Biomedical subjects

G S Martin

Publications and source records attributed to G S Martin.

At least 91 records · Page 5Linked to original sources

PubMed1988

Platelet tyrosine-specific protein phosphorylation is regulated by thrombin.

Intact human platelets, terminally differentiated cells with no growth potential, were found to possess unusually high levels of tyrosine-specific protein phosphorylation. The physiological platelet activator thrombin transiently elevated platelet phosphotyrosine content, apparently through stimulation of one or more tyrosine-specific protein kinases. Immunoblotting with antiphosphotyrosine antiserum showed that thrombin caused dramatic changes in the tyrosine phosphorylation of a number of individual protein bands and that these changes occurred in three distinct temporal waves. Most but not all of the protein bands phosphorylated at tyrosine in response to thrombin were also tyrosine phosphorylated in response to chilling or the combination of ionophore A23187 and tetradecanoylphorbol acetate. Thrombin stimulated the phosphorylation of the tyrosine kinase pp60c-src, primarily at Ser-12 and Tyr-527, although the effects of these phosphorylations on platelet pp60c-src function were not apparent. Together, these results suggest that tyrosine-specific protein kinases of uncertain identity are involved in signal transduction in platelets.

Adult↗

PubMed1987

Absorption and metabolism of vitamin K in Swiss 3T3 mouse fibroblasts--a model system for study of vitamin K absorption and metabolism.

The vitamin K cycle previously described in liver has been demonstrated in Swiss 3T3 mouse fibroblasts. Vitamin K epoxide and gamma-carboxyglutamic acid were isolated from the cells and chemically characterized. Menaquinone (MK4) is also metabolized to its epoxide and vitamin K epoxide is reduced to vitamin K in these cells. Thus Swiss 3T3 mouse fibroblasts provide a useful model system for the study of vitamin K metabolism. Possible functions of the vitamin K-dependent protein(s) in fibroblasts are discussed.

1-Carboxyglutamic Acid↗

PubMed1987

Arthroscopic surgery for the treatment of osteochondral chip fractures in the equine carpus.

The technique and results of arthroscopic surgery for the removal of osteochondral fragments from 1,000 carpal joints in 591 horses are reported. Of the 591 horses, 580 were racehorses (including 349 Quarter Horses and 220 Thoroughbreds). The distal aspect of the radial carpal bone was the most commonly affected site, followed by the proximal aspect of the intermediate carpal bone and distolateral aspect of the radius. More than one carpal joint was simultaneously operated on in 58.9% of the Quarter Horses and in 37.4% of the Thoroughbreds. Marked differences in the amount of damage were noted at arthroscopy, compared with what was observed on radiography. Arthroscopic surgery was an effective technique for removing the osteochondral fragments as well as for treating other lesions. The overall functional ability as well as cosmetic appearance of the limbs were excellent. There was no postoperative intra-articular infection. Postsurgical follow-up information was obtained for 445 racehorses. After surgery, 303 (68.1%) raced at a level equal to or better than their preinjury level, 49 (11.0%) had decreased performance or still had problems referable to the carpus, 23 (5.2%) were retired without returning to training, 28 (6.3%) sustained another chip fracture, 32 (7.2%) developed other problems, and 10 (2.2%) sustained collapsing slab fractures while racing. When horses were separated into 4 categories of articular damage, the performance in the 2 most severely affected groups was significantly inferior. One hundred thirty-three of 187 horses with grade-1 damage (71.1%), 108 of 144 with grade-2 damage (75.0%), 41 of 77 with grade-3 damage (53.2%), and 20 of 37 horses with grade-4 damage (54.1%) returned to racing at a level equal to or better than their preinjury level. In examining the prognosis relative to site of the fracture, the prognosis for both breeds was worst with lesions of the third carpal bone.

Animals↗

PubMed1987

A conserved domain regulates interactions of the v-fps protein-tyrosine kinase with the host cell.

All cytoplasmic protein-tyrosine kinases (PTKs) share a noncatalytic domain, termed SH2, which comprises approximately 100 residues located immediately N-terminal to the kinase domain. A linker in the AX9m mutant of Fujinami avian sarcoma virus (FSV) introduces a dipeptide insertion into the SH2 domain of the P130gag-fps PTK, which abolishes its ability to transform Rat-2 cells. However, at 36 degrees C AX9m FSV elicits focus formation and agar colony formation in infected chicken embryo fibroblasts (CEF) with single hit kinetics. At 41.5 degrees C AX9m FSV is nontransforming for CEF, and the mutant is therefore both host and temperature dependent for transforming activity. Both in vitro and in vivo, the specific kinase activity of AX9m FSV P130gag-fps, measured by autophosphorylation and phosphorylation of exogenous substrates, correlated with transforming activity. The consequences of the AX9m mutation for enzymatic function and transforming activity therefore depend on the cellular environment in which the altered v-fps protein is expressed. We conclude that the SH2 domain directs the interaction of the P130gag-fps catalytic domain with cellular proteins such as substrates for phosphorylation or regulators of kinase activity important for its transforming ability.

Animals↗

PubMed1987

Correlation between anion gap, blood L lactate concentration and survival in horses.

Blood L lactate concentration and anion gap were measured in 32 horses suspected of having metabolic acidosis. There was good linear correlation between these variables (r = 0.90791, P less than 0.0001) and both were good prognostic indicators. Anion gap was a good indicator of the presence but not the severity of L lactic acidosis and was a slightly better prognostic indicator. The ability to predict survival was not improved by the measurement of L lactate in addition to anion gap.

Acid-Base Equilibrium↗

PubMed1987

Phosphorylation of talin at tyrosine in Rous sarcoma virus-transformed cells.

The cytoskeletal protein talin was found to undergo enhanced phosphorylation at tyrosine residues in chicken embryo fibroblasts following transformation by Rous sarcoma virus. An increase in the tyrosine phosphorylation of talin was also observed within 6 h in cells infected by the temperature-sensitive mutant tsNY68 after a shift from the nonpermissive to the permissive temperature. The overall extent of phosphorylation was 0.07 mol of phosphate per mol of talin and was not appreciably altered by transformation. In uninfected cells talin was shown to be phosphorylated at multiple sites by tryptic peptide mapping. Following transformation most of these sites remained phosphorylated, to the same or to a lesser extent, while novel, phosphotyrosine-containing phosphopeptides appeared. Talin was phosphorylated at tyrosine in cells infected by Rous sarcoma virus mutants which induce altered or partial transformation morphologies; thus the increased phosphorylation of talin at tyrosine occurred irrespective of the morphology induced. Transformation by Y73 also induced elevated levels of phosphotyrosine in talin, whereas transformation by the avian erythroblastosis and Fujinami sarcoma viruses did not.

Amino Acids↗

PubMed1986

Protein-tyrosine kinase activity in Saccharomyces cerevisiae.

Saccharomyces cerevisiae was examined for tyrosine kinase activity in vitro because this organism offers molecular and genetic approaches for analyzing the role of tyrosine phosphorylation in cellular growth control that are unavailable in higher eukaryotes. Yeast extracts phosphorylated a random copolymer (glutamic acid:tyrosine, 80:20) at tyrosine in a reaction that was linear with respect to time and protein concentration. In the absence of added copolymer, phosphotyrosine was 0.1 percent of the total phosphoamino acids labeled with [gamma-32P]adenosine triphosphate in endogenous yeast proteins. However, specific activities of these reactions were low (approximately 1 percent of those in extracts of chick embryo fibroblasts). Lack of significant incorporation of label from [alpha-32P]adenosine triphosphate into the copolymer or endogenous yeast proteins demonstrated that nucleotide interconversion, adenylylation, and subsequent hydrolysis could not account for the generation of phosphotyrosine observed.

Intercellular Signaling Peptides and Proteins↗

PubMed1986

The tyrosine phosphorylation substrate p36 is developmentally regulated in embryonic avian limb and is induced in cell culture.

The 36-kD protein-tyrosine kinase substrate p36 has been variously postulated to be involved in membrane-cytoskeletal interactions, membrane traffic, and the regulation of phospholipase A2, and its phosphorylation may play some role in malignant transformation by avian sarcoma viruses. Because embryonic tissues are resistant to transformation by avian sarcoma viruses, we have examined the expression of p36 in the developing avian embryonic limb. The level of p36 increased progressively from day 5 to day 14 of development. It was largely absent from day-5 mesenchyme, and was induced during the differentiation of mesenchymal cells into connective tissue and cartilage, but was not induced in differentiating muscle. In contrast, p36 was detected in ectodermal cells at all developmental stages examined. When day-5 limbs were dissociated and cultured, p36 was induced in all adherent cells, beginning at 2-4 h after plating, and reaching levels comparable to those observed with intact day-14 limb tissue within 48 h. The accumulation of p36 in culture was dependent on substratum adherence, suggesting that its stability is regulated by cell attachment or spreading. These findings are consistent with a structural or mechanical role for p36.

Age Factors↗

PubMed1986

The erbB gene and the EGF receptor.

The epidermal growth factor (EGF) receptor is a plasma membrane glycoprotein. It contains four distinct segments: an N-terminal EGF binding domain which is exposed at the cell surface; a short transmembrane segment; a cytoplasmic domain with protein-tyrosine kinase activity; and a C-terminal regulatory segment. Binding of EGF to the external domain of the receptor activates the protein-tyrosine kinase activity of the receptor, and this elevated kinase activity is presumed to be involved in the activation of cell growth. The v-erbB transforming gene of avian erythroblastosis virus is derived, by retroviral transduction, from the gene (c-erbB) which encodes the avian EGF receptor. The transforming capacity of v-erbB appears to result from truncation of the receptor. In erythroid cells, truncation of the N-terminal ligand binding domain is sufficient for transformation, whereas in fibroblasts removal of an additional C-terminal segment is required for transformation. The EGF receptor is subject to complex regulatory controls, including ligand activation, downregulation by internalization, autophosphorylation and autoregulation and transmodulation involving phosphorylation by kinase C. This review is centered around the hypothesis that the transforming capacity of the truncated v-erbB gene product results from a loss in sensitivity to regulators and the consequent activation of protein kinase activity.

Alpharetrovirus↗

PubMed1986

Cross-sectional area of the aditus laryngis and rima glottidis before and after transection of the left recurrent laryngeal nerve in the horse.

The ventral-to-dorsal height of the rima glottidis was measured from lateral pharyngeal radiographs after correction for magnification. The rima glottidis height was used to enlarge accurately endoscopic photographs of 5 horses taken before and after transection of the left recurrent laryngeal nerve. Areas of the rima glottidis and aditus laryngis were measured, using a computerized digitizer. Mean area of the aditus laryngis was 1,908 mm2 before neurectomy and 1,346 mm2 after neurectomy (P = 0.025). Mean area of the rima glottidis was 1,198 mm2 before neurectomy and 805 mm2 after neurectomy (P = 0.025). Mean width of the rima glottidis was 31 mm before neurectomy and 20 mm after neurectomy (P = 0.001). Significant differences were not found between the pre- and postneurectomy heights of the rima glottidis.

Animals↗

PubMed1985

Uterine rupture as a postpartum complication in two mares.

Uterine rupture was diagnosed in 2 postpartum mares with hemorrhagic vaginal discharge. Both mares had abdominal pain, as evidenced by pawing, kicking at the abdomen, or attempting to roll. Peritoneal fluid analysis was useful in establishing a diagnosis. One mare had many RBC in the peritoneal fluid and was anemic; this mare was managed medically with oxytocin, antibiotics, and blood transfusion. The mare was able to raise her foal to weaning age. The second mare had many RBC, degenerate neutrophils, and intracellular and extracellular bacteria in peritoneal fluid. Surgical repair of the uterus was performed, and the mare was treated for peritonitis. The mare later became pregnant.

Animals↗

PubMed1985

pp60src-dependent protein phosphorylation in membranes from Rous sarcoma virus-transformed chicken embryo fibroblasts.

The Rous sarcoma virus (RSV)-transforming protein, pp60src, is a plasma membrane-associated tyrosine-specific protein kinase. A 36,000-Da cellular polypeptide (p36) which is phosphorylated at tyrosine in RSV-transformed chicken embryo fibroblasts (RSV-CEF) is also plasma membrane associated. To determine if p36 is directly phosphorylation and kinase activity in situ in the plasma membrane, src-dependent protein phosphorylation in membranes isolated from RSV-CEF has been characterized. These membrane preparations contained high ATPase and phosphoprotein phosphatase activities; but when sufficient concentrations of [gamma-32P]ATP were used, the phosphorylation of pp60src and the phosphorylation of p36 were linear for 1 min or more, and the initial rates of phosphorylation could therefore be determined. In membranes from RSV-CEF pp60src and p36 became phosphorylated predominantly at tyrosine, while in membranes from uninfected cells p36 was phosphorylated at low levels at serine. When membranes from RSV-CEF were preincubated with tumor-bearing rabbit (TBR) serum, the IgG became phosphorylated while the phosphorylation of p36 was inhibited, suggesting that p36 is directly phosphorylated by pp60src. Phosphorylation of pp60src, p36, and TBR-IgG was dependent on growth temperature in membranes from cells infected by a temperature-sensitive mutant, tsNY68, although some dependence on growth temperature was observed even with membranes from wild-type RSV-infected cells. However, at the nonpermissive temperature, tsNY68 pp60src retained 20-40% of its kinase activity, providing supporting for the proposal (B. M. Sefton, T. Hunter, and K. Beemon (1980, J. Virol, 33, 220-229) that transformation may result from a small quantitative change in pp60src activity. The phosphorylation of pp60src and its kinase activity were not coordinately affected by growth temperature or mutations within src, indicating that different factors affect the phosphoacceptor capacity and kinase activity of the protein.

Animals↗

PubMed1985

Protein phosphorylation at tyrosine is induced by the v-erbB gene product in vivo and in vitro.

The v-erbB gene product of avian erythroblastosis virus (AEV) has extensive homology with the receptor for epidermal growth factor (EGF). We report here that chicken embryo fibroblasts (CEF) transformed by AEV show enhanced tyrosine phosphorylation of a number of cellular polypeptides, including the 36 kd protein, which is phosphorylated in avian sarcoma virus-transformed fibroblasts, and the 42 kd protein, which is phosphorylated in mitogen-stimulated cells. CEF infected by AEV mutants with deletions in v-erbA showed enhanced tyrosine phosphorylation, whereas CEF infected by mutants with deletions in v-erbB did not. When membranes from AEV-transformed cells were incubated with gamma-32P-ATP, both the v-erbB gene product and the 36 kd cellular protein became phosphorylated at tyrosine. These results indicate that the v-erbB protein induces tyrosine phosphorylation in vivo and in vitro, and suggest that, like the EGF receptor, it possesses tyrosine-specific protein kinase activity.

Alpharetrovirus↗

PubMed1985

Arthroscopic anatomy of the intercarpal and radiocarpal joints of the horse.

Arthroscopic anatomy of the equine intercarpal and radiocarpal joints was documented in six cadaver limbs and on observations made during surgical treatment of horses with carpal osteochondral fractures. Instrument positions and arthroscopic visualisation were recorded. The cadaver limbs were dissected and iatrogenic lesions recorded. A single arthroscopic portal examination was adequate in both joints; however, a second arthroscopic portal improved visualisation. The intercarpal joint was more easily examined than the radiocarpal joint because of anatomical differences. Iatrogenic lesions were associated with failure of joint capsule distention during penetration.

Animals↗

PubMed1984

Long-term results and complications of proximal interphalangeal arthrodesis in horses.

A retrospective study was made of 21 horses in which proximal interphalangeal arthrodesis had been performed. The right hindlimb was the most often affected (52%). Acute trauma was the most common reason for performing the surgery (62%). Follow-up data were obtained from the owners regarding return to serviceability . When available, follow-up radiographs and clinical examinations were reviewed. Of the 20 horses on which follow-up information was available, 16 were serviceable . Of the horses in which a hindlimb was arthrodesed , 86% were serviceable , whereas 67% of the horses affected in the forelimb were serviceable . An average of 1 year was required for return to serviceability . Follow-up radiography of forelimb cases revealed radiographic changes consistent with navicular disease, distal interphalangeal degenerative joint disease, and a bony exostosis off the dorsal surface of the third phalanx; however, these radiographic changes did not correlate well with the owner's assessment of serviceability . Follow-up clinical examination of forelimb cases revealed 2 horses in which the toe came off the ground during weight bearing.

Animals↗

PubMed1984

The role of protein phosphorylation at tyrosine in transformation and mitogenesis.

In cells transformed by avian sarcoma viruses or stimulated by growth factors, certain polypeptides become phosphorylated at tyrosine residues. It is not known if these cellular polypeptides are phosphorylated directly by the tyrosine-kinase activities which are associated with the viral transforming proteins and with growth factor receptors. It is also not clear if phosphorylation of these polypeptides is required for viral transformation or the response to growth factors. We describe here some observations which bear on these questions and discuss possible future approaches.

Alpharetrovirus↗

PubMed1984

Cellular localization of the transforming protein of wild-type and temperature-sensitive Fujinami sarcoma virus.

Fujinami sarcoma virus (FSV) encodes a 140,000-dalton transforming protein, P140, which contains gag- and fps-specific sequences. The cellular localization of this protein was examined by fractionation of [35S]methionine-labeled, FSV-infected chicken embryo fibroblasts. In homogenates of cells infected by wild-type, temperature-resistant FSV prepared in either hypotonic or isotonic buffer, 60 to 80% of the P140 was particulate. Isopycnic separation on discontinuous sucrose gradients indicated that the majority of the particulate P140 was present in a light membrane fraction enriched for plasma membranes. Much of the particulate P140 could be solubilized by the addition of 0.6 M salt to a postnuclear supernatant, suggesting that P140 is not an integral membrane protein. Particulate P140 may be associated with membranes either directly as a peripheral membrane protein or indirectly via cytoskeletal elements. In cells infected by mutants of FSV temperature sensitive for cellular transformation, most of the P140 is particulate at the permissive temperature, whereas most is soluble at the nonpermissive temperature; this change in distribution is not a secondary consequence of the change in cellular phenotype, since it also occurs in nonconditionally transformed cells doubly infected with temperature-sensitive FSV and wild-type Rous sarcoma virus. The movement of P140 from the particulate to the soluble fraction occurs rapidly when cells infected by temperature-sensitive FSV are shifted from the permissive to the nonpermissive temperature. Furthermore, P140 moves from the soluble to the particulate fraction, although somewhat more slowly, when cells are shifted from the nonpermissive to the permissive temperature. These observations suggest that the association of P140 with plasma membranes or the cytoskeleton may play a role in transformation by FSV.

Animals↗

PubMed1984

Cellular localization of c-fps gene product NCP98.

We compared the intracellular location of the product of the c-fps proto-oncogene, NCP98, with that of its viral homolog P140, the transforming protein of Fujinami sarcoma virus. Using the technique of biochemical subcellular fractionation, we determined that 60 to 90% of NCP98 and its associated kinase activity are in the soluble fraction of a chicken myeloblast cell line. This fractionation behavior differs from that of P140, which is found predominantly in the particulate fraction, both in Fujinami sarcoma virus-infected chicken embryo fibroblasts and in Fujinami sarcoma virus-infected myeloblasts. The fractionation behavior of NCP98 is, however, similar to that of the P140 encoded by a temperature-sensitive strain of Fujinami sarcoma virus in infected cells grown at the nonpermissive temperature. The absence of gag sequences from NCP98 is not responsible for the difference in fractionation behavior: the v-fps transforming protein of strain F36, P91, which lacks gag sequences, is also predominantly particulate. These results indicate that association with cellular structural components correlates with the transforming activity of proteins containing fps sequences.

Animals↗