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T Tsao

Publications and source records attributed to T Tsao.

27 records · Page 2Linked to original sources
PubMed1991

Amino acids regulate kidney cell protein breakdown.

Amino acids inhibit breakdown of long-lived intracellular proteins in some but not all tissues studied. Because no information is available relating to the effect of amino acids on kidney cell proteolysis, this study was conducted with cultured proximal-like opossum kidney (OK) cells and primary cultured rabbit proximal tubular cells in which long-lived cell proteins were labeled with carbon 14-labeled valine. These cultured cells were acutely deprived of amino acids; this was followed by a 57% to 66% increase in the proteolytic rate in OK cells and a 22% rate increase in the rabbit kidney cells. In cultured OK cells incubated in serum-free minimal essential medium containing 13 amino acids, proteolysis averaged 4.62% +/- 0.28%/2 hr and increased to 7.66% +/- 0.38%/2 hr when amino acids were deleted. Each amino acid was then added alone. Leucine, phenylalanine, and lysine had significant effects in inhibiting the deprivation response by 40%, 26%, and 22%, respectively. Leucine appears to inhibit proteolysis directly and not through its metabolites, since alpha-ketoisocaproate, the leucine transamination product, was without effect. Similarly, failure of tyrosine to inhibit proteolysis suggests a direct phenylalanine action. When leucine, phenylalanine, and lysine were simultaneously deleted from the incubation medium, the increase in proteolysis corresponded to 56% of the response after deletion of all amino acids. Thus to maximally affect proteolysis, amino acids, which on their own have little effect on protein breakdown, also appear to play a role. From this study we conclude that amino acids seem to play an important and direct role in the regulation of kidney epithelial cell protein breakdown.

Amino Acids↗
PubMed1990

Characterization of the basement membrane glycoprotein entactin synthesized in a baculovirus expression system.

A cDNA clone encoding the entire open reading frame of mouse entactin was constructed. This cDNA was inserted into Autographa californica multiple nuclear polyhedrosis virus and expressed in Spodoptera frugiperda, Sf9, insect cells. The recombinant entactin was produced in large quantities under the control of the polyhedrin promoter. Amino terminus sequence analysis indicated that the signal peptide in the preprotein was correctly cleaved. Polyclonal antibodies prepared against either the naturally occurring or recombinant entactin cross-reacted with both molecules in the native and denatured states. The recombinant molecule promoted cell attachment and exhibited a calcium- and temperature-dependent self-aggregation. These properties reflect those of the naturally occurring mouse molecule. Although entactin is an extracellular matrix component that is normally exocytosed, the vast majority of the molecules were localized inside the cell by immunoelectron microscopy where the molecules formed insoluble aggregates.

Animals↗
PubMed1990

Effect of bacitracin on retroendocytosis and degradation of insulin in cultured kidney epithelial cell line.

In an earlier study, we described the presence of a retroendocytotic pathway for insulin in a cultured kidney epithelial cell line. Derived from the opossum kidney (OK), these cells possess many features of proximal tubule epithelium, which is the major site of kidney insulin metabolism. We studied the interaction between the retroendocytotic and the degradative pathways with bacitracin as a pharmacological probe. Monolayers of OK cells were loaded with 125I-labeled insulin over 30 min, acid washed to remove membrane-bound insulin, then incubated in fresh medium for 60 min while the release of intracellular radioactivity was monitored. In experiments carried out in the presence of bacitracin (2 mM), there was a two-thirds increase in intracellular radioactivity at the end of the loading phase. Measurements made during the subsequent release phase showed that bacitracin reduced the release of degradation products. Thus, although controls released 72.1 +/- 8.1% of the internalized radioactivity as trichloroacetic acid (TCA)-soluble products, bacitracin-treated cells released 59.2 +/- 9.4% (P less than 0.02). In contrast, release of TCA-precipitable insulin increased from 15.2 +/- 4.6% in controls to 25.8 +/- 3.7% in bacitracin-treated cells (P less than 0.01). In separate experiments analyzed by gel-exclusion chromatography, 6.4 +/- 0.6% of radioactivity released from preloaded control cells into medium over 60 min was insulin sized compared to 29.7 +/- 1.4% in bacitracin-treated cells. High-performance liquid chromatography revealed that 61.5 +/- 3.5% of this insulin-sized material released from control cells preloaded with A14-insulin eluted as intact insulin and the remainder as unidentified intermediate degradation products.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Retroendocytosis of insulin in a cultured kidney epithelial cell line.

It has been generally accepted that in renal tubular epithelium endocytosed proteohormones are transported to lysosomes where they undergo complete hydrolysis. En route, as endosomal pH falls, the proteohormone uncouples from the endocytosed membrane binding site, which recycles to the cell surface. However, studies in other tissues have uncovered alternate intracellular pathways for proteins. One such pathway is retroendocytosis (endocytosis then exocytosis). To determine whether a retroendocytotic pathway exists for insulin in renal epithelium, a study was carried out with confluent monolayers of a proximal-like opossum kidney cell line that exhibits receptor-mediated endocytosis of insulin. Cells were preloaded with 125I-labeled insulin (4 X 10(-10) M) for 30 min, surface-bound insulin was then removed by acid washing, and over the next 60 min the release of intracellular radioactivity into the medium was monitored. At 37 degrees C, control cells released on average 7-15% of the intracellular radioactivity as intact insulin [trichloroacetic acid (TCA)-precipitable radioactivity] and approximately 62% as TCA-soluble degradation products. In the presence of 0.1 mM chloroquine (an acidotropic agent) the release of intact insulin increased approximately twofold while degradation fell by nearly one-half. With Sephadex G-50 chromatography we found that the released radioactivity included insulin-size material that increased in the presence of chloroquine. High-performance liquid chromatography revealed that 53 (controls) and 81% (chloroquine treatment) of this latter material consisted of intact insulin. We conclude that, in addition to a major degradative pathway, cultured kidney epithelial cells exhibit a retroendocytotic pathway for insulin. Chloroquine inhibits degradation and appears to divert insulin from the degradative into the retroendocytotic pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Dual trophic effects of the alpha 1-adrenergic receptor in cultured neonatal rat heart muscle cells.

The molecular signals regulating myocardial hypertrophy are unknown. We used a new model system to study this problem. Muscle cells from the neonatal rat ventricle were cultured in serum-free medium. Control cells did not change in size over time and did not show spontaneous contractile activity. Incubation with norepinephrine or epinephrine had two major trophic effects that developed over 1-2 days. The first was stimulation of muscle cell hypertrophy or increase in size. The second was induction of spontaneous contractile activity. The hypertrophic response was mediated through an alpha 1-adrenoceptor. The beating response required both alpha 1- and beta 1-adrenergic receptor stimulation. Alpha 1 stimulation alone produced enlarged cells that did not beat. Alpha 1 plus beta 1 stimulation induced contractile activity even when protein synthesis and hypertrophy were inhibited. Thus, the two alpha 1 responses could be dissociated, providing evidence for two independently-regulated cellular pathways for the dual alpha 1 trophic effects. One pathway leads to hypertrophy. The other, which requires concomitant beta 1 stimulation, controls the development of beating. Preliminary work raises the possibility that different products of inositol phospholipid hydrolysis might initiate the two alpha 1 trophic pathways. Other preliminary work suggests that the growth pathway is associated with the expression of specific genes and might reflect an action of the alpha 1-adrenoceptor on the cell nucleus. These studies define previously unsuspected trophic roles for the alpha 1-adrenergic receptor.

Animals↗
PubMed1985

Myocardial dysfunction in septic shock.

Myocardial depression is a major but poorly understood component of septic shock. This study investigates the morphologic and biochemical abnormalities associated with septic shock. Myocardial cells are incubated in normal and septic plasma in a nutrient-, oxygen-, pH-, electrolyte-, and temperature-controlled environment. Cells and media are tested for basal- and epinephrine-stimulated cyclic adenosine monophosphate (cAMP), lactic dehydrogenase (LDH), and creatine kinase. Electron microscopic studies are done at the end of incubation. Septic LDH and creatine kinase levels in the media are increased substantially, and septic cAMP levels are reduced significantly. Septic cells beat irregularly and arrest along with exhibiting abnormal electron microscopic structure. Septic myocardial dysfunction occurs independently of previously postulated causes that are controlled for in this experiment and therefore may be due to endogenously produced or accumulated toxic factor(s).

Animals↗
PubMedDate not supplied

Paradoxical body and kidney growth in potassium deficiency.

In the growing animal, K deficiency (KD) retards body growth, but paradoxically stimulates renal growth. If KD persists, interstitial infiltrates appear and eventually tubulointerstitial fibrosis develops. In patients with chronic KD, renal cysts may form and with time tubulointerstitial disease with renal failure develops. Since early in KD, kidney IGF-I levels increase and may be a cause of the renal hypertrophy, and as TGF-beta promotes hypertrophy and fibrosis, we examined the expression of these growth factors in chronic KD. Rats were given a KD diet or pair or ad-lib fed a normal K diet. After 21 days, KD rats weighed less than pair fed controls, while the kidneys were 49% larger Serum IGF-I and kidney IGF-I protein levels were depressed, as were IGF-I mRNA levels, and is largely attributable to decreased food intake. Kidney IGFBP-1 and TGF-beta mRNA levels were increased (p < 0.05). There was marked hypertrophy and adenomatous hyperplasia of outer medullary collecting ducts, hypertrophy of thick ascending limbs of Henle (TALH) and interstitial infiltrates. Both nephron segments stained strongly for IGF-I and IGFBP-1. Only the non-hyperplastic TALH was strongly TGF-beta positive. Interstitial infiltrates containing monocytes/macrophages were prominent. These findings are consistent with a sustained role for IGF-I in promoting the renal hypertrophy of KD and appear to be caused by local trapping of IGF-I by the over-expressed IGFBP-1. Localization of TGF-beta to the hypertrophied non-hypoplastic tubules containing IGF-I, suggests that TGF-beta may be acting to convert the proliferative action of IGF-I into a hypertrophic response. TGF-beta may also contribute to the genesis of the tubulointerstitial infiltrate. Finally, the reduced levels of serum IGF-1 levels may be a cause of the blunted body growth.

Angiotensin II↗