Kaposi's sarcoma-associated herpesvirus K-bZIP represses gene transcription via SUMO modification.
Kaposi's sarcoma-associated herpesvirus (KSHV) is a human gammaherpesvirus implicated in AIDS-related neoplasms. Previously, we demonstrated that the early lytic gene product K-bZIP is a transcriptional repressor that affects a subset of viral gene transcriptions mediated by the viral transactivator K-Rta (Y. Izumiya et al. J. Virol. 77:1441-1451, 2003). Sumoylation has emerged as an important posttranslational modification that affects the location and function of cellular and viral proteins and also plays a significant role in transcriptional repression along with Ubc9, the E2 SUMO conjugation enzyme. Here, we provide evidence that K-bZIP is sumoylated at the lysine 158 residue and associates with Ubc9 both in a cell-free system and in virus-infected BCBL-1 cells. Reporter assays showed that the expression of SUMO-specific protease 1 attenuated the transcriptional repression activity of K-bZIP. The expression of a K-bZIPK158R mutant, which was no longer sumoylated, exhibited the reduced transcriptional repression activity. This indicates that sumoylation plays an important part in the transcriptional repression activity of K-bZIP. Finally, chromatin immunoprecipitation experiments demonstrated that K-bZIP interacts with and recruits Ubc9 to specific KSHV promoters. Thus, our data indicate that K-bZIP is a SUMO adaptor, which recruits Ubc9 to specific viral target promoters, thereby exerting its transcriptional repression activity.
Izumiya
Yoshihiro
Y
Department of Biological Chemistry, University of California--Davis (UC Davis), School of Medicine, Sacramento, 95817, USA.
Ellison
Thomas J
TJ
Yeh
Edward T H
ET
Jung
Jae U
JU
Luciw
Paul A
PA
Kung
Hsing-Jien
HJ
D050976:Basic-Leucine Zipper Transcription Factors; D002352:Carrier Proteins; D018929:Cell Culture Techniques; D015967:Gene Expression Regulation, Viral; D019288:Herpesvirus 8, Human / Q000235:genetics / Q000502:physiology*; D006801:Humans; D008239:Lysine / Q000378:metabolism; D010447:Peptide Hydrolases / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins; D025842:SUMO-1 Protein / Q000378:metabolism*; D014158:Transcription, Genetic; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism; D014764:Viral Proteins; D000098843:Ubiquitin-Conjugating Enzyme UBC9
D050976:Basic-Leucine Zipper Transcription Factors; D002352:Carrier Proteins; C118265:K8 protein, Human herpesvirus 8; D012097:Repressor Proteins; D025842:SUMO-1 Protein; D014764:Viral Proteins; D044763:Ubiquitin-Conjugating Enzymes; D010447:Peptide Hydrolases; D000098843:Ubiquitin-Conjugating Enzyme UBC9; D008239:Lysine