Toshio Tsushima

Constitutive tyrosine phosphorylation of ErbB-2 via Jak2 by autocrine secretion of prolactin in human breast cancer.

Overexpression of the oncogene for ErbB-2 is an unfavorable prognostic marker in human breast cancer. Its oncogenic potential appears to depend on the state of tyrosine phosphorylation. However, the mechanisms by which ErbB-2 is constitutively tyrosine-phosphorylated in human breast cancer are poorly understood. We now show that human breast carcinoma samples with ErbB-2 overexpression have higher proliferative and metastatic activity in the presence of autocrine secretion of prolactin (PRL). By using a neutralizing antibody or dominant negative (DN) strategies or specific inhibitors, we also show that activation of Janus kinase Jak2 by autocrine secretion of PRL is one of the significant components of constitutive tyrosine phosphorylation of ErbB-2, its association with Grb2 and activation of mitogen-activated protein (MAP) kinase in human breast cancer cell lines that overexpress ErbB-2. Furthermore, the neutralizing anti-PRL antibody or erbB-2 antisense oligonucleotide or DN Jak2 or Jak2 inhibitor or DNRas or MAP kinase kinase inhibitor inhibits the proliferation of both untreated and PRL-treated cells. Our results indicate that autocrine secretion of PRL stimulates tyrosine phosphorylation of ErbB-2 by Jak2, provides docking sites for Grb2 and stimulates Ras-MAP kinase cascade, thereby causing unrestricted cellular proliferation. The identification of this novel cross-talk between ErbB-2 and the autocrine growth stimulatory loop for PRL may provide new targets for therapeutic and preventive intervention of human breast cancer.

Effect of nicotinic acid administration on plasma growth hormone concentrations.

Summary Serial plasma glucose, NEFA, and HGH concentrations were measured in normal male subjects following saline injection (Group 1, 9 cases), nicotinic acid injection (Group 2, 5 cases), and nicotinic acid plus heparin injection (Group 3, 4 cases) for 180 minutes. There was no appreciable change of plasma glucose in all groups. In Group 1 there was no significant change of plasma, NEFA and HGH. In Group 2, plasma NEFA showed an initial decrease followed by the secondary rise at 180 minutes, and plasma HGH showed a marked rise at 120 minutes and/or at 180 minutes. In Group 3, plasma NEFA did not show significant reduction and plasma HGH showed no significant changes. From the results obtained, it was suggested that the lowering of plasma NEFA levels by nicotinic acid administration can stimulate the secretion of HGH, and an assumption was made that plasma NEFA could be at least one of the factors in regulating HGH secretion. It was also suggested that plasma HGH may, at least in part, participate in inducing the secondary rise of plasma NEFA following the injection of nicotinic acid.

Hypothalamic growth hormone-releasing factor (GRF) participates in the negative feedback regulation of growth hormone secretion

Effects of growth hormone (GH) excess on immunoreactive hypothalamic GH-releasing factor (GRF) and somatostatin (SRIF) were studied in rats. Hypothalamic GRF content significantly reduced after 7-day daily treatment with 160 micrograms of rat GH or after inoculation of GH-secreting rat pituitary tumors, MtT-F4 for 9 or 13 days and GH3 for 3 months. Basal and 59 mM K+-evoked release of GRF from incubated hypothalami diminished, more than the content, by 43-51% in MtT-F4 tumor- or by 67-83% in GH3 tumor-bearing rats. In contrast, there was a small but significant increase in content or release of SRIF in rats harboring the GH3 or MtT-F4 tumor, respectively. These results indicate the existence of a negative feedback loop via hypothalamic GRF as well as SRIF in control of GH secretion.

Effect of Heparin Administration on Plasma Growth-Hormone Concentrations

Summary Plasma HGH, FFA, glucose, and a-amino nitrogen levels were determined in seven young men after heparin administration. Plasma FFA increased rapidly, followed by a gradual fall. Corresponding to the fall of plasma FFA, a marked rise of plasma HGH was demonstrated. This HGH rise was diminished when plasma FFA was kept elevated, or when glucose was given. From these results it was concluded that the fall of plasma FFA could stimulate HGH secretion as in the case of falling blood glucose values and that the fluctuation of plasma FFA could be one of the factors regulating the secretion of HGH. The authors express their thanks to Prof. Kiku Nakao and Dr. Kazuo Shizume (Chief, Dept. of Endocrinology, Toranomon Hospital, Akasaka, Tokyo) for their advice and encouragement. Technical assistance of Miss Junko Shibazaki and Miss Miki Komiyama is greatly appreciated.

Effect of Nicotinic Acid Administration on Plasma HGH, FFA and Glucose in Obese Subjects and in Hypopituitary Patients

Abstract The administration of nicotinic acid in normal subjects caused an acute reduction of plasma FFA followed by a marked progressive secondary rise. Plasma HGH showed a significant rise following the reduction of plasma FFA. Obese subjects displayed a more pronounced reduction and rapid rise of plasma FFA than did normal subjects, but plasma FFA then decreased gradually after it reached its maximum level. There was no significant change of plasma HGH. In hypopituitary patients, the secondary rise of plasma FFA was slow and diminished, and no increase of plasma HGH was observed. From these results, it appears that the late rebound of plasma FFA following nicotinic acid administration is at least partly related to the augmented secretion of HGH. The early and rapid rebound of plasma FFA in obese subjects does not depend on the effect of HGH, but the diminished secretion of HGH might be related to the decrease of lipolysis in these subjects.

Differentiation of human promyelocytic leukemia cells is accompanied by an increase in insulin receptors

Abstract Changes in insulin receptors accompanying cell differentiation in human promyelocytic leukemia cells (HL-60) were studied. Cell differentiation was induced by 1α,25-dihydroxyvitamin D 3 , vitamin A, dimethyl sulfoxide, or phorbol esters. 1α,25-dihydroxy-vitamin D 3 increased the ability of HL-60 cells to bind insulin in a dose-dependent manner. The increase in insulin binding was due to an increase in the number of insulin receptors. Vitamin A, dimethyl sulfoxide and phorbol esters were also effective in increaseing insulin receptors. Thus, the differentiation of HL-60 cells was accompanied by an increase in insulin receptors.

Phorbol ester, not growth hormone releasing factor, consistently stimulates growth hormone release from somatotroph adenomas in culture

In order to study the mechanism of GH secretion from somatotroph adenoma cells, we have compared the effect of 12–O‐tetradecanoyl phorboi‐13‐acetate (TPA) with that of growth hormone releasing factor (GRF) on GH secretion from human somatotroph adenoma cells cultured in monolayer. Pituitary adenoma cells were obtained from 13 patients with acromegaly undergoing surgery. On the 7th day of culture, the cells were exposed for 2 h to secretagogues. All 13 adenoma cell cultures (100%) responded to TPA (1·6–16·0 nmol/I) with a two‐ to six‐fold increase in GH release (240·37% Increase of control: mean±SE). The response was detectable within 10 min, and was maximal at 2 h. Phosphollpase C (7·7 mmol/I) also stimulated a two‐to ten‐fold Increase In GH release in all four adenomas examined (100%). GH release was stimulated by GRF (2·0 nmol/I) in eight out of 12 adenoma cells (67%), but the magnitude of the responses to GRF (60·18% Increase of control: mean ± SE) were much smaller than that of TPA. Five out of 13 adenomas secreted detectable amount of PRL Into the medium and these five adenomas (100%) responded to TPA (16·0 nmol/I) with a two‐ to six‐fold Increase. These observations indicate that the activation of protein kinase C is the consistent stimulator in GH and PRL secretion In human somatotroph adenoma cells. However, It is not determined whether the protein kinase C

Variables that regulate production of insulin-like peptide(s) in human leukemia cell line (HL-60)

A human myeloid leukemia cell line (HL-60) produces a peptide or peptides with insulin-like activity which is distinct from insulin or insulin-like growth factors (somatomedins). Factors regulating the production of this peptide (HL-ILP) were explored in the present study. The production of HL-ILP was maximal in the early log phase of cell growth and declined with increasing cell density. Differentiation of HL-60 cells to macrophages, induced by dihydroxyvitamin D3 or phorbol esters, was also associated with a decrease in HL-ILP production. Glucose consumption by the cells in the early log phase was closely related with HL-ILP production, and HL-ILP was found to stimulate glucose consumption by HL-60 cells. Production of HL-ILP was dependent on glucose concentrations in the culture medium and glucose concentrations higher than 1mg/d1 suppressed the release of HL-ILP. These observations are not inconsistent with a hypothesis that HL-ILP is involved in the glucose metabolism of the HL-60 cells that produce this peptide.

Paradoxic elevation of serum growth hormone levels after splenectomy and/or paraesophagogastric devascularization in patients with portal hypertension

Blood glucose, serum immunoreactive insulin (IRI), and serum growth hormone (GH) levels during 50-g oral glucose tolerance tests (OGTT) were determined before and after splenectomy with or without paraesophagogastric devascularization in patients with portal hypertension (13 liver cirrhosis and 8 idiopathic portal hypertension) and in 5 splenectomized patients with diseases other than portal hypertension. Before splenectomy with devascularization, only 1 of 15 patients with portal hypertension exhibited a paradoxic elevation of serum GH levels of more than 10 ng/ml above the fasting levels after glucose loads. After the operation, however, 10 of these 15 patients showed the paradoxic elevation. Frequency of the paradoxic elevation was significantly higher after the operation than before (p < 0.001). The abnormal response of serum GH levels to glucose loads did not correlate with any of the blood glucose concentrations, serum IRI levels, and values for liver function tests. The paradoxic elevation was also observed in 4 of 6 patients with portal hypertension who underwent splenectomy alone without devascularization. These 4 patients with paradoxic elevation were splenectomized 4 wk and 212, 20, and 29 yr previously. However, none of 5 splenectomized patients without portal hypertension showed the paradoxic elevation. The reason why the paradoxic elevation was observed after splenectomy only in patients with portal hypertension but not in patients without portal hypertension may be sought for in the changes of portal venous flow rather than splenectomy itself.

Effect of Acute Glucose Infusion on Plasma Concentrations of Human Growth Hormone (HGH).

Summary Serial plasma HGH concentrations were measured, in 18 normal subjects, following continuous intravenous glucose infusion performed for periods of 3, 10, 20 and 30 minutes. In 5 of 8 cases infused for 3 minutes, no rise of plasma HGH was observed in spite of the rapid fall of blood glucose with (4 cases) or without (1 case) its reduction below the fasting level. The 3 other cases infused for 3 minutes and all 10 cases of 10, 20 and 30 minutesinfusion showed definite rise of plasma HGH at 90-180 minutes following the infusion. From the results obtained, it appears that the falling blood glucose per se is not a direct stimulus, and the reduction of blood glucose below the fasting level is not necessarily a stimulus to HGH secretion.