HIV-1 Tat protein down-regulates CREB transcription factor expression in PC12 neuronal cells through a phosphatidylinositol 3-kinase/AKT/cyclic nucleoside phosphodiesterase pathway.
The addition of low concentrations (0.1-1 nM) of extracellular HIV-1 Tat protein to PC12 neuronal cells stimulated a rapid (peak at 5 min) elevation of the cAMP intracellular levels, which in turn induced the phosphorylation of CREB transcription factor (peak at 15 min) on serine-133 (Ser-133). On the contrary, at later time points (60-120 min) Tat induced a significant decline of intracellular cAMP with respect to the basal levels observed in control cells treated with bovine serum albumin. In blocking experiments performed with pharmacological inhibitors, Tat decreased the intracellular levels of cAMP and CREB Ser-133 phosphorylation through a signal transduction pathway involving the sequential activation of phosphatidylinositol 3-kinase, AKT, and cyclic nucleoside phosphodiesterases. Moreover, in transient transfection experiments, Tat inhibited transcription of CREB promoter in a manner strictly dependent on the presence of the cAMP-responsive elements (CRE) in the CREB promoter. Consistently, the expression of endogenous CREB protein was significantly reduced in PC12 cells by prolonged (24-48 h) treatment with Tat. This decline in the expression of CREB, which plays an essential role in the survival and function of neuronal cells, anticipated a progressive increase of apoptosis in Tat-treated cells. Although obtained in a neuronal cell line, our findings might help to explain some aspects of the pathogenesis of HIV-1-associated dementia.
Zauli
G
G
Institute of Normal Morphology, G. d'Annunzio University of Chieti; 66100 Chieti, Italy. g.zauli@morpho.unich.it
Milani
D
D
Mirandola
P
P
Mazzoni
M
M
Secchiero
P
P
Miscia
S
S
Capitani
S
S
D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000378:metabolism*; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002417:Cattle; D002867:Chromones / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D017362:Cyclic AMP Response Element-Binding Protein / Q000235:genetics* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation; D015696:Gene Products, tat / Q000494:pharmacology*; D015497:HIV-1 / Q000502:physiology*; D009025:Morpholines / Q000494:pharmacology; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D016716:PC12 Cells; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D011401:Promoter Regions, Genetic; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D012710:Serum Albumin, Bovine / Q000494:pharmacology; D014158:Transcription, Genetic; D014162:Transfection; D000077191:Wortmannin; D054322:tat Gene Products, Human Immunodeficiency Virus
D015105:3',5'-Cyclic-AMP Phosphodiesterases; D000730:Androstadienes; D002867:Chromones; D000242:Cyclic AMP; D017362:Cyclic AMP Response Element-Binding Protein; D004791:Enzyme Inhibitors; D015696:Gene Products, tat; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D010768:Phosphoserine; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D012710:Serum Albumin, Bovine; D000077191:Wortmannin; D054322:tat Gene Products, Human Immunodeficiency Virus; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C494920:Akt1 protein, rat