Phosphorylation of highly purified growth hormone receptors by a growth hormone receptor-associated tyrosine kinase

We have shown previously that growth hormone (GH) promotes the phosphorylation of its receptor on tyrosyl residues (Foster, C. M., Shafer, J. A., Rozsa, F. W., Wang, X., Lewis, S. D., Renken, D. A., Natale, J. E., Schwartz, J., and Carter-Su, C. (1988) Biochemistry 27, 326-334). In the present study, we investigated the possibility that a tyrosine kinase is specifically associated with the GH receptor. GH-receptor complexes were first partially purified from GH-treated 3T3-F442A fibroblasts, a GH-responsive cell, by immunoprecipitation using anti-GH antiserum. 35S-Labeled proteins of Mr = 105,000-125,000 were observed in the immunoprecipitate from GH-treated cells labeled metabolically with 35S-amino-acids. These proteins were not observed in immunoprecipitates from cells not exposed to GH or when non-immune serum replaced the anti-GH antiserum, consistent with the proteins being GH receptors. GH receptors appeared to be phosphorylated, as evidenced by the presence of 32P-labeled bands, comigrating with the 105-125 kDa 35S-labeled proteins, in the immunoprecipitate of GH-treated cells labeled metabolically with [32P]Pi. When partially purified GH receptor preparation was incubated with [gamma-32P]ATP (7-15 microM) for 10 min at 30 degrees C in the presence of MnCl2, a protein of Mr = 121,000 was phosphorylated exclusively on tyrosyl residues. As expected for the GH receptor, this protein was not observed in immunoprecipitates when cells had not been treated with GH nor when non-immune serum replaced the anti-GH antiserum. GH-receptor complexes were also purified to near homogeneity by sequential immunoprecipitation with phosphotyrosyl-binding antibody followed by anti-GH antiserum. When cells were labeled metabolically with 35S-amino acids, the 35S label migrated almost exclusively as an Mr = 105,000-125,000 protein. This protein also incorporated 32P into tyrosyl residues when incubated in solution with [gamma-32P]ATP. These results show that highly purified GH receptor preparations undergo tyrosyl phosphorylation, suggesting that either the GH receptor itself is a tyrosine kinase or is tightly associated with a tyrosine kinase.     

Detection of desamido forms of purified bovine growth hormone

Tryptic peptide mapping and amino acid sequencing were used for the identification of desamido forms of bovine growth hormone. The major desamido forms of bovine growth hormone resulted from deamidation of asparagine in position 13, 148 and glutamine 140. These forms did not seem to be produced by prolonged treatment of bovine growth hormone in tryptic hydrolysis.     

Biological characterization of purified native 20-kDa human growth hormone

Because of the propensity of the 20-kDa variant of human growth hormone (GH) to aggregate with itself and with 22-kDa human GH, it has been difficult to prepare monomeric 20-kDa GH in highly purified form. This has been a major complicating factor in determining whether 20-kDa GH has a biological activity profile distinct from that of 22-kDa GH. In the present study, native 20-kDa GH was isolated from a human GH dimer concentrate and purified by a procedure that included column electrophoresis in agarose suspension as a final separation step. This procedure yielded highly purified monomeric 20-kDa GH, which was contaminated to an extent of less than 1% with 22-kDa GH, and which exhibited only a small degree of dimerization upon storage. The native 20-kDa GH was quite active in stimulating growth in hypophysectomized rats, when growth was assessed by body weight gain, longitudinal bone growth, the stimulation of sulfation of cartilage, and the elevation of serum IGF-1 level. However, in all of these growth assays, the 20-kDa GH was somewhat less active than the native 22-kDa GH to which it was compared; e.g., in the body weight gain and longitudinal bone growth assays, it had an estimated potency of 0.6 relative to the 22-kDa GH. The 20-kDa GH exhibited substantial diabetogenic activity when tested for the ability to raise fasting blood glucose concentration and to impair glucose tolerance in ob/ob mice. Also, the native 20-kDa GH had significant in vitro insulin-like activity, although its potency was approximately 20% that of the native 22-kDa GH to which it was compared. Thus, the biological activity profile of native 20-kDa GH differs from that of 22-kDa GH primarily in that insulin-like activity is markedly attenuated.     

Preparation of highly purified human somatotropin (growth hormone)

A method for preparation of highly purified human somatotropin on large-scale basis is described. Starting from deep-frozen pituitary gland, less time is needed to obtain highly purified hormone than with other published methods for preparation of human somatotropin. The hormone obtained in this fasion is chromatographically and electrophoretically homogeneous; it shows high biological and radioimmunological growth hormone activity and is free of other pituitary hormone activities. The effects of various experimental conditions upon aggregation of somatotropin are critically evaluated.     

Effect of growth hormone on fibrinogen synthesis

A method described by McFarlane (1963a) for the measurement of the absolute rate of synthesis of liver-made plasma proteins was used to show that, within a few hours of giving bovine growth hormone to rats, fibrinogen synthesis increased significantly without a change in albumin synthesis.     

Effect of human growth hormone on adrenal androgens in children with growth hormone deficiency

The effect of human growth hormone (hGH) on adrenal androgen secretion was assessed in 7 patients (5 males, 2 females) with GH deficiency but normal ACTH-cortisol function. Patients ranged in age from 9 5/12 to 14 8/12 years (median 12 years). Plasma concentrations of dehydroepiandrosterone-sulfate (DHEA-S) and urinary excretion of 17-ketosteroids (17-KS) and free cortisol were determined before, during short-term (2 U/day X 3) and after long-term (6 months) treatment with hGH. No significant change was noted in the plasma concentration or urinary excretion of steroids during the short-term administration of hGH. Despite a significant increase in growth velocity during 6 months of hGH therapy (8.2 vs. 4.5 cm/year, p less than 0.01), the plasma concentrations of DHEA-S and the urinary 17-KS and free cortisol levels were unchanged. These results fail to substantiate a role for hGH in the physiologic control of adrenal androgen secretion. Thus, the low plasma levels of adrenal androgens sometimes seen in GH-deficient patients are not due to the absence of GH per se.     

Effect of corticoid therapy on growth hormone secretion

Exogenous corticoids are known to be potent inhibitors of linear growth in children. We investigated the mechanisms underlying growth failure by evaluating growth hormone (GH) release during short-term high-dose prednisone treatment (40 mg/m2/day given orally in 3 divided doses) and 7 days after steroid withdrawal in 7 prepubertal children (4 males, 3 females, age range 3-12 years), affected by acute lymphoblastic leukemia. Patients also received weekly administrations of vincristine (1.5 mg/m2 i.v.), daunomycin (20 mg/m2 i.v.) and L-asparaginase (6,000 IU/m2 i.m.). Corticoid therapy suppressed GH secretion during deep sleep as well as in response to arginine, insulin and GH-releasing hormone (GHRH) administration. A significant recovery of GH responsiveness after drug discontinuation was observed during deep sleep (14.03 +/- 3.47 vs. 1.49 +/- 0.43 ng/ml, p less than 0.025) as well as in response to arginine (13.63 +/- 2.73 vs. 4.95 +/- 1.54 ng/ml, p less than 0.025) and GHRH (32.62 +/- 4.59 vs. 7.27 +/- 3.52 ng/ml, p less than 0.005) but not to insulin (7.12 +/- 0.88 vs. 4.47 +/- 0.96 ng/ml, p = NS). Insulin-like growth factor 1 levels during deep sleep (0.61 +/- 0.13 IU/ml/min) were found to be low in the course of steroid therapy and did not increase after drug withdrawal (0.41 +/- 0.07 IU/ml/min). Our preliminary data suggest that recovery of adrenergic response to insulin does not immediately follow corticosteroid discontinuation.     

Effect of growth hormone on rat liver N-acetyl-L-glutamate

Earlier studies have revealed, upon hypophysectomy, a specific increase in mitochondrial urea cycle enzymes, namely carbamyl phosphate synthetase and ornithine transcarbamylase. Administration of growth hormone to hypophysectomized rats brought these enzyme activities back to normal. Since growth hormone plays a role in the formation of citrulline and ultimately urea, in the present study its effect on the levels of N-acetyl-L-glutamate, an allosteric activator of carbamyl phosphate synthetase has been investigated. A significant increase in N-acetyl-L-glutamate concentration in rat liver on hypophysectomy and its reversal back to normal levels on growth hormone administration was reported. These results suggest that the lack of growth hormone tends to amplify urea production by the liver.     

Effect of potassium iodide on tumor growth

In the experiments on mice with primary tumors the authors studied the effect of iodine potassium on tumoral growth. It was shown that tumors became smaller in those animals who obtained iodine potassium. Possible mechanisms of this effect are being discussed.