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J E Hesketh

Publications and source records attributed to J E Hesketh.

At least 55 records · Page 3Linked to original sources
PubMed1992

Insulin receptor and glucose transporter mRNA expression in skeletal muscle of genetically obese Zucker rats.

Insulin resistance and defective glucose transport are associated with muscle tissue in the genetically obese Zucker rat and are accompanied by changes in the number of insulin receptors and the availability of glucose transporters. The present study was carried out to assess whether, in male Zucker rats at 10 weeks of age, these defects were reflected by changes in the levels of mRNAs for the insulin receptor and for the insulin responsive glucose transporter (GLUT-4). Total RNA was extracted from plantaris and soleus muscles and the levels of insulin receptor and GLUT-4 mRNAs and 18 S rRNA were determined by Northern hybridization and quantified by image analysis of the autoradiographs. A 50% increase in the level of insulin receptor mRNA was detected in both the plantaris and the soleus muscle from the obese rats compared to the lean rats. No change in the level of GLUT-4 mRNA was detected in the plantaris muscle although increases were observed in the soleus muscle from the obese rats.

Animals↗
PubMed1992

Expression of c-myc and c-fos in rat skeletal muscle. Evidence for increased levels of c-myc mRNA during hypertrophy.

The levels of c-myc and c-fos mRNA were investigated in rat skeletal muscle by Northern hybridization. During post-natal development in the rat, c-myc mRNA levels were similar at birth and at 7 and 21 days of age, but then declined at 90 days and were barely detectable at 1 year. c-fos mRNA levels followed this pattern of expression until 90 days, but showed a large increase at 1 year. Hypertrophy of soleus and plantaris muscles was induced either by severance of the tendon to the synergistic gastrocnemius (tenotomy) or by administration of the beta-adrenoceptor agonist clenbuterol. In both cases hypertrophy was associated with a rapid increase in c-myc mRNA levels. Following tenotomy the increase was both greater (8-fold) and more rapid (3 h) in soleus than in plantaris (2-3 fold, 12 h). Similar effects were observed during clenbuterol administration. Neither treatment caused any alteration in c-fos mRNA levels in the plantaris muscle. The results show that increased c-myc mRNA levels are an early event in the response of skeletal muscle to hypertrophic stimuli; it is argued that this occurs within the differentiated skeletal muscle fibres.

Aging↗
PubMed1992

The proto-oncogene c-myc is involved in cell differentiation as well as cell proliferation: studies on growth plate chondrocytes in situ.

A combination of immunocytochemistry and microdensitometry has been used to localize and quantify the expression of the proto-oncogene c-myc within chondrocytes of the proximal growth plates of rat and chick long bones. Although the c-myc protein was localized in all chondrocytes of the growth plate of both species the most intense staining was restricted to the proliferating and differentiating chondrocytes. These were identified by their ability to synthesize DNA (bromodeoxyuridine positive) and the presence of alkaline phosphatase activity, respectively. Species differences did exist with the c-myc concentration of the chick proliferating and differentiating chondrocytes being higher (128% and 240%, respectively) than the respective chondrocytes of the rat. The higher c-myc concentration in the chick proliferating chondrocytes paralleled the differences in the bromodeoxyuridine labelling index between the two species. In the rat, the concentration of c-myc protein present in the differentiating chondrocytes was 74% higher than in the respective proliferating chondrocytes, while in the chick it was 146% higher. The data not only provides further evidence for a role of the c-myc protein in cell proliferation but also suggests involvement of this protein in chondrocyte differentiation and/or hypertrophy.

Alkaline Phosphatase↗
PubMed1992

Alterations in the level of insulin receptor and GLUT-4 mRNA in skeletal muscle from rats fed a kidney bean (Phaseolus vulgaris) diet.

1. A decline in the level of circulating insulin was observed in rats fed a diet containing kidney bean. 2. Consumption of a diet containing kidney bean caused an increase in the level of mRNAs for the insulin receptor (327%) and GLUT-4 (185%) in the gastrocnemius muscle. In contrast there was only a small increase in the amount of actin mRNA (125%). Since the kidney bean-fed rats are euglycaemic the results suggest that insulin receptor and GLUT-4 mRNA levels are regulated in response to circulating insulin concentrations rather than glucose. 3. No increases in the level of insulin receptor and actin mRNA were evident in the soleus muscle of rats fed the diet containing kidney bean; however a decline was observed in the level of GLUT-4 mRNA. 4. It is proposed that a component of kidney beans, most likely the lectin phytohaemagglutinin, has systemic effects which lead to changes in expression of the insulin receptor and GLUT-4 genes and to the sensitivity of muscle to insulin.

Actins↗
PubMed1992

Stimulation of actin and myosin synthesis in rat gastrocnemius muscle by clenbuterol; evidence for translational control.

1. A transient rise in fractional rates of protein and actomyosin synthesis was observed in gastrocnemius muscles of rats fed clenbuterol for 1-2 days but the muscle RNA:protein ratio was unchanged, therefore protein synthesis per unit RNA (kRNA) also increased. 2. Myosin heavy and light chains and actin showed increased incorporation of [3H]phenylalanine at 2 days; these changes were proportional to increases in total protein synthesis. 3. The ratios actin mRNA:18S RNA and fast myosin heavy chain mRNA:18S RNA were unaffected by clenbuterol. 4. The data suggest that the clenbuterol-induced increase in muscle protein synthesis involves both translational control and increased tissue RNA.

Actins↗
PubMed1992

Changes in insulin-receptor mRNA levels in skeletal muscle and brown adipose tissue of weanling rats during fasting and refeeding.

Tissue-specific alterations in insulin sensitivity occur in response to fasting and refeeding, as part of the integrated adaptive mechanisms employed to adjust to major changes in nutritional status. In the present study the effects of fasting and refeeding on insulin-receptor, actin and myosin mRNA levels in skeletal muscle, and insulin-receptor and uncoupling-protein mRNA in brown adipose tissue of rats have been examined. Insulin-receptor mRNA levels increased markedly in both skeletal muscle and brown adipose tissue after a 40 h fast, the increase being greater in brown fat (8-fold) than in muscle (2-fold). On refeeding for 4 h, the insulin-receptor mRNA level in both tissues declined rapidly to control levels. An increase in insulin-receptor mRNA level was also observed in brown adipose tissue after a 16 h fast, although not in skeletal muscle. In contrast to the insulin-receptor mRNA, the level of the mRNA for the mitochondrial uncoupling protein declined markedly in brown adipose tissue during a 40 h fast. These results indicate that insulin-receptor mRNA levels are modulated in response to the alterations in nutritional status that occur during fasting and refeeding; this may reflect a nutritional influence on transcription of the receptor-protein gene.

Actins↗
PubMed1991

Insulin induces changes in the subcellular distribution of actin and 5'-nucleotidase.

An increase in the amount of actin associated with the plasma membrane was visualized by immunocytochemistry 5 min after the addition of insulin to Krebs II ascites tumour cells maintained in serum-free medium. At 1 h of incubation the rim of fluorescence at the plasma membrane as measured by image analysis, was about 30% more intense than in control cells indicating that the initial accumulation of actin at the plasma membrane was not of a transient nature. Since an increase in the total cellular actin content in ascites cells did not occur until after a lag period of about 15 min then the increased amount of actin at the plasma membrane seen at 5 min was attributed to a stimulation of the polymerization of actin. An increase in the association of actin at the plasma membrane was also observed in 3T3 fibroblasts in areas of membrane ruffling, while in some cells there was also increased actin accumulation in the perinuclear area. The putative plasma membrane-microfilament linking protein 5'-nucleotidase was shown to be present in association with actin in the cytoskeletal fraction. Incubation of cells with insulin resulted in a shift of the enzyme toward the bottom of gradients indicating association with actin filaments of a greater length. The results demonstrate that insulin causes a stimulation of actin polymerization and that the hormone can be therefore assigned a role in the regulation of the cytoskeleton.

3T3 Cells↗
PubMed1991

c-myc mRNA in cytoskeletal-bound polysomes in fibroblasts.

3T3 fibroblasts were treated sequentially with 25 mM-KCl/0.05% Nonidet P40, 130 mM-KCl/0.05% Nonidet P40 and finally with 1% Nonidet P40/1% deoxycholate in order to release free, cytoskeletal-bound and membrane-bound polysomes respectively. The membrane-bound fraction was enriched in the mRNA for the membrane protein beta 2-microglobulin, whereas the cytoskeletal-bound polysomes were enriched in c-myc mRNA. Actin mRNA was present in both free and cytoskeletal-bound polysomes. The results suggest that cytoskeletal-bound polysomes are involved in the translation of specific mRNA species.

Actins↗
PubMed1991

The characterization of free, cytoskeletal and membrane-bound polysomes in Krebs II ascites and 3T3 cells.

Polysomes from Krebs II ascites and 3T3 cells were separated into three populations by using a sequential extraction method. Free polysomes were released by using a combination of low salt (25 mM KCl) and NP-40 detergent in the lysis buffer. The cytoskeletal bound polysomes were subsequently released by raising the salt concentration to 130 mM and finally, polysomes bound to the membranes of the endoplasmic reticulum were extracted by the combined treatment with Triton X-100 and deoxycholate. The results presented here illustrate that the three polysome-containing fractions differ in many parameters such as polysome profiles, cytoskeletal components and phospholipid content. When polyA-containing mRNA was isolated from the three polysome fractions and translated in an in vitro system, some differences were observed in the patterns of proteins being synthesized.

Animals↗
PubMed1991

Immunohistochemical evidence for an association of ribosomes with microfilaments in 3T3 fibroblasts.

Ribosome distribution in cultured fibroblasts was investigated immunohistochemically using antibodies which recognize the 60S ribosomal subunit. After treatment of cells with buffer containing 25mM KCl and 0.05% Nonidet-P40 immunostained material was present in punctate patterns and linear arrays consistent with some ribosomes being associated with the cytoskeleton. Treatment of the cells with 130mM KCl caused loss of both the beaded lines of immunostaining and micro-filaments. Double immunostaining showed ribosomes to be closely associated with microfilaments.

Actin Cytoskeleton↗
PubMed1990

Insulin induces cell adhesion and normal flattened morphology in Krebs II ascites tumour cells.

Insulin induced Krebs II ascites cells to attach to the substratum and to adopt a flattened morphology associated with normal adhesion and movement. The changes were associated with a reorganization of cellular actin. The results show that insulin has important effects on cell structure and morphology. Insulin may thus be involved in the nutritional control of normal and malignant growth.

Actins↗
PubMed1990

Insulin and step-up conditions cause a redistribution of polysomes among free, cytoskeletal-bound and membrane-bound fractions in Krebs II ascites cells.

From 30 min to 1h of step-up conditions there was a redistribution of polysomes between free, cytoskeletal-bound and membrane-bound fractions such that more polysomes were recovered bound to the cytoskeleton and less in the free fraction. After 1h incubation with insulin there was a higher proportion of polysomes in the cytoskeletal fraction with a decrease occurring in the membrane-bound fraction. At 2h little change was observed in the presence of insulin while a large increase occurred in the cytoskeletal-bound fraction and a decrease in membrane-bound polysomes was seen in cells incubated in the absence of insulin. The results indicate that the proportions of polysomes in the three different fractions can be modulated by physiological stimuli, such as media replenishment and insulin.

Animals↗