejection, namely, thickened intima in the lumen of vessels, significant IgM deposition, fibrosis and modest mononuclear cell infiltrate of Mac-1+ macrophages and scattered T cells (CD8>CD4). Xenograft rejection in untreated, as well as anti-CD4- and anti-CD8-treated, recipients was associated with increased intragraft IL-6, IFN-gamma and IL-10 mRNA. C3H allografts were rejected in 7 to 9 days by untreated GT-Ko mice and were histologically characterized as cellular rejection. Treatment with anti-CD4 and anti-CD8 mAb resulted in graft survivals of >94.8 and 11.8 days, respectively. Anti-CD4 mAb treatment resulted in a transient inhibition of alloreactive and anti-Gal Ab production. The presence of circulating alloreactive and anti-Gal Abs at >50 days post-transplant was associated with significant IgM and IgG deposition in the graft. Yet, in the anti-CD4 mAb-treated group, the allografts showed no signs of rejection at the time of sacrifice (>100 days post-transplantation). All rejected allografts had elevated levels of intragraft IL-6, IFN-gamma and IL-10 mRNA, while the long-surviving anti-CD4-treated allografts had reduced mRNA levels of these cytokines. Collectively, our studies suggest that the elicited xeno-antibody production and anti-Gal Ab production in GT-Ko mice are CD4+ T-cell dependent. The majority of xenografts succumbed to chronic rejection, while allografts survived with minimal histological change, despite elevated levels of circulating alloAbs. Thus, immunosuppression with anti-CD4 mAb therapy induces long-term survival of allografts more effectively than to xenografts.

Animals↗
PubMed2000

Therapeutic strategies and surgical results for pineal region tumours.

Until recently, surgery for pineal region tumours has met with poor results. Although experience remains limited, developments in imaging, surgical approaches, and microsurgery have improved outcomes. Over 26 years we treated 36 patients including: 24 with germinoma; four, teratoma; three, pineal cyst; and one each, embryonal carcinoma, choriocarcinoma, pineocytoma, pineoblastoma and metastasis. All 24 germinomas responded to radiotherapy, as did one case each for teratoma, pineoblastoma, and choriocarcinoma. Eight patients underwent resection, and one patient with germinoma had biopsy via endoscopy. Occipital transtentorial and parieto-occipital transcallosal approaches were used in three each, and infratentorial supracerebellar and a combined infratentorial supracerebellar and occipital transtentorial approach in one each. Total removal was achieved in four patients (50%), and subtotal removal in two. Postoperative complications resolved within 2 weeks. Two patients had recurrence and one had dissemination. All tumours except germinomas should be explored and diagnosed histologically. Current operative techniques allow safe, effective removal of pineal region tumours.

Adolescent↗