Cell cycle regulation of hepatitis C virus internal ribosomal entry site-directed translation.
OBJECTIVE
Translation of the hepatitis C virus (HCV) polyprotein is mediated by an internal ribosome entry site (IRES) that is located within the 5' nontranslated segment of the viral RNA. This RNA segment is known to form binary complexes with isolated 40S ribosome subunits in vitro, but there is little understanding of how the process of virus translation is regulated in vivo.


METHODS
We established 2 stably transformed cell lines from Huh-7 cells that constitutively express dicistronic RNA transcripts containing sequences encoding 2 reporter proteins (Renilla luciferase and firefly luciferase) separated by a functional HCV IRES. The translation of the upstream Renilla luciferase reading frame is initiated in these cells by the usual cellular cap-dependent mechanism, whereas translation of the downstream firefly luciferase reading frame is initiated by the IRES.


RESULTS
Compared with cap-dependent translation, the activity of the IRES was greatest in actively growing cells and relatively reduced in resting cells. In synchronized cultures of these stably transformed cells, the IRES activity varied with the cell cycle and was greatest during the mitotic (M) phases and lowest during the quiescent (G(0)) phases.


CONCLUSIONS
These findings suggest that HCV translation is regulated by cellular proteins that vary in abundance during the cell cycle and that viral translation may be enhanced by factors that stimulate the regeneration of hepatocytes in patients with chronic hepatitis C.
Honda
M
M
First Department of Internal Medicine, Kanazawa University, Kanazawa, Japan. mhonda@medf.m.kanazawa-u.ac.jp
Kaneko
S
S
Matsushita
E
E
Kobayashi
K
K
Abell
G A
GA
Lemon
S M
SM
D020121:5' Untranslated Regions / Q000502:physiology*; D000818:Animals; D002453:Cell Cycle / Q000502:physiology*; D002461:Cell Line, Transformed; D001517:Coleoptera / Q000201:enzymology; D003513:Cycloheximide / Q000494:pharmacology; D017930:Genes, Reporter; D016174:Hepacivirus / Q000235:genetics*; D008156:Luciferases / Q000378:metabolism; D014176:Protein Biosynthesis; D012367:RNA, Viral / Q000235:genetics*; D014158:Transcription, Genetic
D020121:5' Untranslated Regions; D012367:RNA, Viral; D003513:Cycloheximide; D008156:Luciferases