Hubert Hug

Indolocarbazoles have been identified as novel inhibitors of protein kinase C (PKC), with Gö 6976 as one of its most potent and selective representatives. Recombinant PKC isozymes alpha, beta 1, delta, epsilon, and zeta were used in in vitro kinase assays to investigate Gö 6976 with respect to isozyme-specific PKC inhibition. Gö 6850, identical with GF 109203X, another PKC-specific kinase inhibitor, was included in this study as a reference compound. Nanomolar concentrations of the indolocarbazole Gö 6976 inhibited the Ca(2+)-dependent isozymes alpha and beta 1, whereas even micromolar concentration of Gö 6976 had no effect on the kinase activity of the Ca(2+)-independent PKC subtypes delta, epsilon, and zeta. In contrast, the bisindolymaleimide Gö 6850 inhibited all PKC isozymes, however, with a ranked order of potency (alpha > beta 1 > epsilon > delta > zeta). Kinetic analysis revealed that PKC inhibition by Gö 6976 was competitive with respect to ATP, non-competitive with respect to the protein substrate, and mixed type with respect to phosphatidylserine. Further experiments in the presence of different amounts of free Ca2+ indicated that interference with Ca2+ or its binding site is not responsible for the differential inhibition of PKC isozymes by Gö 6976.

Research Article| April 15 1993 Protein kinase C isoenzymes: divergence in signal transduction? H Hug; H Hug 1Institute of Molecular Cell Biology, University of c/o Gödecke AG, Mooswaldallee 1-9, 7800 Freiburg, Freiburg, Federal Republic of Germany. Search for other works by this author on: This Site PubMed Google Scholar T F Sarre T F Sarre 1Institute of Molecular Cell Biology, University of c/o Gödecke AG, Mooswaldallee 1-9, 7800 Freiburg, Freiburg, Federal Republic of Germany. Search for other works by this author on: This Site PubMed Google Scholar Biochem J (1993) 291 (2): 329–343. https://doi.org/10.1042/bj2910329 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Cite Icon Cite Get Permissions Citation H Hug, T F Sarre; Protein kinase C isoenzymes: divergence in signal transduction?. Biochem J 15 April 1993; 291 (2): 329–343. doi: https://doi.org/10.1042/bj2910329 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsBiochemical Journal Search Advanced Search This content is only available as a PDF. © 1993 The Biochemical Society, London1993 Article PDF first page preview Close Modal You do not currently have access to this content.

Chemotherapeutic drugs are cytotoxic by induction of apoptosis in drug-sensitive cells. We investigated the mechanism of bleomycin-induced cytotoxicity in hepatoma cells. At concentrations present in the sera of patients during therapy, bleomycin induced transient accumulation of nuclear wild-type (wt) p53 and upregulated expression of cell surface CD95 (APO-1/Fas) receptor in hepatoma cells carrying wt p53 (HepG2). Bleomycin did not increase CD95 in hepatoma cells with mutated p53 (Huh7) or in hepatoma cells which were p53-/- (Hep3B). In addition, sensitivity towards CD95-mediated apoptosis was also increased in wt p53 positive HepG2 cells. Microinjection of wt p53 cDNA into HepG2 cells had the same effect. In contrast, bleomycin did not enhance susceptibility towards CD95-mediated apoptosis in Huh7 and in Hep3B cells. Furthermore, bleomycin treatment of HepG2 cells increased CD95 ligand (CD95L) mRNA expression. Most notably, bleomycin-induced apoptosis in HepG2 cells was almost completely inhibited by antibodies which interfere with CD95 receptor/ligand interaction. These data suggest that apoptosis induced by bleomycin is mediated, at least in part, by p53-dependent stimulation of the CD95 receptor/ligand system. The same applies to other anti-cancer drugs such as cisplatin and methotrexate. These data may have major consequences for drug treatment of cancer and the explanation of drug sensitivity and resistance.