The exposure of carcinogen-initiated primary neonatal rat hepatocytes to tumor promoters modulates both the transcripts and the enzymatic activity of nuclear poly(ADP-ribose) polymerase

Induction of hepatic poly(ADP-ribose) polymerase by peroxisome proliferators, non-genotoxic hepatocarcinogens

Two peroxisome proliferators, [4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio] acetic acid (Wy-14,643) or di(2-ethylhexyl) phthalate (DEHP), were given orally to male F-344 rats for up to 78 or 97 weeks. At 1 week, the activity of poly(ADP-ribose) polymerase (pADPRP) was increased 2- and 1.8-fold in the liver of rats treated with Wy-14,643 and DEHP, respectively. The induction of the activity was maintained at 2.5- or 2-fold for up to 52 weeks. The immunoblot and Northern blot analyses revealed that the induction of pADPRP activity would be responsible for the increase in the amount of mRNA. In addition, in the liver tumor induced by Wy-14,643 and DEHP, the pADPRP mRNA level increased 3.6- or 3.7-fold. The magnitude of the increase in the mRNA level was higher than that in the non-tumor portion. These findings suggest that the induction of pADPRP may play an important role in the hepatocarcinogenesis induced by peroxisome proliferators.

TPA and cycloheximide modulate the activation of NF-kappa B and the induction and stability of nitric oxide synthase transcript in primary neonatal rat hepatocytes

12-O-Tetradecanoylphorbol 13-acetate (TPA) elicited a transient increase in the transcription of the inducible nitric oxide synthase (iNOS) gene coupled with a shortening of the half-life of its mRNA in primary neonatal rat hepatocytes. These effects of TPA were preceded by a surge in nuclear translocation of the transcription factor NF-kappa B, and followed by a mounting accumulation of NO-2 in the growth medium. Even cycloheximide (CHX) added by itself elicited an early, sustained activation of NF-kappa B followed by an intense induction of iNOS gene expression, irrespective of what degree of protein synthesis inhibition was brought about by the several concentrations tested. When given together, TPA and CHX exerted additive effects on hepatocellular iNOS mRNA levels. These results suggest the likelihood of an ordered sequence of events by which an activated NF-kappa B mediates the induction of iNOS gene expression in TPA- and/or CHX-treated primary hepatocytes.

Extracellular calcium modulates prereplicative cyclic AMP surges in EGF-stimulated primary neonatal rat hepatocytes

The cells in nearly pure (96-98%) primary cultures of hepatocytes from neonatal rat liver in high (1.0 mM)-Ca2+, serum-free, synthetic HiWo5Ba2000 medium initiated DNA synthesis and entered mitosis between 11 and 30 h after the addition of 10 ng/ml EGF. During the 10-h prereplicative period, the cultured hepatocytes, like regenerating rat liver cells, generated two large cyclic AMP transients, one peaking between 30 min and 2 h and the other around 6 h. Hepatocytes stimulated by the same concentration of EGF in low (0.02 mM)-Ca2+ medium increased cyclic AMP synthesis as much as the EGF-treated hepatocytes in high-Ca2+ medium, but they released the additional cyclic AMP into the medium and could not generate prereplicative internal cyclic AMP surges, initiate DNA replication, or enter mitosis. These results suggest that one of the ways external Ca2+ controls prereplicative development of hepatocytes is to restrain the release of cyclic AMP and thus enable the cell to accumulate enough internal cyclic AMP to stimulate events required to initiate DNA replication.

Morphology, growth, and gene expression in five newly isolated murine hepatocellular tumor cell lines

Five murine hepatocellular tumor cell lines (HepM-1-5) were isolated and grown in a synthetic medium added with hormones, growth factors and/or serum. The morphology of these lines ranged from a nearly homogeneous epithelial-like shape (HepM-2) to a stromal appearance (HepM-1). The remaining lines displayed a mixed morphology. For their proliferation all of the cell lines retained a clear dependence on the extracellular calcium level and hormonal and/or serum growth factors and, rather homogeneously, they did not express the albumin, alpha-fetoprotein (with the exception of HepM-2 cells), tyrosine aminotransferase, and ornithine transcarbamylase genes, whereas they all exhibited discrete levels of the ornithine aminotransferase mRNA. Only HepM-3 and HepM-5 lines expressed the procollagen type I gene.

Induction of poly(ADP-ribosyl)ation in the kidney after in vivo application of renal carcinogens

Dichlorovinylcysteine, the key metabolite thought to be responsible for the nephrocarcinogenicity of trichloroethene and dichloroacetylene, induces DNA double-strand breaks followed by increased poly(ADP-ribosyl)ation of nuclear proteins in cultured renal cells (Vamvakas et al., 1992, Biochem. Pharmacol. 44, 1131-1138). Poly(ADP-ribosyl)ation represents a post-translational modification of nuclear proteins involved in DNA repair, DNA replication, and modulation of gene expression. The present study investigates the induction of DNA double-strand breaks and poly(ADP-ribosyl)ation in the renal cortex after in vivo administration of several renal carcinogens to male Wistar rats, and the temporal relationship between these two processes. Dichlorovinylcysteine caused a time-dependent increase in the amount of poly(ADP-ribosyl)conjugates in the kidney cortex, which was preceded by increased formation of DNA double-strand breaks. Potassium bromate and ferric nitrilotriacetate, whose nephrocarcinogenicity is thought to result from increased formation of reactive oxygen species, both induced poly(ADP-ribosyl)ation with the concomitant formation of DNA double-strand breaks. Dimethylnitrosamine, an indirect acting methylating agent, and trimethylpentane, a non-genotoxic renal carcinogen, failed to induce poly(ADP-ribosyl)ation or a significant increase in DNA double-strand breaks in the renal cortex. The results indicate that nephrocarcinogens capable of inducing DNA fragmentation also induce post-translational modification of renal proteins via increased poly(ADP-ribosyl)ation.

Cell cycle-related expression of poly(ADP-ribosyl)transferase in proliferating rat thymocytes

The activity profile of poly(ADP-ribosyl)transferase was assayed during a complete cell cycle of rat thymocytes stimulated in the presence of interleukin-2 by concanavalin A or monoclonal antibodies against the T-cell antigen receptor (TCRmAB). Poly ADP-ribosylation was measured in permeabilized cells by the incorporation of [adenine-3H]NAD+ into protein bound poly ADP-ribose. The polymers of ADP-ribose were separated from the monomers using dihydroxyboronyl-Bio-Rex 70 columns. The rate of poly(ADP-ribosyl)ation increases during the G1 phase with a maximum 12 h after stimulation. This increase in activity is due to enhanced de novo synthesis of poly(ADP-ribosyl)transferase which can be abolished by the addition of cycloheximide. The half-life of this enzyme during the induction period was estimated to be 4 h. A second activity peak appears during the S-phase of the cell cycle 48 h after stimulation. The maxima of the poly(ADP-ribosyl)ation rate coincide with elevated immunoreactive enzyme levels at 12 and 48 h of culture assayed by Western blotting. The mRNA levels of pADPRT do not correlate with the first maximum of activity, whereas the second maximum was accompanied by a 5-fold increase of the specific mRNA. These results suggest a translational regulation of pADPRT in the G1 phase of the cell cycle, whereas the second activity peak in the S-phase is due to an increased transcription and translation. The induction of pADPRT activity in the G1 phase of TCRmAB-stimulated cells points to a function of poly(ADP-ribosyl)ation in the proliferation of thymocytes.