Inhibition of PP1 phosphatase activity by HBx: a mechanism for the activation of hepatitis B virus transcription.
The regulatory protein HBx is essential for hepatitis B virus (HBV) replication in vivo and for transcription of the episomal HBV genome. We previously reported that in infected cells HBx activates genes targeted by the transcription factor CREB [cyclic adenosine monophosphate (cAMP) response element-binding protein]. cAMP induces phosphorylation and activation of CREB, and CREB inactivation is promoted by protein phosphatase 1 (PP1), which binds to CREB through histone deacetylase 1 (HDAC1). We showed that CREB was recruited to HBV DNA. Phosphorylation induced by cAMP had a longer half-life when CREB was bound to the episomal HBV genome compared to when it was bound to the promoter of a host target gene not regulated by HBx, suggesting that the virus has developed a mechanism to favor its own transcription. This mechanism required HBx, which interacted with and inhibited PP1 to extend the half-life of CREB phosphorylation. Silencing of PP1 rescued replication of an HBx-deficient HBV genome, suggesting that HBx enhances viral transcription in part by neutralizing PP1 activity. Our results illustrate a previously unknown mechanism of HBV transcriptional activation by HBx in which HBx interferes with the inactivation of CREB by the PP1 and HDAC1 complex.
Oncogenèse et Virologie Moléculaire, Institut Pasteur, 28 Rue du Dr. Roux, 75724 Paris Cedex 15, France.
Delphine
D
Cougot
Eric
E
Allemand
Lise
L
Rivière
Shirine
S
Benhenda
Karine
K
Duroure
Florence
F
Levillayer
Christian
C
Muchardt
Marie-Annick
MA
Buendia
Christine
C
Neuveut
D000704:Analysis of Variance; D015152:Blotting, Northern; D047369:Chromatin Immunoprecipitation; D002850:Chromatography, Gel; D005576:Colforsin; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism*; D017931:DNA Primers / Q000235:genetics; D004279:DNA, Viral / Q000378:metabolism; D057809:HEK293 Cells; D006367:HeLa Cells; D006515:Hepatitis B virus / Q000502:physiology*; D006801:Humans; D008954:Models, Biological; D010766:Phosphorylation; D054645:Protein Phosphatase 1 / Q000037:antagonists & inhibitors*; D034741:RNA, Small Interfering / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D015534:Trans-Activators / Q000378:metabolism* / Q000502:physiology; D015533:Transcriptional Activation / Q000502:physiology*; D054334:Viral Regulatory and Accessory Proteins
D017362:Cyclic AMP Response Element-Binding Protein; D017931:DNA Primers; D004279:DNA, Viral; D034741:RNA, Small Interfering; D015534:Trans-Activators; D054334:Viral Regulatory and Accessory Proteins; C057628:hepatitis B virus X protein; D005576:Colforsin; D054645:Protein Phosphatase 1