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C K Sung

Publications and source records attributed to C K Sung.

At least 19 recordsLinked to original sources
PubMed1998

Insulin-stimulated cell growth in insulin receptor substrate-1-deficient ZR-75-1 cells is mediated by a phosphatidylinositol-3-kinase-independent pathway.

In many human breast cancers and cultured cell lines, insulin receptor expression is elevated, and insulin, via its own insulin receptor, can stimulate cell growth. It has recently been demonstrated that the enzyme phosphatidylinositol-3-kinase (PI3-K) mediates various aspects of insulin receptor signaling including cell growth. In order to understand the mechanisms for insulin-stimulated cell growth in human breast cancer, we measured insulin-stimulable PI3-K activity in a non-transformed breast epithelial cell line, MCF-10A, and in two malignantly transformed cell lines, ZR-75-1 and MDA-MB157. All three cell lines express comparable amounts of insulin receptors whose tyrosine autophosphorylation is increased by insulin, and in these cell lines insulin stimulates growth. In MDA-MB157 and MCF-10A cells, insulin stimulated PI3-K activity three- to fourfold. In ZR-75-1 cells, however, insulin did not stimulate PI3-K activity. In ZR-75-1 cells PI3-K protein was present, and its activity was stimulated by epidermal growth factor, suggesting that there might be a defect in insulin receptor signaling upstream of PI3-K and downstream of the insulin receptor. Next, we studied insulin receptor substrate-1 (IRS-1), a major endogenous substrate for the insulin receptor which, when tyrosine is phosphorylated by the insulin receptor, interacts with and activates PI3-K. In ZR-75-1 cells, there were reduced levels of protein for IRS-1. In these cells, both Shc tyrosine phosphorylation and mitogen-activated protein kinase (MAP-K) activity were increased by the insulin receptor (indicating that the p21ras pathway may account for insulin-stimulated cell growth in ZR-75-1 cells). The PI3-K inhibitor LY294002 (50 microM) reduced insulin-stimulated growth in MCF-10A and MDA-MB157 cell lines, whereas it did not modify insulin effect on ZR-75-1 cell growth. The MAP-K/Erk (MEK) inhibitor PD98059 (50 microM) consistently reduced insulin-dependent growth in all three cell lines. Taken together, these data suggest that in breast cancer cells insulin may stimulate cell growth via PI3-K-dependent or-independent pathways.

Breast Neoplasms↗
PubMed1998

Overexpression of membrane glycoprotein PC-1 can influence insulin action at a post-receptor site.

An elevated content of membrane glycoprotein PC-1 has been observed in cells and tissues of insulin resistant patients. In addition, in vitro overexpression of PC-1 in cultured cells induces insulin resistance associated with diminished insulin receptor tyrosine kinase activity. We now find that PC-1 overexpression also influences insulin receptor signaling at a step downstream of insulin receptor tyrosine kinase, independent of insulin receptor tyrosine kinase. In the present studies, we employed Chinese hamster ovary cells that overexpress the human insulin receptor (CHO IR cells; approximately 10(6) receptors per cell), and transfected them with human PC-1 c-DNA (CHO IR PC-1). In CHO IR PC-1 cells, insulin receptor tyrosine kinase activity was unchanged, following insulin treatment of cells. However, several biological effects of insulin, including glucose and amino acid uptake, were decreased. In CHO IR PC-1 cells, insulin stimulation of mitogen-activated protein (MAP) kinase activity was normal, suggesting that PC-1 overexpression did not affect insulin receptor activation of Ras, which is upstream of MAP kinase. Also, insulin-stimulated phosphatidylinositol (PI)-3-kinase activity was normal, suggesting that PC-1 overexpression did not interfere with the activation of this enzyme by insulin receptor substrate-1. In these cells, however, insulin stimulation of p70 ribosomal S6 kinase activity was diminished. These studies suggest, therefore, that, in addition to blocking insulin receptor tyrosine kinase activation, PC-1 can also block insulin receptor signaling at a post-receptor site.

Animals↗
PubMed1998

Production of antibody against saikosaponin a, an active component of bupleuri radix.

High titer rabbit polyclonal antibodies (pAbs) which show a specificity for saikosaponin a (SSA), have been generated. The immunogen used was a conjugate of SSA linked through its glucose moiety to bovine serum albumin by periodate oxidation method. The antibody titers obtained from two rabbits, inoculated with the immunogen, reached a plateau after the fourth and third booster injection, respectively. The specificity of the pAbs was determined by hapten inhibition assays using several SSA-like structures. SSA competitively inhibited the binding of the rabbit anti-SSA pAbs to SSA-ovalbumin on solid phase, a coated antigen on the well. The antibodies showed high specificity to SSA, exhibiting no significant cross-reactivity with any of SSA analogues tested.

Animals↗
PubMed1998

In vitro angiogenic activity of Aloe vera gel on calf pulmonary artery endothelial (CPAE) cells.

Angiogenic activity of Aloe vera gel was investigated by in vitro assay. We obtained the most active fraction from dichloromethane extract of Aloe vera gel by partitioning between hexane and 90% aqueous methanol. The most active fraction (F3) increased the proliferation of calf pulmonary artery endothelial (CPAE) cells. In addition, F3 fraction induced CPAE cells to invade type 1 collagen gel and form capillary-like tube through in vitro angiogenesis assay, and increased the invasion of CPAE cells into matrigel through in vitro invasion assay. Furthermore, the effect on the mRNA expression of proteolytic enzymes which are key participants in the regulation of extracellular matrix degradation was investigated by northern blot analysis. F3 fraction enhanced mRNA expression of urokinase-type plasminogen activator (u-PA), matrix metalloproteinase-2 (MMP-2), and membrane-type MMP (MT-MMP) in CPAE cells whereas the expression of plasminogen activator inhibitor-1 (PAI-1) mRNA was not changed.

Aloe↗
PubMed1998

Clinical significance of intrahepatic biliary stricture in efficacy of hepatic resection for intrahepatic stones.

In the Far East, hepatic resection is the definitive treatment for complicated intrahepatic stones (IHS). However, many investigators have reported that the associated intrahepatic biliary stricture is the main cause of treatment failure. A retrospective comparative study was undertaken to clarify the long-term efficacy of hepatic resection for treatment of IHS and to investigate the clinical significance of intrahepatic biliary stricture in treatment failure after hepatic resection performed in 44 patients with symptomatic IHS. The patients were divided into two study groups: group A, with intrahepatic biliary stricture (n = 28) and group B, without stricture (n = 16). Residual or recurrent stones, recurrence of intrahepatic biliary stricture, late cholangitis, and final outcomes were analyzed and compared statistically between the two groups. The patients were followed up for a median duration of 65 months after hepatectomy. The overall incidence of residual or recurrent stones was 36% and 11%, respectively, in groups A and B. The initial treatment failure rate was 50% in group A and 31% in group B. Intrahepatic biliary stricture recurred in 46% of patients in group A, while none of the group B patients had biliary stricture recurrence (P = 0.001). More than two-thirds of the restrictures in group A were identified at the primary site. The incidence of late cholangitis was higher in group A (54%) than in group B (6%) (P = 0. 002). Three-quarters of the patients with cholangitis in group A had severe cholangitis, that was recurrent, and related to stones and strictures (n = 11). They and 2 asymptomatic patients in group B required secondary procedures done at a median of 12 months after hepatectomy. Final outcomes after hepatectomy with or without secondary management were good in 80%, fair in 16%, and poor in 4% of our 44 patients. Most recurrent cholangitis after hepatectomy in patients with IHS was related to recurrent intrahepatic ductal strictures. Therefore, to be effective, hepatic resection should include the strictured duct. However, with hepatectomy alone it is difficult to clear the IHS or relieve the ductal strictures completely, particularly in patients with bilateral IHS, so perioperative team approaches that include both radiologic and cholangioscopic interventions should be combined for the effective management of IHS.

Bile Ducts, Intrahepatic↗
PubMed1998

Guanosine triphosphatase-activating protein-associated protein, but not src-associated protein p68 in mitosis, is a part of insulin signaling complexes.

The insulin receptor, following insulin stimulation of cells, triggers formation of various signaling complexes. In rat HTC hepatoma cells overexpressing normal human insulin receptors (HTC-IR), p85 regulatory subunit of phosphatidylinositol-3-kinase (PI3K) forms signaling complexes containing the insulin receptor, insulin receptor substrate 1 (IRS-1), guanosine triphosphatase-activating protein (GAP) and 60-70 kDa phosphotyrosine proteins (p60-70). In the present study, we demonstrate that p60-70 interacts directly with the p85 subunit via src homology 2 domain of the latter. Employing antibodies specific to two p85 isoforms, p85alpha and p85beta, we demonstrate that HTC-IR cells express both p85 isoforms, and these isoforms induce the formation of similar signaling complexes in response to insulin. p60-70, present in both alpha-p85alpha and alpha-p85beta immunoprecipitates, is a GAP-associated protein, but is distinct from the p68 src-associated protein in mitosis (Sam68) by several criteria. These data suggest that 1) GAP-associated protein, but not Sam68, is a part of insulin signaling complexes; and 2) p85alpha and p85beta form similar, but distinct, insulin receptor signaling complexes.

Adaptor Proteins, Signal Transducing↗
PubMed1998

ELISA for the determination of saikosaponin a, an active component of Bupleuri Radix.

In order to quantify saikosaponin a (SSA), one of the major active components of Bupleuri Radix, a competitive and indirect ELISA method was developed. High titer rabbit polyclonal antibodies (pAbs) were raised against a conjugate of SSA and bovine serum albumin, coupled with a periodate oxidation method. SSA competitively inhibited the binding of rabbit anti-SSA pAbs to SSA-ovalbumin on the solid phase, a coated antigen on the well. The quantity of pAbs bound to the well was monitored using a peroxidase-conjugated anti-rabbit IgG as a secondary antibody, and tetramethylbenzidine solution as a substrate. The measuring range extended from 50 pg/ml to 20 ng/ml of SSA, with a detection limit of 40 pg/ml (5.13 pM). Antibodies showed some cross-reactivity with saikosaponin c (12.74%). However, the antibodies showed only slight cross-reactivities with saikosaponin d (0.3%), which differs from SSA only in the stereochemistry of the 16-hydroxyl group, and the artificial saikosaponins, saikosaponin b1 (2.1%) and saikosaponin g (0.53%). The specific and sensitive ELISA is especially suited for determination of SSA in samples when only small quantities of materials can be extracted for analysis.

Animals↗
PubMed1996

The development of insulin resistance with high fat feeding in rats does not involve either decreased insulin receptor tyrosine kinase activity or membrane glycoprotein PC-1.

Recent studies have suggested that the insulin receptor tyrosine kinase inhibitor, membrane glycoprotein PC-1, may play a role in certain insulin resistant states. In the present study, we examined whether either insulin receptor function or PC-1 activity was altered during the development of insulin resistance that occurs with high fat feeding in normal rats. Over the course of 14 days of high fat feeding, both maximal and submaximal (physiological) insulin-stimulated skeletal muscle glucose uptake decreased gradually; after 14 days of high fat feeding, submaximal and maximal insulin-stimulated glucose uptake decreased by approximately 40 and approximately 50%, respectively. In contrast, in the same muscles (tibialis anterior) of these animals, neither insulin receptor content nor insulin-stimulated insulin receptor autophosphorylation was altered after 14 days of high fat feeding. PC-1 has both nucleotide pyrophosphatase (EC 3.6.1.9) and alkaline phosphodiesterase I (EC 3.1.4.1) enzyme activities. These enzyme activities showed no changes during the course of 14 days of high fat feeding. Individual data revealed that there was no significant correlation between insulin-stimulated glucose uptake and alkaline phosphodiesterase or nucleotide pyrophosphatase activity (P > 0.05). Together, these data indicate that neither defects in insulin receptor function nor elevated PC-1 activities are involved in the development of insulin resistance in rats with high fat feeding, and the insulin resistance induced with high fat feeding is likely due to postreceptor defects in skeletal muscle.

Animals↗
PubMed1996

Missed injuries in abdominal trauma.

Injuries missed at initial diagnoses or operations have the potential to cause disastrous complications in abdominal trauma patients. The aim of this retrospective study is to assess the causes and the outcomes of missed abdominal injuries. Twelve patients (2%) with missed injuries were identified among 607 abdominal trauma patients operated on from 1985 to 1993. Ten patients were male and two were female. The modes of the trauma were ten blunt injuries (83%) and two stab penetrating injuries (17%). Five cases had delayed operations because of clinical errors in the initial diagnosis. Their causative factors were obscured trauma history (two cases), radiologic misinterpretation (two cases), no reliable radiologic finding (one case), and admission to inappropriate department (one case). Missed injured organs were spleen (two cases), liver (one case), diaphragm (one case), and rectum (one case). Median delayed time was 7 days (3 to 96 days). Another seven cases of injuries were missed at the time of initial operation because of incomplete exploration. Their causative factors were surgical inexperience (two cases), severe peritoneal adhesions (one case), neglected exploration of retroperitoneal hematoma (two cases), underestimated mesocolic vascular injury (one case), and early contraction of the perforating wound with intraoperative hypotension (one case). Missed injured organs were stomach (two cases), duodenum (one case), rectum (one case), pancreas (one case), urinary bladder (one case), and rectosigmoid mesocolon (one case). Median time interval between initial and second operation was 9 days (4 to 32 days). Two patients died of complications directly related to their missed injuries. Major complication and mortality rates of missed injuries were 83 and 17%, respectively. These were significantly higher compared with those (39 and 6.3%, respectively) of detected abdominal injuries. We conclude that missed abdominal injuries can cause high mortality and morbidity, and, therefore, a systematic approach, including careful history taking, complete diagnostic procedure, complete surgical explorations, and early reoperation are mandatory for patients with multiple trauma.

Abdominal Injuries↗
PubMed1995

Insulin-like growth factor-1 stimulation of cells induces formation of complexes containing phosphatidylinositol-3-kinase, guanosine triphosphatase-activating protein (GAP), and p62 GAP-associated protein.

The insulin-like growth factor-1 (IGF-1) receptor is structurally related to the insulin receptor and shares common features in receptor signaling. These features include receptor autophosphorylation, phosphorylation of insulin receptor substrate-1, and activation of Ras and phosphatidylinositol-3-kinase (PI3K). Previously, we reported that after insulin treatment of rat HTC cells expressing human insulin receptors, a unique insulin receptor signaling complex was formed that contained the insulin receptor, the p85 subunit of PI3K, GTPase-activating protein (GAP), and p62 GAP-associated protein. In the present study, using wild type HTC cells, we investigated whether the activated IGF-1 receptor also forms a similar signaling complex. To study the proteins present in IGF-1 receptor signaling complexes, we used immunoprecipitation and Western blotting analysis with appropriate antibodies. In response to IGF-1, insulin receptor substrate-1 was tyrosine phosphorylated and formed a complex with the PI3K heterodimer that consists of a p85 regulatory subunit and a p110 catalytic subunit. In addition, a separate complex was formed, consisting of p85, p62 GAP-associated protein and GAP. The p62 in this complex was tyrosine phosphorylated. These studies suggest, therefore, that the IGF-1 receptor, like the insulin receptor, induces the formation of multiple signaling complexes that most likely mediate the proliferative effects of these receptors.

Animals↗
PubMed1995

Role of p85 subunit of phosphatidylinositol-3-kinase as an adaptor molecule linking the insulin receptor to insulin receptor substrate 1.

After insulin stimulation of cells, signaling complexes are formed, containing the insulin receptor (IR), insulin receptor substrate-1 (IRS-1), and phosphatidylinositol-3-kinase. To study the nature of these complexes, we employed purified IR, recombinant IRS-1, antibodies to IR and IRS-1, and fusion proteins containing the two SH2 domains of p85. In intact cells, insulin increased tyrosine phosphorylation of both the IR and IRS-1. Both of these proteins were immunoprecipitated with antibodies to p85. Also, fusion proteins containing the two SH2 domains of p85 directly precipitated both the IR and IRS-1. Next, these signaling complexes were reconstituted in vitro with purified IR, recombinant IRS-1, and the two SH2 domains of p85. In the presence of both SH2 domains of p85, the IR associated with IRS-1. Other data, both in intact cells and in vitro, demonstrated that N- and C-terminal SH2 domains of p85 had preferential binding affinities for the IR and IRS-1, respectively. Studies with an IR mutant truncated in the C terminus indicated that the C-terminal phosphotyrosines of the IR play a major role in interacting with the SH2 domains of p85. In conclusion, both in vivo and in vitro data support a role for p85 in directly linking the IR to IRS-1 via its SH2 domains. The formation of these complexes, therefore, may provide a mechanism for the translocation to the plasma membrane of phosphatidylinositol-3-kinase and other molecules that are involved in IR signaling.

Animals↗
PubMed1995

Molecular cloning of cDNA encoding human lanosterol synthase.

A cDNA encoding human lanosterol synthase, the enzyme responsible for the backbone formation step in sterol biosynthesis, was cloned by extensive application of PCRs. Five degenerate oligonucleotide primers (139S, 440S, 528A, 575A and 712A) corresponding to the homologous amino acid sequences among the known 2,3-oxidosqualene cyclase(OSC) were designed. PCR with one pair(440S and 528A) of five primers yielded a 285-bp fragment. PCRs with the primers based on the obtained fragment and the degenerate primers (139S and 712A) gave longer fragments. Finally, full nucleotide sequence of cDNA was obtained by a "rapid amplification of cDNA ends" (RACE) method.

Amino Acid Sequence↗
PubMed1994

Role of phosphatidylinositol-3-kinase in insulin receptor signaling: studies with inhibitor, LY294002.

In order to study the role of phosphatidylinositol-3-kinase (PI3K) in insulin action, we employed a specific inhibitor of PI3K, LY294002, and measured five biological functions of insulin in mouse 3T3 fibroblasts overexpressing human insulin receptors. LY294002 had no effect on tyrosine phosphorylation of both the insulin receptor beta-subunit and insulin receptor substrate 1 (IRS-1) and did not influence the association of the p85 subunit of PI3K with IRS-1. However, LY294002 partially inhibited insulin stimulated glucose uptake, amino acid uptake and protein synthesis, while it completely inhibited insulin stimulation of DNA synthesis and p70 S6 kinase activation. These data suggest that: 1) PI3K plays a crucial role in various functions of insulin; and 2) there exist multiple signaling pathways (both PI3K dependent and PI3K independent) for the insulin receptor.

3T3 Cells↗
PubMed1994

Role of p85 subunit of phosphatidylinositol-3-kinase as an adaptor molecule linking the insulin receptor, p62, and GTPase-activating protein.

After insulin stimulation of rat HTC hepatoma cells overexpressing normal human insulin receptors (IR), an antiserum to the p85 subunit of phosphatidylinositol-3-kinase (PIK) (alpha-p85) immunoprecipitated three major tyrosine-phosphorylated proteins: IR, insulin receptor substrate-1 (IRS-1), and a new 62-kDa protein (p62). Studies with antibodies to GTPase activating protein (alpha-GAP) and p62 GAP-associated protein suggested that p62 was the same as (or closely related to) p62 GAP-associated protein. In order to understand how p62 interacts with p85, we employed: 1) antibodies to the p110 subunit of PIK (alpha-p110); and 2) antiserum to IRS-1. To determine which subunit of PIK (p110 or p85) p62 associates with, we first immunoprecipitated insulin-treated cell lysates with alpha-p110 and subsequently immunoprecipitated with alpha-p85 followed by Western blotting analysis with anti-phosphotyrosine antibody (alpha-PY). In response to insulin, most of the tyrosine-phosphorylated p62 was complexed to p85 alone rather than with the PIK heterodimer. Moreover, p62 was absent in alpha-IRS-1 immunoprecipitates. These data suggest that: 1) p62 GAP-associated protein is tyrosine phosphorylated after insulin stimulation of cells; 2) p62 and IRS-1 form separate complexes with p85; 3) p62-GAP complex may be linked to p85 that is not bound to p110; 4) p85 may serve as an adaptor molecule in insulin receptor signaling, interacting with and regulating other intracellular proteins via SH2 domains.

Animals↗
PubMed1994

Deletion of residues 485-599 from the human insulin receptor abolishes antireceptor antibody binding and influences tyrosine kinase activation.

We have studied insulin and antireceptor antibody binding to mutated human insulin receptors deleted of residues 485-599 in the alpha-subunit by site-directed mutagenesis. Both normal and mutated receptors were expressed in rat HTC hepatoma cells. Cells expressing either the normal receptor or the mutated receptor retained the ability to bind insulin. In contrast to the normal receptor, however, the mutated receptor failed to interact with antireceptor alpha-subunit antibodies. The inability of the mutated receptor to interact with various antireceptor antibodies was further documented by photoaffinity labeling studies. In intact HTC cells expressing mutated receptors, basal insulin receptor tyrosine autophosphorylation was 2-fold elevated when compared to cells expressing normal receptors. In these cells, however, the response of this function to insulin was blunted. When receptors were isolated from these cells and assayed for both autophosphorylation and phosphotransferase activities toward the synthetic substrate poly(Glu, Tyr), the response to insulin was also blunted. To study the ability of the mutated receptor to transmembrane signal, insulin stimulation of S6 kinase activity was measured. In cells with mutated receptors, in concert with the insulin receptor kinase data, basal S6 kinase activity was elevated, and the response to insulin was blunted. The data suggest, therefore, that residues 485-599 in the alpha-subunit of the insulin receptor are critical for antireceptor antibody binding, but not for insulin binding. Moreover, these data suggest that residues 485-599 contain a regulatory domain for insulin regulation of receptor beta-subunit functions.

Animals↗
PubMed1992

Phosphatidylinositol-3-kinase is a non-tyrosine phosphorylated member of the insulin receptor signalling complex.

In rat HTC cells expressing a large number of human insulin receptors, insulin stimulated phosphatidylinositol-3-kinase (PI-3-kinase) activity. This activity was more effectively immunoprecipitated with anti-phosphotyrosine antibody (alpha-PY) than with anti-insulin receptor antibody (alpha-IR), suggesting that PI-3-kinase was not directly associated with the insulin receptor. alpha-PY immunoprecipitable PI-3 kinase activity, which was regulated by insulin, corresponded to a small pool of the total cellular PI-3-kinase activity. PI-3-kinase was not directly tyrosine phosphorylated by insulin treatment. A comparison of both catalytic activity and content of PI-3-kinase in alpha-PY immunoprecipitates indicated that after insulin treatment PI-3-kinase activity was enhanced by its association with tyrosine phosphorylated proteins. These studies suggest therefore that PI-3-kinase is a non-tyrosine phosphorylated member of the insulin receptor signalling complex.

Animals↗
PubMed1992

Regulation of biological functions by an insulin receptor monoclonal antibody in insulin receptor beta-subunit mutants.

We investigated the effects of MA-5, a human-specific monoclonal antibody to the insulin receptor alpha-subunit, on transmembrane signaling in cell lines transfected with and expressing both normal human insulin receptors and receptors mutated in their beta-subunit tyrosine kinase domains. In cell lines expressing normal human insulin receptors, MA-5 stimulated three biological functions: aminoisobutyric acid (AIB) uptake, thymidine incorporation, and S6 kinase activation. Under conditions where these biological functions were stimulated, there was no detectable stimulation of receptor tyrosine kinase. We then combined the use of this monoclonal antibody with cells expressing insulin receptors with mutations in the beta-subunit tyrosine kinase domain; two of ATP binding site mutants V1008 (Gly----Val) and M1030 (Lys----Met) and one triple-tyrosine autophosphorylation site mutant F3 (Tyr----Phe at 1158, 1162, and 1163). In cells expressing V1008 receptors, none of the three biological functions of insulin was stimulated. In cells expressing M1030 receptors, AIB uptake was stimulated to a small, but significant, extent whereas the other two functions were not. In cells expressing F3 receptors, AIB uptake and S6 kinase activation, but not thymidine incorporation, were fully stimulated. The data suggest, therefore, that (1) activation of insulin receptor tyrosine kinase may not be a prerequisite for signaling of all the actions of insulin and (2) there may be multiple signal transduction pathways to account for the biological actions of insulin.

Aminoisobutyric Acids↗