Biomedical subjects

H Y Lin

Publications and source records attributed to H Y Lin.

At least 19 recordsLinked to original sources

PubMed1998

Potentiation by thyroid hormone of human IFN-gamma-induced HLA-DR expression.

We have investigated the mechanism by which thyroid hormone potentiates IFN-gamma-induced HLA-DR expression. IFN-gamma-induced HLA-DR expression requires activation of STAT1alpha and induction of the Class II trans-activator, CIITA. HeLa and CV-1 cells treated only with L-thyroxine (T4) demonstrated increased tyrosine phosphorylation and nuclear translocation (= activation) of STAT1alpha; this hormone effect on signal transduction, and T4 potentiation of IFN-gamma-induced HLA-DR expression, were blocked by the inhibitors CGP 41251 (PKC) and genistein (tyrosine kinase). Treatment of cells with T4-agarose also caused activation of STAT1alpha. In the presence of IFN-gamma, T4 enhanced cytokine-induced STAT1alpha activation. Potentiation by T4 of IFN-gamma action was associated with increased mRNA for both CIITA and HLA-DR, with peak enhancement at 16 h (CIITA), and 2 d (HLA-DR). T4 increased IFN-gamma-induced HLA-DR protein 2.2-fold and HLA-DR mRNA fourfold after 2 d. Treatment with actinomycin D after induction of HLA-DR mRNA with IFN-gamma, with or without T4, showed that thyroid hormone decreased the t(1/2) of mRNA from 2.4 to 1.1 h. HeLa and CV-1 cells lack functional nuclear thyroid hormone receptor. Tetraiodothyroacetic acid (tetrac) and 3,5,3'-triiodo-thyroacetic acid (triac) blocked T4 potentiation of IFN-gamma-induced HLA-DR expression and T4 activation of STAT1alpha. These studies define an early hormone recognition step at the cell surface that is novel, distinct from nuclear thyroid hormone receptor, and blocked by tetrac and triac. Thus, thyroid hormone potentiation of IFN-gamma-induced HLA-DR transcription is mediated by a cell membrane hormone binding site, enhanced activation of STAT1alpha, and increased CIITA induction.

Biological Transport↗

PubMed1998

Effects of en bloc esophagectomy on nutritional and immune status in patients with esophageal carcinoma.

BACKGROUND AND OBJECTIVES: En bloc esophagectomy has been established as the treatment of choice for patients with resectable esophageal carcinoma. However, an extensive surgical procedure may result in further impairment of the patient's nutritional status and immune system. Thus a prospective study was undertaken to evaluate the perioperative sequential changes in patients' nutritional and immune status and the timing to institute postoperative adjuvant therapy. METHODS: Thirty-seven patients (34 male, 3 female) who had undergone en bloc esophagectomy with gastric institution for epidermoid carcinoma of the esophagus were studied. The mean age was 62.3 years. The nutritional and immune assessments were performed preoperatively, on the third postoperative day, in the first week, second week, third week, and at the end of the first and third month. The biochemical studies for nutritional evaluation included serum albumin, cholesterol, iron, transferrin, magnesium, zinc, total iron binding capacity (TIBC), and nitrogen balance. Evaluation of the immune status consisted of: (1) total lymphocyte count, (2) lymphocyte subpopulation, (3) immunoglobulins, (4) complements (C3 and C4), (5) lymphocyte blastogenic responses, (6) tumor necrosis factor-alpha and interleukin-2 secretion activity from mononuclear cells, and (7) C-reactive protein (CRP) level. RESULTS: All the parameters in nutritional assessment declined profoundly by the third postoperative day (P < 0.05). The most severe deterioration was in serum iron, followed by transferrin, TIBC, cholesterol, and zinc. Most of them returned to the preoperative levels within 2-3 weeks after surgery. However, the serum levels of iron, transferrin, and TIBC required a longer period of time (> 1 month) to return to normal. A remarkable increase of serum CRP was detected in the first postoperative week (P < 0.05), but immunoglobulins and complements decreased significantly yet variably (P < 0.05) in the second or third postoperative week before gradually returning to preoperative levels. Moreover, during the first week after surgery, CD3 and CD8 diminished following esophageal surgery, whereas CD20, CD4/CD8 ratio, and lymphocyte blastogenic responses increased significantly (P < 0.05). CONCLUSIONS: Except for iron-related parameters, all the other nutritional parameters returned to the preoperative level by the third postoperative week. An adequate supplementation of iron and protein for 1-3 months after surgery is needed. En bloc esophagectomy might have only a mild and temporarily adverse effect on the host immune defense. Regarding the postoperative recovery of a patient's nutritional and immune status, postoperative chemo-radiotherapy is optimally instituted after the third postoperative week, instead of within 2 weeks of surgery.

Aged↗

PubMed1998

Identification of the cytoplasmic regions of fibroblast growth factor (FGF) receptor 1 which play important roles in induction of neurite outgrowth in PC12 cells by FGF-1.

Fibroblast growth factor 1 (FGF-1) induces neurite outgrowth in PC12 cells. Recently, we have shown that the FGF receptor 1 (FGFR-1) is much more potent than FGFR-3 in induction of neurite outgrowth. To identify the cytoplasmic regions of FGFR-1 that are responsible for the induction of neurite outgrowth in PC12 cells, we took advantage of this difference and prepared receptor chimeras containing different regions of the FGFR-1 introduced into the FGFR-3 protein. The chimeric receptors were introduced into FGF-nonresponsive variant PC12 cells (fnr-PC12 cells), and their ability to mediate FGF-stimulated neurite outgrowth of the cells was assessed. The juxtamembrane (JM) and carboxy-terminal (COOH) regions of FGFR-1 were identified as conferring robust and moderate abilities, respectively, for induction of neurite outgrowth to FGFR-3. Analysis of FGF-stimulated activation of signal transduction revealed that the JM region of FGFR-1 conferred strong and sustained tyrosine phosphorylation of several cellular proteins and activation of MAP kinase. The SNT/FRS2 protein was demonstrated to be one of the cellular substrates preferentially phosphorylated by chimeras containing the JM domain of FGFR-1. SNT/FRS2 links FGF signaling to the MAP kinase pathway. Thus, the ability of FGFR-1 JM domain chimeras to induce strong sustained phosphorylation of this protein would explain the ability of these chimeras to activate MAP kinase and hence neurite outgrowth. The role of the COOH region of FGFR-1 in induction of neurite outgrowth involved the tyrosine residue at amino acid position 764, a site required for phospholipase C gamma binding and activation, whereas the JM region functioned primarily through a non-phosphotyrosine-dependent mechanism. In contrast, assessment of the chimeras in the pre-B lymphoid cell line BaF3 for FGF-1-induced mitogenesis revealed that the JM region did not play a role in this cell type. These data indicate that FGFR signaling can be regulated at the level of intracellular interactions and that signaling pathways for neurite outgrowth and mitogenesis use different regions of the FGFR.

Amino Acid Sequence↗

PubMed1997

Bioactive and nuclease-resistant L-DNA ligand of vasopressin.

In vitro selection experiments have produced nucleic acid ligands (aptamers) that bind tightly and specifically to a great variety of target biomolecules. The utility of aptamers is often limited by their vulnerability to nucleases present in biological materials. One way to circumvent this problem is to select an aptamer that binds the enantiomer of the target, then synthesize the enantiomer of the aptamer as a nuclease-insensitive ligand of the normal target. We have so identified a mirror-image single-stranded DNA that binds the peptide hormone vasopressin and have demonstrated its stability to nucleases and its bioactivity as a vasopressin antagonist in cell culture.

Animals↗

PubMed1997

Ligand-binding specificity of human fibroblast growth factor receptor-3 IIIc.

Earlier studies indicated that human fibroblast growth factor receptor (FGFR)-3 IIIc was activated equally well by both FGF-1 and FGF-2. In contrast, murine FGFR-3 IIIc was preferentially activated by FGF-1. To address this issue, we determined the ligand-binding specificity of human FGFR-3 IIIc in comparison with human FGFR-1 IIIc. By equilibrium binding human FGFR-3 IIIc preferentially bound FGF-1 with high affinity, whereas FGFR-1 IIIc bound both FGF-1 and -2 with high affinity. By competition binding using FGF-1, -2, -4, or -6, FGF-1 competed more efficiently than the other FGFs. These results suggest that like the murine FGFR-3 III, FGF-1 is a preferred ligand for human FGFR-3 IIIc.

Animals↗

PubMed1997

Biosynthesis of the type I and type II TGF-beta receptors. Implications for complex formation.

The TGF-beta type I and type II receptors (TbetaRI and TbetaRII) are signaling receptors that form heteromeric cell surface complexes with the TGF-betas as one of the earliest events in the cellular response to these multifunctional growth factors. Using TGF-beta-responsive mink lung epithelial cells (Mv1Lu), we have determined the half-lives of the endoplasmic reticulum (ER) and mature forms of these receptors. In metabolically labeled cells, approximately 90% of newly synthesized type II receptor undergoes modification of N-linked sugars in the Golgi, with a half-life of 30-35 min; the Golgi-processed form of the receptor has a relatively short metabolic half-life of 2.5 h. In contrast, only 50% of pulse-labeled type I receptor is converted to the Golgi-processed and therefore endoglycosidase H-resistant form, and the endoglycosidase H-sensitive ER form has a half-life of 2.8-3 h. Addition of 100 pM TGF-beta1 causes the Golgi-processed type II receptor to become less stable, with a half-life of 1.7 h, and also destabilizes the Golgi-processed type I receptor. TGF-beta1 binding and cross-linking experiments on cells treated with tunicamycin for various times confirm different ER to cell surface processing times for TbetaRI and TbetaRII. Our results, which suggest that stable complexes between type I and II TGF-beta receptors do not form until the proteins reach a post-ER compartment (presumably the cell surface), have important implications for our understanding of complex formation and receptor regulation.

Activin Receptors, Type I↗

PubMed1997

Protein synthesis-dependent potentiation by thyroxine of antiviral activity of interferon-gamma.

We have studied the prenuclear signal transduction pathway by which thyroid hormone potentiates the antiviral activity of human interferon-gamma (IFN-gamma) in HeLa cells, which are deficient in thyroid hormone receptor (TR). The action of thyroid hormone was compared with that of milrinone, which has structural homologies with thyroid hormone. L-Thyroxine (T4), 3,5,3'-L-triiodothyronine (T3), and milrinone enhanced the antiviral activity of IFN-gamma up to 100-fold, a potentiation blocked by cycloheximide. The 5'-deiodinase inhibitor 6-n-propyl-2-thiouracil did not block the T4 effect. 3,3',5,5'-Tetraiodothyroacetic acid prevented the effect of T4 but not of milrinone. The effects of T4 and milrinone were blocked by inhibitors of protein kinases C (PKC) and A (PKA) and restored by PKC and PKA agonists; only the effect of T4 was blocked by genistein, a tyrosine kinase inhibitor. In separate models, milrinone was shown not to interact with nuclear TR-beta. T4 potentiation of the antiviral activity of IFN-gamma requires PKC, PKA, and tyrosine kinase activities but not traditional TR.

Amrinone↗

PubMed1997

Application of dipole modeling in localization of mesio-temporal epileptogenic focus.

Improved methods for noninvasive localization of an epileptic focus, modeled as an electrical dipole, are developed in this research. For the head geometrical model, a three-dimensional (3-D) electromagnetic tracking system is utilized to measure the exact positions of electrodes. A nonlinear optimization technique, the Levenberg-Marquardt method, is adopted for dipole localization. For the optimization algorithm to converge to correct solution, the singular value decomposition (SVD) technique is used to extract the dominant component of the EEG spike for initial estimation and dipole localization. The localization results of varied montages, including standard 10-20 electrodes and enhanced temporal electrodes, with or without invasive sphenoid electrodes, are compared. Our experimental results indicate that dipole localization with enhanced temporal electrodes can be used as an alternative for the invasive sphenoid electrodes to differentiate the epileptogenic foci of mesio-temporal area from temporal convexity.

Algorithms↗

PubMed1997

Pneumocephalus and respiratory depression after accidental dural puncture during epidural analgesia--a case report.

A case of pneumocephalus and respiratory depression after dural puncture during lumbar epidural analgesia is reported. The loss of resistance to air technique was employed to identify the epidural space. Severe respiratory depression and stuporous consciousness developed one hour after a bolus of 2 mg morphine was given epidurally at the end of operation. With computerized tomographic brain scanning and continuous observation of clinical course, the neurologic symptoms were thought to be a mixed complication of pneumocephalus and possible intrathecal morphine overdose. We suggest that in order to avoid iatrogenic pneumocephalus by inadvertent dural puncture in the attempt to identify the epidural space the use of the loss of resistance to normal saline technique or the hanging-drop technique is more reliable than the loss of resistance to air technique. A small test dose prior to a full dose is given and should not be omitted to further confirm the proper placement of the epidural catheter during epidural analgesia.

Aged↗

PubMed1996

The fibroblast growth factor receptor-1 is necessary for the induction of neurite outgrowth in PC12 cells by aFGF.

The PC12 subclone, fnr-PC12 cells, is defective in neurite outgrowth in response to acidic fibroblast growth factor (aFGF); however, its response to nerve growth factor (NGF) is normal. Examination of the expression of FGF receptors (FGFRs) revealed that although PC12 cells express FGFR-1, -3, and -4, fnr-PC12 cells have a reduced level of expression of FGFR-1 but not FGFR-3 and -4. Transfection of FGFR-1 into fnr-PC12 cells efficiently restored aFGF-induced neurite outgrowth, whereas transfection of FGFR-3 was much less efficient. Transfection of a chimeric receptor consisting of the extracellular domain of FGFR-3 fused to the transmembrane and intracellular domain of FGFR-1, termed FR31b, efficiently restored aFGF-induced neurite outgrowth. This demonstrates that the difference between these two receptors in their ability to induce neurite outgrowth is attributable to differences in the signaling capacity of their cytoplasmic domains. Activation of the chimeric receptor by aFGF induced a stronger and more persistent increase in the tyrosine phosphorylation of cellular proteins than did activation of FGFR-3 alone. In particular, the activation of MAP kinase by FR31b was more persistent than when activated by FGFR-3. This difference in signaling potential of FGFR-1 and -3 in fnr-PC12 cells may account for the difference in the potential for induction of neurite outgrowth. These results demonstrate that FGF-induced neurite outgrowth in PC12 cells occurs mainly via FGFR-1 and not via the other FGFRs expressed in these cells.

Amino Acid Sequence↗

PubMed1996

Thyroid hormone analogues potentiate the antiviral action of interferon-gamma by two mechanisms.

L-thyroxine (L-T4) potentiates the antiviral activity of human interferon-gamma (IFN-gamma) in HeLa cells. We have added thyroid hormone and analogues to cells either 1) for 24 h pretreatment prior to 24 h of IFN-gamma (1.0 IU/ml), 2) for 24 h cotreatment with IFN-gamma, 3) for 4, after 20 h cell incubation with IFN-gamma, alone, or 4) for 24 h pretreatment and 24 h cotreatment with IFN-gamma. The antiviral effect of IFN-gamma was then assayed. L-T4 potentiated the antiviral action of IFN-gamma by a reduction in virus yield of more than two logs, the equivalent of a more than 100-fold potentiation of the IFN's antiviral effect. 3,3 of the IFN's antiviral effect. 3,3',5-L-triiodothyronine (L-T3) was as effective as L-T4 when coincubated for 24 h with IFN-gamma but was less effective than L-T4 when coincubated for only 4 h. D-T4, D-T3, 3,3',5-triiodothyroacetic acid (triac), tetraiodothyroacetic acid (tetrac), and 3,5-diiodothyronine (T2) were inactive. When preincubated with L-T4 for 24 h prior to IFN-gamma treatment, tetrac blocked L-T4 potentiation, but, when coincubated with L-T4 for 4 h after 20 h IFN-gamma, tetrac did not inhibit the L-T4 effect. 3,3',5-L-triiodothyronine (rT3) also potentiated the antiviral action of IFN-gamma, but only in the preincubation model. Furthermore, the effects of rT3 preincubation and L-T3 coincubation were additive, resulting in 100-fold potentiation of the IFN-gamma effect. When L-T4, L-T3, or rT3, plus cycloheximide (5 micrograms/ml), was added to cells for 24 h and then removed prior to 24 h IFN-gamma exposure, the potentiating effect of the three iodothyronines was completely inhibited. In contrast, IFN-gamma potentiation by 4 h of L-T4 or L-T3 coincubation was not inhibited by cycloheximide (25 micrograms/ml). These studies demonstrate two mechanisms by which thyroid hormones can potentiate IFN-gamma's effect: 1) a protein synthesis-dependent mechanism evidenced by enhancement of IFN-gamma's antiviral action by L-T4, L-T3, or rT3 preincubation, and inhibition of enhancement by tetrac and cycloheximide, and 2) a protein synthesis-independent (posttranslational) mechanism, not inhibited by tetrac or cycloheximide, demonstrated by 4 h coincubation of L-T4 or L-T3, but not rT3, with IFN-gamma. The protein synthesis-dependent pathway is responsive to rT3, a thyroid hormone analogue generally thought to have little effect on protein synthesis. A posttranslational mechanism by which the antiviral action of IFN-gamma can be regulated has not previously been described.

Antiviral Agents↗

PubMed1996

Potentiation by thyroxine of interferon-gamma-induced HLA-DR expression is protein kinase A- and C-dependent.

L-Thyroxine (T4) and 3,3',5-L-triiodothyronine (T3) potentiate the antiviral state induced by interferon-gamma(IFN-gamma) in homologous cells by a mechanism that is dependent upon calcium/phospholipid-dependent protein kinase (PKC). L-T4 and T3 also potentiate induction by IFN-gamma of MHC class II HLA-DR antigen expression in HeLa cells. In the present studies of HLA-DR expression, the PKC inhibitor staurosporine (0.1-1 nM) enhanced the expression of HLA-DR when the inhibitor was added simultaneously with IFN-gamma, 100 IU/ml. In the presence of IFN-gamma and 10(-7) M T4, the same concentrations of staurosporine inhibited potentiation of HLA-DR expression by thyroid hormone. A more specific PKC inhibitor, CGP41251 (0.5-5 nM), similarly enhanced HLA-DR expression in the presence of IFN-gamma but inhibited thyroid hormone potentiation of antigen expression. Both actions of CGP41251 were suppressed when cells were also treated with phorbol 12-myristate 13-acetate (PMA). A phospholipase C inhibitor, U73122 (1-1000 nM), did not alter the potentiating ability of T4, although it inhibited in a concentration-dependent manner the expression of HLA-DR induced by IFN-gamma. The potentiating effect of T4 was much more sensitive to a cyclic AMP-dependent protein kinase (PKA) inhibitor,KT5720 (1-1000nM), than was the induction of HLA-DR by IFN-gamma. The inhibitory effects of KT5720 were reversed by concurrent 8-bromo-cAMP treatment. The calmodulin antagonist W-7 (5-50 microM) did not alter IFN-gamma induction of HLA-DR in either the presence or absence of T4. HLA-DR expression in HeLa cells appears to be under PKC-associated inhibition; IFN-gamma reverses this inhibition to promote the appearance of the DR antigen. In contrast, potentiation by T4 of induction of HLA-DR by IFN-gamma requires activation of PKC. PKA is involved both in DR induction by IFN-gamma and in potentiation of the latter by T4. Thus, PKA and PKC have discrete roles in IFN-gamma-induced MHC class II antigen expression and its modulation by thyroid hormone.

Antiviral Agents↗

PubMed1996

The relationship of aging to endotoxin shock and to production of TNF-alpha.

BACKGROUND: Aged people are considered prone to gram-negative bacteremia and septic shock. This relationship was tested in murine endotoxin shock. METHODS: Balb/c mice of various ages (1.4-13.4 months) were intraperitoneally injected with lipopolysaccharide (LPS), and rates of survival were observed. The production of TNF-alpha in vivo induced by LPS was measured. RESULTS: The survival rates were the smallest in the oldest and youngest groups. Production of TNF-alpha attained a maximum at 2 h after LPS injection and was smaller in the oldest group; it had a reciprocal relationship to survival rates in each group except the youngest group. CONCLUSION: Old and young mice had smaller rates of survival and greater production of TNF-alpha following endotoxin shock induced by LPS.

Aging↗

PubMed1996

Potentiation by thyroxine of interferon-gamma-induced antiviral state requires PKA and PKC activities.

Added to HeLa cells previously exposed to recombinant human interferon (IFN)-gamma for 20 h, thyroid hormone [L-thyroxine (T4)] in physiological concentrations potentiates the antiviral action of IFN-gamma by more than 100-fold in 4 h. We examined protein kinase activities for their contributions to the mechanism of this posttranslational effect of thyroid hormone. Added concurrently with thyroid hormone, the protein kinase C (PKC) inhibitor CGP-41251 (5 nM) blocked T4 potentiation of IFN-gamma action. Coincubated with CGP-41251, phorbol 12-myristate 13-acetate (PMA) reversed the effect of the inhibitor on thyroid hormone action. U-73122 (10 nM), a phospholipase C inhibitor, also blocked hormone potentiation. KT-5720 (500 nM), a protein kinase A (PKA) inhibitor, completely inhibited the T4 effect, whereas 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP) restored hormone action in the presence of KT-5720. In the absence of T4, 8-BrcAMP and PMA, added together to cells in the 4-h paradigm, fully reproduced hormone potentiation of the antiviral effect of IFN-gamma. Incubated individually with IFN-gamma-treated cells, the two agonists had no potentiating action. Thyroid hormone apparently must activate both PKA and PKC in the nongenomic pathway of IFN-gamma action to enhance antiviral activity in HeLa cells.

Animals↗

PubMed1996

Clinical significance of complements in ascitic diseases: elevated complement levels disapproving the liver disease origin.

In a two-year period, ascitic fluid concentrations of complement 3c and complement 4 were measured in 110 patients with sterile cirrhotic ascites, 31 patients with spontaneous bacterial peritonitis, 65 patients with hepatocellular carcinoma, 36 patients with peritoneal carcinomatosis and 12 patients with miscellaneous diseases (nephrotic syndrome 4, systemic lupus erythematosus 3, secondary peritonitis 2, cardiac ascites 1, eosinophilic peritonitis 1 and tuberculosis peritonitis 1) to assess the clinical utility of ascitic fluid complements. The ascitic fluid level of complements 3c or C4 was significantly higher in patients with peritoneal carcinomatosis (32.8 +/- 10.2, 13.4 +/- 7.4 mg/dL) than in patients with sterile cirrhotic ascites (9.2 +/- 5.2, 4.5 +/- 3.9 mg/dL, p < 0.001), spontaneous bacterial peritonitis (8.2 +/- 4.1, 3.8 +/- 2.4 mg/dL, p < 0.001) or hepatocellular carcinoma (12.8 +/- 8.3, 5.6 +/- 4.4 mg/dL, p < 0.001). However, it was not significantly different from the miscellaneous disease group. To verify that ascites formation is not related to liver disease origin, diagnostic sensitivity, specificity and accuracy were 83.3%, 92.7% and 90.9%, respectively, by the ascitic fluid level of complement 3c higher than the cut-off value (20 mg/dl); or 60.4%, 89.8% and 84.3%, respectively, by the ascitic fluid level of complement 4 higher than the cut-off value (10 mg/dL). A direct correlation was found between the ascitic fluid protein level and the ascitic fluid complement 3c (r = 0.70) or complement 4 (r = 0.57) level. Based on results in this study, we can conclude that measuring ascitic fluid complements is clinically useful in disapproving the liver disease origin of ascites formation. However, it is of little value in diagnosing spontaneous bacterial peritonitis or hepatocellular carcinoma.

Ascites↗

PubMed1995

Endothelin-induced endocytosis of cell surface ETA receptors. Endothelin remains intact and bound to the ETA receptor.

We demonstrate unusual features of the intracellular processing of endothelin-1 (ET-1) and its receptor ETA, the receptor subtype that mediates contraction of vascular smooth muscle cells. First, we show that in stably transfected CHO cells expressing ETA, binding of an ET-1 ligand induces rapid endocytosis of cell surface ETA. Receptor endocytosis was measured both by immunofluorescence and by radioiodinated antibodies specific for ETA. Second, we demonstrate that ET-1 remains intact for up to 2 h after endocytosis and, as judged by co-immunoprecipitation, internalized 125I-ET-1 remains bound to ETA receptors. We hypothesize that internalized ET-1, bound to ETA receptors, continues to activate a signal-transducing G protein, thus accounting for the prolonged period of contraction induced in smooth muscle cells by a single administration of ET-1.

Animals↗

PubMed1995

The soluble exoplasmic domain of the type II transforming growth factor (TGF)-beta receptor. A heterogeneously glycosylated protein with high affinity and selectivity for TGF-beta ligands.

The transforming growth factor (TGF)-beta type II receptor is a transmembrane serine/threonine kinase which is essential for all TGF-beta-induced signals. In several cell types TGF-beta 2 is as potent as TGF-beta or TGF-beta 3 in inducing cellular responses, yet TGF-beta 2 does not bind to the majority of expressed type II receptors. Here we characterized the properties of the soluble extracellular domain of the human TGF-beta type II receptor synthesized in COS-7 cells. Like the membrane-attached type II receptor, the soluble receptor contains complex N-linked oligosaccharides as well as additional sialic acid residues that cause it to migrate heterogenously upon SDS-polyacrylamide gel electrophoresis. 125I-TGF-beta 1 binds to and is chemically cross-linked to this protein. Unlabeled TGF-beta 1 inhibits the binding of 125I-TGF-beta 1 with an apparent dissociation constant (Kd) of approximately 200 pM, similar to the apparent Kd (approximately 50 pM) of the cell-surface type II receptor. TGF-beta 3 inhibits the binding of 125I-TGF-beta 1 to the soluble type II receptor with a similar dissociation constant, approximately 500 pM. In contrast, 125I-TGF-beta 2 cannot bind and be chemically cross-linked to the soluble type II receptor, nor does as much as a 125-fold excess of unlabeled TGF-beta 2 inhibit the binding of 125I-TGF-beta 1 to the soluble receptor. This is the first demonstration of the binding affinities of the type II receptor in the absence of the other cell-surface molecules known to bind TGF-beta. Expressed alone in COS-7 cells the type II receptor also cannot bind TGF-beta 2; co-expression of type III receptor enables the type II receptor to bind TGF-beta 2. Thus, the type III receptor or some other component is required for transmission of TGF-beta 2-induced signals by the type II receptor.

Animals↗

PubMed1995

GH3 pituitary tumor cells contain heteromeric type I and type II receptor complexes for transforming growth factor beta and activin-A.

Transforming growth factors beta (TGF-beta s) and activins induce and inhibins block secretion of follicle-stimulating hormone by rat GH3 pituitary tumor cells. Cheifetz et al. (Cheifetz, S., Ling, N., Guillemin, R., and Massagué, J. (1988) J. Biol. Chem. 263, 17225-17228) reported that GH3 cells express a approximately 50-kDa surface protein, termed the type IV TGF-beta receptor, that directly binds all of these peptide hormones. Here we show that GH3 cells express the previously identified type I and type II receptors for TGF-beta and activin-A. Immunoprecipitation of affinity-labeled surface binding proteins with antisera specific to known receptors demonstrated independent heteromeric complexes of TGF-beta types I and II receptors and of activin types I and II receptors. As judged by ligand-binding and cross-linking analysis, TGF-beta binding to the TGF-beta receptors is not inhibited by activin-A and activin-A binding to its receptors is not inhibited by TGF-beta. Screening of a cDNA library from GH3 cells for potential receptor serine-threonine kinases yielded the known types I and II TGF-beta and activin receptors. The presumed common intracellular signaling pathway for TGF-beta and activin in GH3 cells appears to be mediated by distinct cell-surface receptors.

Activin Receptors↗