Bone marrow-transforming activity of linker insertion mutants of Abelson murine leukemia virus.

Two sets of mutants of the Abelson murine leukemia virus, generated by linker insertion mutagenesis of a cloned proviral DNA, were tested for their ability to transform bone marrow cultures in vitro. All the viruses retained an intact tyrosine kinase domain and were competent for transformation of NIH3T3 fibroblasts in culture. One series contained 12-bp linker insertions in the regions flanking the kinase domain, and the other contained frameshift mutations that truncated the gene product downstream of the kinase domain.

Isolation and characterization of flat revertant cell lines from A-MuLV-transformed fibroblasts.

Transformation of lymphoid and fibroblastic cells by Abelson murine leukemia virus (A-MuLV) is mediated by the viral tyrosine protein kinase. We do not yet know the important target proteins in the cell, the host proteins that modulate the kinase activity, or the host proteins involved in the signal-transduction pathway ultimately leading to altered patterns of cell growth. As a first step toward identifying these host proteins, we have isolated and characterized several flat revertant cell lines from transformed lines carrying v-abl.

Abelson murine leukemia virus induces platelet-derived growth factor-independent fibroblast growth: correlation with kinase activity and dissociation from full morphologic transformation.

Abelson murine leukemia virus (A-MuLV) encodes a single protein product, a tyrosine-specific protein kinase, whose activity is necessary for cell transformation by this retrovirus. Using a defined medium culture system, we demonstrate that transformation of NIH 3T3 fibroblasts by A-MuLV abrogates their normal requirement for platelet-derived growth factor (PDGF) for cell growth. Analysis of constructed insertional mutant viruses revealed an absolute correlation between A-MuLV-encoded tyrosine kinase activity and PDGF-independent fibroblast growth.

Insertional mutagenesis of the Abelson murine leukemia virus genome: identification of mutants with altered kinase activity and defective transformation ability.

A library of Abelson murine leukemia virus (A-MuLV) proviral DNAs with 12- or 6-base-pair (bp) insertional mutations was constructed. The 29 mutations characterized spanned the entire protein-coding region of the provirus. We tested the effects of these mutations both on the kinase activity of the gag-abl fusion protein encoded by the provirus and on the ability of the provirus to transform NIH 3T3 fibroblasts.

Insulin stimulates phosphorylation of a 120-kDa glycoprotein substrate (pp120) for the receptor-associated protein kinase in intact H-35 hepatoma cells.

The insulin receptor possesses protein kinase activity, which may play a role in mediating insulin action. Recently, we have identified a glycoprotein (pp120) in rat liver plasma membranes that is phosphorylated by the solubilized insulin receptor in a cell-free system. We now report that insulin stimulates phosphorylation of pp120 in intact H-35 cells.

Tissue distribution and subcellular localization of an endogenous substrate (pp 120) for the insulin receptor-associated tyrosine kinase.

The beta-subunit of the insulin receptor possesses a tyrosine-specific protein kinase activity which may play a role in coupling insulin binding to insulin action. Previously, we have identified a substrate for the receptor-associated protein kinase in a cell-free system. This endogenous substrate (pp120), which appeared to be a glycoprotein with an apparent mol wt of 120,000, was detected in rat liver microsomes.

Characterization of insulin-like growth factor I-stimulated tyrosine kinase activity associated with the beta-subunit of type I insulin-like growth factor receptors of rat liver cells.

We previously reported that insulin-like growth factor I (IGF-I) stimulates the phosphorylation of a Mr 98,000 protein thought to be the beta-subunit of the type I IGF receptor of BRL-3A2 rat liver cells, as well as phosphorylation of the exogenous tyrosine-containing substrate poly(Glu,Tyr), 4:1. The present study provides additional evidence that the type I IGF receptor possesses intrinsic tyrosine kinase activity and characterizes the properties of this receptor kinase. IGF-I stimulates receptor phosphorylation and phosphorylation of poly(Glu,Tyr), 4:1, by lectin-purified receptor preparations with the same concentration dependence; half-maximal stimulation was observed with approximately 3 nM IGF-I and approximately 3-fold higher concentrations of insulin.

An endogenous substrate for the insulin receptor-associated tyrosine kinase.

Insulin binding to its receptor stimulates a tyrosine-specific protein kinase. This enzyme phosphorylates the insulin receptor, as well as a variety of exogenous substrates in vitro. In the present studies, we have identified an endogenous substrate for the insulin receptor-associated kinase.

Use of tyrosine-containing polymers to characterize the substrate specificity of insulin and other hormone-stimulated tyrosine kinases.

Synthetic copolymers containing tyrosine residues were used to characterize the substrate specificity of the insulin receptor kinase and compare it to tyrosine kinases stimulated by epidermal growth factor, insulin-like growth factor-1 and phorbol ester. In partially purified receptor preparations from eight different tissues insulin best stimulated (highest V) phosphorylation of a random copolymer composed of glutamic and tyrosine residues at a 4:1 ratio (Glu/Tyr, 4:1). The insulin-stimulated phosphorylation of this polymer was highly significant also in receptor preparations from fresh human monocytes, where insulin binding and autophosphorylation were difficult to detect.

Proton-translocating adenosinetriphosphatase in rough and smooth microsomes from rat liver.

Rat liver smooth and rough microsomal membranes exhibit an ATP-dependent H+ transport which can be inhibited by sulfhydryl reagents and dicyclohexylcarbodiimide but is resistant to oligomycin. On the basis of inhibitor sensitivities and substrate specificities, this H+ pump was found to be different from that of mitochondria, lysosomes, gastric H+-K+-ATPase, and yeast plasma membrane H+-ATPase but to resemble that of endocytic vesicles and the H+ pump responsible for urinary acidification. The transport process is accelerated by valinomycin in the presence of potassium, suggesting that it is an electrogenic pump.

The role of antireceptor antibodies in stimulating phosphorylation of the insulin receptor.

Four polyclonal antisera directed against the insulin receptor were tested for their capability to activate the tyrosine-specific protein kinase associated with the receptor. All four antisera were shown to inhibit insulin binding to the receptor in cultured human lymphoblastoid cells and to stimulate lipogenesis in isolated rat adipocytes. Although two antisera (B-d, B-8) stimulated the activity of the tyrosine kinase of partially purified receptor preparations from rat liver, two other antisera (B-2 and B-10) failed to do so.

The insulin receptor of rat brain is coupled to tyrosine kinase activity.

Insulin receptors from rat brain were studied for receptor-associated tyrosine kinase activity. In solubilized, lectin-purified receptor preparations, insulin stimulated the phosphorylation of the beta subunit of its receptor as well as of exogenous substrates. Phosphoamino acid analysis of casein phosphorylated by these preparations revealed that 32P incorporation occurred predominantly on tyrosine residues.

Insulin-like growth factor-I (IGF-I) stimulates tyrosine kinase activity in purified receptors from a rat liver cell line.

Solubilized, lectin-purified receptor preparations from BRL 3A2 rat liver cells are rich in Type I and Type II IGF receptors, but possess few insulin receptors. High concentrations of IGF-I or insulin stimulate phosphorylation of a Mr congruent to 98K membrane protein in these preparations. Phosphorylation of a synthetic polymer of tyrosine and glutamic acid was stimulated by IGF-I greater than IGF-II congruent to insulin.

The insulin-stimulated receptor kinase is a tyrosine-specific casein kinase.

Insulin stimulates a kinase that phosphorylates tyrosines in the insulin receptor; this kinase is tightly associated with the insulin receptor itself. We now show that the insulin-stimulated casein kinase, present in solubilized, lectin-purified receptor preparations from rat liver, is indistinguishable from the insulin receptor kinase. As with phosphorylation of the insulin receptor, insulin selectively enhanced by 2-3-fold the phosphorylation of tyrosines in casein.

Insulin-stimulated phosphorylation of the insulin receptor precursor.

The alpha and beta subunits of the insulin receptor, Mr = 135K and 95K, appear to be synthesized via a single polypeptide precursor of Mr = 190K. We have investigated whether insulin stimulates the phosphorylation of this proreceptor, as is the case with mature receptor. Rat liver endoplasmic reticulum membranes were solubilized in Triton X-100 and chromatographed sequentially on wheat-germ agglutinin-agarose and lentil lectin-agarose columns.

Triiodothyronine and thyroxine content of desiccated thyroid tablets.

Triiodothyronine (T3) and thyroxine (T4) were measured by radioimmunoassay in Pronase hydrolysates of four lots each of 1- and 2-grain tablets of desiccated thyroid (Thyroid, Armour) and thyroglobulin (Proloid, Warner-Chilcott). The methodology used was verified by studies of tablets containing known quantities of T4 and T3. One grain of desiccated thyroid contained 12 +/- 1 and 64 +/- 3 microgram (mean +/- SD) of T3 and T4 per tablet, respectively (T4/T3 molar ratio, 4.