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Biomedical subjects

D A Shafritz

Publications and source records attributed to D A Shafritz.

At least 19 recordsLinked to original sources
PubMed1992

Mitogenic effects of hepatic stimulator substance on cultured nonparenchymal liver epithelial cells.

We determined whether hepatic stimulator substance shares its mitogenic specificity for hepatocytes with nonparenchymal epithelial cells in the hepatocyte lineage. Cell lines designated HTC (derived from a rat hepatoma known to respond to hepatic stimulator substance) and FNRL, K-16 and K-22 (derived from rat liver nonparenchymal epithelial cells) were used. After exposure to hepatic stimulator substance, [3H]-thymidine incorporation into DNA was significantly increased (p less than 0.001) in HTC, FNRL and K-16 cells, but not in K-22 cells. Fluorescence-activated cell sorting demonstrated that the mitogenic response to hepatic stimulator substance was associated with a greater proportion of cells entering the S phase. Epidermal growth factor, alone or in combination with hepatic stimulator substance, had no significant mitogenic effect on FNRL cells, but exposure of these cells to transforming growth factor-beta 1 inhibited [3H]-thymidine incorporation into DNA and reduced the proportion of cells in the S and G2/M phases. Simultaneous exposure of FNRL cells to hepatic stimulator substance and transforming growth factor-beta 1 abrogated the inhibitory effect of transforming growth factor-beta 1. Comparison of butyrate-synchronized HTC cells with hepatic stimulator substance-treated HTC cells showed that S-phase progression in these conditions was different, with no intervening cell cycle arrest after treatment with hepatic stimulator substance. Mitogenic stimulation of FNRL and K-16 cells with the liver-specific growth factor hepatic stimulator substance suggests that these cells are of hepatocyte lineage. These results strengthen the evidence for a possible link between hepatocytes and nonparenchymal liver epithelial cells during liver biogenesis and differentiation.

Animals↗
PubMed1992

Widespread differentiation stage-specific expression of the gene encoding phosphoprotein p19 (metablastin) in mammalian cells.

p19 is a highly conserved 19 kD cytosolic protein that undergoes phosphorylation in response to diverse extracellular factors in mammalian cells. Its expression is abundant in brain and testis and is developmentally regulated. To gain insights regarding its function, we analyzed the expression of p19 mRNA in a variety of cell types during induction of differentiation. Murine erythroleukemia cells showed a moderate increase followed by a marked decrease in the abundance of p19 mRNA during induction of differentiation. In murine C2 myoblasts and primary fetal rat osteoblasts, p19 mRNA was abundant in replicating cells and decreased to undetectable levels during differentiation. In resting human peripheral blood lymphocytes, p19 mRNA was virtually undetectable but was strongly induced during blast transformation of both B and T cells. In rat liver, p19 mRNA was abundant on embryonic day 17 and decreased during early postnatal development. Upon fractionation of adult rat liver cells by centrifugal elutriation, p19 mRNA was not detected in hepatocytes while a low level was observed in a fraction enriched in non-parenchymal epithelial cells. CCl4-induced liver regeneration resulted in induction of p19 mRNA in hepatocytes. Primary cultures of embryonic and neonatal rat brain were analyzed by indirect immunofluorescence using co-staining with stage-specific markers. p19 expression was restricted to immature neurons and oligodendrocyte precursors. In contrast to the other cell types examined, the neuronal and glial precursors that express p19 were shown, using BrdU labeling, to be postmitotic both in primary culture and in vivo. The data demonstrate widespread, stage-specific expression of p19 and suggest that the protein exerts a general, lineage-independent function during induction of differentiation of mammalian cells. In view of the available evidence on the stimulation of serine phosphorylation of p19 by several growth factors, our working hypothesis is that phosphorylation of p19 may be involved in the mechanism by which growth factors control cell differentiation.

Animals↗
PubMed1992

Albumin gene expression is down-regulated by albumin or macromolecule infusion in the rat.

A novel feedback regulatory mechanism operating on transcription of the albumin gene is described in the rat. In 1946, it was proposed that circulating colloids, including serum albumin, may affect the synthesis and/or secretion of albumin in the liver. The molecular basis for this proposed regulation has now been investigated by adding oncotically active macromolecules to the circulation of normal or genetically albumin-deficient Nagase analbuminemic rats (NAR) and analyzing the hepatic expression of genes, including albumin after 24 h. The transcription rate of the albumin gene was higher in NAR than in normal rats and was dramatically reduced by raising serum albumin to 1.6 g/dl. Intravenous infusion of albumin into normal rats also decreased transcriptional activity of the albumin gene by 50-60%, and this decrease correlated with changes in serum colloid osmotic pressure after albumin infusion. Inhibition of albumin gene transcription was also observed upon intravenous infusion of other protein or nonprotein macromolecules, such as gamma-globulin and dextran. This down-regulation appears to control the steady-state level of albumin mRNA in the liver. Aside from a concomitant decrease in apo E gene transcription after albumin or macromolecule infusion, there was no change in the transcription rate of other genes, including those exhibiting liver-preferred or -specific expression (e.g., tyrosine amino-transferase, cytochrome P-450, alpha 1-antitrypsin, apolipoproteins A-I and B, and transferrin) or general cellular expression (e.g., alpha-tubulin, pro alpha 2 collagen, and beta-actin). Feedback regulation of albumin gene expression by serum colloids may serve as a specific homeostatic mechanism to maintain the steady-state level of total protein in the circulation.

Animals↗
PubMed1992

Distribution of albumin and alpha-fetoprotein mRNAs in normal, hyperplastic, and preneoplastic rat liver.

The nature of bile duct-like (oval) cells proliferating during chemical hepatocarcinogenesis has been controversial. To investigate this issue further, the authors compared the hepatic distribution of albumin (ALB) and alpha-fetoprotein (AFP) mRNAs in rats in which oval cell proliferation was induced by feeding a choline-devoid diet containing 0.1% ethionine (CDE, a hepatocarcinogenic diet) with that in normal rats and in rats in which biliary epithelial cell hyperplasia was induced by either bile duct ligation or feeding alpha-naphthylisothiocyanate (ANIT). Northern blot analysis in parenchymal and nonparenchymal liver cells isolated from these animals demonstrated that ALB mRNA was present in the hepatocytes of both control and experimental animals, whereas this transcript was detected in nonparenchymal epithelial cells only in CDE-fed rats. Alpha-fetoprotein mRNA was not seen in either parenchymal or nonparenchymal cells isolated from normal or hyperplastic livers induced by bile duct ligation or ANIT feeding. In CDE-fed rats, however, both parenchymal and nonparenchymal cell populations displayed AFP message. In situ hybridization directly demonstrated nonparenchymal cell expression of both ALB and AFP transcripts in CDE-fed rats. Most surprisingly, ALB and AFP mRNAs were also detected by in situ hybridization in occasional nonparenchymal cells located in portal tracts near the limiting plate in normal liver, as well as under conditions associated with bile duct hyperplasia. Immunohistochemical studies of intermediate filament proteins, cytokeratin 19 (a marker of glandular epithelia), vimentin (a marker of mesenchymal lineage), and desmin (a marker of muscle cell differentiation) demonstrated that oval cells, as well as normal and hyperplastic bile duct cells, were positive for cytokeratin 19 and negative for both vimentin and desmin. Cytokeratin-positive oval cells formed duct profiles and were connected to preexisting ductules and ducts. These results are construed to suggest that oval cells proliferating during CDE hepatocarcinogenesis are derived from epithelial cells within the biliary tree. The presence of cells with similar morphologic appearance, periportal location, and AFP and ALB expression in normal liver suggests that these cells may be the progenitors of oval cells induced by some carcinogenic regimens.

Animals↗
PubMed1991

Receptor-mediated gene delivery in vivo. Partial correction of genetic analbuminemia in Nagase rats.

A plasmid (palb3) was constructed containing the structural gene for human serum albumin driven by mouse albumin enhancer-rat albumin promoter elements. Using an asialoglycoprotein-polycation conjugate consisting of asialoorosomucoid coupled to poly-L-lysine, a soluble DNA complex was formed that was capable of targeting specifically to hepatocytes via asialoglycoprotein receptors present on these cells. Groups of Nagase analbuminemic rats were injected with complexed DNA or controls, followed by two-thirds partial hepatectomy to stimulate hepatocyte replication. Using a cDNA probe for the human albumin structural gene, hybridizable sequences were detected in analbuminemic rats treated with complex as determined by Southern blot analysis. Two weeks post-injection, the targeted DNA was found to exist primarily in plasmid form with an average copy number of 1000/diploid cell. Human albumin mRNA was detected by dot-blot hybridization with a specific oligonucleotide cDNA probe and confirmed by RNase protection assay using a vector-specific probe. Circulating human albumin was detected in the serum of palb3-treated Nagase analbuminemic rats by Western blots using an antibody specific for human serum albumin. A time course demonstrated that circulating human albumin was not detectable 24 h after injection, but became measurable at a level of 0.05 micrograms/ml within 48 h and increased in concentration to a maximum of 34 micrograms/ml by 2 weeks post-injection. This level of expression remained stable through 4 weeks after injection and partial hepatectomy.

Animals↗
PubMed1991

Thymosin treatment of chronic hepatitis B: a placebo-controlled pilot trial.

Chronic hepatitis B is a severe and frequently progressive disease. We assessed the safety and efficacy of thymosin fraction 5 and thymosin-alpha 1 in a prospective, placebo-controlled trial in 12 patients with chronic hepatitis B. All patients had histological and biochemical evidence of active liver disease for at least 6 mo before treatment and were positive for serum hepatitis B virus DNA and HBsAg. Seven patients received thymosin fraction 5 or thymosin-alpha 1 and five patients received placebo twice weekly for 6 mo. By the conclusion of the study (1 yr), serum aminotransferase levels had improved significantly in thymosin-treated patients, but not in the placebo group. Six (86%) of the thymosin treated patients and one (20%) patient given placebo cleared hepatitis B virus DNA from serum (p less than 0.04, Fisher's exact test). After treatment, replicative forms of hepatitis B virus DNA were present in the liver specimens of four of five placebo-treated patients but in only one of seven thymosin-treated patients (p less than 0.04, Fisher's exact test). Response to thymosin therapy was associated with significant improvements in peripheral blood lymphocyte and CD3 and CD4 counts and in in vitro production of interferon-gamma over initial values. No significant side effects were observed in patients given thymosin or in placebo-treated patients. Clinical, biochemical and serological improvement in patients responding to thymosin were sustained during 26 +/- 3 mo of follow-up. The results of this pilot trial suggest that thymosin therapy promotes disease remission and cessation of hepatitis B virus replication in patients with chronic viral infection.

Adolescent↗
PubMed1990

Transcriptional and posttranscriptional regulation of apolipoprotein E, A-I, and A-II gene expression in normal rat liver and during several pathophysiologic states.

Assessment of the relative transcription rates and mRNA steady-state levels for apolipoprotein genes E, A-I, and A-II has been performed in normal rat liver, during liver regeneration and following induction of cirrhosis, as well as in rats with inherited analbuminemia associated with hyperlipidemia. Apo E exhibits primarily transcriptional control with an additional component of posttranscriptional control, whereas Apo A-I is controlled primarily at the posttranscriptional level, thus indicating that these genes are regulated independently. The level of control for Apo A-II has not been determined, because of difficulty experienced in measuring the transcription rate of this gene. During liver regeneration, cirrhosis, and analbuminemia, there is a marked increase in the ratio of Apo A-I to Apo E mRNA, resulting from an increase in the Apo A-I mRNA steady-state level and a decrease in Apo E mRNA. These changes are similar in the three pathophysiologic states and seem to occur through a combination of transcriptional and posttranscriptional mechanisms.

Animals↗
PubMed1990

Exon skipping during splicing of albumin mRNA precursors in Nagase analbuminemic rats.

Based on the observation that albumin transcripts accumulate in the liver nuclear RNA fraction of Nagase analbuminemic rats (NAR), it was proposed [Esumi, H., Takahashi, Y., Sato, S., Nagase, S. & Sugimura, T. (1983) Proc. Natl. Acad. Sci. USA 80, 95-99] [corrected] that a 7-base-pair deletion at the splice donor site of intron H-I of the albumin gene in these animals leads to impaired processing of albumin pre-mRNA. To identify the specific splicing abnormality, we examined the primary structure of cytoplasmic albumin mRNA across the junctions of exons G-H-I by RNase protection mapping, Northern blot hybridization, Southern blot analysis of polymerase chain reaction-amplified cDNA, and DNA sequencing. The major albumin mRNA species in NAR showed precise deletion of exon H, suggesting that this exon was skipped during albumin pre-mRNA processing. Since the intron G-H splice donor and acceptor sites and exon H sequence are normal, the finding of exon H skipping in NAR has important implications regarding the mechanism of splice site selection. Moreover, the NAR model provides an excellent system to study splicing in vivo in a higher animal.

Animals↗
PubMed1990

Alpha interferon suppresses hepatitis B virus enhancer activity and reduces viral gene transcription.

Interferons inhibit replication of hepatitis B virus (HBV). The mechanism for this inhibition was investigated by analyzing the effect of interferons on transcription of a chloramphenicol acetyltransferase reporter gene under control of HBV regulatory sequences and by determining the steady-state level of viral mRNAs in permanently HBV-transfected HepG2 cells. Low doses (100 U/ml) of alpha interferon (IFN-alpha) but not IFN-gamma inhibited chloramphenicol acetyltransferase expression in cultured cells transfected with plasmids containing the HBV enhancer linked to either HBV or simian virus 40 promoters. IFN-alpha also lowered expression of HBV mRNA in HBV-transfected HepG2 cells actively replicating virus, suggesting that IFN-alpha inhibits HBV replication by reducing transcription of viral genes driven by the HBV enhancer.

Chloramphenicol O-Acetyltransferase↗
PubMed1990

Albumin and collagen mRNA expression in normal and analbuminemic rodent liver: analysis by in situ hybridization using biotinylated probes.

We used in situ nucleic acid hybridization cytochemistry to examine cell types and subcellular sites expressing albumin (alb) or pro alpha 2 collagen (col) mRNA in livers from normal and analbuminemic rodents. Biotinylated cDNA or RNA probes were applied to aldehyde-fixed, non-frozen sections and the resulting DNA-RNA or RNA-RNA hybrids were subsequently visualized by enzymatic detection of either peroxidase or alkaline phosphatase conjugated to anti-biotin IgG or streptavidin. In normal rat liver, alb mRNA was expressed in all hepatocytes and was localized to discrete subcellular structures distributed as aggregates in the cytoplasm and in specific structures encircling the nucleus; these subcellular structures most likely represent the endoplasmic reticulum and nuclear envelope. In mouse liver, pro alpha 2 col mRNA was identified in a subpopulation of sinusoidal lining cells which have the morphological appearance of lipocytes. In liver from analbuminemic rats, a small number of hepatocytes, distributed throughout the hepatic lobule, expressed alb mRNA at high levels; the subcellular distribution of this alb mRNA was essentially identical to that observed in normal rat hepatocytes. Since non-radioactive in situ hybridization detected mRNA within the boundaries of individual cells and showed its precise subcellular location under conditions in which there was excellent preservation of tissue morphology, this procedure should be useful for a wide variety of histopathologic studies.

Albumins↗
PubMed1990

A novel system for transplantation of isolated hepatocytes utilizing HBsAg-producing transgenic donor cells.

Hepatocytes from donor transgenic mice that produce an easily assayable circulating marker have been used to develop a novel hepatocyte transplantation system. Isolated G7 HBV transgenic donor hepatocytes secreting HBsAg were transplanted into congeneic or allogeneic mouse recipients. Serum HBsAg was present three days after hepatocyte transplantation in congeneic animals and persisted indefinitely when hepatocytes were transplanted into the spleen. Transplanted hepatocytes within the splenic pulp were identified by morphologic and histochemical analysis. Migration of hepatocytes injected into the spleen to the liver was demonstrated by in situ hybridization using an RNA probe for HBsAg. Transplantation into nonimmunosuppressed allogeneic recipients resulted in disappearance of detectable hepatocytes in the spleen within two weeks. This novel transplantation system should facilitate studies of hepatocyte engraftment and survival, modulation of allograft rejection, and development of hepatocyte-directed gene therapy.

Animals↗
PubMed1988

Comparative morphology and tumourigenicity of human hepatocellular carcinoma cell lines in athymic rats and mice.

Four human hepatoma cell lines PLC/PRF/5, Hep G2, Sk-Hep 1 and Mahlavu were inoculated subcutaneously into athymic Balb/c nude mice and N/NIH outbred nude rats, producing well encapsulated tumours. The 4 hepatoma tumour types in the athymic rodents differ morphologically. PLC/PRF/5 and Hep G2 cells are well differentiated polygonal cells which resemble normal hepatocytes. Tumour arrangement is characterized by solid masses and trabeculae while stromal support is minimal. In contrast, Mahlavu and Sk-Hep 1 tumours have a sarcomatous appearance and consist of spindle shaped cells arranged in solid masses with a rich stromal support. Tumourigenicity of hepatoma cells in the athymic rodents was dependent on injected cell type, inoculation density, relative immunocompetence of the host and the species of animals used. In nude mice, Sk-Hep 1 cells were the most tumourigenic, while Hep G2 cells were tumourigenic only at very high inoculation densities. In nude rats, which were more resistant to tumour formation, PLC/PRF/5 cells were the most tumourigenic. Pre-treatment of athymic mice and rats with total body irradiation resulted in enhanced tumourigenicity for all hepatoma cell lines tested. This was manifested as increased "take" rates, a decreased latency from tumour cell injection to tumour detection, increased tumour weight, and for PLC/PRF/5 cells an increased invasiveness to adjacent body cavities. Furthermore, following irradiation, the minimal number of injected cells required to produce subcutaneous tumours was markedly reduced in both animal species, regardless of tumour cell type. The protocols described enable the reproducible growth of human hepatoma tumours in athymic rodents.

Animals↗
PubMed1988

Interrupted replication of hepatitis B virus in liver tissue of HBsAg carriers with hepatocellular carcinoma.

To search for events underlying reduction of peripheral viremia and integration of hepatitis B virus (HBV) DNA into the liver cell genome in long-term virus carriers with hepatocellular carcinoma, paired samples of liver and tumor tissue were analyzed by molecular hybridization and immunological methods. Most tumor tissues contained integrated viral DNA; in none was extrachromosomal HBV DNA detected. Integrated HBV DNS was also found in peritumor liver tissue in the majority of patients. However, liver of patients either with or without peripheral viremia also contained free HBV DNA and replicative intermediates. In three nonviremic patients with replicative HBV DNA in liver, viral core antigen expression was markedly reduced or absent, whereas viral envelope protein (surface antigen) expression was normal. In one case, replicative intermediates in liver were sensitive to DNase I digestion, indicating that viral DNA was not encapsidated in normal viral core particles. These results suggest that decreased or defective core antigen production can lead to reduced viremia associated with blocked virus assembly/secretion and accumulation of unencapsidated HBV DNA replicative intermediates in the liver cell. Accumulation of such HBV DNA molecular forms in the liver may lead to an increased propensity for HBV DNA to integrate into the host genome, which has been found with high frequency in hepatic neoplasms from patients infected with hepatitis B virus.

Carcinoma, Hepatocellular↗
PubMed1988

The glucocorticoid receptor recognizes a specific nucleotide sequence in hepatitis B virus DNA causing increased activity of the HBV enhancer.

The hepatitis B virus (HBV) genome contains a specific DNA binding site for the glucocorticoid receptor. Using DNase I footprinting, this binding site was localized at HBV map positions 341-370 clockwise from the EcoRI site. The DNA sequence protected in the footprint contains two tandem copies of the GRE core hexanucleotide 5'-TGTTCCT-3'. Deletion analysis and reconstruction experiments in plasmid expression vectors demonstrated that this glucocorticoid receptor binding sequence serves as a signal for augmenting glucocorticoid-dependent activity of the HBV enhancer, which is located approximately 730 nucleotides downstream in the HBV genome. Even though it does not serve as an independent enhancer element, the HBV glucocorticoid receptor domain can therefore be categorized as a functional GRE.

Base Sequence↗