Journal Article

Basal and Human Papillomavirus E6 Oncoprotein-Induced Degradation of Myc Proteins by the Ubiquitin Pathway

Gross-Mesilaty, Shlomit, Reinstein, Eyal, Tobias, Karin E., Ciechanover, Aaron, Bercovich, Beatrice, Schwartz, Alan L., Kahana, Chaim

1998

Overview

We have previously shown that the degradation of c-myc and N-myc in vitro is mediated by the ubiquitin system. However, the role of the system in targeting the myc proteins in vivo and the identity of the conjugating enzymes and possible ancillary proteins involved has remained obscure. Here we report that the degradation of the myc proteins in cells is inhibited by lactacystin and MG132, two inhibitors of the 20S proteasome. Inhibition is accompanied by accumulation of myc-ubiquitin conjugates. Dissection of the ancillary proteins involved revealed that the high-risk human papillomavirus oncoprotein E6-16 stimulates conjugation and subsequent degradation of the myc proteins in vitro. Expression of E6-16 in cells results in significant shortening of the t1/2of the myc proteins with subsequent decrease in their cellular level. Analysis of the conjugating enzymes revealed that under basal conditions the proteins can be conjugated by two pairs of E2s and E3s--E2-14 kDa and E3α involved in the ``N-end rule'' pathway, and E2-F1 (UbcH7) and E3-Fos involved also in conjugation of c-Fos. In the presence of E6-16, a third pair, E2-F1 and E6-AP mediate conjugation of myc by means of a mechanism that appears to be similar to that involved in the targeting of p53, formation of a myc· E6· E6-AP targeting complex. It is possible that in certain cells E6-mediated targeting of myc prevents myc-induced apoptosis and thus ensures maintenance of viral infection.

• Publisher: National Academy of Sciences of the United States of America,National Acad Sciences,National Academy of Sciences,The National Academy of Sciences
• Subject: Acetylcysteine - analogs & derivatives / Acetylcysteine - pharmacology / Antibodies / Apoptosis / Biological Sciences / Cell cycle / Cell lines / Cellular biology / COS cells / Cysteine Proteinase Inhibitors - pharmacology / DNA-Binding Proteins / Enzymes / Genes / Humans / Leupeptins - pharmacology / Myeloid cells / Neuroblastoma / Oncogene Proteins, Viral - metabolism / Papillomaviridae - physiology / Papillomavirus Infections - virology / Proteins / Proto-Oncogene Proteins c-myc - metabolism / Reticulocytes / Signal Transduction / Tumor Cells, Cultured / Tumor Virus Infections - virology / Ubiquitins / Ubiquitins - metabolism / Viruses