PubMed Health⌕ Search

Biomedical subjects

J Look

Publications and source records attributed to J Look.

6 recordsLinked to original sources
PubMed1995

Marked resistance of RAR gamma-deficient mice to the toxic effects of retinoic acid.

Excessive intake of retinol or of retinoic acid causes a syndrome of characteristic toxic effects known as hypervitaminosis A. To test the role of the nuclear retinoic acid receptor (RAR gamma) in this process we produced mice with a targeted disruption of the RAR gamma gene and examined toxic effects of repeated doses of retinoic acid and two other synthetic retinoids, Ro 15-1570 and Ro 40-6055. Surprisingly, homozygous mutant mice were resistant to fourfold higher doses of retinoic acid than wild-type mice as well as to elevated doses of the synthetic retinoids, indicating that RAR gamma may have a major role in mediating retinoid toxicity, a finding that possibly has practical implications for reducing the toxicity of synthetic retinoids in clinical use.

Animals↗
PubMed1992

The hepatocyte-specific phenotype of murine liver cells correlates with high expression of connexin32 and connexin26 but very low expression of connexin43.

This investigation was initiated in order to find out whether expression of the hepatocyte-specific phenotype is accompanied by expression of certain connexin genes coding for gap junctional protein subunits. Several clones of mouse embryonic hepatocytes immortalized in serum-free MX83 medium by infection with recombinant retrovirus-expressed transcripts for connexin32, connexin26, albumin, alpha-fetoprotein, tyrosine aminotransferase, as well as aldolase A and B, at more than half of the levels found in primary mouse hepatocytes. In addition the immortalized hepatocyte clones contained low levels of connexin43 mRNA of which only trace amounts were detected in primary embryonic mouse hepatocytes and in rat liver. Two of the immortalized hepatocyte clones were shifted from serum-free MX83 medium to Dulbecco's modified Eagle medium (DMEM) containing 10% fetal calf serum and, after 2, 14, or 180 days, back to MX83 medium. We found that expression of connexin32 and connexin26 mRNAs as well as transcripts of other liver-specific proteins was reversibly decreased in serum-containing medium, whereas the expression level of connexin43 transcripts was increased in serum-containing DMEM compared to serum-free MX83 medium. The expression levels of connexin26, connexin32, or connexin43 mRNAs were altered by the addition of fetal calf serum or arginine or by the absence of hydrocortisone in MX83 medium, all of which contributed to the shift in phenotype. Furthermore several dedifferentiated cell lines derived from rat or mouse liver and cultivated in serum-containing medium were found to express little connexin32 or connexin26 mRNA but relatively high levels of connexin43 mRNA.

Animals↗
PubMed1989

Comparative characterization of the 21-kD and 26-kD gap junction proteins in murine liver and cultured hepatocytes.

Affinity-purified antibodies to mouse liver 26- and 21-kD gap junction proteins have been used to characterize gap junctions in liver and cultured hepatocytes. Both proteins are colocalized in the same gap junction plaques as shown by double immunofluorescence and immunoelectron microscopy. In the lobules of rat liver, the 21-kD immunoreactivity is detected as a gradient of fluorescent spots on apposing plasma membranes, the maximum being in the periportal zone and a faint reaction in the perivenous zone. In contrast, the 26-kD immunoreactivity is evenly distributed in fluorescent spots on apposing plasma membranes throughout the rat liver lobule. Immunoreactive sites with anti-21 kD shown by immunofluorescence are also present in exocrine pancreas, proximal tubules of the kidney, and the epithelium of small intestine. The 21-kD immunoreactivity was not found in thin sections of myocardium and adult brain cortex. Subsequent to partial rat hepatectomy, both the 26- and 21-kD proteins first decrease and after approximately 2 d increase again. By comparison of the 26- and 21-kD immunoreactivity in cultured embryonic mouse hepatocytes, we found (a) the same pattern of immunoreactivity on apposing plasma membranes and colocalization within the same plaque, (b) a similar decrease after 1 d and subsequent increase after 3 d of both proteins, (c) cAMP-dependent in vitro phosphorylation of the 26-kD but not of the 21-kD protein, and (d) complete inhibition of intercellular transfer of Lucifer Yellow in all hepatocytes microinjected with anti-26 kD and, in most cases, partial inhibition of dye transfer after injection of anti-21 kD. Our results indicate that both the 26-kD and the 21-kD proteins are functional gap junction proteins.

Animals↗
PubMed1987

Cyclic adenosine monophosphate stimulates biosynthesis and phosphorylation of the 26 kDa gap junction protein in cultured mouse hepatocytes.

Hepatocytes prepared from 18-day-old mouse embryos were grown in serum-free medium and reached confluence after two days in culture. The total amount of the 26 kDa gap junction protein decreased in these cells during the first 24 h in culture and increased again between day 1 and day 3 more than 10-fold. At day 3 a half-life time of 2.5 to 3 h was determined for the 26 kDa protein by [35S]methionine incorporation and immunoprecipitation using affinity-purified anti-26 kDa. Incorporation of [32P]orthophosphate into the 26 kDa protein of cultured hepatocytes was found at serine residues (98%) and tyrosine residues (about 2%). The addition of dibutyryl cyclic adenosine monophosphate (db cAMP) to the culture medium at day 2 had two effects: After 15 min the extent of phosphorylation of the 26 kDa protein increased 2.7-fold whereas the total amount of the 26 kDa protein increased only 1.2-fold. After 3 h of incubation with db cAMP, a 2.5-fold increase of the 26 kDa protein was noticed which was accompanied by a 3.2-fold increase in phosphorylation of serine residues. The effects of db cAMP on phosphorylation of the 26 kDa protein could be augmented or mimicked by the addition of isoproterenol, theophylline or forskolin to the culture medium of hepatocytes. In extracts of rat hepatocarcinoma MH1C1 cells and dog kidney MDCK cells, a phosphorylated 26 kDa protein can be immunoprecipitated using anti-liver 26 kDa. These results demonstrate that the gap junction 26 kDa protein can be posttranslationally modified by cAMP-dependent phosphorylation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗