Tip60 inhibits activation of CREB protein by protein kinase A.
We have previously identified a cDNA encoding a cellular protein, Tip60 (Tat interactive protein, 60 kDa), that specifically interacts with the Tat (transactivating transcriptional regulator) protein of the human immunodeficiency virus-1 (HIV-1). In this report, we have characterized cellular Tip and find that it is a 60 kDa nuclear protein expressed in a wide variety of differentiated cell lines from insects to man. To identify cellular functions of Tip, we have assayed the effects of Tip on cellular pathways that Tat has been reported to affect. Overexpression of Tip results in an almost complete block in activation of a Gal4-CREB (cAMP response element binding protein) fusion protein by cyclic AMP dependent protein kinase A (PKA). This inhibition appears to be mediated through direct interaction of Tip and CREB, since Tip directly binds to CREB protein in vitro. We show that amino acid substitutions of two conserved amino acids found in the putative acetyl coenzyme A binding motif of Tip completely abolishes the histone acetyltransferase (HAT) activity of recombinant Tip. Inhibition of CREB activation by Tip is not diminished in a HAT negative Tip mutant, indicating that Tip can negatively regulate gene expression independent of HAT activity. Recently, Tip has also been shown to be a transcriptional coactivator of nuclear hormone receptors; therefore, Tip can both activate transcription factors of one signaling pathway (nuclear hormone receptors) and bind to a different transcription factor (CREB) and inhibit activation of another signaling pathway.
Gavaravarapu
S
S
Infectious Diseases Section, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
Kamine
J
J
D000123:Acetyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D017124:Conserved Sequence; D017362:Cyclic AMP Response Element-Binding Protein / Q000235:genetics / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004268:DNA-Binding Proteins; D004789:Enzyme Activation; D005656:Fungal Proteins / Q000378:metabolism; D005982:Glutathione Transferase / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D051548:Histone Acetyltransferases; D006801:Humans; D007700:Kinetics; D000074443:Lysine Acetyltransferase 5; D008715:Methionine / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D017354:Point Mutation; D011506:Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D016415:Sequence Alignment; D014157:Transcription Factors / Q000378:metabolism
D017362:Cyclic AMP Response Element-Binding Protein; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C052130:GAL4 protein, S cerevisiae; D011506:Proteins; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D008715:Methionine; D000123:Acetyltransferases; D051548:Histone Acetyltransferases; C098489:KAT5 protein, human; D000074443:Lysine Acetyltransferase 5; D005982:Glutathione Transferase; D017868:Cyclic AMP-Dependent Protein Kinases