Association of Tat with promoters of PTEN and PP2A subunits is key to transcriptional activation of apoptotic pathways in HIV-infected CD4+ T cells.
Apoptosis in HIV-1-infected CD4+ primary T cells is triggered by the alteration of the PI3K and p53 pathways, which converge on the FOXO3a transcriptional activator. Tat alone can cause activation of FOXO3a and of its proapoptotic target genes. To understand how Tat affects this pathway, we carried out ChIP-Chip experiments with Tat. Tat associates with the promoters of PTEN and two PP2A subunit genes, but not with the FOXO3a promoter. PTEN and PP2A encode phosphatases, whose levels and activity are increased when Tat is expressed. They counteract phosphorylation of Akt1 and FOXO3a, and so activate transcriptional activity of FOXO3a. FOXO3a promotes increased transcription of Egr-1, which can further stimulate the transcription of PTEN, thereby reinforcing the pathway that leads to FOXO3a transcriptional activation. RNAi experiments support the role of PTEN and PP2A in the initiation of the Tat-mediated cascade, which is critical to apoptosis. The increased accumulation of PTEN and PP2A subunit mRNAs during Tat expression is more likely to be the result of increased transcription initiation and not relief of promoter-proximal pausing of RNAPII. The Tat-PTEN and -PP2A promoter interactions provide a mechanistic explanation of Tat-mediated apoptosis in CD4+ T cells.
Kim
Nayoung
N
Children's Hospital Boston, Department of Medicine, and Harvard Medical School, Department of Pediatrics, Boston, Massachusetts, United States of America.
Kukkonen
Sami
S
Gupta
Sumeet
S
Aldovini
Anna
A
D017209:Apoptosis; D015415:Biomarkers / Q000378:metabolism; D015153:Blotting, Western; D015496:CD4-Positive T-Lymphocytes / Q000378:metabolism / Q000473:pathology / Q000821:virology; D047369:Chromatin Immunoprecipitation; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D051858:Forkhead Transcription Factors / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D020869:Gene Expression Profiling; D015658:HIV Infections / Q000378:metabolism / Q000473:pathology* / Q000821:virology; D015497:HIV-1 / Q000472:pathogenicity*; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D051059:PTEN Phosphohydrolase / Q000235:genetics* / Q000378:metabolism; D010766:Phosphorylation; D011401:Promoter Regions, Genetic / Q000235:genetics; D054648:Protein Phosphatase 2 / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D021122:Protein Subunits; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D015533:Transcriptional Activation; D054322:tat Gene Products, Human Immunodeficiency Virus / Q000235:genetics / Q000378:metabolism*
D015415:Biomarkers; D051858:Forkhead Transcription Factors; D021122:Protein Subunits; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D054322:tat Gene Products, Human Immunodeficiency Virus; D008156:Luciferases; D051057:Proto-Oncogene Proteins c-akt; D054648:Protein Phosphatase 2; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human