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K Nawa

Publications and source records attributed to K Nawa.

35 records · Page 2Linked to original sources
PubMed1986

Glucocorticoid-dependent expression of the albumin gene in adult rat hepatocytes.

In primary cultures of adult rat hepatocytes, transcription of the albumin gene, measured as incorporation of [alpha-32P]UTP into mRNA in isolated nuclei, decreased dramatically during culture without addition of serum and hormone, becoming almost negligible 10 h after plating. Of the hormones tested, dexamethasone (0.1 microM) prevented this decrease and restored the transcription within 2 h to the same level as that before culture. The half-maximum dose of dexamethasone for induction of transcription of the albumin gene was about 30 nM. The in vitro finding that expression of the albumin gene is strictly regulated by glucocorticoid was confirmed by an in vivo experiment in adrenalectomized rats showing that the transcription decreased markedly 14 days after adrenalectomy, but was restored rapidly by administration of hydrocortisone. This finding was also supported by identification of a glucocorticoid regulatory sequence from -50 to -62 base pairs between the TATA box and CAT box upstream of the 5'-end of the albumin gene. Cycloheximide inhibited the induction of transcription of the albumin gene by dexamethasone, suggesting that a rapidly induced mediator protein, which is also regulated by glucocorticoid, is involved in the induction of albumin gene expression by glucocorticoid. The albumin gene was also regulated by various other hormones besides glucocorticoid. Glucagon markedly enhanced the transcription induced by dexamethasone, although glucagon alone had no effect. Conversely, epinephrine suppressed stimulation of expression of the albumin gene by dexamethasone. Insulin and triiodothyronine had no effect on transcription of the albumin gene. From these findings we conclude that expression of the albumin gene depends strictly on glucocorticoid, and this dependence is modulated by other hormones.

Adrenalectomy↗
PubMed1984

Partial purification and characterization of hepatocyte growth factor from serum of hepatectomized rats.

When rat serum was subjected to gel filtration on a Sephadex G-200 column, a factor, "hepatotropin", that promoted hepatocyte growth in primary culture was separated. Its Mr was about 150 KD and it was an anionic protein that was unstable on acid- and heat-treatments. Hepatotropin was purified 20-fold further by affinity chromatography on heparin-Sepharose CL-6B. The purified hepatotropin was effective at 20 micrograms/ml and maximally effective at 120 micrograms/ml, and its effect was additive with that of insulin plus epidermal growth factor. In rats after partial hepatectomy, the hepatotropin activity in the serum increased time-dependently reaching a maximum of about 5-fold the initial level 24 h after the operation. Various known growth factors, such as fibroblast growth factor, platelet derived growth factor, somatomedin, thrombin and transferrin, did not stimulate DNA synthesis in cultured hepatocytes. These results suggest that hepatotropin is a new growth factor.

Animals↗
PubMed1984

Loss of reciprocal modulations of growth and liver function of hepatoma cells in culture by contact with cells or cell membranes.

In mature rat hepatocytes in primary culture, many metabolic functions and cell growth are controlled reciprocally by cell density, and this reciprocal regulation is mediated by a cell-surface modulator through cell-cell contact. Cultured RY-121B cells from Reuber hepatoma and MH1C1 cells from Morris hepatoma, which retain some liver-specific functions, did not show any cell-density dependency of either cell growth or hepatocyte-specific functions, such as induction of tyrosine aminotransferase by dexamethasone. However, when RY-121B cells were cocultured with a low density of rat hepatocytes as monolayers in direct contact, they exerted contact-dependent control of DNA synthesis and of differentiated function of the hepatocytes. Furthermore, plasma membranes from various tumor cells including these hepatoma cells had strong modulator activity on primary cultures of normal rat hepatocytes, and their activity mimicked the reciprocal effects of cell density on DNA synthesis and induction of tyrosine aminotransferase. On the contrary, addition of plasma membranes from normal adult rat liver to sparse cultures of RY-121B or MH1C1 cells did not cause any inhibition of active DNA synthesis or enhancement of induction of tyrosine aminotransferase in these cells. These results suggest that hepatoma cells have lost cell density-dependent regulations of many cellular activities and cell growth because they have lost the ability to respond to the cell surface modulator, although they retain modulator activity on their plasma membranes.

Animals↗
PubMed1983

Hormonal regulation of translatable mRNA of tryptophan 2,3-dioxygenase in primary cultures of adult rat hepatocytes.

Tryptophan 2,3-dioxygenase [EC 1.13.11.11] in primary cultures of adult rat hepatocytes was induced 3-4 fold by 1 microM dexamethasone and 6-7 fold by dexamethasone plus glucagon (0.1 microM). Changes of the enzyme activity, amount of enzyme, measured by immunotitration, and rate of enzyme synthesis, assayed by measurement of [3H]leucine incorporation into the enzyme protein, were closely correlated. Furthermore, in a reticulocyte lysate system for cell-free protein synthesis, mRNA of the enzyme was translated to the protein corresponding to the subunit of tryptophan 2,3-dioxygenase, which was identified by SDS-polyacrylamide gel electrophoresis. The activity of translatable mRNA of the enzyme was increased more than 10-fold by dexamethasone and its final content in total mRNA was 0.34%. Glucagon alone did not increase mRNA activity, but dexamethasone plus glucagon increased mRNA activity to twice that with dexamethasone alone, the maximal content of the mRNA being 0.77% of the total mRNA content 12 h after addition of hormones. Insulin (0.1 microM) caused 75% inhibition of the maximum increase of mRNA activity of the enzyme induced by dexamethasone and glucagon. Epinephrine (10 microM) also caused 58% inhibition of the maximum increase. Insulin and epinephrine also suppressed increase of mRNA of tryptophan 2,3-dioxygenase induced by dexamethasone alone. Therefore, dexamethasone alone or together with glucagon stimulated transcription of tryptophan 2,3-dioxygenase increasing its mRNA and enzyme synthesis in hepatocytes. Conversely, insulin and epinephrine suppressed these increases of mRNA synthesis and thus decreased enzyme synthesis.

Animals↗