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Biomedical subjects

J K Chen

Publications and source records attributed to J K Chen.

At least 127 records · Page 7Linked to original sources
PubMed1989

Growth factor requirements of normal and polyomavirus middle T gene transformed REF52 cells in serum-free medium: indications of a reduced vasopressin requirement and its relationship to the control of phosphatidylinositol metabolism.

The growth factor requirement of normal and polyomavirus middle T gene transformed REF52 cells was studied in serum-free medium in an attempt to elucidate the possible linkage between an altered growth factor requirement and one or more altered physiological properties of the transformed cells. For optimal growth, REF52 cells required vasopressin, epidermal growth factor (EGF), high-density lipoprotein (HDL), hydrocortisone, insulin, transferrin, and fibronectin. Deletion of vasopressin or hydrocortisone from the medium resulted in a 50 to 60% reduction in cell growth and the deletion of HDL, transferrin, or the combination of EGF and vasopressin led to an 80 to 90% growth retardation. The same medium supported the growth of the transformed variant (PyMLV-REF52) at a rate comparable to that of 10% serum, and deletion of hydrocortisone, vasopressin, or the combination of EGF and vasopressin had virtually no effect on PyMLV-REF52 cell growth. In vasopressin-deleted medium, vasopressin elicited a rapid increase of intracellular inositol phosphate levels in REF52 cells and the control of phosphoinositide turnover was strictly regulated. In contrast, both cell proliferation and intracellular inositol phosphate levels of PyMLV-REF52 cells were not affected by vasopressin treatment under identical culture conditions, and control of phosphoinositide metabolism was lost. Thus, a correlation may exist between the trigger of a mitogenic signal and the stimulation of the phosphoinositol pathway by vasopressin in REF52 cells and this relationship was disrupted in PyMLV-REF52 cells.

Animals↗
PubMed1989

[Suggestion to physiological role of the frog tongue off-response to continuous tactile stimulation, from the viewpoint of the response figures].

The responses of the bullfrog lingual surface to continuous tactile flow stimulation for 3 minutes were characterized by a presence of conspicuous off-response. At that time the on-responses of the lingual surface were uniform in shape. The off-responses in the same situation were not uniform but multiform against expectation. These multiform off-responses could be roughly classified into two groups; one was high slender triangular shape resembling phasic response and slightly static response, and the other was low isosceles or ladder shape. The difference of the shape probably indicates the difference in the time series of centripetal input signalling. The tactile off-response on the whole tongue surface could be reconstructed by summing up the off-response on the lingual apex region and that of the radix region. This was one possibility to explain the multiform lingual tactile off-response pattern.

Animals↗
PubMed1989

[One mechanical property of contraction of isolated bullfrog geniohyoid muscle].

In general, skeletal muscle activity has been understood on the basis that the muscle is functionally consisted of contractile element and elastic element. In this paper it has been attempted to clarify the specific role of the geniohyoid muscle which is one member of the oro-basal muscular system, because our previous reports suggested an elastic specificity of only this muscle as supposed, for example, from the presence of posttetanic twitch attenuation under isotonic condition. For this reason, the experiments have been carried out with paying attention to an interrelationship between loading and contraction figure. When the geniohyoid muscle, weighing over 320 mg, was contracted without any loading, downward undulation under the base line (abbreviated by negative deflection) could be obviously seen within the period succeeding after a falling or relaxation phase of a contraction curve. This negative deflection which presumably indicates the elastic behavior disappeared with increasing the loads from nothing to 4 times the muscle weight. This 3-4 times loading was peculiar to the geniohyoid muscle. In the same situation, 4-5 times loading was specific to the rectus abdominis muscle, and 7-8 times loading was specific to the sartorius muscle. Furthermore, when the geniohyoid muscle was divided first to 1/2 and then to 1/4, the negative deflection of each muscle block was shifted to the lighter side of the applied load. Additional experimental results will be accumulated in the next report.

Animals↗
PubMed1989

Primary dapsone resistance in China.

Ninety-seven strains of Mycobacterium leprae recovered from patients with previously untreated multibacillary leprosy were tested for dapsone susceptibility. The specimens originated from Shanghai Municipality, Jiang-su Province and Fu-jian Province. Approximately 28% of the strains either did not infect the mice or the results of susceptibility were inconclusive due to the low proportion of viable organisms in the bacterial populations. Among the 70 strains in which dapsone susceptibility could be tested in mice, 31 (44%) strains were found with primary dapsone resistance. Although the majority of the primary dapsone resistant strains were shown to be of a low- or intermediate-degree, one-sixth of them were of high-degree resistance.

Animal Feed↗
PubMed1988

Enhancement of transformed cell growth in agar by serine protease inhibitors.

We investigated the effects of three serine protease inhibitors (leupeptin, soybean trypsin inhibitor, and aprotinin) on the serum-free growth of two transformed cell lines in soft agar. Aprotinin markedly enhanced the growth of rat embryo fibroblasts that had been transformed by polyoma middle T antigen (PyMLV-REF52), while having only a slight effect on the colonial growth of SV40 transformed Balb/c 3T3 cells (SV3T3-Aga). Leupeptin and soybean trypsin inhibitor, on the other hand, significantly enhanced the growth of SV3T3-Aga cells while having little effect on PyMLV-REF52 growth. We observed no stimulatory effect of any of the protease inhibitors on serum-free monolayer growth. Under conditions of excess aprotinin, PyMLV-REF52 cells were found to be unresponsive to epidermal growth factor (EGF) at a concentration that would normally stimulate agar colony growth. However, aprotinin was not capable of supporting colony formation with transforming growth factor-beta. These results indicate that aprotinin acts primarily as a protease inhibitor in spite of its structural homology to EGF and that EGF may promote the soft agar growth of these cell lines either by inhibiting proteolysis directly or by enhancing the synthesis of a serine protease inhibitor.

Antigens, Polyomavirus Transforming↗
PubMed1988

Heparin-binding growth factor type one and platelet-derived growth factor are required for the optimal expression of cell surface low density lipoprotein receptor binding activity in human adult arterial smooth muscle cells.

Purified heparin-binding growth factor-1 (HBGF-1) stimulated low density lipoprotein binding, internalization, and degradation in isolated human adult arterial smooth muscle cells. Exposure of quiescent cells to HBGF-1 in serum-free, defined medium increased both low density lipoprotein (LDL) receptor activity and de novo cholesterol biosynthesis. Both events preceded the onset of DNA synthesis by 6 to 9 h. HBGF-1 acted additively with platelet-derived growth factor (PDGF) to maximally stimulate cell surface LDL receptor binding activity and DNA synthesis in the smooth muscle cells. The presence of LDL was required for maximal mitogenic activity of HBGF-1 and PDGF. In the presence of LDL, growth factor-stimulated, proliferating human smooth muscle cells accumulated cholesterol ester and triglycerides. The results suggest that HBGF-1, PDGF, and LDL act together to promote the maximal proliferation of smooth muscle cells in culture. Chronic exposure to the three growth promoters may contribute to the smooth muscle cell hyperplasia and lipid accumulation observed in atherosclerotic lesions.

Adult↗
PubMed1988

Comparative endocrinology-paracrinology-autocrinology of human adult large vessel endothelial and smooth muscle cells.

Endothelial and smooth muscle cells were isolated from human adult large blood vessels to compare their proliferative response to hormones and growth factors. Neural extracts and the medium from differentiated hepatoma cells were used as concentrated sources of required hormones and growth factors that supported both cell types. Active hormones and growth factors were identified from the neural extracts and hepatoma medium by substitution or direct isolation and biochemical characterization. Epidermal growth factor, lipoproteins, and heparin-binding growth factors elicited growth-stimulatory effects on both endothelial and smooth muscle cells. Both types of human vascular cells displayed 7600 to 8600 specific heparin-binding growth factor receptors per cell with a similar and apparent dissociation constant (Kd) of 200 to 250 pM. Heparin modified the response of both endothelial and smooth muscle cells to heparin-binding growth factors dependent on the type of heparin-binding growth factor and amount of heparinlike material present. In addition, heparin exerted a growth factor-independent inhibition of smooth muscle cell proliferation. Platelet-derived growth factor, insulinlike growth factors, and glucocorticoid specifically supported proliferation of smooth muscle cells with no apparent effect on endothelial cell proliferation. Growth-factorlike proteinase inhibitors had an impact specifically on endothelial cell proliferation. Transforming growth factor beta was a specific inhibitor of endothelial cells, but had a positive effect on smooth muscle cell proliferation. The results provide a framework for differential control of the two vascular cell types at normal and atherosclerotic blood vessel sites by the balance among positive and negative effectors of endocrine, paracrine and autocrine origin.

Cell Division↗
PubMed1988

Altered low density lipoprotein receptor regulation is associated with cholesteryl ester accumulation in Simian virus 40 transformed rodent fibroblast cell lines.

Several SV40 transformed REF52 cell lines were found to accumulate 5 to 10 times more cholesteryl esters compared to their parent line REF52 when cultured in 10% serum. Under this culture condition, the cholesteryl ester to phospholipid ratio was 0.4:1 and 2.0:1 to 3.8:1 for normal and SV40 transformed cells, respectively. The mechanism underlying cholesteryl ester accumulation in SV40 transformed lines was investigated. We found that 1) the rate of the de novo cholesterol and cholesteryl ester synthesis was roughly equal in normal and transformed derivatives; 2) the accumulation of cholesteryl esters in the transformants would not occur when cultured in lipoprotein-deficient medium and reappeared upon their return to low density lipoprotein-containing medium; 3) the transformants expressed twice as many low density lipoprotein receptors and were less sensitive to LDL-induced receptor down regulation compared to their nontransformed counterparts. The results indicate that SV40 transformed lines exhibited an accelerated lipid uptake from the culture medium due to an altered regulation of low density lipoprotein receptor activity.

Animals↗
PubMed1988

Phorbol ester reduces number of heparin-binding growth-factor receptors in human adult endothelial cells.

Heparin-binding growth factors (HBGF) are essential and key mitogens for human adult large vessel endothelial cells. At 170 pg/ml, the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) caused a 50% inhibition of heparin-binding growth factor type one (HBGF-1)-stimulated DNA synthesis in human adult large vessel endothelial cells. TPA at 1 ng/ml completely inhibited HBGF-1-stimulated proliferation. TPA at 5 ng/ml reduced specific HBGF-1 receptor sites from 6600 per cell to 3200 per cell without affecting receptor affinity. Since phorbol esters are potent activators of protein kinase C, desensitizes both animal capillary and human adult large vessel endothelial cells to the mitogenic effects of HBGF by down-regulation of specific HBGF receptors.--HOSHI, H; KAN, M.; MIOH, H.; CHEN J.-K.; McKEEHAN, W. L. Phorbol ester reduces number of heparin-binding growth factor receptors in human adult endothelial cells.

Adult↗
PubMed1987

Differential responsiveness of normal and simian virus 40-transformed BALB/c 3T3 cells to retinoic acid: rapid enhancement of epidermal growth factor receptor binding in a simian virus 40-3T3 variant.

The effects of retinoic acid on the epidermal growth factor (EGF) receptor binding and cell growth of normal and simian virus 40 (SV40)-transformed BALB/c 3T3 cells were compared under identical culture conditions. Retinoic acid induced a rapid enhancement of EGF binding to SV40-transformed cells. Half-maximal enhancement occurred at about 7 h after the cells were exposed to 20 ng/ml of retinoic acid, and maximal stimulation (from 2.5- to 3.5-fold over the control) was obtained after 12 h of exposure. The kd of the control and retinoic acid-treated cells was calculated to be 8.0 X 10(-10) M and 8.2 X -10 M, respectively. However, the number of unoccupied EGF binding sites increased from 0.98 X 10(4) to 2.28 X 10(4) per cell. Normal 3T3 cells would not respond to retinoic acid unless they were cultured in serum-containing medium. After 96 h of exposure, only a 50% enhancement of EGF binding was observed. The EGF receptor number of the untreated normal cells was calculated to be 1.82 X 10(4) per cell, twice the number expressed by untreated SV40-transformed cells. The increase of EGF receptor number caused by retinoic acid in SV40-transformed cells was blocked by either actinomycin D or cycloheximide treatment. These results indicated that SV40 transformation of BALB/c 3T3 cells altered the regulatory mechanism governing the complement of cell surface EGF receptors.

Cell Division↗
PubMed1987

Acidic heparin binding growth factor transiently activates adenylate cyclase activity in human adult arterial smooth muscle cells.

Acidic heparin binding growth factor (HBGF-1) is a potent mitogen for human adult arterial smooth muscle cells (SMC) in culture. Exposure of quiescent SMC to HBGF-1 resulted in a rapid and transient stimulation of the adenylate cyclase activity. Maximal stimulation (2-fold) was observed at 60 sec after growth factor exposure and there was a concurrent elevation of intracellular cAMP levels. GTP analogue was required indicating that the activation of this enzyme is mediated through G-proteins. The results suggest that part of the signal transduction pathway of HBGF-1 might be mediated by cAMP dependent protein kinase.

Adenylyl Cyclases↗
PubMed1987

Effect of Anordrin on serum levels of sex hormone binding globulin, caeruloplasmin and ovarian function.

Ten doses of 7.5 mg Anordrin were administered on alternate days from day 5 of the menstrual cycle to 20 women. Serum concentrations of both SHBG and CP were significantly increased after the fourth dose but the increases were minor compared to those produced by ethynyloestradiol. Two weeks after stopping Anordrin, serum concentrations of the proteins were still elevated in most women. Ovarian activity was studied in 8 women; serum oestradiol and progesterone concentrations indicated that ovulation occurred at the normal time in three women but was delayed for two weeks or more in the remaining five. The findings suggest that in humans, Anordrin acts as a weak oestrogen and may also have antioestrogenic activity.

Adult↗
PubMed1987

Sterol depletion reduces receptor-mediated low-density lipoprotein binding in NS-1 mouse myeloma cells.

NS-1 mouse myeloma cells, a cholesterol auxotrophic cell line with a lesion in the cholesterol biosynthetic pathway at the demethylation of lanosterol to C-29 sterol, were depleted of cholesterol by incubation in cholesterol-free medium for 24 to 48 h. The low-density lipoprotein receptor activities in untreated and in cholesterol-depleted cells were then compared. The cholesterol-depleted NS-1 cells consistently exhibited a 75 to 90% reduction in receptor-mediated low-density lipoprotein binding compared to untreated cells. The decline of the low-density lipoprotein binding of cholesterol-free medium-incubated NS-1 cells was prevented by addition of free cholesterol or its biosynthetic intermediate, demosterol, to the medium. The addition of lanosterol, an intermediate upstream to the lesion site in the cholesterol biosynthetic pathway, was completely ineffective. The results indicate that proper membrane cholesterol content is necessary for the maintenance of normal low-density lipoprotein receptor function in NS-1 cells.

Animals↗
PubMed1987

Transforming growth factor type beta specifically stimulates synthesis of proteoglycan in human adult arterial smooth muscle cells.

Myo-intimal proteoglycan metabolism is thought to be important in blood vessel homeostasis, blood clotting, atherogenesis, and atherosclerosis. Human platelet-derived transforming growth factor type beta (TGF-beta) specifically stimulated synthesis of at least two types of chondroitin sulfate proteoglycans in nonproliferating human adult arterial smooth muscle cells in culture. Stimulation of smooth muscle cell proteoglycan synthesis by smooth muscle cell growth promoters (epidermal growth factor, platelet-derived growth factor, and heparin-binding growth factors) was less than 20% of that elicited by TGF-beta. TGF-beta neither significantly stimulated proliferation of quiescent smooth muscle cells nor inhibited proliferating cells. The extent of TGF-beta stimulation of smooth muscle cell proteoglycan synthesis was similar in both nonproliferating and growth-stimulated cells. TGF-beta, which is a reversible inhibitor of endothelial cell proliferation, had no comparable effect on endothelial cell proteoglycan synthesis. These results are consistent with the hypothesis that TGF-beta is a cell-type-specific regulator of proteoglycan synthesis in human blood vessels and may contribute to the myo-intimal accumulation of proteoglycan in atherosclerotic lesions.

Adult↗
PubMed1986

Purified HDL-apolipoproteins, A-I and C-III, substitute for HDL in promoting the growth of SV40-transformed REF52 cells in serum-free medium.

The lipid-free apolipoproteins of human high density lipoprotein (HDL) have been assayed for their ability to substitute for native HDL in promoting the growth of a SV40-transformed REF52 cell line in serum-free medium. Total HDL-apolipoproteins (apoHDL) were found to mimic almost exactly the growth promoting effects of whole HDL. The apoHDL-associated growth promoting activity eluted from a Sephacryl S-200 column in two separate fractions coinciding with the protein peaks of apolipoprotein A-I and the C group of apolipoproteins. These two fractions, designated S-II and S-IV, respectively, acted additively in promoting WT1A cell growth when tested at saturating concentrations. The active component in the S-II fraction maximally stimulated WT1A cell growth at 40-60 micrograms/ml and was identified as apolipoprotein A-1 by NaDodSO4 polyacrylamide gel electrophoresis and affinity chromatography on anti-(apoA-I). The active component in the S-IV fraction was maximally active at 1-2 micrograms/ml and was identified as apolipoprotein C-III by DEAE ion exchange high pressure liquid chromatography and polyacrylamide gel electrophoresis (at pH 8.3) in 6 M urea. These results indicate that the growth promoting effect of HDL on WT1A cells is mediated via the HDL-apolipoproteins, A-I and C-III, and that the mechanism responsible does not necessarily involve their participation in the uptake (or utilization) of HDL-associated lipids.

Animals↗